Hepatitis B Virus X Protein Linked to Liver Cancer Development

Strategic Insights -

Scientists in the United States have reported a link between hepatitis B virus (HBV) infection and the development of liver cancer, specifically hepatocellular carcinoma (HCC). The HBV X protein (pX) is implicated as a weak oncogene or a cofactor in hepatocarcinogenesis. Research has shown that pX induces DNA re-replication, DNA damage, and partial polyploidy in hepatocytes, leading to oncogenic transformation. A study conducted at Purdue University found that the pX-induced polyploid cells undergo apoptosis and display proliferation sensitive to p53, but after 40 cell generations, they exhibit loss of p53 function and become growth factor- and anchorage-independent, indicative of oncogenic transformation. The study also identified Polo-like kinase 1 (Plk1) as crucial in pX-mediated oncogenic transformation and a promising therapeutic target for HBV-mediated HCC.

Key Takeaways:

  • The HBV X protein (pX) is implicated in hepatocarcinogenesis, inducing DNA re-replication, DNA damage, and partial polyploidy in hepatocytes.
  • pX-induced polyploid cells undergo apoptosis and display proliferation sensitive to p53, but after 40 cell generations, they exhibit loss of p53 function and become growth factor- and anchorage-independent.
  • The pX-induced polyploid cultures in the course of 70 cell generations undergo progressively increasing DNA damage, propagate damaged DNA to daughter cells, and display increased expression of a cluster of proliferation genes, including HBV-HCC genes.
  • One of these genes is the mitotic kinase Polo-like kinase 1 (Plk1), which is crucial in pX-mediated oncogenic transformation.
  • Oncogenic transformation is suppressed in the absence of pX expression, and significantly, by inhibition of Plk1.
  • The study suggests that Pfizer-like kinase 1 (Plk1) may be a promising therapeutic target for HBV-mediated HCC.

Statistics:

  • Nearly 40% of pX-induced polyploid cells undergo apoptosis immediately after live cell-sorting.
  • The surviving cells exhibit proliferation sensitive to p53.
  • After 40 cell generations, the pX-expressing polyploid cultures exhibit loss of p53 function and become growth factor- and anchorage-independent.
  • 70 cell doublings were observed in the pX-induced polyploid cultures.
  • Expression of Plk1 is elevated in pX-induced polyploid cultures after 40 cell generations.

Sources:

  • Studach, L.L., et al. "Polo-Like Kinase 1 Inhibition Suppresses Hepatitis B Virus X Protein-Induced Transformation in an In Vitro Model of Liver Cancer Progression." Hepatology, vol. 50, no. 2, 2009, pp. 414-423.
  • (HEPATOLOGY 2009;50:414-423.)
  • John Wiley & Sons Inc. (publisher of Hepatology)