HBx protein of hepatitis B virus promotes reinitiation of DNA replication by regulating expression and intracellular stability of replication licensing factor CDC6

J Biol Chem. 2012 Jun 8;287(24):20545-54. doi: 10.1074/jbc.M112.359760. Epub 2012 Apr 19.

Abstract

Prevention of re-replication via negative regulation of replication initiator proteins, such as CDC6, is key to maintenance of genomic integrity, whereas their up-regulation is generally associated with perturbation in cell cycle, genomic instability, and potentially, tumorigenesis. The HBx oncoprotein of hepatitis B virus is well known to deregulate cell cycle and has been intricately linked to development of hepatocellular carcinoma. Despite a clear understanding of the proliferative effects of HBx on cell cycle, a mechanistic link between HBx-mediated hepatocarcinogenesis and host cell DNA replication remains poorly perused. Here we show that HBx overexpression in both the cellular as well as the transgenic environment resulted in the accumulation of CDC6 through transcriptional and post-translational up-regulation. The HBx-mediated increase in CDK2 activity altered the E2F1-Rb (retinoblastoma) balance, which favored CDC6 gene expression by E2F1. Besides, HBx impaired the APC(Cdh1)-dependent protein degradation pathway and conferred intracellular stability to CDC6 protein. Increase in CDC6 levels correlated with increase in CDC6 occupancy on the β-globin origin of replication, suggesting increment in origin licensing and re-replication. In conclusion, our findings strongly suggest a novel role for CDC6 in abetting the oncogenic sabotage carried out by HBx and support the paradigm that pre-replicative complex proteins have a role in oncogenic transformation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Transformation, Viral*
  • Cyclin-Dependent Kinase 2 / genetics
  • Cyclin-Dependent Kinase 2 / metabolism
  • DNA Replication*
  • E2F1 Transcription Factor / genetics
  • E2F1 Transcription Factor / metabolism
  • HEK293 Cells
  • Hep G2 Cells
  • Hepatitis B virus / genetics
  • Hepatitis B virus / metabolism*
  • Humans
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Stability
  • Replication Origin / genetics
  • Retinoblastoma Protein / genetics
  • Retinoblastoma Protein / metabolism
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Up-Regulation*
  • Viral Regulatory and Accessory Proteins

Substances

  • CDC6 protein, human
  • Cell Cycle Proteins
  • E2F1 Transcription Factor
  • E2F1 protein, human
  • Nuclear Proteins
  • Retinoblastoma Protein
  • Trans-Activators
  • Viral Regulatory and Accessory Proteins
  • hepatitis B virus X protein
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2