ASSAY METHODS FOR IDENTIFYING COMPOUNDS WHICH MAY PROTECT STRATIFIED SQUAMOUS EPITHELIUM AGAINST DAMAGE BY NOXIOUS SUBSTANCES

Abstract: Novel assay methods for screening compounds or identifying compounds useful for treating gastroesophageal disease (GERD) are described, which involve determining the level of or presence of an interaction between the test compound and a polypeptide sequence comprising a portion of the extracellular domain of the junctional protein E-cadherin or a related polypeptide sequence.

Description: ASSAY METHODS FOR IDENTIFYING COMPOUNDS WHICH MAY PROTECT STRATIFIED SQUAMOUS EPITHELIUM AGAINST DAMAGE BY NOXIOUS SUBSTANCES STATEMENT OF RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH This invention was made in part during work supported by a grant from the National Institutes of Health (NIH) ROI DK 36013. The government has certain rights in this invention. TECHNICAL FIELD The field of this invention relates to assay methods for the identification of compounds which may protect stratified squamous epithelial tissue against injury by noxious substances. More specifically, the field of the invention includes methods for identifying compounds which may be useful in the treatment of conditions associated with gastric reflux, more particularly, diseases such as gastroesophageal reflux disease (GERD). BACKGROUND ART Gastroesophageal Reflux Disease Gastroesophageal reflux (GER) is the effortless movement of gastric contents from the stomach to the esophagus. It is a physiologic process, occurring in everyone, many times a day throughout life and without symptoms or signs of tissue injury. However, beginning at about 35-40 years old, GER is increasingly associated with the symptom of heartburn and morphologic injury to the esophagus. Indeed, a Gallup poll reported that up to 44% of adult Americans experience heartburn at least monthly and up to 10% have heartburn daily. The proximate cause for the transition from GER to gastroesophageal reflux disease (GERD) is the ability of noxious materials from the stomach to contact the esophagus with sufficient duration to result in damage to the epithelium. Moreover, it is well established that the major injurious substance within the refluxate is gastric acid, though the latter may be aided by the presence of pepsin within the refluxate. The damage resulting from acid exposure can be demonstrated morphologically and/or physiologically by changes in potential difference (PD), electrical resistance (R), or permeability to ions and molecules (Chung, R.S. et al. (1975) Am. J. Physiol. 229(2):496-500; Dodds, W.J. etάl. (1970) Invest Radiol 5:209-219; Harmon, J.W. et al. (1981) Dig Dis Sci 26:65-72; Kidder, J.W. et al. (1983) JLab Clin Med 102:477-486; Kivilaakso, E. et al. (1980) Surgery 87:280- 285; Salo, J. et al. (1982) Surgery 92:61-68). In esophageal epithelium the decline in R, in the absence of extensive tissue necrosis, is a direct reflection of increases in paracellular permeability as evidenced by a correlation between the decline in R with an increase in mannitol flux (Orlando, R.C. et al (1981) J Clin Invest 68:286, Orlando, R.C. et al (1984) Am J Physiol 246:G718-G724). The pathophysiology of acid injury has been most thoroughly explored using the rabbit esophageal epithelium as a model for the human esophageal epithelium. Both human and rabbit esophageal epithelia are Na + -absorbing 'electrically-tight' stratified squamous epithelia. Each junctional complex consists of tight junctions with a few strands and an intercellular glycoprotein matrix. Moreover, rabbit and human esophageal epithelia both respond to high luminal acidity with a time- dependent biphasic change in transepithelial PD. Further, individual squamous cells utilize a basolateral membrane, acid-extruding, NaVFf 1" exchanger (NHE-1 isotype) as a principal mechanism for regulation of intracellular pH (pHi) (Orlando, R.C. et al. In: Castell, D.O. et α/., eds. The Esophagus (3rd Edition). Philadelphia: Lippincott Williams & Wilkins, 1999, 409-419, and Orlando, R.C., et al. In: Orlando, R.C., et al., eάs. Gastroesophageal Reflux Disease. Marcel Decker, in press). Key observations in humans that support a similar pathogenesis for acid reflux-induced injury to human esophageal epithelium as defined in the rabbit model are: 1) luminal perfusion in vivo with high concentrations of HC1 (Bernstein test) produces a similar biphasic pattern in esophageal PD (Orlando, R.C. et al. (2000) Am. J. Med. 108 (4A):104S-108S, and Orlando, R.C. et al. In: Allen, A. et al, eds. Mechanisms of Mucosal Protection in the Upper Gastrointestinal Tract. New York: Raven Press, 1984, 75-79); and, 2) patients with both erosive and nonerosive GERD have the same morphologic hallmark of early acid damage to esophageal epithelium, t ' .e. dilated intercellular spaces. Tobey, N.A. et al. (1996) Gastroenterology 111:1200-1205. Previous work has shown that sodium sulfate has a cytoprotective effect in acid exposed rabbit esophagus (Tobey, N.A. et al. (1986) Am J Physiol 251 (Gastrointest. Liver Physiol. 14):G866-G869). In U.S. Patents Numbers 5,374,537 and 5,189,056 it was alleged that protection of stratified squamous epithelia against damage from noxious luminal substances, e.g. HC1, was afforded by chemical compounds having one of the following reactive groups in their molecule: X-SO 3 " , where X represents oxygen or carbon, and XO 4 ~ or X 2 O 7 ~ , where X represents an element from Group Nib of the periodic table or sulfur. The compounds which were shown to provide protection against injury to stratified squamous epithelia included 4- acetamido-4'-isothiocyano-2,2'-stilbene disulfonate (SITS), 8-anilino-naphthalene-l- sulfonate (AΝS), dinitrodisulfonic acid stilbene (DΝDS), sulfonazo III, 4,4'- diisothiocyano-2,2'-stilbene disulfonate (DIDS), bromophenol blue, ethane disulfonate, 1,3 -benzene disulfonate, sucrose octasulfate (SOS), dextran sulfate, sodium chromate, sodium dichromate, sodium molybdate, sodium tungstate and sodium sulfate. Labeaga et al. disclose dosmalfate as a gastrointestinal and esophageal cytoprotective agent (Labeaga, L. et al. (2000) Drugs of Today 2000, Vol. 36, Suppl. A:59-66). Sulfate ester compounds useful for treating and/or preventing gastroesophageal reflux disease (GERD) are disclosed in pending U.S. Provisional Patent Application titled "Methods For Protection Of Stratified Squamous Epithelium Against Injury By Noxious Substances And Novel Agents For Use Therefor" to Hudson et ah, including disodium 3-(4-isothiocyanatophenyl)-3 phenoxypropane- 1 ,2- disulfate (CDDD-1192) and disodium 3-(4-isothiocyanatophenoxy)-3-(4- isothiocyanatophenyl)propane-l,2-disulfate (CDDD-1193). In vitro methods for identification of potential agents useful for protection of stratified squamous epithelia against damage from noxious substances are disclosed in U.S. Patent Nos. 5,374,537 and 5,189,056, Tobey, N.A. et al (1986) Am J Physiol 251 :G866-G869, and Orlando, R.C. et al (1987) Gastroenterology 93:352-361. There is a continued need for agents for treating gastroesophageal reflux disease (GERD) and other conditions associated with the exposure of stratified squamous epithelial tissue to noxious substances. There is a corresponding need for methods for identification of compounds which may protect stratified squamous epithelial tissue from injury resulting from exposure to noxious substances. E-cadherin E-cadherin belongs to the classical cadherin family of proteins, a subfamily of the cadherin superfamily of proteins. Classical cadherins are characterized as Ca 2+ dependent glycosylated proteins consisting of anN-terminal extracellular domain, a single transmembrane domain and C-terminal cytosolic domain. Plott, R.T. et al. (1994) J Invest Dermatol 103:168-172. Cadherins are known to mediate cell-cell interactions, such as adhesion. E-cadherin in particular is implicated in the defense of cells against invasive mechanisms, such as in neoplasia, as well as playing an important role in embryonic development and tissue morphogenesis. Bussemakers, M.J. et al. (1993) Molec Biol Reports 17:123-128; Swami, S. et al. (1995) Am J Gastroenterology 90:1808-1813; Takeichi, M. (1991) J Cell Biol 75:464-474. The polynucleotide encoding human E-cadherin has been isolated and characterized. Human E-cadherin cDNA has an open reading frame of 882 amino acids (SEQ ID NO:l) and a 3 ' non-coding region of 2035 nucleotides, and has an overall homology with mouse E-cadherin of 78%, and with the chicken E- cadherin related sequence, L-CAM, of 65%. There are few evident evolutionary changes across species, and those that are present are conservative amino acid substitutions. The transmembrane domain of the human and mouse proteins are identical, and the cytoplasmic domain, important for the regulation of the cell-cell binding function of the extracellular domain, is almost identical (with only conservative amino acid substitutions). Bussemakers, M.J. et al. (1993) Molec Biol Reports 17:123-128. Processing of the human E-cadherin precursor results in a mature protein with amino acids numbered from 155 to 882. Analysis of human E-cadherin suggests an extracellular domain of approximately 553 amino acids (amino acid 155 to approximately amino acid 707) with five internally repeated domains of approximately 110 amino acids which are involved in Ca binding. The corresponding nucleotide bases for the extracellular domain are from approximately nucleotide 557 to approximately nucleotide 2215 (nucleotide numbering according to Bussemakers, M.J. et al. (1993) Molec Biol Reports 17:123-128). The five extracellular repeat domains (EC1-EC5) have been reported to correspond to amino acid residues approximately: EC1 - 155-262; EC2 - 263-375; EC3 - 376-486; EC4 - 487-593; EC5 - 594-697, according to the sequence reported in GenBank accession number P12830 (http://www.ncbi.nlm.mh.gov/PubMed/). EC1-EC4 have from 19-29% internal sequence identity, while EC5 is less related to the other four subdomains with only 10-16% sequence identity. Alattia, J.R. et al. (1999) Cell Mol Life Sci 55:359-367. Several structural studies of isolated portions of the extracellular domain of E-cadherin have also been carried out, including X-ray crystallography and NMR studies. Alattia, J.R. et al. (1999) Cell Mol Life Sci 55:359-367 and references cited therein; Overduin, M. (1996) J