Dr. Naik and his colleagues previously characterized a platelet membrane glycoprotein which was specifically recognized by a stimulatory monoclonal antibody. Crosslinking of this receptor lead to the activation of platelets resulting in platelet aggregation and secretion. They have now cloned the complete cDNA of this receptor. The deduced amino acid sequence shows significant homology to a mouse junctional adhesion molecule and to other cell adhesion molecules belonging to the Ig superfamily. This protein, which is named Junctional Adhesion Molecule 1 (JAM-1), has two Ig-like domains, a transmembrane domain, and a short cytoplasmic domain. Interestingly, JAM-1 is expressed on various cells of the cardiovascular system including platelets, endothelial cells and leukocytes. They found that overexpression of JAM-1 induces endothelial cell proliferation and migration. This JAM-1 induced endothelial cell migration is specific to integrin alphaVbeta3, the vitronectin receptor. Northern and Western blot analysis show the predominant expression of a higher form of JAM-1 on these cells.
The specific aims of this project are: 1) To determine the role of JAM-1 in cell adhesion and migration. 2) cDNA cloning and characterization of the higher molecular form of JAM-1. 3) Identification of the physiological ligand/receptor that binds JAM-1 or its higher form. 4) To determine the signaling pathway induced through JAM-1. Dr. Naik will express recombinant JAM-1 in CHO cells to determine the role of JAM-1 in cell adhesion. Understanding the role of JAM-1 in cell adhesion and migration is the focus of this proposal. Priorities will be given to the studies that involve cloning of cDNA of the higher form of JAM-1, and identification of the physiological ligand to this novel cell adhesion molecule. They will use platelet functional studies as tools to elucidate the various steps of the signal transduction pathway induced through JAM-1. These steps include intracellular Ca2+ increase, protein kinase activation, protein phosphorylation, granular secretion, and activation of integrin alpha IIb beta3. Various specific inhibitors of each of these steps will be used. These signaling events will be then confirmed in other cell types. The results obtained will help to determine the signaling pathway induced through JAM-1 and the role of JAM-1 or its homologue in the process of cell adhesion, migration, angiogenesis, and tissue architecture. Characterizing the cell adhesion function of this novel protein will open up a new line of investigation that is important in inflammatory diseases and vascular biology.
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