COMPOSITIONS AND METHODS OF USE OF HET

Abstract: Disclosed are methods for the detection of tumor cells, in particular human breast cancer cells. Genetic and antibody probes and methods useful in determining the presence and monitoring of tumor cell proliferation are also described. The methods involve determining HET polypeptide expression or loss of heterozygosity at human chromosomal locus 19p13 as a measure of tumor cell malignancy. Also described are procedures for transforming cells with HET gene containing vectors that express HET polypeptide.

Description: DESCRIPTION COMPOSITIONS AND METHODS OF USE OF HET 1.0 BACKGROUND OF THE INVENTION This application claims priority under 35 U.S.C. § 119(e) to provisional application Serial No. 60/068,132, filed on December 4, 1997. The entire text of the above-referenced disclosure is specifically incorporated herein by reference without disclaimer. The United States government has rights to use the present invention pursuant to Grant No. # PHS P50 CA58183, from the National Institutes of Health. 1.1 Field of the Invention The present invention relates generally to methods of detecting tumor cell proliferation and progression and the use of HET polypeptides and nucleic acids for such methods. More particularly, certain methods utilizing loss of heterozygosity with respect to chromosome 19pl3 are described that may provide the basis for prognostic and diagnostic evaluations of human cancer patients. Other methods utilizing point mutations in the HET gene sequence that may provide the basis for prognostic and diagnostic evaluations are also described. 1.2 Description of Related Art Breast cancer is the leading cause of death for women between 30-50 years of age in the United States. Pathological breast cancer staging (tumor size, nodal status) is still the most reliable method for predicting outcome. In contrast to other forms of cancer, only a few tumor markers have been identified for breast cancer (e.g., estrogen receptor, progesterone receptor, S-phase, P53, Erb-2, cathepsin D) (see, e.g. Slamon et al, 1987). Mutational analysis of important tumor suppressor genes such as p53 (Elledge, 1994) and BRCA1 (Miki et al., 1994) has recently been introduced as a diagnostic and prognostic test for breast cancer. However, many of those markers are not reliable enough to be used for routine purposes in the clinic. Therefore, there is an urgent need for better prognostic markers in breast cancer diagnosis, measured either by "traditional" methods (e.g., immunohistochemistry, Western blot), or genetic test. 1.2.1 Tumor Suppressor Genes Many tumor suppressor genes were first identified by studying loss of function in families having a predisposition to cancer (Sager, 1989; Stanbridge, 1990). In these families, a germ line mutation in one allele is inherited. Therefore, mutation or loss of the other allele can lead to a transformed phenotype. However, the majority of cancers appear to arise as a result of sporadic mutation, which involves loss or mutation of both alleles. A useful marker for tumor suppressor genes involved in sporadic cancer is loss of heterozygosity (LOH) within a tumor. Loss of one of the alleles (i.e., LOH) in a carrier can indicate the presence of a tumor suppressor, and this ultimately can be confirmed by the finding of mutations in the other copy of the gene. Many recognized tumor suppressor genes are regulators of cell proliferation, also referred to as cell cycle "gatekeepers" (e.g., retinoblastoma or Rb). However a new series of tumor suppressor genes is emerging that does not control the cell cycle directly, but rather is involved in DNA repair, i.e., genome "caretakers" or repair genes. A model recently has been developed for the different properties of gatekeepers and caretakers (Kinzler and Vogelstein, 1997). 1.2.2 Tumor Suppressor Genes in Human Breast Cancer The genetic events involved in breast cancer are poorly understood. As in other cancers, there is clearly a multistage process involving genetic changes that result in mutational activation of any of a number of oncogenes, as well as the mutational inactivation of any of a growing number of tumor suppressor genes. Two tumor suppressor genes that are mutated in a number of other cancers (Rb and p53) show a frequency of mutation of only about 30% in breast cancer (Cox et al, 1994). Mutations in tsg 101 were reported in about 40% of breast tumors (Li et al, 1997), but this result has generally not been confirmed (Lee and Feinberg, 1997; Trink et al, 1998). Mutations in the recently identified breast cancer susceptibility genes BRCA1 (chromosome 17q21) and BRCA2 (chromosome 13ql3) are associated with familial breast cancer, accounting for about 5% of total breast cancer cases, but have not been found in sporadic breast cancer (Stratton and Wooster, 1996). There has yet to be found a single genetic change that accounts for the majority of sporadic breast cancers. The inventors previously have established that the small heat shock protein hsp27 plays a role in both growth and drug resistance of human breast cancer cells in culture (Oesterreich et al, 1993). Supporting this observation, hsp27 has been found to contribute to increased drug resistance in CHO cells (Lavoie et al, 1993), colon cancer cells (Garrido et al, 1996), and testis cancer cells (Richards et al, 1996). More recently, it has been reported that elevated hsp27 levels also correlate with increased invasiveness of human breast cancer cells (Lemieux et al, 1996). Although many contradictory studies have been published on the prognostic value of hsp27 in various tumors, an immunohistochemical and Western blot analysis of samples from 425 breast cancer patients showed that hsp27 is not an independent prognostic marker in breast cancer (Oesterreich et al, 1996b). However, this large study did show that hsp27 predicts a significantly worse outcome in a subset of estrogen receptor (ER) positive/untreated breast cancer patients. Furthermore, this study confirmed previous findings (Dunn et al, 1993; Tandon et al, 1990) that the expression of hsp27 is strongly correlated with the expression of ER in breast tumors. The correlation of hsp27 and ER expression agrees with the finding of estrogen induction of hsp27, which has been described in breast tumors (Seymor et al, 1990) and in breast cancer cell lines (Moretti-Rojas et al, 1988). The majority of the basal transcriptional activity of hsp27 resides in the most proximal region of hsp27 (Oesterreich et al, 1996a). In this fragment there is a region of DNA, 70 bp upstream from the start site, consisting of an imperfect palindromic estrogen response element (ERE) which instead of being separated by the normal 3 bp spacer, is separated by a 13 bp spacer containing a TATA box. Another TATA box 40 bp downstream of this region is the major transcriptional start site, however transcription can also occur from the upstream TATA box (Hickey et al, 1986). The present invention concerns a novel therapeutic strategy in the treatment of breast cancer involving the characterization of the hsp27 promoter and the development of genes and gene products capable of targeting the hsp27 promoter and thereby decreasing expression of hsp27. Many attempts have been made to decrease the expression of heat shock proteins (hsp) in general to circumvent drug resistance in tumors. For example, the antiestrogen toremifene (Mahvi et al, 1996) and the bioflavonoid quercetin (Sliutz et al, 1996) both decrease hsp expression and have been used successfully as chemosensitisers in tissue culture. However, neither of these agents have resulted in a significant decline in the mortality rate from breast cancer. There remains a great need to develop effective means of diagnosing, prognosing, and treating breast cancer. 2.0 SUMMARY OF THE INVENTION The present invention addresses these and other deficiencies in the art by identifying and characterizing an HET protein (SEQ ID NO:2) that can bind to and regulate gene expression from the hsp27 promoter. An unexpected role of HET as a tumor suppressor gene was discovered as a consequence of the observation that a majority of breast cancer samples examined showed allelic loss of a chromosomal region in which HET was mapped, as detected by a loss of heterozygosity (LOH) assay. This represents the most frequently observed genetic defect associated with breast cancer to date. Samples were examined from infiltrating duct carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, ductal carcinoma in situ and lobular carcinoma in situ. These results provide the basis for assays directed toward detection of genetic defects in HET in breast tissue samples which will have utility for diagnosis and prognosis of breast cancer. Examination of samples from a variety of breast tumors, including infiltrating duct carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, ductal carcinoma in situ and lobular carcinoma in situ, indicates that HET expression is inversely correlated with breast cancer progression, with either low levels or loss of expression of HET observed in the most rapidly growing breast tumors. Thus, assays directed towards detection and measurement of HET in tissue samples are expected to have utility for the diagnosis and prognosis of breast cancer. One aspect of the present invention encompasses antibodies specific for HET and immunological methods for detection and measurement of HET in tissue samples. Such methods may include the use of Western blots, immunohistochemistry (IHC), ELISA, and other well known techniques for antibody assay of protein expression. Another aspect concerns the use of such antibodies for methods of cancer cell detection, diagnosis and prognosis, by comparing the levels of HET polypeptide in suspected cancer cells with levels present in normal cells. In one embodiment, the antibodies are specific for mutant forms of the HET protein, exemplified by the substitution of a glutamine residue for the arginine residue at position forty-six of SEQ ID NO:2, or the substitution of an aspartate for the asparagine residue at position seventy-one of SEQ ID NO:2. Yet another embodiment of the invention encompasses a kit for use in the detection and measurement of HET in tissue samples, comprising an HET specific antibody. Additional components of kits for immunologic detection of disease-state associated antigens are well known in the art, and may include components such as molecular weight marker proteins, secondary antibodies, reagents for staining or otherwise detecting bound antibodies, control samples containing known amounts of HET protein or peptide, and negative controls lacking HET protein. The invention also comprises nucleic acid segments that are either identical to or complementary with the cDNA sequence of HET, reported herein as SEQ ID NO:l as well as nucleic acid segments of at least 2253 contiguous nucleotides of SEQ ID NO:l . Such nucleic acid segments are expected to have utility, for example, not only as probes or primers for the genetic analysis of breast tumor samples but also as comprising vectors for transformation of het gene deficient cells. An additional embodiment encompasses polypeptides encoded by HET genes, exemplified by SEQ ID NO:2. It is contemplated that such polypeptides may comprise substitutions in the amino acid sequence of SEQ ID NO:2, exemplified by the substitution of a glutamine residue for the arginine residue at position forty-six of SEQ ID NO:2, or the substitution of an aspartate for the asparagine residue at position seventy-one of SEQ ID NO:2. Such polypeptides may be used, for example, as antigens for induction of polyclonal or monoclonal antibodies. A further embodiment encompasses genetic analysis of tissue samples to obtain information relating to tumor malignancy. Such analyses typically employs PCR™ amplification, using primers specific for human chromosomal locus 19p 13 , more particularly at 19pl3.2-13.3 (for example, primers comprising the sequences of SEQ ID NO:7 and SEQ ID NO:8), followed by LOH assay to detect allelic loss at 19p 13. The inventors have demonstrated the presence of a gene, located at 19p 13 , that suppresses tumor cell growth. In particular cases, the loss of heterozygosity at this locus is associated with a malignant phenotype of breast tumor cells. Thus, particular embodiments of the present invention relate to the diagnosis of individuals with breast tumors by employing LOH assay of 19p 13. Rapidly growing tumors are recognized as associated with a poorer five-year survival rate for breast cancer patients. One may therefore assess potential survival rates in such patients by using a LOH assay of 19pl3. Previously described tumor suppressor genes show frequent loss of heterozygosity of one allele, followed by point mutation of the remaining allele. Thus, mutational analysis of HET will have utility for the diagnosis or prognosis of breast cancer. An embodiment of the present invention comprises PCR™ amplification of nucleic acids from tissue samples, using primers specific for HET, to detect mutations in the HET gene (for example by SSCP analysis or DNA sequencing). Further embodiments of the present invention encompass methods for the prognosis or diagnosis of breast cancer patients by SSCP or other mutational analysis of HET. Additional embodiments of the present invention comprise methods directed to the detection of specific point mutations associated with the HET gene, such as the substitution of an adenosine residue for the guanosine residue at position 190 or the substitution of a guanosine for the adenosine residue at position 264 of SEQ ID NO:l. Detection of such specific point mutations in suspected cancer cells may be useful in the diagnosis or prognosis of breast cancer. Yet another aspect of the present invention encompasses host cells or vectors comprising a nucleic acid encoding HET. Such cells or vectors are expected to have utility in the therapeutic treatment of breast cancer. Studies with isolated cancer cell lines show that insertion of an expression vector comprising an HET encoding nucleic acid into tumor cells from breast and other types of tumors results in suppression of tumor growth and colony formation. Thus, an embodiment of the present invention comprises a method for altering the phenotype of a tumor cell by contacting the cell with a nucleic acid encoding HET, operably linked to a functional promoter, under conditions permitting uptake and expression of the nucleic acid by the tumor cell. 3.0 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A shows a gel-retardation assay using a P-labeled consensus ERE (lanes 1 and 2) and the hsp27 promoter fragment (-99 bp to -15 bp) containing the ERE/TATA site (lanes 3 and 4), respectively, as probes and whole cell extracts from MCF-7/MG cells. ER-antibodies were added to lanes 2 and 4. FIG. IB shows a Southwestern blot of MCF-7/MG nuclear extract (25 μg) separated 32 bbyy SSDDSS--PPAAGGEE,, ttrraannssffeerrrreedd ttoo n nitrocellulose, renatured, and probed with the P- labeled hsp27 promoter fragment. FIG. 2A shows the Coomassie-blue stained SDS-PAGE of extracts from E. coli expressing GST-HET and GST only (pGEX-lλT) as a negative control, before (lanes 2 and 3) and after purification (lanes 4 and 5) on glutathione beads. Molecular weight markers were loaded in lane 1. FIG. 2B shows a gel -retardation assay of 2 and 10 μl of purified GST (lanes 1 and 2) and GST-HET (lanes 3 and 4), respectively, using the hsp27 promoter fragment as a probe. FIG. 3A illustrates the use of plasmid for coupled in vitro transcription/translation analysis. The HET cDNA was cloned into pcDNAl . Samples containing plasmid with HET cDNA (lane 1) or vector only (lane 2) were in vitro transcribed and translated using the TNT coupled Reticulocyte Lysate system (Promega) in the presence of [ S]-methionine. Radioactively labeled bands were detected by autoradiography. FIG. 3B illustrates an analysis similar to FIG. 3 A wherein HET cDNA (lane 1) or vector only (lane 2) were in vitro transcribed and translated using the TNT coupled Reticulocyte Lysate system (Promega). The products were then separated by SDS- PAGE and reacted with an HET specific polyclonal antibody by Western blotting. FIG. 4A illustrates a diagram of the subcellular fractionation scheme. FIG. 4B shows a Western blot analysis using HET-antibodies of 20 μg of protein from various subcellular fractions (as indicated). FIG. 4C shows a Western Blot similar to FIG. 4B using HET-antibodies and 20 μg of nuclear matrix proteins from various breast cancer cells (as indicated). FIG. 5 describes transient transfection assays in which HET was cotransfected with an hsp27 promoter-luciferase construct containing the ERE/TATA site. These assays show that HET overexpression results in a decreased activity of hsp27 promoter. The luciferase values were corrected for transfection efficiency. Values represent the mean of triplicate wells ± S.E.M. Significance was calculated by ANOVA test. FIG. 6 illustrates a human metaphase spread with the HET PI probe fluorescently labeling both chromosome 19 homologs at 19pl3.2→pl3.3 FIG. 7 illustrates a PCR™ amplification of somatic cell hybrids using primers designed from the HET cDNA. The lanes are numbered for the human chromosome present in that hybrid. H = hamster control; M = mouse control; +ve = human genomic DNA. FIG. 8 shows an LOH analysis at human chromosomal locus 19pl3 of breast tumor specimens. Breast biopsy DNA (normal and tumor) was analyzed using PCR™ based microsatellite markers corresponding to 19-pter (Genethon, see Gyapay et al, 1994). The resulting PCR™ products were separated on a high resolution sequencing gel, dried and exposed to a Molecular Dynamics (MD) storage phosphor screen. The level of allelic imbalance was determined by normalizing the ratio of the allele intensities. The larger ratio was divided by the smaller to determine allelic imbalance. A cut-off of 1.5X difference was used to score LOH. This figure is representative of a single LOH that was observed. FIG. 9 illustrates HET expression in primary breast cancers. Frozen tumor powder was homogenized in 5% SDS, and 25 μg protein was resolved on 7.5% PAGE. After transferring onto nitrocellulose, HET was detected by Western blot using an HET- specific polyclonal antibody. FIG. 10A and FIG. 10B show that HET inhibits the growth of NIH3T3 cells. NIH3T3 cells transfected with pcDNAl vector alone (control clones 1 and 6), and cells overexpressing HET (clone HET 25), were plated at 2500 cells/well in a 96 well plate. The next day cell number was assessed by MTT assay (Day 0). Cells were then incubated in serum-free medium or 10% serum, and cell number calculated at days 2, 4, and 6 by MTT assay. Each point represents quadruplicate wells ± S.E.M. FIG. 11 shows that transient transfection of antisense HET into 293 cancer cells causes an increased rate of cell division, as measured by [ H]-thymidine incorporation into DNA. Cells were transfected with 0.02, 0.2 or 2.0 μg of HET/pcDNAl antisense vector. Control cells were transfected with pcDNAl plasmid alone. After 24 h recovery, the rate of [ H] thymidine incorporation was determined by scintillation counting and the numbers were corrected for protein concentration. FIG. 12A demonstrates that total cellular levels of HET decrease progressively when MCF-7/MG cells were stimulated with 5% and 10% serum, respectively, compared to cells in serum-free medium (SFM). HET levels increased in MCF-7 cells exposed to 50 nM TPA, which has been shown to cause growth inhibition of these cells. These results are consistent with an inverse correlation between HET expression and cell proliferation. FIG. 12B shows the effect of expression of HET on colony growth in MCF-7/MG cells. Cells transfected with an HET expression construct (HET sense) showed a dramatic reduction in number of colonies formed, compared with control vector alone (PCDNA1) or an HET antisense construct (HET antisense). 4.0 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 4.1 Proteins 4.1.1 Definitions and Techniques Relating to HET Gene Products and Genes. The present invention relates to a novel HET protein ("HET"), which has been cloned and characterized. The HET protein binds to the ERE-TATA region of hsp27 (HET = Hsp27-ERE-TATA-binding protein). HET is a nuclear matrix protein affecting the transcriptional activity of the hsp27 promoter. It is not identical to the pi 14 kDa matrix attachment region binding protein of Yanigasawa et al. (1996). "Biologically active" forms of HET gene product and HET are capable of binding to the hsp27 promoter and suppressing expression of hsp27. As used herein, the terms "HET" and "HET gene product" refer to proteins having amino acid sequences which are substantially identical to the native amino acid sequence in SEQ ID NO:2. The term "HET gene product" also includes analogs of HET molecules which exhibit at least some biological activity in common with native HET. For example, HET analogs may be constructed wherein certain amino acid residues recited in SEQ ID NO:2 are substituted by other amino acid residues of similar charge, size, shape and hydrophobicity. Furthermore, those skilled in the art of mutagenesis will appreciate that such analogs of HET may be generated by well- known techniques such as site-directed mutagenesis, as described below. In referring to the function of HET or "wild-type" activity, it is meant that the molecule in question has the ability to inhibit cell transformation, or to prevent metastasis or invasive tumor growth. Other phenotypes that may be regulated by the normal HET gene product are angiogenesis, cell adhesion, migration, cell-to-cell signaling, cell growth, cell proliferation, density-dependent growth, anchorage- dependent growth, and others. Molecules possessing this activity may be identified using assays familiar to those of skill in the art. For example, transfer of genes encoding HET, or variants thereof, into cells that do not have a functional HET product, and hence exhibit impaired growth control, will identify, by virtue of growth suppression, those molecules having HET function. The term "tumor suppressor" is well-known to those of skill in the art. Examples of other tumors suppressors are p53, Rb and pi 6, to name a few. While these molecules are structurally distinct, they form a group of functionally-related molecules, of which HET is a member. The uses for which these other tumor suppressors now are being exploited are equally applicable here. The term "HET gene" refers to any DNA sequence that is substantially identical to a DNA sequence encoding an HET gene product as defined above. Allowing for the degeneracy of the genetic code, sequences that have at least about 50%), usually at least about 60%, more usually about 70%>, most usually about 80%, preferably at least about 90%, and most preferably about 95%> of nucleotides that are identical to the nucleotides of SEQ ID NO:l will be sequences that are "as set forth in SEQ ID NO: 1." Sequences that are substantially identical or "essentially the same" as those set forth in SEQ ID NO:l also may be functionally defined as sequences that are capable of hybridizing to a nucleic acid segment containing the complement of SEQ ID NO:l under conditions of relatively high stringency. Such conditions are typically relatively low salt and/or high temperature conditions, such as provided by about 0.02 M to about 0.15 M NaCl at temperatures of about 50°C to about 70°C. Such selective conditions tolerate little, if any, mismatch between the complementary stands and the template or target strand. "HET gene" is also intended to include RNA, or antisense sequences compatible with the nucleic acid sequence set forth in SEQ ID NO:l . Any HET gene sequences may also comprise associated control sequences. The term "substantially identical," when used to define either a HET amino acid sequence or a HET gene nucleic acid sequence, means that a particular subject sequence, for example, a mutant sequence, varies from the sequence of natural HET or HET gene by one or more substitutions, deletions, or additions, the net effect of which is to retain at least some biological activity of the HET protein or gene. Alternatively, DNA analog sequences are "substantially identical" to specific DNA sequences disclosed herein if: (a) the DNA analog sequence is derived from coding regions of the natural HET gene; or (b) the DNA analog sequence is capable of hybridization of DNA sequences of (a) under moderately stringent conditions and which encode biologically active HET; or (c) DNA sequences which are degenerative as a result of the genetic code to the DNA analog sequences defined in (a) or (b). The inventors have discovered that the gene encoding the HET protein ("the HET gene") is a tumor suppressor gene. HET has been mapped to chromosomal locus 19pl3.2-pl3.3. Using LOH technology, it was found that this locus is lost in 50-60%) of breast cancer patients, which is higher than the LOH described for any other tumor suppressor gene described to date (e.g., p53, Rb). In addition to the entire HET molecule, the present invention also relates to fragments of the polypeptide that may or may not retain the tumor suppressing (or other) activity of HET. Fragments including the N-terminus of the molecule may be generated by genetic engineering of translation stop sites within the coding region (discussed below). Alternatively, treatment of the HET molecule with proteolytic enzymes, known as proteases, can produce a variety of N-terminal, C-terminal and internal fragments. Examples of fragments may include contiguous residues of the HET amino acid sequence given in SEQ ID NO:2 of 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 35, 40, 45, 50, 55, 60, 65, 75, 80, 85, 90, 95, 100, 200, 300, 400, or more amino acids in length. These fragments may be purified according to known methods, such as precipitation (e.g., ammonium sulfate), HPLC, ion exchange chromatography, affinity chromatography (including immunoaffinity chromatography), or various size separations (e.g., sedimentation, gel electrophoresis, gel filtration). Substantially identical analog proteins will be greater than about 80% similar to the corresponding sequence of the native protein. Sequences having lesser degrees of similarity but comparable biological activity are considered to be equivalents. In determining nucleic acid sequences, all subject nucleic acid sequences capable of encoding substantially similar amino acid sequences are considered to be substantially similar to a reference nucleic acid sequence, regardless of differences in codon sequence. 