Mig-6 Is a Negative Regulator of the Epidermal Growth Factor Receptor Signal

Abstract

In contrast to signal generation and transmission, the mechanisms and molecules that negatively regulate receptor tyrosine kinase (RTK) signaling are poorly understood. Here we characterize Mig-6 as a novel negative feedback regulator of the epidermal growth factor receptor (EGFR) and potential tumor suppressor. Mig-6 was identified in a yeast two-hybrid screen with the kinase active domain of the EGFR as bait. Upon EGF stimulation Mig-6 binds to the EGFR involving a highly acidic region between amino acids 985-995. This interaction is kinase activity-dependent, but independent of tyrosine 992. Mig-6 overexpression results in reduced activation of the mitogenactivated protein kinase ERK2 in response to EGF, but not FGF or PDGF, stimulation and in enhanced receptor internalization without affecting the rate of degradation. The induction of Mig-6 mRNA expression in response to EGF, but not FGF, indicates the existence of a negative regulatory feedback loop. Consistent with these findings, a possible role as tumor suppressor is indicated by Mig-6-mediated inhibition of EGFR overexpression-induced transformation of Rati cells.

Feedback inhibition by RALT controls signal output by the ErbB network

“…Despite its suppressive activity towards mitogenic and transforming signals triggered by ErbB-2 and EGFR, ectopically expressed RALT altered neither mitogenic responses of murine fibroblasts to serum nor cell transformation induced by v-ras and v-src (Fiorentino et al, 2000;Hackel et al, 2001). The issue of RALT specificity was further addressed in the experiments shown in Figure 1.…”

“…Receptor-associated late transducer (RALT) has been recently identified as a feedback inhibitor of mitogenic signals propagated by ErbB-2 (Fiorentino et al, 2000) and EGFR (Hackel et al, 2001). RALT expression is activated by EGF, TGF-a and NRG-1 in fibroblasty and epithelial cells (Fiorentino et al, 2000), via a mechanism entailing transcriptional activation of the Ralt gene by the Ras-Raf-ERK pathway (Fiorini et al, 2002).…”

“…RALT expression is activated by EGF, TGF-a and NRG-1 in fibroblasty and epithelial cells (Fiorentino et al, 2000), via a mechanism entailing transcriptional activation of the Ralt gene by the Ras-Raf-ERK pathway (Fiorini et al, 2002). Constitutive overexpression of RALT markedly inhibits the mitogenic and transforming activity of EGFR (Hackel et al, 2001) and ErbB-2 (Fiorentino et al, 2000). Conversely, neutralization of endogenous RALT function by microinjection of anti-RALT antibodies enhances the mitogenic activity of an EGFR/ ErbB-2 chimeric receptor (Fiorini et al, 2002).…”

Loss of RALT/MIG-6 expression in ERBB2-amplified breast carcinomas enhances ErbB-2 oncogenic potency and favors resistance to Herceptin

“…Owing to ErbB-2 refractoriness to downregulation via the IDP (Marmor and Yarden, 2004), FI could represent a primary element of regulation of ErbB-2 signalling. We and others (Hackel et al, 2001) have identified RALT/MIG-6 as a feedback inhibitor whose activity is restricted to receptors of the ErbB family via still undefined mechanism/s. RALT expression is triggered by ErbB signalling via activation of the Ras-ERK pathway (Fiorini et al, 2002).…”

“…RALT expression is triggered by ErbB signalling via activation of the Ras-ERK pathway (Fiorini et al, 2002). The RALT protein is in turn able to complex with activated ErbB RTKs and inhibit their signalling function in cultured cells (Hackel et al, 2001;Fiorini et al, 2002;Anastasi et al, 2003). In addition, a skin phenotype similar to that generated by a dominantnegative EGFR allele (Murillas et al, 1995) is observed in mice carrying a RALT transgene expressed by the K14 promoter (Costanza Ballaro`, Oreste Segatto and Stefano Alema`, manuscript in preparation).…”