Role of transactivation of the EGF receptor in signalling by G-protein-coupled receptors

Abstract

Transduction of a mitogenic signal from the cell membrane to the nucleus involves the adapter proteins SHC and Grb2, which mediate activation of the Ras/mitogen-activated protein (MAP) kinase pathway. In contrast to receptor tyrosine kinases (RTKs), the signalling steps leading to Ras/MAP kinase activation by G-protein-coupled receptors (GPCRs) are still poorly characterized but appear to include beta gamma subunits of heterotrimeric G-proteins and as-yet unidentified tyrosine kinases. We report here that the epidermal growth factor receptor (EGFR) and the neu oncoprotein become rapidly tyrosine-phosphorylated upon stimulation of Rat-1 cells with the GPCR agonists endothelin-1, lysophosphatic acid and thrombin, suggesting that there is an intracellular mechanism for transactivation. Specific inhibition of EGFR function by either the selective tyrphostin AG1478 or a dominant-negative EGFR mutant suppressed MAP kinase activation and strongly inhibited induction of fos gene expression and DNA synthesis. Our results demonstrate a role for RTKs as downstream mediators in GPCR mitogenic signalling and suggest a ligand-independent mechanism of RTK activation through intracellular signal crosstalk.

The G12 coupled thrombin receptor stimulates mitogenesis through the Shc SH2 domain

“…Delayed injection of the GST-Shc SH2 into thrombin stimulated astrocytoma cells results in a time course of inhibition similar to that observed with EGF-stimulated fibroblasts (Ricketts et al, 1996). Ullrich's group recently reported that EGFR are activated in response to thrombin stimulation of Rat1 ®broblasts (Daub et al, 1996). The mitogenic inhibition following microinjection of the GST-Shc SH2 in 1321N1 cells could therefore result from inhibition of an EGFR signaling component.…”

Regulation of cell proliferation by G proteins

“…Interestingly, tissue-speci®c expression of activated Ga i2 (Ga i2 Q205L) mimicked the actions of insulin, thus further supporting a`permissive' role for Ga i2 in insulin-receptor signaling pathway . Recently it has been shown that the stimulation of receptors for endothelin, thrombin, and LPA transactivate EGFR and this transactivation is necessary for the activation of ERK activation, fos gene expression, and DNA synthesis suggesting the critical role played by EGFR in G protein mediated signaling (Daub et al, 1996). Such interactions between di erent Gasubunits and other signaling cascades such as those between Ga i1 and TGFbR (Kataoka et al, 1993), Ga i and bFGFR (Sa and Fox, 1994), Ga q and PDGFR (De Vivo and Iyengar, 1994), Ga i2 and CSF-1R (Corre and Hermouet, 1995), Ga 13 and IGF-1R (Liu et al, 1997) and Ga 13 and EGFR (Gohla, 1998) have been identi®ed.…”

Neurotensin stimulates mitogenesis of prostate cancer cells through a novel c-Src/Stat5b pathway

“…Numerous, recent reports have shown that transactivation of the epidermal growth factor (EGF) receptor (EGFR) is critical for the mitogenic activity of multiple GPCR agonists (Daub et al, 1996(Daub et al, , 1997Prenzel et al, 1999;Madarame et al, 2003;Xiao et al, 2003;Zhao et al, 2004) and that EGFR transactivation requires metalloproteinase (MMP) cleavage of pro-heparin-binding EGF-like growth factor (pro-HB-EGF) into HB-EGF, which is released from the cell surface to bind the EGFR in an autocrine or paracrine manner (Prenzel et al, 1999;Madarame et al, 2003;Santiskulvong and Rozengurt, 2003;Yano et al, 2004;Zhao et al, 2004;Hassan and Carraway, 2006). However, the detailed signaling events following EGFR transactivation that are required for mitogenic activation are not fully understood, particularly in prostate cancer cells.…”