Phospholipase C-γ, protein kinase C and Ca2+/calmodulin-dependent protein kinase II are involved in platelet-derived growth factor-induced phosphorylation of Tiam1

In Swiss 3T3 fibroblasts. the Rad-specific guanine nucleotide exchange factor Tiam1 is phosphorylated by several different agonists. We show here that PDGF induces threonine phosphorylation of Tiam1 in a time- and dose-dependent manner. Tiam1 phosphorylation was significantly reduced by the selective protein kinase C inhibitor Ro-31-8220 and by KN93, an inhibitor of Ca2+/calmodulin-dependent protein kinase II, The Ca2+ chelator BAPTA/AM totally abrogated Tiam1 phosphorylation, indicating that Ca2+ is essential for this phosphorylation. Moreover, PDGF-stimulated Tiam1 phosphorylation was markedly reduced by 72 +/- 10% in PLC-gamma l deficient mouse fibroblasts, compared to wild-type cells, indicating that phosphoinositide phospholipase C is involved. (C) 1998 Federation of European Biochemical Societies.