Mitogen-inducible gene-6 is a negative regulator of epidermal growth factor receptor signaling in hepatocytes and human hepatocellular carcinoma

Abstract

The mitogen-inducible gene-6 (mig-6) is a multi-adaptor protein implicated in the regulation of the HER family of receptor tyrosine kinases. We have reported recently that mig-6 is a negative regulator of epidermal growth factor receptor (EGFR)-dependent skin morphogenesis and tumor formation in vivo. In the liver, ablation of mig-6 leads to an increase in EGFR protein levels, suggesting that mig-6 is a negative regulator of EGFR function. In line with this observation, primary hepatocytes isolated from mig-6 knockout and wild-type control mice display sustained mitogenic signaling in response to EGF. In order to explore the role of mig-6 in the liver in vivo, we analyzed liver regeneration in mig-6 knockout and wild-type control mice. Interestingly, mig-6 knockout mice display enhanced hepatocyte proliferation in the initial phases after partial hepatectomy. This phenotype correlates with activation of endogenous EGFR signaling, predominantly through the protein kinase B pathway. In addition, mig-6 is an endogenous inhibitor of EGFR signaling and EGFinduced tumor cell migration in human liver cancer cell lines. Moreover, mig-6 is downregulated in human hepatocellular carcinoma and this correlates with increased EGFR expression. Conclusion: Our data implicate mig-6 as a regulator of EGFR activity in hepatocytes and as a suppressor of EGFR signaling in human liver cancer. (HEPATOLOGY 2010;51: 1383-1390.)I n rodents, the liver has a tremendous capacity to regenerate. Normally, hepatocytes are in a quiescent state and rarely divide. In response to two-thirds partial hepatectomy (PH), however, 95% of all hepatocytes synchronously re-enter the cell cycle and restore the liver to its full size. 1 This rapid growth provides an excellent model to study the molecular mechanisms of cell proliferation in vivo. Importantly, defects in liver regeneration can contribute to the development of severe diseases such as liver cirrhosis and liver cancer. 2 The process of liver regeneration is dependent on various growth factors, cytokines, and metabolic processes. Cytokines, like tumor necrosis factor-␣ or interleukin-6, act as the priming factors of liver regeneration, driving quiescent hepatocytes into the cell cycle. 3 Several growth factors and receptor tyrosine kinases control cell cycle progression by stimulating the S-phase entry of hepatocytes. The epidermal growth factor receptor (EGFR), heparin-binding EGFlike growth factor (HB-EGF), transforming growth factor-␣ (TGF␣), amphiregulin, and the MET receptor have been described to be potent regulators of liver regeneration. [4][5][6][7][8] Mitogen-inducible gene-6 (mig-6)-also known as RALT, gene33, or Errfi1-is an adaptor protein implicated in the regulation of receptor tyrosine kinases. 9,10 Mig-6 can be induced by a variety of external stimuli including growth factors, hypoxia, and stress. 11 Overexpression or small interfering RNA (siRNA)-mediated knockdown studies have shown that mig-6 is a negative regulator of EGF receptor signaling. Mig-6 is induced upon EGFR activati...

Regulation of epidermal growth factor receptor signalling by inducible feedback inhibitors

“…that in control littermates. This is correlated with increased EGFR levels and enhanced EGFR signalling in Errfi1 -/-hepatocytes (Reschke et al, 2010) and is consistent with the slower liver regeneration observed in mice carrying liver-specific Egfr ablation .…”

“…EGFR IFIs are expected to provide a key balance to these positive feedback loops, because (i) LRIG1, SOCS4 and/or SOCS5 might promote ligand-independent EGFR degradation; (ii) RALT inhibits EGFR catalytic function regardless of the activating ligand (Anastasi et al, 2007); and (iii) LRIG1, SOCS4, SOCS5 and RALT antagonise the activity of all ErbB family members, including ERBB2, which acts as a signal amplifier. Consistent with this view, levels of EGFR ligands, such as heparin-binding EGF-like growth factor (HB-EGF), which activates both EGFR and ErbB4, and amphiregulin, which stimulates EGFR without inducing receptor degradation, are increased in the lung and liver of Errfi1 -/-mice (Reschke et al, 2010;Jin et al, 2009), which might be regarded as both a consequence and cause of the unabated EGFR activity generated by unbalanced feedback control. that in control littermates.…”

“…ADAM-mediated cleavage at, so far, unidentified sequences (the putative cleavage region is highlighted by an arrow) is proposed to release the soluble LRIG1 extracellular domain, which is capable of inhibiting EGF binding (see also Fig. 2 (Hackel et al, 2001;Anastasi et al, 2003;Ballaro et al, 2005;Anastasi et al, 2005;Xu et al, 2005a;Reschke et al, 2010). RALT is recruited to the EGFR kinase domain in a ligand-dependent fashion.…”

Low expression of Mig-6 is associated with poor survival outcome in NSCLC and inhibits cell apoptosis via ERK-mediated upregulation of Bcl-2

“…In papillary thyroid cancer, tumor size was inversely correlated with Mig-6 expression (21). In immunohistochemical analysis using a tissue microarray of 111 liver cancer patients, Reschke et al found that Mig-6 expression was barely detectable in the majority of analyzed tumors (64%) (22). We previously demonstrated that Mig-6 expression was downregulated or absent in NSCLC (14).…”

“…Downregulation of Mig-6 promotes proliferation and invasion in glioblastoma multiforme (GBM) and PTC cell lines (21,24). Mig-6 is also an endogenous inhibitor of EGF-induced cell migration in human live cancer cell line HepG2 (22). Our previous study showed that Mig-6 specific siRNA promotes proliferation and invasion of H1299 and BE1 cells.…”