ERK Negatively Regulates the Epidermal Growth Factor-mediated Interaction of Gab1 and the Phosphatidylinositol 3-Kinase

Abstract

We have examined the ability of epidermal growth factor (EGF)-stimulated ERK activation to regulate Grb2-associated binder-1 (Gab1)/phosphatidylinositol 3-kinase (PI3K) interactions. Inhibiting ERK activation with the MEK inhibitor U0126 increased the EGF-stimulated association of Gab1 with either full-length glutathione S-transferase-p85 or the p85 C-terminal Src homology 2 (SH2) domain, a result reproduced by coimmunoprecipitation of the native proteins from intact cells. This increased association of Gab1 and the PI3K correlates with an increase in PI3K activity and greater phosphorylation of Akt. This result is in direct contrast to what we have previously reported following HGF stimulation where MEK inhibition decreased the HGFstimulated association of Gab1 and p85. In support of this divergent effect of ERK on Gab1/PI3K association following HGF and EGF stimulation, U0126 decreased the HGF-stimulated association of p85 and the Gab1 c-Met binding domain but did not alter the EGF-stimulated association of p85 and the c-Met binding domain. An examination of the mechanism of this effect revealed that the treatment of cells with EGF ؉ U0126 increased the tyrosine phosphorylation of Gab1 as well as its association with another SH2-containing protein, SHP2. Furthermore, overexpression of a catalytically inactive form of SHP2 or pretreatment with pervanadate markedly increased EGF-stimulated Gab1 tyrosine phosphorylation. These experiments demonstrate that EGF and HGF-mediated ERK activation result in divergent effects on Gab1/PI3K signaling. HGF-stimulated ERK activation increases the Gab1/PI3K association, whereas EGF-stimulated ERK activation results in a decrease in the tyrosine phosphorylation of Gab1 and a decreased association with the PI3K. SHP2 is shown to associate with and dephosphorylate Gab1, suggesting that EGFstimulated ERK might act through the regulation of SHP2.

NO donor and MEK inhibitor synergistically inhibit proliferation and invasion of cancer cells

“…1 and 2). These results are in accordance with previous reports (43,44). Furthermore, we showed that U0126 upregulates IGF-Iand EGF-stimulated phosphorylation of IGF-IR and EGFR.…”

Differential phosphorylation of the docking protein Gab1 by c-Src and the hepatocyte growth factor receptor regulates different aspects of cell functions

“…The identity of Ser/Thr kinase(s) responsible for phosphorylating those Ser and Thr is currently unknown. The Ser/Thr phosphorylation of Gab1 by PKC or extracellular signal-regulated kinase has been shown to either positively or negatively regulate the tyrosine phosphorylation of Gab1 and its interaction with the other SH2 domain-containing proteins in response to growthfactor stimulation (Yu et al, 2001(Yu et al, , 2002Lehr et al, 2004). However, the effect of Ser/Thr phosphorylation identified in this study on tyrosine phosphorylation of Gab1 remains to be clarified.…”

Phosphorylation of Grb2-Associated Binder 2 on Serine 623 by ERK MAPK Regulates Its Association with the Phosphatase SHP-2 and Decreases STAT5 Activation

“…Protein kinase C has been reported to phosphorylate Gab1 resulting in negative regulation of hepatocyte growth factor signaling, whereas ERK phosphorylation of Gab1 in this system results in increased stimulation (43,44). In contrast, ERK-mediated phosphorylation of Gab1 on threonine 476 in response to epidermal growth factor down-regulates PI3K activation (45). Another negative feedback mechanism has been proposed as a consequence of protein kinase B phosphorylation of serine 159 in Gab2 in heregulin-stimulated MCF7 epithelial cells (46).…”