The platelet cytoskeleton regulates the aggregation-dependent synthesis ofphosphatidylinositol 3,4-bisphosphate induced by thrombin

Pretreatment of intact platelets with cytochalasin D prevented actin polyme rization and cytoskeleton reorganization induced by thrombin, but did not a ffect platelet aggregation. Under these conditions, synthesis of phosphatid ylinositol 3,4-bisphosphate (PtdIns(3,4)P-2) stimulated by thrombin was str ongly inhibited, while production of phosphatidic acid was unaffected. The inhibitory effect of cytochalasin D was not observed when platelet aggregat ion was prevented by the RGDS peptide, We also found that cytochalasin D di d not affect PtdIns(3,4)P-2 synthesis induced by concanavalin A (ConA), whi ch is known to occur through an aggregation-independent mechanism. Moreover , thrombin, but not ConA, induced the translocation of phosphatidylinositol 3-kinase to the cytoskeleton. This process was equally inhibited by both t he RGDS peptide and cytochalasin D. These results demonstrate that the cyto skeleton represents a functional link between thrombin-induced aggregation and synthesis of PtdIns(3,4)P-2. (C) 2000 Federation of European Biochemica l Societies.