Cell adhesion and migration contribute to normal processes such as cellular differentiation, embryonic development, and wound healing as well as to the progression of diseases and pathological conditions that can result from either acute or chronic exposure to environmental toxicants, such as cancer and inflammatory responses. Such cell adhesive processes result from the interactions of extracellular glycoproteins such as fibronectins, laminins, and collagens with specific receptors, the best characterized of which are the integrins. Integrins are all non-covalent, heterodimeric complexes consisting of an alpha subunit and a beta subunit. The alpha5-beta1 integrin is the major fibronectin receptor on most cells. The major research focus of this project is to characterize the molecular mechanisms of integrin- mediated adhesion processes, integrin activation, and the resulting downstream processes induced by adhesive proteins such as fibronectin important for the control of proliferation, adhesion, migration, and invasion of cells, especially focusing on human tumor cells. The primary approaches use monoclonal antibodies, protein and peptide biochemistry, physical biochemistry, and cell and molecular biology to characterize the structure and function of fibronectin and its integrin receptors. Integrins can exist in both an active or inactive state. Integrin ligands, divalent cations (especially manganese ion), and certain anti-beta1 monoclonal antibodies can all activate integrins directly. Optimal ligand binding requires that an integrin is in the activated state. Integrin activators were initially identified by their ability to promote or increase cell-substrate adhesion, but they can also modulate other processes such as cell-cell adhesion and signaling pathways. The biochemical and biological consequences of integrin activation are currently being characterized. Cell-substrate adhesion- induced signaling processes can be very complex affecting multiple systems including cytoskeletal proteins and second messenger signaling pathways, leading to biochemical changes such as protein phosphorylation, protein dephosphorylation, lipid turnover, stimulation of protein kinase C (PKC), activation of the Ras/Raf/MAPK cascade, increased intracellular pH and Ca2+, and eventually modulation of gene expression. Furthermore, integrin receptor activation andoccupancy may play a role the modulation of receptor crosstalk. We have also characterized the role of the alpha3-beta1 as a docking protein that functions to localize the membrane-bound protease, seprase, to specific membrane protrusions on the surfaces of tumor cells called invadopodia. Finally, we have identified and characterized a novel focal adhesion component named vinexin. Vinexin has been found to promote cell spreading and focal contact assembly by binding to vinculin. Vinexin has also been found to bind to SOS in a regulatable manner and participate in the JNK/SAPK signaling pathway. - integrin, fibronectin, cell adhesion, signal transduction, monoclonal antibodies, cancer, metastasis
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