Ethanol-TGFα-MEK Signaling Promotes Growth of Human Hepatocellular Carcinoma

BackgroundChronic ethanol intake is a significant risk factor for the development of cirrhosis and hepatocellular carcinoma (HCC). The effects of ethanol on extracellular signal-regulated kinase (ERK) activation, transforming growth factor alpha (TGF-α), and HCC growth were examined in this study.MethodsHepG2, SKHep, Hep3B human HCC cells, or normal human hepatocytes were treated with ethanol (0–100 mM), exogenous TGF-α, TGF-α neutralization antibody or the MEK inhibitor U0126. TGF-α levels were quantified by ELISA. Growth was determined by trypan blue-excluded cell counts. Cell cycle phase distribution was determined by flow cytometry. Protein expression was determined by Western blot.ResultsEthanol treatment (10–40 mM) increased ERK activation in HepG2 and SKHep HCC cells but not in Hep3B or human hepatocyte cells. Growth increased in HepG2 (174 ± 29%, P < 0.05) and SKHep (149 ± 12%, P < 0.05) cells in response to ethanol treatment. Correspondingly, ethanol increased S phase distribution in these cells. U0126 suppressed ethanol-induced growth increases. Ethanol treatment for 24 h also raised TGF-α levels in HepG2 cells (118%–198%) and SKHep cells (112%–177%). Exogenous administration of recombinant TGF-α mimicked the ethanol-induced growth in HepG2 and SKHep cells; TGF-α neutralization antibody effectively abrogated this effect. The TGF-a neutralization antibody also prevented ERK activation by ethanol in HepG2 cells.ConclusionsThese data demonstrate that clinically relevant doses of ethanol stimulate ERK-dependent proliferation of HCC cells. Ethanol up-regulates TGF-α levels in HCC cells and enhances growth through cell cycles changes, which appear to be mediated through TGF-α-MEK-ERK signaling. Ethanol-MEK signaling in normal hepatocytes is absent, suggesting that ethanol promotion of HCC growth may in part depend upon the acquisition of cancer-specific signaling by hepatocytes.