4.1.2 Variants of HET Amino acid sequence variants of the HET polypeptide can be substitutional, insertional or deletion variants. Deletion variants lack one or more residues of the native protein which are not essential for function or immunogenic activity. Another common type of deletion variant is one lacking secretory signal sequences or signal sequences directing a protein to bind to a particular part of a cell. Insertional variants typically involve the addition of material at a non-terminal point in the polypeptide. This may include the insertion of an immunoreactive epitope or simply a single residue. Terminal additions, called fusion proteins, are discussed below. Substitutional variants typically contain the exchange of one amino acid for another at one or more sites within the protein, and may be designed to modulate one or more properties of the polypeptide, such as stability against proteolytic cleavage, without the loss of other functions or properties. Substitutions of this kind preferably are conservative, that is, one amino acid is replaced with one of similar shape and charge. Conservative substitutions are well known in the art and include, for example, the changes of: alanine to serine; arginine to lysine; asparagine to glutamine or histidine; aspartate to glutamate; cysteine to serine; glutamine to asparagine; glutamate to aspartate; glycine to proline; histidine to asparagine or glutamine; isoleucine to leucine or valine; leucine to valine or isoleucine; lysine to arginine; methionine to leucine or isoleucine; phenylalanine to tyrosine, leucine or methionine; serine to threonine; threonine to serine; tryptophan to tyrosine; tyrosine to tryptophan or phenylalanine; and valine to isoleucine or leucine. The following is a discussion based upon changing of the amino acids of a protein to create an equivalent, or even an improved, second-generation molecule. For example, certain amino acids may be substituted for other amino acids in a protein structure without appreciable loss of interactive binding capacity with structures such as, for example, antigen-binding regions of antibodies or binding sites on substrate molecules. Since it is the interactive capacity and nature of a protein that defines that protein's biological and functional activity, certain amino acid substitutions can be made in a protein sequence, and its underlying DNA coding sequence, and nevertheless obtain a protein with like properties. It is thus contemplated by the inventors that various changes may be made in the DNA sequences of genes without appreciable loss of their biological utility or activity, as discussed below. Table 1 shows the codons that encode particular amino acids. In making such changes, the hydropathic index of amino acids may be considered. The importance of the hydropathic amino acid index in conferring interactive biologic function on a protein is generally understood in the art (Kyte and Doolittle, 1982). It is accepted that the relative hydropathic character of the amino acid contributes to the secondary structure of the resultant protein, which in turn defines the interaction of the protein with other molecules, for example, enzymes, substrates, receptors, DNA, antibodies, antigens, and the like. Each amino acid has been assigned a hydropathic index on the basis of its hydrophobicity and charge characteristics (Kyte and Doolittle, 1982), these are: isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine/cystine (+2.5); methionine (+1.9); alanine (+1.8); glycine (-0.4); threonine (-0.7); serine (- 0.8); tryptophan (-0.9); tyrosine (-1.3); proline (-1.6); histidine (-3.2); glutamate (- 3.5); glutamine (-3.5); aspartate (-3.5); asparagine (-3.5); lysine (-3.9); and arginine (- 4.5). It is known in the art that certain amino acids may be substituted by other amino acids having a similar hydropathic index or score and still result in a protein with similar biological activity, i.e., still obtain a biological functionally equivalent protein. In making such changes, the substitution of amino acids whose hydropathic indices are within ± 2 is preferred, those which are within ± 1 are particularly preferred, and those within ± 0.5 are even more particularly preferred. It is also understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity. U.S. Patent 4,554,101, incorporated herein by reference, states that the greatest local average hydrophilicity of a protein, as governed by the hydrophilicity of its adjacent amino acids, correlates with a biological property of the protein. As detailed in U.S. Patent 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0); lysine (+3.0); aspartate (+3.0 ± 1); glutamate (+3.0 ± 1); serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0); threonine (-0.4); proline (-0.5 ± 1); alanine (-0.5); histidine -0.5); cysteine (-1.0); methionine (-1.3); valine (-1.5); leucine (-1.8); isoleucine (-1.8); tyrosine (-2.3); phenylalanine (-2.5); tryptophan (-3.4). It is understood that an amino acid can be substituted for another having a similar hydrophilicity value and still obtain a biologically equivalent and immunologically equivalent protein. In such changes, the substitution of amino acids whose hydrophilicity values are within ± 2 is preferred, those that are within ± 1 are particularly preferred, and those within ± 0.5 are even more particularly preferred. As outlined above, amino acid substitutions are generally based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like. Exemplary substitutions that take various of the foregoing characteristics into consideration are well known to those of skill in the art and include: arginine and lysine; glutamate and aspartate; serine and threonine; glutamine and asparagine; and valine, leucine and isoleucine. Another embodiment for the preparation of polypeptides according to the invention is the use of peptide mimetics. Mimetics are peptide-containing molecules that mimic elements of protein secondary structure. See, for example, Johnson et al. (1993). The underlying rationale behind the use of peptide mimetics is that the peptide backbone of proteins exists chiefly to orient amino acid side chains in such a way as to facilitate molecular interactions, such as those of antibody and antigen. A peptide mimetic is expected to permit molecular interactions similar to the natural molecule. These principles may be used, in conjunction with the principles outline above, to engineer second generation molecules having many of the natural properties of HET, but with altered and even improved characteristics. 4.1.3 Fusion Proteins A specialized kind of insertional variant is the fusion protein. This molecule generally has all or a substantial portion of the native molecule, linked at the N- or C- terminus, to all or a portion of a second polypeptide. For example, fusions typically employ leader sequences from other species to permit the recombinant expression of a protein in a heterologous host. Another useful fusion includes the addition of an immunologically active domain, such as an antibody epitope, to facilitate purification of the fusion protein. Inclusion of a cleavage site at or near the fusion junction will facilitate removal of the extraneous polypeptide after purification. Other useful fusions include linking of functional domains, such as active sites from enzymes, glycosylation domains, cellular targeting signals or transmembrane regions. 4.1.4 Purification of Proteins It will be desirable to purify HET or variants thereof. Protein purification techniques are well known to those of skill in the art. These techniques involve, at one level, the crude fractionation of the cellular milieu to polypeptide and non- polypeptide fractions. Having separated the polypeptide from other proteins, the polypeptide of interest may be further purified using chromatographic and electrophoretic techniques to achieve partial or complete purification (or purification to homogeneity). Analytical methods particularly suited to the preparation of a pure peptide are ion-exchange chromatography, gel exclusion chromatography, polyacrylamide gel electrophoresis, affinity chromatography, immunoaffϊnity chromatography and isoelectric focusing. A particularly efficient method of purifying peptides is fast protein liquid chromatography (FPLC) or even HPLC. Certain aspects of the present invention concern the purification, and in particular embodiments, the substantial purification, of an encoded protein or peptide. The term "purified protein or peptide" as used herein, is intended to refer to a composition, isolatable from other components, wherein the protein or peptide is purified to any degree relative to its naturally-obtainable state. A purified protein or peptide, therefore, also refers to a protein or peptide free from the environment in which it may naturally occur. Generally, "purified" will refer to a protein or peptide composition that has been subjected to fractionation to remove various other components, and which composition substantially retains its expressed biological activity. Where the term "substantially purified" is used, this designation will refer to a composition in which the protein or peptide forms the major component of the composition, such as constituting about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or more of the proteins in the composition. Various methods for quantifying the degree of purification of the protein or peptide will be known to those of skill in the art in light of the present disclosure. These include, for example, determining the specific activity of an active fraction, or assessing the amount of polypeptides within a fraction by SDS/PAGE analysis. A preferred method for assessing the purity of a fraction is to calculate the specific activity of the fraction, to compare it to the specific activity of the initial extract, and to thus calculate the degree of purity therein, assessed by a "-fold purification number." The actual units used to represent the amount of activity will, of course, be dependent upon the particular assay technique chosen to follow the purification, and whether or not the expressed protein or peptide exhibits a detectable activity. Various techniques suitable for use in protein purification will be well known to those of skill in the art. These include, for example, precipitation with ammonium sulphate, PEG, antibodies and the like, or by heat denaturation, followed by: centrifugation; chromatography steps such as ion exchange, gel filtration, reverse phase, hydroxylapatite and affinity chromatography; isoelectric focusing; gel electrophoresis; and combinations of these and other techniques. As is generally known in the art, it is believed that the order of conducting the various purification steps may be changed, or that certain steps may be omitted, and still result in a suitable method for the preparation of a substantially purified protein or peptide. There is no general requirement that the protein or peptide always be provided in their most purified state. Indeed, it is contemplated that less substantially purified products will have utility in certain embodiments. Partial purification may be accomplished by using fewer purification steps in combination, or by utilizing different forms of the same general purification scheme. For example, it is appreciated that a cation-exchange column chromatography performed utilizing an HPLC apparatus will generally result in a greater "-fold" purification than the same technique utilizing a low pressure chromatography system. Methods exhibiting a lower degree of relative purification may have advantages in total recovery of protein product, or in maintaining the activity of an expressed protein. It is known that the migration of a polypeptide can vary, sometimes significantly, with different conditions of SDS/PAGE (Capaldi et al, 1977). It will, therefore, be appreciated that under differing electrophoresis conditions, the apparent molecular weights of purified or partially purified expression products may vary. High Performance Liquid Chromatography (HPLC) is characterized by a very rapid separation with extraordinary resolution of peaks. This is achieved by the use of very fine particles and high pressure to maintain an adequate flow rate. Separation can be accomplished in a matter of min, or at most an h. Moreover, only a very small volume of the sample is needed because the particles are so small and close-packed that the void volume is a very small fraction of the bed volume. Also, the concentration of the sample need not be very great because the bands are so narrow that there is very little dilution of the sample. Gel chromatography, or molecular sieve chromatography, is a special type of partition chromatography that is based on molecular size. The theory behind gel chromatography is that the column, which is prepared with tiny particles of an inert substance that contain small pores, separates larger molecules from smaller molecules as they pass through or around the pores, depending on their size. As long as the material of which the particles are made does not adsorb the molecules, the sole factor determining rate of flow is the size of the pores. Hence, molecules are eluted from the column in decreasing size, so long as the shape is relatively constant. Gel chromatography is unsurpassed for separating molecules of different size because separation is independent of all other factors such as pH, ionic strength, temperature, etc. Thus the elution volume is related in a simple matter to molecular weight. Affinity chromatography is a chromatographic procedure that relies on the specific affinity between a substance to be isolated and a molecule to which it can specifically bind to. This is a receptor-ligand type of interaction. The column material is synthesized by covalentiy coupling one of the binding partners to an insoluble matrix. The column material is then able to specifically adsorb the substance from the solution. Elution occurs by changing the conditions to those in which binding will not occur (e.g., altered pH, ionic strength, temperature, etc.). The matrix should be a substance that itself does not adsorb molecules to any significant extent and that has a broad range of chemical, physical and thermal stability. The ligand should be coupled in such a way as to not affect its binding properties. The ligand should also provide relatively tight binding. And it should be possible to elute the substance without destroying the sample or the ligand. One of the most common forms of affinity chromatography is immunoaffinity chromatography. The generation of antibodies that would be suitable for use in accord with the present invention is discussed below. 4.1.5 Synthetic Peptides The present invention also describes smaller HET-related peptides for use in various embodiments of the present invention. Because of their relatively small size, the peptides of the invention can also be synthesized in solution or on a solid support in accordance with conventional techniques. Various automatic synthesizers are commercially available and can be used in accordance with known protocols. See, for example, Stewart and Young, (1984); Tarn et al, (1983); Merrifield, (1986); and Barany and Merrifield (1979), each incorporated herein by reference. Short peptide sequences, or libraries of overlapping peptides, usually from about 6 up to about 35 to 50 amino acids, which correspond to selected regions of the HET protein, can be readily synthesized and then screened in screening assays designed to identify reactive peptides. Alternatively, recombinant DNA technology may be employed wherein a nucleotide sequence which encodes a peptide of the invention is inserted into an expression vector, transformed or transfected into an appropriate host cell, and cultivated under conditions suitable for expression. 4.1.6 Antigen Compositions The present invention also provides for the use of HET proteins or peptides as antigens for the immunization of animals relating to the production of antibodies. It is envisioned that either HET, or portions thereof, will be coupled, bonded, bound, conjugated, or chemically-linked to one or more agents via linkers, polylinkers, or derivatized amino acids. This may be performed such that a bispecific or multivalent composition or vaccine is produced. It is further envisioned that the methods used in the preparation of these compositions will be familiar to those of skill in the art and should be suitable for administration to animals, i.e., pharmaceutically acceptable. Preferred agents are the carriers are keyhole limpet hemocyanin (KLH) or bovine serum albumin (BS A). 4.2 Nucleic Acids The present invention also provides, in another embodiment, genes encoding HET. The present invention is not limited to the specific nucleic acids disclosed herein as SEQ ID NO:l. As discussed below, a "HET gene" may contain a variety of different bases and yet still produce a corresponding polypeptide that is indistinguishable functionally, and in some cases structurally, from the genes disclosed herein. Similarly, any reference to a nucleic acid should be read as encompassing a host cell containing that nucleic acid and, in some cases, capable of expressing the product of that nucleic acid. In addition to therapeutic considerations, cells expressing nucleic acids of the present invention may prove useful in the context of screening for agents that induce, repress, inhibit, augment, interfere with, block, abrogate, stimulate, or enhance the function of HET. 4.2.1 Nucleic Acids Encoding HET Nucleic acids according to the present invention may encode an entire HET gene, a domain of HET that expresses a tumor suppressing function, or any other fragment of the HET sequences set forth herein. The nucleic acid may be derived from genomic DNA, i.e., cloned directly from the genome of a particular organism. In preferred embodiments, however, the nucleic acid would comprise complementary DNA (cDNA). Also contemplated is a cDNA plus a natural intron or an intron derived from another gene; such engineered molecules are sometime referred to as "mini-genes." At a minimum, these and other nucleic acids of the present invention may be used as molecular weight standards in, for example, gel electrophoresis. The term "cDNA" is intended to refer to DNA prepared using messenger RNA (mRNA) as template. The advantage of using a cDNA, as opposed to genomic DNA or DNA polymerized from a genomic, non- or partially-processed RNA template, is that the cDNA primarily contains coding sequences of the corresponding protein. There may be times when the full or partial genomic sequence is preferred, such as where the non-coding regions are required for optimal expression or where non- coding regions such as introns are to be targeted in an antisense strategy. It also is contemplated that HET may be represented by natural variants that have slightly different nucleic acid sequences but, nonetheless, encode the same protein (see Table 1 below). As used in this application, the term "a nucleic acid encoding a HET" refers to a nucleic acid molecule that has been isolated free of total cellular nucleic acid. In preferred embodiments, the invention concerns a nucleic acid sequence essentially as set forth in SEQ ID NO:l . The term "as set forth in SEQ ID NO:l " means that the nucleic acid sequence substantially corresponds to a portion of SEQ ID NO:l. The term "functionally equivalent codon" is used herein to refer to codons that encode the same amino acid, such as the six codons for arginine or serine (Table 1 , below), and also refers to codons that encode biologically equivalent amino acids, as discussed in the following pages. TABLE 1 Amino Acids Codons Alanine Ala A GCA GCC GCG GCU Cysteine Cys C UGC UGU Aspartic acid Asp D GAC GAU Glutamic acid Glu E GAA GAG Phenylalanine Phe F UUC UUU Glycine Gly G GGA GGC GGG GGU Histidine His H CAC CAU Isoleucine He I AUA AUC AUU Lysine Lys K AAA AAG Leucine Leu L UUA UUG CUA CUC CUG CUU Methionine Met M AUG Asparagine Asn N AAC AAU Pro line Pro P CCA CCC CCG CCU Glutamine Gin Q CAA CAG Arginine Arg R AGA AGG CGA CGC CGG CGU Serine Ser S AGC AGU UCA UCC UCG UCU Threonine Thr T ACA ACC ACG ACU Valine Val V GUA GUC GUG GUU Tryptophan Trp W UGG Tyrosine Tyr Y UAC UAU The DNA segments of the present invention include those encoding biologically functional equivalent HET proteins and peptides, as described above. Such sequences may arise as a consequence of codon redundancy and amino acid functional equivalency that are known to occur naturally within nucleic acid sequences and the proteins thus encoded. Alternatively, functionally equivalent proteins or peptides may be created via the application of recombinant DNA technology, in which changes in the protein structure may be engineered, based on considerations of the properties of the amino acids being exchanged. Changes designed by man may be introduced through the application of site-directed mutagenesis techniques or may be introduced randomly and screened later for the desired function, as described below. A search of the GenBank nucleic acid sequence database identified the scaffold attachment factor SAF-B (GenBank accession number L43631) as the sequence most homologous to HET. SAF-B recently was cloned from a HeLa cell cDNA library (Renz and Fackelmayer, 1996) based on its ability to bind to scaffold/matrix attachment regions (S/MAR). A sequencing error in the reported sequence of SAF-B at position 344 bp (position 548 bp in HET) resulted in a frameshift of the first 100 amino acids of the reported SAF-B sequence (Renz and Fackelmayer, 1996). In addition, the 5' end of the HET gene is missing from the published SAF-B sequence (Renz and Fackelmayer, 1996). The HET cDNA disclosed herein has 205 bp at the 5' end which are not present in the SAF-B sequence, of which 152 bp code for amino acids. Thus, the reported N-terminal amino acid sequences of SAF-B and HET differ substantially (Renz and Fackelmayer, 1996). Additionally, there are 15 mismatches in the 3' untranslated region of SAF-B compared to the HET sequence. 4.2.2 Oligonucleotide Probes and Primers Naturally, the present invention also encompasses DNA segments that are complementary, or essentially complementary, to the sequence set forth in SEQ ID NO:l . Nucleic acid sequences that are "complementary" are those that are capable of base-pairing according to the standard Watson-Crick complementary rules. As used herein, the term "complementary sequences" means nucleic acid sequences that are complementary to the extent that they are capable of hybridizing to the nucleic acid segment of SEQ ID NO: 1 under relatively stringent conditions such as those described herein. Such sequences may encode the entire HET protein or functional or nonfunctional fragments thereof. Alternatively, the hybridizing segments may be shorter oligonucleotides. Sequences of 17 bases long should occur only once in the human genome and, therefore, suffice to specify a unique target sequence. Although shorter oligomers are easier to make and increase in vivo accessibility, numerous other factors are involved in determining the specificity of hybridization. Both binding affinity and sequence specificity of an oligonucleotide to its complementary target increases with increasing length. It is contemplated that exemplary oligonucleotides of 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or more base pairs will be used, although others are contemplated. Longer polynucleotides encoding 250, 500, 1000, 1212, 1500, 2000, 2500, 3000, or 3040 bases and longer are contemplated as well. Such oligonucleotides will find use, for example, as probes in Southern and Northern blots and as primers in amplification reactions. 4.2.3 Hybridization Conditions Suitable hybridization conditions will be well known to those of skill in the art. In certain applications, for example, substitution of amino acids by site-directed mutagenesis, it is appreciated that lower stringency conditions are required. Under these conditions, hybridization may occur even though the sequences of probe and target strand are not perfectly complementary, but are mismatched at one or more positions. Conditions may be rendered less stringent by increasing salt concentration and decreasing temperature. For example, a medium stringency condition could be provided by about 0.1 to 0.25 M NaCl, at temperatures of about 37°C to about 55°C, while a low stringency condition could be provided by about 0.15 M to about 0.9 M salt, at temperatures ranging from about 20°C to about 55°C. Thus, hybridization conditions can be readily manipulated, and thus will generally be a method of choice depending on the desired results. In other embodiments, hybridization may be achieved under conditions of, for example, 50 mM Tris-HCl (pH 8.3), 75 mM KC1, 3 mM MgCl 2 , 10 mM dithiothreitol, at temperatures between approximately 20°C to about 37°C. Other hybridization conditions utilized could include approximately 10 mM Tris-HCl (pH 8.3), 50 mM KC1, 1.5 μM MgCl 2 , at temperatures ranging from approximately 40°C to about 72°C. Formamide and SDS (sodium dodecylsulphate) also may be used to alter the hybridization conditions. One method of using probes and primers of the present invention is in the search for genes related to HET. Normally, the target DNA will be a genomic or cDNA library, although screening may involve analysis of RNA molecules. By varying the stringency of hybridization, and the region of the probe, different degrees of homology may be discovered. 4.2.4 Site-Directed Mutagenesis Another way of exploiting probes and primers of the present invention is in site-directed, or site-specific mutagenesis. Site-specific mutagenesis is a technique useful in the preparation of individual peptides, or biologically functional equivalent proteins or peptides, through specific mutagenesis of the underlying DNA. The technique further provides a ready ability to prepare and test sequence variants, incorporating one or more of the foregoing considerations, by introducing one or more nucleotide sequence changes into the DNA. Site-specific mutagenesis allows the production of mutants through the use of specific oligonucleotide sequences which encode the DNA sequence of the desired mutation, as well as a sufficient number of adjacent nucleotides, to provide a primer sequence of sufficient size and sequence complexity to form a stable duplex on both sides of the deletion junction being traversed. Typically, a primer of about 17 to 25 nucleotides in length is preferred, with about 5 to 10 residues on both sides of the junction of the sequence being altered. The technique typically employs a bacteriophage vector that exists in both a single stranded and double stranded form. Typical vectors useful in site-directed mutagenesis include vectors such as the Ml 3 phage. These phage vectors are commercially available and their use is generally well known to those skilled in the art. Double stranded plasmids are also routinely employed in site directed mutagenesis, which eliminates the step of transferring the gene of interest from a phage to a plasmid. In general, site-directed mutagenesis is performed by first obtaining a single- stranded vector, or by melting two strands of a double stranded vector, which includes within its sequence a DNA sequence encoding the desired protein. An oligonucleotide primer bearing the desired mutated sequence is synthetically prepared. This primer is then annealed with the single-stranded DNA preparation, taking into account the degree of mismatch when selecting hybridization conditions, and subjected to DNA polymerizing enzymes such as E coli polymerase I Klenow fragment, in order to complete the synthesis of the mutation-bearing strand. Thus, a heteroduplex is formed wherein one strand encodes the original non-mutated sequence and the second strand bears the desired mutation. This heteroduplex vector is then used to transform appropriate cells, such as E. coli cells, and clones are selected that include recombinant vectors bearing the mutated sequence arrangement. The preparation of sequence variants of the selected gene using site-directed mutagenesis is provided as a means of producing potentially useful species and is not meant to be limiting, as there are other ways in which sequence variants of genes may be obtained. For example, recombinant vectors encoding the desired gene may be treated with mutagenic agents, such as hydroxylamine, to obtain sequence variants. 