CLONING AND EXPRESSION OF beta APP-C100 RECEPTOR (C100-R)

Abstract: The present invention relates to the cloning of beta APP-C100 receptor (C100-R), and genetically engineered host cells which express the C100-R. Such engineered cells may be used to evaluate and screen drugs and analogs of beta -APP involved in Alzheimer's Disease.

Description: CLONING AND EXPRESSION OF βAPP-ClOO RECEPTOR (C100-R) 1. INTRODUCTION The present invention relates to the cloning of the receptor for the carboxy-terminus of the /S-amyloid precursor protein (including the amyloid domain) , referred to herein as C100-R, and genetically engineered host cells which express the C100-R. Such engineered cells may be used to evaluate and screen drugs and analogs of the β-amyloid precursor protein (3-APP) which may be used for the diagnosis and/or treatment of Alzheimer's Disease. 2. BACKGROUND OF THE INVENTION Alzheimer's disease is a neurodegenerative disorder that is the most frequent cause of dementia among aged individuals. The disease is characterized by the accumulation of amyloid-containing plaques in the brain, particularly in the temporal cortex and hippocampus and along the walls of the cerebral vascu- lature (Roch et al., 1966, Nature 209:109-110; Terry et al., 1981, Ann. Neurol. 10:184-192; Glenner G.G., 1983, Arch. Pathol. Lab. Med. 107:281-282; Katzman, R. , 1983, Banbury Report 15, Cold Spring Harbor Lab., Cold Spring, N.Y.). The amyloid peptide (0A4) , found in the plagues of the brain derives from a protein referred to as the amyloid (or beta-amyloid) precursor protein (/SAPP) . / SAPP is normally cleaved within the amyloid domain, which lies near its C-terminus, so that no intact amyloid is produced. An alternative processing pathway results in cleavage of βAPP N-terminal to the amyloid domain, releasing the entire C-terminal from which intact amyloid peptide (j3A4) of the amyloid protein precursor may be produced (Glenner and Wong, 1984, Biochem Biophys Res. Commun. 120:885-890; Masters et al., 1985, Proc. Natl Acad. Sci. USA 82:4245-4249) . Recent evidence suggests that aberrant processing of 5-APP underlies the neuronal degeneration that occurs in Alzheimer's Disease. Neve and coworkers have proposed that the primary ,9APP processing event in Alzheimer's Disease is cleavage of the amino terminus of the β/ 4 sequence, producing a carboxy- terminal / SAPP fragment of 100 amino acid residues (3APP-C100) which was expressed from a cDNA sequence encoding the carboxyterminal 104 amino acids of / 3APP (Yankner et al., 1989, Science 245:417-420). Hereinafter, this fragment of 0APP will be referred to as 3APP-C100 regardless of whether it is expressed from a cDNA encoding the carboxyterminal 100 or 104 amino acid residueε of SAPP. Expression of the / SAPP- C100 peptide in primate cells has been shown to lead to production of a protein that aggregates and accumu¬ lates into deposit-like structures that result in formation of amyloid-like fibrils (Wolf et al., 1990 EMBO J. 9:2079-2084). A retroviral recombinant which directs the expression of 3APP-C100 has also been shown to be neurotoxic when transfected into PC-12 cells that have been induced to differentiate by addition of NGF (nerve growth factor) . Furthermore, the conditioned media from these transfected cells is toxic to differentiated neuroblastoma and neural cells, and the neurotoxicity can be removed from the medium by immunoabsorption with an antibody to jSAPP- C100 suggesting that 3APP-C100 is secreted by transfected cells and is neurotoxic (Yankner et al., 1989, Science 245:417-420). The toxicity of 0APP-C1OO has been further demonstrated by transplantation of cells expressing the peptide into the brains of newborn mice and by creation of mice transgenic for human /3APP-C100 (Neve et al., 1992, Proc. Natl. Acad. Sci. USA 89:3448-3452). Taken together, evidence indicates a role for 5APP-C100 in development of the neurodegeneration in Alzheimer's disease. Despite the intense interest in the 5APP-C100 peptide, and its biological role in development of Alzheimer's Disease, very little is known about the proteins, receptors or other tissue elements with which the 3APP-C100 peptide interacts to produce neurotoxicity. Very recently, the high affinity binding of SAPP-CIOO to the surface of differentiated PC-12 cells has been demonstrated and correlated with neurotoxicity (Kozlowski et al., 1992, J. of Neuroscience 12:1679-1687). Both the binding interaction and the occurrence of the neurotoxic response have the same pH dependence. In addition, in PC-12 cells, both the binding and the susceptibility to neurotoxicity develop with similar time courses during NGF-induced differentiation. Furthermore, a single amino-acid change in the jSAPP-ClOO peptide TyX tr to Phe) , which eliminates its neurotoxic effect, also produces a loss of binding potency. However, the molecular species responsible for binding has not been identified or characterized. The isolation of a cDNA clone coding for the SAPP-CIOO binding site or receptor would facilitate studies aimed at determining the biological function of C100-R and its role in development of Alzheimer's Disease. However, this has not, heretofore, been accomplished. 3. SUMMARY OF THE INVENTION The present invention relates to the C100-R genes and proteins. The neurotoxic effects, resulting from the interaction between / 3APP-C100 and the C100-R suggest that therapeutic applications designed to block this particular receptor/ligand interaction may be useful for treatment of AlzTieimer's Disease. The DNA sequences disclosed herein may be engineered into expression systems designed for the production of C100-R and/or cell lines which express the CIOO-R. Such cell lines may be used advantageously for screening and identifying β-APP analogs, including agonists and antagonists. In accordance with another aspect of the invention, the C100-R DNA, antisense oligonucleotide sequences, or antagonists including antibodies to CIOO-R may be used in the diagnosis and therapy of Alzheimer's Disease. Transgenic animals containing the C100-R transgene may be used as animal models for the evaluation of β-APP-ClOO analogs in vivo. The invention is based, in part, on the discovery, identification and cloning of a / SAPP-C100 binding εite that is expressed in neuronally derived cells. The cDNA represents an -11 kb mRNA with a 1632 base pair (bp) open reading frame encoding a novel 61 kilodalton (kDa) putative serine/threonine kinase. Immunoprecipitated C100-R, expressed recombinantly in COS-7 cells, phosphorylates a myelin basic protein substrate in the presence of the activated p21 proteins Racl and Cdc42. These two members of the Ras-related Rho subfamily of small GTPases regulate cytoskeletal organization; and in particular, Racl is a key component of the machinery controlling axonal outgrowth. Therefore, the interaction of the C-terminal domain of APP with C100- R is likely to be involved in neuronal signal transduction mediated by Racl and Cdc42. Disruption of this εignal transduction pathway may play a part in the disassembly of the cytoskeleton that occurs in Alzheimer's disease. Therefore, the cDNA clone encoding the CIOO-R may be of therapeutic value for the diagnoses and design of drugs for treatment of Alzheimer's Disease. 4. BRIEF DESCRIPTION OF THE FIGURES FIG. 1. - Representative curve showing the inhibition of 35 S-0APP-C1OO binding to (A) NGF-treated (5d) PC12 cells and (B) SK-N-MC cells, by 3APP-C100. FIG. 2. - Representative saturation isotherm (top panel) and Scatchard plot (bottom panel) of 35 S-SAPP- C100 binding to NGF-treated (6d) PC12 cells. The lines were computer generated and represent the best interpretation of the data. FIG. 3. - Screening of λgtll rat cDNA libraries using the Direct Binding method. FIG. 4. - Nucleotide Sequence of cDNA insert of rat CIOO-R clone, AB1R. Underlined region represents SER/THR Kinase "signature" or conserved catalytic core sequence. FIG. 5. - Sequence homology between CIOO-R and (A) "B" type calcium channels, (B) calreticulin, and (C) Ryanodine calcium channel. FIG. 6. - Southern blot analysis of the AB1R cDNA. Lane A is EcoRI digested human DNA. Lane B is EcoRI digested mouse DNA. Lane C is Hindlll digested mouse DNA. Lane D is Hindlll digested human DNA. λ/Hindlll markers were run to establish molecular weights. FIG. 7 A and B. - Representative autoradiographs of specific binding to rat brain sections at (FIG. 7A) anterior and (FIG. 7B) middle to posterior levels. The images were digitized and enhanced so that areas with higher levels of binding are lighter. Note that certain areas of the olfactory tubercle (lower part of sections in (A) and hippocampus (mid-lateral part of section in (B) stand out against the relatively uniform labelling of the rest of the grey matter. FIG. 8. - Representative autoradiographs of the in situ hybridization of the pABlR antisense probe, section locations and method of reproduction are as in FIG. 7. Note the areas of high labelling (lightest areas) in the olfactory tubercle and hippocampus in agreement with the results from the binding autoradiography (FIG. 7) . FIG. 9. - Nucleotide sequence of cDNA insert of rat CIOO-R clone, AB2R. The EcoRI fragment from nucleotide 31 through nucleotide 409 was used to screen a human hippocampal cDNA library. FIG. 10. - Nucleotide sequence of rat C100-R clone. The disclosed sequence is the result of cloning and sequencing of a number of overlapping rat cDNA clones. The * above nucleotide 686 represents the junction with the rat C100-R nucleotide sequence depicted in Figure 4 (nucleotide 40) . FIG. 11. - Nucleotide sequence of the cDNA encoding the complete C100-R. Alternative splicing of the transcript occurs at position -27, as indicated by a backslash; the sequence of only one of the spliced forms is shown. Peptide sequences that were used to make antisera are underlined. The 3'UTR is not shown in its entirety. FIG. 12. - Amino acid sequence homology between C100-R, Pakl, and STE20. Note the strong homology in the C-terminal kinase domain. The Cdc 2/Racl-binding domain near the N-terminus is boxed. Additional members of the Pak family, not shown in this figure, have been cloned. FIG. 13. - Co-immunoprecipitation of radiolabelled C100-R by APP-695, APP-C100, and GTP- activated p21 GST fusion proteins. The 61-kDa C100-R in vitro translation product is indicated. Note that it is absent in the control GST lane. It also fails to bind to GST-Rho, whether GDP-or GTP-bound, and to GDP-bound GST-Cdc42 and GST-Racl. FIG. 14A. - Activation of C100-R by GTP-bound Cdc42 and Racl. Immunoprecipitated myc-ClOO-R fusion protein was incubated for 20 min at 25°C with GST(a), GST-RhoA (b,c) GST-Racl (d,e) or GST-Cdc42 (f,g) which were bound to either GDP/Ss (b,d,f) or GTPγS (c,e,g). The precipitates were washed and the bound C100-R was assayed for its ability to phosphorylate myelin basic protein (MBP) . Molecular mass standards are shown on the left (kDa) . FIG. 14B. Quantitation of the amount of MBP phosphoprotein following MBP incubation with the immunoprecipitated myc-ClOO-R and the indicated GST- p21 fusion proteins. FIG. 15A. - Immunoblot analyses of C100-R in human and rat brain homogenates. As indicated by the arrows, two independent immunoaffinity-purified antibodies (1AB1R and 2AB1R) generated against distinct peptides within the C100-R sequence immunodetected a 61 kDa band in total human (Hu) and rat brain homogenates. The higher molecular weight band may represent the product of an alternatively spliced C100-R mRNA, or may represent a closely- related protein with which the antibody cross-reacts. FIG. 15B. Immunoabsorption experiments demonstrate the specificity of the two antibodies in immunoblots of total rat brain homogenates. Lane l, 1AB1R antibody preabsorbed with the 1AB1R peptide; lane 2, 1AB1R antibody preabsorbed with the 2AB1R peptide; lane 3, 1AB1R antibody without preabsorption; lane 4, 2AB1R antibody preabsorbed with the 2AB1R antibody without preabsorption. FIG. 15C. - Fractions of human fetal brain were immunoblotted with 1AB1R (top) or the anti-APP antibody S369 (bottom) . Note co-localization of C- 100-R and APP immunoreactivity in the synaptosomal plasma membrane fraction. "Sup 1" refers to the supernatant retrieved after the first low-speed spin following homogenation of the brain tissue. FIG. 16A. - RNA blot analyses of CIOO-R gene expression. The C100-R cDNA was used to probe an RNA blot containing RNA from a range of human fetal (20-22 week) tissues. 20 ug of total RNA was loaded in each lane. FIG. 16B. - Analysis of C100-R mRNA expression in subregions of human fetal (20 week) brain. Tha, thalamus; Cb, cerebellum; Hi, hippocampus; C-P, caudate-putamen; Al, primary sensory cortex; A4, primary motor cortex; AlO, frontal cortex; A17/18, visual cortex. FIG. 16C. - Expression of C100-R mRNA expression in human and rat nervous system tissues. FIG. 17. - In situ hybridization analysis of c- 100-R gene expression in the rat brain. FIG. 18. - Nucleotide sequence of cDNA inserts of human C100-R clone. The nucleotide designated M is either A or C and the nucleotide designated K is either T or G. FIG. 19A. - Sequence homology between human C100- R and rat C100-R. Human #4.t3 sequence is aligned with the rat C100-R sequence depicted in Figure 9 starting at nucleotide 544. FIG. 19B. - Sequence homology between human C100- R and rat C100-R. Human clone HABIR #1#4 is aligned with the rat C100-R sequence depicted in Figure 4, starting at nucleotide 182. FIG. 19C. - Sequence homology between human C100- R and rat C100-R. Human clone #1#1T3 is aligned with the rat C100-R sequence depicted in Figure 4 starting at nucleotide 1868. 5. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the cloning and expression of the C100-R. The C100-R was initially characterized as a binding site present in neuronally derived cells, that bound specifically to the amyloid peptide 3APP-C100. Expression of the /3APP-C100 amyloid peptide has been shown in animal models to correlate with the specific type of neuronal degeneration that occurs in Alzheimer's Disease. The C100-R produced herein may be used to evaluate and screen drugs and analogs of β-APP that may be used in the diagnosis and/or treatment of Alzheimer's Disease. 