Erythropoietin induces the tyrosine phosphorylation of GAB1 and its association with SHC, SHP2, SHIP, and phosphatidylinositol 3-kinase

Five tyrosine-phosphorylated proteins with molecular masses of 180, 145, 11 6, 100, and 70 kD are associated with phosphatidylinositol 3-kinase (PI 3-k inase) in erythropoietin (Epo)-stimulated UT-7 cells. The 180- and 70-kD pr oteins have been previously shown to be IRS2 and the Epo receptor. In this report, we show that the 116-kD protein is the IRS2-related molecular adapt er, GAB1. Indeed, Epo induced the transient tyrosine phosphorylation of GAB 1 in UT-7 cells. Both kinetics and Epo dose-response experiments showed tha t GAB1 tyrosine phosphorylation was a direct consequence of Epo receptor ac tivation. After tyrosine phosphorylation, GAB1 associated with the PI 3-kin ase, the phosphotyrosine phosphatase SHP2, the phosphatidylinositol 3,4,5 t risphosphate 5-phosphatase SHIP, and the molecular adapter SHC, GAB1 was al so associated with the molecular adapter GRB2 in unstimulated cells, and th is association dramatically increased after Epo stimulation. Thus, GAB1 cou ld be a scaffold protein able to couple the Epo receptor activation with th e stimulation of several intracellular signaling pathways. Epo-induced tyro sine phosphorylation of GAB1 was also observed in normal human erythroid pr ogenitors isolated from cord blood. Granulocyte-macrophage colony-stimulati ng factor (GM-CSF) and thrombopoietin (TPO) also induced the tyrosine phosp horylation of GAB1 in UT-7 cells, indicating that this molecule participate s in the signal transduction of several cytokine receptors. (C) 1999 by The American Society of Hematology.