Cancer Letters

Cancer Letters

Volume 345, Issue 2, 10 April 2014, Pages 210-215
Cancer Letters

Mini-review
Mechanisms of HCV-induced liver cancer: What did we learn from in vitro and animal studies?

https://doi.org/10.1016/j.canlet.2013.06.028Get rights and content

Highlights

  • Persistent HCV infection is the most common cause of HCC in many developed countries.

  • Virus-induced inflammation and oxidative DNA damage are mechanisms of carcinogenesis.

  • HCV infection disrupts several important tumor suppressor pathways.

  • Progress in research on HCV-associated HCC depends on appropriate experimental models.

  • New transgenic mouse models show promise in understanding of HCV-induced HCC.

Abstract

Hepatitis C virus (HCV) is a cause of liver diseases that range from steatohepatitis, to fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The challenge of understanding the pathogenesis of HCV-associated liver cancer is difficult as most standard animal models used in biomedical research are not permissive to HCV infection. Herein, we provide an overview of a number of creative in vivo, mostly in the mouse, and in vitro models that have been developed to advance our understanding of the molecular and cellular effects of HCV on the liver, specifically with their relevance to HCC.

Introduction

A recent re-analysis of the worldwide global burden of cancer [1] places liver as the 5th most prevalent target organ in terms of the estimated new cases in man, and 7th in women. Most importantly, liver cancer is one of the most deadly cancers, as it is the 2nd leading cause of cancer death in man and 6th in women worldwide. An estimated 748,000 new liver cancer cases and 696,000 cancer deaths occurred worldwide in 2008 with the highest liver cancer rates are reported in East and South-East Asia, and in Middle and Western Africa. Among primary liver cancers, hepatocellular carcinoma (HCC) represents the major subtype, accounting for 70–85% of the total liver cancer burden worldwide.

Among many potential etiological factors that have been causally linked to human cancers, including HCC, infectious agents represent an important sub-group of agents that have been classified as “carcinogenic to humans” (Group 1) by the International Agency for Research on Cancer Monographs Program [2]. Liver is a major cancer site associated with four Group 1 infectious agents: hepatitis B and C viruses, O. viverrini and C. sinensis. With regards to hepatitis C virus (HCV), the relative risk estimate for developing liver cancer in patients with serologically-confirmed HCV infection is estimated to be 17, as compared to 2.5 for HCV-associated non-Hodgkin lymphomas [3]. Importantly, the age-adjusted incidence of HCC is increasing in many countries, including the United States [4], and has been widely attributed to the spread of HCV infection in many industrialized countries [5].

About 2–3% of the world’s population is living with HCV infection, with country-specific prevalence rates ranging from <1% to over 10% [6]. Each year, it is estimated that over 350,000 people die worldwide of HCV-related diseases, predominantly liver cirrhosis and liver cancer [6]. In the United States alone, HCV and associated diseases carry a very high economic burden and it was estimated in 2012 that there are over 50 new drugs in development to treat hepatitis C [7], [8]. Given the societal, economic and other pressures, the field of HCV studies is very vibrant and spans the spectrum of investigations in infectious disease and virology from mechanistic and clinical research, to drug development and epidemiology. However, relatively few studies have focused on the mechanisms underlying the association of liver cancer with HCV, and it is still largely unresolved whether the virus is directly carcinogenic (e.g. causes mutations, genomic instability, or transformation of liver cells), or whether other pathological conditions in the liver (steatosis, inflammation, oxidative stress, and fibrogenesis) that are associated with the chronic viral infection are to blame [5].

Since the discovery of HCV in 1989 [9], our knowledge has expanded exponentially and a plethora of model systems is being utilized by researchers who are interested in HCV itself, or the diseases that HCV has been associated with. These include human subjects, non-human primates, genetically engineered mice, as well as both human- and animal-derived cells. The types of research questions that are being investigated using one or more of these model systems include: (i) the mechanisms of infection, viral life cycle and persistence; (ii) types, pathogenesis and mechanisms of HCV-associated liver diseases, including HCC; (iii) the role of co-morbidity and environmental co-exposure factors; (iv) pharmacotherapy options and treatment strategies; and (v) individual susceptibility factors. While there are a number of animal models for the study of HCV infection and related liver diseases (see [10] for a recent comprehensive review), few models have been applied to study the etiology and mechanisms of liver cancer.