5.1. THE CIOO-R CODING SEQUENCE The initial rat C100-R cDNA clone, designated λABlR, was obtained by screening a λgtll rat brain expression library with / 3-APP-C100 ligand labeled with 35 S-methionine or a peptide epitope "flag" sequence as described in Section 6, infra. The initial clone, designated pABIR-rat, was found to contain a 1970 bp insert comprised of the nucleotide coding sequence and deduced amino acid sequence depicted in Figure 4. A corresponding cDNA clone has been deposited with the ATCC and assigned numbers described in Section 8, infra. Sequence analysis reveals that the clone encompasses the carboxy-terminal section of the gene and contains 1395 base pairs of coding sequence and 575 bp of 3' untranslated sequence (FIG. 4). As indicated by the detection of an 11 Kb C100-R mRNA on Northern blots, the nucleotide sequence depicted in Figure 4 is only a partial representation of the C100-R gene. Full length rat CIOO-R cDNA sequence may be obtained using a variety of different methods. For example, in a specific embodiment of the invention described herein, RNA prepared from rat brain and a primer specific for the most 5• end of the ABIR cDNA insert, was utilized for first strand synthesis in a reverse transcriptase reaction. Following second strand synthesis, the cDNA was inserted into the bacterial Bluescript plasmid (Stratagene) . Additional rat C100-R cDNA clones were isolated and sequenced (FIG. 9 and FIG. 10) . The new sequences overlap with those rat sequences shown in Figure 4 and extend the coding region towards the amino-terminal end of the CIOO-R protein (FIG. 10) . The sequence disclosed in Figure 9 diverges upstream of nucleotide 106 from the rat sequence shown in Figure 10, indicating that alternatively spliced mRNAs may exist for the C100-R clone. The partial C100-R cDNA clones were used to reprobe rat brain cDNA libraries, and numerous cDNA clones overlapping with the original clone and extending it at the 5' end were isolated. At least three of these cDNAs contained a full-length coding sequence. Sequence analysis of these clones revealed a 1632 bp open reading frame (Figure 11) encoding a 544 amino acid protein with a calculated molecular mass of 60.7 kDa. A portion of the sequence of the cDNA was found to be homologous to that coding for the serine/theonine kinase domain of the yeast STE20 protein (Leberer et al., 1992, EMBO J. 11:4815-4824; Ramer and Davis, 1993, Proc. Natl. Acad. Sci. USA 90:452-456), with 67% identity over an interval of 683 bp at the 3' end of each coding sequence. A search of the protein database revealed that the putative neural APP binding protein (C100-R) was closely related to rat p65 PAK (Pakl; Manser et al. , 1994) and yeast STE20 proteins (Figure 12) with highest homology in the serine/theonine kinase domain (70% between C100-R and STE20; 90% between C100-R and p65 PAK ) . In addition, these three kinases shared, in their N-terminal domains, a peptide motif representing the Cdc42/Racl- binding domain of Pakl (Figure 12) . The overall identity between C100-R and p65 PAK protein sequences was 83%. P65 PAK is a serine/theonine protein kinase that is activated by the Rho family p21 proteins Cdc 2 and Racl. The very close similarity between C100-R and p65 PAK indicates an analogous function for C100-R. At least four spliced forms of C100-R mRNA were identified. All four spliced forms diverged within the 5' UTR, at bp -27 (Figure 10). The invention also relates to CIOO-R genes iso¬ lated from other species, including humans, in which C100-R activity exists. Members of the CIOO-R family are defined herein as those receptors that bind SAPP- C100 or fragments of the peptide. Such receptors may demonstrate about 80% homology at the nucleotide level, and even 90% homology at the amino acid level in substantial stretches of DNA sequence. Therefore, in addition to the C100-R nucleotide sequence that encodes the amino acid sequence of the ClOO-R protein shown in FIGS. 10 and 11, nucleotide sequences capable of hybridizing to such CIOO-R sequences under highly or less highly stringent hybridization conditions are well within the scope of the invention. High stringent hybridization conditions may be defined as hybridization to filter-bound DNA in 0.5M NaHP0 4 , 7% sodium dodesyl sulfate (SDS) , 1mm EDTA at 65°C, followed by washing in 0.1X SSC/0.1% SDS at 68°C. (Ausubel, F.M. et al. , eds, 1989 Current Protocols in Molecular Biology, Vol. I, Green Publishing Associates, Inc., and John Wiley & Sons, Inc., New York at p. 2.10.3). Less highly stringent conditions, such as moderately stringent conditions, may be defined as hybridization carried out as described above, followed by washing in 0.2X SSC/0.1% SDS at 42°C. (Ausubel et al., 1989, supra). To identify C100-R genes isolated from other species a bacteriophage cDNA library may be screened, under moderately stringent hybridization conditions, using a radioactively labeled fragment of the rat CIOO-R clone. Alternatively, the rat CIOO-R sequence can be used to design degenerate or fully degenerate oligonucleotide probes which can be used as PCR probes or to screen bacteriophage cDNA libraries. A poly¬ merase chain reaction (PCR) based strategy may be used to clone human C100-R. Two pools of degenerate oiigo¬ nucleotides, corresponding to conserved motifs between the rat C100-R and the serine/theonine p65 PAK /STE20 family of kinases, may be designed to serve as primers in a PCR reaction. The template for the reaction is cDNA obtained by reverse transcription of mRNA prepared from cell lines or tissue known to express human APP-R. The PCR product may be subcloned and sequenced to insure that the amplified sequences represent the C100-R sequences. The PCR fragment may ■ fchen be used to isolate a full length C100-R cDNA clone by radioactively labeling the amplified fragment and screening a bacteriophage cDNA library. Alternatively, the labeled fragment may be used to screen a genomic library. For a review of cloning strategies which may be used, see e.g. , Maniatis, 1989, Molecular Cloning, A Laboratory Manual, Cold Springs Harbor Press, N.Y.; and Ausubel et al., 1989, Current Protocols in Molecular Biology, (Green Publishing Associates and Wiley Interscience, N.Y.) A cDNA library may also be constructed in a mammalian expression vector such as pcDNAl, that contains SV40 origin of replication sequences which permit high copy number expression of plasmids when transferred into COS cells. The expression of C100-R on the surface of transfected COS cells may be detected in a number of ways, including the use of a labeled ligand such as 3APP-C100 or a /SAPP-C100 agonist labeled with a radiolabel, fluorescent label or an enzyme. Cells expressing the human CIOO-R may be enriched by subjecting transfected cells to a FACS (fluorescent activated cell sorter) sort. In a specific embodiment described herein, an adult hippocampal cDNA library was screened with a labeled nucleotide fragment from the rat C100-R clone. The large EcoRI fragment, extending from nucleotide 31 through nucleotide 409 of the AB2R rat clone (FIG. 9) was used to probe the human cDNA library. The library was screened using the followinghybridization and washing conditions: hybridization in 6x55C at 68°C followed by washingt at .lx55C at 65°C. Several clones were obtained and the cDNA inserts were sequenced. Human C100-R sequence is shown in Figure 11, and regions of homology between the rat and human C100-R sequences are shown in Figure 12. Any of the methods described above for isolation of full length rat C100-R clones may be used equally well for isolation of full length human CIOO-R clones. For instance, probes specific for the most 5' sequence of the human clone may be used to rescreen the human cDNA library. With each successful round of sequencing new 5' probes may be designed and used to reprobe libraries until the entire sequence has been obtained. In accordance with the invention, nucleotide sequences which encode C100-R, fragments, fusion proteins or functional equivalents thereof, may be used to generate recombinant DNA molecules that direct the expression of the CIOO-R, or a functionally active peptide, fusion protein or functional equivalent thereof, in appropriate host cells. Alternatively, nucleotide sequences which hybridize to portions of the CIOO-R sequence may also be used in nucleic acid hybridization assays. Southern and Northern blot analyses, etc. Due to the degeneracy of the genetic code, other DNA sequences which encode substantially the ClOO-R amino acid sequence, e.g.. such as the rat sequence depicted in Figure 4 or a functional equivalent may be used in the practice of the present invention for the cloning and expression of the CIOO-R. Such DNA sequences also include those which are capable of hybridizing to the rat or human CIOO-R sequence and encode a naturally occurring CIOO-R in another species or cell type. The stringency conditions may be adjusted in a number of ways. For example, when performing polymerase chain reactions (PCR) , the temperature at which annealing of primers to template takes place or the concentration of MgCl 2 in the reaction buffer may be adjusted. When using radioactively labeled DNA fragments or oiigonucleotides to probe filters, the stringency may be adjusted by changes in the ionic strength of the wash solutions or by careful control of the temperature at which the filter washes are carried out. Altered DNA sequences which may be used in accor¬ dance with the invention include deletions, additions or substitutions of different nucleotide residues resulting in a sequence that encodes the same or a functionally equivalent gene product. The gene product itself may contain deletions, additions or substitutions of amino acid residues within the C100-R sequence, which result in a silent change thus produ¬ cing a functionally equivalent CIOO-R. Such amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipatic nature of the residues involved. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; amino acids with uncharged polar head groups having similar hydrophilicity values include the following: leucine, isoleucine, valine; glycine, alanine; asparagine, glutamine; serine, threonine; phenylalanine, tyrosine. As used herein, a functionally equivalent C100-R refers to a receptor which binds to β-APP-ClOO or fragments, but not necessarily * with the same binding affinity of its counterpart native CIOO-R. The DNA sequences of the invention may be engi¬ neered in order to alter the C100-R coding sequence for a variety of ends including but not limited to alterations which modify processing and expression of the gene product. For example, mutations may be introduced using techniques which are well known in the art, e.g. site-directed mutagenesis, to insert new restriction sites, to alter glycosylation patterns, phosphorylation, etc. For example, in certain expression systems such as yeast, host cells may over glycosylate the gene product. When using such expres¬ sion systems it may be preferable to alter the C100-R coding sequence to eliminate any N-linked glycosyla¬ tion site. In another embodiment of the invention, the ClOO-R or a modified C100-R sequence may be ligated to a heterologous sequence to encode a fusion protein. The fusion protein may be engineered to contain a cleavage site located between the CIOO-R sequence and the heterologous protein sequence, so that the C100-R can be cleaved away from the heterologous moiety. In a specific embodiment described herein the C100-R coding sequence was ligated in frame to the N-terminal myc epitope [EQKLISEEDL] in expression vector pMT3 (Kaufman R.J. et al., 1987, EMBO J. 6:187- 193) . Following transfection of the recombinant expression vector into mammalian cells, expression of a C-lOOR/myc fusion protein was detected in immunoprecipitation assays utilizing anti-myc antibodies. In an alternate embodiment of the invention, the coding sequence of C100-R could be synthesized in whole or in part, using chemical methods well known in the art. See, for example, Caruthers, et al. , 1980, Nuc. Acids Res. Symp. Ser. 7:215-233; Crea and Horn, 180, Nuc. Acids Res. 9(10):2331; Matteucci and Caruthers, 1980, Tetrahedron Letters 21:719; and Chow and Kempe, 1981, Nuc. Acids Res. 9(12) :2807-2817. Alternatively, the protein itself could be produced using chemical methods to synthesize the CIOO-R amino acid sequence in whole or in part. For example, peptides can be synthesized by solid phase techniques, cleaved from the resin, and purified by preparative high performance liquid chromatography. (E.g.. see Creighton, 1983, Proteins Structures And Molecular Principles, W.H. Freeman and Co., N.Y. pp. 50-60). The composition of the synthetic peptides may be confirmed by amino acid analysis or sequencing (e.g.. the Edman degradation procedure; see Creighton, 1983, Proteins, Structures and Molecular Principles, W.H. Freeman and Co., N.Y., pp. 34-49. 5.2. EXPRESSION OF THE C100-R In order to express a biologically active C100-R, the nucleotide sequence coding for C100-R, or a func¬ tional equivalent as described in Section 5.1 supra f is inserted into an appropriate expression vector, i.e. f a vector which contains the necessary elements for the transcription and translation of the inserted coding sequence. The C100-R gene products as well as host cells or cell lines transfected or transformed with recombinant C100-R expression vectors can be used for a variety of purposes. These include but are not limited to generating antibodies (i.e. f monoclonal or polyclonal) that bind to the receptor, including those that competitively inhibit binding and "neutralize" β- APP activity of BAPP or fragments of BAPP, and the screening and selection of β-APP analogs or drugs that act via the C100-R; etc. 5.2.1. EXPRESSION SYSTEMS Methods which are well kn'own to those skilled in the art can be used to construct expression vectors containing the C100-R coding sequence and appropriate transcriptional/translational control signals. These methods include in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination/genetic recombination. See, for example, the techniques described in Maniatis et al., 1989, Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory, N.Y. and Ausubel et al., 1989, Current Protocols in Molecular Biology, Greene Publishing Associates and Wiley Interscience, N.Y. A variety of host-expression vector systems may bd utilized to express the C100-R coding sequence. These include but are not limited to microorganisms such as bacteria transformed with recombinant bacteriophage DNA, plasmid DNA or cosmid DNA expres¬ sion vectors containing the C100-R coding sequence; yeast transformed with recombinant yeast expression vectors containing the C100-R coding sequence; insect cell systems infected with recombinant virus expres¬ sion vectors (e.g.. baculovirus) containing the C100-R coding sequence; plant cell systems infected with recombinant virus expression vectors (e.g.. cauli¬ flower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g.. Ti plasmid) containing the CIOO-R coding sequence; or animal cell systems infected with recombinant virus expression vectors (e.g. , adenovirus, vaccinia virus) including cell lines engineered to contain multiple copies of the C100-R DNA either stably amplified (e.g. , CHO/dhfr) or unstably amplified in double-minute chromosomes (e.g. , murine cell lines) . The expression elements of these systems vary in their strength and specificities. Depending on the host/vector system utilized, any of a number of suit¬ able transcription and translation elements, including constitutive and inducible promoters, may be used in the expression vector. For example, when cloning in bacterial systems, inducible promoters such as pL of bacteriophage λ, plac, ptrp, ptac (ptrp-lac hybrid promoter) and the like may be used; when cloning in insect cell systems, promoters such as the baculovirus polyhedrin promoter may be used; when cloning in plant cell systems, promoters derived from the genome of plant cells (e.g.. heat shock promoters; the promoter for the small subunit of RUBISCO; the promoter for the chlorophyll a/b binding protein) or from plant viruses (e.g.. the 35S RNA promoter of CaMV; the coat protein promoter of TMV) may be used; when cloning in mamma¬ lian cell systems, promoters derived from the genome of mammalian cells (e.g.. metallothionein promoter) or from mammalian viruses (e.g.. the adenovirus late promoter; the vaccinia virus 7.5K promoter) may be used; when generating cell lines that contain multiple copies of the C100-R DNA, SV40-, BPV- and EBV-based vectors may be used with an appropriate selectable marker. In bacterial systems a number of expression vectors may be advantageously selected depending upon the use intended for the ClOO-R expressed. For example, when large quantities of C100-R are to be produced for the generation of antibodies, vectors which direct the expression of high levels of fusion protein products that are readily purified may be desirable. Such vectors include but are not limited to the J s . coli expression vector pUR278 (Ruther et al., 1983, EMBO J. 2:1791), in which the C100-R coding sequence may be ligated into the vector in frame with the lacZ coding region so that a hybrid ClOO-R/lacZ protein is produced; pIN vectors (Inouye & Inouye, 1985, Nucleic acids Res. 13:3101-3109; Van Heeke & Schuster, 1989, J. Biol. Chem. 264:5503-5509); and the like. Alternatively, pMT3 vectors may be used to express c-myc/ClOO-R fusion proteins. pGEX vectors may also be used to express foreign polypeptides as fusion proteins with glutathione S-transferase (GST) . In general, such fusion proteins are soluble and can easily be purified from lysed cells by affinity chromatography, e.g.. adsorption to glutathione- agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned polypeptide of interest can be released from the GST moiety. See also Booth et al., 1988, Immunol. Lett. 19: 65-70; and Gardella et al., 1990, J. Biol. Chem. 265: 15854-15859; Pritchett et al., 1989, Biotechniques 7:580. In yeast, a number of vectors containing consti¬ tutive or inducible