Association of pp60c-src with alpha IIb beta 3 in resting platelets.

To detect whether 125I-alpha IIb beta 3 is associated with tyrosine kinases in platelets, antibodies specific to pp60c-src, pp54/58lyn, and pp62Fyn were used to precipitate their homologous antigens. In contrast to Lyn and Fyn kinases, pp60c-src appears to be complexed with alpha IIb beta 3. Both proteins, pp60c-src and alpha IIb beta 3, coprecipitated when antibodies to pp60c-src were used in the immunoprecipitation experiments. This conclusion was further supported by immunoprecipitation of alpha IIb beta 3 from Triton X-100 extracts of nonlabelled platelets with P2 antibodies. There was no pp60c-src detectable in immunoprecipitates obtained with antibodies specific to alpha 2 beta 1 or GPIb. Since PGE1 was used to prevent platelet activation in buffers throughout all procedures and there was no phosphorylation of pp72syk we assume that the platelets were in the resting state. Therefore, we conclude that alpha IIb beta 3 and pp60c-src can form a complex in resting platelets suggesting that pp60c-src is directly involved in initiating the outside-in signaling cascades in blood platelets.