Hepatitis B virus X protein activates the ATM–Chk2 pathway and delays cell cycle progression

Abstract

Genetic instability is intimately associated with tumour development. In particular, liver cancers associated with hepatitis B virus (HBV) exhibit high genetic instability; however, our understanding of the underlying molecular mechanisms remains limited. In this study, we found that c-H2AX, a marker of DNA double-strand breaks (DSBs), and the levels of phospho-Chk2 (p-Chk2, the activated form) were significantly elevated in HBV-associated hepatocellular carcinomas and neighbouring regenerating nodules. Likewise, introduction of the pHBV or pMyc-HBx plasmids into cells induced accumulation of c-H2AX foci and increased the p-Chk2 level. In these cells, inhibitory phosphorylation of Cdc25C phosphatase (Ser 216 ) and CDK1(Tyr 15 ) was elevated; consequently, cell-cycle progression was delayed at G 2 /M phase, suggesting that activation of the ATM-Chk2 pathway by the HBV X protein (HBx) induces cell-cycle delay. Accordingly, inhibition of ataxia telangiectasia mutated (ATM) by caffeine or siRNA abolished the increase in the p-Chk2 level and restored the delayed CDK1 kinase activity in ChangX cells. We also found that cytoplasmic HBx, but not nuclear HBx, induced reactive oxygen species (ROS) production and led to the accumulation of c-H2AX foci and the increased p-Chk2 level. Together, these data indicate that HBx-induced ROS accumulation induces DNA damage that activates the ATM-Chk2 pathway. Our findings provide insight into the mechanisms of HBV pathogenesis.

Downregulation of long non‑coding RNA GAS5 promotes cell proliferation, migration and invasion in esophageal squamous cell carcinoma

“…Loss of ATM-CHK2-tumor protein p53 pathway components has been shown to accelerate tumor development in gliomas (22). Additionally, hepatitis B virus X protein can delay the cell cycle progression in liver cancer by activating the ATM-Chk2 pathway (23). Naphthalimides have been confirmed to induce G 2 arrest in HCT116 cells via activating the ATM-CHK2 pathway (24).…”

Oxidative stress, a trigger of hepatitis C and B virus-induced liver carcinogenesis

“…One can speculate that DNA oxidation and concomitant removal of oxidized nucleic bases in HBV-infected cells is compensated by a defective repair of the oxidative damage, with a concomitant accumulation of single-strand breaks. This hypothesis is supported by data which indicate that HVB infection leads to activation of the ATM-Chk2 pathway [339] responsible for the repair of double-strand breaks, DNA damage response resulting in an increased genomic instability [340]. …”

Chronic Hepatitis B Virus Infection Associated with Increased Colorectal Cancer Risk in Taiwanese Population

“…First, HBx interferes with nucleotide excision repair, which leads to DNA damage through both p53-dependent and -independent pathways [30,31]. Second, HBx protein also acts on anti-and pro-apoptotic pathways, particularly important in the inhibition of p53 [30][31][32]. Third, HBx protein may increase the expression of TERT and telomerase activity by which it enhances the life-span of hepatocytes and contributes to hepatocarcinogenesis [31].…”