Biol NMR 7:173-189; Gumbiner, B.M. et al. (1996) Cell 84:345-357. The basic structure of the intra-domain repeats appear to be a fold consisting of a seven stranded β-sheet with the N and C termini of the fragment at opposite ends of the fold. The fold resembles a barrel and contains two small helices. It is thought that the N-terminal tip of the molecule is involved in cell adhesion, with the adhesion specificity residing in the HAN region in domain 1 of E-cadherin. Overduin, M. et al. (1995) Science 267:386-389; Takeichi, M. (March 22, 1991) Science 251:1451-1455; Pertz, O. et al. (1999) EMBOJ 18:1738-1747; Geiger et al. (1992) Ann Rev Cell Biol 8:307-332. E-cadherm can also be characterized by its Ca dependency. In the presence of Ca 2+ , E-cadherin is resistant to cleavage by trypsin, while in the absence of Ca 2+ , the protein can be cleaved by trypsin, resulting in an approximately 80kD fragment, which corresponds to the extracellular domain. These findings are consistent with the presence of Ca 2+ binding regions in the extracellular domain. Plott, R.T. et al. (1994) J Invest Dermatol 103:168-172; Gumbiner, B.M. et al. (1986) J Cell Biol 102:457-468. Cadherins have been identified as the major adhesion receptors of the zonula adherens junctions of epithelia. In addition, the expression and activity of E-cadherin is vital for the tight association of cells and the maintenance of the macromolecular structure of epithelial tissue. In the absence of functional E- cadherin, intercellular adhesion is not maintained, despite the presence of other adhesion and junctional proteins. Gumbiner, B.M. (1996) Cell 84:345-357. Calcium also appears necessary for cell-cell adhesion. Alattia, J.R. et al (1999) Cell Mol Life Sci 55:359-367. Studies of kidney epithelial tissue reveal that antibodies which can bind E- cadherin also inhibit the recovery of R injunctions made permeable by the removal of Ca 2+ from the surrounding solution. The antibody recognizes a 118 kD polypeptide from kidney epithelium that is the same as or related to the cell adhesion molecule Uvomorulin/E-cadherin. Additionally, after the junction has been made permeable in the absence of Ca 2+ , incubation with trypsin leads to poor recovery of R upon the restoration of Ca 2+ . The lack of recovery in these cells compared to cells not treated with trypsin or cells treated with trypsin in the 94- presence of Ca , without concomitant loss of cells, suggests that the lack of recovery is due to the degradation by trypsin of a cell-surface protein. Gumbiner, B.M. et al. (1986) J Cell Biol 102:457-468. The antibody isolated in the experiments described above also recognized the approximately 80kD fragment of E-cadherin resulting from E-cadherin cleaved by trypsin in the presence of Ca 2+ . Desmosomal Subfamily Desmocollin 3, which belongs to the desmosomal subfamily of the cadherin superfamily, is a 896 residue protein, with the extracellular domain having 555 amino acids numbered 136-690, as described in GenBank accession number Q14574 (SEQ ID NO:5). The desmogleins, a subfamily of the desmosomal cadherins, share amino acid homologies in both the cytoplasmic and extracellular domains with the classical cadherins. Desmoglein 1 is a 1049 residue protein, with the extracellular domain having 499 amino acids numbered 50-548, as described in GenBank accession number IJHUG1 (SEQ ID NO:2) (http://www.ncbi.nlm.nih.gov/PubMed/). Desmoglein 2 is a 1117 residue protein, with the extracellular domain having 560 amino acids numbered 49-608, as described in GenBank accession number Q 14126 (SEQ ID NO:3). Desmoglein 3 (also known as pemphigus vulgaris antigen) is a 999 residue protein, with the extracellular domain having 566 amino acids numbered 50-615, as described in GenBank accession number IJHUG3 (SEQ ID NO:4). Desmoglein 3 has been shown to have an overall sequence identity of 33% to human E-cadherin. Plott, R.T. et al (1994) J Invest Dermatol 103:168-172. Additionally, alignment of the human E-cadherin sequence with extracellular subdomains 1-5 of desmoglein 3 result in sequence identities between the two proteins of EC 1, 31%, EC2, 45%, EC3, 33%, EC4, 30% and EC5, 28%. Plott, R.T. et al. (1994) J Invest Dermatol 103:168-172. Other Polypeptides With Substantial Homology to E-cadherin The HA(V/N) region of HA1 chain influenza strain A hemagglutinins show substantial sequence homology with cadherins. Blaschuk et al. (1990) J Mol Biol 211 :679-682. The hemagglutinins examined were split into two groups, with the overall HA(N/N) domain of group 1 hemagglutinins (SEQ H) NOS: 6- 13) having 25% of residues that are identical to the consensus sequence for the cadherin family, and an additional 25% of residues being either partially conserved or homologous according to the Dayhoff matrix. For group 2 hemagglutinins (SEQ ID NOS:14-21) the percent identity and homology are 13% and 30%, respectively. HAN domains of fibroblast growth factor receptors (FGF-R) (SEQ ID ΝOS:22-25) showed sequence identity of 25% with cadherins with an additional 33% being partially conserved or homologous. Byers, S. et al. (1992) Dev Biol 152:411-414. All references cited herein are hereby incorporated by reference in their entirety. DISCLOSURE OF THE INVENTION One method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; and b) determining whether the compound binds to the polypeptide; wherein binding of the compound to the polypeptide indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. Another method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a labeled cytoprotective agent; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a compound; and c) comparing binding of the agent to the polypeptide contacted with the compound to a control conducted where the polypeptide is contacted with the agent and is not contacted with the compound; wherein a decrease in binding of the agent to the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia against damage by a noxious substance. Another method of the present invention comprises identifying a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a monoclonal antibody to the polypeptide; and c) comparing the amount of antibody binding to the polypeptide contacted with the compound to the amount of antibody binding to a control; wherein a decrease in the amount of antibody binding to the polypeptide which has been contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. Another method for use in the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted with in the extracellular domain of SEQ ID NO:l; b) determining the stability of the polypeptide; and c) comparing the stability of the polypeptide contacted with the compound to the stability of a control; wherein a greater stability for the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. Another method for use in the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; and c) determining the stability of the polypeptide; and d) comparing the stability of the polypeptide contacted with the compound and the noxious substance to the stability of a control; wherein if the stability of the polypeptide contacted with the compound and noxious substance is greater than that of the control, the compound may protect stratified squamous epithelium against damage by the noxious substance. An additional method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; c) determining the amount of fragmentation of the polypeptide; and d) comparing the amount of fragmentation of the polypeptide to a control; wherein a decrease in the amount of fragmentation of the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. MODES FOR CARRYING OUT THE INVENTION Definitions As used herein, the term "compound" means a biological or chemical compound such as a simple or complex organic or inorganic molecule, a peptide, a protein or an oligonucleotide. A vast array of compounds can be synthesized, for example oligomers, such as oligopeptides and oligonucleotides, and synthetic organic compounds based on various core structures, and these are also included in the term "compound". In addition, various natural sources can provide compounds for screening, such as plant or animal extracts, and the like. Compounds can be tested singly or in combination with one another. "Compounds" may also be referred to as "drugs" or "pharmaceutical compounds" or "pharmaceutical candidates". A "noxious substance", as used herein, refers to a substance which causes injury to stratified squamous epithelium in vivo or in vitro. Examples of such "noxious substances" include acids or other substances, including, but not limited to, gastric acid, HCl, N-acetylcysteine, pepsin, acid-pepsin, gastrointestinal fluid, or other irritant which contacts epithelial tissue. The term "noxious substance" may also be used to refer to a combination of noxious substances, such as two or more noxious substances. An "individual" is a vertebrate, preferably a mammal, more preferably a human. Mammals include, but are not limited to, farm animals, sport animals, primates, rodents and pets, including pigs, sheep, horses, cows, rabbits, mice and rats. A "susceptible individual" is an individual who suffers from or is likely to or predisposed to suffer from a condition(s) which causes contact or exposure between their epithelial tissues and noxious substances. In humans these conditions may include, for example, gastroesophageal reflux disease (GERD), heartburn, indigestion, laryngitis, Barrett's Esophagus, or pharyngitis. In animals these conditions may include, for example, peptic ulcers, gastritis, erosions, perforation and hemorrhage. The terms "injury" or "damage" as used herein are interchangeable and refer to the cellular and morphological manifestations and symptoms resulting from exposure to or contact with a noxious substance. Indications of injury or damage include, but are not limited to, acid-induced decline in PD, acidification of the intracellular or intercellular space, prominently dilated intercellular spaces, increased permeability of intercellular junctions to noxious substances; macroscopic erosions and ulceration of epithelial tissue, cell edema, inflammation and necrosis, peptic stricture, Barrett's Esophagus, heartburn, laryngitis, pharyngitis, hoarseness and sore throat. The terms "stratified squamous epithelium", "stratified epithelium", "epithelia" and "epithelium" are interchangeable as used herein. Sources of stratified squamous epithelium include, for example, buccal, oropharyngeal, esophageal and laryngeal epithelium, rumen and forestomach. The polypeptide known as "E-cadherin" is also known as "CAM 120/80", "L-CAM", "Arc-1" and "Uvomorulin". Unless otherwise noted, these terms may be used interchangeably herein. A preferred form of E-cadherin is the human sequence. The term "cadherin" refers to a protein which is a member of the cadherin superfamily of proteins. The cadherin superfamily includes, for example, the subfamily of classical cadherins, specific examples of which include E-cadherin, N-cadherin, and P-cadherin, and the subfamily of desmosomal proteins, specific examples of which include desmogleins 1, 2 and 3, and desmocollin 3. Natural sources of cadherins may be found in vertebrates, including humans, farm animals, sport animals, primates, rodents and pets, for example, chickens, pigs, sheep, horses, cows, rabbits, mice and rats. The term "extracellular domain" refers to the region of a protein that is not embedded in the membrane and exists outside the cellular membrane. The term "extracellular portion" refers to an isolated polypeptide comprising at least 5 amino acid residues of an extracellular domain of a protein. For example, the term "extracellular portion" may encompass smaller domains or subdomains, such as the 5 repeat regions of approximately 110 residues within the extracellular domain of E-cadherin. The isolated polypeptide may be purified from a natural source or maybe obtained by synthetic methods known in the art. A "cytoprotective agent" is an agent which protects stratified squamous epithelia from damage by a noxious substance. Classes of compounds which include examples of such agents include sulfonates, sulfate esters and inorganic tetrahedral-shaped divalent oxyanions. Specific examples include SITS, SOS, CDDD-1192 and CDDD-1193. The term "protection" as used herein refers to the reduction of damage by a noxious substance to epithelium which has been contacted with an agent in vivo or in vitro. The protection provided by the agent may last for at least 10 minutes, at least 20 minutes, at least 30 minutes; at least 1 hour, at least 2 hours, at least 4 hours, at least 8 hours, at least 12 hours, at least 24 hours after contact with the compound. The term "irreversible protection" refers to protection afforded by compounds, which, when contacted with the epithelium, are resistant to being washed off the epithelium. Irreversible protection may be indicated by compounds, which for example, when contacted with the epithelium in vitro, continue to prevent or reduce acid-induced decline in R after at least one washing with a buffer such as normal Ringer solution. The term "control" refers to an experiment conducted under the same conditions as the experiment to which it is being compared and is designed to measure the same experimental parameter. "Controls" may be used to establish typical values for the experimental parameter being measured under particular conditions. A "control" is not required to be run in parallel with the experiment in question and may be run within hours, days, weeks or months of the experiment in question. An "antibody" (interchangeably used in plural form) is an immunoglobulin molecule capable of specific binding to a target, such as a polypeptide, through at least one antigen recognition site which is located in the variable region of the immunoglobulin molecule. An antibody can be from any source of animal capable of producing them, for example, mouse, rat, rabbit, primate, or human antibodies. As used herein, the term encompasses not only intact antibodies, but also fragments thereof (such as Fab, Fab', F(ab') 2 , Fv, single chain (ScFv)), mutants thereof, fusion proteins, chimeric antibodies, humanized antibodies, and any other modified configuration of the immunoglobulin molecule that comprises an antigen recognition site of the required specificity. The term "antibody" includes polyclonal antibodies and monoclonal antibodies. The terms "polypeptide", "oligopeptide", "peptide" and "protein" are used interchangeably herein to refer to polymers of amino acids of any length. The polymer may be linear or branched, it may comprise modified amino acids, and it may be assembled into a complex of more than one polypeptide chain. The terms also encompass an amino acid polymer that has been modified naturally or by intervention; for example, by disulfide bond formation, glycosylation, lipidation, acetylation, phosphorylation, or any other manipulation or modification, such as conjugation with a labeling component. Also included within the definition are, for example, polypeptides containing one or more analogs of an amino acid (including, for example, unnatural amino acids, etc.), as well as other modifications known in the art. In the context of polypeptides, a "linear sequence" or a "sequence" is an order of amino acids in a polypeptide in an N-terminal to C-terminal direction in which residues that neighbor each other in the sequence are contiguous in the primary structure of the polypeptide. A "partial sequence" is a linear sequence of part of a polypeptide which is known to comprise additional residues in one or both directions. An "isolated" or "purified" polynucleotide, polypeptide, antibody or cell is one that is substantially free of the materials with which it is associated in nature. By substantially free is meant at least 50%, preferably at least 70%, more preferably at least 80%, and even more preferably at least 90%, at least 95%, at least 99% free of the materials with which it is associated in nature. As used herein, an "isolated" polynucleotide or polypeptide also refers to recombinant polynucleotides or polypeptides, which, by virtue of origin or manipulation: (1) are not associated with all or a portion of a polynucleotide or polypeptide with which it is associated in nature, (2) are linked to a polynucleotide or polypeptide other than that to which it is linked in nature, or (3) does not occur in nature, or (4) in the case of polypeptides arising from expression of recombinant polynucleotides. Thus, for example, an isolated substance may be prepared by using a purification technique to enrich it from a source mixture. Enrichment can be measured on an absolute basis, such as weight per volume of solution, or it can be measured in relation to a second, potentially interfering substance present in the source mixture. Increasing enrichments of the embodiments of the compositions used in the methods of this invention are increasingly more preferred. Thus, for example, a 2-fold enrichment is preferred, 10-fold enrichment is more preferred, 100-fold enrichment is more preferred, 1000-fold enrichment is even more preferred. A substance can also be provided in an isolated state by a process of artificial assembly, such as by chemical synthesis or recombinant expression. A substance is said to be "selective" or "specific" if it reacts or associates more frequently, more rapidly, with greater duration and/or with greater affinity with a particular cell or substance than it does with alternative cells or substances. An antibody "specifically binds" to a target if it binds with greater affinity, avidity, more readily, and/or with greater duration than it binds to other substances. As used herein, "naturally occurring," "native," or "wild type" refers to endogenous E-cadherin polynucleotides and the E-cadherin protein(s) expressed thereby, including alleles and allelic forms of the protein(s). These terms include full-length and processed polynucleotides and polypeptides. Processing can occur in one or more steps, and these terms encompass all stages of processing. For instance, polypeptides having or lacking a signal sequence may be used. "Non-naturally occurring", "non-native", or "non-wild type" refer to all other E-cadherin polynucleotides and polypeptides. The term "stability" refers to the measure of the ability of a protein or fragment thereof to maintain its native conformation and/or activity. Stability may be measured by techniques well known in the art. A polypeptide or polypeptide region having a certain percentage (for example, 10%, 13%, 20%, 50%, 70%, 75%, 80%, 85%, 90%, or 95%) of "sequence identity" to another sequence means that, when aligned, that percentage of amino acids are the same in comparing the two sequences. This alignment and percent identity may be determined using software programs known in the art, for examples those described in Short Protocols in Molecular Biology (John Wiley and Sons., eds., 1999). Sequence identity is generally determined after sequences have been aligned to maximize the number of matches between the sequences. A variety of alignment programs and algorithms are known in the art. One suitable program for polypeptide sequences is blastn which uses a heuristic search algorithm (BLAST) that is also useful for sequence alignments. See, for example, Altschul, S.F. etal. (1990) J Mol Biol 215:403-410. BLAST programs may be accessed through the National Center for Biotechnology Information (NCBI) internet site (www.ncbi.nlm.nih.gov/BLAST/). The default parameters of the NCBI blastn programs are suitable for generating sequence alignments for the sequences described herein. Other suitable alignment programs are commercially available. The GAP program from Genetics Computer Group, Inc. (GCG; Madison, WI), for example, uses the algorithm of Needleman and Wunsch (1970, JMol Biol 48:443- 453) to generate the alignment of two complete sequences that maximizes the number of matches and minimizes the number of gaps. For another example, the BESTFIT program from GCG uses the local homology algorithm of Smith and Waterman (1981, Advances in Applied Mathematics 2:482-489) to generate the optimal alignment of the best segment similarity between two sequences through the insertion of gaps to maximize the number of matches. When identifying the best alignment, the default gap penalty is 50 and the default gap extension penalty is 3 for the GAP and BESTFIT programs. Chemical terms, unless otherwise defined, are used as known in the art. "A", "an" and "the" include plural references unless the context clearly dictates otherwise. General Techniques Techniques for isolation and manipulation of