4.2.5 Antisense Constructs In some cases, mutant tumor suppressors may not be non-functional. Rather, they may have aberrant functions that cannot be overcome by replacement gene therapy, even where the "wild-type" molecule is expressed in amounts in excess of the mutant polypeptide. Antisense treatments are one way of addressing this situation. Antisense technology also may be used to "knock-out" function of HΕT in the development of cell lines or transgenic mice for research, diagnostic and screening purposes. Antisense methodology takes advantage of the fact that nucleic acids tend to pair with "complementary" sequences. By complementary, it is meant that polynucleotides are those which are capable of base-pairing according to the standard Watson-Crick complementarity rules. That is, the larger purines will base pair with the smaller pyrimidines to form combinations of guanine paired with cytosine (G:C) and adenine paired with either thymine (A:T) in the case of DNA, or adenine paired with uracil (A:U) in the case of RNA. Inclusion of less common bases such as inosine, 5-methylcytosine, 6-methyladenine, hypoxanthine and others in hybridizing sequences does not interfere with pairing. Targeting double-stranded (ds) DNA with polynucleotides leads to triple-helix formation; targeting RNA will lead to double-helix formation. Antisense polynucleotides, when introduced into a target cell, specifically bind to their target polynucleotide and interfere with transcription, RNA processing, transport, translation and or stability. Antisense RNA constructs, or DNA encoding such antisense RNAs, may be employed to inhibit gene transcription, or translation, or both within a host cell, either in vitro or in vivo, such as within a host animal, including a human subject. Antisense constructs may be designed to bind to the promoter and other control regions, exons, introns, or even exon-intron boundaries of a gene. It is contemplated that the most effective antisense constructs will include regions complementary to intron exon splice junctions. Thus, it is proposed that a preferred embodiment includes an antisense construct with complementarity to regions within about 50-200 bases of an intron-exon splice junction. It has been observed that some exon sequences can be included in the construct without seriously affecting the target selectivity thereof. The amount of exonic material included will vary depending on the particular exon and intron sequences used. One can readily test whether too much exon DNA is included simply by testing the constructs in vitro to determine whether normal cellular function is affected or whether the expression of related genes having complementary sequences is affected. As stated above, "complementary" or "antisense" means polynucleotide sequences that are substantially complementary over their entire length and have very few base mismatches. For example, sequences of fifteen bases in length may be termed complementary when they have complementary nucleotides at thirteen or fourteen positions. Naturally, sequences which are completely complementary will be sequences which are entirely complementary throughout their entire length and have no base mismatches. Other sequences with lower degrees of homology also are contemplated. For example, an antisense construct which has limited regions of high homology, but also contains a non-homologous region (e.g., ribozyme; see below) could be designed. These molecules, though having less than 50% homology, would bind to target sequences under appropriate conditions. It may be advantageous to combine portions of genomic DNA with cDNA or synthetic sequences to generate specific constructs. For example, where an intron is desired in the ultimate construct, a genomic clone will need to be used. The cDNA or a synthesized polynucleotide may provide more convenient restriction sites for the remaining portion of the construct and, therefore, would be used for the rest of the sequence. 4.2.6 Ribozymes Another approach for addressing the "dominant negative" mutant tumor suppressor is through the use of ribozymes. Although proteins traditionally have been used for catalysis of nucleic acids, another class of macromolecules has emerged as useful in this endeavor. Ribozymes are RNA-protein complexes that cleave nucleic acids in a site-specific fashion. Ribozymes have specific catalytic domains that possess endonuclease activity (Kim and Cech, 1987; Gerlach et al, 1987; Forster and Symons, 1987). For example, a large number of ribozymes accelerate phosphoester transfer reactions with a high degree of specificity, often cleaving only one of several phosphoesters in an oligonucleotide substrate (Cech et al. , 1981; Michel and Westhof, 1990; Reinhold-Hurek and Shub, 1992). This specificity has been attributed to the requirement that the substrate bind via specific base-pairing interactions to the internal guide sequence ("IGS") of the ribozyme prior to chemical reaction. Ribozyme catalysis has primarily been observed as part of sequence-specific cleavage/ligation reactions involving nucleic acids (Joyce, 1989; Cech et al, 1981). For example, U.S. Patent No. 5,354,855 reports that certain ribozymes can act as endonucleases with a sequence specificity greater than that of known ribonucleases and approaching that of the DNA restriction enzymes. Thus, sequence-specific ribozyme-mediated inhibition of gene expression may be particularly suited to therapeutic applications (Scanlon et al, 1991 ; Sarver et al, 1990). Recently, it was reported that ribozymes elicited genetic changes in some cell lines to which they were applied; the altered genes included the oncogenes H-ras, c-fos and genes of HIV. Most of this work involved the modification of a target mRNA, based on a specific mutant codon that is cleaved by a specific ribozyme. 4.2.7 Vectors for Cloning, Gene Transfer and Expression Within certain embodiments expression vectors are employed to express the HET polypeptide product, which can then be purified and, for example, be used to vaccinate animals to generate antisera or monoclonal antibody with which further studies may be conducted. In other embodiments, the expression vectors are used in gene therapy. Expression requires that appropriate signals be provided in the vectors, and which include various regulatory elements, such as enhancers/promoters from both viral and mammalian sources that drive expression of the genes of interest in host cells. Elements designed to optimize messenger RNA stability and translatability in host cells also are defined. The conditions for the use of a number of dominant drug selection markers for establishing permanent, stable cell clones expressing the products are also provided, as is an element that links expression of the drug selection markers to expression of the polypeptide. 4.2.7.1 Regulatory Elements Throughout this application, the term "expression construct" is meant to include any type of genetic construct containing a nucleic acid coding for a gene product in which part or all of the nucleic acid coding sequence is capable of being transcribed. The transcript may be translated into a protein, but it need not be. In certain embodiments, expression includes both transcription of a gene and translation of mRNA into a gene product. In other embodiments, expression only includes transcription of the nucleic acid encoding a gene of interest. In preferred embodiments, the nucleic acid encoding a gene product is under transcriptional control of a promoter. A "promoter" refers to a DNA sequence recognized by the synthetic machinery of the cell, or introduced synthetic machinery, required to initiate the specific transcription of a gene. The phrase "under transcriptional control" means that the promoter is in the correct location and orientation in relation to the nucleic acid to control RNA polymerase initiation and expression of the gene. The term promoter will be used here to refer to a group of transcriptional control modules that are clustered around the initiation site for RNA polymerase II. Much of the thinking about how promoters are organized derives from analyses of several viral promoters, including those for the HSV thymidine kinase (tk) and SV40 early transcription units. These studies, augmented by more recent work, have shown that promoters are composed of discrete functional modules, each consisting of approximately 7-20 bp of DNA, and containing one or more recognition sites for transcriptional activator or repressor proteins. At least one module in each promoter functions to position the start site for RNA synthesis. The best known example of this is the TATA box. However, in some promoters lacking a TATA box, such as the promoter for the mammalian terminal deoxynucleotidyl transferase gene and the promoter for the SV40 late genes, a discrete element overlying the start site itself helps to fix the place of initiation. Additional promoter elements regulate the frequency of transcriptional initiation. Typically, these are located in the region 30-110 bp upstream of the start site, although a number of promoters have recently been shown to contain functional elements downstream of the start site as well. The spacing between promoter elements frequently is flexible, so that promoter function is preserved when elements are inverted or moved relative to one another. In the tk promoter, the spacing between promoter elements can be increased to 50 bp before activity begins to decline. Depending on the promoter, it appears that individual elements can function either cooperatively or independently to activate transcription. The particular promoter employed to control the expression of a nucleic acid sequence of interest is not believed to be important, so long as it is capable of directing the expression of the nucleic acid in the targeted cell. Thus, where a human cell is targeted, it is preferable to position the nucleic acid coding region adjacent and under the control of a promoter that is capable of being expressed in a human cell. Generally speaking, such a promoter might include either a human or viral promoter. In various embodiments, the human cytomegalovirus (CMV) immediate early gene promoter, the SV40 early promoter, the Rous sarcoma virus long terminal repeat, rat insulin promoter, and glyceraldehyde-3 -phosphate dehydrogenase promoter can be used to obtain high-level expression of the coding sequence of interest. The use of other viral or mammalian cellular or bacterial phage promoters which are well-known in the art to achieve expression of a coding sequence of interest is contemplated as well, provided that the levels of expression are sufficient for a given purpose. By employing a promoter with well-known properties, the level and pattern of expression of the protein of interest following transfection or transformation can be optimized. Further, selection of a promoter that is regulated in response to specific physiologic signals can permit inducible expression of the gene product. Tables 2 and 3 list several elements/promoters which may be employed, in the context of the present invention, to regulate the expression of the gene of interest. This list is not intended to be exhaustive of all the possible elements involved in the promotion of gene expression but, merely, to be exemplary thereof. Enhancers are genetic elements that increase transcription from a promoter located at a distant position on the same molecule of DNA. Enhancers are organized much like promoters. That is, they are composed of many individual elements, each of which binds to one or more transcriptional proteins. The basic distinction between enhancers and promoters is operational. An enhancer region as a whole must be able to stimulate transcription at a distance; this need not be true of a promoter region or its component elements. On the other hand, a promoter must have one or more elements that direct initiation of RNA synthesis at a particular site and in a particular orientation, whereas enhancers lack these specificities. Promoters and enhancers are often overlapping and contiguous, often seeming to have a very similar modular organization. Below is a list of viral promoters, cellular promoters/enhancers, and inducible promoters/enhancers that could be used in combination with the nucleic acid encoding a gene of interest in an expression construct (Table 2 and Table 3). Additionally, any promoter/enhancer combination (as per the Eukaryotic Promoter Data Base EPDB) also could be used to drive expression of the gene. Eukaryotic cells can support cytoplasmic transcription from certain bacterial promoters if the appropriate bacterial polymerase is provided, either as part of the delivery complex or as an additional genetic expression construct. TABLE 2 ENHANCER/PROMOTER Immunoglobulin Heavy Chain Immunoglobulin Light Chain T-Cell Receptor HLA DQ α and DQ β β-Interferon Interleukin-2 Interleukin-2 Receptor MHC Class II 5 MHC Class II HLA-DRα β-Actin Prealbumin (Transthyretin) Muscle Creatine Kinase Elastase / Metallothionein Collagenase Albumin Gene TABLE 2 (cont'd) ENHANCER/PROMOTER α-Fetoprotein τ-Globin β-Globin e-fos c-HA-ras Insulin Neural Cell Adhesion Molecule (NCAM) αl-Antitrypsin H2B (TH2B) Histone Mouse or Type I Collagen Glucose-Regulated Proteins (GRP94 and GRP78) Rat Growth Hormone Human Serum Amyloid A (SAA) TroponinI (TNI) Platelet-Derived Growth Factor Duchenne Muscular Dystrophy SV40 Polyoma Retro viruses Papilloma Virus Hepatitis B Virus TABLE 2 (cont'd) ENHANCER/PROMOTER Human Immunodeficiency Virus Cytomegalovirus TABLE 3 Where a cDNA insert is employed, typically one will typically include a polyadenylation signal to effect proper polyadenylation of the gene transcript. The nature of the polyadenylation signal is not believed to be crucial to the successful practice of the invention, and any such sequence may be employed, such as human growth hormone and SV40 polyadenylation signals. Also contemplated as an element of the expression construct is a terminator. These elements can serve to enhance message levels and to minimize read through from the construct into other sequences. 4.2.7.2 Selectable Markers In certain embodiments of the invention, the cells containing nucleic acid constructs of the present invention may be identified in vitro or in vivo by including a marker in the expression construct. Such markers would confer an identifiable change to the cell permitting easy identification of cells containing the expression construct. Usually the inclusion of a drug selection marker aids in cloning and in the selection of transformants. For example, genes that confer resistance to neomycin, puromycin, hygromycin, DHFR, GPT, zeocin, and histidinol are useful selectable markers. Alternatively, enzymes such as herpes simplex virus thymidine kinase (tk) or chloramphenicol acetyltransferase (CAT) may be employed. Immunologic markers also can be employed. The selectable marker employed is not believed to be important, so long as it is capable of being expressed simultaneously with the nucleic acid encoding a gene product. Further examples of selectable markers are well known to one of skill in the art. 4.2.7.3 Delivery of Expression Vectors There are a number of ways in which expression vectors may introduced into cells. In certain embodiments of the invention, the expression construct comprises a virus or engineered construct derived from a viral genome. The ability of certain viruses to enter cells via receptor-mediated endocytosis, to integrate into a host cell genome, and express viral genes stably and efficiently have made them attractive candidates for the transfer of foreign genes into mammalian cells (Ridgeway, 1988; Nicolas and Rubenstein, 1988; Baichwal and Sugden. 1986; Temin, 1986). Preferred gene therapy vectors are generally viral vectors. Although some viruses that can accept foreign genetic material are limited in the number of nucleotides they can accommodate and in the range of cells they infect, these viruses have been demonstrated to successfully effect gene expression. However, adenoviruses do not integrate their genetic material into the host genome and therefore do not require host replication for gene expression making them ideally suited for rapid, efficient, heterologous gene expression. Techniques for preparing replication infective viruses are well known in the art. Of course in using viral delivery systems, one will desire to purify the virion sufficiently to render it essentially free of undesirable contaminants, such as defective interfering viral particles or endotoxins and other pyrogens such that it will not cause any untoward reactions in the cell, animal or individual receiving the vector construct. A preferred means of purifying the vector involves the use of buoyant density gradients, such as cesium chloride gradient centrifugation. Viruses used as gene vectors such as DNA viruses may include the papovaviruses (e.g., simian virus 40, bovine papilloma virus, and polyoma) (Ridgeway, 1988; Baichwal and Sugden, 1986) and adenoviruses (Ridgeway, 1988; Baichwal and Sugden, 1986). One of the preferred methods for in vivo delivery involves the use of an adenovirus expression vector. Although adenovirus vectors are known to have a low capacity for integration into genomic DNA, this feature is counterbalanced by the high efficiency of gene transfer afforded by these vectors. "Adenovirus expression vector" is meant to include those constructs containing adenovirus sequences sufficient to (a) support packaging of the construct and (b) to express an antisense polynucleotide that has been cloned therein. The expression vector comprises a genetically engineered form of adenovirus. Knowledge of the genetic organization of adenovirus, a 36 kb, linear, double-stranded DNA virus, allows substitution of large pieces of adenoviral DNA with foreign sequences up to 7 kb (Grunhaus and Horwitz, 1992). In contrast to retro viral infection, the adenoviral infection of host cells does not result in chromosomal integration because adenoviral DNA can replicate in an episomal manner without potential genotoxicity. Also, adenoviruses are structurally stable, and no genome rearrangement has been detected after extensive amplification. Adenovirus can infect virtually all epithelial cells regardless of their cell cycle stage. So far, adenoviral infection appears to be linked only to mild disease such as acute respiratory disease in humans. Adenovirus is particularly suitable for use as a gene transfer vector because of its mid-sized genome, ease of manipulation, high titer, wide target cell range and high infectivity. Both ends of the viral genome contain 100-200 base pair inverted repeats (ITRs), which are cis elements necessary for viral DNA replication and packaging. The early (E) and late (L) regions of the genome contain different transcription units that are divided by the onset of viral DNA replication. The El region (El A and E1B) encodes proteins responsible for the regulation of transcription of the viral genome and a few cellular genes. The expression of the E2 region (E2A and E2B) results in the synthesis of the proteins for viral DNA replication. These proteins are involved in DNA replication, late gene expression and host cell shut-off (Renan, 1990). The products of the late genes, including the majority of the viral capsid proteins, are expressed only after significant processing of a single primary transcript issued by the major late promoter (MLP). The MLP, (located at 16.8 m.u.) is particularly efficient during the late phase of infection, and all the mRNAs issued from this promoter possess a 5'-tripartite leader (TPL) sequence which makes them preferred mRNAs for translation. In currently used systems, recombinant adenovirus is generated from homologous recombination between shuttle vector and provirus vector. Due to the possible recombination between two proviral vectors, wild-type adenovirus may be generated from this process. Therefore, it is critical to isolate a single clone of virus from an individual plaque and examine its genomic structure. Generation and propagation of adenovirus vectors which are replication deficient depend on a unique helper cell line, designated 293, which is transformed from human embryonic kidney cells by Ad5 DNA fragments and constitutively expresses El proteins (Graham et al, 1977). Since the E3 region is dispensable from the adenovirus genome (Jones and Shenk. 1978). the current adenovirus vectors, with the help of 293 cells, carry foreign DNA in either the El , the E3, or both regions (Graham and Prevec, 1991). In nature, adenovirus can package approximately 105% of the wild-type genome (Ghosh-Choudhury et al, 1987), providing capacity for about 2 extra kb of DNA. Combined with the approximately 5.5 kb of DNA that is replaceable in the El and E3 regions, the maximum capacity of the current adenovirus vector is under 7.5 kb, or about 15% of the total length of the vector. More than 80% of the adenovirus viral genome remains in the vector backbone and is the source of vector-borne cytotoxicity. Also, the replication deficiency of the El -deleted virus is incomplete. For example, leakage of viral gene expression has been observed with the currently available vectors at high multiplicities of infection (MOI) (Mulligan, 1993). Helper cell lines may be derived from human cells such as human embryonic kidney cells, muscle cells, hematopoietic cells or other human embryonic mesenchymal or epithelial cells. Alternatively, the helper cells, may be derived from the cells of other mammalian species that are permissive for human adenovirus. Such cells include, e.g., Vero cells or other monkey embryonic mesenchymal or epithelial cells. As discussed, the preferred helper cell line is 293. Recently, Racher et al, (1995) disclosed improved methods for culturing 293 cells and propagating adenovirus. In one format, natural cell aggregates are grown by inoculating individual cells into 1 liter siliconized spinner flasks (Techne, Cambridge, UK) containing 100-200 ml of medium. Following stirring at 40 rpm, the cell viability is estimated with trypan blue. In another format, Fibra-Cel microcarriers (Bibby Sterlin, Stone, UK) (5 g/1) are employed as follows. A cell innoculum, resuspended in 5 ml of medium, is added to the carrier (50 ml) in a 250 ml Erlenmeyer flask and left stationary, with occasional agitation, for 1 to 4 h. The medium is then replaced with 50 ml of fresh medium and shaking is initiated. For virus production, cells are allowed to grow to about 80% confluence, after which time the medium is replaced (to 25% of the final volume) and adenovirus added at an MOI of 0.05. Cultures are left stationary overnight, following which the volume is increased to 100%) and shaking is commenced for another 72 h. Other than the requirement that the adenovirus vector be replication defective, or at least conditionally defective, the nature of the adenovirus vector is not believed to be crucial to the successful practice of the invention. The adenovirus may be of any of the 42 different known sero types or subgroups A-F. Adenovirus type 5 of subgroup C is the preferred starting material in order to obtain the conditional replication-defective adenovirus vector for use in the present invention. This is because Adenovirus type 5 is a human adenovirus about which a great deal of biochemical and genetic information is known, and it has historically been used for most constructions employing adenovirus as a vector. A typical vector applicable to practicing the present invention is replication defective and will not have an adenovirus El region. Thus, it will be most convenient to introduce the polynucleotide encoding the HET gene at the position from which the El -coding sequences have been removed. However, the position of insertion of the construct within the adenovirus sequences is not critical. The polynucleotide encoding the HET gene may also be inserted in lieu of the deleted E3 region in E3 replacement vectors as described by Karlsson et al, (1986) or in the E4 region where a helper cell line or helper virus complements the E4 defect. Adenovirus is easy to grow and manipulate and exhibits broad host range in vitro and in vivo. This group of viruses can be obtained in high titers, e.g., 10 -10 plaque-forming units per ml, and they are highly infective. The life cycle of adenovirus does not require integration into the host cell genome. The foreign genes delivered by adenovirus vectors are episomal and, therefore, have low genotoxicity to host cells. No side effects have been reported in studies of vaccination with wild-type adenovirus (Couch et al, 1963; Top et al, 1971), demonstrating their safety and therapeutic potential as in vivo gene transfer vectors. Adenovirus vectors have been used in eukaryotic gene expression (Levrero et al, 1991; Gomez-Foix et al, 1992) and vaccine development (Grunhaus and Horwitz, 1992; Graham and Prevec, 1991). Recently, animal studies suggested that recombinant adenovirus could be used for gene therapy (Stratford-Perricaudet and Perricaudet, 1991; Stratford-Perricaudet et al, 1990; Rich et al, 1993). Studies in administering recombinant adenovirus to different tissues include trachea instillation (Rosenfeld et al, 1991 ; Rosenfeld et al, 1992), muscle injection (Ragot et al, 1993), peripheral intravenous injections (Herz and Gerard, 1993) and stereotactic inoculation into the brain (Le Gal La Salle et al, 1993). Other gene transfer vectors may be constructed from retroviruses. The retroviruses are a group of single-stranded RNA viruses characterized by an ability to convert their RNA to double-stranded DNA in infected cells by a process of