A POLYNUCLEOTIDE ENCODING A HUMAN JUNCTIONAL ADHESION PROTEIN (JAM-2)

Abstract: The present invention relates to an isolated and purified polynucleotide encoding for a human junctional adhesion protein.

Description: A POLYNUCLEOTIDE ENCODING A HUMAN .TUNCTIONA ADHESION PROTEIN (JAM -2. Technical Field of the Invention The present invention relates to molecular biology. More specifically, the present invention relates to a polynucleotide which encodes a human junctional adhesion protein, a polypeptide encoded by said polynucleotide and to recombinant vectors expressing said polypeptide. Background of the Invention Cell adhesion is of prime importance for the formation and functional maintenance of multicellular organisms. Adhesion proteins can be classified as cell surface molecules that mediate intercellular bonds and/or participate in cell-substratum interactions. Their intracellular domains provide a functional link to the cytoskeleton and this appears to be important for efficient cell-cell adhesion to take place. They are expressed in characteristic spatiotemperal sequences. Different superfamilies have been described including immunoglobulin (hereinafter, "Ig"), cadherin, integrin, selectin (Aplin AE, Howe A, Alahari SK, Juliano RL, (1998) Pharmacol. Rev. 50: 197-263). Adhesion proteins belonging to the immunoglobulin superfamily may operate in both a homotypic and/or heterotypic manner. The common building block is the Ig domain and the prototype is neural cell adhesion molecule (hereinafter, "NCAM") which possesses five Ig domains. This family participates in diverse biological functions including leukocyte-endothelial cell interactions, neural crest cell migration, neurite guidance and tumor invasion. It is well demonstrated that during inflammation members of the Ig superfamily interact with and participate in leukocyte adhesion, invasion and migration through the vessel wall (Gonzalez- Amaro R, Diaz-Gonzalez F, Sanchez-Madrid F, (1998) Drugs 56:977-88). Selectins are involved in the initial interactions (tethering/rolling) of leukocytes with activated endothelium, whereas integrins and Ig superfamily CAMs mediate the firm adhesion of these cells and their subsequent extravasation. Tight junctions (hereinafter, "TJ") and adherens junctions (hereinafter, "AJ") are specialized structures that occur between apposing endothelial and epithelial cells. They form a semipermeable intercellular diffusion barrier that is both dynamic and regulated. Obviously these structures must be disrupted, or reorganized, in order to facilitate leukocyte passage from the circulation. The tight junction is the most apical component of the junctional complex. In recent years, two types of transmembrane protein, namely occludin and claudins, have been described that constitute the tight junction (Fanning AS, Mitic LL, Anderson JM, (1999) J. Am. Soc Nephrol. 10: 1337-45). They possess four putative transmembrane domains and occludin itself can function as an adhesion molecule. Occludin directly interacts with ZO-1, a member of the membrane-associated guanylate kinases (Furuse M, Itoh M, Hirase T, Nagafuchi A, Yonemura S, Tsukita S, Tsukita S, (1994) J. Cell. Biol. 127:1617- 26). ZO-1 provides a connection to the perijunctional cytoskeleton through its ability to associate with actin filaments (Itoh M, Nagafuchi A, Moroi S, Tsukita S, (1997) J. Cell. Biol. 138(l): 181-92). The platelet endothelial cell adhesion molecule, PECAM-1, a member of the Ig superfamily of adhesion proteins, localizes to the lateral membranes between endothelial cells (Zocchi MR, Ferrero E, Leone BE, Rovere P, Bianchi E, Toninelli E, Pardi R, (1996) Eur. J. Immunol. 26:759-67). However, it is not associated with the TJ and AJ structures (Ayalon O, Sabanai H, Lampugnani MG, Dejana E, Geiger B, (1994) J. Cell. Biol.126(l):247-58). The crucial role of PECAM-1 in paracellular migration of leukocytes to extravascular sites has been established (Muller WA, Weigl SA, Deng X, Phillips DM, (1993) J. Exp. Med. 178:449-60). In 1998 a novel mouse junctional adhesion molecule (hereinafter, "JAM") was cloned and identified as an additional transmembrane protein component of the tight junction (Martin-Padura I, Lostaglio S, Schneemann M, Williams L, Romano M, Fruscella P, Panzeri C, Stoppacciaro A, Ruco L, Villa A, Simmons D, Dejana E, (1998) J. Cell. Biol. 142(1): 117-27). JAM possesses two Ig domains; a single transmembrane and a short intracellular domain. Thus it belongs to the Ig superfamily of adhesion molecules and evidence suggests that it influences the paracellular transmigration of immune cells. Whether its extracellular domain engages in heterotypic interactions remains to be elucidated. Nevertheless, the ability to inhibit JAM function may allow alleviation of inflammatory diseases such as arthritis, asthma, rheumatoid arthritis, IBD and Crohns. Tight junctions are crucial structures for maintenance of the blood-brain (hereinafter, "BBB") and blood-retinal (hereinafter, "BRB") barriers. In some instances it may be desirable to selectively disrupt endothelial TJs. For example disruption of the BBB may provide a method for transvascular delivery of therapeutic agents to the brain. ( Muldoon LL, Pagel MA, Kroll RA, Roman-Goldstein S, Jones RS, Neuwelt EA, (1999) Am. J. Neuroradiol. 20:217-22). In another instance, strategies designed to open the tight junctions of polarized epithelial cells may improve gene delivery for diseases such as cystic fibrosis: here the polarized apical membranes of airway epithelial cells are resistant to transfection by lipid:pDNA complexes (Chu Q, Tousignant JD, Fang S, Jiang C, Chen LH, Cheng SH, Scheule RK, Eastman SJ, (1999) Hum. Gene. Ther. 10:25-36). Summary of the Invention The present invention relates to an isolated and purified human JAM2 polynucleotide encoding a human JAM2 polypeptide or fragment thereof. Moreover, the present invention further relates to an isolated and purified polynucleotide having the nucleotide sequence of SEQ ID NO: 1. The present invention also relates to an isolated and purified human JAM2 polypeptide or fragment thereof. Moreover, the present invention relates to an isolated and purified polypeptide having the amino acid sequence of SEQ ID NO: 2. The present invention also relates to a recombinant vector. This vector contains a polynucleotide having the nucleotide sequence of SEQ ID NO: l, which encodes for a human junctional adhesion protein. The polynucleotide is operatively linked to a promoter that controls expression of the nucleotide sequence and a termination segment. The present invention also relates to a host cell containing the recombinant vector. The host cell can be a bacterial cell, an animal cell or a plant cell. The present invention also relates to a transgenic mammal containing the recombinant vector described herein. Finally, the present invention relates to an antibody which binds to the hereinbefore described polypeptide. Brief Description of the Figures Fig. 1A shows the alignment of an homologous Expressed Sequence Tag (hereinafter referred to as "EST") obtained from the databases accessed through the home page of the National Center for Biotechnology Information at www.ncbi.nlm.nih.gov. with the open reading frame of mouse junctional adhesion protein (hereinafter referred to as "mouse JAM"). Fig IB shows the alignment of an overlapping EST that encodes the 3' end of a human junctional adhesion protein (hereinafter "human JAM2") including the stop codon. Identity is shown on the DNA level. Fig. 1C summarizes the Rapid Amplification of cDNA Ends (hereinafter referred to as "RACE") procedure employed to obtain the full open reading frame of human JAM2. The longest clones identified from each reaction are aligned with mouse JAM. Fig. 