Section snippets

Mechanisms of HCV-associated liver carcinogenesis

Evidence exists to suggest that HCV may be both directly and indirectly involved in the development and progression of HCC [5]. The evidence for the direct carcinogenic action of HCV is less prominent than that for other carcinogenic viruses (e.g. papillomaviruses, herpesviruses, Epstein-Barr virus) which integrate into cellular DNA and/or impair normal controls of proliferation and cell death. HCV is a positive-strand RNA virus that replicates outside of the nucleus and does not have any

Human genome-wide association studies (GWAS)

Current human research in HCV field is primarily focused on understanding liver disease susceptibility and progression and development of new treatments and patient management strategies. There are major differences in how people respond to HCV infection and its treatment. In addition to the virus serotype-specific reasons, host-specific factors play a clear role in whether HCV will lead to chronic infection, as about 30% of persons who acquire HCV infection resolve viremia, leaving only the

Non-human primates

Chimpanzees are the most relevant animal model for studies of HCV infection and related immune and other effects [30]. They are considered a “complete” model with replication, infection and virus production steps of the viral cycle. While the viremia levels are generally high and the human-like host response comprises both innate and adaptive immunity, the pathogenicity of HCV is relatively low in chimpanzees, making them a poor model for chronic liver disease and HCV-associated HCC [10]. Only

Mouse models

The restricted host range of HCV has hampered the development of a suitable small animal model of HCV infection; however, a number of research strategies have been proposed to take advantage of the genetic engineering tools available in the mouse [10]. Of many mouse models that have been developed in the past decade, only HCV transgenic mouse strains have been employed in chronic studies designed to detect liver cancer as an endpoint.

Primary human hepatocytes

Among many in vitro models that have been used in HCV research, adult primary human hepatocytes are considered to be the most human-relevant cell-based liver model [53]. It has been demonstrated more than a decade ago that human serum-derived HCV may infect these cells in culture [54]. Primary adult human hepatocytes are permissive to viral genome replication, although the level of replication is typically very restricted in magnitude [55], [56]. Primary adult human hepatocytes are closest to

Use of mouse model systems to understand factors that facilitate cancer development in HCV-infected liver

Spontaneous development of liver tumors have been observed only in a couple of HCV transgenic mouse strains, usually between 13 and 24 months of age [40], [41], [42]. Most of the HCV transgenic mouse models exhibit a limited overt liver phenotype, even late in life [42], yet are susceptible to a number of additional hepatotoxic challenges such as iron overload [80], carbon tetrachloride [81], alcohol [49], acetaminophen [82], or aflatoxin B1 [83].

Studies in HCV transgenic mice have demonstrated

Conflict of Interest

The authors have nothing to disclose.

Acknowledgements

The authors were supported, in part, by grants from the National Institutes of Health: P42-ES005948, R01-ES015241, R01-CA164029 and R01-AI095690.

References (85)

  • M.L. Washburn et al.

    A humanized mouse model to study hepatitis C virus infection, immune response, and liver disease

    Gastroenterology

    (2011)
  • H. Lerat et al.

    Steatosis and liver cancer in transgenic mice expressing the structural and nonstructural proteins of hepatitis C virus

    Gastroenterology

    (2002)
  • M. Korenaga et al.

    Hepatitis C virus core protein inhibits mitochondrial electron transport and increases reactive oxygen species (ROS) production

    J. Biol. Chem.

    (2005)
  • T.J. Liang et al.

    Pathogenesis of hepatitis C-associated hepatocellular carcinoma

    Gastroenterology

    (2004)
  • T.W. Chong et al.

    Primary human hepatocytes in spheroid formation to study hepatitis C infection

    J. Surg. Res.

    (2006)
  • S. Molina et al.

    The low-density lipoprotein receptor plays a role in the infection of primary human hepatocytes by hepatitis C virus

    J. Hepatol.

    (2007)
  • R.B. Ray et al.

    Hepatitis C virus core protein promotes immortalization of primary human hepatocytes

    Virology

    (2000)
  • K. Si-Tayeb et al.