reverse- transcription (Coffin, 1990). The resulting DNA then stably integrates into cellular chromosomes as a provirus and directs synthesis of viral proteins. The integration results in the retention of the viral gene sequences in the recipient cell and its descendants. The retroviral genome contains three genes, gag, pol, and env. that code for capsid proteins, polymerase enzyme, and envelope components, respectively. A sequence found upstream from the gag gene contains a signal for packaging of the genome into virions. Two long terminal repeat (LTR) sequences are present at the 5' and 3' ends of the viral genome. These contain strong promoter and enhancer sequences, and also are required for integration in the host cell genome (Coffin, 1990). In order to construct a retroviral vector, a nucleic acid encoding a HET gene is inserted into the viral genome in the place of certain viral sequences to produce a virus that is replication-defective. In order to produce virions, a packaging cell line containing the gag, pol, and env genes, but without the LTR and packaging components, is constructed (Mann et al, 1983). When a recombinant plasmid containing a cDNA, together with the retroviral LTR and packaging sequences is introduced into this cell line (by calcium phosphate precipitation for example), the packaging sequence allows the RNA transcript of the recombinant plasmid to be packaged into viral particles, which are then secreted into the culture media (Nicolas and Rubenstein, 1988; Temin, 1986; Mann et al, 1983). The media containing the recombinant retroviruses is then collected, optionally concentrated, and used for gene transfer. Retroviral vectors are capable of infecting a broad variety of cell types. However, integration and stable expression require the division of host cells (Paskind et al, 1975). A novel approach designed to allow specific targeting of retrovirus vectors was recently developed based on the chemical modification of a retrovirus by the chemical addition of lactose residues to the viral envelope. This modification could permit the specific infection of hepatocytes via sialoglycoprotein receptors. A different approach to targeting of recombinant retroviruses has been designed in which biotinylated antibodies against a retroviral envelope protein and against a specific cell receptor were used. The antibodies were coupled via the biotin components by using streptavidin (Roux et al, 1989). Using antibodies against major histocompatibility complex class I and class II antigens, the infection of a variety of human cells that bear those surface antigens with an ecotropic virus in vitro was demonstrated (Roux et al, 1989). There are certain limitations to the use of retrovirus vectors. For example, retrovirus vectors usually integrate into random sites in the cell genome. This can lead to insertional mutagenesis through the interruption of host genes or through the insertion of viral regulatory sequences that can interfere with the function of flanking genes (Varmus et al, 1981). Another concern with the use of defective retrovirus vectors is the potential appearance of wild-type replication-competent virus in the packaging cells. This may result from recombination events in which the intact sequence from the recombinant virus inserts upstream from the gag, pol, env sequence integrated in the host cell genome. However, new packaging cell lines are now available that should greatly decrease the likelihood of recombination (Markowitz et al, 1988; Hersdorffer et a/., 1990). Other viral vectors may be employed as expression constructs. Vectors derived from viruses such as vaccinia virus (Ridgeway, 1988; Baichwal and Sugden, 1986; Coupar et al, 1988), adeno-associated virus (AAV) (Ridgeway, 1988; Baichwal and Sugden, 1986; Hermonat and Muzycska, 1984), and herpes viruses may be employed. They offer several attractive features for various mammalian cells (Friedmann, 1989; Ridgeway, 1988; Baichwal and Sugden, 1986; Coupar et al, 1988; Horwich et al, 1990). With the recent recognition of defective hepatitis B viruses, new insight has been gained into the structure-function relationship of different viral sequences. In vitro studies showed that the virus could retain the ability for helper-dependent packaging and reverse transcription despite the deletion of up to 80% of its genome (Horwich et al, 1990). This suggests that large portions of the genome can be replaced with foreign genetic material. The hepatotropism and persistence (integration) are particularly attractive properties for liver-directed gene transfer. Chang et al. (1991) recently introduced the chloramphenicol acetyltransferase (CAT) gene into duck hepatitis B virus genome in the place of the polymerase, surface, and pre-surface coding sequences. It was co-transfected with wild-type virus into an avian hepatoma cell line. Culture media containing high titers of the recombinant virus were used to infect primary duckling hepatocytes. Stable CAT gene expression was detected for at least 24 days after transfection (Chang et al, 1991). To effect expression of sense or antisense gene constructs, the expression construct must be delivered into a cell. This delivery may be accomplished in vitro, as in laboratory procedures for transforming cells lines, or in vivo or ex vivo, as in the treatment of certain disease states. One mechanism for delivery is via viral infection where the expression construct is encapsidated in an infectious viral particle. Several non-viral methods for the transfer of expression constructs into cultured mammalian cells also are contemplated by the present invention. These include calcium phosphate precipitation (Graham and Van Der Eb, 1973; Chen and Okayama, 1987; Rippe et al, 1990), DEAE-dextran (Gopal, 1985), electroporation (Tur-Kaspa et al, 1986; Potter et al, 1984), direct microinjection (Harland and Weintraub, 1985), DNA-loaded liposomes (Nicolau and Sene, 1982; Fraley et al, 1979) and lipofectamine-DNA complexes, cell sonication (Fechheimer et al, 1987), gene bombardment using high velocity microprojectiles (Yang et al, 1990), and receptor-mediated transfection (Wu and Wu, 1987; Wu and Wu, 1988). Some of these techniques may be successfully adapted for in vivo or ex vivo use. Once the expression construct has been delivered into the cell the nucleic acid encoding the HET gene may be positioned and expressed at different sites. In certain embodiments, the nucleic acid encoding the gene may be stably integrated into the genome of the cell. This integration may be in the cognate location and orientation via homologous recombination (gene replacement) or it may be integrated in a random, non-specific location (gene augmentation). In yet further embodiments, the nucleic acid may be stably maintained in the cell as a separate, episomal segment of DNA. Such nucleic acid segments or "episomes" encode sequences sufficient to permit maintenance and replication independent of or in synchronization with the host cell cycle. How the expression construct is delivered to a cell and where in the cell the nucleic acid remains is dependent on the type of expression construct employed. In yet another embodiment of the invention, the expression construct may simply consist of naked recombinant DNA or plasmids. Transfer of the construct may be performed by any of the methods mentioned above which physically or chemically permeabilize the cell membrane. This is particularly applicable for transfer in vitro but it may be applied to in vivo use as well. Dubensky et al (1984) successfully injected polyomavirus DNA in the form of calcium phosphate precipitates into liver and spleen of adult and newborn mice demonstrating active viral replication and acute infection. Benvenisty and Neshif (1986) also demonstrated that direct intraperitoneal injection of calcium phosphate-precipitated plasmids results in expression of the transfected genes. It is envisioned that DNA encoding a HET gene may also be transferred in a similar manner in vivo and express the gene product. In still another embodiment of the invention for transferring a naked DNA expression construct into cells may involve particle bombardment. This method depends on the ability to accelerate DNA-coated microprojectiles to a high velocity allowing them to pierce cell membranes and enter cells without killing them (Klein et al, 1987). Several devices for accelerating small particles have been developed. One such device relies on a high voltage discharge to generate an electrical current, which in turn provides the motive force (Yang et al, 1990). The microprojectiles used have consisted of biologically inert substances such as tungsten or gold beads. In a further embodiment of the invention, the expression construct may be entrapped in a liposome. Liposomes are vesicular structures characterized by a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh and Bachhawat. 1991 ). Also contemplated are lipofectamine-DNA complexes. Liposome-mediated nucleic acid delivery and expression of foreign DNA in vitro has been very successful. Wong et al, (1980) demonstrated the feasibility of liposome-mediated delivery and expression of foreign DNA in cultured chick embryo, HeLa, and hepatoma cells. Nicolau et al, (1987) accomplished successful liposome- mediated gene transfer in rats after intravenous injection. In certain embodiments of the invention, the liposome may be complexed with a hemagglutinating virus (HVJ). This has been shown to facilitate fusion with the cell membrane and promote cell entry of liposome-encapsulated DNA (Kaneda et al, 1989). In other embodiments, the liposome may be complexed or employed in conjunction with nuclear non-histone chromosomal proteins (HMG-1) (Kato et al, 1991). In yet further embodiments, the liposome may be complexed or employed in conjunction with both HVJ and HMG-1. In that such expression constructs have been successfully employed in transfer and expression of nucleic acid in vitro and in vivo, then they are applicable for the present invention. Where a bacterial promoter is employed in the DNA construct, it also will be desirable to include within the liposome an appropriate bacterial polymerase. Other expression constructs which can be employed to deliver a nucleic acid encoding a HET gene into cells are receptor-mediated delivery vehicles. These take advantage of the selective uptake of macromolecules by receptor-mediated endocytosis in almost all eukaryotic cells. Because of the cell type-specific distribution of various receptors, the delivery can be highly specific (Wu and Wu, 1993). Receptor-mediated gene targeting vehicles generally consist of two components: a cell receptor-specific ligand and a DNA-binding agent. Several ligands have been used for receptor-mediated gene transfer. The most extensively characterized ligands are asialoorosomucoid (ASOR) (Wu and Wu, 1987) and transferrin (Wagner et al, 1990). Recently, a synthetic neoglycoprotein, which recognizes the same receptor as ASOR, has been used as a gene delivery vehicle (Ferkol et al, 1993; Perales et al, 1994) and epidermal growth factor (EGF) has also been used to deliver genes to squamous carcinoma cells (Myers, EPO 0273085). In other embodiments, the delivery vehicle may comprise a ligand and a liposome. For example, Nicolau et al, (1987) employed lactosyl-ceramide, a galactose-terminal asialganglioside, incorporated into liposomes and observed an increase in the uptake of the insulin gene by hepatocytes. Thus, it is feasible that a nucleic acid encoding a HET gene also may be specifically delivered into a cell type such as lung, epithelial, or tumor cells, by any number of receptor-ligand systems with or without liposomes. For example, epidermal growth factor (EGF) may be used as the receptor for mediated delivery of a nucleic acid encoding a gene in many tumor cells that exhibit upregulation of EGF receptor. Mannose can be used to target the mannose receptor on liver cells. Also, antibodies to CD5 (CLL), CD22 (lymphoma), CD25 (T-cell leukemia), and MAA (melanoma) can be used similarly as targeting moieties. In certain embodiments, gene transfer may more easily be performed under ex vivo conditions. Ex vivo gene therapy refers to the isolation of cells from an animal, the delivery of a nucleic acid into the cells in vitro, and then the return of the modified cells back into an animal. This may involve the surgical removal of tissue/organs from an animal or the primary culture of cells and tissues. Primary mammalian cell cultures may be prepared in various ways. In order for the cells to be kept viable while in vitro and in contact with the expression construct, it is necessary to ensure that the cells maintain contact with the correct ratio of oxygen and carbon dioxide and nutrients but are protected from microbial contamination. Cell culture techniques are well documented and are disclosed herein by reference (Freshner, 1992). Examples of useful mammalian host cell lines are Vero and HeLa cells and cell lines of Chinese hamster ovary, W138, BHK, COS-7, 293, HepG2, NIH3T3, RIN, and MDCK cells. In addition, a host cell strain may be chosen that modulates the expression of the inserted sequences, or modifies and processes the gene product in the manner desired. Such modifications (e.g., glycosylation) and processing (e.g., cleavage) of protein products may be important for the function of the protein. Different host cells have characteristic and specific mechanisms for the post- translational processing and modification of proteins. Appropriate cell lines or host systems can be chosen to insure the correct modification and processing of the foreign protein expressed. A number of selection systems may be used including, but not limited to, HSV thymidine kinase, hypoxanthine-guanine phosphoribosyltransferase and adenine phosphoribosyltransferase genes, in tk-, hgprt- or aprt- cells, respectively. Also, anti- metabolite resistance can be used as the basis of selection for dhfr: that confers resistance to methotrexate; gpt, that confers resistance to mycophenolic acid; neo, that confers resistance to the aminoglycoside G418; and hygro, that confers resistance to hygromycin. Animal cells can be propagated in vitro in two modes: as non-anchorage dependent cells growing in suspension throughout the bulk of the culture or as anchorage-dependent cells requiring attachment to a solid substrate for their propagation (i. e. , a monolayer type of cell growth). Non-anchorage dependent or suspension cultures from continuous established cell lines are the most widely used means of large scale production of cells and cell products. However, suspension cultured cells have limitations, such as tumorigenic potential and lower protein production than adherent T-cells. Large scale suspension culture of mammalian cells in stirred tanks is a common method for production of recombinant proteins. Two suspension culture reactor designs are in wide use - the stirred reactor and the airlift reactor. The stirred design has been used successfully on an 8000 liter capacity for the production of interferon. Cells are grown in a stainless steel tank with a height-to-diameter ratio of 1 : 1 to 3 : 1. The culture usually is mixed with one or more agitators, based on bladed disks or marine propeller patterns. Agitator systems offering less shear forces than blades have been described. Agitation may be driven either directly or indirectly by magnetically coupled drives. Indirect drives reduce the risk of microbial contamination through seals on stirrer shafts. The airlift reactor, also initially described for microbial fermentation and later adapted for mammalian culture, relies on a gas stream to both mix and oxygenate the culture. The gas stream enters a riser section of the reactor and drives circulation. Gas disengages at the culture surface, causing denser liquid which is free of gas bubbles to travel downward in the downcomer section of the reactor. The main advantage of this design is the simplicity and lack of need for mechanical mixing. Typically, the height-to-diameter ratio is 10:1. The airlift reactor scales up relatively easily, has good mass transfer of gases and generates relatively low shear forces. 4.3 Generating Antibodies Reactive With HET In another aspect, the present invention contemplates an antibody that is immunoreactive with an HET molecule of the present invention, or any portion thereof. An antibody can be a polyclonal or a monoclonal antibody. In a preferred embodiment, an antibody is a monoclonal antibody. Means for preparing and characterizing antibodies are well known in the art (see, e.g., Harlow and Lane, 1988). Briefly, a polyclonal antibody is prepared by immunizing an animal with an immunogen comprising a polypeptide of the present invention and collecting antisera from that immunized animal. A wide range of animal species can be used for the production of antisera. Typically an animal used for production of anti-antisera is a non-human animal, for example, rabbits, mice, rats, hamsters, pigs or horses. Because of the relatively large blood volume of rabbits, a rabbit is a preferred choice for production of polyclonal antibodies. Antibodies, both polyclonal and monoclonal, specific for isoforms of antigen may be prepared using conventional immunization techniques, as will be generally known to those of skill in the art. A composition containing antigenic epitopes of the compounds of the present invention can be used to immunize one or more experimental animals, such as a rabbit or mouse, which will then proceed to produce specific antibodies against the compounds of the present invention. Polyclonal antisera may be obtained, after allowing time for antibody generation, simply by bleeding the animal and preparing serum samples from the whole blood. It is proposed that the antibodies of the present invention will find useful application in standard immunochemical procedures, such as ELISA and Western blot methods and in immunohistochemical procedures such as tissue staining, as well as in other procedures which may utilize antibodies specific to HET-related antigen epitopes. The antibodies of the present invention are also useful for the isolation of HET polypeptides by immunoprecipitation. Immunoprecipitation involves the separation of the target antigen component from a complex mixture, and is used to discriminate or isolate minute amounts of protein. For the isolation of membrane proteins cells must be solubilized into detergent micelles. Nonionic salts are preferred, since other agents such as bile salts, precipitate at acid pH or in the presence of bivalent cations. Antibodies are and their uses are discussed further, below. In general, both polyclonal and monoclonal antibodies against HET may be used in a variety of embodiments. For example, they may be employed in antibody cloning protocols to obtain cDNAs or genes encoding other isoforms of HET or related proteins. They also may be used in inhibition studies to analyze the effects of HET-related peptides in cells or animals. Anti-HET antibodies also will be useful in immunolocalization studies to analyze the distribution of HET during various cellular events, for example, to determine the cellular or tissue-specific distribution of HET polypeptides under different points in the cell cycle. A particularly useful application of such antibodies is in purifying native or recombinant HET, for example, using an antibody affinity column. The operation of all such immunological techniques will be known to those of skill in the art in light of the present disclosure. Means for preparing and characterizing antibodies are well known in the art (see, e.g., Harlow and Lane, 1988; incorporated herein by reference). More specific examples of monoclonal antibody preparation are give in the examples below. As is well known in the art, a given composition may vary in its immunogenicity. It is often necessary, therefore, to boost the host immune system, as may be achieved by coupling a peptide or polypeptide immunogen to a carrier. Exemplary and preferred carriers are keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA). Other albumins such as ovalbumin, mouse serum albumin or rabbit serum albumin also can be used as carriers. Means for conjugating a polypeptide to a carrier protein are well known in the art and include glutaraldehyde, w-maleimidobenzoyl-N-hydroxysuccinimide ester, carbodiimide and bis-biazotized benzidine. As also is well known in the art, the immunogenicity of a particular immunogen composition can be enhanced by the use of non-specific stimulators of the immune response, known as adjuvants. Exemplary and preferred adjuvants include complete Freund's adjuvant (a non-specific stimulator of the immune response containing killed Mycobacterium tuberculosis), incomplete Freund's adjuvants and aluminum hydroxide adjuvant. The amount of immunogen composition used in the production of polyclonal antibodies varies upon the nature of the immunogen as well as the animal used for immunization. A variety of routes can be used to administer the immunogen (subcutaneous, intramuscular, intradermal, intravenous and intraperitoneal). The production of polyclonal antibodies may be monitored by sampling blood of the immunized animal at various points following immunization. A second, booster, injection also may be given. The process of boosting and titering is repeated until a suitable titer is achieved. When a desired level of immunogenicity is obtained, the immunized animal can be bled and the serum isolated and stored, and/or the animal can be used to generate monoclonal antibodies. Monoclonal antibodies may be readily prepared through use of well-known techniques, such as those exemplified in U.S. Patent 4,196,265, incorporated herein by reference. Typically, this technique involves immunizing a suitable animal with a selected immunogen composition, e.g., a purified or partially purified HET protein, polypeptide, or peptide or a cell expressing high levels of HET. The immunizing composition is administered in a manner effective to stimulate antibody producing cells. Cells from rodents such as mice and rats are preferred, however, the use of rabbit, sheep or frog cells is also possible. The use of rats may provide certain advantages (Goding, 1986), but mice are preferred, with the BALB/c mouse being most preferred as this is most routinely used and generally gives a higher percentage of stable fusions. Following immunization, somatic cells with the potential for producing antibodies, specifically B-lymphocytes (B-cells), are selected for use in the mAb generating protocol. These cells may be obtained from biopsied spleens, tonsils or lymph nodes, or from a peripheral blood sample. Spleen cells and peripheral blood cells are preferred, the former because they are a rich source of antibody-producing cells that are in the dividing plasmablast stage, and the latter because peripheral blood is easily accessible. Often, a panel of animals will have been immunized and the spleen of the animal with the highest antibody titer will be removed and the spleen lymphocytes obtained by homogenizing the spleen with a syringe. Typically, a spleen 7 8 from an immunized mouse contains approximately 5 x 10 to 2 x 10 lymphocytes. The antibody-producing B lymphocytes from the immunized animal are then fused with cells of an immortal myeloma cell, generally one of the same species as the animal that was immunized. Myeloma cell lines suited for use in hybridoma-producing fusion procedures preferably are non-antibody-producing, have high fusion efficiency, and enzyme deficiencies that render then incapable of growing in certain selective media which support the growth of only the desired fused cells (hybridomas). Any one of a number of myeloma cells may be used, as are known to those of skill in the art (Goding, 1986; Campbell, 1984). For example, where the immunized animal is a mouse, one may use P3-X63/Ag8, P3-X63-Ag8.653, NSl/l .Ag 4 1, Sp210-Agl4, FO, NSO/U, MPC-11, MPC11-X45-GTG 1.7 and S194/5XX0 Bui; for rats, one may use R210.RCY3, Y3-Ag 1.2.3, IR983F and 4B210; and U-266, GM1500-GRG2, LICR-LON-HMy2 and UC729-6 are all useful in connection with cell fusions. Methods for generating hybrids of antibody-producing spleen or lymph node cells and myeloma cells usually comprise mixing somatic cells with myeloma cells in a 2:1 ratio, though the ratio may vary from about 20:1 to about 1 :1, respectively, in the presence of an agent or agents (chemical or electrical) that promote the fusion of cell membranes. Fusion methods using Sendai virus (Kohler and Milstein, 1975; 1976), and those using polyethylene glycol (PEG), such as 37% (v/v) PEG, have been described by Gefter et al, (1977). The use of electrically induced fusion methods is also appropriate (Goding, 1986). Fusion procedures usually produce viable hybrids at low frequencies, around 1 x 10 " to 1 x 10A However, this does not pose a problem, as the viable, fused hybrids are differentiated from the parental, unfused cells (particularly the unfused myeloma cells that would normally continue to divide indefinitely) by culturing in a selective medium. The selective medium is generally one that contains an agent that blocks the de novo synthesis of nucleotides in the tissue culture media. Exemplary and preferred agents are aminopterin, methotrexate, and azaserine. Aminopterin and methotrexate block de novo synthesis of both purines and pyrimidines, whereas azaserine blocks only purine synthesis. Where aminopterin or methotrexate is used, the media is supplemented with hypoxanthine and thymidine as a source of nucleotides (HAT medium). Where azaserine is used, the media is supplemented with hypoxanthine. The preferred selection medium is HAT. Only cells capable of operating nucleotide salvage pathways are able to survive in HAT medium. The myeloma cells are defective in key enzymes of the salvage pathway, e.g., hypoxanthine phosphoribosyl transferase (HPRT), and they cannot survive. The B-cells can operate this pathway, but they have a limited life span in culture and generally die within about two wk. Therefore, the only cells that can survive in the selective media are those hybrids formed from myeloma and B-cells. This culturing provides a population of hybridomas from which specific hybridomas are selected. Typically, selection of hybridomas is performed by culturing the cells by single-clone dilution in microtiter plates, followed by testing the individual clonal supernatants (after about two to three wk) for the desired reactivity. The assay should be sensitive, simple and rapid, such as radioimmunoassays, enzyme immunoassays, cytotoxicity assays, plaque assays, dot immunobinding assays, and the like. The selected hybridomas would then be serially diluted and cloned into individual antibody-producing cell lines, which clones can then be propagated indefinitely to provide mAbs. The cell lines may be exploited for mAb production in two basic ways. A sample of the hybridoma can be injected (often into the peritoneal cavity) into a histocompatible animal of the type that was used to provide the somatic and myeloma cells for the original fusion. The injected animal develops tumors secreting the specific monoclonal antibody produced by the fused cell hybrid. The body fluids of the animal, such as serum or ascites fluid, can then be tapped to provide mAbs in high concentration. The individual cell lines also could be cultured in vitro, where the mAbs are naturally secreted into the culture medium from which they can be readily obtained in high concentrations. mAbs produced by either means may be further purified, if desired, using filtration, centrifugation, and various chromatographic methods such as HPLC or affinity chromatography. 