promoters may be used. For a review see. Current Protocols in Molecular Biology, Vol. 2, 1988, Ed. Ausubel et al., Greene Publish. Assoc. & Wiley Interscience, Ch. 13; Grant et al., 1987, Expression and Secretion Vectors for Yeast, in Methods in Enzymology, Eds. Wu & Grossman, 1987, Acad. Press, N.Y., Vol. 153, pp. 516-544; Glover, 1986, DNA Cloning, Vol. II, IRL Press, Wash., D.C, Ch. 3; and Bitter, 1987, Heterologous Gene Expression in Yeast, Methods in Enzymology, Eds. Berger & Kimmel, Acad. Press, N.Y., Vol. 152, pp. 673-684; and The Molecular Biology of the Yeast Saccharomyces, 1982, Eds. Strathern et al.. Cold Spring Harbor Press, Vols. I and II. In cases where plant expression vectors are used, the expression of the C100-R coding sequence may be driven by any of a number of promoters. For example, viral promoters such as the 35S RNA and 19S RNA promoters of CaMV (Brisson et al., 1984, Nature 310:511-514), or the coat protein promoter of TMV (Takamatsu et al., 1987, EMBO J. 6:307-311) may be used; alternatively, plant promoters such as the small subunit of RUBISCO (Coruzzi et al., 1984, EMBO J. 3:1671-1680; Broglie et al. , 1984, Science 224:838- 843); or heat shock promoters, e.g. , soybean hspl7.5-E or hspl7.3-B (Gurley et al. , 1986, Mol. Cell. Biol. 6:559-565) may be used. These constructs can be introduced into plant cells using Ti plasmids, Ri plasmids, plant virus vectors, direct DNA transforma¬ tion, microinjection, electroporation, etc. For reviews of such techniques see, for example, Weissbach & Weissbach, 1988, Methods for Plant Molecular Biology, Academic Press, NY, Section VIII, pp. 421- 463; and Grierson & Corey, 1988, Plant Molecular Biology, 2d Ed., Blackie, London, Ch. 7-9. An alternative expression system which could be used to express C100-R is an insect system. In one such system, Autographa califomica nuclear polyhidrosis virus (AcNPV) is used as a vector to express foreign genes. The virus grows in Spodoptera frugiperda cells. The C100-R coding sequence may be cloned into non-essential regions (for example the polyhedrin gene) of the virus and placed under control of an AcNPV promoter (for example the polyhedrin promoter) . Successful insertion of the C100-R coding sequence will result in inactivation of the polyhedrin gene and production of non-occluded recombinant virus (i.e.. virus lacking the proteinaceous coat coded for by the polyhedrin gene) . These recombinant viruses are then used to infect Spodoptera frugiperda cells in which the inserted gene is expressed. (E.g.. see Smith et al., 1983, J. Viol. 46:584; Smith, U.S. Patent No. 4,215,051). In mammalian host cells, a number of viral based expression systems may be utilized. In cases where an adenovirus is used as an expression vector, the CIOO-R coding sequence may be ligated to an adenovirus trans¬ cription/translation control complex, e.g. , the late promoter and tripartite leader sequence. This chimeric gene may then be inserted in the adenovirus genome by in vitro or in vivo recombination. Inser- tion in a non-essential region of the viral genome (e.g. f region El or E3) will result in a recombinant virus that is viable and capable of expressing C100-R in infected hosts. (E.g.. See Logan & Shenk, 1984, Proc. Natl. Acad. Sci. (USA) 81:3655-3659). Alterna¬ tively, the vaccinia 7.5K promoter may be used. (E.g.. see Mackett et al., 1982, Proc. Natl. Acad. Sci. (USA) 79:7415-7419; Mackett et al., 1984, J. Virol. 49:857-864; Panicali et al., 1982, Proc. Natl. Acad. Sci. 79:4927-4931). Specific initiation signals may also be required for efficient translation of inserted CIOO-R coding sequences. These signals include the ATG initiation codon and adjacent sequences. In cases where the entire C100-R gene, including its own initiation codon and adjacent sequences, is inserted into the appro¬ priate expression vector, no additional translational control signals may be needed. However, in cases where only a portion of the CIOO-R coding sequence is inserted, exogenous translational control signals, including the ATG initiation codon, must be provided. Furthermore, the initiation codon must be in phase with the reading frame of the C100-R coding sequence to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency of expression may be enhanced by the inclusion of appropriate transcription enhancer elements, transcription terminators, etc. (see Bitter et al., 1987, Methods in Enzymol. 153:516- 544) . In addition, a host cell strain may be chosen which modulates the expression of the inserted sequences, or modifies and processes the gene product in the specific fashion 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 charac¬ teristic and specific mechanisms for the post-transla¬ tional processing and modification of proteins. Appropriate cells lines or host systems can be chosen to ensure the correct modification and processing of the foreign protein expressed. To this end, eukary¬ otic host cells which possess the cellular machinery for proper processing of the primary transcript, glycosylation, and phosphorylation of the gene product may be used. Such mammalian host cells include but are not limited to CHO, VERO, BHK, HeLa, COS, MDCK, 293, WI38, etc. For long-term, high-yield production of recombi¬ nant proteins, stable expression is preferred. For example, cell lines which stably express the C100-R may be engineered. Rather than using expression vectors which contain viral origins of replication, host cells can be transformed with the C100-R DNA controlled by appropriate expression control elements (e.g.. promoter, enhancer, sequences, transcription terminators, polyadenylation sites, etc.), and a selectable marker. Following the introduction of foreign DNA, engineered cells may be allowed to grow for 1-2 days in an enriched media, and then are switched to a selective media. The selectable marker in the recombinant plasmid confers resistance to the selection and allows cells to stably integrate the plasmid into their chromosomes and grow to form foci which in turn can be cloned and expanded into cell lines. This method may advantageously be used to engineer cell lines which express the C100-R on the cell surface, and which respond to βAPP-ClOO mediated signal transduction. Such engineered cell lines are particularly useful in screening for BAPP-C100 analogs. A number of selection systems may be used, including but not limited to the herpes simplex virus thymidine kinase (Wigler, et al., 1977, Cell 11:223), hypoxanthine-guanine phosphoribosyltransferase (Szybalska & Szybalski, 1962, Proc. Natl. Acad. Sci. USA 48:2026), and adenine phosphoribosyltransferase (Lowy, et al., 1980, Cell 22:817) genes can be employed in tk " , hgprt" or aprt" cells, respectively. Also, antimetabolite resistance can be used as the basis of selection for dhfr, which confers resistance to methotrexate (Wigler, et al., 1980, Natl. Acad. Sci. USA 77:3567; O'Hare, et al., 1981, Proc. Natl. Aσad. Sci. USA 78:1527); gpt, which confers resistance to mycophenolic acid (Mulligan & Berg, 1981, Proc. Natl. Acad. Sci. USA 78:2072); neo, which confers resistance to the aminoglycoside G-418 (Colberre- Garapin, et al., 1981, J. Mol. Biol. 150:1); and hygro, which confers resistance to hygromycin (Santerre, et al., 1984, Gene 30:147) genes. Recently, additional selectable genes have been described, namely trpB, which allows cells to utilize indole in place of tryptophan; hisD, which allows cells to utilize histinol in place of histidine (Hartman & Mulligan, 1988, Proc. Natl. Acad. Sci. USA 85:8047); and ODC (ornithine decarboxylase) which confers resistance to the ornithine decarboxylase inhibitor, 2-(difluoromethyl)-DL-ornithine, DFMO (McConlogue L. , 1987, In: Current Communications in Molecular Biology, Cold Spring Harbor Laboratory ed.). 5.2.2. IDENTIFICATION OF TRANSFECTANTS OR TRANSFORMANTS THAT EXPRESS THE C100-R The host cells which contain the coding sequence and which express the biologically active gene product may be identified by at least four general approaches; (a) DNA-DNA or DNA-RNA hybridization; (b) the presence or absence of "marker" gene functions; (c) assessing the level of transcription as measured by the expres¬ sion of C100-R mRNA transcripts in the host cell; and (d) detection of the gene product as measured by immunoassay or by its biological activity. In the first approach, the presence of the C100-R coding sequence inserted in the expression vector can be detected by DNA-DNA or DNA-RNA hybridization using probes comprising nucleotide sequences that are homologous to the CIOO-R coding sequence, respectively, or portions or derivatives thereof. In the second approach, the recombinant expres¬ sion vector/host system can be identified and selected based upon the presence or absence of certain "marker" gene functions (e.g.. thymidine kinase activity, resistance to antibiotics, resistance to methotrexate, transformation phenotype, occlusion body formation in baculovirus, etc.). For example, if the CIOO-R coding sequence is inserted within a marker gene sequence of the vector, recombinants containing the ClOO-R coding sequence can be identified by the absence of the marker gene function. Alternatively, a marker gene can be placed in tandem with the C100-R sequence under the control of the same or different promoter used to control the expression of the C100-R coding sequence. Expression of the marker in response to induction or selection indicates expression of the CIOO-R coding sequence. In the third approach, transeriptional activity for the C100-R coding region can be assessed by hybridization assays. For example, RNA can be isolated and analyzed by Northern blot using a probe homologous to the CIOO-R coding sequence or particular portions thereof. Alternatively, total nucleic acids of the host cell may be extracted and assayed for hybridization to such probes. In the fourth approach, the expression of the C100-R protein product can be "assessed immunologically, for example by Western blots, immunoassays such as radioimmuno-precipitation, enzyme-linked immunoassays and the like. The ultimate test of the success of the expression system, however, involves the detection of the biologically active CIOO-R gene product. A number of assays can be used to detect receptor activity including but not limited to β-APP binding assays; and β-APP biological assays using engineered cell lines as the test substrate. 5.2.3. RECOVERY OF THE C100-R Once a clone that produces high levels of biolo¬ gically active C100-R is identified, the clone may be expanded and used to produce large amounts of the receptor which may be purified using techniques well- known in the art including, but not limited to immuno¬ affinity purification, chromatographic methods including high performance liquid chromatography, affinity chromatography using immobilized ligand such as β-APP-ClOO or analogs thereof bound to beads, immunoaffinity purification using antibodies and the like. Where the C100-R coding sequence is engineered to encode a cleavable fusion protein, purification may be readily accomplished using affinity purification tech¬ niques. For example, a collagenase cleavage recog¬ nition consensus sequence may be engineered between the carboxy terminus of C100-R and protein A. The resulting fusion protein may be readily purified using an IgG column that binds the protein A moiety. Unfused C100-R may be readily released from the column by treatment with collagenase. Another example would be the use of pGEX vectors that express foreign polypeptides as fusion proteins with glutathionine S- transferase (GST) . The fusion protein may be engi¬ neered with either thrombin or factor Xa cleavage sites between the cloned gene and the GST moiety. The fusion protein may be easily purified from cell extracts by adsorption to glutathione agarose beads followed by elution in the presence of glutathione. In this aspect of the invention, any cleavage site or enzyme cleavage substrate may be engineered between the ClOO-R sequence and a second peptide or protein that has a binding partner which could be used for purification, e.g.. any antigen for which an immuno¬ affinity column can be prepared. 5.3. GENERATION OF ANTIBODIES THAT DEFINE THE C100-R Various procedures known in the art may be used for the production of antibodies to epitopes of the recombinantly produced C100-R. Neutralizing antibodies i.e.. those which compete for the BAPP-CIOO binding site of the receptor are especially preferred for diagnostics and therapeutics. Such antibodies include but are not limited to polyclonal, monoclonal, chimeric, single chain. Fab fragments and fragments produced by an Fab expression library. For the production of antibodies, various host animals may be immunized by injection with the C100-R including but not limited to rabbits, mice, rats, etc. Various adjuvants may be used to increase the immuno¬ logical response, depending on the host species, including but not limited to Freund's (complete and incomplete) , mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin, dinitrophenol, and poten¬ tially useful human adjuvants such as BCG (bacille Calmette-Guerin) and Corynebacterium parvum. Monoclonal antibodies to C100-R may be prepared by using any technique which provides for the production of antibody molecules by continuous cell lines in culture. These inclu.de but are not limited to the hybridoma technique originally described by Kohler and Milstein, (Nature, 1975, 256:495-497), the human B-cell hybridoma technique (Kosbor et al., 1983, Immunology Today, 4:72; Cote et al., 1983, Proc. Natl. Acad. Sci., 80:2026-2030) and the EBV-hybridoma tech¬ nique (Cole et al., 1985, Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96). In addition, techniques developed for the production of "chimeric antibodies" (Morrison et al., 1984, Proc. Natl. Acad. Sci., 81:6851-6855; Neuberger et al., 1984, Nature, 312:604-608; Takeda et al., 1985, Nature, 314:452-454) by splicing the genes from a mouse antibody molecule of appropriate antigen specificity together with genes from a human antibody molecule of appropriate biological activity can be used. Antibody fragments which contain specific binding sites of C100-R may be generated by known techniques. For example, such fragments include but are not limited to: the F(ab') 2 fragments which can be produced by pepsin digestion of the antibody molecule and the Fab fragments which can be generated by reducing the disulfide bridges of the F(ab') 2 fragments. Alterna¬ tively, Fab expression libraries may be constructed (Huse et al., 1989, Science, 246:1275-1281) to allow rapid and easy identification of monoclonal Fab fragments with the desired specificity to CIOO-R. In a specific embodiment described herein, anti- C100-R peptide antibodies to two different epitopes of the predicted C100-R amino acid sequence were generated. The peptides SPAAPNKEATPPS (amino acids 212-223 Of C100-R; 1AB1) and NTDRQRKKSKMTDEE (amino acids 235-249 of C100-R; 2AB1R) were synthesized and injected into rabbits. The resulting polyclonal serum was immunoaffinity purified and the antibodies were used to probe immunoblots of human and rat brain homogenates (Figure 15A) . The two antibodies recognized a protein that migrated at a molecular weight of 61 kDA in both human and rat brain. Antibody 2AB1R cross-reacted with an - 80 kDa protein in rat brain. This 80 kDa protein may represent another member of the C100-R family, the product of yet-undiscovered alternatively spliced transcript from the C100-R gene, or an unrelated protein. Immunoabsorption of antibody 1AB1R with its cognate peptide (Figure 15B, lane 1) but not with the 2AB1R peptide (lane 2) abolished its immunoreactivity with the 61 kDa band; similarly, immunoabsorption of antibody 2AB1R with the 2AB1R peptide 9 lane 4) but not with the 1AB1R peptide (lane 5) abolished its specific staining of the 61 kDa protein. Immunoblots of tissue that had been fractionated into soluble and integral membrane components revealed that C100-R is a soluble protein. Synaptic plasma membrane fractions were prepared from human fetal brain tissue. Immunoblot analysis of the fractions showed the C100-R and APP are associated with (although neither is restricted to) synaptic plasma membranes (Figure 15C) , suggesting that C100-R like APP is present in the synaptic terminal (Koo et al., 1990 Proc. Natl. Acad. Sci. USA 87:1561-1565; Schubert et al. , 1991 Brain Res. 563: 184-194; Moya et al., 1994 Dev. Biol.l 171:597-603) . 