Defining the role of heterotrimeric G-proteins in EGF receptor trafficking and signaling

RGS-PX1 functions as a GAP that inactivates G[alpha]s and regulates EGFR trafficking and signaling, while GIV binds G[alpha]i to form a molecular switch that and activates G[alpha]i and promotes efficient receptor signaling. Yet the mechanisms by which G[alpha]s/RGS-PX1 and G[alpha]i/ GIV affect EGFR signaling remained unclear. I set out to further define the roles of G[alpha]s/RGS-PX1 and G[alpha]i/GIV in EGFR trafficking and signaling. We found that G[alpha]s regulates EGFR degradation. Specifically, G[alpha]s depletion by RNAi delayed and G[alpha]s overexpression promoted EGF-induced degradation of EGFR, a key step in the downregulation of receptor signaling. In addition, G[alpha]s and RGS-PX1 form a complex with Hrs, a component necessary for receptor sorting for degradation. Thus, G[alpha]s promotes EGFR degradation and forms a complex with RGS-PX1 and Hrs that might be required for efficient receptor sorting. G[alpha]s depletion also enhanced ligand-induced EGFR autophosphorylation and ERK 1 /2 signaling, and a siRNA-resistant, inactive G[alpha]s- G226A mutant but not an active G[alpha]s-Q227L mutant reversed these effects. Together, these data indicate that activation of G[alpha]s delays and inactivation of G[alpha]s by RGS-PX1 promotes downregulation of EGFR signaling. We also found that the G[alpha]i-GIV switch reprograms EGFR signaling to influence whether cells migrate or proliferate. Specifically, GIV interacts with EGFR, and GIV's GEF motif promotes several events including formation of a ligand-induced complex between EGFR, G[alpha]i, and actin which promotes receptor signaling within the plasma membrane (PM)-actin bed, receptor autophosphorylation, PM-based signaling to Akt and PLC[gamma], and cell migration. Disabling GIV's GEF motif by mutation (GIV-F1685A) disrupts this complex which promotes receptor signaling trafficking from endosomes, inhibits receptor autophosphorylation, and enhances endosome-based signaling to ERK 1/2 MAPK and c-Src/STAT5b and cell proliferation. Furthermore, early during progression of colorectal carcinomas, before metastatic invasion the G[alpha]i-GIV switch is disabled due to the loss of GIV's carboxy-terminus and critical GEF motif by alternative splicing. Later during metastatic invasion the switch is assembled by upregulation of GIV. Therefore, the switch is selectively assembled or not at different stages of oncogenesis leading to pro-migration or proliferative cellular profiles, respectively. These traits might cumulatively influence growth and invasiveness of tumors during oncogenic progressio

A Gαi–GIV Molecular Complex Binds Epidermal Growth Factor Receptor and Determines Whether Cells Migrate or Proliferate

Migrating cells do not proliferate and vice versa, but the mechanism involved remains unknown. Ghosh et al. reveal how this cellular decision is made by showing that a Gαi–GIV molecular complex interacts with EGF receptor and programs growth factor signaling, triggering migration when assembled and favoring mitosis when assembly is prevented