cadherin proteins may be found in, for example, Gumbiner, B.M. (1996) J Cell 5rø :102:457-468, Gumbiner, B.M. (1996) Cell 84:345-357, Takeichi, M. (1911) J Cell Biol 75:464-474, and Takeichi, M. (1988) Development 102:639-655. Techniques and protocols for manipulating epithelial tissue and using Ussing chambers may be found in the art and in particular in: U.S. Patent No. 5,374,537; U.S. Patent No. 5,189,056; Abdulnour-Nakhoul, S. et al (2000) Am J Physiol 278:G113-G120, Carney,C.N. et al (1981) Lab Invest 45:198-208, Orlando, R.C. et al (1981) J Clin Invest 68:286, Orlando, R.C. et al (1984) Am J Physiol 246:G718-G724, Khalbuss, W.E. et al (1995) 108:662-672, Tobey, N.A. et al (2000) J Invest Med 108(4A):144A, Tobey, N.A. et al (1999) Gastroenterology 116:A334, Orlando, R.C. et al. (2000) Am JMed 108(4A):104S-108S, Tobey, N.A. et al. (1989) Gastroenterology 96:1466-1477, Orlando, R.C. et al (1984) New York: Raven Press:15-19, Orlando, R.C. et al (1982) Gastroenterology 83:1026-1032, and Tobey, N.A. etal (1996) Gastroenterology 83:1026-1032. πMethods of Assaying for Compounds Which May Protect Stratified Squamous Epithelia As described in the following examples, we have identified the mechanism by which cytoprotective agents, such as SITS or SOS, protect epithelial tissue from exposure to noxious substances. Without being bound by any particular theory, it appears that this mechanism comprises the binding of the agent to the extracellular domain, portion, or a region or fragment thereof, of E-cadherin, a junctional protein found in the zonula adherens of epithelial tissue. Based upon this discovery, novel assay techniques have been designed to screen for compounds which will bind to a polypeptide selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of E- cadherin (SEQ ID NO:l), where binding is indicative of a compound which may protect stratified squamous epithelial from damage or injury by noxious substances, such as damage stemming from acid reflux. Accordingly, one method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; and b) determining whether the compound binds to the polypeptide; wherein binding of the compound to the polypeptide indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. An additional embodiment further comprises the step of: c) comparing the binding of the compound to the polypeptide with the binding of a cytoprotective agent to the polypeptide; wherein a greater than or equal level of binding by the compound indicates that the compound may protect stratified squamous epithelia from damage by the noxious substance. Another method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a labeled cytoprotective agent; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a compound; and c) comparing binding of the agent to the polypeptide contacted with the compound to a control conducted where the polypeptide is contacted with the agent and is not contacted with the compound; wherein a decrease in binding of the agent to the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia against damage by a noxious substance. The determination of protein to substrate binding, in this context, binding to either compound or cytoprotective agent, is well known in the art, and need not be discussed in detail herein. Exemplary techniques for determining binding include, for example, labeling the substrate (i.e. the compound or agent binding to the protein) with, for example, a radioactive isotope or fluorescent label. Examples of fluorescent labels include, but are not limited to, biotin, fluoroscein, Texas red, Lucifer yellow, and rhodamine. Other labeling methods include electron dense tracers, such as, alkaline phosphatase, horseradish peroxidase and glucose oxidase. Another method of the present invention comprises identifying a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a monoclonal antibody to the polypeptide; and c) comparing the amount of antibody binding to the polypeptide contacted with the compound to the amount of antibody binding to a control; wherein a decrease in the amount of antibody binding to the polypeptide which has been contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. In one embodiment of the above method, the control may comprise contacting the polypeptide with the monoclonal antibody or may comprise contacting the polypeptide with a cytoprotective agent and then contacting the polypeptide with the monoclonal antibody. Another method for use in the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted with in the extracellular domain of SEQ ID NO:l; b) determining the stability of the polypeptide; and c) comparing the stability of the polypeptide contacted with the compound to the stability of a control; wherein a greater stability for the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. In one embodiment, controls for the method described above includes where the control comprising the polypeptide is not contacted with the compound or where the polypeptide is contacted with a cytoprotective agent and is not contacted with the compound. Another method for use in the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; and c) determining the stability of the polypeptide; and d) comparing the stability of the polypeptide contacted with the compound and the noxious substance to the stability of a control; wherein if the stability of the polypeptide contacted with the compound and noxious substance is greater than that of the control, the compound may protect stratified squamous epithelium against damage by the noxious substance. Controls for the above method may include, in certain embodiments, where a control comprising the polypeptide is not contacted with the compound but is contacted with the noxious substance or where the polypeptide is contacted with a cytoprotective agent and then contacted with the noxious substance. While not wishing to be bound by any particular theory, it appears, from the data presented in the Examples, that the mechanism by which cytoprotective agents function is to maintain the stability of the junctional protein E-cadherin in the presence of noxious substances. While the overall stability of the protein is not enhanced by the binding of cytoprotective agents over that of the native protein, under, for example, denaturing conditions or in the presence of a noxious substance, native-like characteristics should be maintained, such as exemplified by conformation or biological activity (e.g. the maintenance of junctional impermeability). The stability of the extracellular portion may be measured by techniques well known in the art, and need not be discussed herein. Examples of such techniques include, but are not limited to, calorimetric measurement, such as the determination of the temperature of denaturation, for example, digital scanning calorimetry, resistance to denaturation, as measured by, for example, titration against temperature, pH or chemical denaturants such as guanidine hydrochloride or urea. Stability may be measured under varying conditions of hypertonicity, hypotonicity, and concentrations of N-acetylcysteine, EMPIGEN® detergent (Calbiochem, San Diego, CA),bile acids and bile salts. Titrations may be monitored by a number of means, including HPLC (high performance liquid chromatography), FPLC (fast performance liquid chromatography), and spectroscopic or optical means, such as fluorescence. Additional examples of measures of stability include resistance to fragmentation by, for example, acid cleavage or enzymatic digestion, including but not limited to enzymes such as pepsin, trypsin, chymotrypsin and concentrated acids such as hydrochloric acid, sulfuric acid, phosphoric acid, gastric acid and others. Fragmentation upon exposure to noxious substances occurring within the digestive system or testing analogues thereof, is also contemplated. Examples of such substances include acid, acid-pepsin and N-acetylcysteine. Examples of determining the degree of fragmentation are discussed below. Persons of skill in the art will recognize that numerous biophysical techniques are available to measure the stability of proteins, or portions thereof, with or without substrate (i.e. compound or agent) bound to the protein or protein fragment. An additional method of the present invention comprises assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; c) determining the amount of fragmentation of the polypeptide; and d) comparing the amount of fragmentation of the polypeptide to a control; wherein a decrease in the amount of fragmentation of the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. In certain embodiments, controls for the above-described method may include where the polypeptide is not contacted with the compound but is contacted with the noxious substance or where the polypeptide is contacted with a cytoprotective agent and then contacted with the noxious substance. In the present embodiment, fragmentation is the result of exposure to a noxious substance, such as acid, N-acetylcysteine or acid-pepsin. The degree of fragmentation is indicative of the amount of protection afforded by the compound being assayed, where a decrease in fragmentation compared to a control indicates protection. Determination of the degree or amount of fragmentation may be accomplished using techniques known in the art, exemplary techniques including electrophoresis, including SDS gel electrophoresis and capillary electrophoresis, isoelectric focusing, HPLC, FPLC, mass spectrometry, 2D-gels, amino acid analysis, and amino acid sequencing. In general, for any of the methods of the present invention, controls are run such that they comprise the same polypeptide under the same experimental conditions, except that controls are not contacted with the compound which is being tested or are instead contacted with a cytoprotective agent, as specified. Controls need not be run in parallel to the experiment in question, and may consist of prior experimentation done days, weeks or months prior to the experiment in question, that establishes typical values for a set of experimental conditions. Examples of particular cytoprotective agents for use in control experiments may be found, for example in U.S. Patent Nos. 5,374,537 and 5,189,056, and in pending U.S. Provisional Patent Application titled "Methods For Protection Of Stratified Squamous Epithelium Against Injury