Cell adhesion is critical in migration and placement of cells during development, in wound healing, immune recognition and targeting of lymphocytes to areas of infection. The interaction of cells with extracellular matrix molecules and with other cells is mediated by receptors on the cell surface. Integrins are a family of receptors that recognize specific extracellular matrix molecules and also mediate cell- cell interactions. Integrins are dimeric containing alpha and beta subunits. They can be divided into three subgroups based on their beta subunits. Within each subgroup, different alpha subunits interact with a common beta subunit. The beta1 subgroup contains six different alpha subunits that interact with beta1 to form receptors with different ligand specificity. This ligand specificity is dictated by the alpha subunit. alpha4beta1 is a multifunctional receptor found on lymphocytes and is the only integrin that mediates both cell-cell and cell-matrix interactions. alpha4beta1 is required for cytolytic T-cell recognition of target cells and homing of lymphocytes to Peyer's patches. In addition, alpha4beta1 is involved in the control of T-cell proliferation. alpha4beta1 appears to signal the nucleus by increasing cAMP levels in response to binding of a ligand on suppressor T-cells. cAMP then inhibits expression of the IL-2 receptor which is required for T-cell proliferation. The alpha4beta1 heterodimer on lymphocytes also acts as a receptor for the extracellular matrix protein fibronectin (FN). It binds FN at a site near its carboxyterminus which is encoded by an exon that is alternatively spliced into mRNA. The presence of this exon is tissue specific and also varies during development suggesting that binding of lymphocytes to FN may vary in different tissues and at different points in development. Four different transcripts arise from a single alpha4 gene. Some, if not all, of the mRNAs appear to encode different forms of alpha4. We hypothesize that the different forms of alpha4 are functionally distinct proteins thus accounting for the multiple functions attributed to alpha4. This proposal is designed to examine how expression of alpha4 is controlled. The studies can be divided into two parts. First, expression and structure of the different alpha4 cDNAs will be examined. This will involve the isolation and characterization of alpha4 cDNA clones from a cDNA library which is made from cells that express the four different alpha4 transcripts. The sequence of the cDNAs will be compared to determine structural differences in the proteins that they encode. Second, we will clone the promoter region of the alpha4 gene and characterize it in transfection assays looking for the presence of transcriptional regulatory elements.