2 shows the full cDNA and amino acid sequence for the open reading frame (ORF) of human JAM2. The predicted signal sequence and transmembrane domain are underlined. N-linked glycosylation sites are highlighted as are cysteine residues which form disulfide bonds within the immunoglobulin-like folds in the extracellular domain. A PKC phosphorylation site is highlighted in the intracellular domain. Fig. 3 shows the alignment of human JAM2 (top) and mouse JAM (bottom) open reading frames. Conserved cysteine residues predicted to form disulfide bonds are bolded. Conserved PKC phosphorylation sites are single underlined. Fig. 4 shows identification of the human JAM2 transcript on normalized multiple tissue Northern blots probed under high stringency. Transcripts were viewed by hybridization to human JAM2, actin or GAPDH [α 32 P]dCTP labeled probes. Fig. 4A JAM2 (i) and actin (ii) probes: peripheral blood leukocytes (lane 1); lung (lane 2); placenta (lane 3); small intestine (lane 4); liver (lane 5); kidney (lane 6); spleen (lane 7); thymus (lane 8); colon (lane 9); skeletal muscle (lane 10); heart (lane 11); brain (lane 12). Fig. 4B shows JAM2 (i) and GAPDH (ii) probes: right ventricle (lane 1); left ventricle (lane 2); right atrium (lane 3); left atrium (lane 4); apex (lane 5); aorta (lane 6); adult heart (lane 7); fetal heart (lane 8). The arrows indicate the human JAM2 transcripts. Fig. 5 shows a Western Blot Analysis of JAM2. Cell lysis from control (lane 1) of JAM2 expressing CHO cells (lane 2) was probed with mouse polyclonal anti-JAM2 extracellular domain antibody. HSB cell lysis probed with either preimmune (lane 3) or anti- JAM2 (lane 4) antibody. Equivalent amounts of protein were loaded in all lanes. Fig. 6 shows the localization of JAM2 expressed in Chinese Hamster Ovary cells by immunofluorescence. Stable cell lines expressing full-length JAM2 (A) or control (B) were fixed with paraformaldehyde, stained with 1:100 dilution of primary mouse anti-JAM2 antibody followed by GAM-FITC. Single angle view of cellular staining volumetrically reconstructed from 26 x 0.4 um z-axis planes. Working magnification, x 400. Digital contrast levels were not changed during image capture. Scale bar, 20 μm. Fig. 7 shows screening for JAM2 counter-receptors on various leukocyte cell lines. Calcein loaded cells were added to JAM2-Fc captured in 96 well plates. Binding was performed in TBS + Ca/Mg/Mn (n=6); Wells were washed, retained cells lysed and fluorescence quantitated with a fluorimeter at excitation 485/emission 530nm. Data from a representative experiment. Average ± SEM. FU, arbitrary fluorescence units. Fig. 8 shows cation dependence of JAM2 adhesion. Binding of HSB cells performed in TBS + Ca/Mg/Mn, BB (n=10); TBS (n=7); TBS + EDTA (n=5); TBS + Ca (n=4); TBS + Mg (n=4); TBS + Mn (n=10). Averaged data from (n) independent experiments expressed as % Binding Buffer (BB) ±SEM. FU, arbitrary fluorescence units. Pairwise comparisons, by Fisher's PLSD post-hoc test, significantly different from TBS: *p<0.0001, from TBS+Ca: 'pθ.0001 and from TBS + Mg: pO.OOl. Fig. 9 shows the effects of cations on manganese stimulated JAM2 adhesion. Binding of HSB cells performed in TBS + Ca/Mg Mn (BB); TBS+ Mn; TBS + Mn/Mg; TBS + Mn/Ca. Averaged data from seven (7) independent experiments expressed as % Binding Buffer (BB) ±SEM. FU, arbitrary fluorescence units. Pairwise, comparisons, by Fisher's PLSK post-hoc test, significantly different from TBS: * p<0.0001; V<0.01. Significantly different from TBS + Mn "jxO.OOl. Significantly different from TBS + Mn/Mg: "pO-01. Fig. 10 shows the adhesion of JAM2 Ig domains to HSB cells. Secreted Fc fusion proteins of JAM2 Ig domain 1, and domains 1+2, were immobilized on ELISA wells by capture with GAM from the media of infected SF21 cells. Fig. 11 shows the precipitation of surface biotinylated proteins from HSB cells. Plasma membranes of K562 (lane 1) and HSB (lanes 2, 3) cells were surface biotinylated and specific binding proteins precipitated with either JAM2-Fc (lanes 1, 2) or JAMl-Fc (lane 3). JAM1 is the human homologue of mouse JAM, Genbank ACC No. U89915. Bands were viewed with avidin-HRP and ECL following electrophoresis and transfer. Equivalent amounts of protein were loaded in all lanes. Detailed Description of the Invention I. The Present Invention The present invention relates to an isolated and purified polynucleotide sequence which encodes for a human junctional adhesion protein (referred to herein as "human JAM2"). In another embodiment, the present invention relates to polypeptides for human JAM 2. In yet another embodiment, the present invention relates to recombinant vectors which, upon expression, produce human JAM2. The present invention also relates to host cells transformed with these recombinant vectors. II. Sequence Listing The present application also contains a sequence listing that contains 9 sequences. The sequence listing contains nucleotide sequences and amino acid sequences. For the nucleotide sequences, the base pairs are represented by the following base codes: Svmbol Meaning A A; adenine C C; cytosine G G; guanine T T; thymine u U; uracil M A or C R A or G W A or T/U S C or G Svmbol Meaning Y C or T/U K G or T/U V A or C or G; not T/U H A or C or T/U; not G D A or G or T U; not C B C or G or T/U; not A N (A or C or G or T/U) The amino acids shown in the application are in the L-form and are represented by the following amino acid-three letter abbreviations: Abbreviation Amino acid name Ala L-Alanine Arg L-Arginine Asn L-Asparagine Asp L-Aspartic Acid Asx L-Aspartic Acid or Asparagine Cys L-Cysteine Glu L-Glutamic Acid Gin L-Glutamine Glx L-Glutamine or Glutamic Acid Gly L-Glycine His L-Histidine He L-Isoleucine Leu L-Leucine Lys L-Lysine Met L-Methionine Phe L-Phenylalanine Pro L-Proline Ser L-Serine Thr L-Threonine Trp L-Tryptophan Tyr L-Tyrosine Val L-Valine Xaa L-Unknown or other III. Polynucleotides In one aspect, the present invention provides an isolated and purified polynucleotide which encodes human JAM2. This polynucleotide can be a DNA molecule, such as a gene sequence, cDNA or synthetic DNA. The DNA molecule can be double-stranded or single- stranded, and if single stranded, may be the coding strand. In addition, the polynucleotide can be RNA molecules such as mRNAs. The present invention also provides non-coding strands (antisense) which are complementary to the coding sequences as well as RNA sequences identical to or complementary to those coding sequences. One of ordinary skill in the art will readily appreciate that corresponding RNA sequences contain uracil (U) in place of thymidine (T). In one embodiment, the polynucleotide of the present invention is an isolated and purified cDNA molecule that contains the coding sequence of human JAM2. An exemplary cDNA molecule is shown as SEQ ID NO: l. As is well known in the art, because of the degeneracy of the genetic code, there are numerous other DNA and RNA molecules that can code for the same polypeptides as those encoded by SEQ ID NO: 1 or portions or fragments thereof. The present invention also contemplates homologous polynucleotides having at least 70% homology to the sequence shown in SEQ ID NO: l, preferably at least 80%> homology, and most preferably at least 90% homology. The term "homology", as used herein, refers to a degree of complementarity. There may be partial homology or complete homology (i.e., identity). A partially complementary sequence is one that at least partially inhibits an identical sequence from hybridizing to a target nucleic acid; it is referred to using the functional term "substantially homologous." The inhibition of hybridization of the completely complementary sequence to the target sequence may be examined using a hybridization assay (Southern or Northern blot, solution hybridization and the like) under conditions of low stringency. A substantially homologous sequence or probe will compete for and inhibit the binding (i.e., the hybridization) of a completely homologous sequence or probe to the target sequence under conditions of low stringency. This is not to say that conditions of low stringency are such that non-specific binding is permitted; low stringency conditions require that the binding of two sequences to one another be a specific (i.e., selective) interaction. The absence of nonspecific binding may be tested by the use of a second target sequence which lacks even a partial degree of complementarity (e.g., less than about 30%> identity); in the absence of nonspecific binding, the probe will not hybridize to the second non-complementary target sequence. Moreover, the present invention also contemplates naturally occurring allelic variations and mutations of the cDNA sequence set forth above so long as those variations and mutations code, on expression, for the human junctional adhesion protein. The present invention also encompasses splice variations of the JAM2 polynucleotide. The polynucleotide of the present invention can be used in marker-aided selection using techniques which are well-known in the art. Marker-aided selection does not require the complete sequence of the gene. Instead, partial sequences can be used as hybridization probes or as the basis for oligonucleotide primers to amplify by PCR or other methods to identify nucleotides specific for junctional adhesion proteins in other mammals. IV. Polypeptides The present invention also provides for human JAM2 polypeptides. The amino acid sequence for human JAM2 is provided in SEQ ID NO:2 and contains 298 amino acid residues. The present invention also contemplates amino acid sequences that are substantially duplicative of the sequences set forth herein such that those sequences demonstrate like biological activity to the disclosed sequences. Such contemplated sequences include those sequences characterized by a minimal change in amino acid sequence or type (e.g., conservatively substituted sequences) which insubstantial change does not alter the basic nature and biological activity of the polypeptides. It is well known in the art that modifications and changes can be made in the structure of a polypeptide without substantially altering the biological function of that peptide. For example, certain amino acids can be substituted for other amino acids in a given polypeptide without any appreciable loss of function. In making such changes, substitutions of like amino acid residues can be made on the basis of relative similarity of side-chain substitutents, for example, their size, charge, hydrophobicity, hydrophilicity, and the like. As detailed in United States Patent No. 4,554,101, incorporated herein by reference, the following hydrophilicity values have been assigned to amino acid residues: Arg (+3.0); Lys (+3.0); Asp (+3.0); Glu (+3.0); Ser (+0.3); Asn (+0.2); Gin (+0.2); Gly (0); Pro (-0.5); Thr (-0.4); Ala (-0.5); His (-0.5); Cys (-1.0); Met (-1.3); Val (-1.5); Leu (-1.8); lie (-1.8); Tyr (-2.3); Phe (-2.5); and Tip (-3.4). It is understood that an amino acid residue can be substituted for another having a similar hydrophilicity value (e.g., within a value of plus or minus 2.0) and still obtain a biologically equivalent polypeptide. In a similar manner, substitutions can be made on the basis of similarity in hydropathic index. Each amino acid residue has been assigned a hydropathic index on the basis of its hydrophobicity and charge characteristics. Those hydropathic index values are: He (+4.5); Val (+4.2); Leu (+3.8); Phe (+2.8); Cys (+2.5); Met (+1.9); Ala (+1.8); Gly (-0.4); Thr (-0.7); Ser (-0.8); Trp (-0.9); Tyr (-1.3); Pro (-1.6); His (-3.2); Glu (-3.5); Gin (-3.5); Asp (-3.5); Asn (-3.5); Lys (-3.9); and Arg (-4.5). In making a substitution based on the hydropathic index, a value of within plus or minus 2.0 is preferred. The polypeptides of the present invention can be chemically synthesized using standard methods known in the art, preferably solid state methods, such as the methods of Merrifield (J. Am. Chem. Soc., 85:2149-2154 (1963)). Alternatively, the proteins of the present invention can be produced using methods of DNA recombinant technology (Sambrook et al., in "Molecular Cloning - A Laboratory Manual", 2 nd . Ed., Cold Spring Harbor Laboratory (1989)). V. Recombinant Vectors The present invention also relates to recombinant vectors which contain the polynucleotide of the present invention, host cells which are genetically engineered with recombinant vectors of the present invention and the production of the polypeptide of the present invention by recombinant techniques. The polynucleotide of the present invention can be employed for producing polypeptides using recombinant techniques which are well known in the art. For example, the polynucleotide may be included in any one of a variety of expression vectors for expressing a polypeptide. Such vectors include chromosomal, nonchromosomal and synthetic DNA sequences, e.g., derivatives of SV40, bacterial plasmids, phage DNA, baculovirus, yeast plasmids, vectors derived from combinations of plasmids and phage DNA, viral DNA such as vaccinia, adenovirus, fowl pox virus, and pseudorabies. One of the most popular vectors for obtaining genetic elements is from the well known cloning vector pBR322 (available from the American Type Culture Collection, Manassas, Virginia as ATCC Accession Number 37017). The pBR322 "backbone" sections can be combined with an appropriate promoter and the structural sequence to be expressed. However, any other vector may be used as long as it is replicable and viable in the host. The polynucleotide sequence of the present invention may be inserted into one of the hereinbefore mentioned recombinant vectors, in a forward or reverse orientation. A variety of procedures, which are well known in the art may be used to achieve this. In general, the polynucleotide is inserted into an appropriate restriction endonuclease site(s). When inserted into an appropriate expression vector, the polynucleotide of the present invention is operatively linked to an appropriate expression control sequence(s), such as a promoter, to direct mRNA synthesis. As used herein, the term "operatively linked" includes reference to a functional linkage between a promoter and a second sequence, wherein the promoter sequence initiates and mediates transcription of the DNA sequence corresponding to the second sequence. Generally, operably linked means that the nucleotide sequences being linked are contiguous and, where necessary to join two protein coding regions, contiguous and in the same reading frame. The heterologous structural sequence can encode a fusion protein including either an N-terminal or C-terminal identification peptide imparting desired characteristics, such as stablization or simplified purification of expressed recombinant product. Promoter regions can be selected from any desired gene using chloramphenicol transferase (CAT) vectors or other vectors with selectable markers. Such promoters can be derived from operons encoding glycolytic enzymes such as 3-phosphoglycerate kinase (PGK), α- factor, acid phosphatase, or heat shock proteins. Examples of bacterial promoters which can be used include, but are not limited to, lad, lacZ, T3, T7, gpt, lambda P R , P L and trp. Eukaryotic promoters include CMV immediate early, HSV thymidine kinase, early and late SV40, LTRs from retrovirus, and mouse metallothionein-I. Examples of other promoters that can be used include the polyhedrin promoter of baculovirus. Typically, recombinant expression vectors contain an origin of