pp60(c-src) and related tyrosine kinases: a role in the assembly and reorganization of matrix adhesions

Activation of tyrosine kinases during integrin-mediated cell-matrix adhesio n is involved both in the regulation of focal contact assembly and in the i nitiation of signaling processes at the cell-matrix adhesive interface. In order to determine the role of pp60(c-src) and related kinases in these pro cesses, we have compared the dynamic reorganization of phosphotyrosine, vin culin, focal adhesion kinase and tensin in cells with altered expression of Src-family kinases, Both null cells for pp60(c-src) and triple knockout ce lls for pp60(c-src), pp59(fyn), and pp62(c-yes) exhibited decreased phospho tyrosine levels in focal contacts when compared with wild-type cells. pp60( c-src)-null cells also exhibited faster assembly of cell-matrix adhesions a nd a more exuberant recruitment of FAK to these sites. Tensin, which normal ly segregates into fibrillar adhesions was localized in large focal contact s in the two mutant cell lines, suggesting involvement of pp60(c-src) in th e segregation of focal contacts and fibrillar adhesions. Moreover, treatmen t of wild-type cells with tyrphostin AG1007, which inhibits both pp60(c-src ) and FAK activity, induced accumulation of tensin in peripheral focal adhe sions. These findings demonstrate that Src family kinases, and pp60(c-src) in particular, have a central role in regulating protein dynamics at cell-m atrix interfaces, both during early stages of interaction and in mature foc al contacts.