By Noxious Substances And Novel Agents For Use Therefor" to Hudson et al. Preferred classes of compounds for use as cytoprotective agents include sulfate esters and sulfonates. Examples of preferred cytoprotective agents includes SITS, SOS and CDDD-1193 and CDDD- 1192. Experimental conditions may include, for example, pH, temperature, duration of contact with a noxious substance, concentration of noxious substance, concentration of polypeptide, number and duration of washes, composition of wash solutions and the like. Preferred experimental conditions include, for example, pH from about 1-14, temperature from about 0-100°C, duration of contact with noxious substances from about 1 minute to 24 hours, duration of washes from about 1 minute to 24 hours; number of washes from about 1 to 20, concentration of noxious substances from about 1 μmolar to 1 molar, concentration of polypeptide from about 1 picomolar to 10 millimolar. More preferred experimental conditions may include, for example, pH from about 1-4, pH from about 1-2.5, pH about 1.6, temperature from about 25-37°C, temperature of about 37°C, duration of contact with noxious substances from about 1 minute to 1 hour, duration of contact with noxious substances from about 1 to 30 minutes, duration of washes from about 1 to 5 minutes, number of washes from about 1 to 5, number of washes from about 3 to 4, concentration of HCl from about 10 millimolar to 100 millimolar, concentration of pepsin from about 0.1 to 10 mg/ml, concentration of bile salts from about 500 μM to 1 mM, concentration of polypeptide from about 1 nanomolar to 10 micromolar, and concentration of polypeptide from about 1 micromolar to 10 millimolar. In vitro experiments may be run in physiologic buffers or serum. Wash solutions may be any aqueous vehicle. Preferred examples include water, saline, Ringer, HEPES buffer, Tris- buffer, saliva, or salivary ion composition solutions. The compound or agent may be contacted with the polypeptide, for example, for at least 30 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 60 minutes, or at least 90 minutes. Preferred compounds to be assayed include, but are not limited to, compounds selected from the group including sulfonates and sulfate esters. As discussed in detail in the Examples, we have identified the extracellular domain of the zonula adherens junctional protein E-cadherin as the region where cytoprotective agents bind. In addition, monoclonal antibodies to desmoglein 1 and 2, and desmocollin 3, members of the cadherin superfamily of proteins, appear to bind to the extracellular domain of E-cadherin. While not wishing to be bound by a particular theory, this monoclonal antibody cross-reactivity is likely a result of the degree of homology or identity of the extracellular domains of these cadherin proteins, and suggests that compounds which bind the extracellular domain of E-cadherin will also bind the extracellular domains of similar proteins. Members of the cadherin superfamily of proteins, and extracellular portions thereof, may be used as polypeptides in the novel assays techniques described herein. Preferred sequences include extracellular portions of proteins of the classical cadherin and desmosomal subfamilies. More preferred are extracellular portions from the proteins E-cadherin (SEQ ID NO:l), desmoglein 1 (SEQ ID NO:2), 2 (SEQ ID NO:3), or 3 (SEQ ID NO:4), and desmocollin 3 (SEQ ID NO:5). Even more preferred are extracellular portions from E-cadherin. Particularly preferred are extracellular portions from E-cadherin residues 155-262, desmoglein 1 residues 52-157, desmoglein 2 residues 49-159, desmoglein 3 residues 52-157, and desmocollin 3 residues 136-243. Additional peptides with sequence similarity to extracellular portions of E- cadherin may also be used as polypeptides for testing possible drug candidates or compounds and may be used in any of the methods of the invention described herein. Examples of such peptides include the HA(V/N) region of the HAl chain of influenza A hemagluttinin, examples of which are shown in SEQ ID NOS: 6- 21 and HAV region sequences from fibroblast growth factor receptor, examples of which are shown in SEQ ID NOS:22-25 (Table 1). Preferably, the peptide for use in the assay methods described herein will have at least 13%, at least 19%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70% sequence identity with an extracellular portion of E-cadherin as depicted in SEQ ID ΝO:l. In certain embodiments, the polypeptide may comprise the sequence, or fragment thereof, of the sequences described above, wherein the fragment of the sequence is at least 5, at least 6, at least 10, at least 25, at least 50, at least 100, at least 110, at least 120; at least 150, at least 200, at least 220, or at least 300 amino acids in length. In a preferred embodiment, the human sequence of the protein will be used. In another embodiment, other variants may be used in the methods of the invention described herein, including those from farm animals, pet, rodents, primates and sport animals, such as chicken, rabbit, rat, mouse, horse, cow, sheep, and pig sequences. Embodiments of any of the assay methods described above may further comprise the following steps, in order: contacting a sample comprising stratified squamous epithelial tissue with the compound; contacting the sample with a noxious substance; and determining if the epithelia is damaged. These steps further the level of screening of the compound and therefore increase the likelihood of identification of an effective drug candidate. Techniques for performing the above-listed steps may be found in the art, particularly in: Tobey, N.A. et al (1986) Am J Physiol 25LG866-G869, Orlando, R.C. et al (1987) Gastroenterology 93:352-361, U.S. Patent No. 5,374,537, and U.S. Patent No. 5,189,056. In particular embodiments, stratified squamous epithelial tissue may be obtained from esophageal, oral cavity, cheek, pharynx, larynx, or vocal cord tissue from an individual. A preferred embodiment is where the epithelia is obtained from rabbit esophageal tissue. Certain additional embodiments include tissue from rats, pigs, horses, or sheep and may also be selected from the forestomach or rumen of such animals. Additional embodiments include human epithelial tissue which may be obtained, for example from autopsy, surgical or biopsy specimens. In vivo, epithelial tissue is exposed to gastrointestinal fluid, which comprises, in part, acid, acid-pepsin and other constituents, such as rennin, lipase, bile salts and acids, pancreatic enzymes such as trypsin, elastase, chymotrypsin and amylase, and hydrochloric acid (HCl). In vitro experiments performed on stratified squamous epithelial tissue in Ussing chambers, as discussed previously, for example in U.S. Patent Nos. 5,374,537 and 5,189, 056; Tobey, N.A. et al (1986) Am J Physiol 251 :G866-G869; and Orlando, R.C. et al (1987) Gastroenterology 93 :352-361 primarily use acid, acid-pepsin or N-acetylcysteine, a disulfide bond breaking molecule, to mimic the conditions existing in vivo. Further embodiments of the above-described methods therefore include methods wherein the noxious substance may be N-acetylcysteine, acid, acid- pepsin or gastrointestinal fluid. In particular embodiments the noxious substance is gastric acid, such as HCl or HCl-pepsin. In other embodiments the noxious substance may comprise other acids such as phosphoric or sulfuric acid. Additional noxious substances include bile salts, bile acids, with and without HCl, nitric acid, acetic acid and other organic acids. Particular embodiments of the invention may also include where the polypeptide is immobilized on a solid support. A variety of appropriate solid supports are known to persons of skill in the art. Exemplary supports may include beads, such as resin beads, slides, glass and plastic wells, test tubes, and plates. The attachment of the polypeptide to a solid support may facilitate performing the steps of the methods of the present invention, including, for example, contacting the polypeptide with a compound or noxious substance. Attachment to a solid support will also facilitate washing the polypeptide between steps. To a person of skill in the art, it will be apparent that any of the above described methods may comprise washing steps between, for example, the contact of the polypeptide with the compound and contact with a noxious substance. Further, washing after contacting the polypeptide with the noxious substance may also be performed before determining, for example, the degree of fragmentation or binding or stability of the polypeptide. The present invention also encompasses embodiments comprising at least one or multiple washing steps between at least one or more of the steps of the assay methods. The following examples are meant by way of further description of the invention and are not intended to limit the invention described herein in any way. EXAMPLES EXAMPLE 1: Identification of the Protein Governing Paracellular Permeability in Rabbit Esophageal Epithelium Sections of rabbit esophageal epithelium, mounted in Ussing chambers and stabilized for 45 min, were exposed both luminally and serosally to calcium- free solution containing EDTA, 3 mM. In the presence of a calcium-free solution there was a progressive decline in R, the decline shown for representative single tissues reaching 40% below the initial R at 1 hr, 60% at 2 hrs and 80% at 4 hrs. This contrasted with a control tissue in normal calcium-containing Ringer solution which showed a small increase in R of 10% over initial R at 1 hr, 12% at 2 hrs, and 12% at 4 hrs. The decline in R was the result of the calcium-free state and was not an effect of EDTA treatment since 3 mM EDTA alone had no effect on R over the described time frame. When calcium-containing (normal Ringer) solution was restored to the bathing solutions after 1 , 2, or 4 hrs of calcium-free exposure, there was a progressive return of R toward initial baseline values, with complete reversibility observed for tissue exposed to calcium-free solution for 1 hr and 2 hr exposures and an 80% recovery in R for tissue exposed to calcium-free for 4 hrs within 1 hr of restoring calcium to the baths. These results established that the protein(s) regulating paracellular permeability in the rabbit esophageal epithelium is calcium-dependent. One protein known to be