replication to ensure maintenance of the vector. They preferably contain one or more selectable marker genes to provide a phenotypic trait for selection of transformed host cells. Examples of selectable marker genes which can be used include, but are not limited to, dihydrofolate reductase or neomycin resistance for eukaryotic cell culture, tetracycline or ampicillin resistance for E. coli. and the TRPl gene for S. cerevisiae. The expression vector may also contain a ribosome binding site for translation initiation and a transcription termination segment. The vector may also include appropriate sequences for amplifying expression. Appropriate cloning and expression vectors for use with prokaryotic and eukaryotic hosts are described in Sambrook, et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., (1989), which is herein incorporated by reference. Large numbers of suitable vectors and promoters are commercially available and can be used in the present invention. Examples of vectors which can be used include, but are not limited to: Bacterial: pQE70, pQE60, pQE-9 (Qiagen), pBS, pDIO, phagescript, psiX174, pBluescript SK, pSKS, pNH8A, pkrH16a, pNH18A, pNH46A (Stratagene); ptrc99a, PKK223-3, pKK233-3, pDR540, pRIT5 (Pharmacia); pGEM (Promega). Eukaryotic: pWLNEO, pSV2CAT, p)G44, pXTl, pSG (Stratagene), pSVK3, pBPV, pMSG, pSVL (Pharmacia). In another embodiment, the present invention relates to host cells containing the hereinbefore described recombinant vectors. The vector ( such as a cloning or expression vector ) containing the hereinbefore described polynucleotide, may be employed to transform, transduce or transfect an appropriate host to permit the host to express the protein. Appropriate hosts which can be used in the present invention, include, but are not limited to prokaryotic cells such as E. coli, Streptomyces, Bacillus subtilis, Salmonella typhimurium, as well as various species within the general Pseudomonas, Streptomyces, and Staphylococcus. Lower eukaryotic cells such as yeast and insect cells such as Drosophila S2 and Spodoptera Sf9. Introduction of the recombinant construct into the host cell can be effected by calcium phosphate transfection, DEAE-Dextran mediated transfection, or electroporation (see, Davis, L., Dibner, M., Battey, L. Basic Methods in Molecular Biology, (1986), herein incorporated by reference). Various higher eukaryotic cells such as mammalian cell culture systems can also be employed to express recombinant protein. Examples of mammalian expression systems include the COS-7 lines of monkey kidney fibroblasts, described by Gluzman, Cell, 23: 175 (1981), and other cell lines capable of expressing a compatible vector, for example, the C127, 3T3, CHO, HeLa and BHK. cell lines. Mammalian expression vectors will contain an origin of replication, a suitable promoter and enhancer, and any necessary ribosome binding sites, polyadenylation site, splice donor and acceptor sites, transcriptional termination sequences, and 5' flanking nontranscribed sequences. DNA sequences derived from the SV40 splice, and polyadenylation sites may be used to provide the required nontranscribed genetic elements. The engineered host cells can be cultured in conventional nutrient media modified as appropriate for activating promoters, selecting transformants or amplifying genes encoding for the human junctional adhesion protein of the present invention. The culture conditions, such as temperature, pH and the like, are those previously used with the host cell selected for expression and can be determined experimentally, using techniques which are well known in the art. Transcription of the polynucleotide encoding the polypeptides of the present invention by higher eukaryotes can be increased by inserting an enhancer sequence into the vector. Enhancers are cis-acting elements of DNA which are about from 10 to about 300 base pairs in length, which act on a promoter to increase its transcription. Examples of suitable enhancers which can be used in the present invention include the SV40 enhancer on the late side of the replication origin base pairs 100 to 270, a cytomegalovirus early promoter enhancer, the polyoma enhancer on the late side of the replication origin, and adenovirus enhancers. Following transformation of a suitable host strain and growth of the host strain to an appropriate cell density, the selected promoter is induced by appropriate means (such as temperature shift or chemical induction) and cells are cultured for an additional period. Cells are typically harvested by centrifugation, disrupted by physical or chemical means, and the resulting crude extract retained for further purification. Microbial cells employed in expression of proteins can be disrupted by any convenient method, including freeze-thaw cycling, sonication, mechanical disruption, or use of cell lysing agents. Such methods are well-known to those skilled in the art. The polypeptides of the present invention can be recovered and purified from recombinant cell cultures, the cell mass or otherwise according to methods of protein chemistry which are known in the art. For example, ammonium sulfate or ethanol precipitation, acid extraction, and various forms of chromatography e.g. anion / cation exchange, phosphocellulose, hydrophobic interaction, affinity chromatography including immunoaffinity, lectin and hydroxylapatite chromatography. Other methods may include dialysis, ultrafiltration, gelfiltration, SDS-PAGE and isoelectric focusing. Protein refolding steps can be used, as necessary, in completing configuration of the mature protein. Finally, high performance liquid chromatography (hereinafter, "HPLC") on normal or reverse systems or the like, can be employed for final purification steps. Cell-free translation systems can also be employed to produce such polypeptides using RNAs derived from the DNA constructs of the present invention. The cDNA sequence can be used to prepare stable cell lines expressing either wt JAM2 or JAM2 mutated at pertinent positions to determine which part of the molecule is responsible for function. Stable or transient cell lines can be created with JAM2 possessing a tag at either the 5' or 3' end, e.g. HA epitope, to enable monitoring of JAM2 function/modification/cellular interactions. Additionally, cell lines expressing recombinant JAM2, can be used to screen for small molecule inhibitors of JAM2 function. The extracellular sequence of JAM2 can be used to make recombinant protein fused to the Fc region of mouse human IgG. This protein can be used: a) To screen for a JAM2 ligand. Briefly, JAM2-Fc fusion can be captured on ELISA plates. Cultured cells e.g. monocytes can be labeled with calcien dye, incubated with the immobilized JAM2-Fc, washed and fluorescence monitored. Alternatively, the JAM2-Fc can be coupled to a solid support and then used to prepare a column for purification of solubilized proteins derived from various cells/tissues. Peptide sequencing could then identify the ligand. Another approach would be to bind the JAM2-Fc to cell lysates and perform cross-linking with DSS. b) Upon identification of a JAM2 ligand, the JAM2-Fc can be used to screen for a small molecule inhibitor of JAM2 heterotypic interactions. c) As a tool to neutralize JAM2 function, either heterotypic or homotypic interactions. The JAM2-Fc may be administered in vivo in various animal models in order to perturb JAM2 function. Alternatively, proof of concept studies may be conducted in vitro. If it is discovered that JAM2 binds in a homotypic manner, recombinant protein derived from the extracellular domain can be used to analyze such interactions. Protein would not possess an Fc Tag. Single immunoglobulin-like domains can be made to determine which one is responsible for homotypic