4.4 Diagnosing Cancers Involving HET The present inventors have determined that alterations in HET are associated with breast cancer and may be associated with other malignancies. Therefore, HET and the corresponding gene may be employed as a diagnostic or prognostic indicator of cancer. More specifically, point mutations, deletions, insertions, allelic loss, or regulatory perturbations relating to HET may cause cancer or promote cancer development, cause or promote tumor progression at a primary site, and/or cause or promote metastasis. Other phenomena associated with malignancy that may be affected by HET expression include angiogenesis and tissue invasion. 4.4.1 Genetic Diagnosis One embodiment of the instant invention comprises a method for detecting variation in the expression of HET. This may comprise determining the level of expression of HET or determining specific alterations in the expressed product in a biological sample. In particular, the present invention relates to the diagnosis or prognosis of breast cancer. The nucleic acid used in the disclosed methods is isolated from cells contained in a biological sample, according to standard methodologies (Sambrook et al, 1989). The nucleic acid may be genomic DNA or fractionated or whole cell RNA. Where RNA is used, it may be desirable to convert the RNA to a complementary DNA. In one embodiment, the RNA is whole cell RNA; in another embodiment, it is poly-A RNA. Normally, the nucleic acid is amplified. Depending on the format, the specific nucleic acid of interest is identified directly in the sample using amplification or by hybridization with a second, known nucleic acid following amplification. Next, the identified product is detected. In certain applications, the detection may be performed by visual means (e.g., ethidium bromide staining of a gel). Alternatively, the detection may involve indirect identification of the product via chemiluminescence, radioactive scintigraphy of radiolabel or fluorescent label, or even via a system using electrical or thermal impulse signals (Affymax Technology; Bellus, 1994). Following detection, one compares the results obtained from a patient with a sufficiently large reference group of normal patients and patients that have HET- related pathologies, such as malignant breast tumors. In this way, it is possible to correlate the amount or type of HET detected (for example, mutant or truncated HET polypeptides) with various clinical states. In particular applications, such as breast cancers, it is contemplated that different levels of progression of breast cancer may be identified. Various types of defects are to be identified. Thus, "alterations" should be read as including deletions, insertions, point mutations and duplications. Point mutations result in stop codons, frameshift mutations or amino acid substitutions. Somatic mutations are those occurring in non-germline tissues. Germ-line mutations can occur in reproductive tissue and are inherited. Mutations in and outside the coding region also may affect the amount of HET produced, both by altering the transcription of the gene or in destabilizing or otherwise altering the processing of either the transcript (mRNA) or protein. A variety of different assays are contemplated in this regard, including but not limited to, fluorescent in situ hybridization (FISH), direct DNA sequencing, PFGE analysis, Southern or Northern blotting, single-stranded conformation polymorphism (SSCP), RNAse protection assay, allele-specific oligonucleotide (ASO), dot blot analysis, denaturing gradient gel electrophoresis, RFLP and PCR™-SSCP. An alternative method for detection of mutations in the HET sequence involves the recently developed protein truncation assay (PTT) to detect mutations affecting the length of the protein. This method is based on RT-PCR™ using an upstream PCR™ primer containing a RNA polymerase promoter and a eukaryotic translation initiation signal. Approximately 200 ng of the PCR™ product is used directly for the coupled in vitro transcription translation reaction (coupled TNT T7 reticulocyte system, Promega) which is substituted with S methionine. The TNT system has been used successfully to analyze the inventors' HET cDNA clones (Oesterreich et al, 1997). If "hotspot" regions for HET mutations are found, genomic DNA may be used as a template instead of total RNA to perform PCR™ using primers covering the appropriate HET exon. The amplified oligonucleotide products may be sequenced by standard techniques known to those skilled in the art. 4.4.1.1 Primers and Probes The term primer, as defined herein, is meant to encompass any nucleic acid that is capable of priming the synthesis of a nascent nucleic acid in a template- dependent process. Typically, primers are oligonucleotides from ten to twenty base pairs in length, but longer sequences can be employed. Primers may be provided in double-stranded or single-stranded form, although the single-stranded form is preferred. Probes are defined differently, although they may act as primers. Probes, while perhaps capable of priming, are designed to bind to the target DNA or RNA and need not be used in an amplification process. In preferred embodiments, the probes or primers are labeled with radioactive species ( 32 P, 14 C, 35 S, 3 H, or other label), with a fluorophore (rhodamine, fluorescein), or a chemilluminescent moiety (luciferase). 4.4.1.2 Template Dependent Amplification Methods A number of template dependent processes are available to amplify the marker sequences present in a given template sample. One of the best known amplification methods is the polymerase chain reaction (referred to as PCR™) which is described in detail in U.S. Patent Nos. 4,683,195, 4,683,202 and 4,800,159, and in Innis et al, 1990, each of which is incorporated herein by reference in its entirety. Briefly, in PCR™, two primer sequences are prepared that are complementary to regions on opposite complementary strands of the marker sequence. An excess of deoxynucleoside triphosphates are added to a reaction mixture along with a DNA polymerase, e.g., Taq polymerase. If the marker sequence is present in a sample, the primers will bind to the marker and the polymerase will cause the primers to be extended along the marker sequence by adding on nucleotides. By raising and lowering the temperature of the reaction mixture, the extended primers will dissociate from the marker to form reaction products, excess primers will bind to the marker and to the reaction products and the process is repeated. A reverse transcriptase PCR™ amplification procedure may be performed in order to quantify the amount of mRNA amplified. Methods of reverse transcribing RNA into cDNA are well known and described in Sambrook et al, 1989. Alternative methods for reverse transcription utilize thermostable, RNA-dependent DNA polymerases. These methods are described in WO 90/07641 filed December 21, 1990. Polymerase chain reaction methodologies are well known in the art. Another method for amplification is the ligase chain reaction ("LCR"), disclosed in EPO No. 320 308, incorporated herein by reference in its entirety. In LCR, two complementary probe pairs are prepared, and in the presence of the target sequence, each pair will bind to opposite complementary strands of the target such that they abut. In the presence of a ligase, the two probe pairs will link to form a single unit. By temperature cycling, as in PCR™, bound ligated units dissociate from the target and then serve as "target sequences" for ligation of excess probe pairs. U.S. Patent 4,883,750 describes a method similar to LCR for binding probe pairs to a target sequence. Qbeta Replicase, described in PCT Application No. PCT/US87/00880, may also be used as still another amplification method in the present invention. In this method, a replicative sequence of RNA that has a region complementary to that of a target is added to a sample in the presence of an RNA polymerase. The polymerase will copy the replicative sequence that can then be detected. An isothermal amplification method, in which restriction endonucleases and ligases are used to achieve the amplification of target molecules that contain nucleotide 5'-[alpha-thio]-triphosphates in one strand of a restriction site also may be useful in the amplification of nucleic acids in the present invention, Walker et al. , (1992). Strand Displacement Amplification (SDA) is another method of carrying out isothermal amplification of nucleic acids which involves multiple rounds of strand displacement and synthesis, i.e., nick translation. A similar method, called Repair Chain Reaction (RCR), involves annealing several probes throughout a region targeted for amplification, followed by a repair reaction in which only two of the four bases are present. The other two bases can be added as biotinylated derivatives for easy detection. A similar approach is used in SDA. Target specific sequences also can be detected using a cyclic probe reaction (CPR). In CPR, a probe having 3' and 5' sequences of non-specific DNA and a middle sequence of specific RNA is hybridized to DNA that is present in a sample. Upon hybridization, the reaction is treated with RNase H, and the products of the probe identified as distinctive products that are released after digestion. The original template is annealed to another cycling probe and the reaction is repeated. Still other amplification methods described in GB Application No. 2 202 328, and in PCT Application No. PCT/US89/01025, each of which is incorporated herein by reference in its entirety, may be used in accordance with the present invention. In the former application, "modified" primers are used in a PCR™-like, template- and enzyme-dependent synthesis. The primers may be modified by labeling with a capture moiety (e.g., biotin) and/or a detector moiety (e.g., enzyme). In the latter application, an excess of labeled probes is added to a sample. In the presence of the target sequence, the probe binds and is cleaved catalytically. After cleavage, the target sequence is released intact to be bound by excess probe. Cleavage of the labeled probe signals the presence of the target sequence. Other nucleic acid amplification procedures include transcription-based amplification systems (TAS), including nucleic acid sequence based amplification (NASBA) and 3SR (Kwoh et al, 1989; Gingeras et al, PCT Application WO 88/10315, incorporated herein by reference in their entirety). In NASBA, the nucleic acids can be prepared for amplification by standard phenol/chloroform extraction, heat denaturation of a clinical sample, treatment with lysis buffer, and minispin columns for isolation of DNA and RNA or guanidinium chloride extraction of RNA. These amplification techniques involve annealing a primer which has target specific sequences. Following polymerization, DNA/RNA hybrids are digested with RNase H while double stranded DNA molecules are heat denatured again. In either case the single stranded DNA is made fully double stranded by addition of second target specific primer, followed by polymerization. The double-stranded DNA molecules are then multiply transcribed by an RNA polymerase such as T7 or SP6. In an isothermal cyclic reaction, the RNA's are reverse transcribed into single stranded DNA, which is then converted to double stranded DNA, and then transcribed once again with an RNA polymerase such as T7 or SP6. The resulting products, whether truncated or complete, indicate target specific sequences. Davey et al, EPO No. 329 822 (incorporated herein by reference in its entirety) disclose a nucleic acid amplification process involving cyclically synthesizing single-stranded RNA ("ssRNA"), ssDNA, and double-stranded DNA (dsDNA), which may be used in accordance with the present invention. The ssRNA is a template for a first primer oligonucleotide, which is elongated by reverse transcriptase (RNA-dependent DNA polymerase). The RNA is then removed from the resulting DNA:RNA duplex by the action of ribonuclease H (RNase H, an RNase specific for RNA in duplex with either DNA or RNA). The resultant ssDNA is a template for a second primer, which also includes the sequences of an RNA polymerase promoter (exemplified by T7 RNA polymerase) 5' to its homology to the template. This primer is then extended by DNA polymerase (exemplified by the large "Klenow" fragment of E. coli DNA polymerase I), resulting in a double-stranded DNA ("dsDNA") molecule having a sequence identical to that of the original RNA between the primers, and having additionally, at one end, a promoter sequence. This promoter sequence can be used by the appropriate RNA polymerase to make many RNA copies of the DNA. These copies can then re-enter the cycle leading to very swift amplification. With proper choice of enzymes, this amplification can be done isothermally without addition of enzymes at each cycle. Because of the cyclical nature of this process, the starting sequence can be chosen to be in the form of either DNA or RNA. Miller et al, PCT Application WO 89/06700 (incorporated herein by reference in its entirety) disclose a nucleic acid sequence amplification scheme based on the hybridization of a promoter/primer sequence to a target single-stranded DNA ("ssDNA") followed by transcription of many RNA copies of the sequence. This scheme is not cyclic, i.e., new templates are not produced from the resultant RNA transcripts. Other amplification methods include "RACE" and "one-sided PCR™" (Frohman, 1990; Ohara et al, 1989; each herein incorporated by reference in their entirety). Methods based on ligation of two (or more) oligonucleotides in the presence of nucleic acid having the sequence of the resulting "di-oligonucleotide", thereby amplifying the di-oligonucleotide, may also be used in the amplification step of the present invention as described in Wu et al, (1989), incorporated herein by reference in its entirety. 4.4.1.3 Separation Methods It normally is desirable, at one stage or another, to separate the amplification product from the template and the excess primer for the purpose of determining whether specific amplification has occurred. In one embodiment, amplification products are separated by agarose, agarose-acrylamide or polyacrylamide gel electrophoresis using standard methods. (See Sambrook et al, 1989) Alternatively, chromatographic techniques may be employed to effect separation. There are many kinds of chromatography which may be used in the present invention: adsorption, partition, ion-exchange and molecular sieve, and many specialized techniques for using them including column, paper, thin-layer and gas chromatography (Freifelder, 1982). 4.4.1.4 Detection Methods Products may be visualized in order to confirm amplification of the marker sequences. One typical visualization method involves staining of a gel with ethidium bromide and visualization under UV light. Alternatively, if the amplification products are integrally labeled with radio- or fluorometrically-labeled nucleotides, the amplification products can then be exposed to X-ray film or visualized under the appropriate stimulating spectra, following separation. In one embodiment, visualization is achieved indirectly. Following separation of amplification products, a labeled nucleic acid probe is brought into contact with the amplified marker sequence. The probe preferably is conjugated to a chromophore but may be radiolabeled. In another embodiment, the probe is conjugated to a binding partner, such as an antibody or biotin, and the other member of the binding pair carries a detectable moiety. In one embodiment, detection is by a labeled probe. The techniques involved are well known to those of skill in the art and can be found in many standard books on molecular protocols. (See Sambrook et al, 1989) For example, chromophore or radiolabel probes or primers identify the target during or following amplification. One example of the foregoing is described in U.S. Patent No. 5,279,721, incorporated by reference herein, which discloses an apparatus and method for the automated electrophoresis and transfer of nucleic acids. The apparatus permits electrophoresis and blotting without external manipulation of the gel and is ideally suited to carrying out methods according to the present invention. In addition, the amplification products described above may be subjected to sequence analysis to identify specific kinds of variations using standard sequence analysis techniques. General techniques for determination of the DNA sequence of amplification products are well known in the art and include standard dideoxy sequencing by the Sanger technique (See Sambrook et al, 1989). Within certain methods, exhaustive analysis of genes is carried out by sequence analysis using primer sets designed for optimal sequencing (Pignon et al, 1994). The present invention may utilize any or all of these types of analyses. Using the sequences disclosed herein, oligonucleotide primers, such as those exemplified by SEQ ID NO: 10 and SEQ ID NO:l 1 , may be designed to permit the amplification of sequences throughout the HET gene that may then be analyzed by direct sequencing. The amplified sequences may then be identified and quantitated. The presence of the HET gene or mutants thereof may be used in the methods disclosed herein to determine degree of malignancy, cell tumorigenicity, and potential prognosis/diagnosis of cancers such as breast cancers. 4.4.1.5 Southern/Northern Blotting Blotting techniques are well known to those of skill in the art. Southern blotting involves the use of DNA as a target, whereas Northern blotting involves the use of RNA as a target. Each provide different types of information, although cDNA blotting is analogous, in many aspects, to blotting RNA species. Briefly, a probe is used to target a DNA or RNA species that has been immobilized on a suitable matrix, often a filter of nitrocellulose. The different species should be spatially separated to facilitate analysis. This often is accomplished by gel electrophoresis of nucleic acid species followed by transfer of the separated nucleic acids ("blotting") on to the filter. Subsequently, the blotted target is incubated with a probe (usually labeled) under conditions that promote denaturation and rehybridization. Because the probe is designed to base pair with the target, the probe will bind a portion of the target sequence under renaturing conditions. Unbound probe is then removed, and the labeled probe detected using standard techniques known to those skilled in the art. 4.4.1.6 Kit Components All the essential materials and reagents required for detecting, measuring, or sequencing HET and variants thereof may be assembled together in a kit. This generally will comprise preselected primers and probes. Also included may be enzymes suitable for amplifying nucleic acids including various polymerases (RT, Taq, Sequenase™ etc.), deoxynucleotides and buffers to provide the necessary reaction mixture for amplification. Such kits also generally will comprise, in suitable means, distinct containers for each individual reagent and enzyme as well as for each primer or probe. Materials and reagents for detecting loss of heterozygosity (LOH) may also be assembled in kit form. This will comprise primers selected to amplify a polymorphic marker at chromosomal locus 19p 13 , for example at 19pl3.2-13.3. Primers for additional loci are contemplated within the scope of the instant invention, so long as they are capable of detecting LOH at 19pl3. Additional components as described in the preceding paragraph may also be included. 4.4.1.7 Chip Technologies Specifically contemplated by the present inventors are chip-based DNA technologies such as those described by Hacia et al. (1996) and Shoemaker et al. (1996). Briefly, these techniques involve quantitative methods for analyzing large numbers of genes rapidly and accurately. By tagging genes with oligonucleotides or using fixed probe arrays, one can employ chip technology to segregate target molecules as high density arrays and screen these molecules on the basis of hybridization. See also Pease et al. (1994); Fodor et al. (1991). 4.4.2 Immunodiagnosis Antibodies of the present invention can be used in characterizing the HET content of healthy and diseased tissues, through techniques such as ELISA and Western blotting. This may provide a screen for the presence or absence of malignancy or as a predictor of future cancer. The use of antibodies of the present invention, in an ELISA assay is contemplated. For example, anti-HET antibodies are immobilized onto a selected surface, preferably a surface exhibiting a protein affinity such as the wells of a polystyrene microtiter plate. After washing to remove incompletely adsorbed material, it is desirable to bind or coat the assay plate wells with a non-specific protein that is known to be antigenically neutral with regard to the test antisera, such as bovine serum albumin (BSA), casein or solutions of powdered milk. This allows for blocking of non-specific adsorption sites on the immobilizing surface and thus reduces the background caused by non-specific binding of antigen onto the surface. After binding of antibody to the well, coating with a non-reactive material to reduce background, and washing to remove unbound material, the immobilizing surface is contacted with the sample to be tested in a manner conducive to immune complex (antigen/antibody) formation. Following formation of specific immunocomplexes between the test sample and the bound antibody, and subsequent washing, the occurrence and even amount of immunocomplex formation may be determined by subjecting the same to a second antibody having specificity for HET that differs from that of the first antibody. Appropriate conditions preferably include diluting the sample with diluents such as BSA, bovine gamma globulin (BGG), and phosphate buffered saline (PBS)/Tween . These added agents also tend to assist in the reduction of nonspecific background. The layered antisera is then allowed to incubate for from about 2 to about 4 h, at temperatures preferably on the order of about 25° to about 27°C. Following incubation, the antisera-contacted surface is washed so as to remove non- immunocomplexed material. A preferred washing procedure includes washing with a solution such as PBS/Tween or borate buffer. To provide a detecting means, the second antibody will preferably have an associated enzyme that will generate a color development upon incubating with an appropriate chromogenic substrate. Thus, for example, one will desire to contact and incubate the second antibody-bound surface with a urease or peroxidase-conjugated anti-IgG for a period of time and under conditions which favor the development of immunocomplex formation (e.g., incubation for 2 h at room temperature in a PBS- containing solution such as PBS/Tween ). After incubation with the second enzyme-tagged antibody, and subsequent to washing to remove unbound material, the amount of label is quantified by incubation with a chromogenic substrate such as urea and bromocresol purple or 2,2'-azino-di-(3- ethyl-benzthiazoline)-6-sulfonic acid (ABTS) and H 2 O 2 , in the case of peroxidase as the enzyme label. Quantitation is then achieved by measuring the degree of color generation, e.g., using a visible spectrum spectrophotometer. The preceding format may be altered by first binding the sample to the assay plate. Then, primary antibody is incubated with the assay plate, followed by detecting of bound primary antibody using a labeled second antibody with specificity for the primary antibody. The antibody compositions of the present invention will find great use in immunoblot or Western blot analysis. The antibodies may be used as high-affinity primary reagents for the identification of proteins immobilized onto a solid support matrix, such as nitrocellulose, nylon or combinations thereof. In conjunction with immunoprecipitation, followed by gel electrophoresis, these may be used as a single step reagent for use in detecting antigens against which secondary reagents used in the detection of the antigen cause an adverse background. Immunologically-based detection methods for use in conjunction with Western blotting include enzymatically-, radiolabel-, or fluorescently-tagged secondary antibodies against HET protein or the primary antibody. 4.5 Methods for Screening Active Compounds The present invention also contemplates the use of HET and active fragments, and nucleic acids coding therefor, in the screening of compounds for activity in either stimulating HET activity, overcoming the lack of HET or blocking the effect of a mutant HET molecule. These assays may make use of a variety of different formats and may depend on the kind of "activity" for which the screen is being conducted. Contemplated functional "read-outs" include binding to a compound, inhibition of binding to a substrate, ligand, receptor or other binding partner by a compound, phosphatase activity, anti-phosphatase activity, phosphorylation of HET, dephosphorylation of HET, or inhibition or stimulation of cell-to-cell signaling, growth, metastasis, cell division, cell migration, soft agar colony formation, contact inhibition, invasiveness, angiogenesis, apoptosis, tumor progression or other malignant phenotype. Preferred embodiments include assay of cell replication by incorporation of radiolabeled thymidine or colony formation. A preferred ligand for HET-binding activity comprises the hsp27 promoter. The functional activity of different forms of HET protein may be determined by assaying their effects on transcription of reporter genes functionally linked to an hsp27 promoter. 