    Hepatocyte-like cells differentiated from human induced pluripotent stem cells (iHLCs) are permissive to hepatitis C virus (HCV) infection: HCV study gets personal

    J. Hepatol.

    (2012)
  • T. Furutani et al.

    Hepatic iron overload induces hepatocellular carcinoma in transgenic mice expressing the hepatitis C virus polyprotein

    Gastroenterology

    (2006)
  • P. Chouteau et al.

    Hepatitis C virus (HCV) protein expression enhances hepatic fibrosis in HCV transgenic mice exposed to a fibrogenic agent

    J. Hepatol.

    (2012)
  • T. Uehara et al.

    Acetaminophen-induced acute liver injury in HCV transgenic mice

    Toxicol. Appl. Pharmacol.

    (2013)
  • V.V. Keasler et al.

    Increased liver pathology in hepatitis C virus transgenic mice expressing the hepatitis B virus X protein

    Virology

    (2006)
  • A. Jemal et al.

    Global cancer statistics CA Cancer

    J. Clin.

    (2011)
  • H.B. El-Serag

    Hepatocellular carcinoma

    N. Engl. J. Med.

    (2011)
  • F.M. Averhoff et al.

    Global burden of hepatitis C: considerations for healthcare providers in the United States

    Clin. Infect. Dis.

    (2012)
  • A.C. El Khoury et al.

    Economic burden of hepatitis C-associated diseases in the United States

    J. Viral. Hepat.

    (2012)
  • C. Welsch et al.

    New direct-acting antiviral agents for the treatment of hepatitis C virus infection and perspectives

    Gut

    (2012)
  • Q.L. Choo et al.

    Isolation of a cDNA clone derived from a blood-borne non-A, non-B viral hepatitis genome

    Science

    (1989)
  • J. Bukh

    Animal models for the study of hepatitis C virus infection and related liver disease

    Gastroenterology

    (2012)
  • T. Munakata et al.

    Down-regulation of the retinoblastoma tumor suppressor by the hepatitis C virus NS5B RNA-dependent RNA polymerase

    Proc. Natl. Acad. Sci. USA

    (2005)
  • K.A. Walters et al.

    Genomic analysis reveals a potential role for cell cycle perturbation in HCV-mediated apoptosis of cultured hepatocytes

    PLoS Pathog.

    (2009)
  • D.R. McGivern et al.

    Virus-specific mechanisms of carcinogenesis in hepatitis C virus associated liver cancer

    Oncogene

    (2011)
  • Y. Li et al.

    Hepatitis C virus activates Bcl-2 and MMP-2 expression through multiple cellular signaling pathways

    J. Virol.

    (2012)
  • S. Bruno et al.

    DItalian association of the study of the liver sustained virological response to interferon-alpha is associated with improved outcome in HCV-related cirrhosis: a retrospective study

    Hepatology

    (2007)
  • C.B. Bigger et al.

    Intrahepatic gene expression during chronic hepatitis C virus infection in chimpanzees

    J. Virol.

    (2004)
  • A. Rauch et al.

    Genetic variation in IL28B is associated with chronic hepatitis C and treatment failure: a genome-wide association study

    Gastroenterology

    (2010)
  • J.J. Feld et al.

    Mechanism of action of interferon and ribavirin in treatment of hepatitis C

    Nature

    (2005)
  • C.L. Thio et al.

    An analysis of tumor necrosis factor alpha gene polymorphisms and haplotypes with natural clearance of hepatitis C virus infection

    Genes Immun.

    (2004)
  • P. An et al.

    Regulatory polymorphisms in the interleukin-18 promoter are associated with hepatitis C virus clearance

    J. Infect. Dis.

    (2008)
  • Y. Huang et al.

    A functional SNP of interferon-gamma gene is important for interferon-alpha-induced and spontaneous recovery from hepatitis C virus infection

    Proc. Natl. Acad. Sci. USA

    (2007)
  • V. Kumar et al.

    Genome-wide association study identifies a susceptibility locus for HCV-induced hepatocellular carcinoma

    Nat. Genet.

    (2011)
  • D. Miki et al.

    Variation in the DEPDC5 locus is associated with progression to hepatocellular carcinoma in chronic hepatitis C virus carriers

    Nat. Genet.

    (2011)
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