interactions. Such recombinant protein can be used to assess its ability to decrease paracellular permeability in cells expressing native or recombinant JAM2. The interactions of the separate domains with each other or with a recombinant form possessing both Ig-like domains may be assessed by various means. Examples are cross-linking with DSS, analytical ultracentrifugation or sizing columns. The JAM2 sequence can be used to identify antisense oligonucleotides for inhibition of JAM2 function in cell systems. Further, degenerate oligonucleotides may be designed to aid in the identification of additional members of this family by the polymerase chain reaction. Alternatively, low stringency hybridization of cDNA libraries may be performed with JAM2 sequence to identify closely related sequences. The intracellular domain of JAM2 can be used to "fish" for novel interacting partners in the yeast two-hybrid system. Further, JAM2 sequence may be used to inactivate an endogenous gene by homologous recombination and thereby create a JAM2 deficient cell, tissue or animal. Such cells, tissue or animals may then be used to define specific in vivo processes normally dependent upon JAM2. JAM2 is expressed to a low level in many tissues and it is likely that JAM2 can be upregulated during pathological conditions. This expression pattern suggests that JAM2 localizes to endothelia. However, it is certainly possible that other cell types also express JAM2. If JAM2 localizes to the tight junction of epithelial cells, it is proposed that it plays a role during metastasis. Either defective JAM2 or decreased expression may not only decrease adhesion between tumor cells but also facilitate their movement through the endothelium into the vessel. JAM2 expression in the brain may indicate a role in the blood brain barrier. JAM2 expression in the aorta and heart indicates it may play a role during conditions which display inflammatory or permeability changes such as atherogenesis and reperfusion injury. Further, it is possible that JAM2 localizes to the intercalated discs of the myocyte and thus play a role in maintenance of the syncitium. VI. Antibodies The polypeptides of the present invention, fragments thereof, or cells expressing said polypeptides can be used as an immunogen to produce antibodies. These antibodies can be, for example, polyclonal or monoclonal antibodies. The present invention also includes chimeric, single chain, and humanized antibodies, as well as Fab fragments, or the product of a Fab expression library. Antibodies generated against the polypeptides of the present invention can be obtained by administering the polypeptides to an animal, preferably a nonhuman. Even a sequence encoding only a fragment of a polypeptide of the present invention can be used to generate antibodies binding to the whole native polypeptide. Such antibodies can then be used to isolate the polypeptide from tissue expressing that polypeptide. For preparation of monoclonal antibodies, any technique which provides antibodies produced by continuous cell line cultures can be used. Examples include the hybridoma technique (described by Kohler and Milstein, 1975, Nature, 256:495-497, herein incorporated by reference), the trioma technique, the human B-cell hybridoma technique (described by Kozbor et al., 1983, Immunology Today 4:72, herein incorporated by reference), and the EBV-hybridoma technique to produce human monoclonal antibodies (described by Cole, et al., 1985, in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp-77-96, herein incorporated by reference). Techniques for the production of single chain antibodies, such as those described in U.S. Patent 4,946,778, herein incorporated by reference, can be adapted to produce single chain antibodies to immunogenic polypeptides of the present invention. The antibodies of the present invention can be used to: a) Probe cellular localization/expression of JAM2 in tissues under normal and disease states. b) Immunoprecipitate JAM2 protein from cells and/or stroke tissues to determine whether it is modified by e.g. glycosylation, phosphorylation etc. c) For helping determine JAM2 function. For example, if it is found that JAM2 interacts with inflammatory cells or influences their paracellular migration, neutralizing antibodies will be developed to inhibit this function both in vitro and in vivo. By way of example, and not of limitation, examples of the present invention shall now be given. EXAMPLE 1 : CLONING AND EXPRESSION OF HUMAN JAM2 The polynucleotide sequence shown in SEQ ID NO: 1 was cloned using a combination of electronic and conventional cloning techniques. The electronic techniques used involved utilizing the Expressed Sequence Tag (EST) databases accessed through the home page of the National Center for Biotechnology Information (NCBI) at www.ncbi.nlm.nih.gov. As a template for electronic cloning, the cDNA sequence of a novel mouse Junctional Adhesion Protein (JAM) published by Martin-Padura I, Lostaglio S, Schneemann M, Williams L, Romano M, Fruscella P, Panzeri C, Stoppacciaro A, Ruco L, Villa A, Simmons D, Dejana E, J. Cell. Biol. (1998) 142(1): 117-27, herein incorporated by reference, was used. The mouse JAM cDNA sequence is also available on GenBank (Accession #U89915). The advanced Basic Local Alignment Search Tool (BLAST 2.0) was used to identify ESTs displaying homology with mouse JAM. Electronic Cloning The complete mouse JAM peptide sequence (GenBank Accession # U89915) was searched for homology with human EST sequences using the tblastn program which compares a protein query sequence against a nucleotide sequence database dynamically translated in all reading frames. The complete mouse JAM protein sequence is 300 amino acids in length. The initiation codon begins at base pair (hereinafter "bp") 71 and the stop codon at 971 (see Fig. 1A). Of the EST hits, one was chosen for further analysis. The criteria used were reasonable homology to mouse JAM and conservation of the cysteine residues specific to the immunoglobulin-like fold. AA406389 showed 42%> identity at the amino acid level with mouse JAM over a 161 amino acid overlap and was chosen for assembly of a virtual cDNA (see Fig. 1A). Throughout assembly, translation was monitored in all reading frames to identify the putative codons for initiation and termination of the virtual protein. Where possible, examination of multiple overlapping ESTs was conducted in order to identify sequencing errors. The final 3' 130 bp of AA406389 was blasted through the human dbEST using the blastn program. AA912674 showed 99.6% identity over a 257bp overlap (see Fig. IB). Further searching in the database for sequence at the 5'-end of AA406389 did not reveal additional ESTs. Conventional Cloning In order to obtain further 5' sequence for this cDNA, RACE was performed. The prime purpose was to identify a putative ribosome start site (ATG) that coincided approximately in a linear sequence with that in mouse JAM. Three separate RACE reactions were performed consecutively using the Marathon cDNA amplification kit (Clontech, Palo Alto, CA.) on human placental mRNA (Clontech). The first was performed with an oligonucleotide, 5' - CCCCGCATCACTTCTTGTCACATTTTTGATCCGG - 3' (SEQ ID NO:3), directed against AA406389. An alignment of this primer with mouse JAM positioned it some 318 bp downstream of the translational start site. mRNA was reverse transcribed with AMV reverse transcriptase (Clontech) at 42°C. RACE was performed according to the following protocol: Products were ligated into the E. coli vector pCRII-TOPO (Invitrogen, Carlsbad, CA.) and eleven clones selected for sequencing (ABI sequencer, Seqwright, TX). The longest clone extended 45 bps 5' of an ATG that approximately aligned with that of mouse JAM (see