5.4. ANTI-SENSE RNA AND RIBOZYMES Also within the scope of the invention are oligo- ribonucleotide sequences, that include anti-sense RNA and DNA molecules and ribozymes that function to inhibit the translation of C100-R mRNA. Anti-sense RNA and DNA molecules act to directly block the translation of mRNA by binding to targeted mRNA and preventing protein translation. In regard to antisense DNA, oligodeoxyribonucleotides derived from the translation initiation site, e.g.. between -10 and +10 regions of the C100-R nucleotide sequence, are preferred. Ribozymes are enzymatic RNA molecules capable of catalyzing the specific cleavage of RNA. The mecha¬ nism of ribozyme action involves sequence specific hybridization of the ribozyme molecule to complemen¬ tary target RNA, followed by a endonucleolytic cleav¬ age. Within the scope of the invention are engineered hammerhead motif ribozyme molecules that specifically and efficiently catalyze endonucleolytic cleavage of ClOO-R RNA sequences. Specific ribozyme cleavage sites within any potential RNA target are initially identified by scanning the target molecule for ribozyme cleavage sites which include the following sequences, GUA, GUU and GUC. Once identified, short RNA sequences of between 15 and 20 ribonucleotides corresponding to the region of the target gene containing the cleavage site may be evaluated for predicted structural features such as secondary structure that may render the oligo¬ nucleotide sequence unsuitable. The suitability of candidate targets may also be evaluated by testing their accessibility to hybridization with complemen¬ tary oiigonucleotides, using ribonuclease protection assays. Both anti-sense RNA and DNA molecules and ribozymes of the invention may be prepared by any method known in the art for the synthesis of RNA molecules. These include techniques for chemically synthesizing oligodeoxyribonucleotides well known in the art such as for example solid phase phosphoramidite chemical synthesis. Alternatively, RNA molecules may be generated by in vitro and in vivo transcription of DNA sequences encoding the antisense RNA molecule. Such DNA sequences may be incorporated into a wide variety of vectors which incorporate suitable RNA polymerase promoters such as the T7 or SP6 polymerase promoters. Alternatively, antisense cDNA constructs that synthesize antisense RNA constitutively or inducibly, depending on the promoter used, can be introduced stably into cell lines. Various modifications to the DNA molecules may be introduced as a means of increasing intracellular stability and half-life. Possible modifications include but are not limited to the addition of flanking sequences of ribo- or deoxy- nucleotides to the 5• and/or 3 ' ends of the molecule or the use of phosphorothioate or 2• O-methyl rather than phospho¬ diesterase linkages within the oligodeoxyribonucleo¬ tide backbone. 5.5. USES OF THE C100-R, DNA AND ENGINEERED CELL LINES The C100-R DNA, antisense oiigonucleotides and ribozymes, APP-R expression products, antibodies and engineered cell lines described above have a number of uses for the diagnosis and treatment of Alzheimer's Disease. For example, the C100-R DNA sequence may be used in hybridization assays of biopsies or autopsies to diagnose abnormalities of C100-R expression; e.g.. Southern or Northern analysis, including in situ hybridization assays. In therapeutic applications, antisense or ribozyme molecules designed on the basis of the C100-R DNA sequence may be utilized to block transcription and expression of the C100-R gene product. Alternatively, the C100-R DNA could be used in gene therapy approach to introduce the normal recombinant gene into the defective cells of an individual or to correct an endogenous mutation in order to reconstitute the C100-R and its function. In another embodiment of the invention, anti¬ bodies specific for the C100-R may be used to determine the pattern of receptor expression in biopsy tissue, or for diagnostic imaging in vivo; in such applications, "neutralizing" antibodies may be preferred. For example, an antibody conjugated to an imaging compound could be administered to a patient to "map" the locations and distribution of the C100-R in vivo. In another embodiment of the invention, the APP-R itself, or a fragment containing its BAPP-CIOO binding site, could be administered in vivo. The free C100-R or the peptide fragment could competitively bind to β- APP and inhibit its interaction with the native receptor in vivo. In yet another embodiment of the invention, the engineered cell lines which express the entire C100-R or its ligand binding domain may be utilized to screen and identify active / 8APP-C100 agonists or antagonists. Alternatively, cell lines that endogenously express the C100-R may be used for this purpose; e.g.. neuroblastoma cell lines such as SK-N-MC as exemplified herein may be used. /SAPP-derived peptides, other peptides, synthetic compounds, natural products, and other sources of potentially biologically active materials can be screened in the following manners. The ability of a test compound to inhibit the binding of SAPP-CIOO (which can be labelled e.g.. with 35 Met or a "flag" sequence or detected with antibodies to the peptide) to the C100- R, and thus its potential to act as either agonists or antagonists may be measured. As a source of the receptor either whole ClOO-R-expressing cells homogenates, or subcellular fractions may be used. The binding may be measured using standard receptor binding techniques, such as those described in Section 6.1.3. The ability, of agents to prevent, or mimic, the effects of /SAPP-C100 on signal transduction responses in the ClOO-R-expressing cells may be measured. For example, responses such as changes in cytosolic concentrations of calcium, activation of specific protein kinases, altered secretion of hormones or neurotransmitters, modulation of second messenger production, or changes in cellular metabolism may be monitored. These assays may be performed in whole cells or membrane preparations using conventional techniques developed for these purposes. In engineered cells or cell lines that respond to the toxic effects /8APP-C100, the ability of substances to induce or prevent the toxicity may be measured. Toxicity may be monitored as described in the literature (Yankner et al., 1989, Science 245:417- 420), or by other established techniques. Transgenic animals that contain the C100-R DNA as the transgene may be engineered to determine the in vivo effects of the /SAPP-CIOO agonists or antagonists found in the above or other screens, or to profile other agents that are potentially therapeutic for Alzheimer's Disease. Recently, computer generated models for ligand- receptor interactions have been developed, and in a specific embodiment of the invention, information derived from computer modeling of C100-R may be used for design of receptor agonist or antagonist. Changes made to C100-R sequences, using for example techniques for site directed mutagenesis, and expression of mutant receptors in cell lines may be used to further define the functional role of particular receptor regions and residues. In an embodiment of the invention the C100-R and/or cell lines that express the C100-R may be used to screen for antibodies, peptides, organic molecules or other ligands that act as agonists or antagonists of neuronal signal transduction mediated by C100-R. For example, anti-ClOO-R antibodies capable of neutralizing the activity of /SAPP-CIOO, may be used to inhibit C100-R function. Alternatively, screening of peptide libraries or organic compounds with recombinantly expressed soluble C100-R protein or cell lines expressing CIOO-R protein may be useful for identification of therapeutic molecules that function by inhibiting the biological activity of C100-R. In an embodiment of the invention, engineered cell lines which express the entire C100-R coding region or its ligand binding domain may be utilized to screen and identify /SAPP-CIOO agonists or antagonists. Synthetic compounds, natural products, and other sources of potentially biologically active materials can be screened in a number of ways. The ability of a test compound to inhibit binding of /SAPP-CIOO to C100- R may be measured using standard receptor binding techniques, such as those described in Section 5.3.2. The ability of agents to prevent the /SAPP signal transduction response resulting from /SAPP-CIOO binding to CIOO-R may be measured. For example, responses such as activation of C100-R kinase activity, modulation of second messenger production or changes in cellular metabolism may be monitored. These assays may be performed using conventional techniques developed for these purposes. The ability of a test compound to modulate signal transduction through the C100-R system may also be measured in vivo . The ability of agents to prevent the effect of /3APP-C100 binding on signal transduction responses of ClOO-R expressing cells may be measured. For example, responses such as inhibition of neurotoxicity or decrease in accumulation of deposit¬ like structures resulting in formation of amyloid-like fibrils may be assayed. 5.5.1. SCREENING OF PEPTIDE LIBRARY WITH C100-R PROTEIN OR ENGINEERED CELL LINES Random peptide libraries consisting of all possible combinations of amino acids attached to a solid phase support may be used to identify peptides that are able to bind to the ligand binding site of a given receptor or other functional domains of a receptor such as kinase domains (Lam, K.S. et al., 1991, Nature 354: 82-84). The screening of peptide libraries may have therapeutic value in the discovery of pharmaceutical agents that act to inhibit the biological activity of ClOO-R receptor through their interaction with the receptor. Identification of molecules that are able to bind to the C100-R may be accomplished by screening a peptide library with recombinant soluble CIOO-R protein. Methods for expression and purification of C100-R are described in Section 5.2.1 and may be used to express recombinant full length CIOO-R or fragments of ClOO-R depending on the functional domains of interest. For example, the kinase and /SAPP-CIOO ligand binding domains of the CIOO-R may be separately expressed and used to screen peptide libraries. To identify and isolate the peptide/solid phase support that interacts and forms a complex with C100- R, it is necessary to label or "tag" the CIOO-R molecule. The C100-R protein may be conjugated to enzymes such as alkaline phosphatase or horseradish peroxidase or to other reagents such as fluorescent labels which may include fluorescein isothyiocynate (FITC) , phycoerythrin (PE) or rhodamine. Conjugation of any given label, to ClOO-R, may be performed using techniques that are routine in the art. Alternatively, CIOO-R expression vectors may be engineered to express a chimeric ClOO-R protein containing an epitope for which a commercially available antibody exist. The epitope specific antibody may be tagged using methods well known in the art including labeling with enzymes, fluorescent dyes or colored or magnetic beads. The "tagged" C100-R conjugate is incubated with the random peptide library for 30 minutes to one hour at 22°C to allow complex formation between and peptide species within the library. The library is then washed to remove any unbound C100-R protein. If C100- R has been conjugated to alkaline phosphatase or horseradish peroxidase the whole library is poured into a petri dish containing a substrates for either alkaline phosphatase or peroxidase, for example, 5- bromo-4-chloro-3-indoyl phosphate (BCIP) or 3,3 ',4,4'- diaminobenzidine (DAB) , respectively. After incubating for several minutes, the peptide/solid phase-ClOO-R complex changes color, and can be easily identified and isolated physically under a dissecting microscope with a raicromanipulator. If a fluorescent tagged C100-R molecule has been used, complexes may be isolated by fluorescent activated sorting. If a chimeric C100-R protein expressing a heterologous epitope has been used, detection of the peptide/ClOO-R complex may be accomplished by using a labeled epitope specific antibody. Once isolated, the identity of the peptide attached to the solid phase support may be determined by peptide sequencing. In addition to using soluble C100-R molecules, in another embodiment, it is possible to detect peptides that bind to the receptor using intact cells. The use of intact cells is preferred for use with receptors that are multi-subunits or labile or with receptors that require the lipid domain of the cell membrane to be functional. Methods for generating cell lines expressing C100-R are described in Sections 5.2.1. and 5.2.2. The cells used in this technique may be either live or fixed cells. The cells will be incubated with the random peptide library and will bind to certain peptides in the library to form a "rosette" between the target cells and the relevant solid phase support/peptide. The rosette can thereafter be isolated by differential centrifugation or removed physically under a dissecting microscope. As an alternative to whole cell assays for membrane bound receptors or receptors that require the lipid domain of the cell membrane to be functional, the receptor molecules can be reconstituted into liposomes where label or "tag" can be attached. 5.5.2. SCREENING OF ORGANIC COMPOUNDS WITH CIOO-R PROTEIN OR ENGINEERED CELL LINES Cell lines that express CIOO-R may be used to screen for molecules that modulate CIOO-R activity or CIOO-R mediated signal transduction. Such molecules may include small organic or inorganic compounds, or other molecules that modulate C100-R activity or that promote or prevent the formation of /SAPP-CIOO/CIOO-R complex. Synthetic compounds, natural products, and other sources of potentially biologically active materials can be screened in a number of ways. The ability of a test molecule to interfere with /3APP-C100/C100-R binding and/or C100-R signal transduction may be measured using standard biochemical techniques. Other responses such as activation or suppression of catalytic activity, phosphorylation or dephosphorylation of other proteins, activation or modulation of second messenger production, changes in cellular ion levels, association, dissociation or translocation of signalling molecules, or transcription or translation of specific genes may also be monitored. These assays may be performed using conventional techniques developed for these purposes in the course of screening. Ligand binding to its cellular receptor may, via signal transduction pathways, affect a variety of cellular processes. Cellular processes under the control of the /SAPP C100/C100-R signalling pathway may include, but are not limited to, normal cellular functions, proliferation, differentiation, maintenance of cell shape, and adhesion, in addition to abnormal or potentially deleterious processes such as axonal degeneration, unregulated cell proliferation, loss of contact inhibition, blocking of differentiation or cell death. The qualitative or quantitative observation and measurement of any of the described cellular processes by techniques known in the art may be advantageously used as a means of scoring for signal transduction in the course of screening. Various embodiments are described below for screening, identification and evaluation of compounds that interact with the C100-R receptor, which compounds may affect various cellular processes under the control of the CIOO-R receptor signalling pathway. The present invention includes a method for identifying a compound which is capable of modulating signal transduction, comprising: (a) contacting the compound with CIOO-R, or a functional derivative thereof, in pure or semi-pure form, in a membrane preparation, or in a whole live or fixed cell; (b) incubating the mixture of step (a) in the presence of /SAPP-CIOO, for an interval sufficient for the compound