4.5.1 In Vitro Assays In one embodiment, the invention is to be applied for the screening of compounds that bind to the HET molecule or a fragment thereof. The polypeptide or fragment may be either free in solution, fixed to a support, or expressed in or on the surface of a cell. Either the polypeptide or the compound may be labeled, thereby permitting the determination of binding. In another embodiment, the assay may measure the inhibition of binding of HET to a natural or artificial substrate or binding partner. Competitive binding assays can be performed in which one of the agents (HET, binding partner or compound) is labeled. Usually, the polypeptide will be the labeled species. One may measure the amount of free label versus bound label to determine binding or inhibition of binding. Another technique for high throughput screening of compounds is described in WO 84/03564, the contents of which are incorporated herein by reference. Large numbers of small peptide test compounds are synthesized on a solid substrate, such as plastic pins or some other surface. The peptide test compounds are reacted with HET and washed. Bound polypeptide is detected by various methods. Purified HET can be coated directly onto plates for use in the aforementioned drug screening techniques. However, non-neutralizing antibodies to the polypeptide can be used to immobilize the polypeptide to a solid phase. Also, fusion proteins containing a reactive region (preferably a terminal region) may be used to link the HET active region to a solid phase. Various cell lines containing wild-type or natural or engineered mutations in HET can be used to study various functional attributes of HET and how a candidate compound affects these attributes. Methods for engineering mutations are described elsewhere in this document, as are naturally-occurring mutations in HET that lead to, contribute to and/or otherwise cause malignancy. In such assays, the compound would be formulated appropriately, given its biochemical nature, and contacted with a target cell. Depending on the assay, culture may be required. The cell may then be examined by virtue of a number of different physiologic assays. Alternatively, molecular analysis may be performed in which the function of HET, or related pathways, may be explored. This may involve assays such as those for protein expression, enzyme function, substrate utilization, phosphorylation states of various molecules including HET, cAMP levels, mRNA expression (including differential display of whole cell or polyA RNA) and others. 4.5.2 In Vivo Assays The present invention also encompasses the use of various animal models. By developing or isolating mutant cells lines that fail to express normal HET, one can generate cancer models in mice that will be predictive of cancers in humans and other mammals. These models may employ the orthotopic or systemic administration of tumor cells to mimic primary and/or metastatic cancers. Alternatively, one may induce cancers in animals by providing agents known to be responsible for certain events associated with malignant transformation and/or tumor progression. Finally, transgenic animals (discussed below) that lack a wild-type HET may be utilized as models for cancer development and treatment. Treatment of animals with test compounds will involve the administration of the compound, in an appropriate form, to the animal. Administration will be by any route that could be utilized for clinical or non-clinical purposes, including but not limited to oral, nasal, buccal, rectal, vaginal or topical. Alternatively, administration may be by intratracheal instillation, bronchial instillation, intradermal, subcutaneous, intramuscular, intraperitoneal or intravenous injection. Specifically contemplated are systemic intravenous injection, regional administration via blood or lymph supply and intratumoral injection. Determining the effectiveness of a compound in vivo may involve a variety of different criteria. Such criteria include, but are not limited to, survival, reduction of tumor burden or mass, arrest or slowing of tumor progression, elimination of tumors, inhibition or prevention of metastasis, increased activity level, improvement in immune effector function and improved food intake. 4.5.3 Rational Drug Design The goal of rational drug design is to produce structural analogs of biologically active polypeptides or compounds with which they interact (agonists, antagonists, inhibitors, binding partners, etc.). By creating such analogs, it is possible to fashion drugs which are more active or stable than the natural molecules, which have different susceptibility to alteration or which may affect the function of various other molecules. In one approach, one would generate a three-dimensional structure for HET or a fragment thereof. This could be accomplished by x-ray crystallography, computer modeling or by a combination of both approaches. By virtue of the availability of the cloned HET sequence, sufficient amounts of HET can be produced to perform crystallographic studies. In addition, knowledge of the polypeptide sequences permits computer employed predictions of structure-function relationships. An alternative approach, an "alanine scan," involves the random replacement of residues throughout molecule with alanine, followed by determining the resulting effect(s) on protein function. By virtue of the availability of the cloned HET sequence, sufficient amounts of HET can be produced to perform crystallographic studies. In addition, knowledge of the polypeptide sequences permits computer employed predictions of structure-function relationships. It also is possible to isolate a HET specific antibody, selected by a functional assay, and then solve its crystal structure. In principle, this approach yields a pharmacore upon which subsequent drug design can be based. It is possible to bypass protein crystallography altogether by generating anti-idiotypic antibodies to a functional, pharmacologically active antibody. As a mirror image of a mirror image, the binding site of an anti-idiotype antibody would be expected to be an analog of the original antigen. The anti-idiotype could then be used to identify and isolate peptides from banks of chemically- or biologically-produced peptides. Selected peptides would then serve as the pharmacore. Anti-idiotypes may be generated using the methods described herein for producing antibodies, using an antibody as the antigen. Thus, one may design drugs which have improved HET activity or which act as stimulators, inhibitors, agonists, or antagonists of HET or molecules affected by HET function. 4.6 Methods for Treating HET Related Malignancies The present invention also contemplates, in another embodiment, the treatment of cancer. The types of cancer that may be treated, according to the present invention, are limited only by the involvement of HET. By involvement is meant that, it is not even a requirement that HET be mutated or abnormal - the overexpression of this tumor suppressor may actually overcome other lesions within the cell. Thus, it is contemplated that a wide variety of tumors may be treated using HET therapy. In many contexts, it is not necessary that the tumor cell be killed or induced to undergo normal cell death or "apoptosis." Rather, to accomplish a meaningful treatment, all that is required is that the tumor growth be slowed to some degree. It may be that the tumor growth is completely blocked, however, or that some tumor regression is achieved. Clinical terminology such as "remission" and "reduction of tumor" burden also are contemplated given their normal usage. 4.6.1 Genetic Based Therapies One of the therapeutic embodiments contemplated by the present inventors is the intervention, at the molecular level, in the events involved in the tumorigenesis of some cancers. Specifically, the present inventors intend to provide, to a cancer cell, an expression construct capable of providing HET to that cell. Any of the gene sequence variants discussed above which would encode the same, or a biologically equivalent polypeptide could be used. The lengthy discussion of expression vectors and the genetic elements employed therein is incorporated into this section by reference. Particularly preferred expression vectors are viral vectors such as adenovirus, adeno-associated virus, herpes virus, vaccinia virus and retrovirus. Also preferred is liposomally-encapsulated expression vector. Those of skill in the art are well aware of how to apply gene delivery to in vivo and ex vivo situations. For viral vectors, one generally will prepare a viral vector stock. Depending on the kind of virus and the titer attainable, one will deliver between about 1 x 10 and 1 x 10 infectious particles to the patient. Similar figures may be extrapolated for liposomal or other non-viral formulations by comparing relative uptake efficiencies. Formulation as a pharmaceutically acceptable composition is discussed below. Various routes are contemplated for various tumor types. The section below on routes contains an extensive list of possible routes. For practically any tumor, systemic delivery is contemplated. This will prove especially important for attacking microscopic or metastatic cancer. Where discrete tumor mass may be identified, a variety of direct, local and regional approaches may be taken. For example, the tumor may be injected directly with the expression vector. A tumor bed may be treated prior to, during or after resection. Following resection, one generally will deliver the vector by a catheter left in place following surgery. One may utilize the tumor vasculature to introduce the vector into the tumor by injecting a supporting vein or artery. A more distal blood supply route also may be utilized. In a different embodiment, ex vivo gene therapy is contemplated. This approach is particularly suited, although not limited, to treatment of bone marrow associated cancers. In an ex vivo embodiment, cells from the patient are removed and maintained outside the body for at least some period of time. During this period, a therapy is delivered, after which the cells are reintroduced into the patient. Preferably, any tumor cells in the sample have been killed. Autologous bone marrow transplant (ABMT) is an example of ex vivo gene therapy. Basically, the concept underlying ABMT is that the patient will serve as his or her own bone marrow donor. Thus, a normally lethal dose of irradiation or chemotherapeutic may be delivered to the patient to kill tumor cells, and the bone marrow repopulated with the patient's own cells that have been maintained (and perhaps expanded) ex vivo. Because bone marrow is often contaminated with tumor cells, it is desirable to purge the bone marrow of these cells. Use of gene therapy to accomplish this goal is yet another way HET may be utilized according to the present invention. 4.6.2 Immunotherapies Immunotherapeutics, generally, rely on the use of immune effector cells and molecules to target and destroy cancer cells. The immune effector may be, for example, an antibody specific for some marker on the surface of a tumor cell. The antibody alone may serve as an effector of therapy or it may recruit other cells to actually effect cell killing. The antibody also may be conjugated to a drug or toxin (chemotherapeutic, radionuclide, ricin A chain, cholera toxin, pertussis toxin, etc.) and serve merely as a targeting agent. Alternatively, the effector may be a lymphocyte carrying a surface molecule that interacts, either directly or indirectly, with a tumor cell target. Various effector cells include cytotoxic T cells and NK cells. According to the present invention, native or wild type HET may not be a likely target for an immune effector given that (i) it has not been shown to be expressed on the surface of the cell and (ii) the presence, not absence, of HET is associated with the normal state. However, it is possible that particular mutant forms of HET may be targeted by i munotherapy, either using antibodies, antibody conjugates, or immune effector cells. A more likely scenario is that immunotherapy could be used as part of a combined therapy, in conjunction with HET-targeted gene therapy. The general approach for combined therapy is discussed below. Generally, the tumor cell must bear some marker that is amenable to targeting, i.e., is not present on the majority of other cells. Many tumor markers exist and any of these may be suitable for targeting in the context of the present invention. Common tumor markers include carcinoembryonic antigen, prostate specific antigen, urinary tumor associated antigen, fetal antigen, tyrosinase (p97), gp68, TAG-72, HMFG, sialyl Lewis antigen, MucA, MucB, PLAP, estrogen receptor, laminin receptor, erb B and pi 55. 4.6.3 Combined Therapy with Immunotherapy, Traditional Chemo- or Radiotherapy Tumor cell resistance to DNA damaging agents represents a major problem in clinical oncology. One goal of current cancer research is to find ways to improve the efficacy of chemo- and radiotherapy. One way is by combining such traditional therapies with gene therapy. For example, the herpes simplex-thymidine kinase (HS-t/c) gene, when delivered to brain tumors by a retroviral vector system, successfully induced susceptibility to the antiviral agent ganciclovir (Culver et al, 1992). In the context of the present invention, it is contemplated that HET replacement therapy could be used similarly in conjunction with chemo- or radiotherapeutic intervention. It also may prove effective to combine HET gene therapy with immunotherapy, as described above. To kill cells, inhibit cell growth, inhibit metastasis, inhibit angiogenesis or otherwise reverse or reduce the malignant phenotype of tumor cells, using the methods and compositions of the present invention, one would generally contact a "target" cell with an HET expression construct and at least one other agent. These compositions would be provided in a combined amount effective to kill or inhibit proliferation of the cell. This process may involve contacting the cells with the expression construct and the agent(s) or factor(s) at the same time. This may be achieved by contacting the cell with a single composition or pharmacological formulation that includes both agents, or by contacting the cell with two distinct compositions or formulations simultaneously, wherein one composition includes the expression construct and the other includes the agent. Alternatively, the gene therapy treatment may precede or follow the other agent treatment by intervals ranging from min to wk. In embodiments where the other agent and expression construct are applied separately to the cell, one would generally ensure that a significant period of time did not expire between the time of each delivery, such that the agent and expression construct would still be able to exert an advantageously combined (e.g., synergistic) effect on the cell. In such instances, it is contemplated that one would contact the cell with both modalities within about 12-24 h of each other and, more preferably, within about 6-12 h of each other, with a delay time of only about 12 h being most preferred. In some situations, it may be desirable to extend the duration of treatment with only the therapeutic agent significantly, for example, where several days (2, 3, 4, 5, 6 or 7) to several wk (1 , 2, 3, 4, 5, 6, 7 or 8) lapse between the respective administrations. It also is conceivable that more than one administration of either HET or the other agent will be desired. Various combinations may be employed, where HET is "A" and the other agent is "B", as exemplified below: A/B/A B/A/B B/B/A A/A/B B/A/A A/B/B B/B/B/A B/B/A/B A/A/B/B A/B/A/B A B/B/A B/B/A/A B/A/B/A B/A/A/B B/B/B/A A/A/A/B B/A/A/A A/B/A/A A/A/B/A A/B/B/B B/A/B/B B/B/A/B In addition, other combinations are contemplated. To achieve cell killing, both agents are delivered to a cell in a combined amount effective to kill the cell. Agents or factors suitable for use in a combined therapy are any chemical compound or treatment method that induces DNA damage when applied to a cell. Such agents and factors include radiation and waves that induce DNA damage such as γ-irradiation, X-rays, UV-irradiation, microwaves, electronic emissions, and the like. A variety of chemical compounds, also described as "chemotherapeutic agents," function to induce DNA damage, all of which are intended to be of use in the combined treatment methods disclosed herein. Chemotherapeutic agents contemplated to be of use include, e.g., adriamycin, 5-fluorouracil (5FU), etoposide (VP-16), camptothecin, actinomycin-D, mitomycin C, cisplatin (CDDP) and even hydrogen peroxide. The invention also encompasses the use of a combination of one or more DNA damaging agents, whether radiation-based or actual compounds, such as the use of X-rays with cisplatin or the use of cisplatin with etoposide. In certain embodiments, the use of cisplatin in combination with a HET expression construct is particularly preferred. In treating cancer according to the invention, one would contact the tumor cells with an agent in addition to the expression construct. This may be achieved by irradiating the localized tumor site with radiation such as X-rays, UV-light, γ-rays or even microwaves. Alternatively, the tumor cells may be contacted with the agent by administering to the subject a therapeutically effective amount of a pharmaceutical composition comprising a compound such as, adriamycin, 5-fluorouracil, etoposide, camptothecin, actinomycin-D, mitomycin C, or more preferably, cisplatin. The agent may be prepared and used as a combined therapeutic composition, or kit, by combining it with a HET expression construct, as described above. Agents that directly cross-link nucleic acids, specifically DNA, are envisaged to facilitate DNA damage leading to a synergistic, antineoplastic combination with HET. Agents such as cisplatin, and other DNA alkylating agents may be used. Cisplatin has been widely used to treat cancer, with efficacious doses used in clinical applications of 20 mg/m for 5 days every three wk for a total of three courses. Cisplatin is not absorbed orally and must therefore be delivered via injection intravenously, subcutaneously, intratumorally or intraperitoneally. Agents that damage DNA also include compounds that interfere with DNA replication, mitosis and chromosomal segregation. Such chemotherapeutic compounds include adriamycin, also known as doxorubicin, etoposide, verapamil, podophyllotoxin, and the like. Widely used in a clinical setting for the treatment of neoplasms, these compounds are administered intravenously through bolus injections at doses ranging from 25-75 mg/m at 21 day intervals for adriamycin, to 35-50 mg/m for etoposide intravenously or double the intravenous dose orally. Agents that disrupt the synthesis and fidelity of nucleic acid precursors and subunits also lead to DNA damage. A number of nucleic acid precursors have been developed for this purpose. Particularly useful are agents that have undergone extensive testing and are readily available, such as 5-fluorouracil (5-FU). Although quite toxic, 5- FU is applicable in a wide range of carriers, including topical. However intravenous administration with doses ranging from 3 to 15 mg/kg/day is commonly used. Other factors that cause DNA damage and have been used extensively include γ- rays, X-rays, and/or the directed delivery of radioisotopesto tumor cells. Other forms of DNA damaging factors also are contemplated such as microwaves and UV-irradiation. It is most likely that all of these factors effect a broad range of damage to DNA, on the precursors of DNA, the replication and repair of DNA, and the assembly and maintenance of chromosomes. Dosage ranges for X-rays range from daily doses of 50 to 200 roentgens for prolonged periods of time (3 to 4 wk), to single doses of 2000 to 6000 roentgens. Dosage ranges for radioisotopes vary widely, and depend on the half- life of the isotope, the strength and type of radiation emitted, and the uptake by the neoplastic cells. The skilled artisan is directed to "Remington's Pharmaceutical Sciences" 15th Edition, chapter 33, and in particular to pages 624-652. Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject. Moreover, for human administration, preparations should meet sterility, pyrogenicity, and general safety and purity standards as required by the FDA Office of Biologies standards. The inventors propose that the regional delivery of HET expression constructs to patients with breast cancer or other HET related tumors will be a very efficient method for delivering a therapeutically effective gene to counteract the clinical disease. Similarly, chemo- or radiotherapy may be directed to a particular, affected region of the subject's body. Alternatively, systemic delivery of expression construct and/or the agent may be appropriate in certain circumstances, for example, where extensive metastasis has occurred. In addition to combining HET-targeted therapies with chemo- and radiotherapies, it also is contemplated that combination with other gene therapies will be advantageous. For example, simultaneous targeting of therapies directed toward HET and p53, BRCAl or BRCA2 mutations may produce an improved anti-cancer treatment. Any other tumor-related gene conceivably can be targeted in this manner, for example, p21, Rb, APC, DCC, NF-1, NF-2, pi 6, FHIT, WT-1, MEN-I, MEN-II, VHL, FCC, MCC, ras, myc, neu, raf, erb, sre, fins, jun, trk, ret, gsp, hst, bcl and abl. 4.6.4 Formulations and Routes for Administration to Patients Where clinical applications are contemplated, it will be necessary to prepare pharmaceutical compositions - expression vectors, virus stocks, proteins, antibodies and drugs - in a form appropriate for the intended application. Generally, this will entail preparing compositions that are essentially free of pyrogens, as well as other impurities that could be harmful to humans or animals. One generally will desire to employ appropriate salts and buffers to render delivery vectors stable and allow for uptake by target cells. Buffers also will be employed when recombinant cells are introduced into a patient. Aqueous compositions of the present invention comprise an effective amount of the vector to cells, dissolved or dispersed in a pharmaceutically acceptable carrier or aqueous medium. Such compositions also are referred to as innocula. The phrase "pharmaceutically or pharmacologically acceptable" refers to molecular entities and compositions that do not produce adverse, allergic, or other untoward reactions when administered to an animal or a human. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutically active substances is well know in the art. Except insofar as any conventional media or agent is incompatible with the vectors or cells of the present invention, its use in therapeutic compositions is contemplated. Supplementary active ingredients also can be incorporated into the compositions. The active compositions of the present invention may include classic pharmaceutical preparations. Administration of these compositions according to the present invention will be via any common route so long as the target tissue is available via that route. This includes oral, nasal, buccal, rectal, vaginal or topical. Alternatively, administration may be by orthotopic, intradermal, subcutaneous, intramuscular, intraperitoneal or intravenous injection. Such compositions normally would be administered as pharmaceutically acceptable compositions, described supra. The active compounds also may be administered parenterally or intraperitoneally. Solutions of the active compounds as free base or pharmacologically acceptable salts can be prepared in water suitably mixed with a surfactant, such as hydroxypropylcellulose. Dispersions also can be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin. Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile- filtered solution thereof. For oral administration the polypeptides of the present invention may be incorporated with excipients and used in the form of non-ingestible mouthwashes and dentifrices. A mouthwash may be prepared incorporating the active ingredient in the required amount in an appropriate solvent, such as a sodium borate solution (Dobell's Solution). Alternatively, the active ingredient may be incorporated into an antiseptic wash containing sodium borate, glycerin and potassium bicarbonate. The active ingredient may also be dispersed in dentifrices, including: gels, pastes, powders and slurries. The active ingredient may be added in a therapeutically effective amount to a paste dentifrice that may include water, binders, abrasives, flavoring agents, foaming agents, and humectants. The compositions of the present invention may be formulated in a neutral or salt form. Pharmaceutically-acceptable salts include the acid addition salts (formed with the free amino groups of the protein) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, histidine, procaine and the like. Upon formulation, solutions will be administered in a manner compatible with the dosage formulation and in such amount as is therapeutically effective. The formulations are easily administered in a variety of dosage forms such as injectable solutions, drug release capsules and the like. For parenteral administration in an aqueous solution, for example, the solution should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal administration. In this connection, sterile aqueous media which can be employed will be known to those of skill in the art in light of the present disclosure. For example, one dosage could be dissolved in 1 ml of isotonic NaCl solution and either added to 1000 ml of hypodermoclysis fluid or injected at the proposed site of infusion, (see for example, "Remington's Pharmaceutical Sciences" 15th Edition, pages 1035-1038 and 1570-1580). Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject. Moreover, for human administration, preparations should meet sterility, pyrogenicity, general safety and purity standards as required by FDA Office of Biologies standards. 5.0 EXAMPLES The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. 