Fig 1C). However, a STOP codon upstream of this putative translational initiation codon could not be identified. In an attempt to identify a STOP codon, in frame and upstream of this ATG, two additional RACE reactions were performed. The first used the same primer for extension as RACE reaction 1. However, mRNA was reverse transcribed with thermoscript (BRL Life Technologies, New York, U.S.A.) at 58°C. Products were ligated into pCR-Blunt II - TOPO (Invitrogen). Of six clones sequenced, the longest only possessed 22 additional base pairs (Fig. 1C). For RACE reaction 3, an oligonucleotide was designed within the sequence obtained from RACE reaction 2, 5' - CTGCTCTGAGGAGGTCGAGGGTCCC - 3' (SEQ ID NO:4). The mRNA was transcribed with thermoscript at 58°C. Three clones were sequenced and the longest possessed 167 additional base pairs to that identified in RACE reaction 2 (see Fig. 1C). RACE reactions produced in total an additional 234 bp 5' of the putative translational initiation codon. A stop codon was not identified within this sequence that was in frame with the ATG. However, the inventors believe it to be the true start of the open reading frame for several reasons. First, alignment of the human JAM2 reading frame with the published mouse JAM reading frame (see Fig. 3) shows that this ATG approximately coincides with that of mouse JAM. Second, the nucleotides surrounding this site (GGAAGATGG. possess an A at the -3 position and a G at the +4 position thus conforming to the initiation consensus sequence. Third, the first 28 amino acids of JAM2 predict a signal peptide. Construction of a Full-Length JAM-2 In order to construct full-length human JAM2, the products of two separate PCR reactions were ligated together via an internal EcoNI restriction site. For the synthesis of the 5'-section of the open reading frame, a sense primer encompassing the initiation codon, 5'- GCCGCGGATCCAAGATGGCGAGGAGG-3' (SEQ ID NO:5) and an antisense primer targeted at the end of the extracellular domain, 5'- GCTATTATGCCCιGTA_XGTTGAGATCATCTAC-3' (SEQ ID NO:6), were designed (restriction sites incorporated into the primers for subsequent manipulation are underlined). A product was amplified from human placental mRNA (Clontech) using the following program: 2 min at 95°C, 1 cycle; 20 s at 95°C, 20 s at 58°C, 30 s at 72°C, 35 cycles; 3 min at 72°C, 1 cycle. The approximate 720 bp product was ligated into pCR II - TOPO. For synthesis of the 3 '-section of the open reading frame sense primer, 5' - TAAAAATCGAGCTGAGATGATAG - 3' (SEQ ID NO:7), located 248bp into the reading frame was coupled with antisense primer, 5' - TTAAATTATAAAGGATTTTGTG - 3' (SEQ ID NO:8), that incorporated the stop codon (bold). A product was amplified from mRNA derived from human embryonic kidney cells (HEK-293, available from the American Type Culture Collection, Manassus, Virginia, ATCC Accession #CRL-1573) using the following program: 7 min at 95°C, 1 cycle; 20 s at 95°C, 20 s at 56°C, 30 s at 72°C, 28 cycles; 5 min at 72°C, 1 cycle. The approximate 649 bp product was ligated into pCR II - TOPO. Two independent PCR reactions were performed and a clone from each sequenced for verification of each base. Sequence Features The human JAM2 nucleotide and amino acid sequence is shown in Fig. 2 and in SEQ NOS: 1 and 2, respectively. As shown in Fig. 2, the complete coding region of 298 amino acids features a putative signal sequence, two immunoglobulin-like domains, a single transmembrane domain (underlined) and a short intracellular domain. There are two possible cleavage sites for the signal peptide i.e. VVA-LG (single underline) or AYG-FS (dotted underline). The designated ATG is the true translational initiation signal based on the fact that it lies within a Kozak consensus and it aligns with human JAM1 ATG. The four cysteine residues predicted to form disulfide bonds within the immunoglobulin-like domains are highlighted. The 1 st and 2 nd cysteine are located in the first immunoglobulin-like fold and the 3 rd and 4 th in the second immunoglobulin-like fold. Highlighted are potential N-linked glycosylation sites (NxS/T) at amino acids #98, #187, #236 and a potential PKC phosphorylation site (S/TxR/K) at amino acid #279. Thus, JAM2 function may be modified by PKC. Further, the amino acids at the extreme C-terminus of JAM2 (SFII) conform to a consensus that would be predicted to interact with PDZ domains (Songyang Z, Fanning AS, Fu C, Xu J, Marfatia SM, Chishti AH, Crompton A, Chan AC, Anderson, JM, Cantley, LC (1997) Science 275:73-77). Proteins containing PDZ domains are predominantly localized to the plasma membrane and are recruited to specialized sites of cell-cell contact. Most recently, it has been reported that the intracellular domain of human JAM (JAM1) binds to the tight junction associated proteins ZO- 1 and AF-6 via their PDZ domains (Bazzoni G, Martinez- Estrada OM, Orsenigo F, Cordenonsi M, Citi S, Dejana E, (2000) J. Biol. Chem. 275:20520- 20526; Ebnet K, Schulz CU, Meyer Zu, Brickwedde MK, Pendl GG, Vestweber D. (2000) J. Biol Chem Jun 15; [epub ahead of print]). Thus it is highly likely that JAM2 will display similar binding activities. Sequence Alignment An alignment of the human junctional adhesion sequence with mouse JAM reveals 43% similarity and 35% identity at the amino acid level (see Fig. 3). The positions of the conserved cysteines are highlighted in both sequences. Expression Pattern Tissue expression of JAM2 was examined on a normalized human Multiple Tissue Northern blot (Clontech) with an [α 32 P]dCTP labeled probe derived from the extracellular domain. The results show that JAM2 is expressed as two transcripts of approximately 4.5kb and 1.5kb (see Fig. 4). The blots were probed at high stringency and thus these two species likely represent alternatively spliced products. Fig. 4 shows that human JAM2 is abundantly expressed in the heart. Expression also occurs in the placenta with much lower levels apparent in brain and skeletal muscle. Fig. 4B shows a more detailed examination of the JAM2 transcript in the heart. A clear chamber specific expression was not apparent. Relative to GAPDH, there is somewhat lower expression in fetal heart. However, major differences in the aorta, atrium and ventricles were not observed. Table 1 Expression Characteristics of Human JAM2 While not wishing to be bound by any theory, due to the homology of JAM2 with mouse JAM, the inventors predict that JAM2 localizes to the endothelial cells of these tissues. This is confirmed by PCR analysis of mRNA derived from human aortic endothelial cells and cardiac microvascular endothelial cells (see Table 1, above). Interestingly, a product from human umbilical vein endothelial cells (hereinafter referred to as "HUVEC") was barely detectable. Thus, JAM2 expression may be restricted to certain vascular beds. In addition to the endothelium, mouse JAM is also expressed in epithelial cells. Using the polymerase chain reaction, expression in human embryonic kidney cell line (HEK-293) can be detected but only very low levels in the colonic epithelial cell line, CaCo2. The EST database contains many ESTs that partially encode the human JAM2 sequence. Table 1 documents the tissues from which sequence was derived. It does not provide information about the level of expression in each tissue. The expression pattern is consistent with that of the mouse JAM, a protein that is specific to both the endothelium and epithelium. EXAMPLE 2: FUNCTIONAL PROPERTIES OF JAM2 A. METHODS 1. EXPRESSION OF EXTRACELLULAR DOMAIN IN INSECT CELLS Oligonucleotides were designed to amplify the extracellular domain of human JAM2 from the full-length clone. Sense 5'- GCCGCGGATCCAAGATGGCGAGGAGG-3'(SEQ ID NO:5) and antisense 5' - GCTATTATGCCC£TA££GTTGAGATCATC-3'(SEQ ID NO:6) oligonucleotides incorporated BamHI and Kpnl restriction sites (underlined) for subcloning of the product into a pFastBacl (Life Technologies, GIBCO BRL, Grand Island, NY ) vector that possessed the constant region of mouse IgG-2a (Cunningham SA, Tran TM, Arrate MP, Brock TA, (1999) J. Biol. Chem. 274:18421-7). This vector drives protein expression from the polyhedrin promotor. The recombinant protein is secreted from the Sf21 insect cells as a fusion to mIgG2a. 2. EXPRESSION OF THE FULL LENGTH CLONE IN MAMMALIAN CELLS The full-length clone of JAM2 was modified at its C-terminus by PCR mutagenesis to incorporate an HA-Tag for detection purposes. The sense 5'- GCCGCGGAICCAAGATGGCGAGGAGG-3' (SEQ ID NO:5) oligonucleotide contained a BamHI site (underlined) for subsequent manipulation. The antisense 5'- TCAGGCGr^GrCGGGC4CGrCG7__GGGGZ4AATTATAAAGGATTTTGTGTGC- 3 '(SEQ ID NO:9) oligonucleotide incorporated a stop codon (underlined) and sequence (italics) that specified the HA-tag amino acids, YPYDVPDYA, (SEQ ID NO: 10) to be inserted. JAM2-HA, modified in the pGEM-7 (Promega, Madison, WI) vector, was digested with BamHI and Xhol (polylinker) and ligated into the BamHI and Xhol sites of pcDNA6 V5-His (B) (Invitrogen, Carlsbad, CA). This vector utilizes the CMV promoter to drive protein expression. CHO-K1 cells were transfected with either 10 μg of vector possessing no insert, or pcDNA6-JAM2 using FuGENE™ 6 reagent (Roche Diagnostics Corporation, Indianapolis, IN). Stable cells lines, control and JAM2, were selected with 5-10 μg/ml of Blasticidin. For Western blot analysis, cells were lysed in 1%> TX-100 buffer in the presence of protease inhibitors (cocktail set III, Calbiochem, La Jolla, CA). Some 36 μg of protein was electrophoresed through 10% polyacrylamide gels and probed with 1 :2000X dilution of preimmune or anti-JAM2 polyclonal serum. Specific bands were viewed using enhanced chemiluminesence with 1 :30,000X dilution of GAM-HRP (Fischer, Pittsburgh, PA). 3. CHROMOSOMAL LOCALIZATION AND INTRON/EXON BOUNDARIES In order to identify genomic sequence, the public non-redundant database was searched using the Blastn program with JAM2 cDNA sequence. The results required minor manual modification due to dual designation of isolated bases at the end of some exon boundaries. The correct designation was based on 5' and 3' splice-site consensus sequences. It was possible to confirm all intron/exon boundaries by retrieving identical information from more than one deposit of genomic sequence. 4. ANTIBODIES Female BALB/c mice (8-week-old; Harlan, Indianapolis, IN) were immunized and then boosted 3X, 28 days apart, by intraperitoneal and subcutaneous injections of 100 μg purified JAM2 extracellular domain emulsified with an equal volume of Freund's adjuvant. Complete Freund's adjuvant was used for the first immunization and incomplete Freund's adjuvant for subsequent injections. Serum was collected 10 days following each boost. 5. IMMUNOFLUORESCENCE CHO-K1, control or JAM2 expressing, grown on glass slides to confluence, were fixed with 1% paraformaldehyde and stained with 1:100X dilution of either preimmune or anti-JAM2 mouse polyclonal serum. GAM-FITC at 1:100X was used as secondary. Fluorescence was viewed using a NoranTM Confocal laser-scanning microscope (Noran Instruments, Middleton, WI) equipped with argon laser and appropriate optics and filter module for FITC detection. Digital images were obtained at x400 using a 0.75N/A Nikon x20 lens. A Z-axis motor attached to the inverted microscope stage was calibrated to move the plane of focus at 0.4 μm steps through the sample. Collected 12-bit grey scale images at 512x480 resolution, stored on a re-writable optical hard disk, were volumetrically reconstructed using the Image- 1/MetamorphTM 3-D module (Universal Imaging Corp., Brandywine Parkway, PA). 6. ADHESION ASSAY In vitro adhesion assays were performed in 96 well plates essentially as described in Todderud, G.,J. J. Leukoc. Biol. 52:85 (1992), herein incorporated by reference. Briefly, 50 μl of goat anti-mouse IgG2a was coated at 5 μg/ml in PBS and used to capture 4.8 pmoles of JAM2-Fc or mIgG2a (control). Various leukocyte cell lines i.e. T lymphocytes, HSB, HPB- ALL; B lymphocytes, RAMOS; monocytic cells, HL60, THP-1, and the erythroleukemic, K562 lines were labeled with calcein (Molecular Probes Inc., Eugene, OR) at 50 μg/ml for 25 minutes at 37°C with 250,000 cells/well in binding buffer that consisted of Tris buffered saline plus ImM each of CaCK, MgCl 2 and MnCl 2 . Wells were washed 3X, lysed with 50 mM Tris (pH 7.5), 5mM EDTA, 1%> NP40, and fluorescence read in a Cytofluor with excitation at 485/20 nm and emission at 530/25 nm. Specific binding was calculated as fluorescence with JAM2-Fc minus fluorescence with mIgG2a. For antibody inhibition, protein captured on wells or HSB cells were incubated for 30min at RT in binding buffer with 1 :100X dilution of preimmune (normal mouse serum) or anti-JAM2 mouse polyclonal serum. Following incubation, excess antibody was removed by washing 3X prior to continuation of the assay. Overall differences among experimental groups for each parameter were first assessed by one-way analysis of variance (ANOVA) and individual pair- wise group comparisons were analyzed by Fisher's protected least significance difference (PLSD) post hoc test. 7. CELL SURFACE BIOTINYLATION HSB or K562 cells were surface biotinylated using EZ-Link Sulfo-NHS-Biotin (Pierce, Rockford, IL) according to the manufacturer's instructions. Cells (2.5x10 7 /ml) were washed 3X following incubation with 0.5 mg/ml Sulfo-NHS-Biotin for 30min at RT. Cell lysis was achieved in Tris buffered saline (pH 7.5), 1% Triton X-100, ImM MnCl 2 , ImM MgCl 2 , ImM CaCl 2 with the inclusion of Protease Inhibitor Cocktail Set III (Calbiochem, La Jolla, CA). Some 5 μg of JAM-Fc fusion was added to approximately lmg of lysis and incubated at 4°C ON. Proteins bound to JAM were precipitated with Protein A sepharose (30 μl), boiled 5 minutes with lOmM DTT in SDS sample buffer and separated on 9% SDS gels. Following transfer to PDVF membrane, biotinylated proteins were detected using streptavidin-HRP (1 :4000) and enhanced chemiluminescence (ECL) (Amersham Pharmacia Biotech, Piscataway, NJ). B. RESULTS JAM2 was mapped to chromosome 21 at position q21.2 using the public database. Sequence was retrieved at 100% identity from two contiguous non-overlapping sequences of 100,000 bp each (Accession No. AP000087.1 and AP000086.1). The coding region of JAM2, which constitutes 897bp, is distributed over 10 exons as shown below in Table 2. Table 2 *n/N - represents unknown bases Splice site (/) Exon refers to coding exons The limits of the JAM2 cDNA sequence shown in Fig. 2 spans some 74,853 bp of genomic DNA. Various exons were also found in AP000223 (coding exon 1), AP000225 (coding exons 2, 3, 4, 5 and 6) and AP000226 (coding exons 6, 7, 8, 9 and 10). Since the complete JAM2 transcript(s) is considerably larger than 897 bp (Fig. 4), further exons in the untranslated regions remain to be identified either up and/or downstream. All intron/exon boundaries conform to the consensus CT/AG rule (see Breathnach, R., et al., Annu. Rev. Biochem., 50:359 (1981)). A mouse polyclonal serum was raised against the ectodomain of JAM2 in order to study protein expression and localization. The antibody was not useful for studying endogenous levels of JAM2 in native tissues. To gain further insight, a stable CHO cell line over-expressing JAM2 was generated. Using these cells detection of JAM2 protein by Western blot analysis was possible. Fig. 5 estimates the molecular mass of JAM2 to be 48kDa. This is some 14kDa larger than the size predicted from the peptide sequence. Glycosylation of JAM2 on at least one of its