to stimulate or inhibit the signal transduction; (c) measuring the signal transduction; (d) comparing the signal transduction activity to that of C100-R, incubated without the compound, thereby determining whether the compound stimulates or inhibits signal C100- R mediated transduction. CIOO-R, or functional derivatives thereof, useful in identifying compounds capable of modulating signal transduction may have, for example, amino acid deletions and/or insertions and/or substitutions as long as they retain significant signal transducing capacity. A functional derivative of CIOO-R may be prepared from a naturally occurring or recombinantly expressed C100-R by proteolytic cleavage followed by conventional purification procedures known to those skilled in the art. Alternatively, the functional derivative may be produced by recombinant DNA technology by expressing parts of C100-R which include the functional domain in suitable cells. Functional derivatives may also be chemically synthesized. Cells expressing C100-R may be used as a source of C100-R, crude or purified, or in a membrane preparation, for testing in these assays. Alternatively, whole live or fixed cells may be used directly in those assays. C100-R signal transduction activity may be measured by standard biochemical techniques or by monitoring the cellular processes controlled by the signal. To assess modulation of kinase activity, the test molecule is added to a reaction mixture containing C100-R and a substrate test. To assess modulation of kinase activity of the C100-R receptor, the test molecule is added to a reaction mixture containing the CIOO-R. The kinase reaction is then initiated with the addition of /SAPP-CIOO and ATP. An immunoassay is performed on the kinase reaction to detect the presence or absence of the phosphorylated tyrosine residues on the substrate or to detect phosphorylated tyrosine residues on autophosphorylated C100-R, and results are compared to those obtained for controls i.e.. reaction mixtures not exposed to the test molecule. The invention also includes a method whereby a molecule capable of binding to C100-R in a chemical or biological preparation may be identified comprising: (a) immobilizing C100-R, or functional fragments thereof, to a solid phase matrix; (b) contacting the chemical or biological preparation with the solid phase matrix produced in step (a) , for an interval sufficient to allow the compound to bind; (c) washing away any unbound material from the solid phase matrix; (d) detecting the presence of the compound bound to the solid phase, thereby identifying the compound. The above method may further include the step of: (e) eluting the bound compound from the solid phase matrix, thereby isolating the compound. The term "compound capable of binding to CIOO-R" refers to a naturally occurring or synthetically produced molecule which interacts with CIOO-R. Such a compound may directly or indirectly modulate CIOO-R signal transduction and may include molecules that are natively associated with the functional domains of ClOO-R. Examples of such compounds are (i) a natural substrate of CIOO-R; (ii) a naturally occurring molecule which is part of the signalling complex; and/or a naturally occurring signalling molecule produced by other cell types. 5.6. USE OF C100-R OR LIGANDS Receptor/ligand interaction between C100-R and SAPP-CIOO is believed to play an important role in the signalling system during neuronal signal transduction. Expression of /8APP-C100 peptide in primate cells results in production and accumulation of deposit-like structures that result in formation of amyloid structures indicating a role /3APP-C100 in development of neurodengeration in Alzheimer's disease. In one embodiment of the invention, ligands for C100-R, the C100-R itself, or a fragment containing its /SAPP-CIOO binding site, could be administered in vivo to modulate neuronal signal transduction. For example, administration of the C100-R or a fragment containing the / 3APP-C100 binding site, could competitively bind to /3APP-C100 and inhibit its interaction with the native C100-R An vivo to inhibit signal transduction. Alternatively, ligandε for C100- R, including anti-ClOO-R antibodies or fragments thereof, may be used to modulate signal transduction. Antagonists of /8APP-C100 activity may be used to inhibit the development of Alzheimer's disease. The particular peptides, proteins, organic compounds or antibodies that modulate C100-R signal transduction can be administered to a patient either by itself, or in pharmaceutical compositions where it is mixed with suitable carriers or excipient(s) . These agents may be formulated and administered systemically or locally. Techniques for formulation and administration may be found in "Remington's Pharmaceutical Sciences," Mack Publishing Co., Easton, PA, latest edition. Suitable routes may, for example, include oral, rectal, transmucosal, or intestinal administration; parenteral delivery, including intramuscular, subcutaneous, intramedullary injections, as well as intrathecal, direct intraventricular, intravenous, intraperitoneal, intranasal, intraocular injections or intranasal. For injection, the agents of the invention may be formulated in aqueous solutions, preferably in physiologically compatible buffers such as Hanks's solution. Ringer's solution, or physiological saline buffer. For transmucosal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art. The compounds can be formulated readily using pharmaceutically acceptable carriers well known in the art into dosages suitable for *oral administration. Such carriers enable the compounds of the invention to be formulated as tablets, pills, capsules, liquids. gels, syrups, slurries, suspensions and the like, for oral ingestion by a patient to be treated. Pharmaceutical compositions suitable for use in the present invention include compositions wherein the active ingredients are contained in an effective amount to achieve its intended purpose. Determination of the effective amounts is well within the capability of those skilled in the art, especially in light of the detailed disclosure provided herein. In addition to the active ingredients these pharmaceutical compositions may contain suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically. The preparations formulated for oral administration may be in the form of tablets, dragees, capsules, or solutions. The pharmaceutical compositions of the present invention may be manufactured in a manner that is itself known, e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping or lyophilizing processes. Pharmaceutical formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form. Additionally, suspensions of the active compounds may be prepared as appropriate oily injection suspensions. Suitable lipophilic solvents or vehicles include fatty oils such as sesame oil, or synthetic fatty acid esters, such as ethyl oleate or triglycerides, or liposomes. Aqueous injection suspensions may contain substances which increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol, or dextran. Optionally, the suspension may also contain suitable stabilizers or agents which increase the solubility of the compounds to allow for the preparation of highly concentrated solutions. Pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipient, optionally grinding a resulting mixture, and processing the mixture of granules, after adding suitable auxiliaries, if desired, to obtain tablets or dragee cores. Suitable excipients are, in particular, fillers such as sugars, including lactose, sucrose, mannitol, or sorbitol; cellulose preparations such as, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, gum tragacanth, methyl cellulose, hydroxypropylmethyl-cellulose, sodium carboxymethylcellulose, and/or polyvinylpyrrolidone (PVP) . If desired, disintegrating agents may be added, such as the cross-linked polyvinyl pyrrolidone, agar, or alginic acid or a salt thereof such as sodium alginate. Dragee cores are provided with suitable coatings. For this purpose, concentrated sugar solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dyestuffs or pigments may be added to the tablets or dragee coatings for identification or to characterize different combinations of active compound doses. Pharmaceutical preparations which can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a plasticizer, such as glycerol or sorbitol. The push-fit capsules can contain the active ingredients in admixture with filler such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds may be dissolved or suspended in suitable liquids, such as fatty oils. liquid paraffin, or liquid polyethylene glycols. In addition, stabilizers may be added. Compositions comprising a compound of the invention formulated in a compatible pharmaceutical carrier may be prepared, placed in an appropriate container, and labelled for treatment of an indicated condition. Suitable conditions indicated on the label may include treatment of a tumor, such as a glioma or glioblastoma; and inhibition of angiogenesis. Alternatively, other delivery systems for hydrophobic pharmaceutical compounds may be employed. Liposomes and emulsions are well known examples of delivery vehicles or carriers for hydrophobic drugs. Certain organic solvents such as DMSO also may be employed, although usually at the cost of greater toxicity. The pharmaceutical compositions also may comprise suitable solid or gel phase carriers or excipients. Examples of such carriers or excipients include but are not limited to calcium carbonate, calcium phosphate, various sugars, starches, cellulose derivatives, gelatin, and polymers such as polyethylene glycols. Many of the C100-R modulating compounds of the invention may be provided as salts with pharmaceutically compatible counterions. Pharmaceutically compatible salts may be formed with many acids, including but not limited to hydrochloric, sulfuric, acetic, lactic, tartaric, malic, succinic, etc. Salts tend to be more soluble in aqueous or other protonic solvents that are the corresponding free base forms. For any compound used in the method of the invention, the therapeutically effective dose can be estimated initially from cell "culture assays. For example, a dose can be formulated in animal models to achieve a circulating concentration range that includes the IC50 as determined in cell culture (i.e.. the concentration of the test compound which achieves a half-maximal inhibition of the neuronal signal transduction activity) . Such information can be used to more accurately determine useful doses in humans. A therapeutically effective dose refers to that amount of the compound that results in amelioration of symptoms of Alzheimers Disease or a prolongation of survival in a patient. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g.. for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population) . The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. Compounds which exhibit large therapeutic indices are preferred. The data obtained from these cell culture assays and animal studies can be used in formulating a range of dosage for use in human. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. The exact formulation, route of administration and dosage can be chosen by the individual physician in view of the patient's condition. (See e.g. Fingl et al., 1975, in "The Pharmacological Basis of Therapeutics", Ch. 1 pl) . Dosage amount and interval may be adjusted individually to provide plasma levels of the active moiety which are sufficient to maintain the C100-R inhibitory effects. Alternately, one may administer the compound in a local rather than systemic manner, for example, via injection of the compound directly into neural tissue, often in a depot or sustained release formulation. Furthermore, one may administer the drug in a targeted drug delivery system, for example, in a liposome coated with a neuronal specific antibody. In such a case the liposomes will be targeted to and taken up selectively by the neuronal tissue. In cases of local administration or selective uptake, the effective local concentration of the drug may not be related to plasma concentration. 6. EXAMPLES The subsection below describes the initial characterization of an APP binding protein expressed on neuronally derived cells and the cloning and sequencing of a complementary DNA representing part of the rat C100-R. The deduced amino acid sequence of C100-R reveals several motifs shared in common between "B" type calcium channels, Ryanodine calcium channels, calreticulin and protein Serine/Threonine Kinases. 6.1. MATERIAL AND METHODS 6.1.1. IN VITRO TRANSLATION OF FLAG-gAPP-ClOO The following "flag" sequence-containing oligonucleotide was synthesized and inserted into pGEM7, ACC ATG GAC TAC AAA GAC GAT GAC GAT AAA TCG AT MET ASP TYR LYS ASP ASP ASP ASP LYS SER. (Immunex; Prickett et al. 1989 BioTechniques 7:580). In addition, prior to the MET codon, the ACC triplet gives a consensus sequence for eucaryotic translation start and the Clal site after the flag sequence was added for cloning as was Hindlll linker at the five prime end of the oligio. The pGEM7 flag construct was cut with Smal and Clal and the Clal site was filled in. The Bgll/Smal fragment from / SAPP-695 was cloned into this construct. Clones with the proper orientation were selected. This recombinant was utilized to make 35 S-/8APP-C100 peptide in two ways. First, in the coupled transcription/translation system, TNT Coupled Reticulocyte Lysate System (Promega Corp.). Closed circular plasmid DNA was added to the lysate along with 3S S-methionine (6 μC following the recommended procedure. Second, in uncoupled reactions, the recombinant was linearized with Spe I, and 5 μg DNA was utilized to produce RNA in vitro («20-30μg) following the manufacturer's protocol (Promega Corp.). 1-5 μg of this RNA was translated in either a wheat germ or rabbit reticulocyte translation system according to manufac¬ turer's protocol (Promega Corp.). The in vitro translations either had one-tenth volume of 100 mM N- acetyl glucosamine (Sigma) added, and were aliquotted and frozen at -80°C, and dialyzed prior to use; were aliquotted and frozen directly, then dialyzed and spin column purified prior to use (Boehringer-Mannheim) ; or were affinity purified using the commercially avail¬ able Flag Anti-body (CA ++ -dependent binding Ml Ab, IBI) coupled to Affigel 10 (Biorad) . Affinity chroma¬ tography was accomplished by passing the in vitro translations over the Affigel lθ-coupled Ml antibody column (1 ml bed volume) equilibrated in PBS (120 mM NaCl, 2.7 mM KCI, 10 mM phosphate buffer, pH 7.4) with 0.5 mM CaCl 2 . After thorough washing (5-10 column volumes) , the peptide waε eluted from the column with PBS with Na 2 EDTA (2 mM) . The peptide eluted as a sharp 0.7 ml peak. EDTA was removed by dialysiε for uεe in binding or autoradiography. The flag-/3APP-C100 construct was sequenced and the product peptide from the in vitro translation analyzed for amino acid composition by mass spectroscopic techniques to confirm its identity. 6.1.2. CELL CULTURE PC12 cells (ATCC) for the binding assays were grown in RPMI1640 supplemented with 10% heat-inacti¬ vated horse serum and 5% fetal bovine serum. T-175 flasks were seeded with 5 x 10 5 cells/ml in 60 ml of growth medium containing 10 ng/ml NGF. An additional 60 ml of this medium were added every 2 days until the cells were harveεted (usually at 6 days) . Where indicated, PC12 cells were cultured as above except in the absence of NGF. Cells were collected by centrifu¬ gation at 138 X g for 8 minutes. The supernatant waε discarded and the pellet resuspended in 5 ml of the growth medium. The cells were triturated 3 times through a 23g needle attached to a 10 cc syringe to provide a single cell suspension or, at most, small cell aggregates. Trypan blue dye exclusion indicated that over 99% of the cellε were viable. SK-N-MC cells (ATCC) were grown in DME supplemented with 10% calf serum. The SK-N-MC cells were cultured as described for PC-12 cells except NGF is not included. 