calcium-sensitive and to act as a bridge to seal off the intercellular space is the zonula adherens junctional protein, Uvomorulin, also known as E-cadherin (and also known as L-CAM, CAM 120/80, Arc-1). Gumbiner, B.M et al (1986) J Cell Biol 102:457-468. E-cadherin is known to be insensitive to degradation by trypsin in the presence of calcium but sensitive to degradation in the absence of calcium (Takeichi, M. (1911) J Cell Biol 75:464-474). The junctional adhesive protein in esophageal epithelium was shown to be trypsin-sensitive in the absence, but not in the presence, of calcium, which further supports the conclusion that this adhesive protein is E-cadherin. Sections of rabbit esophageal epithelium were mounted in Ussing chambers and exposed luminally to trypsin, 0.01%, in the presence or absence of a calcium-free bathing solution. There was no significant change in R for tissues exposed to trypsin in the calcium-containing normal Ringer solution over a 2 hr period compared to tissues in calcium-containing normal Ringer not exposed to trypsin (R of 117+8% vs 107+8%, respectively, n=4, p>0.05). However, tissues exposed to calcium-free solution 3 mM EDTA both luminally and serosally with or without trypsin showed the expected decline in R over time, as evidenced by declines to 62+7% and 74+5%, respectively. Upon restoration of calcium to the baths, junctional resealing as evidenced by recovery in R, was shown to be inhibited at 1 hr in tissues exposed to trypsin compared to those unexposed to trypsin (62+8% vs 82+6%, respectively, n=4, p<0.05). This lack of recovery in R in tissues exposed to calcium-free solution suggests that trypsin degraded the junction adhesive protein, while the lack of trypsin's effect on R in calcium-containing solution suggests that the junctional protein is resistant to trypsin under these conditions. Further, similar to the glycoprotein E-cadherin, whose sugar side chains are known to play little or no role in its ability to provide cell-to-cell adhesion (Takeichi, M. (1988) Development 102:639-655), the junctional protein that regulates paracellular permeability in esophageal epithelium was shown to be relatively insensitive to glycosidases. This was evident by the fact that luminal treatment of esophageal epithelium in Ussing Chambers with glycosidases had little (< 20% decrease) or no (decrease approximately 0%) effect on junctional permeability as reflected by change in R. E-cadherin contains cysteine residues with disulfide bridges in its extracellular domain (Takeichi, M. (1988) Development 102:639-655). The junctional protein regulating paracellular permeability in esophageal epithelium is also highly sensitive to disulfide-bond breaking compounds such as N-acetylcysteine. U.S. Pat. No. 5,374,537; 5,189,056. Further, like E-cadherin, which is known to be heat labile, the junctional protein regulating paracellular permeability in esophageal epithelium is heat-sensitive, i.e. heating the luminal bath resulted in a temperature-sensitive decline in R (Tobey, N.A. et al (1999) Am J Physiol 276:G1322-G1330). EXAMPLE 2: Junctional Resealing In Esophageal Epithelium is Inhibited by Exposure to Mab to the Extracellular Domain Of E-Cadherin Sections of rabbit esophageal epithelium prepared as in Example 1 were exposed luminally and serosally to a calcium-free solution containing 3 mM EDTA to open the junctions as shown by the progressive decline in R to 60±4% and 65±4% of initial R for experimental and control tissues, respectively, by 2 hrs (n = 8 for each group, p > 0.05). Tissues were then treated luminally for 20 min with either 10 μg/ml of a monoclonal antibody (Mab) to Uvomorulin/E-cadherin (Sigma Chemical, St. Louis, MO) or, as control, to 10 μg/ml of nonspecific immune serum globulin (IgG). Following exposure to Mab or IgG, a calcium-containing (normal Ringer) solution was restored to the bathing solutions and the recovery of R monitored over time. Tissues treated with the Mab to Uvomorulin/E-cadherin showed significant inhibition in recovery of R toward baseline compared to that of tissues treated with IgG; recovery being 70±5% for Mab vs 86±6% for IgG by 1 hr after calcium restoration and 73±4% for Mab vs 88±4% for IgG by 2 hrs (p< 0.05 for each comparison). This indicated that the resealing of the junctions in stratified squamous epithelium is dependent upon the adhesive function of Uvomorulin E-cadherin. The intercellular junctions of stratified squamous epithelium can also be opened by exposure to hypertonic saline. Junctional opening was indicated by a drop in R. Treatment with the same Mab to Uvomorulin/E-cadherin as above also blocked the resealing of the junctions, i.e. return of Rto baseline, upon reestablishing the isoosmolality of the bathing solution. An antibody to the intracellular domain of a cadherin (N-cadherin) was also similarly tested and found to have no ability to block junctional resealing, i.e. tissues exposed to Mab to the intracellular domain of N-cadherin recovered to 104%+5%, using IgG recovery as 100% as control (n=3, p>0.05). This supports the specificity for inhibition of junctional resealing by Mab to the extracellular domain of Uvomorulin E-cadherin. EXAMPLE 3: Junctional Resealing in Esophageal Epithelium is not Inhibited by Mabs to Occludin or Claudin-1 Sections of rabbit esophageal epithelium prepared as in Example 1 were exposed luminally and serosally to a calcium-free solution containing 3 mM EDTA to open the junctions as shown by the progressive decline in R over 2 hrs to approximately 40% of initial R. Tissues were then treated luminally for 20 min with either 10 μg/ml of a monoclonal antibody (Mab) to Occludin or a polyclonal antibody to Claudin-1 (both from Zymed, San Francisco, CA), or to nonspecific immune serum globulin (IgG), as control. Following the restoration of calcium-containing (normal Ringer) solution to the bathing solutions, the recovery of R toward baseline was monitored. Unlike the prior inhibition noted with Mab to Uvomorulin/E-cadherin, R had increased similarly by 2 hrs after calcium replacement for tissues exposed to antibodies to occludin or claudin-1 compared with the IgG controls. For example, at 2 hrs post-calcium restoration, using IgG recovery as 100% as control, tissues exposed to Mab for occludin recovered to 96%+6%, and to polyclonal antibodies to claudin-1 recovered to 108%+8% (n=3 per group, p> 0.05 compared to control IgG for each group). This demonstrated that junctional resealing in esophageal epithelium was independent of the adhesive function of occludin or claudin-1, junctional proteins which are not members of the cadherin superfamily of proteins. EXAMPLE 4: Junctional Resealing in Esophageal Epithelium Inhibited by Mab to Desmogleins 1 and 2 and Desmocollin 3 Sections of rabbit esophageal epithelium prepared as in Example 1 were exposed luminally and serosally to calcium-free solution containing 3 mM EDTA to open the junctions as shown by the progressive decline in R over 2 hrs to approximately 40% of initial R. Tissues were then treated luminally for 20 min with either 10 μg/ml of a Mab to desmoglein 1 and 2 (Research Diagnostics, Flanders, NJ), desmocollin 3 (Research Diagnostics, Flanders, NJ), Uvomorulin/E-cadherin (Sigma Chemical, St. Louis, MO), or nonspecific immune serum globulin (IgG) as control. Following restoration of calcium-containing (normal Ringer) solution, the Mab for desmoglein, desmocollin and Uvomorulin/E-cadherin were observed to significantly inhibit return of R toward initial values compared to controls exposed to IgG. For example, when expressed as a percent recovery in relation to IgG (IgG recovery normalized to 100%) at 2 hrs, Uvomorulin Mab was 83+6%, desmocollin Mab was 83+0.5% and desmoglein 1 and 2 Mab was 90+8% (n=4-6/group, p<0.05 for each group compared to the IgG control). This indicated that junctional resealing in esophageal epithelium can also be inhibited by Mab to desmoglein 1 and 2, and desmocollin 3, which are members of the cadherin superfamily of proteins with known sequence homology to Uvomorulin E-cadherin. The ability of desmosomal antibodies for desmoglein 1 and 2 or desmocollin 3 to block resealing similar to that of Mab to Uvomorulin/E-cadherin is likely due to homology between the proteins desmoglein 1 and 2, desmocollin 3 and Uvomorulin/E-cadherin. Desmosomes are structures that provide tensile strength to the epithelium but do not regulate permeability through the paracellular pathway, and thus the mechanism of action is not by Mab binding to desmogleins 1 or 2, or desmocollin 3. (Gumbiner, B.M. (1996) Cell 84:345-357, Swami, S. et al (1995) Am J Gastroenterol 90: 1808-1813, Dobson, H. et al (1994) Gut 35:1343-1347). EXAMPLE 5: Method for Measuring Mab Competition with Mab to E- cadherin for Binding to Extracellular Domain of E-cadherin A commercial immunoassay test kit (Human E-cadherin EIA kit, Zymed Laboratories, San Francisco, CA) that contains an antigen (Uvomorulin/E-cadherin), and a Mab to the extracellular domain of Uvomorulin/E-cadherin was used to demonstrate that Mab to desmocollin 3 can bind to the extracellular domain of Uvomorulin/E-cadherin. The kit enables the antigen to be exposed to agents or antibodies prior to exposure to the standard Mab to the extracellular domain of Uvomorulin/E-cadherin. The ability of the agent or antibody to block the binding of the Mab to the extracellular domain of Uvomorulin/E-cadherin can then be used to determine if competition for binding sites on the antigen has occurred. Comparative binding is based on the quantity of binding observed when the Mab to Uvomorulin/E-cadherin is placed in contact with antigen in the absence of prior exposure to test agent or antibody. The experimental control for test agents is vehicle (normal Ringer solution) and for monoclonal or polyclonal antibodies is an equivalent amount of nonspecific immune serum globulin (IgG). The quantity of binding of the Mab to Uvomorulin E-cadherin to antigen in the absence of test agent or test antibody is labeled as control and whose value is normalized to 100%. Antigen which was first exposed to a similar quantity of a Mab to desmocollin 3 (3 μg/100 μL) (Research Diagnostics, Flanders, NJ) prior to exposure of the Mab to Uvomorulin/E-cadherin demonstrated significantly reduced binding of Uvomorulin/E-cadherin Mab (64+5.8% compared to 3 μg/100 μL of IgG