We examined the role of the Src kinase Lyn in phospholipase C-gamma2 (PLC-gamma2) and phosphatidylinositol (PI) 3-kinase activation in erythropoietin (Epo)-stimulated FDC-P1 cells transfected with a wild type (WT) Epo-receptor (Epo-R). We showed that two inhibitors of Src kinases, PP1 and PP2, abolish both PLC-gamma2 tyrosine phosphorylation and PI 3-kinase activity in WT Epo-R FDC-P1 cells. We also demonstrated that Epo-phosphorylated Lyn is associated with tyrosine phosphorylated PLC-gamma2 and PI 3-kinase in WT Epo-R FDC-P1-stimulated cells. Moreover Epo-activated Lyn phosphorylates in vitro PLC-gamma2 immunoprecipitated from unstimulated cells. Our results suggest that the Src kinase Lyn is involved in PLC-gamma2 phosphorylation and PI 3-kinase activation induced by Epo. (C) 2002 Elsevier Science (USA). All rights reserved.