In order to explore the functional consequence of the increased EGFR signaling in mig-6 knockdown cells, we first measured cell proliferation. However, we did not observe a difference in EGF-mediated cell proliferation between mig-6 knockdown and control cells (data not shown). Surprisingly, we noticed
that EGF-stimulated mig-6 knockdown cells changed their morphology toward a scatterlike appearance, whereas control transfected cells largely retained their round and compact cell shape (Fig. 5B). This observation prompted us to examine EGF-induced migration of HepG2 cells upon interference with mig-6 expression. Strikingly, mig-6 knockdown cells display increased cell migration toward EGF, suggesting that mig-6 is a negative regulator of EGFR-mediated cell migration (Fig. 5C). Based on the results from the liver cancer cell lines, we aimed to determine HTS assay if loss of mig-6 is sufficient to generate EGFR overexpression in HCCs. Toward this end, we analyzed the expression levels of EGFR and mig-6 by way of immunohistochemical analysis using a tissue microarray of 111 liver cancer patients.
EGFR was found to be predominately expressed at the cell membrane, whereas mig-6 expression was restricted to the cell cytoplasm. Interestingly, we found moderate to high EGFR expression in 36% of the patients, suggesting that EGFR signaling may contribute to the development of a subset of HCCs (Supporting Fig. 1A). In contrast, mig-6 expression was barely detectable in the majority of analyzed tumors (64%; Cyclin-dependent kinase 3 Supporting Fig. 1B). Interestingly, cells expressing EGFR did not show selleck kinase inhibitor mig-6 expression and vice versa (Fig. 6A ). Interestingly, EGFR overexpressing tumors (36%) displayed a significant down-regulation or loss of mig-6 expression in 64% of the cases (P = 0.006; Fig. 6B). These data suggest that mig-6 is a possible regulator of the EGFR in HCC and that loss of mig-6 may result in EGFR activation and tumor development. In recent years, several studies have significantly improved our understanding of the complex mechanisms underlying liver regeneration.
In humans, liver regeneration occurs upon liver damage by cirrhosis or hepatitis. Defects in proper liver regeneration can result in severe diseases like liver cancer or even death. Several studies in rodents have identified different receptor tyrosine kinase signaling cascades to be key regulators of proper liver regeneration. In particular, members of the EGF and MET receptor pathways are critically involved in proper hepatocyte proliferation after liver injury. Recently, Natarajan et al.4 demonstrated in mice that the EGFR is a critical regulator of efficient liver regeneration after PH. However, the role of negative regulators of receptor tyrosine kinase signaling in the regulation of hepatocyte proliferation remains largely elusive.