as control, p<0.05, n=6). This indicated that the Mab to desmocollin 3 competes effectively for the same binding sites as the Mab to the extracellular domain of Uvomorulin/E-cadherin. Without being bound to any particular theory, it appears, in effect, that the Mab to desmoglein 1 and 2, and desmocollin 3 exert their effect on resealing by binding to the extracellular domain of Uvomorulin E-cadherin. This conclusion is further supported by the fact that the Mab to desmoglein 1 and 2, and desmocollin 3 cross react on SDS gel electrophoresis with one or more of the same protein bands as the Mab to Uvomorulin/E-cadherin. EXAMPLE 6: SITS Provides Protection Against Noxious Substances Uvomorulin/E-cadherin was identified by SDS gel electrophoresis in homogenates of esophageal epithelium. These findings are supported by reports from others of the presence of Uvomorulin/E-cadherin on immunostaining, and on SDS gel electrophoresis in human esophageal epithelium (Swami, S. et al (1995) Am J Gastroenterol 90: 1808- 1813). When epithelia were treated with acid-pepsin or N-acetylcysteine and then homogenized, bands which stain with the Mab to E-cadherin are visible at 50kD and 80kD. The band at approximately 80 kD should correspond to the extracellular domain of E-cadherin, as identified elsewhere, after treatment of E- cadherin with trypsin in the absence of calcium, an approximately 80kD band is identified. Gumbiner, B.M. et al. (1986) J Cell Biol 102:457-468. SITS was selected to investigate the mechanism of protection because of its commercial availability, high level of protection against acid injury to esophageal epithelium, and lack of reversibility of its protective effect even with repeated washes of the tissue prior to acid exposure. When epithelia were treated first with SITS, and then contacted with acid-pepsin or N-acetylcysteine, the two bands at approximately 50 kD were not seen, suggesting that the cytoprotective agent SITS prevents the breakdown or fragmentation of the extracellular domain in the presence of the noxious substances acid-pepsin and N-acetylcysteine. Protection of Uvomorulin/E-cadherin against damage by acid or N-acetylcysteine was shown to be direct, i.e., by binding of the compound to the protein itself (rather than indirect by the binding of the compound to other proteins providing a shield against the access of acid or N-acetylcysteine to the critical junctional protein). Sections of rabbit esophageal epithelium were mounted in Ussing chambers and exposed luminally to either SITS, 4 mM, or vehicle (Ringer) as control for 30 min. Following exposures, both bathing solutions were made calcium-free solutions (3 mM EDTA and 4 mM SITS, or 3 mM EDTA without SITS (control)) to open the junctions as evidenced by the decline in R. In the presence of calcium-free solution with or without 4 mM SITS, R over a 2 hr period declined similarly for the two groups to 68+3% or 67+3 %, respectively. However, recovery of R following restoration of calcium- containing bathing solutions (0 mM SITS) showed that the recovery of R of tissues previously exposed to SITS was significantly reduced over that of the unexposed tissue (SITS treated recovery of 75+3% vs untreated controls of 90+5%, n=3, p<0.05). This showed that luminal SITS inhibits junctional resealing, a function of the adhesive protein E-cadherin, and this interference is likely through its ability to bind to the extracellular domain of E-cadherin. EXAMPLE 7: Method for Determining the Ability of Compounds to Bind to the Extracellular Domain of Uvomorulin E-Cadherin The Human E-cadherin EIA kit (Zymed Laboratories, San Francisco, CA) was used as in the method described in Example 5 to determine binding of test compounds, SITS, SOS, CDDD-1192, CDDD-1193 and 1,3-benzene disulfonic acid (1,3-BDSA) to the approximately 80 kD extracellular domain of Uvomorulin E-Cadherin provided in the E-cadherin EIA kit. This was done by adding the extracellular domain of human Uvomorulin/E-Cadherin to a solution with varying concentrations of the compounds in the nanomolar to millimolar range or with vehicle (control, normal Ringer solution) for 30 min. Following incubation for 2 hrs, the solution is added to a solid phase microtiter plate, provided in the EIA kit, to which a mouse monoclonal anti-human Uvomorulin/E- cadherin antibody (Zymed Laboratories, San Francisco, CA) is bound. This permits antigen with epitopes unoccupied by test compound to bind to the plate. After washing the plate with Tris buffer containing 0.1% Tween-20 (Promega, Madison, Wisconsin) and 5 mM calcium chloride, the second mouse monoclonal anti-human Uvomorulin/E-cadherin antibody labeled with peroxidase is used to tag the bound antigen. After an additional incubation for 1 hr and washing with Tris buffer, the peroxidase is detected with substrate (hydrogen peroxide and tetramethyl-benzidine in buffered solution, as included in the EIA test kit) by incubating for 15 min at room temperature and stopping of the reaction with IN H O 4 . This results in color development with intensities proportional to the amount of Uvomorulin/E-cadherin present in the samples. The amount of Uvomorulin/E-cadherin is quantitated by measuring absorbance at 450 nm within an hour following development using an EIA plate reader (Vmax Plate Reader, Molecular Devices, Sunnyvale, CA). The degree of binding of a compound to the extracellular domain of Uvomorulin/E-cadherin is determined by the reduction in antigen detection in the plate exposed to test compound compared to that for the control plate (100%) where no compound was present (Table 2). Table 2. The ability of selected agents to alter binding of a Mab to the extracellular domain of Uvomorulin/E-cadherin to its antigenic sites. Agent Concentration % Binding Control (vehicle) 100 1,3 BDSA 4 mM 104+3 SITS 40 uM 77+3* SITS 4 mM 26+3* SITS 8 mM 20+3* SOS 4 mM 83+0.3 * SOS 10 mM 76+0.3 * CDDD-1192 0.4 uM 103+6 CDDD-1192 4 mM 77+13 * CDDD-1193 40 nM 110+6 CDDD-1193 40 uM 83+3 * CDDD-1193 4 mM 38+0.75 * * p <0.05 compared to control; n=3-6 for each experimental group The experimental results depicted in Table 2 establish the ability of protective doses of SITS, SOS, CDDD-1192 and CDDD-1193, but not non-protective doses of 1 ,3-BDSA, a compound ineffective against acid injury in the Ussing chamber experiments at a concentration of 4 mM (as shown in U.S. Patent No. 5,189,056 and 5,374,537), to bind to the extracellular domain of E-cadherin. Further, the binding affinity for the epitope identified by the Mab to the extracellular domain for E-cadherin is greatest for CDDD-1193 and SITS at 4 mM concentrations when compared to that of CDDD- 1192 or SOS . Esophageal epithelium luminally pretreated with SITS (even without prior junctional opening by calcium-free solution) is found to inhibit the binding of a Mab to Uvomorulin/E-cadherin to its antigen (Uvomorulin/E-cadherin) when applied to homogenized epithelium run on SDS gel electrophoresis. Additionally, esophageal epithelium luminally pretreated with SITS in Ussing chambers that were subsequently exposed to acid-pepsin or N-acetylcysteine were resistant to the degradation of Uvomorulin E-cadherin into component proteins (Example 6). This was demonstrated by showing additional protein bands with Mab staining for Uvomorulin/E-cadherin of homogenized esophageal epithelium on SDS gel electrophoresis for tissues exposed to acid- pepsin or N-acetylcysteine compared to similarly exposed tissues that were pretreated with luminal SITS. Taken together, these data support the conclusion that the previously identified luminally-active cytoprotective compounds inhibit the junctional breakdown (and concomitant increase in paracellular permeability) in esophageal epithelium upon direct damage by acid, acid-pepsin or N-acetylcysteine, by direct binding to the extracellular domain of Uvomorulin/E-cadherin. Without being bound by any particular theory, it appears that the mechanism of action of these compounds is the stabilization of the target protein, i.e. Uvomorulin E-cadherin, which results in protection against acid, acid-pepsin or N-acetylcysteine induced increases in junctional (paracellular) permeability. It appears that sulfonates like SITS and sulfate esters, e.g. SOS, CDDD-1192 and CDDD-1193, act via the same mechanism. Sucrose octasulfate (previously shown to irreversibly protect against acid-induced injury to esophageal epithelium (U.S. Patent No. 5,374,537 and 5,189,056)) also dose- dependently binds to the extracellular domain of Uvomorulin/E-cadherin. A third category of alleged cytoprotective compounds known as inorganic tetrahedral-shaped oxyanions containing compounds such as sulfates, molybdates, chromates, and tungstates did not, like organic sulfonates and sulfate esters, inhibit binding of the Mab to the extracellular domain of Uvomorulin E-cadherin to its antigen, Uvomorulin/E-cadherin, using a commercially available immunoassay kit, as described above. This likely reflects the fact that these compounds demonstrate readily reversible protection against acid injury in the Ussing chamber, such that their binding to the protective site is most likely reversible and so ineffective at inhibiting the Mab to Uvomorulin/E-cadherin from binding to its antigen. Thus, compounds like the inorganic tetrahedral-shaped oxyanions described may show cytoprotective activity in rabbit esophageal epithelial tissue models as described in U.S. Pat. Nos. 5,374,537 and 5,189,056, but may not be suitable for use as control cytoprotective agents in the assay methods described herein. Further, the reversibility of binding suggests that these compounds may also not be as effective in vivo, where the esophageal tissues are being washed by saliva. Identification of the isolated extracellular domain of Uvomorulin/E-cadherin as the protective site supports use of this protein and its extracellular domain specifically as a test system for identifying, screening, selecting and designing compounds, chemicals, molecules, antibodies or other substances for protective effects against luminal damaging compounds, e.g. HCl, to stratified squamous epithelia. Modifications of the above described modes for carrying out the invention that are obvious to those of ordinary skill in the chemical, pharmaceutical, or related arts are intended to be within the scope of the following claims.

