INVOLVEMENT OF CALPAIN IN INTEGRIN-MEDIATED SIGNAL-TRANSDUCTION

An antibody specific to the calpain cleavage site in talin, a cytoskel etal protein, was produced, This antibody selectively recognizes the C -terminal 200-kDa fragment generated when talin is digested by calpain and does not react at all with intact talin or the N-terminal 47-kDa fragment. To assess the involvement of calpain in the integrin-mediate d signaling pathway, the effect of limited proteolysis of talin by cal pain on platelet activation and aggregation was analyzed using this an tibody, It was revealed that thrombin-stimulated platelet aggregation accompanies the autolytic activation of mu-calpain and the accumulatio n of the mu-calpain-generated 200-kDa fragment of talin. These changes were blocked by RGDS peptide which inhibits the binding of fibrinogen , an adhesive ligand, to the major integrin in platelets, alpha IIb be ta 3, while RGES peptide, which has no fibrinogen-binding-inhibitory a ctivity, had no effect. Membrane-permeable calpain inhibitors calpepti n and E-64d inhibited platelet aggregation, mu-calpain activation, and the limited proteolysis of talin. These results strongly suggest that calpain is involved in the integrin-mediated signal transduction path way. (C) 1996 Academic Press, Inc.