5.1 Materials and Methods Utilized in Examples 1 through 7 5.1.1 Cell Culture and Transfection The human breast cancer cell line MCF-7/MG was originally obtained from Dr. Herbert Soule (Michigan Cancer Foundation), and has been maintained in the inventors' laboratory for the last 14 years. MDA-MB-231 cells were obtained from the American Type Tissue Culture Collection (Rockville, MD). MCF-7/MG, MDA- MB-231, and COS cells were maintained as described in (Oesterreich et al, 1996a). For HeLa cells, the media was not supplemented with insulin or gentamicin sulfate. T47DE and ZR-75 human breast cancer cell lines were maintained in Dulbecco's Modified Eagle Medium (DMEM) (Gibco-BRL), Grand Island, New York) supplemented with 1% (v/v) L-glutamine, 1% (v/v) glucose, 1% (v/v) penicillin/streptomycin and 5% fetal bovine serum (FBS). Transient transfections were performed as previously described (Oesterreich et al. , 1996a) except that Renilla luciferase plasmid (pRL-TK) (Promega, Madison, WS) (50 ng) instead of pRSV-βgal was cotransfected to correct for transfection efficiency. Cells were plated at 2 x 10 cells/well in triplicate in six-well plates. The next day cells were transfected using Lipofectamine (Life Technologies, Grand Island, NY) and OPTIMEM™ (Gibco-BRL). Cells were transfected with 0.5 μg CF (hsp27 promoter fragment; see below) and with 100 ng HET (MDA-MB-231 and HeLa) or 250 ng HET (T47D, MCF-7/MG and COS cells), respectively. Cells were exposed for 16 h, and then incubated in MEM plus 10% FBS for a further 24 h. Cells were lysed and the Dual Luciferase assay (Promega Corp., Madison, WI) performed according to the manufacturer's protocol, and the values are expressed as relative luciferase units (RLU). The RLU were compared between co-transfection with pcNDAI and HET, respectively, and statistical analysis performed using a two-way ANOVA test. 5.1.2 Materials and Plasmids All materials and chemicals were purchased from SIGMA (St. Louis, MO) unless otherwise stated. The source of the human hsp27 promoter fragment containing the nonconsensus ERE and the TATA box was a genomic clone originally described in (Fuqua et al, 1989). The fragment (-99 to -15 bp) was amplified by PCR™ using the following primers: sense 5'-CTCAAACGGGTCATTG-3' (SEQ ID NO:3) and antisense 5'-TCGGCTGCGCTTTTAT-3' (SEQ ID NO:4). Hinάlll sites plus 2 additional nucleotides (GC) were added to the same primers for cloning purposes. The purified PCR™ product was digested with Hwdlll and ligated into pGL-2-Basic (Promega) to create the fragment CF. The vector pRLTK (Renilla luciferase gene under thymidine kinase promoter) was also obtained from Promega. 5.1.3 Cloning of ΗET An MCF-7 expression library was screened as described (Moretti-Rojas et al, 1988) using a random prime-labeled (Boehringer Mannheim, Indianapolis, IN) hsp27 ERE-TATA promoter fragment. The following modifications were also included in the protocol: the filters were first immersed in 10 mM IPTG for 30 min, followed by denaturation renaturation steps including incubation in decreasing concentrations (30 min in 6M, 3M, 1.5M, 0.75M, 0.375 M, and 0.19 M, respectively) of GnΗCl (guanidinium HCI) in HEPES-buffer (25 mM HEPES, pH 7.5, 25 mM NaCl, 5 mM MgCl 2 , 0.5 mM DTT). Positive phage DNA was purified and analyzed by dideoxy sequencing of both strands using the USB (Cleveland, OH) sequencing kit. This partial cDNA (position 680-1202 bp in the HET sequence) was expressed as a GST-fusion protein to confirm binding to the hsp27 promoter by cloning it into the EcoRI site of pGΕX-lλT (Pharmacia, Piscataway, NJ). The pGΕX-lλT vector clone was used as a negative control in all studies. GST-HΕT and pGΕX-lλT only were transformed into DH5α and protein was isolated according to the manufacturer's protocol (Pharmacia). Briefly, single clones were grown overnight in LB medium (50 μg/ml ampicillin), the next day an aliquot was grown for 4 h, and then 100 mM IPTG was added for an additional 1.5 h. The bacteria were pelleted, resuspended in PBS and sonicated for 10 sec. After the insoluble material was removed by centrifugation the supernatant was incubated with glutathione Sepharose 4B for 10 min at room temperature. The beads were then extensively washed with PBS, followed by a 10 min incubation with 5 mM glutathione in order to elute the bound proteins. Aliquots were analyzed on SDS-PAGΕ and also were used for gel-retardation assays. The same partial cDNA clone was then used as a probe to screen another MCF-7 cDNA library (λZap) which was obtained from Dr. Jeffrey Marks (Duke University, Durham, NC). Bluescript subclones were excised according to the manufacturer (Stratagene, La Jolla, CA) and analyzed by dideoxy sequencing of both strands using the USB sequencing kit. Since the library was originally constructed by cloning cDNAs into the EcoRI site of λZap vectors the HΕT cDNA insert was excised with EcoRI and ligated into the eukaryotic expression vector pcDNAl (Invitrogen, Carlsbad, CA). 5.1.4 Southwestern Blotting Nuclear extracts from MCF-7 cells were separated on a 12.5% SDS-PAGΕ gel, transferred onto nitrocellulose and the proteins were denatured/renatured by incubating the membrane in decreasing concentrations (10 min each in 6M, 3M, 1.5 M., 0.75M, 0.375M, and 0.19 M, respectively) of GnHCl in Z-buffer (25 mM HEPES, pH 7.6, 12.5 mM MgCl 2 , 20% glycerol, 0.1% NP40, 100 mM KC1, 1 mM DTT, and 10 μM ZnSO 4 ) at 4°C. After blocking for 30 min in Z-buffer and 3% nonfat dry milk, the membrane was incubated with random prime-labeled hsp27 ERE/TATA fragment (l-2χl0 6 cpm/ml) in Z-buffer and 0.25% nonfat dry milk with 10 μg/ml sonicated calf thymus DNA. Finally the membrane was washed three times in Z-buffer in 250 mM KC1 for a total of 15 min, and exposed to X-ray film. 5.1.5 Gel-Retardation Assay Gel-retardation assays were carried out as published (Fuqua et al, 1994). The hsp27 promoter fragment was dephosphorylated and 5'-end labeled using [α- PJATP and T4 polynucleotide kinase. The end-labeled fragment was incubated in the presence of 20 μg whole cell extracts (Fuqua et al, 1994), and after a 30 min incubation at room temperature the samples were loaded onto a 5% polyacrylamide gel and electrophoresed for 2.5 h. For supershift studies, ER-specific antibody MAb H222 which was obtained from Dr. G. Greene (Ben May Institute, University of Chicago, IL) was added (40 ng/reaction), and the reaction mixtures were incubated on ice for an additional 2 h. 5.1.6 In vitro Transcription/Translation TNT rabbit reticulocyte lysate (Promega) was used according to the manufacturer's recommendation with 2 μg of HET cloned into pcDNAl as a template and 1 μl of T7 polymerase added last to the reaction mixture, followed by a 90 min incubation at 30°C. 5.1.7 Preparation of HET-Specific Antibodies Antigenicity and hydrophobicity plots were generated from the HET amino acid sequence to predict immunogenic peptides for the generation of polyclonal antibodies to HET. A 13 amino acid peptide, PEARDSKEDGRKF (SEQ ID NO:9) was synthesized, coupled to KLH (keyhole limpet hemocyanin) via a cysteine residue (A156: C-PEARDSKEDGRKF) and injected into rabbits (Alpha Diagnostic, San Antonio, TX). The N-terminal cysteine residue is not part of the sequence of HET, but was added for purposes of coupling to KLH. The resulting antiserum was purified by affinity chromatography. The immunogenic peptide was cross-linked through the N-terminal cysteine onto an activated Sepharose column (Sulfolink, Pierce) according to the manufacturer's protocol. After loading with anti-HET antibody, the column was washed with low and high-salt buffer. Antibody bound to the cross-linked peptide was eluted from the column with 100 mM glycine, pH 2.5. Purified antibody was dialyzed overnight against PBS (phosphate buffered saline) with 0.02% NaN 3 . Monoclonal antibodies against HET protein were generated against the same synthetic peptide sequence (SEQ ID NO:9), using standard techniques as described above. 5.1.8 Western Blotting Protein extracts were resolved on polyacrylamide gels as previously described (Tandon et al, 1989), transferred from the gel to nitrocellulose membranes and subjected to immunodetection (Tandon et al, 1989) with an HET-specific polyclonal antibody and the Enhanced Chemiluminescence (ECL) system (DuPont, Boston, MA). Both the HET-specific antibody as well as the anti-rabbit Ig HRP-conjugated secondary antibody (Amersham, Arlington Heights, IL) were used at a dilution of 1 :1000. 5.1.9 Purification of Nuclear Matrix Proteins Nuclear matrices were prepared according to methodologies as previously described (Fey and Penman, 1988; Samuel et al, 1997). Samples were resuspended in 10 ml of ice cold TNM (100 mM NaCl, 300 mM sucrose, 10 mM Tris pH 8.0, 2 mM MgCl 2 , 1%) (v/v) thiodiglycol) with 100 mM PMSF (phenylmethylsulfonyl fluoride). The cell suspension was homogenized with a Teflon pestle on ice with 0.5% (v/v) Triton X-100 and the nuclei collected by centrifugation. Following centrifugation, the nuclei were resuspended to a concentration of 10 A 260 /ml in cold digestion buffer (DIG) (50 mM NaCl, 300 mM sucrose, 10 mM Tris-HCl pH 7.4, 3 mM MgC12, 1% (v/v) thiodiglycol, 0.5% (v/v) Triton X-100) and digested with DNase I (D5025, Sigma Chemical Company, St. Louis, Missouri) for 20 min at room temperature. Ammonium sulphate (final concentration of 0.25 M) was added and the nuclear matrix (NM-IF) pellet was obtained by centrifugation. The NM-IF pellet was resuspended in ice cold DIG buffer with 1 mM PMSF, extracted by adding 4 M NaCl to a final concentration of 2 M, and incubated on ice for 30 min. The NM2-IF pellet was collected by centrifugation and once again resuspended in ice cold DIG buffer, reextracted with 2 M NaCl and centrifuged. The NM2-IF was then resuspended in disassembly buffer (8 M urea, 20 mM 2[N- morpholino] ethane sulfonic acid, pH 6.6, 1 mM EGTA, 1 mM PMSF, 0.1 mM MgC12, 1% (v/v) - mercaptoethanol) and dialyzed overnight at room temperature against two liters of assembly buffer (0.15 M KCl, 25 mM imidazole, pH 7.1, 5 mM MgC12, 2 mM DTT, 0.125 M EGTA, 0.2 mM PMSF). Intermediate filaments (IFs) were removed by ultracentrifugation and the resulting supernatant containing NMPs (nuclear matrix proteins) was removed. The NMP containing supernatant was then dialyzed against ddH20 (double distilled water) for 8 h to reduce the salt concentration, followed by lyophilization. Lyophilized samples were resuspended in appropriate volumes of 8 M urea, aliquoted and frozen at -20°C. The protocol for Western blot analysis was slightly modified in that the Tween concentration was increased from 0.1% to 0.2%, and the secondary antibody was used at a dilution of 1 :5000. 5.1.10 Identification of the Chromosomal Locus of HET To identify the chromosomal locus of the HET gene, polymerase chain reaction (PCR™) primers (Saiki et al, 1988) were designed from HET cDNA (Oesterreich et al, 1997, GeneBank accession No. U72355). Forward and reverse primer sequences were 5'-GATGTCCACAGCAGAAGAGGC-3' (SEQ ID NO:5) and 5'-GTCACTGTTGCTC GACTTCTCC-3' (SEQ ID NO:6). These primers were used to amplify a 180 bp (basepair) product from human monochromosomal somatic hybrid cells obtained from the NIGMS human Genetic Mutant Cell Repository (Camden, NJ). Reaction conditions were 200 ng template DNA, 0.01 mg of each primer, 2.0 mM MgCl 2 , 200 mM dNTPs, 50 mM KCl, and 1 U of Taq Gold polymerase. An initial denaturation step of 15 min at 94°C was followed by 30 cycles of 1 min at 94°C, 1 min at 60°C, and 1 min at 72°C, with a final extension at 72°C for 10 min. PCR™ products were electrophoresed through 2.0% agarose gel and visualized by staining with ethidium bromide. A recombinant PI library was obtained from DuPont (Shepherd et al, 1994) and screened using the PCR™ primers listed above (SEQ ID NO:5 and SEQ ID NO: 6). The library was screened using the pooling strategies first described by Green and Olsen (1990). DNA was isolated from positive clones using a preparation protocol obtained from DuPont Biosciences. Slides of metaphase spreads for FISH were prepared using normal chromosomes by standard methods with the addition of ethidium bromide to produce prometaphase spreads (Ikeuchi, 1984; Moorehead et al, 1960). The HET PI human genomic probe was labeled with biotin- 14-dATP by nick translation (GIBCO/BRL). Fresh metaphase spreads were prepared the day before use and baked for 4 h at 65 °C. Slides were denatured for 2 min at 70°C, dehydrated and allowed to air dry. Labeled probe (40-80 ng) was mixed with hybridization buffer and human CoT-1 DNA and denatured for 5 min at 70°C. The probe was immediately added to denatured slides and incubated overnight. The slides were washed in 50% formamide, 2XSSC, pH 7.0 at 42°C followed by washing in 2XSSC, pH 7.0. The biotin-labeled HET probe was fluorescently-tagged with avidin-FITC (Vector Laboratory). Signal amplification was performed using biotin-labeled anti-avidin (Vector Laboratory) followed by avidin- FITC. The chromosomes were counterstained with DAPI and examined using a Zeiss Axioscope fluorescent microscope equipped with FITC, DAPI and triple band pass filter sets. Digital images were captured by computer using Applied Imaging Probevision software (Pittsburg) and photographs printed on a Kodak XL 7700 color image printer. 5.1.11 Loss of Heterozygosity (LOH) Assay Samples for LOH analysis were prepared by thin sectioning of tissue samples. Alternating 3 μm and 10 μm histologic sections were cut from selected formalin- fixed, paraffin-embedded tissue blocks and float mounted on glass slides. Areas of interest on the H&E (hemotoxylin and eosin)-stained 3 μm slides were outlined with a felt-tip pen, and used as a template to guide the independent microdissection of corresponding regions on the unstained 10 μm slides. Microdissection was performed on a light box viewed under a dissecting microscope, and was precise enough to insure that > 75% of the cellularity of each sample was derived from the targeted tissue. Cellular enrichment was about 90% in the majority of samples. DNA was liberated from samples by a modification of the method of Wright and Manos (1990). Paraffin and lipids were first extracted by adding 0.4 ml of octane to 1.5 ml microcentrifuge tubes containing the samples. Cell debris was then digested for 3 h at room temperature with 50 μl of 0.01 M Tris-HCl (pH 8.5), 0.001 M EDTA, 0.045% NP-40, and 0.045% Tween-20 containing 1.0 mg/ml proteinase K. The digest was heated to 95° C for 15 min to inactivate the protease, and the lysate was stored at -80° C until use. Loss of heterozygosity was analyzed using primers for the D19S216 marker, located on human chromosome 19pter. The marker has 5 alleles ranging from 179- 191 base pairs and a heterozygosity of 76%. The antisense primer was 5'-labeled in a standard polynucleotide kinase reaction with 3000 Ci/mmole [γ PJ-ATP (NEN) at a molar ratio of 18:1. The locus-specific PCR™ assay was performed in a total volume of 15 μl in an assay containing approximately 1.5 mM MgCl 2 , 1 mM spermidine base, 0.75 U of Taq polymerase, 100 μM of each dNTP, 100 nM of each primer, and 5 μl of 1 :15 diluted DNA template. Thirty PCR™ cycles consisting of 30 sec denaturing at 94°C, 1 min annealing at approximately 55-60°C and 1 min extension at 72°C were be carried out in a thermocycler. Amplified DNA was diluted 1 : 1 with stop solution (97%) formamide, 1% EDTA, 0.1 %> bromphenol blue, 0.1 % xylene cyanol), and denatured at 90°C for 2 min. Primers for the D19S216 Locus Used in LOH Assays AFM 164zb8a 5'-TCTTGTCACTCTAACTCCGC-3' (SEQ ID NO:7) AFM 164zb8m 5'-GGCCCATGTCTTTTTTAGGT-3' (SEQ ID NO:8) Three μl of the denatured DNA sample was loaded on a 7% polyacrylamide gel (19:1 acrylamide/bis-acrylamide), containing 32% formamide and 34% urea and fractionated over 2.5 h at 60 W. The gel was then transferred onto Whatman 3M paper, covered with plastic wrap, equilibrated with 20% methanol-20% acetic acid solution, and dried at 80°C. Gels were exposed to X-ray film with an intensifying screen to identify allelic bands in normal versus tumor tissue samples from the same individual. Loss of heterozygosity is indicated by the disappearance of one or more bands from the tumor DNA sample that were present in the normal tissue DNA sample from the same individual. To evaluate the intensity ratio of the two allelic bands from informative normal DNAs relative to the tumor DNA, digital autoradiographic data may be collected with a Phosphorlmager 1 " ; laser scanning device, and analyzed with the Phosphorlmager ImageQuant™ software package. 5.1.12 Inhibition of Tumor Cell Growth and Colony Formation by HET Full-length HET cDNA was excised by EcoRI digestion from the Bluescript clone and ligated into the eukaryotic expression vector pcDNAl. This plasmid was then used to transfect NIH 3T3 cells. Thus, 1.5 x 10 cells were plated onto 10 cm petri dishes and co-transfected with HΕT-pcDNAl and the G418 selectable expression vector pSV-neo (molar ratio 25:1). Control transfection was performed using the pcDNAl vector alone plus pSV-neo. The lipofectamine method was used for transfection. After 16 h in OPTIMΕM™ the cells were washed. One day later the cells were split into four 15 cm-dishes in media containing 1 mg/ml G418. Clones were picked 2-3 wk later. For analysis of cell growth rate, cells were plated at 2500 cells/well into a 96- well plate. The next day cell number was assessed by MTT assay (Day 0). Cells were then incubated in serum-free medium, or 10%> serum, and cell number calculated at days 2, 4 and 6 by MTT assay. The effect of transient expression of HΕT on cell growth rate in 293 cancer cells was determined as follows. Aliquots containing 8 10 293 cells were plated into 6-well plates. The next day they were transfected with increasing amounts of HET/pcDNAl antisense (0.02, 0,2 and 2 μg). As a control the inventors transfected pcDNAl plasmids only. Cells were kept overnight in serum-free OPTIMEM™, and than allowed to recover for 24 h in 10% serum containing media. The number of transfected 293 cells in S-phase was determined by incorporating H-thymidine into DNA as a measurement of cell proliferation. After the recovery phase the cells were incubated in media containing H-thymidine (1 μCi/ml) for 1 h. After washing the cells with cold PBS and with 5% cold TCA, cells were fixed with 5% cold TCA for 30 min on ice. Cells were than washed four times with cold water, and lysed in 1 ml 0.5 M NaOH. 750 μl lysate was added to scintillation fluid, and cpm were counted. In parallel, 50 μl of lysate was used to determine protein concentration (BCA method). Each transfection was set up in triplicate, and the measurements for each point were done in duplicates. The 3H- thymidine incorporation was corrected for protein content. The effect of HET expression on MCF-7 colony formation was assayed by transfection of MCF-7 cells with 20 μg of pcDNAl control vector or pcDNAl -HET sense strand, along with 1 μg of pSVneo. Cells were incubated in 400 μg/ml G418S for 3 wk, after which colonies were stained with 1% crystal violet. 5.1.13 Identification of HET Point Mutations in Breast Cancer Cells RNA was purified from MDA-MB-468 breast cancer cells using standard techniques. A 1.9 kb 5' HET amplification product was generated by RT-PCR™, using the following primers: YTH49 5'-CCTGGAATGGCGGAGACTCTGTCA-3' (SEQ ID NO: 10) SAFB3 5'-GTTCGCGTTCACTGCGTTCACG-3' (SEQ ID NO:l 1) The RT reaction was started by heating the sample for 2 min at 94°C, then incubating at 42°C for 45 min in the presence of reverse transcriptase and substrates. The PCR™ step utilized the Expand High Fidelity PCR™ system (Boehringer Mannheim, Indianapolis, IN) and following the manufacturer's instructions. The PCR™ product was TA-cloned (Invitrogen, Carlsbad, CA). DNA was isolated and sequenced using the T7 Sequenase version 2.0 (Amersham, Carlsbad, CA). Both strands from multiple clones were sequenced. 5.2 Example 1: HET Binds to the hsp27 Promoter Protein factors binding to the most transcriptionally active region of the hsp27 promoter were identified by gel retardation and Southwestern blotting (Oesterreich et al, 1996a). Gel-retardation analysis with an 84 bp promoter fragment containing the ERE-TATA box (-99 bp to -15 pb) and whole cell extracts from MCF-7/MG cells revealed binding of a protein complex (FIG. 1A, lane 3). Since this fragment contains an ERE, separated by a TATA box, the protein was named HET (Hsp27 ERE-TATA- binding protein). As hsp27 has been described as an estrogen-inducible protein, the possibility that the protein was the estrogen receptor (ER) was excluded by performing supershift studies using ER-specific antibodies. As a positive control, a consensus ERE sequence was used as a probe, resulting in retardation of the probe by ER, which was then further upshifted by adding antibodies to ER (FIG. 1A, lanes 1 and 2). However, ER antibodies did not upshift the protein complex bound to the hsp27 promoter fragment (FIG. 1 A, lanes 3 and 4). Southwestern blotting of MCF-7/MG nuclear extracts with the same hsp27 promoter fragment (FIG. IB) indicated binding of two proteins with molecular weights of approximately 120 kDa and 45 kDa. The 45 kDa protein has a molecular weight consistent with it being TATA-binding protein. The difference in size of HET (the 120 kDa protein) as compared to the ER (65 kDa) again indicates that HET is distinct from the ER. Furthermore, binding of HET was detected using extracts of MDA-MB-231 cells, which are ER-negative breast cancer cells. These observations eliminated the trivial possibility that the hsp27 promoter binding factor was ER. 5.3 Example 2: Cloning of HET as an hsp27 Promoter-Binding Protein A partial (900 bp) HET cDNA clone was isolated by screening an MCF-7 expression library (Moretti-Rojas et al, 1988) with the hsp 27 promoter fragment from -99 bp to -15 bp. This partial cDNA was expressed as a GST fusion protein (FIG. 2A, lane 3), using GST only (FIG. 2A, lane 2) as a negative control. After purification of GST only (FIG. 2A, lane 4) and GST-HET fusion proteins (FIG. 2A, lane 5), these extracts were used in a gel-retardation assay. Specific binding of purified GST-HET to the hsp27 promoter fragment was observed (FIG. 2B, lanes 3 and 4) in a dose-dependent manner, whereas purified GST alone failed to bind (FIG. 2B, lanes 1 and 2). This partial clone was used to screen another MCF-7 breast cancer cell cDNA library (obtained from Dr. Jeff Marks, Duke University, Durham, NC). An HET clone of 3040 bp in length was obtained (GENEbank accession number U72355, SEQ ID NO:l). The original partial cDNA clone isolated by the inventors was identical to position 860-1202 bp in the full-length HET sequence. The identity of the HET cDNA sequence within the full-length clone was confirmed by sequencing another four positive clones, all of which overlapped with the sequence from the full-length HET cDNA. The original, partial cDNA clone may represent a portion corresponding to an mRNA splicing variant of HET, a hypothesis which is supported by the appearance of minor bands on Northern blots. There is a putative initiation codon at nucleotide 54 in the full-length HET cDNA clone which shows a weak homology to the translation initiation consensus sequence (Kozak, 1983). There is also a translation stop codon at nucleotide 2799 which is followed by a polyadenylation signal and a poly(A) tract. A potential open reading frame (ORF) coding for 916 amino acids is present, which results in a predicted molecular weight of approximately 100 kDa for the HET protein. The protein sequence contains an unusually high number of charged amino acids (221 negatively-charged and 164 positively-charged; theoretical pl=5.05). No classical DNA-binding motif was identified using PROSITE. However, a potential RNA binding domain, located at amino acid residues 375 to 500 of SEQ ID NO:2, was identified based on sequence homology to various other proteins which contain RNA-binding domains. This region displays homology to RNA-binding domains from a large variety of proteins, including a glycine rich RNA-binding protein (Zea mays), transformer-SR ribonucleoprotein (Nicotiana tabacum), low temperature- responsive RNA-binding protein (Hordeum vulgarc) and single stranded nucleic acid binding protein (Triticum aestivum). The homology search was performed in GenBank. Two point mutations have been identified in the HET sequence of MDA-MB- 468 breast cancer cells, using RT-PCR™ and DNA sequencing as described in section 5.1.13 above. The first identified mutation involves the substitution of an adenosine residue for the guanosine at position 190 of SEQ ID NO: 1. This substitution results in a change from a CGG codon, encoding arginine, to a CAG codon, encoding glutamine. The second point mutation involves the substitution of a guanosine residue for the adenosine residue at position 265 of SEQ ID NO: 1. This results in a change from a AAT codon, encoding asparagine, to a GAT codon, encoding aspartate. These point mutations were confirmed by sequencing both strands from multiple clones obtained from the MDA-MB-468 cell line. 5.4 Example 3: Antibodies Specific for HET A rabbit polyclonal antiserum was developed as described above. This antiserum recognized HET in whole cell extracts. However, binding to other nonspecific bands was observed. After affinity purification using an HET peptide, the polyclonal antibody recognized a single band of approximately 120 kDa, which is in agreement with the Southwestern blot analysis (FIG. IB). The discrepancy between the predicted and the approximate molecular weight by SDS-PAGE, may be a result of post-translational modification. The purified antibody preparation was used to determine if it would recognize the HET protein prepared by coupled in vitro transcription/translation. HET cDNA was transcribed in vitro and translated in the presence (FIG. 3A) and absence (FIG. 35 15 3B) of [ S]-methionine and the protein products were analyzed by SDS-PAGE. [ S]- Methionine in vitro transcription translation of HET cDNA resulted in expression of a single high molecular weight protein (FIG. 3 A, lane 1), whereas no protein was detected with control DNA (vector only) (FIG. 3 A, lane 2). The protein product from the unlabelled in vitro transcription/translation was exposed to Western blot analysis using the HET-specific purified polyclonal antibody. As expected, a band comparable in size to the product from the in vitro transcription/translation in the presence of [ S]-methionine was detected (FIG. 3B, lane 1). Again there was no band detected when control DNA was used (FIG. 3B, lane 2). Taken together, these facts strongly indicate that the cloned cDNA encodes the full-length HET protein. 5.5 Example 4: HET is Localized in the Nuclear Matrix Scaffold attachment factors are a specific subset of nuclear matrix proteins (NMP), that specifically bind to S/MAR. The inventors hypothesize that HET is a scaffold attachment factor localized in the nuclear matrix which might also influence hsp27 promoter activity in breast cancer cells. To determine if HET is localized within the nuclear matrix, various subnuclear fractions from ZR-75, an ER-positive human breast cancer cell line, were isolated as described above and outlined in FIG. 4A. Briefly, cells were homogenized in buffer containing 0.5% Triton X-100 to release lipids and soluble proteins. The nuclei were then digested with DNase I and precipitated with 0.25 M ammonium sulphate to facilitate chromatin removal. The resulting nuclear matrix-intermediate filament (NF- IF) pellet containing nuclear matrix and associated intermediate filaments was then subjected to sequential salt extractions with 2M NaCl for the further removal of residual histones (Courts et al, 1996). The NM2-IF pellet was resuspended in disassembly buffer containing 8M urea and dialyzed against assembly buffer. Dialysis allowed for the urea to be removed and IF reassembly. The IFs were collected by centrifugation and the resulting supernatant contained nuclear matrix proteins. Western blotting was done on all fractions using HET-specific antibodies (FIG. 4B). While there was some HET protein detected in the NM2-IF fraction (S2) (FIG. 4B, lane 2), most of it was observed to be localized in the nuclear matrix (FIG. 4B, lane 4). Similar fractions were also prepared from two other ER-positive human breast cancer cell lines (T47DE and MCF-7) to assess if HET was also localized to the nuclear matrix in these cell lines. Both of these cell lines were observed to contain similar levels of HET as compared to ZR-75 (FIG. 4C). In contrast, lower levels of HET were detected in the nuclear matrix of MDA-MB 231 cells, an ER-negative human breast cancer cell line. These results were confirmed by in situ staining of 293 cells using transient transfection with either green fluorescent protein (GFP) alone or a GFP-HET fusion protein. Using fluorescent microscopy, the GFP protein was detected mainly in the cytosol, while GFP-HET was localized exclusively in the nuclei (but not in nucleoli). 