6.1.3. BINDING TO CELLS For /3APP-C100 binding experiments, PC-12 or SK-N- MC cells grown and prepared as described above, were counted, collected by low speed centrifugation (138xg) , and resuspended in phosphate-buffered saline (PBS, pH 7.4) with 1% BSA and 1% glucose (PBG). An 0.08 ml volume of the cell suεpension, containing 2 x 10* cellε, was mixed with 0.01 ml of 35 S-/SAPP-C100 and 0.01 ml of PBG, or PBG containing either unlabeled /8APP-C100 or its vehicle. For kinetic and inhibition experiments, the concentration of 35 S-/SAPP-C100 was either 25 pM or 50 pM. For saturation experiments, the ligand concentration ranged from 15 pM to 6 nM. The mixture was incubated at 4 > °C for 3 hours, unless otherwise indicated. At the end of the incubation period, the cells were pelleted by centrifugation at 138 X g for 90 sec, the supernatant (containing the unbound ligand) was removed, and 0.2 ml of fresh, ice- cold PBG was added. The cells and fresh buffer were briefly agitated, and again centrifuged and suspended in fresh, ice-cold buffer as above. Finally, the cells were pelleted by centrifugation, filtered through BSA (0.1%) treated filters and washed with 4 1-ml rinses of ice-cold PBS with 0.1% BSA. The duration of the period between resuspension of the cellε in fresh, ice-cold buffer and filtration of the cells was less than 10 min. In the dissociation experiments, and to collect a sample of bound ligand, the cells were incubated in the buffer added as the second wash for up to 3 hours to allow the bound ligand to disεociate. The cells were then pelleted by centrifugation and the supernatant (containing the bound ligand that had dissociated) was removed. The cells were then rewashed and harvested as described above. Radioactivity retained by filters was measured by scintillation counting. Nonspecific binding was taken as that occurring in the presence of excess (3.2 nM to 18 nM) /3APP-C100. Saturation data were analyzed by computer using commercially available software. The binding model that best fitted the experimental data was determined by F-test (p<.05). 6.1.4. BINDING AUTORADIOGRAPHY Sprague-Dawley rats were sacrificed by hyper- capnia and placed on ice until their brains could be removed (lesε than an hour) . The brainε were rapidly frozen in isopentane chilled to -20°C with dry ice and either used immediately or stored at -80°C until use. The brains were affixed to the specimen holder of a cryostat and 25 μM coronal sections were collected onto gelatin-coated microscope slides. The sections were either frozen overnight at -80°C or used imme¬ diately. The sections were air-dried at 4°C and then preincubated with the binding buffer (PBS, 1% BSA) for 30 minutes at 4°C. This buffer was replaced by fresh buffer containing either the ligand alone ( 35 S- / 8APP- C100, O.OlnM) or the ligand with up to a 10-fold excess of unlabeled / 3APP-C100 or its vehicle. The incubation was continued for 3 h at 4°C. The ligand- containing buffer was then removed and the sections were washed twice with fresh buffer (15 min. and 1 min., 4°C). The sectionε were then dipped into ice cold diεtilled water 10 times and dried under a stream of air at room temperature. The sectionε were then apposed to a εheet of X-ray film for a period of 1 to 14 dayε and the film developed. Some sections were stained with Cresyl violet for identification of brain region. The optical densitieε of regionε of the autoradiographε were determined quantitatively using an image analysis system. 6.1.5. SCREENING FOR THE C100-R cDNA BY EXPRESSION CLONING cDNA was constructed from embryonic day 18 rat brain mRNA according to the protocol of Neve et al. (1986; delineated in detail by Klickstein and Neve in Current Protocols in Molecular Biology) . λgtll libraries (rat brain cDNA library, RL Neve; human brain cDNA library, Clontech) were plated on Y1090 Ej_ coli cells at 150,000 pfu/150mm plate. Plates were incubated at 42°C for 3 h, at which time plaques were just visible. Plates were overlaid with Schleicher and Schuell 132 mm nitrocellulose filters which had been saturated with 10 mM IPTG (isopropyl-i3.D- thiogalactoside) and slightly air dried. Plates were set at 37°C for 3 hours, and the first filter removed and placed in TBS (50 mM Tris, pH 7.7, 150 mM NaCl). A second, duplicate IPTG-soaked nitrocellulose filter was placed on the plate surface and left for two hours. The second filter was removed and placed in TBS. The filters were allowed to sit in TBS without blocking agent for at least 12 hours and up to four days to allow refolding. Filters were blocked in TBS with 5% nonfat skimmed milk for periods ranging from 2 h to overnight. Filters were washed in binding buffer (50 m Tris-HCl, Ph 7.7, 50 mM NaCl, 2 mM MgCl 2 , ImM Dithiothreitol) . Filters were incubated with in vitro translated 3J S-/8APP-C100 at 3 nM for two hours at 4°C. Three 3 minutes washes (4°C) were used to remove non- bound labeled peptide: (i) binding buffer alone, (ii) binding buffer + 0.1% NP40, and (iii) binding buffer. Filters were immediately removed from the wash and air dried. The processed filters were exposed to X-OMAT RP film with a screen at -70°C for 6 days to two weeks. It was found that wet plates were necessary to get sufficient protein/plaque to get significant signal. Also, throughout the procedure it was necessary to plate many more phage than routinely required at the comparable stage of purification for nucleic acid probes. Even when a "plaque"-pure phage population containing the /SAPP-CIOO binding protein site was plated as described above, only a low percentage of the plaques bound to the /3APP-C100, possibly due to the requirement of proper folding for binding. Duplicate filters were compared to identify plaques expressing protein which bound to the 35 S-/3APP- C100. Positive plaques were picked and taken through further rounds of binding and purification. Six rounds of isolation were required to obtain a single positive clone from a rat brain cDNA library. This rat clone is designated λABlR. Five rounds of isola¬ tion were required to isolate five poεitive clones from a human brain cDNA library. The insert from λABlR was subcloned by PCR amplification using λgtll sequencing primers which include restriction enzyme sites (Sal I and Not I) . The amplified fragment was purified, cut with the restriction enzymes aε per manufacturer'ε specifica- tions and subcloned into Sall/Notl-cut Bluescript (SK+, Stratagene) . The rat subclone was designated pABlR-rat. This clone was subsequently used to screen additional rat brain cDNA libraries to isolate full length ClOO-R. A second cloning strategy was developed utilizing the commercially available antibody to the "flag" tag. Libraries were plated, filter lifts produced, processed, probed and washed as described above with the exception that the /SAPP-CIOO was not labeled with 35 S-methionine. Filters were cross-linked in a Stratalinker cross-linker (Stratagene) and blocked by 2 h incubation in TBS with 5% nonfat milk. The filters were then probed with a commercial anti-flag antibody at 10 μg/ml (M2, IBI) in TBS. Excess anti¬ body was removed by three 10 minute washes in TBS (4°C) , with the middle wash solution supplemented with 0.1% NP40. Filterε were incubated with a εecond antibody, goat anti-mouse IgG (heavy and light chain) biotin conjugate (NEN) in the same manner as with the first antibody. After washing, the filters were incubated with [ m I]-Avidin (NEN) at 0.5 μC,/ml in binding buffer as above. The last three washeε were in TBS with the middle waεh including 0.1% NP40. Filterε were air dried, and expoεed to XOMAT-RP film with εcreen at -70°C for 6 d to three weeks. Autora¬ diographs of the filters were compared for duplicates. Positive plaques were picked and carried through further rounds of screening. Phage containing the human cognate of the /SAPP- CIOO binding protein were cloned by both the direct binding method and the flag-antibody method. These cDNAs have been subcloned and "are being sequenced. 6.1.6. CDNA CHARACTERIZATION cDNAs were either subcloned into high copy plasmid vectors and transformed into bacteria or were amplified directly from the phage recombinants by the polymerase chain reaction. In the former case, double-stranded miniprep DNA was sequenced using Sequenase (U.S. Biochemicals) ; in the latter case, the PCR products were purified and sequenced with the femtomole sequencing system (Promega) . Sequencing of the clones was done by standard dideoxy methodology (Sequenase; USBiochem) . Computer analysiε was done primarily with GenePro (Riverside Scientific Enterprises) and PCGene (Intelligenics) . Southern tranεferε of human DNA or rat DNA (PC12) were probed with a 32 P-labeled 260 bp fragment (EcoRI/Scal) representing the 5' end of the AB1R cDNA. 8 μg of DNA was cut with various restriction enzymes, run on a 0.8% agarose gel, and transferred to nylon or nitrocellulose. Northern analysis was carried out on total cellular RNA isolated with the guanidinium thiocyanate method (Chirgwin et al. 1979 Biochemistry 18 5294) . Glyoxal gels, formaldehyde-agarose gels and dot blots were utilized to quantitate and evaluate the RNA under different conditions and from different sources (Tanzi et al., 1987, Science 235:880-884; Tanzi et al., 1988, Nature 331:528-530). RNA from PC12 cells treated with nerve growth factor for various periods of time, RNA from brains of patients with Alzheimer's Disease and Down's Syndrome, RNA from brain subregions, RNA from various developmental stages, etc. was run. Samples from AD or Downs brains were attained from the Children's Hospital (Boston) Pathology Dept. and from the McLean Hospital Brain Tissue Resource. A lysogen of the 1985 bp AB1R cDNA in λgtll was constructed in Y1089 by infecting Y1089 bacteria with the recombinant phage at a moi of 10,000:1, and identifying temperature sensitive clones from the unlysed bacteria. The lyεogen was induced with heat and IPTG, and the resultant cell lysate resuspended in Laemmil gel sample buffer. A portion of the sample was eiectrophoresed on 10% PAGE, transferred to nitrocellulose, and incubated in successively more dilute concentrations of urea in PBS-Triton-X at 4°C over two days after the method of Kageyama and Pastan (1989, Cell 59:815). Binding to 35 S-/SAPP-C100 was then carried out according to the protocol used for isolating the AB1R clone from the cDNA libraries, with the change that PBS instead of TBS was used. The cDNA insert from λABlR was subcloned into the mammalian expresεion vector pCDNAl in the antisenεe orientation, and PC12 cellε were tranεfected by electroporation. These transient cells were grown in DME media for 3 d, treated with NGF and tested for their ability to bind 35 S-labeled /SAPP-CIOO. Stable transfectant cells were selected for by the inclusion of G418 in the media and neomycin resistant cells were subsequently tested in the binding assay for their ability to bind the labeled /SAPP-CIOO after treatment with NGF. 6.1.7. IN SITU HYBRIDIZATION USING /3APP-C100 BINDING PROTEIN PROBE Hybridization probes were prepared by labeling the pABlR-rat construct linearized at various restriction sites. Anti-sense RNA probes were made from the plasmid template linearized at the Ncol site utilizing the T3 promoter of Bluescript, and sense- control RNA probes were made from the plasmid linearized at the BamHI site utilizing the T7 promoter of Bluescript. Probes were made in various ways. In vitro transcription was used to produce RNA probes. RNA was labeled With either 3S S,-UTP (Promega reagents) or Digoxigenin-UTP (Boehringer-Mannhei reagents) . Digoxigenin-labeled DNA probes were produced by PCR (Lanzillo, 1991; M. McKenna and J. Carlson, personal communication) ; PCR primers were made to produce the appropriate fragments (Genosyε Biotechnologieε, Inc.). Sectionε for in situ hybridization were prepared in the same manner as for binding autoradiography, only using RNAse free conditions. Prior to hybrid¬ ization, the sectionε were given two 3m washes with phosphate buffer (0.1 M) containing glycine (0.75 g/ml) followed by two 15 m washes with phosphate buffer alone. They were then treated with proteinase K^ (1 μg/ml in 15 mM Tris-HCl, pH 7.5 and 15 mM EDTA) for 30 m at 37°C and washed with acetic acid anhydride (0.25% in 0.1 M triethanolamine, pH 7.5) for 10 m. This was followed by two 15 washes with SSC (0.15 M NaCl, 0.015 M sodium citrate, pH 7.0) at twice its normal concentration (2X) , defatting with EtOH and chloroform, and air drying. The hybridization probe, prepared as described above, was then placed onto the sectionε in a εolution containing 50% formamide, 20X Denhardt's reagent, 300 μg/ml single stranded DNA, 150 μg/ml tRNA, 20 mM /S-mercaptoethanol (BME) , and 2X SSC. Coverslipε were placed over the sections and hybrid¬ ization solution and sealed to the slides with rubber cement. The hybridization was carried out overnight at 60°C. The coverslips were then removed and the sectionε were washed twice for 30 m at 60°C with 4X SSC supplemented with 300 mM BME. Following this, they were treated with RNAse (20μg/ml in 2X SSC, 20 m BME) for 30 m at 45°C. The sections were then washed four times with 2X SSC (60 m, 30 , 30 m, and 30 at 60°c) , washed one time with IX SSC (30 m, 60°C) , and left overnight in 2X SSC. The following day the sectionε were quickly rinsed in 0.05 M phoεphate buffer and then distilled water. They were then air dried and placed in contact with X-ray film. The films were developed Id to 2 weeks later and used to establiεh gross distribution of hybridized probe. Finer localization of the probe was achieved by coating the sections with a photoemulsion then developing the emulsion and measuring the grain densities over cell bodies in various brain regions. 6.1.8. CLONING OF THE FULL LENGTH RAT APP-4 In order to obtain the full-length CIOO-R the rat libraries were screened with various probes made from pABlR-rat. These probes are specific for "the most 5' sequence of the rat clone. After more rat sequence is available, subsequent rounds of screening will utilize probes specific to the most 5' sequence available at each round of screening. In addition, a second rat-brain cDNA library was constructed in λZAP (Stratagene) with a primer specific for the 5' region of the cDNA insert. The library was constructed using the RACE (rapid amplification of cDNA ends) protocol (Frohmann et al., 1988, Proc. Natl. Acad. Sci. USA 85:8998-9002) with the following modifications: (1) The cDNA syntheεis was primed with AB1RT3-1 or with AB1RT3-3, specific for the 3' UTR of the AB1R mRNA, instead of with oligo(dT). (2) The mRNA was denatured with methylmercury hydroxide prior to cDNA synthesiε. (3) MMLV reverse transcriptase ("Superscript," Bethesda Research Labs) was used instead of AMV reverse transcriptase. (4) NotI adapters instead of EcoRI linkers were attached to the ends of the cDNAs so that no subsequent digestion of the cDNA was necessary before cloning. The cDNAs were cloned into NotI digested, and partially filled in λ ZAP II, to make two libraries of approximately 10 5 cDNA clones each.This library will be screened with probes specific for the most 5' sequence available at each round of cloning. Another approach to cloning the full-length gene will be to utilize PCR technology. Using hippocampal messenger RNA we will use a primer specific for the 5' end of the cDNA insert and perform the reverse transcriptaεe reaction. The RNA/DNA hybrid will then be "tailed" with guanineε by terminal transferase, the RNA digested with RNAse H and the second strand primed with a poly-C primer. By using primerε with reεtric¬ tion sites incorporated into them, these "clone- specific" cDNAs will be cloned and sequenced. The process will be repeated through multiple rounds until the entire ll kb sequence has been attained (Frohmann et al. , 1988, Proc. Natl. Acad. Sci. USA 85:8998- 9002) . 6.1.9. PRECIPITATION ASSAYS WITH /SAPP-CIOO GST FUSION A cDNA fragment encoding APP-C100 was inserted in frame into the GST fusion protein vector pGEX-KG (Guan and Dixon, 1991, Anal. Biochem. 