Erythropoietin Induces the Tyrosine Phosphorylation of GAB1 and Its Association With SHC, SHP2, SHIP, and Phosphatidylinositol 3-Kinase

Abstract

Five tyrosine-phosphorylated proteins with molecular masses of 180, 145, 116, 100, and 70 kD are associated with phosphatidylinositol 3-kinase (PI 3-kinase) in erythropoietin (Epo)-stimulated UT-7 cells. The 180- and 70-kD proteins 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 adapter, GAB1. Indeed, Epo induced the transient tyrosine phosphorylation of GAB1 in UT-7 cells. Both kinetics and Epo dose-response experiments showed that GAB1 tyrosine phosphorylation was a direct consequence of Epo receptor activation. After tyrosine phosphorylation, GAB1 associated with the PI 3-kinase, the phosphotyrosine phosphatase SHP2, the phosphatidylinositol 3,4,5 trisphosphate 5-phosphatase SHIP, and the molecular adapter SHC. GAB1 was also associated with the molecular adapter GRB2 in unstimulated cells, and this association dramatically increased after Epo stimulation. Thus, GAB1 could be a scaffold protein able to couple the Epo receptor activation with the stimulation of several intracellular signaling pathways. Epo-induced tyrosine phosphorylation of GAB1 was also observed in normal human erythroid progenitors isolated from cord blood. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and thrombopoietin (TPO) also induced the tyrosine phosphorylation of GAB1 in UT-7 cells, indicating that this molecule participates in the signal transduction of several cytokine receptors.

Tissue inhibitor of metalloproteinases-1 signalling pathway leading to erythroid cell survival

“…In haematopoietic cells, Epo protects cultured human erythroid precursor cells from apoptosis by PI 3-kinase activation [22]. Epo induces association of PI 3-kinase with the activated Epo-receptor through a direct interaction or via phosphorylated intermediates [23,24]. In the present study, we demonstrate that TIMP-1 induces survival of both erythroid UT-7 and myeloid 32D cell lines and provide evidence for the first time that TIMP-1 signalling involves the PI 3-kinase pathway.…”

A Role for SHIP in Stem Cell Biology and Transplantation

“…SHIP is recruited to receptor-associated signaling complexes via adapters (e.g. Shc, Grb2, Dok3), scaffold proteins like Gab1/2 or directly via its SH2 domain [22,25,[30][31][32][33][34][35][42][43][44]. After recruitment to the plasma membrane, SHIP can then hydrolyze PI(3,4,5)P 3 and in so doing attenuate several different PI3K effector pathways [11,13].…”

Constitutively active STAT5 variants induce growth and survival of hematopoietic cells through a PI 3-kinase/Akt dependent pathway

“…The binding of the SH2 domains of p85 to proteins containing phosphorylated tyrosine residues present in YXXM motifs increases PI 3-kinase activity (Backer et al, 1992). Binding of p85 to activated cytokine receptor, to adaptor molecules like IRS1/2 and the related proteins Gab1 and Gab2, to SHP-2 and STAT3 have been reported indicating that PI 3-kinase can be activated by dierent mechanisms in response to cytokines or growth factors (Craddock and Welham, 1997;Gu et al, 1998;Lecoq-Lafon et al, 1999;Nishida et al, 1999;Pfeer et al, 1997;Verdier et al, 1997;Yamauchi et al, 1998). The PI 3-kinase then catalyzes the production of phosphatidylinositol 3,4-biphosphate (PIP2) and phosphatidylinositol 3,4,5-triphosphate (PIP3), two lipid products needed to activate various isoforms of PKC and Akt proteins (Datta et al, 1995;Franke et al, 1995;Toker et al, 1994).…”