Hepatitis C Virus core+1/ARF Protein Modulates the Cyclin D1/pRb Pathway and Promotes Carcinogenesis

Abstract

Viruses often encompass overlapping reading frames and unconventional translation mechanisms in order to maximize the output from a minimum genome and to orchestrate their timely gene expression. Hepatitis C virus (HCV) possesses such an unconventional open reading frame (ORF) within the core-coding region, encoding an additional protein, initially designated ARFP, F, or core+1. Two predominant isoforms of core+1/ARFP have been reported, core+1/L, initiating from codon 26, and core+1/S, initiating from codons 85/87 of the polyprotein coding region. The biological significance of core+1/ARFP expression remains elusive. The aim of the present study was to gain insight into the functional and pathological properties of core+1/ARFP through its interaction with the host cell, combining and approaches. Our data provide strong evidence that the core+1/ARFP of HCV-1a stimulates cell proliferation in Huh7-based cell lines expressing either core+1/S or core+1/L isoforms and in transgenic liver disease mouse models expressing core+1/S protein in a liver-specific manner. Both isoforms of core+1/ARFP increase the levels of cyclin D1 and phosphorylated Rb, thus promoting the cell cycle. In addition, core+1/S was found to enhance liver regeneration and oncogenesis in transgenic mice. The induction of the cell cycle together with increased mRNA levels of cell proliferation-related oncogenes in cells expressing the core+1/ARFP proteins argue for an oncogenic potential of these proteins and an important role in HCV-associated pathogenesis. This study sheds light on the biological importance of a unique HCV protein. We show here that core+1/ARFP of HCV-1a interacts with the host machinery, leading to acceleration of the cell cycle and enhancement of liver carcinogenesis. This pathological mechanism(s) may complement the action of other viral proteins with oncogenic properties, leading to the development of hepatocellular carcinoma. In addition, given that immunological responses to core+1/ARFP have been correlated with liver disease severity in chronic HCV patients, we expect that the present work will assist in clarifying the pathophysiological relevance of this protein as a biomarker of disease progression.

Hepatitis C Virus Translation Regulation

“…Another clear evidence for a role of the ARF/core+1 protein comes from the analysis of cell cycle control. Overexpression of the HCV genotype 1a (H) protein in two isoforms resulted in slightly higher expression of cyclin D1 and in strongly enhanced phosphorylation of the retinoblastoma (Rb) protein, correlating with higher cell proliferation rates in Huh-7.5 cells [245]. Concomitantly, expression of cellular proto-oncogenes including hras, c-fos, c-jun, c-myc, and vav1 was elevated under ARF/core+1 overexpression, and the number of tumors in mice overexpressing the ARF/core+1 protein during chemically induced tumorigenesis was significantly increased [245].…”

“…Overexpression of the HCV genotype 1a (H) protein in two isoforms resulted in slightly higher expression of cyclin D1 and in strongly enhanced phosphorylation of the retinoblastoma (Rb) protein, correlating with higher cell proliferation rates in Huh-7.5 cells [245]. Concomitantly, expression of cellular proto-oncogenes including hras, c-fos, c-jun, c-myc, and vav1 was elevated under ARF/core+1 overexpression, and the number of tumors in mice overexpressing the ARF/core+1 protein during chemically induced tumorigenesis was significantly increased [245]. This indicates that HCV not only rapidly reprograms the hepatocyte metabolism to promote the Warburg effect that is a characteristic of tumor cells [11,246] but also establishes proto-oncogene expression changes that lead to cancer in the long run.…”

A Novel Cis-Acting RNA Structural Element Embedded in the Core Coding Region of the Hepatitis C Virus Genome Directs Internal Translation Initiation of the Overlapping Core+1 ORF

“…Moreover, studies conducted by us revealed a high prevalence of core+1 antibodies in HCV patients with advanced cirrhosis [35] and hepatocellular carcinoma (HCC) [36], suggesting that core+1 antibodies in HCV infection may present a marker for the progression of liver disease and the development of liver cancer. Consistently, we recently showed that core+1/S isoform promotes the cell cycle in hepatoma cells and enhances liver regeneration and oncogenesis in transgenic mice [37]. However, the regulatory mechanism controlling the translation initiation of core+1/S protein remains elusive.…”

DNA hypermethylation of aurora kinase A in hepatitis�C virus‑positive hepatocellular carcinoma

“…HCV stimulates excessive cell proliferation in hepatocytes by dysregulating the cell cycle, which induces the development of HCC (25,26). Several positive cell cycle regulators (such as cyclin D1, cyclin E and Rb/p105) have been identified to be upregulated, whereas negative regulators [such as cyclin-dependent kinase 4 (CDK4), CDK6, p21Cip1, p27Kip1 and p57Kip2) are downregulated in patients with HCV-positive HCC compared with patients with chronic hepatitis C with or without liver cirrhosis (27).…”