Claims: CLAIMS 1. A method of assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; and b) determining whether the compound binds to the polypeptide; wherein binding of the compound to the polypeptide indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. 2. The method of claim 1, further comprising: c) comparing the binding of the compound to the polypeptide with the binding of a cytoprotective agent to the polypeptide; wherein a greater than or equal level of binding by the compound indicates that the compound may protect stratified squamous epithelia from damage by the noxious substance. 3. The method of claim 2, wherein the cytoprotective agent is chosen from the group consisting of sulfate esters and sulfonates. 4. The method of claim 3 , wherein the cytoprotective agent is chosen from the group consisting of SITS, SOS, CDDD-1192 and CDDD-1193. 5. The method of claim 1 , wherein the polypeptide is an extracellular portion of E-cadherin. 6. The method of claim 5, wherein the extracellular portion comprises at least 5 residues of the extracellular domain of E-cadherin. 7. The method of claim 1, wherein the polypeptide comprises at least 5 residues of a sequence depicted within one of SEQ ID NOS:6-21, SEQ ID NOS:22-25, or within the extracellular domain of SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4; or SEQ ID NO:5. 8. The method of claim 1, wherein the polypeptide comprises at least 5 residues of a sequence depicted within residues 155-262 of SEQ ID NO:l, residues 52-157 of SEQ ID NO:2, residues 49-159 of SEQ ID NO:3, residues 52-157 of SEQ ID NO:4, and residues 136-243 of SEQ ID NO:5. 9. The method of claim 1 , wherein the compound is selected from the group consisting of sulfate esters and sulfonates. 10. The method of claim 1, further comprising, in order: c) contacting a sample comprising stratified squamous epithelial tissue with the compound; d) contacting the sample with a noxious substance; and e) determining if the epithelia is damaged. 11. The method of claim 10, wherein the epithelia is selected from the group of epithelia consisting of esophageal, oral cavity, cheek, pharynx, larynx and vocal cord tissue. 12. The method of claim 10, wherein the epithelia comprises rabbit esophageal epithelia. 13. The method of claim 10, wherein the noxious substance is selected from the group consisting of gastric acid, HCl, N-acetylcysteine, pepsin, acid- pepsin, and gastrointestinal fluid. 14. The method of claim 13, wherein the noxious substance is HCl. 15. The method of claim 13, wherein the noxious substance is HCl-pepsin. 16. The method of claim 1, wherein the polypeptide further comprises a solid support. 17. The method of claim 16, wherein the solid support is chosen from the group consisting of resin beads, glass slides, plastic slides, glass test tubes, plastic test tubes, glass wells, plastic wells, glass plates and plastic plates. 18. A method of assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising in order: a) contacting a polypeptide with a labeled cytoprotective agent; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a compound; and c) comparing binding of the agent to the polypeptide contacted with the compound to a control conducted where the polypeptide is contacted with the agent and is not contacted with the compound; wherein a decrease in binding of the agent to the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia against damage by a noxious substance. 19. The method of claim 18, wherein the agent is labeled with a radioactive isotope, fluorescent label or electron dense tracer. 20. The method of claim 19, wherein the electron dense tracer is selected from the group consisting of horseradish peroxidase, glucose oxidase, and alkaline phosphatase. 21. A method for identifying a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising, in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a monoclonal antibody to the polypeptide; and c) comparing the amount of antibody binding to the polypeptide contacted with the compound to the amount of antibody binding to a control; wherein a decrease in the amount of antibody binding to the polypeptide which has been contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. 22. The method of claim 21, wherein the control comprises contacting the polypeptide with the monoclonal antibody or wherein the control comprises contacting the polypeptide with a cytoprotective agent and then contacting the polypeptide with the monoclonal antibody. 23. A method of assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising in order: a) contacting a polypeptide with a compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted with in the extracellular domain of SEQ ID NO:l; b) determining the stability of the polypeptide; and c) comparing the stability of the polypeptide contacted with the compound to the stability of a control; wherein a greater stability for the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. 24. The method of claim 23, wherein the control comprises where the polypeptide is not contacted with the compound or where the polypeptide is contacted with a cytoprotective agent and is not contacted with the compound. 25. The method of claim 23, wherein stability is determined using a technique selected from the group consisting of calorimetry; titration of chemical denaturation and titration of thermal denaturation. 26. A method of assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising in order: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; c) determining the stability of the polypeptide; and d) comparing the stability of the polypeptide contacted with the compound and the noxious substance to the stability of a control; wherein if the stability of the polypeptide contacted with the compound and noxious substance is greater than that of the control, the compound may protect stratified squamous epithelium against damage by the noxious substance. 27. The method of claim 26, wherein the control comprises where the polypeptide is not contacted with the compound but is contacted with the noxious substance or where the polypeptide is contacted with a cytoprotective agent and then contacted with the noxious substance. 28. The method of claim 26, wherein stability is determined using a technique selected from the group consisting of calorimetry; titration of chemical denaturation and titration of chemical denaturation. 29. A method of assaying for a compound which may protect stratified squamous epithelia from damage by a noxious substance, comprising in order: a) contacting a polypeptide with the compound; wherein the polypeptide is selected from the group consisting of an extracellular portion of a cadherin or a peptide sequence having at least 13% sequence identity to a sequence depicted within the extracellular domain of SEQ ID NO:l; b) contacting the polypeptide with a noxious substance; c) determining the amount of fragmentation of the polypeptide; and d) comparing the amount of fragmentation of the polypeptide to a control; wherein a decrease in the amount of fragmentation of the polypeptide contacted with the compound compared to the control indicates that the compound may protect stratified squamous epithelia from damage by a noxious substance. 30. The method of claim 29, wherein the control comprises where the polypeptide is not contacted with the compound but is contacted with the noxious substance or where the polypeptide is contacted with a cytoprotective agent and then contacted with the noxious substance. 31. The method of claim 29, wherein fragmentation is determined using a technique from the group consisting of SDS gel electrophoresis, mass spectrometry, HPLC, or amino acid analysis. 32. The method of claim 29, wherein the technique is SDS gel electrophoresis.

Inventors: ORLANDO ROY C, TOBEY NELIA A, ORLANDO, ROY, C., TOBEY, NELIA, A.
Applicants: ORLANDO ROY C, TOBEY NELIA A, UNIV TULANE, ORLANDO, ROY, C., THE ADMINISTRATORS OF THE TULANE EDUCATIONAL FUND, TOBEY, NELIA, A.
Application year: 2001
Main classification: G01N33
IPC codes: G01N33