three N-lined glycosylation consensus sites could explain this phenomenon. The CHO stable cell line was also used to determine cellular localization on confluent monolayers. Fig. 6 shows that JAM2 partitions to both surface membranes in addition to sites of cell-cell contact. The border pattern of staining is identical to that shown by mouse JAM (JAM1) expressed in CHO cells and endogenous human JAM (JAM1) in HUVECs (see, Martin-Padura, I., et al., J. Cell Biol. 142: 117 (1998)). The capacity of JAM2 extracellular domain to adhere to various leukocyte cell lines according to a previously established in vitro binding assay performed under static conditions was next examined (see Todderud, G., J. Leukoc. Biol. 52:85(1992)). Calcein loaded cells were allowed to interact with JAM2-Fc captured in 96 well plates in binding buffer (hereinafter "BB") which contained TBS plus 1 mM calcium, magnesium and manganese. Non-specific binding of cells to captured mIgG2a was determined simultaneously and subtracted. Fig. 7 shows that JAM2-Fc is able to capture the T lymphocyte cell lines HSB and HPB-ALL quite efficiently compared to interactions with B lymphocytes (RAMOS) and the monocytic cells HL60 and THP-1. Binding to the erythroleukemic K562 cell lines was non-existent. To further characterize the adhesion, the cation independence was investigated. Buffers were modified such that binding was performed in the presence of no cations or calcium, magnesium or manganese alone (see Fig. 8). There are two components to the adhesion. Firstly, a cation-independent interaction is demonstrated by the fact that EDTA does not inhibit binding below that obtained in the presence of all three cations. Secondly, a cation dependent interaction is described by a manganese specific enhancement of binding above that obtained in TBS or TBS+EDTA. This latter suggests integrin involvement. Since the screen conducted in Fig. 7 was performed under conditions favourable for cation- independent binding, all cell interactions in TBS plus manganese were reanalyzed. Manganese enhanced binding was not apparent on any of the other cell types. The JAM2/HSB manganese stimulated binding component is vitually abolished in the presence of calcium and magnesium (for example, in binding buffer). In order to determine if only one or both of these cations were inhibitory to the manganese augmentation, assays were performed using various cation combinations (see Fig. 9). The data show that inclusion of calcium in the manganese only buffer reduced interactions considerably (pO.OOl). The effect of magnesium was statistically insignificant. Mouse JAM (JAM1) is capable of homotypic interactions. Thus, it was examined whether JAM2 ectodomain bound HSB cells through this mechanism. Figure 4 shows that, unlike human JAM (JAM1), JAM2 does not show expression in peripheral blood leukocytes. Nevertheless, to verify lack of expression in HSB cells, the mouse polyclonal serum was used to probe for JAM2 protein expression by Western blotting. No protein was detected (Figure 5). As further proof , the surface JAM2 expression level was compared using the following more sensitive test. The HSB, control and JAM2 expressing CHO cells were loaded with calcein and incubated with either NMS or anti-JAM2 serum. Cell surface bound JAM2 antibody was detected by cell capture in 96 well plates coated with goat anti-mouse secondary antibodies. Table 3 shows that whilst the anti-JAM2 serum was very effective at capturing CHO cells expressing the JAM2 protein, no HSB cell binding was apparent. TABLE 3 Cell Type Antibody Av ± SEM HSB pre 1,877 ± 234 JAM2 1,135 ± 97 CHO control pre 1,210 ± 63 JAM2 1,019 ± 44 CHO JAM2 pre 2,151 ± 287 JAM2 112,329 ± 4457 To extend these studies, the ability of the mouse anti-JAM2 serum to neutralize HSB binding to recombinant JAM2 was tested. Antibody was used to block epitopes on recombinant JAM2 captured on 96 well plates. Table 4 shows that whilst preimmune serum is ineffective, anti-JAM2 serum successfully prevents HSB binding. Since relatively high levels of JAM2 are coated on these wells, we were confident that if low levels were expressed on HSB cells, the antibody should be capable of producing inhibition when incubated directly with HSB cells. As predicted, under this experimental set-up, the anti- JAM2 antibody is unable to inhibit HSB interactions with recombinant JAM2. TABLE 4 Antibody Av ± SEM A) Preincubation with captured JAM2-Fc Preimmune 1221 ± 54 anti-JAM2 5 ± 2 B) Preincubation with HSB cells Preimmune 950 ± 45 anti-JAM2 1 138 ± 33 Many adhesion proteins belonging to the Ig superfamily utilize the most N-terminal Ig domain to achieve adhesion. To assess the binding capacity of the first Ig domain of JAM2, it was synthesized as a secreted protein in insect cells and binding compared with the full extracellular domain. Figure 10 shows that this N-terminal Ig-fold of JAM2 is indeed capable of adhering to HSB cells. Further, the enhancement of binding in the presence of manganese was also retained. The inventors postulate that HSB cells express a counter-receptor for JAM2. To strengthen this hypothesis, and gain a preliminary characterization of the protein, the inventors performed precipitation experiments using JAM2-Fc. HSB cells were surface biotinylated, washed, lysed and incubated with JAM2-Fc in binding buffer. Bound proteins were precipitated using protein A and viewed on Western blots with avidin-HRP. Figure 1 1 reveals that indeed JAM2 can specifically capture a surface protein from HSB cells of approximately 43kDa. This band is not apparent in surface biotinylated K562 cells, in agreement with the cell adhesion studies described above. Further, human JAMl-Fc, which is unable to bind calcein loaded HSB cells, does not precipitate this protein. The inventors predict that this protein is responsible for the cation-independent binding of JAM2 to HSB cells. The present invention is illustrated by way of the foregoing description and examples. The foregoing description is intended as a non-limiting illustration, since many variations will become apparent to those skilled in the art in view thereof. It is intended that all such variations within the scope and spirit of the appended claims be embraced thereby. Changes can be made to the composition, operation and arrangement of the method of the present invention described herein without departing from the concept and scope of the invention as defined in the following claims.

Claims: WHAT IS CLAIMED IS: 1. An isolated and purified human JAM2 polynucleotide encoding a human JAM2 polypeptide or fragment thereof. 2. An isolated and purified polynucleotide comprising a nucleotide sequence of SEQ ID NO: l. 3. An isolated and purified human JAM2 polypeptide or fragment thereof. 4. An isolated and purified polypeptide comprising an amino acid sequence of SEQ ID NO: 2. 5. A recombinant vector comprising a human JAM2 polynucleotide or fragment thereof, said polynucleotide being operatively linked to a promoter that controls expression of said polynucleotide sequence and a termination segment. 6. The vector of claim 5 wherein the promoter is a LTR, SV40, E. coli, lac, trp, or phage lambda P L promoter. 7. A host cell comprising the recombinant vector of claim 5. 8. The host cell of claim 7 wherein the host cell is a bacterial cell, an animal cell or a plant cell. 9. A transgenic mammal comprising the recombinant vector of claim 5. 10. An antibody binding to the polypeptide of claims 3 or 4.

Inventors: CUNNINGHAM SONIA, TRINDAD ARRATE BARROS MARIA, CUNNINGHAM, SONIA, TRINDAD ARRATE BARROS, MARIA
Applicants: TEXAS BIOTECHNOLOGY CORP, TEXAS BIOTECHNOLOGY CORPORATION
Application year: 2000
Main classification: C07H21
IPC codes: A01K67, C07K14, C07K16, C12N1, C12N5, C12N15