Hepatitis C virus core protein promotes proliferation of human hepatoma cells through enhancement of transforming growth factor   expression via activation of nuclear factor- B

Abstract

Background: Hepatitis C virus (HCV) infection is a major cause of human hepatocellular carcinoma (HCC). The precise mechanism of hepatocarcinogenesis in humans by HCV is currently unclear. It was recently shown, however, that transgenic mice with the HCV core gene often develop HCC, suggesting tumorigenic activity of the HCV core protein. Further, the HCV core protein expressed in HepG2 cells transfected with the core gene was shown to stimulate proliferation of transfectants through activation of nuclear factor-kB (NF-kB). The downstream target molecule(s) of NF-kB activated by the HCV core protein to evoke cell proliferation is not yet identified. Transforming growth factor (TGF) a, which is often overexpressed in various tumour tissues such as HCC, has been shown to stimulate hepatocyte proliferation through activation of the mitogen-activated protein kinase or extracellular signal-related protein kinase (MAPK/ ERK) cascade. Aims: To explore the possibility that TGFa might be a target molecule for NF-kB activated by the HCV core, and that TGFa participates in the growth promotion of the core transfectants in an autocrine manner, activating the MAPK/ERK pathway. Methods: A HCV core expression vector was transfected into human hepatoma Huh-7, HepG2 and Hep3B cells. NF-kB activity was examined by an electrophoretic mobility shift assay. TGFa transcription was assessed by a luciferase reporter assay. TGFa protein was determined by immunoblot and ELISA. MAPK/ ERK activity was examined by an in vitro kinase assay. Cell proliferation was assessed by a water-soluble tetrazolium salt-1 assay. Results: In the HCV core transfectants, NF-kB bound to the kB site in the TGFa proximal promoter region, resulting in an increase in TGFa transcription. Immunoblot as well as ELISA showed increased TGFa expression in the HCV core transfectants. SN50, a specific inhibitory peptide for NF-kB, cancelled HCV core-induced TGFa expression. HCV core protein increased cell proliferation as well as ERK activity of the HCV core transfectants as compared with the mock transfectants. The growth-promoting activity and activation of ERK by the HCV core protein were negated by treatment with anti-TGFa antibodies. Conclusions: These results suggest that the HCV core protein promotes proliferation of human hepatoma cells by activation of the MAPK/ERK pathway through up regulation of TGFa transcription via activation of NF-kB. Our finding provides a new insight into the mechanism of hepatocarcinogenesis by HCV infection.

Hepatitis C Virus (HCV) Proteins Induce NADPH Oxidase 4 Expression in a Transforming Growth Factor β-Dependent Manner: a New Contributor to HCV-Induced Oxidative Stress

“…Previous reports indicated that ROS induced by the structural core protein has an antiapoptotic and proliferative effect on hepatocytes (48,56,57). Hepatocytes expressing the core protein alone were reported to induce TGF-␤ and connective tissue growth factor mRNA (59).…”

Asian Pacific Association for the Study of the Liver consensus recommendations on hepatocellular carcinoma

“…Expression of transforming growth factor-a, an EGFR ligand, can be induced by hepatitis viral proteins and may act synergistically with viral infection in hepatocarcinogenesis [362][363][364]. Results of EGFR expression in HCC tumor tissues, mainly by immunohistochemistry, varied in different studies [365], and activating mutation of EGFR, the major determinant of efficacy of EGFR inhibitors in lung cancer [366], was rarely found in HCC tumor tissue [367].…”

NF-κB signaling, liver disease and hepatoprotective agents

“…There are two different mechanisms of NF-kB activation by HCV. One is induced by HCV core protein which can bind to the death domain of TNF receptor 1 (TNFR1) and to the cytoplasmic domain of the LTb receptor (LTbR) to activate NF-kB (Tai et al, 2000;Sato et al, 2006). HCV can also promote proliferation of human hepatoma cells by activation of the ERK MAP kinase pathway through upregulation of TGFa transcription through activation of NF-kB.…”

“…The HCV core protein can promote proliferation of human hepatoma cells by activating NF-kB, thereby leading to TGF-a induction and activation of the ERK/ MAP kinase pathway (Sato et al, 2006). The region of the core protein responsible for NF-kB activation encompasses amino acids 9-11 which are highly conserved (93%) in all HCV strains (Mann et al, 2006).…”