192:262-267); full- length APP-695 and APP-751 cDNAs were inεerted in frame into pGEX-1 (Smith and Johnson, 1988, Gene 67:31-40). The resulting recombinants were transformed into CAG456, a htpR165 mutant that is defective in proteolysiε (Baker et al., 1984 Proc. Natl. Acad Sci USA 81:6779-6783). GST-APP fusion protein and control GST expresεion waε induced with 0.1 mM IPTG at 32°C for 2-5 hr. 200-ml cultureε were pelleted and resuspended in homogenization buffer (100 mM NaCl, 1 mM EDTA, 10 mM Tris, pH 7.6, 10 μg/ml leupeptin, 10 μg/ml aprotinin, 1 mM DTT, 05 mg/ml lysoεome) and held at 4°C for 5 min, after which NP-40 was added to a final concentration of 10%. The suεpenεion waε homogenized and centrifuged, and the εupernatant, containing εoluble GST fusion protein, was retained. The fusion protein was bound to 300 μl of 50% glutathione beads that'had been washed 3 times with 10 ml of wash buffer (100 mM NaCl, 1 mM CaCl 2 , 10 mM Tris, 7.5, 5 mM DTT), by rocking the mixture at 4°C overnight. The GST-r αA, -cdc42, and -racl plasmids were transformed into BL21 and fusion protein expresεion waε induced with 50 μM IPTG at 37°C for 4 hr. 100-ml cultureε were pelleted and reεuεpended in ice-cold PBS + 10 μg/ml aprotinin, 10 μg/ml leupeptin, 1 mM PMSF, l mM DTT and 3 mg/ml lysozyme, and held at room temperature for 15 min. Triton X-100 was added to a final concentration of 1%, and the suspension was sonicated and centrifuged. The supernatant, containing the soluble fusion proteins, was retained and incubated with 400 μl of a 50% slurry of glutathione agarose beads by incubating the mixture at 4°C 1-3 hr with shaking. For the precipitation assays, beads containing GST or GST fusion proteins were washed in binding buffer (20 mM Tris, pH 7.5, l mM DTT, 40 μg/ml BSA, 1 mM EDTA) , resuspended as a 50% slurry in binding buffer (+ 0.5 mM GDP/3S or GTP7S for the p21-GST fusionε) , and incubated at 37°C for 20 min, after which MgCl 2 waε added to a final concentration of 5 mM and the mixture incubated for 5 min at room temperature. 40 μl (for p21-GST pull-downε) or 30 ul (for APP-GST pull-downs) of in vitro translated 35 S-N- Pak waε added to 22-60 μl (varied to equalize protein; final volumes were brought to 60 μl with washed beads) of a 50% slurry of the appropriate GST fusion protein and the mixtures incubated at 4°C for 1 hr or overnight with rocking. The beads were then washed 5 times with 1 ml each of PBS + 0.5% NP-40 at 4°C, after which they were resuspended in 20 μl of 2X Laemmli buffer, boiled for 2 min, and subjected to 10% SDS- PAGE. The gels were stained with Coomassie blue to verify that equal amounts of GST fusion proteins had been loaded in the lanes, dried, and exposed to Hyperfil MP (Amersham) for 1-10 days. 6.1.10. IMMUNOPRECIPITATION AND ACTIVATION OF CIOO-R Eight 60 mm dishes of subconfluent HEK 293T cells were transfected with 3 μg each of pJ3M-myc-N-Pak (myc epitope [EQKLISEEDL]-tagged C100-R cDNA in the expression vector pMT3 [ref]) by calcium phosphate precipitation. Each dish was incubated with the precipitated DNA for 12 hr, after which the cells were maintained in growth medium for a further 36 hr. The cells were serum starved for 16 hr, and then each dish was washed twice with ice cold PBS; cells were εcraped into the second wash, centrifuged, and resuspended in buffer A (20 mM Tris, pH 7.5, 1 mM MgCl 2 , 125 mM NaCl, 1% Triton X-100) + 1 mM PMSF, 10 μg/ml leupeptin, 10 μg/ml aprotinin, 50 mM NaF, 100 μM Na 3 V0 4 . The extracts were centrifuged at 13,000g for 10 min at 4°C, after which the supernatantε were pooled and incubated for 2 hr at 4°C with anti-myc antibody (9E10, 1:20) and protein A Sepharose (1:20) . The beads were washed 3 times in PBS/1% Triton X-100 followed by one wash with buffer A, and then resuspended in 400 ul of buffer A. GST-RhoA, -Cdc42, and -Racl were purified from transformed BL21 cells as described above. The fusion proteins were purified on glutathione beads, which were washed in buffer A + 5 MM DTT. The GST-fusion proteins were then eluted with 20 mM Tris, pH 8.0, 150 mM NaCl, 10 mM glutathione, 5 mM DTT. The eluted protein waε diluted in 300 μl of buffer C (20 mM Tris, pH 7.5, 1 mM DTT, 40 μM BSA, 1 mM EDTA) to a final concentration of 100 μg/ml. Either GDP/Ss OR GTPγS was added to a final concentration of 0.5 mM, and the mixtures were incubated at 37°C for 20 min. Then MgCl 2 was added to a final concentration of 5 mM and each sample was incubated at 25°C for a further 5 min. Five μg of each nucleotide-bound GST-GTPase was added to 50 μl of purified myc-N-Pak/protein A Sepharose suspension, and incubated at 25°C for 20 min. The mixtures were washed twice in buffer A and twice in kinase buffer (50 mM Tris, pH 7.4, 5 mM MgCl 2 , 10 M MnCl 2 , 1 mM DTT) . 30 μl of kinase buffer containing 0.1 μCi/μl [.T 32 P]-ATP, 25 μM ATP and 50 μM MPB were added to each sample, and the mixtures were incubated at 25°C for 3 min. the phosphoproteins were separated by SDS-PAGE and identified and quantitated using a phosphorimager. 6.1.11. ANTIBODIES AND IMMUNOBLOTS The peptides SPAAPNKEATPPS (amino acids 212-223 of N-Pak; 1AB1R) and NTDRQRKKSKMTDEE (amino acids 235- 249 of N-Pak; 2AB1R) were synthesized by Research Genetics using MAP resin technology. Antibodies were generated in rabbits, and the serum was immunoaffinity purified. 10 μg each of total human fetal or rat postnatal day (P)21 brain homogenate were subjected to 10% SDS- PAGE, and were transferred to PVDF (Millipore) membranes. The membranes were incubated in 0.2% I- block (Tropix, Bedford, MA) and 0.5% Tween-20 overnight at 4°C, then were incubated with a 1:1000 dilution of 1AB1R or a 1:2000 dilution of 2AB1R for 1 hr at room temperature. The membrane was washed and incubated with alkaline phosphatase-conjugated goat anti-rabbit IgG (1:10,000) for 1 hr, after which the manufacturer's (Tropix) protocol for chemiluminescent detection was followed. For the preabsorption experiments, each diluted antibody was incubated with 30 μg/ml of peptide overnight at 4°C prior to being used for the immunoblots. 6.1.12. SYNAPTOSOMAL PLASMA MEMBRANE PREPARATIONS Synaptosomal plaεma membrane (SPM) fractions were isolated from human brain specimens as described by Perrone-Bizzozero et al. (1988) . Briefly, tissue was homogenized in 0.32 M sucrose, 50 mM Tris-HCl pH 7.4, and 0.1 mM PMSF in a glass Teflon homogenizer and fractionated by sucrose gradient centrifugation. SPMs were resuspended in buffer containing 10 mM Tris-HCl pH 7.4, 5 mM EGTA pH 7.4, and 5 mM MgCl 2 (TEM) and protein concentration was determined by the Coomassie Blue method using bovine serum albumin as a standard. Samples were stored at -80°C at a concentration of 1 mg/ml. 6.1.13. RNA BLOT ANALYSIS RNA was obtained from brain tissue and other organs of fetal abortuses. RNA was isolated from each tissue or brain region by the guanidinium thiocyanate procedure (Chirgwin et al., 1979, Biochemistry 18:5294-5299) as modified by Neve et al. (1986, Mol. Brain Res. 1:271-280). The amount of RNA purified from each tissue sample was determined by OD 260 ; OD 260/2β0 ratios were also determined to confirm uniformity of thiε ratio among the samples. For the human fetal tisεue blot and the human/rat nervous system subregion blot, 20 μg of total RNA from each tissue was subjected to electrophoresis on agarose/formaldehyde gels, transferred to Biotrans membrane (ICN) , and hybridized with radiolabeled probe as described previously (Neve et al., 1986, Mol. Brain Res. 1:271- 280) . The blots were exposed to Kodak X-Omat AR film for 4 days (human fetal tissue) or 12 days (human/rat nervous system subregions) . For the blot of the human fetal brain subregions, 10 μg of total RNA were loaded into each lane. The blot was exposed for 75 hours (n- pak probe) or 22 hours (APP probe) . /3-actin and cyclophilin cDNA probes were used as hybridization controls for the Northern blots, and confirmed equal loading of RNA in the lanes (Schwartz et al., 1994, Hum. Genet. 94:658-664). 6.1.14. JN SITU HYBRIDIZATION HISTOCHEMISTRY Tisεues were fresh-frozen and cut in sectionε 12 μm thick on a cryostat. Sections were fixed in buffered 4% paraformaldehyde for 10 minutes at room temperature, rapidly air-dried, and stored desiccated at -70°C. At the time of use, sections were blocked with 0.1 M glycine, rinsed, and acetylated with 25% acetic anhydride in 0.1 M triethanolamine, pH 8.0. Sections were washed in 2X SSC and delipidated by treatment with ethanol and chloroform. Sections were then partially rehydrated and incubated overnight at 60°C with 10,000 cp /ul 35 S-labeled riboprobes (εynthesized using a template representing bp-24 to 230 of the cDNA) in a solution containing 50% formamide, 10% dextran sulfate, 20X Denhardt's solution, 300 μg/ml sheared salmon sperm DNA, 150 μg/ml tRNA, 2X SSC, and 20 mM 3-mercaptoethanol. Sense and antisenεe riboprobeε were generated uεing the Promega protocol. Following hybridization, εections were treated with RNAse A and were washed with increasing stringency (final stringency 0.1X SSC at 60°C) . Sections were dried, dipped in a 1:1 dilution of Kodak NTB2 emulsion with water, and developed after 5 weeks. Controls included hybridizations with sense strandε. 6.2. RESULTS 6.2.1. RADIOLIGAND BINDING Becauεe /SAPP-CIOO is toxic to NGF-differentiated PC12 cells, we tested the binding of the in vitro synthesized /3APP-C100 fragment to the surface of PC12 cells that had been treated with NGF (Kozlowski et al. 1992 J. Neuroscience 12:1679). 35 S-/3APP-C100 binding to the differentiated PC12 cells was inhibitable by unlabeled /3APP-C100 (FIG. IA) . Similar results were obtained with the neuroblastoma cell line, SK-N-MC (see FIG. IB) . In the NGF-treated PC-12 cells, the inhibitable fraction of the binding accounted for 40%-60% of the total binding. The IC j0 value for the inhibitable binding was 1.7 + 0.7 nM (n=5) . Inhibitable binding reached a maximum after 3 hours of incubation and was completely dissociable (FIG. 2) . Saturation experiments indicated the presence of a single class of binding siteε with a Kj value of 0.81 + 0.37 nJJ, in approximate agreement with the IC J0 value determined above, and a B.^ value of 0.37 + 0.05 fmole/10 6 cells. Binding of 3S S-/SAPP-C100 to NGF-treated PC12 cells was not εignificantly inhibited by other peptides, including a number of tachykinins. In rat brain sectionε, the higheεt levels of specific binding were found in regions of the hippocampus and olfactory tubercle. The amount of inhibitable 3S S- / SAPP-C100 binding was dependent upon the duration of exposure of the PC12 cells to NGF. PC12 cells that were not exposed to NGF showed little inhibitable binding, whereas those cultured in the presence of NGF for 4 or 6 days showed progresεively greater amounts of binding. Another variable affecting binding was pH. The maximum amount of binding occurred at pH 7. Binding was only 25% of maximum at pH 6 and only 52% of maximum at pH 8.5. To asεeεs the stability of 35 S- / 8APP-C100 in the assay conditions, samples of both free ligand at the end of the incubation period (unbound) and ligand which had bound to the cells and been released were examined by SDS-polyacrylamide gel electrophoresis (PAGE) . Before addition to the assay, most of the radioactivity was contained in a single band with an apparent molecular weight of 15 kDa. This represents monomer /SAPP-C100. A small amount of material was also present in two additional diffuse bands. One migrated at approximately twice the molecular weight of the major band and possibly represents a dimer of /SAPP-CIOO. The other band had a much higher molecular weight and may be an aggregate. The gel profile of the unbound ligand at the end of the incubation period was identical to that of the ligand before incubation, indicating that the ligand had not been degraded. Similarly, the ligand released from binding had the same profile as the ligand originally added, with the posεible exception of a εlight reduction in the amount of high molecular weight material. Theεe data show that the binding of /SAPP-CIOO ligand does not cause its modification. A mutation of the tyrosine in /SAPP-CIOO, made to examine the importance of a consensus sequence for phosphotyrosine (Tyr 6g7 to Phe) , produced a peptide that was not toxic to differentiated PC-12 cells. Phe 6g7 - /SAPP-C100 does not significantly inhibit 3S S-/SAPP-CIOO binding at concentrations up to 14nM (n=3) , making it at least 20 times less potent a ligand at the /SAPP- CIOO binding site than the native form. 6.2.2. CLONING AND CHARACTERIZATION OF THE C100-R The autoradiographic signals from the 3S S-/SAPP- C100 binding to λgtll plaques induced to expresε protein in the late lytic cycle were atypical and variable. We uεed the XOMAT-RP high reεolution film and long expoεures in order to establish clear duplicates on the autoradiographs (FIG. 3) . The size of the cDNA insert of the rat clone, λABlR, was 1970 bp. The complete sequence is given in Figure 4 (SEQ. ID. NOS: 1-2) . The sequence given includes a portion of the /S-gal gene derived from the vectors, λgtll and Bluescript. The clone's open reading frame is not in register with the /S-Gal gene, so the clone is being expressed as a nonfusion protein. A number of additional rat cDNA cloneε have been isolated and sequenced (Fig. 9) . The new sequence information extends, in the 5' direction, the coding region of C100-R represented in Figure 4. The * above nucleotide 686 in Figure 9 represents the junction with the rat sequence depicted in Figure 4 at nucleotide 40. In addition, at least 3 full length cDNA clones involving the C100-R have been isolated and sequenced (Figure 10) . Sequence analysis of these clones revealed a 1632 bp open reading frame (Figure 10) encoding a 544 amino acid protein with a calculated molecular mass of 60.7 kDa. A portion of the sequence of the cDNA was found to be homologous to that coding for the serine/threonine kinase domain of the yeast STE20 protein (Leberer et al., 1992, EMBO J. 11:4815- 4824; Ramer and Davis, 1993, Proc. Natl. Acad. Sci. USA 90:452-456), with 67% identity over an interval of 683 bp at the 3' end of each coding sequence. A search of the protein database revealed that the putative neural APP binding protein (C100-R) was closely related to rat p65 PAK (Pakl; Manser et al., 1994) and yeast STE20 proteins (Figure 12) , with highest homology in the serine/threonine kinase domain (70% between C100-R and STE20; >90% between C100-R and Pakl [p65 PAK ]). In addition, these three kinaseε εhared, in their N-terminal domains, a peptide motif repreεenting the Cdc42/Racl-binding domain of Pakl (Figure 12) . The overall identity between C100-R and Pakl protein εequences was 83%. Pakl is a serine/threonine protein kinase that is activated by the Rho family p21 proteins Cdc42 and Racl. The very close similarity between C100-'R and Pakl suggests an analogous function for C100-R. At least four spliced forms of CIOO-R mRNA were identified. All diverged within the 5' UTR, at bp-27 (Figure 10) . No CIOO-R transcripts showing alternative splicing within the coding sequence were found. 