The role of PTEN in the HCV-induced biogenesis of lipid droplets was further investigated in vitro with hepatoma cells transduced with the HCV core protein of genotype 1b or 3a. Our data indicate that PTEN expression was down-regulated at the posttranscriptional level in steatotic patients infected with genotype
3a. Similarly, the in vitro expression of the HCV genotype 3a core protein (but not 1b), typically leading to the appearance of large lipid droplets, down-regulated PTEN expression by a mechanism involving a microRNA-dependent blockade of PTEN messenger RNA translation. PTEN down-regulation promoted in turn a reduction of insulin receptor substrate 1 (IRS1) expression. Interestingly, either PTEN or IRS1 overexpression prevented the development of large lipid droplets, and this indicates that the down-regulation of both PTEN and IRS1 is required to affect the biogenesis
EPZ-6438 nmr of lipid droplets. However, IRS1 knockdown per se did not alter the morphology of lipid droplets, and this suggests that other PTEN-dependent mechanisms are involved in this process. Conclusion: The down-regulation of PTEN and IRS1 is a critical event leading to the HCV genotype 3a–induced formation of large lipid droplets in hepatocytes. (HEPATOLOGY 2011;) Metabolic syndrome and hepatitis C virus (HCV) infection are major causes of progressive liver disease.1 Interestingly, these two conditions share some clinical and histological features, such as insulin resistance (IR), hepatic steatosis, inflammation, fibrosis, and cirrhosis.2 In addition, hepatocellular carcinoma (HCC) is a potential Selleckchem Akt inhibitor end-stage complication of both disorders.3 Abnormal signaling through the phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog deleted on chromosome 10 (PTEN)/Akt pathway is involved in the pathogenesis of liver manifestations associated with metabolic syndrome, that is, nonalcoholic fatty MCE公司 liver disease (NAFLD) and HCC.4 The deregulated expression/activity of PTEN, a potent regulator of PI3K signaling in hepatocytes, importantly contributes to the occurrence of NAFLD and HCC.5 Indeed, liver-specific PTEN knockout mice
spontaneously develop NAFLD and HCC.6, 7 In agreement with these studies, PTEN expression is down-regulated in steatotic livers of obese human subjects and in fatty livers of rodent models.8 We have further demonstrated that fatty acids cause hepatic steatosis, nonalcoholic steatohepatitis, and aberrant cell proliferation through the down-regulation of PTEN expression.8-10 Finally, PTEN is a well-established tumor suppressor that is frequently mutated/deleted in human cancers, including HCC.11, 12 Thus, it is tempting to speculate that the expression or function of PTEN may also be altered in HCV infections and may contribute to the development of steatosis in patients with chronic hepatitis C. HCV induces steatosis, especially in individuals infected with HCV genotype 3,13 and this phenomenon has been reproduced experimentally.