FOCAL ADHESION KINASE AND PAXILLIN BIND TO PEPTIDES MIMICKING BETA-INTEGRIN CYTOPLASMIC DOMAINS

The integrins have recently been implicated in signal transduction. A likely mediator of integrin signaling is focal adhesion kinase (pp125(FAK) Or FAK), a structurally distinct protein tyrosine kinase that becomes enzymatically activated upon engagement of integrins with their ligands, A second candidate signaling molecule is paxillin, a focal adhesion associated, cytoskeletal protein that coordinately becomes phosphorylated on tyrosine upon activation of pp125(FAK). Paxillin physically complexes with two protein tyrosine kinases, pp60(src) and Csk (COOH-terminal src kinase), and the oncoprotein p47(gag-crk), each of which could function as part of a paxillin signaling complex. Using an in vitro assay we have established that the cytoplasmic domain of the beta(1) integrin can bind to paxillin and pp125(FAK) from chicken embryo cell lysates, The NH2-terminal, noncatalytic domain of pp125(FAK) can bind directly to the cytoplasmic tail of beta(1) and recognizes integrin sequences distinct from those involved in binding to alpha-actinin. Paxillin binding is independent of pp125(FAK) binding despite the fact that both bind to the same region of beta(1). These results demonstrate that the cytoplasmic domain of the beta subunits of integrins contain binding sites for both signaling molecules and structural proteins suggesting that integrins can coordinate the generation of cytoplasmic signals in addition to their role in anchoring components of the cytoskeleton.