Abstract 5723: A role of retinoic acid in preventive effect of hepatitis C virus- and oxidative stress-related hepatocarcinogenesis

Abstract

Abstract Aims; It has been reported that hepatitis C virus (HCV) core expression causes hepatocellular carcinoma (HCC) in transgenic mice by reactive oxygen species (ROS). On the other hand, we have reported that loss of signals of retinoic acid (RA), a metabolite of vitamin A, leads to steatohepatitis, eventually to HCC in the receptor for RA (RARα)-knocked-down mice. We have demonstrated that the mechanism by which loss of RA signal causes HCC is mediated by increased oxidative stress via impaired metabolisms of fatty acids and iron. In turn, the effect of oxidative stress on RA signals remains to be clarified. The present study aims to explore the effect of oxidative stress and HCV core expression on RA signals in the context of hepatocarcinogenesis. Methods; The first parts of experiments were done using hydrogen peroxide as the source of ROS Human HCC cell lines HuH7, HLF, HepG2, Hep3B, Li7, Alexander and HuH6 were used. The expression level of RARα and activation of MAPKs such as ERK, JNK and p38, and RA signal by DR5-reporter assay were examined with 0.1∼1μM hydrogen peroxide. Anisomycin, an activator of JNK signal, SP600125, an inhibitor of JNK, and constitutive active MKK7-JNK1 was explored on level of RARα and activation of MAPKs. Phosphorylation and ubiquitination of mutant RARα, of which three phosphorylation sites by JNK are changed from serines to alanines, were examined. The second parts of experiments were performed using tetracycline-inducible HCV core system (Tet-On system), which is constructed in HuH7 cells. The intensity of RA signal after induction of HCV core protein was measured by DR5-reporter assay. The expression Sp101b, which is induced by RA and an adaptive protein of HCV core, was examined on expression and cellular translocation. The level of SRC-3, a coactivator of RAR/RXR, and p38 MAPK, an upstream signal of SRC-3 and a downstream signal of oxidative stress, were examined. The cellular antioxidative ability and hydroxyl radical formation were measured during this process. Results; In the first parts experiment using hydrogen peroxide, oxidative stress suppressed RA signal through degradation of RARα. The degradation of RARα was mediated by its phosphorylation by JNK and followed by ubiquitination. In the second parts of experiments, expression of HCV core protein reached its maximum at 72 h at 5 μg/ml of Tet. RA signal increased at 36 h, however then decreased at 48 h and 72 h. The decreased RA signal was reverted by N-acetyl cystein (NAC), an antioxidative protein. The cellular antioxidative ability was decreased at 24h, and hydroxyl radical formation was increased at 48 h. Activation of p38 and SRC-3 was observed after induction of HCV core expression, however it was inhibited by NAC. Conclusions; The data of the present study suggest that RA plays an important role in preventive effect of hepatitis C virus- and oxidative stress-related hepatocarcinogenesis Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5723.