6.2.3. IN VITRO BINDING OF C100-R TO APP, APP-C100 AND ACTIVATED CDC42 AND RACl A cDNA encoding full-length C100-R was used as template for the synthesis of C100-R RNA in vitro . The RNA was translate din a wheat germ lysate in vitro translation system, and the synthesis of the expected 35 S-labeled 61 kDa protein was verified by SDS- polyacryla ide gel electrophoresis (SDS-PAGE; data not shown) . In "pull-down" asεays, glutathione S- transferase (GST) fuεion proteins (Smith and Johnson, 1988, Gene 67:31-40) of APP-695, APP-751, and APP- C100, and of the p21 proteins RhoA, Cdc42 and Racl were immobilized on glutathione-agarose beads and incubated with the in vitro-synthesized radiolabeled C100-R. The beads were pelleted, washed, and εubjected to SDS-PAGE. Autoradiograms of the gels, shown in Figure 3, demonstrate the precipitation of radiolabeled C100-R by GST-APP-695 and GST-APP-C100. GST-APP-751 also precipitated radiolabeled C100-R. The p21 proteins act as molecular "switches", active when bound to GTP and inactive when bound to GDP. The Cdc42 and Racl GST fusion proteins precipitated C100-R when complexed with GTP and therefore in an active state, but not when bound to GDP. The RhoA GST fusion protein did not precipitate C100-R, whether in an active or an inactive configuration; and GST alone failed to precipitate C100-R. To determine whether association of C100-R with GTP-bound Cdc42 or Racl stimulated its kinase activity, we expressed it with an N-terminal myc epitope (myc-ClOO-R) in HEK 293T cells, immunoprecipitated it with a monoclonal anti-myc antibody, and incubated it with myelin basic protein (MBP) in the presence of [r 32 P]-ATP and GDP- or GTP- bound RhoA, Cdc42, and Racl GST fusion proteins (Figure 14A) . Consistent with the results obtained for Pakl by Manser et al. (1994), MBP was phosphorylated by myc-N-Pak in the presence of GTP- but not GDP-bound Cdc42 or Racl. MBP was not phosphorylated in the absence of N-Pak (lane a) or in the presence of RhoA, whether it was asεociated with GTP or GDP. Theεe data are quantitated in Figure 14B. To determine the tissue specificity of ClOO-R mRNA expresεion, its cDNA was used to probe an RNA blot containing RNA from a range of human fetal (20-22 week) tissues (Figure 16A) . An approximately 11 kb mRNA was detected only in the brain, suggesting that expression of the ClOO-R gene is restricted to the nervous system. Analysis of the expression of C100-R mRNA in subregions of human fetal (20 week) brain (Figure 16B) shows that it is expressed at high levels in the thalamus, primary motor cortex (Brod ann area (A) 4) , frontal cortex (AlO), and visual cortex (A17/18) . C100-R mRNA is expressed at moderate levels in the hippocampus, caudate-putamen, and primary somatosensory cortex (Al) , and at very low levels in the cerebellum. Notably, the pattern of expression of APP mRNA in human fetal brain is similar to that of C100-R (Figure 16B) . The expression of C100-R mRNA in the adult human brain is slightly lower than that in the fetal brain. Northern blot analysis of regions of the human and rat nervous systems revealed robust expression of C100-R in fetal and adult rat spinal cord, and detectable but low expression in human retina and rat pituitary (Figure 16B) . The very large size of the C100-R mRNA (-11 kb) relative to the 1632 bp that encode its protein product suggests that the mRNA contains long untranslated regions (UTRs) . RACE (Rapid Amplification of cDNA Ends) analysis of the 5' ends of the CIOO-R mRNAs have identified 5 » UTR regions of the alternatively spliced C100-R mRNA 3'UTR is, however, unusually long. One of our cDNA clones possesses over 3 kb of 3'UTR and yet does not extend to the polyadenylation site, indicating that the CIOO-R 3'UTR is greater than 3 kb in length. Southern analysis of human and rat genomic DNA demonstrates that AB1R cDNA hybridizes to a small number of bands, which is consistent with the AB1R representing a single copy gene (Figure 6) . A strongly hybridizing 3.0 kb band was observed as well as two more weakly hybridizing bands, one at 8.5 kb and a high molecular weight band between 25 and 30 kb. depending on species. 6.2.4. IN SITU HYBRIDIZATION In rat brain section, levels of hybridization greater than background were obvious only in the hippocampus and olfactory tubercle (FIG. 8) . This agrees with the distribution of binding sites as determined autoradioagraphically (FIG. 7) . To further localize C100-R mRNA in the rat brain, in situ hybridization was carried out using an antisense riboprobe corresponding to the region of CIOO-R cDNA that shares at least homology with the pak-1 cDNA. Consistent with the robust expresεion of C100-R mRNA observed on blots, the expression of C100- R mRNA in rat brain was widespread (Figure 17A) and was similar to that previously shown in the human fetal brain using RNA blots (see above) . Very high levels of C100-R mRNA were observed in brain regions including the hippocampus, amygdala, piriform and entorhinal cortex, and olfactory bulb. A robust signal was also observed in discrete brainstem muclei, including the raphe nucleus. Moderate levels of signal were found in neocortex and thalamus. In εome brain regionε with an overall low level of εignal, including the caudate nucleuε, dispersed intensely- labeled cells were nonetheless observed. The cerebellum was devoid of detectable signal. Control hybridizations with sense riboprobe gave no specific signal (not shown) . To determine whether CIOO-R mRNA was localized outside the brain, in situ hybridization of antisense CIOO-R riboprobe to coronal sections of embryonic day (E) 18 rats was carried out. CIOO-R mRNA was found in spinal cord and dorsal root ganglia, as well as in brain (Figure 17B) , suggeεting that it iε expreεsed in both the central and peripheral nervous systems. Non- neural tissues, including gut, bone, and muscle, were not labeled. 7. EXAMPLE: CLONING OF HUMAN C100-R An adult human hippocampal cDNA library in lambda ZAP 11 (Stratagene) was screened using a labeled fragment from the rat C100-R cDNA insert. The labeled fragment is represented as the EcoRI fragment, from nucleotide 31 through 409, in Figure 9. The rat C100-R EcoRI fragment was labeled uεing a random priming reaction and the library waε screened under stringent conditions using methods routinely employed by one skilled in the art. For a review of screening strategies see e.g. Maniatis, 1989, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Presε, N.Y. Several clones were obtained, ranging from 600 to 1500 base pairs in length. Resultε from partial sequencing of the 1500 base pair clone is εhown in Figure 18. Regionε of εequence homology between the human C100-R εequence and the rat C100-R sequence are depicted in Figures 19A and 19B. 8. DEPOSIT OF MICROORGANISMS The following microorganismε have been depoεited with the American Type Culture Collection, (ATCC) , Rockville, Maryland and have been assigned the following accession numbers: Microorganism Date of Deposit Accession No. pABIR-rat August 7, 1992 69047 The present invention is not to be limited in scope by the microorganisms deposited since the deposited embodiments are intended as illustrations of single aspects of the invention and any microorganisms which are functionally equivalent are within the scope of the invention. The present invention is not to be limited in scope by the exemplified embodiments which are intended as illustrations of single aspectε of the invention, and any clones, DNA or amino acid sequences which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to thoεe skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims. It is also to be understood that all base pair sizeε given for nucleotideε are approximate and are used for purposes of description. Intemabonal Application No: PCT/ MICROORGANISMS Optional Sheet in connection with the microorganism referred to on page 69. lines 1-25 of the descπption A. IDENTIFICATION OF DEPOSIT ' Further deposits are identified on an additional sheet Name of depositary institution ' Ameπcan Type Culture Collection Address of depositary institution (including postal code and country) ' 12301 Parklawn Drive Rockville. MD 20852 US Date of deposit ' August 7, 1992 Accession Number ■ 69047 B. ADDITIONAL INDICATIONS ' (leave Mink if not applicable) Thu information ti continued on a separate attached tract C. DESIGNATED STATES FOR WHICH INDICATIONS ARE MADE ' ««.. D. SEPARATE FURNISHING OF INDICATIONS ' (leave Wank if not appltcable) The Indlcetions Mated below will be submitted to the International Bureau leter ' (Specify the general nature of the indications o o . "Acceaaion Number ot Deposit") E. D This sheet was received with the International applicauon when filed (to be checked by the receiving Office) (Authorized Officer) D The date of receipt (from the applicant) by the International Bureau ' (Authorized Officer) Form PCT/Rθ/134 (January 19811 -69.1

Claims: WHAT IS CLAIMED IB: 1. An isolated nucleic acid molecule comprising a nucleotide seguence that encodes (a) a polypeptide having the amino acid seguence FIG. 11 (SEQ ID No:); or (b) the complement of the nucleotide seguence of (a). 2. An isolated nucleic acid molecule comprising a nucleotide seguence that hybridizes under highly stringent conditions to the nucleic acid of claim 1 and encodes a naturally occurring MCK-10 protein. 3. An isolated nucleic acid molecule comprising the nucleotide seguence of FIG. 11 (SEQ ID No:). 4. An isolated nucleic acid molecule comprising a nucleotide seguence that hybridizes under stringent conditions to the nucleic acid of Claim 1 and encodes a naturally occurring MCK-10 protein, or a fragment thereof, linked uninterrupted by stop codons to a nucleotide seguence that encodes a heterologous protein or peptide. 5. The nucleic acid molecule of Claim 1 or 2 which is a cDNA. 6. The nucleic acid molecule of Claim 1 or 2 which is a genomic DNA. 7. A recombinant vector containing the nucleotide seguence of Claim 1, 2, 3 or 4. 8. An expression vector containing the nucleotide seguence of Claim 1, 2, 3 or 4 operatively associated with a regulatory nucleotide seguence containing transeriptional and translational 70 regulatory information that controls expression of the nucleotide seguence in a host cell. 9. A genetically engineered host cell containing the nucleotide seguence of Claim l, 2, 3 or 4. 10. A genetically engineered host cell containing the nucleotide seguence of Claim 1, 2, 3 or 4 operatively associated with a regulatory nucleotide seguence containing transeriptional and translational regulatory information that controls expression of the nucleotide seguence in a host cell. 11. The genetically engineered host cell of Claim 9 in which the host cell is prokaryotic. 12. The genetically engineered host cell of Claim 9 in which the host cell is eukaryotic. 13. A method for producing recombinant C100-R, comprising: (a) culturing a host cell transformed with the recombinant DNA expression vector of Claim 7 or 8 and which expresses the C100-R; and (b) recovering the C100-R gene product from the cell culture. 14. The method of Claim 13 in which human C100-R is produced. 15. A method for producing recombinant C100-R fusion protein, comprising: (a) culturing a host cell transformed with a recombinant DNA expression vector containing the nucleic acid molecule of Claim 4 and which expresses the C100-R fusion protein; and 71 (b) recovering the CIOO-R fusion protein from the cell culture. 16. The method of Claim 15 in which a human C100-R fusion protein is produced. 17. An isolated recombinant C100-R. 18. The isolated CIOO-R of Claim 17 having a rat CIOO-R amino acid seguence. 19. The isolated C100-R of Claim 17 having a human C100-R amino acid seguence. 20. A fusion protein comprising a ClOO-R linked to a heterologous protein or peptide seguence. 21. The fusion protein of Claim 20 in which the C100-R moiety has a rat C100-R amino acid seguence. 22. The fusion protein of Claim 20 in which the C100-R moiety has a human C100-R amino acid seguence. 23. An oligonucleotide which encodes an antisense seguence complementary to a portion of the C100-R nucleotide seguence, and which inhibits translation of the C100-R gene in a cell. 24. The oligonucleotide of Claim 23 which is complementary to a nucleotide seguence encoding the amino terminal region of the C100-R. 25. A monoclonal antibody which immunospecifically binds to an epitope of the C100-R. 26. The monoclonal antibody of Claim 25 which competitively inhibits the binding of j3APP-Cl00 to the 72 CIOO-R. 27. The monoclonal antibody of Claim 25 or 26 which binds to the human CIOO-R. 28. A method for screening and identifying antagonists of SAPP-CIOO ligand, comprising: (a) contacting a cell line that expresses CIOO-R with a test compound in the presence of the 0APP-C1OO ligand; and (b) determining whether the test compound inhibits the binding and cytotoxic effects of the 3APP-C100 ligand on the cell line, in which antagonists are identified as those compounds that inhibit both the binding and cytotoxic effects of the /SAPP-CIOO ligand on the cell line. 29. A method for screening and identifying agonists of the ,SAPP-C100 ligand, comprising: (a) contacting a cell line that expresses the C100-R with a test compound in the presence and in the absence of the /5APP-C100 ligand; (b) determining whether, in the presence of the /3APP-C100 ligand, the test compound inhibits the binding of the / 8APP-C100 ligand to the cell line; and (c) determining whether, in the absence of the /3APP-C100 ligand, the test compound mimics the cytotoxic effects of the /8APP-C100 ligand on the cell line, in which agonists are identified as those test compounds that inhibit the binding but mimic the cytotoxic effects of the /3APP-C100 ligand on the cell line. 73 30. The method according to Claim 28 or 29 in which the cell line is a genetically engineered cell line. 31. The method according to Claim 28 or 29 in which the cell line endogenously expresses the C100-R. 32. The method according to Claim 31 in which the cell line is a neuroblastoma cell line. 33. The method according to Claim 32 in which the neuroblastoma cell line is SK-N-MC. 34. A method for screening and identifying antagonists of /3APP-C100 comprising: (a) contacting C100-R protein with a random peptide library such that C100-R will recognize and bind to one or more peptide species within the library; (b) isolating the ClOO-R/peptide combination; (c) determining the seguence of the peptide isolated in step b; and (d) determining whether the test compound inhibits the binding and signal transduction effects of /SAPP-CIOO, in which antagonists are identified as those peptides that inhibit both the binding and signal transduction effects of /SAPP-CIOO. 35. A method for screening and identifying agonists of /SAPP-CIOO comprising: (a) contacting C100-R protein with a random peptide library such that C100-R will recognize and bind to one or more peptide species within the library; 74 (b) isolating the ClOO-R/peptide combination; (c) determining the seguence of the peptide isolated in step b; and (d) determining whether, in the absence of the /SAPP-CIOO, the peptide mimics the cellular effects of /SAPP-CIOO, in which agonists are identified as those peptides that inhibit the binding but mimic the cellular effects of CIOO-R. 36. The method according to Claims 34 or 35 in which the C100-R protein is genetically engineered. 37. A method of modulating the endogenous enzymatic activity of the serine/threonine kinase C100-R in a mammal comprising administering to the mammal an effective amount of a ligand to the ClOO-R protein to modulate the enzymatic activity. 38. The method of Claim 37 in which the ligand to the C100-R receptor is /8APP-C100. 39. The method of Claim 37 in which the ligand to the C100-R receptor is a / 8APP-C100 agonist. 40. The method of Claim 37 in which the ligand to the C100-R is an antagonist of 3APP-C100. 41. The antagonist of Claim 40 that iε a monoclonal antibody which immunospecifically binds to an epitope of C100-R. 42. The antagonist of Claim 37 that is a soluble C100-R receptor. 75 43. The method of Claim 42 in which the enzymatic activity of the receptor protein is decreased. 44. The method of Claim 42 in which the ligand inhibits neurotoxicity. 45. The method of Claim 42 in which the ligand inhibits amyloid plague formation. 46. A method of modulating the cellular effects of /SAPP-CIOO in a mammal comprising administrating to the mammal an effective amount of truncated C100-R receptor protein which inhibits the cellular effects of /SAPP-CIOO binding. 47. A method of identifying a compound that inhibits the kinase activity of C100-R receptor comprising: (a) measuring C100-R receptor phosphorylation in the presence of /3APP-C100 and the compound; (b) measuring C100-R receptor phosphorylation in the presence of /SAPP-CIOO in the absence of the compound; and (c) determining the difference in C100-R autophosphorylation in the presence and absence of the compound, wherein descreased autophosphorylation indicates inhibition. 48. A compound that inhibits kinase activity of C100-R receptor. 76

Inventors: KOZLOWSKI MICHAEL R, MANLY SUSAN P, NEVE RACHAEL L, KOZLOWSKI, MICHAEL, R., MANLY, SUSAN, P., NEVE, RACHAEL, L.
Applicants: MCLEAN HOSPITAL CORP, SQUIBB BRISTOL MYERS CO, BRISTOL-MYERS SQUIBB COMPANY, MCLEAN HOSPITAL CORPORATION
Application year: 1996
Main classification: C07H21
IPC codes: A61K31, A61K38, A61K39, A61P25, C07K14, C07K19, C12N1, C12N5, C12N15, C12P21, C12Q1, C12R1, G01N33