Abstract 1112: Human rhomboid family-1 gene RHBDF1 assists trafficking of TGFa for GPCR-mediated transactivation of EGFR

Abstract

Abstract Epidermal growth factor receptor (EGFR) can be transactivated by ligands of G protein-coupled receptors (GPCR). GPCR signaling pathways often involve the formation of clathrin-coated endosomes, which interact with endoplasmic reticulum/Golgi complex to form recycling endosome and secretion vesicles containing EGFR pro-ligands such as pro-TGFα, which is proteolytically processed and released on the cell surface to activate EGFR in an autocrine manner. We showed previously that human rhomboid family-1 gene RHBDF1 is essential for GPCR-EGFR transactivation by assisting the secretion of TGFα, a ligand of EGFR. We show here silencing the RHBDF1 with shRNA leads to inhibition of EGFR ligand-dependent transactivation induced by GPCR ligands such as gastrin release peptide (GRP) and sphingosine-1-phosphate. However, RHBDF1 is not involved in EGFR ligand-independent GPCR-EGFR transactivation induced by isoproterenol. Inhibitors of endosome formation and membrane trafficking such as chlorpromazine, nocodazole, and cytochalasin-D also inhibit GRP-induced EGFR phosphorylation. Inhibitors of endosome acidification such as chloroquine and BFA lessen the inhibitory effect of RHBDF1 shRNA on GRP-induced EGFR phosphorylation. The RHBDF1 protein localizes mainly to the endoplasmic reticulum with pro-TGFα and GRASP55 in starved, quiescent cancer cells, but is phosphorylated and translocated to the cell surface upon GPCR ligands stimulation. GPCR ligands also activate the intracellular signaling molecule Src which then co-translocates with RHBDF1 and clathrin to the plasma membrane. Src-clathrin interaction and co-localization to the cell surface are RHBDF1-dependent. These findings are consistent with the view that, in response to GPCR activation, RHBDF1 assists pro-TGFα trafficking to the cell surface through clathrin coated trafficking. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1112. doi:10.1158/1538-7445.AM2011-1112