Degraded collagen fragments promote rapid disassembly of smooth muscle focal adhesions that correlates with cleavage of pp125(FAK), paxillin, and talin

Active matrix metalloproteinases and degraded collagen are observed in dise ase states, such as atherosclerosis. To examine whether degraded collagen f ragments have distinct effects on vascular smooth muscle cells (SMC), colla genase-digested type I collagen was added to cultured human arterial SMC, A fter addition of collagen fragments, adherent SMC lose their focal adhesion structures and round up, Analysis of components of the focal adhesion comp lex demonstrates rapid cleavage of the focal adhesion kinase (pp125(FAK)), Daxillin, and talin, Cleavage is suppressed by inhibitors of the proteolyti c enzyme, calpain I. In vitro translated pp125(FAX); is a substrate for bot h calpain I- and II-mediated processing. Mapping of the proteolytic cleavag e fragments of pp125(FAK) predicts a dissociation of the focal adhesion tar geting (FAT) sequence and second proline-rich domain from the tyrosine kina se domain and integrin-binding sequence. Coimmunoprecipitation studies conf irm that the ability of pp125(FAK) to associate with paxillin, vinculin, an d p130cas is significantly reduced in SMC treated with degraded collagen fr agments. Further, there is a significant reduction in the association of in tact pp125(FAK) with the cytoskeletal fraction, while pp125(FAK) cleavage f ragments appear in the cytoplasm in SMC treated with degraded collagen frag ments. Integrin-blocking studies indicate that integrin-mediated signals ar e involved in degraded collagen induction of pp125(FAK) cleavage. Thus, col lagen fragments induce distinct integrin signals that lead to initiation of calpain-mediated cleavage of pp125(FAK), paxillin, and talin and dissoluti on of the focal adhesion complex.