ASSOCIATION OF PP60(C-SRC) WITH ALPHA(IIB)BETA(3) IN RESTING PLATELETS

To detect whether I-125-alpha(IIb)beta(3) is associated with tyrosine kinases in platelets, antibodies specific to pp60(c-src), pp54/58(lyn) , and pp62(Fyn) were used to precipitate their homologous antigens. In contrast to Lyn and Fyn kinases, pp60(c-src) appears to be complexed with alpha(IIb)beta(3). Both proteins, pp60(c-src) and alpha(IIb)beta( 3), coprecipitated when antibodies to pp60(c-src) were used in the imm unoprecipitation experiments. This conclusion was further supported by immunoprecipitation of alpha(IIb)beta(3) from Triton X-100 extracts o f nonlabelled platelets with P2 antibodies. There was no pp60(c-src) d etectable in immunoprecipitates obtained with antibodies specific to a lpha(2)beta(1) or GPIb. Since PGE, was used to prevent platelet activa tion in buffers throughout all procedures and there was no phosphoryla tion of pp72(syk) we assume that the platelets were in the resting sta te. Therefore, we conclude that alpha(IIb)beta(3) and pp60(c-src) can form a complex in resting platelets suggesting that pp60(c-src) is dir ectly involved in initiating the outside-in signaling cascades in bloo d platelets.