Intrahepatic hepatitis B virus large surface antigen induces hepatocyte hyperploidy via failure of cytokinesis

Abstract

Hepatitis B virus (HBV) is an aetiological factor for liver cirrhosis and hepatocellular carcinoma (HCC). Despite current antiviral therapies that successfully reduce the viral load in patients with chronic hepatitis B, persistent hepatitis B surface antigen (HBsAg) remains a risk factor for HCC. To explore whether intrahepatic viral antigens contribute directly to hepatocarcinogenesis, we monitored the mitotic progression of HBV-positive cells. Cytokinesis failure was increased in HBV-positive HepG2.2.15 and 1.3ES2 cells, as well as in HuH-7 cells transfected with a wild-type or X-deficient HBV construct, but not in cells transfected with an HBsAg-deficient construct. We show that expression of viral large surface antigen (LHBS) was sufficient to induce cytokinesis failure of immortalized hepatocytes. Premitotic defects with DNA damage and G /M checkpoint attenuation preceded cytokinesis in LHBS-positive cells, and ultimately resulted in hyperploidy. Inhibition of polo-like kinase-1 (Plk1) not only restored the G /M checkpoint in these cells, but also suppressed LHBS-mediated in vivo tumourigenesis. Finally, a positive correlation between intrahepatic LHBS expression and hepatocyte hyperploidy was detected in >70% of patients with chronic hepatitis B. We conclude that HBV LHBS provokes hyperploidy by inducing DNA damage and upregulation of Plk1; the former results in atypical chromatin structures, and the latter attenuates the function of the G /M DNA damage checkpoint. Our data uncover a mechanism by which genomic integrity of hepatocytes is disrupted by viral LHBS. These findings highlight the role of intrahepatic surface antigen as an oncogenic risk factor in the development of HCC. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Polyploid Giant Cancer Cells, a Hallmark of Oncoviruses and a New Therapeutic Challenge

“…Most importantly, FL-HBx transgenic mice exhibited an important increase of 4n hepatocytes during HCC initiation, along with an increase in HCC progenitor cell markers ( 92 ). This is endorsed by the fact that in the HBV-positive hepatoma cell lines HepG2.2.15 and 1.3ES2, a higher hyperploidy is detected compared to HBV-negative cells ( 93 ). Although a high fraction of pX-induced polyploid cells undergo apoptosis in poorly differentiated, immortalized hepatocytes, the surviving cells demonstrated two-fold increase in polyploidy, displayed characteristics of oncogenic transformation and an increase in the expression of proliferation genes know to be elevated in HCC, an effect repressed in the absence of pX ( 94 ).…”

Aneuploidy and oncoviruses

“…A recent study by Li et al shows that expression of viral large surface antigen (LHBS) is conducive to cytokinesis failure of immortalized hepatocytes and ultimately results in aneuploidy. So, LHBS‐induced cytokinesis failure may be the beginning of HCC development (Figure C) …”

Hepatitis B virus large surface protein is priming for hepatocellular carcinoma development via induction of cytokinesis failure

“…The risk of HCC development in patients with chronic HBV infection can be estimated by several parameters, including blood levels of markers such as HBV e antigen (HBeAg) and HBV‐DNA . Serum levels >1000 IU/ml of HBV surface antigen (HBsAg), which is encoded by the preS1/preS2/S open reading frame (ORF) of the HBV genome and which is the hallmark of HBV infection , is also associated with risk of disease progression in patients with chronic HBV infection harboring low viral load . Unfortunately, HBsAg seroclearance is infrequently achieved after treatment with current antiviral drugs , raising the question of mechanisms mediating HBsAg seroclearance failure after antiviral therapy and the question of direct oncogenic functions of HBV surface proteins.…”

“…Regarding the high rates of HBsAg persistence after antiviral therapy and oncogenic functions of HBV surface proteins, it is essential to understand molecular mechanisms of HBsAg seroclearance failure after antiviral therapy and HCC development mediated by HBV surface proteins to establish new strategies for HCC prevention and/or therapy. The recent study by Li et al , published in The Journal of Pathology has shown that LHBs contributes to HCC development by inducing cytokinesis failure and consequent aneuploidy via induction of DNA damage and G2/M checkpoint override in hepatocytes (Figure ). This cytokinesis failure and consequent aneuploidy may lead to chromosome/genome instability , generating genetic diversity that facilitates the acquisition of cancer hallmarks .…”

“…As initial cytokinesis failure can give rise to further aneuploidy, self‐propagating cycles of chromosomal instability may emerge and drive intra‐tumor heterogeneity and clonal cancer evolution , LHBs‐induced cytokinesis failure may be a priming event for HCC development. Therefore, inhibition of PLK1, shown to be effective in reducing tumor burden by Li et al , appears to be a promising target to disrupt this vicious circle, but the clinical role of PLK1‐inhibitors needs to be evaluated in various phases of clinical trials . Other drugs may be also considered, such as aneuploidy‐selective antiproliferative drugs, e.g.…”