5.6 Example 5: HET Decreases hsp27 Promoter Activity in a Dose- Dependent Fashion To analyze if HET would not only bind to the hsp27 promoter, but also influence its transcriptional activity, transient transfection assays were performed with an hsp27 promoter-luciferase reporter construct (called CF) and an expression plasmid containing full-length HET (FIG. 5). CF contains the imperfect ERE and the TATA box region from the hsp27 promoter initially used to clone HET and harbors the HET- binding site. The CF fragment displays relatively low basal transcriptional activity. However, it is about 12-fold higher than that of the pFL2 basic vector alone. The relative luciferase activity of the CF fragment was measured either in the presence of vector alone (pcDNAl) or HET (FIG. 5). In all cell lines analyzed (MDA-231 , T47D, MCF-7/MG, COS and HeLa), co- transfection with HET significantly reduced transcriptional activity of the hsp27 promoter fragment (p<0.05). In contrast, the activity of the Renilla-luciferase construct which contains a thymidine kinase promoter, used to correct for transfection efficiency, did not decrease after adding HET. To further address the question of specificity a transient assay was performed using a 1.5 kb IGF-1 gene promoter construct (Adamo et al, 1993), which was obtained from Dr. M. Adamo (UTHSCSA, San Antonio), and pGL2-control, which contains an SV-40 promoter. The activity of the IGF-1 promoter was not affected by HET, and the SV40-promoter was only affected after adding higher concentrations of HET. Therefore, the inventors conclude that HET is able to specifically decrease the activity of the hsp27 promoter in breast cancer cells. However, it may have other targets as described for other NMPs. 5.7 Example 6: Localization of the HET Gene to Human Chromosome 19 band pl3 and LOH Assays for Breast Cancer Diagnosis. The chromosomal locus of the HET gene was identified by somatic cell hybrid analysis and FISH, as described above. Fluorescent in situ hybridization analysis (FISH) of a human metaphase chromosomal spread with an HET PI probe showed labeling of chromosome 19 (FIG. 6). DAPI counterstaining of the metaphase chromosomes allowed further localization of the HET gene to the locus 19pl 3.2-13.3. No hybridization was observed on any other chromosome (FIG. 6). This chromosomal locus was confirmed by somatic cell hybridization studies. Somatic cells containing the DNA sequences of individual human chromosomes were subjected to PCR™ amplification using primers specific for the HET sequence as described (SEQ ID NO:5 and SEQ ID NO:6). The results shown in FIG. 7 demonstrate that HET specific primers only amplified a DNA sequence contained within human chromosome 19 (FIG. 7, lane 19). No other human chromosomal DNA was amplified by HET specific primers. Thus, the HET gene is located at the human chromosomal locus 19p 13.2- 13.3. LOH assays were performed as described above by comparative PCR™ analysis of DNA from tumor and normal tissue samples, using primers specific for microsatellite marker D19S216 (Genethon). The D19S216 marker was chosen because it is located near the 19pl3.2-13.3 chromosomal locus of HET and it shows a high endogenous level of heterozygosity. Loss of heterozygosity is indicated by the disappearance of an allelic band in the tumor DNA sample which is present in a normal DNA sample from the same individual. As shown in FIG. 8, analysis of PCR™ products of D19S216 indicates that LOH occurs at 19pl3. These results were extended to a sample of 32 primary breast tumors of varying malignancy and tumor type, compared with normal tissue samples from the same individuals. LOH was observed in 56% of these tumors. This is the highest informative rate of LOH observed for any reported marker of breast cancer. Thus, assays directed towards LOH analysis of 19pl3 in human tissue samples are expected to have utility for the diagnosis of breast cancer. These results have been confirmed by the recent publication of Lee et al. (1998), who examined LOH in uterine cervical cancers using the same D19S216 marker. These authors observed a 100%> (6/6) loss of this locus in the sporadic form of adenoma malignum of the uterine cervix, confirming that the 19pl3.3 locus harbors a tumor suppressor gene. 5.8 Example 7: Expression of HET in Breast Tumors and Inhibition of Cancer Cell Growth Rate by HET HET expression levels were measured by Western blot analysis in 61 primary breast tumors, using the polyclonal antibody described above (FIG. 9). HET levels were observed to vary widely. HET expression was negatively associated with S- phase (Spearman's rank correlation -0.22, p = 0.08). Sixteen percent of breast tumors did not express HET protein at a detectable level. Two tumors showed immune reactivity with a lower molecular weight peptide. This may represent a truncated HET product, since the antibody is directed against an N-terminal portion of HET. The inverse correlation between HET expression and S-phase indicates that HET expression can be used as a diagnostic marker for breast cancer. Higher levels of HET expression are found in slowly dividing, less malignant tumors, while lower levels or absence of HET expression are associated with rapidly dividing, highly malignant tumors. These results were confirmed in a sample of 49 additional breast tumors analyzed by Western blotting with an HET-specific monoclonal antibody. Blots were densitometrically scanned and levels determined as arbitrary units (compared to an internal standard). The trend was for patients with higher HET levels to have a better disease free and overall survival. However, the result was not statistically significant at the 0.05%) level. This study confirmed that 18% (9/49) of the tumors did not express any detectable levels of HET. These results suggest that methods of determining HET expression may be of use in the prognosis of breast cancer. Individuals with tumors exhibiting low HET expression, correlated with high growth rate (rapidly dividing cells with a high percentage in S-phase) may have a poorer prognosis than individuals with tumors of high HET expression and low growth rate. These results further suggest that HET expression may be utilized to control the phenotype of tumor cells. Transfection of tumor cells with expression vectors containing an HET gene is expected to lead to loss of the transformed phenotype and slower tumor growth rate. To test this hypothesis, transfected NIH 3T3 cells were transfected with the eukaryotic expression vector pcDNAl, into which a full-length HET cDNA was incorporated. Although many positive clones were originally obtained (by DNA- PCR™ and Western blot analysis), they could not be kept in culture, indicating that HET is growth inhibiting/toxic for the cells. Only one clone overexpressing HET survived, and growth analysis confirmed significant growth inhibition as compared to control clones. Cell growth rate was determined by MTT assay at 0, 2, 4 and 6 days post-transfection. As shown in FIG. 10A and FIG. 10B, transfection with the HET cDNA resulted in a significant inhibition of tumor cell growth rate. Each point on FIG. 10A and FIG. 10B represents the mean and standard deviation for quadruplicate samples of control and HET-transfected cells. The inhibition of tumor cell growth rate was particularly striking in serum-free medium (FIG. 10A and FIG. 10B). Cell growth in serum-free medium is characteristic of the transformed phenotype. Thus, transfection of tumor cells with HET resulted in at least a partial reversal of the transformed phenotype. Conversely, a decreased expression of HET leads to an increased rate of proliferation in 293 cancer cells. Increasing amounts (0.02, 0.2 and 2.0 μg) of HET antisense construct were transiently transfected into 293 cancer cells. Control cells were transfected with vector alone. The number of cells in S-phase was determined by incorporation of [3 H] -thymidine, as described above. As shown in FIG. 11, transfection with increasing amounts of antisense HET was directly correlated with an increased proportion of 293 cells in S-phase, determined by incorporation of [3H]- thymidine into DNA. The inverse correlation between HET levels and cell proliferation is further demonstrated in FIG. 12. As shown in FIG. 12A, total cellular levels of HET decreased progressively when MCF-7/MG cells were stimulated to proliferate with 5% and 10%> serum, respectively, compared to cells in serum free medium (SFM). Treatment of MCF-7 cells with the phorbol ester TPA has been shown to cause growth inhibition. As seen in the lower half of FIG. 12 A, when MCF-7 cells were exposed to 50 nM TPA, HET levels increased within 4 h. A similar effect was observed when MCF-7 cells were transfected with an HET expression vector (FIG. 12B). Expression of HET resulted in an inhibition of MCF-7 colony formation (HET sense), compared with MCF-7 cells transfected with control vector alone (PCDNA1) or with an antisense expression vector (HET antisense). Overexpression of HET results in growth inhibition in cancer cell lines, which is correlated with a block in G0/G1. Expression of HET was negatively correlated with S-phase (a marker of proliferation) in breast tumors. At least two breast tumors showed a truncated protein, suggesting that HET protein is mutated to result in a nonfunctional protein. All these data strongly indicate that HET is a tumor suppressor whose absence predicts a more aggressive type of breast cancer. All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the composition, methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims. 6.0 REFERENCES The following literature citations as well as those cited above are incorporated in pertinent part by reference herein for the reasons cited in the above text. Adamo et al, Endocrinology, 132:935-937, 1993. Baichwal and Sugden, In: Gene Transfer, Kucherlapati R, ed., New York, Plenum Press, pp. 117-148, 1986. Barany and Merrifield, 77ze Peptides, Gross and Meienhofer, eds., Academic Press, New York, pp. 1-284, 1979. Bellus,J Macromol Sci. PureAppl. Chem, A31(l): 1355-1376, 1994. Benvenisty and Neshif, Proc. Nat. Acad. Sci. USA. 83:9551 -9555, 1986. Campbell, In: Monoclonal Antibody Technology, Laboratory Techniques in Biochemistry and Molecular Biology, Burden and Von Knippenberg, Eds., Vol. 13:75-83, Elsevier, Amsterdam, 1984. Capaldi et al, Biochem. Biophys. Res. Comm., 76:425, 1977 Chang et al , Hepatology, 14 : 124 A, 1991. Chen and Okayama, o/. CellBiol, 7:2745-2752, 1987. Coffin, In: Virology, Fields et al, eds., Raven Press, New York, pp. 1437-1500, 1990. Cech et al, Cell, 27:487-496, 1981. Couch et al, Am. Rev. Resp. Dis., 88:394-403, 1963. Coupar et al, Gene, 68:1-10, 1988. Coutts et al, J. of Cellular Biochem., 61 :1-11, 1996. Cox et al, Breast Cane. Res. Treat. 32: 19-38, 1994. Culver et al., Science, 256:1550-1552, 1992. Davey etα/., EP 329822 Dubensky et al, Proc. Nat. Acad. Sci. USA, 81:7529-7533, 1984. Dunn et al, J. of Steroid Biochem. and Mole. Biol, 46:469-479, 1993. Elledge et al, Cancer Res. 54: 3752-3757, 1994 EPO No. 320 308 Fechheimeret al, Proc. Natl. Acad. Sci. USA, 84:8463-8467, 1987. Ferkol et o/., E4SERJ, 7: 1081-1091 , 1993. Fey and Penman, Proc. Natl. Acad. Sci. USA, 85:121-125, 1988. Fodor et al, Science, 251 : 767-773, 1991. Forster and Symons, Cell, 49:211-220, 1987. Fraley et al, Proc. Natl. Acad. Sci. USA, 76:3348-3352, 1979. Freifelder, Physical Biochemistry Applications to Biochemistry and Molecular Biology, 2nd ed., Wm. Freeman and Co., New York, NY, 1982. Freshner, Animal Cell Culture: A Practical Approach, 2nd ed., Oxford/New York, IRL Press, Oxford University Press, 1992. Friedmann,Sc ewc-e, 244: 1275-1281 , 1989. Frohman, In: PCR™ Protocols: A Guide To Methods And Applications, Academic Press, N.Y., 1990. Fuqua et al, Breast Cancer Research and Treatment, 32: 177-186, 1994. Fuqua et al, Cancer Res., 49:4126-4129, 1989. Garrido et al, Eur. J. Biol, 237:653-659, 1996. GB 2 202 328 Gefter et al, Somatic Cell Genet., 3: 231-236, 1977. Gerlach et α/., Nαtwre (London), 328:802-805, 1987. Ghosh-Choudhury et al, EMBO J., 6: 1733-1739, 1987. Ghosh and Bachhawat, In: Liver Diseases, Targeted Diagnosis and Therapy Using Specific Receptors and Ligands. Wu et al. , eds., Marcel Dekker, New York, pp. 87-104, 1991. Gingeras et al, WO 88/10315. Goding, In: Monoclonal Antibodies: Principles and Practice, 2d ed., Academic Press, Orlando, Fla., pp. 60-61, and 71-74, 1986. Gomez-Foix et α/., J Biol. Chem., 267:25129-25134, 1992. Gopal, Mol. Cell Biol. , 5: 1188-1190, 1985. Graham and Prevec, In: Methods in Molecular Biology: Gene Transfer and Expression Protocol, E.J. Murray, ed., Humana Press, Clifton, NJ, 7:109-128, 1991. Graham and van der Eb, Virology, 52:456-467, 1973. Graham et al. , J Gen. Virol , 36:59-72, 1977. Green and Olson, Proc. Natl Acad. Sci. USA, 87:1213-1217, 1990. Grunhaus and Horwitz, Seminar in Virology, 3:237-252, 1992. Gyapay et al, Nat. Genet., 7:246-339, 1994. Hacia et al, Nature Genetics, \4:4Al-441, 1996. Harland and Weintraub,J. Cell Biol. , 101 :1094- 1099, 1985. Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, 1988. Hermonatand Muzycska, Proc. Natl. Acad. Sci. USA, 81 :6466-6470, 1984. Hersdorffer et al, DNA Cell Biol, 9:713-723, 1990. Herz and Gerard, Proc. Natl Acad. Sci. USA, 90:2812-2816, 1993. Hickey et al, Nucl. Acids Res., 14:4127-4145, 1986. Horwich, et al. , J. Virol. , 64:642-650, 1990. Ikeuchi, Cytogenet Cell Genet 38:56-61, 1984. Innis et al. , PCR Protocols, Academic Press, Inc., San Diego CA, 1990. Johnson et al, "Peptide Turn Mimetics," In: Biotechnology And Pharmacy, Pezzuto et al, eds., Chapman and Hall, New York, 1993. Jones and Shenk, Cell, 13:181-188, 1978. Joyce, Nature, 338:217-244, 1989. Kaneda et al. , Science, 243 :375-378, 1989. Karlsson et al, EMBO J., 5:2377-2385, 1986. Kato et α/., J. Biol. Chem., 266:3361-3364, 1991. Kim and Cech, Proc. Natl Acad. Sci. USA, 84:8788-8792, 1987. Kinzlerand Vogelstein,Nαtwre 386: 761-763, 1997. Klein et al, Nature, 327:70-73, 1987. Kohlerand Milstein, Nature, 256:495-497, 1975. Kohler and Milstein, Eur. J. Immunol. , 6: 511 -519, 1976. Kozak, Microbiological Reviews, 47: 1-45, 1983. Kwoh et al, Proc. Nat. Acad. Sci. USA, 86: 1 173, 1989. Kyte and Doolittle, J. Mol. Biol, 157(1):105-132, 1982. Lavoie et al, J. of Biol Chem. , 268:3420-3429, 1993. Le Gal La Salle et al, Science, 259:988-990, 1993. Lee and Feinberg, Cancer Res., 57: 3131-3134, 1997. Lee et al, Cancer Res. 58: 1140-1143, 1998. Lemieux et al, Proc. Am. Assn. Cancer Res., 37:68, 1996. Levrero et al, Gene, 101 :195-202, 1991. Li et al, Cell 88: 143-154, 1997. Mahvi et al, Endocrine, 4:269-275, 1996. Mann et al, Cell, 33:153-159, 1983. Markowitz et al, J. Virol, 62:1 120-1 124, 1988. Merrifield, Science, 232: 341-347, 1986 Michel and Westhof, 1990 Miki et al, Science 266: 66-71, 1994. Miller et A/., WO 89/06700 Moorehead et α/., Exp. Cell Res. 20:613-616, 1960. Moretti-Rojas et al, Breast Cancer Res. Treat., 11 :155-163, 1988. Mulligan, Science, 260:926-932, 1993. Myers, EP 0273085 Nicolas and Rubinstein, In: Vectors: A survey of molecular cloning vectors and their uses, Rodriguez and Denhardt, eds., Stoneham: Butterworth, pp. 494-513, 1988. Nicolau and Sene, Biochim. Biophys. Ada, 721 : 185- 190, 1982. Nicolau et al, Methods En∑ymoL, 149:157-176, 1987. Oesterreich et al, Biochemical and Biophysical Research Communications, 222:155- 163, 1996a. Oesterreich et al, Cancer Research, 53 :4443-4448, 1993. Oesterreich et al, Clinical Cancer Research, 2:1199-1206, 1996b. Oesterreich et al, J. Cell. Biochem., 67: 275-286, 1997. Ohara et al, Proc. Nat'lAcad. Sci. USA, 86:5673-5677, 1989. Paskind et al, Virology, 67:242-248, 1975. PCT/US87/00880 PCT/US89/01025 Pease et al, Proc. Natl Acad. Sci. USA, 91 :5022-5026, 1994. Perales et al, Proc. Natl. Acad. Sci. 91 :4086-4090, 1994. Pignon et al, Hum. Mutat., 3: 126-132, 1994. Potter et al, Proc. Nat. Acad. Sci. USA, 81 :7161-7165, 1984. Racher et al, Biotechnology Techniques, 9:169-174. 1995. Ragot et al, Nature, 361 :647-650, 1993. Reinhold-Hurek and Shub, Nature, 357:173-176, 1992. Remington's Pharmaceutical Sciences, 15th ed., pp. 1035-1038 and 1570-1580. Renan, Radiother. Oncol. , 19:197-218, 1990. Renz and Fackelmayer, Nucl. Acids Res., 24:843-849, 1996. Rich et al, Hum. Gene Ther., 4:461-476, 1993. Richards et al, Intl. J. Oncol, 8: 1265-1271, 1996. Ridgeway, In: Vectors: A Survey of Molecular Cloning Vectors and Their Uses, Rodriguez et al, eds., Stoneham: Butterworth, pp. 467-492, 1988. Rippe et α/., Mol. Cell Biol, 10:689-695, 1990. Rosenfeldet α/., Cell, 68:143-155, 1992. Rosenfeld et al, Science, 252:431-434, 1991. Roux et al, Proc. Nat'lAcad. Sci. USA, 86:9079-9083, 1989. Sager, Science 246, 1406-1412, 1989. Saiki et al, Science, 239:487-491, 1988. Sambrook et al, In: Molecular Cloning: A Laboratory Manual, 2d Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989. Samuel et al, J. Cell. Biochem. 66: 9-15, 1997. Sarver, et al, Science, 247:1222-1225, 1990. Scanlon et A/. , Proc Natl Acad Sci USA, 88:10591-10595, 1991. Seymor et al , British Journal of Cancer, 61 :886-890, 1990. Shepherd et al , Proc Natl Acad Sci USA, 91 :2629-2633, 1994 Shoemaker et al , Nature Genetics 14.450-456, 1996 Slamon et al , Science 235; 177-182, 1987. Sliutz et al , British Journal of Cancer, 74: 172-177, 1996. Stanbridge, Trends Biochem Sci. 6: 213-219, 1990. Stewart and Young, Solid Phase Peptide Synthesis, 2d. ed., Pierce Chemical Co., 1984. Stratford-Perricaudet and Perricaudet, In Human Gene Transfer, O. Cohen- Haguenauer et al , eds., John Libbey Eurotext, France, pp. 51 -61 , 1991. Stratford-Perricaudet et al , Hum Gene Ther , 1.241-256, 1990 Stratton and Woostei, Cwrr Opin Genet Devel 6 93-97, 1996 Tarn et al, J Am Chem Soc, 105:6442, 1983. Tandon et al , Journal of Clinical Oncology, 7:1 120-1128, 1989. Tandon et al , Proc Am Soc Clin Oncol , 9:84, 1990. Temin, In Gene Transfer, Kucherlapati R, ed., New York, Plenum Press, pp. 149-188, 1986. Top et α/ , J Infect Dis , 124: 155-160, 1971. Trink et al , Oncogene 16: 2815-2818, 1998. Tur-Kaspaet α/ , M>/ Cell Biol , 6:716-718, 1986 U.S Patent No. 5,279,721 U.S Patent No. 4,196,265 U.S. Patent No. 4,883,750 U.S. Patent No. 4,683,195 U.S. Patent No. 4,683,202 U.S. Patent No. 4,800,159 U.S. Patent No. 5,354,855 Varmus et al , Cell, 25:23-36, 1981. Wagner et al. , Science, 260: 1510- 1513, 1990. Walker etal, Proc. Natl. Acad. Sci. USA, 89:392-396 1992. WO 90/07641 , filed December 21 , 1990. Wong et al, Gene, 10:87-94, 1980. Wright and Manos, In: PCR™ protocols, Innes et al. (eds.), Academic Press, San Diego, pp. 153-158, 1990. Wu and Wu^Λ. Drug Delivery Rev., 12: 159-167, 1993. Wu and Wu, Biochemistry, 27: 887-892, 1988. Wu and Wu, J. Biol. Chem., 262: 4429-4432, 1987. Wu et al, Genomics, 4:560, 1989. Yanagisawa et al, Cancer Res., 56:457-462, 1996. Yang et al, Proc. Natl. Acad. Sci. USA, 87:9568-9572, 1990.

Claims: CLAIMS: 1. A nucleic acid segment which encodes a HET polypeptide comprising a contiguous amino acid sequence of at least 751 amino acids from SEQ ID NO:2. 5 2. A nucleic acid segment of from 2253 nucleotides to about 10,000 nucleotides in length, comprising at least a 2253 nucleotide sequence of SEQ ID NO:l. 10 3. A nucleic acid segment that comprises the sequence of SEQ ID NO: 1. 4. A nucleic acid segment that is complementary to the nucleic acid segment of 15 SEQ ID NO:! . 5. A host cell comprising the nucleic acid segment of any of claims 1-4. 20 6. The nucleic acid segment of any of claims 1-4 comprised within a vector. 7. A polypeptide encoded by the nucleic acid segment of claim 1 that includes a 25 contiguous amino acid sequence of at least 751 amino acids from SEQ ID NO:2. 8. A polypeptide that has the amino acid sequence of SEQ ID NO:2. 30 9. A polypeptide according to claim 8 wherein a glutamine residue is substituted for the arginine residue at position forty-six of the polypeptide sequence (SEQ ID NO:2). 10. A polypeptide according to claim 8 wherein an aspartate residue is substituted for the asparagine residue at position seventy-one of the polypeptide sequence (SEQ ID NO:2). 1 1. An antibody that specifically binds to a polypeptide having the amino acid sequence of SEQ ID NO:2. 12. An antibody that specifically binds to the polypeptide of claim 9. 13. An antibody that specifically binds to the polypeptide of claim 10. 14. A composition comprising an antibody that binds specifically to a polypeptide having the amino acid sequence of SEQ ID NO:9 or SEQ ID NO:2. 15. A method for detecting tumor cells, comprising: a) obtaining a sample suspected of containing tumor cells; b) contacting said sample with an antibody that specifically binds to an HET polypeptide under conditions effective to bind said antibody and form a complex; c) measuring the amount of HET polypeptide present in said sample by quantitating the amount of said complex; and d) comparing the amount of HET polypeptide present in said sample with the amount of HET polypeptide in normal cells, wherein a difference in the amount of HET polypeptide in said sample compared with the amount in normal cells indicates the presence of tumor cells. 16. The method of claim 15 wherein said antibody is the antibody of claim 12. 17. The method of claim 15 wherein said antibody is the antibody of claim 13. 18. A method of determining tumor malignancy, comprising determining an absence of detectable levels of HET polypeptide in a tissue sample, wherein the absence of detectable levels of said polypeptide in said sample is indicative of a malignant tumor. 19. The method of claim 18 wherein the tumor is a breast tumor. 20. The method of claim 19 wherein the breast tumor is selected from the group consisting of infiltrating duct carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, ductal carcinoma in situ and lobular carcinoma in situ. 21. A method of determining survival for an individual having a tumor, comprising determining the absence of detectable levels of HET polypeptide in a tumor tissue sample from said individual, wherein the absence of detectable levels of HET polypeptide in said tissue sample is associated with a decreased survival of the individual. 22. A method of determining malignancy in a tumor cell, comprising: a) obtaining a tumor cell sample and a normal cell sample from the same individual; b) amplifying chromosomal DNA from said tumor and normal cell samples using primers specific for amplification of a polymorphic marker located at human chromosomal locus 19p 13 ; and c) comparing the amplification products from said suspected tumor and normal cells, wherein loss of heterozygosity (LOH) at locus 19pl3 indicated by an amplification product present in the normal cell and missing in the suspected tumor cell is indicative of malignancy in said tumor cell. 23. The method of claim 22 wherein the tumor cell is a breast tumor cell. 24. The method of claim 22, wherein the primers comprise the sequences of SEQ ID NO:7 and SEQ ID NO:8. 25. A method of malignant tumor cell diagnosis, comprising determining loss of heterozygosity (LOH) at chromosomal locus 19pl3, wherein LOH at chromosomal locus 19pl3 is indicative of a malignant tumor. 26. The method of claim 25, wherein the tumor is a breast tumor. 27. The method of claim 26, wherein the breast tumor is selected from the group consisting of infiltrating duct carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, ductal carcinoma in situ and lobular carcinoma in situ. 28. A method of determining likelihood of survival for a breast tumor subject, comprising determining loss of heterozygosity (LOH) at chromosomal locus 19pl3 in a breast tumor cell sample from said subject, wherein LOH at chromosomal locus 19pl3 compared with a non-tumor cell in the same subject is associated with a decreased probability of survival. 29. A method of detecting a tumor cell, comprising: a) obtaining a sample containing suspected tumor cells; b) amplifying chromosomal DNA from said sample using primers specific for amplification of the HET gene at chromosome 19pl3; and c) identifying one or more point mutations in the HET gene, wherein one or more point mutations are indicative of the presence of a tumor cell. 30. The method of claim 29 wherein said point mutations are identified by single- stranded conformational polymorphism (SSCP) analysis. 31. The method of claim 29 wherein said point mutations are identified by DNA sequencing. 32. The method of claim 29 wherein the tumor cell is a breast tumor cell. 33. The method of claim 32 wherein said breast tumor cell is selected from the group consisting of infiltrating duct carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, ductal carcinoma in situ and lobular carcinoma in situ. 34. The method of claim 29 wherein said point mutation comprises a substitution of an adenosine residue for the guanosine residue at position 190 of SEQ ID NO:l . 35. The method of claim 29 wherein said point mutation comprises a substitution of a guanosine residue for the adenosine residue at position 264 of SEQ ID NO:l . 36. A method for altering the phenotype of a tumor cell comprising contacting the cell with a nucleic acid encoding (i) a tumor suppressor designated HET and (ii) a promoter active in said tumor cell, wherein said promoter is operably linked to the region encoding said tumor suppressor, under conditions effective for the uptake and expression of said nucleic acid by said tumor cell. 37. A kit comprising: a) an antibody that specifically binds to an HET polypeptide; and b) a container for said antibody.

Inventors: ALLRED CRAIG D, FUQUA SUZANNE A W, LEE ADRIAN V, O'CONNELL PETER, OESTERREICH STEFFI, OSBORNE C KENT, ALLRED, CRAIG, D., FUQUA, SUZANNE, A., W., LEE, ADRIAN, V., O'CONNELL, PETER, OESTERREICH, STEFFI, OSBORNE, C., KENT
Applicants: ALLRED CRAIG D, CONNELL PETER O, FUQUA SUZANNE A W, LEE ADRIAN V, OESTERREICH STEFFI, OSBORNE C KENT, UNIV TEXAS, ALLRED, CRAIG, D., BOARD OF REGENTS, THE UNIVERSITY OF TEXAS SYSTEM, FUQUA, SUZANNE, A., W., LEE, ADRIAN, V., O'CONNELL, PETER, OESTERREICH, STEFFI, OSBORNE, C., KENT
Application year: 1998
Main classification: C12N15
IPC codes: A61K38, A61K48, C07K14, C07K16, C12N15, C12Q1