Abstract
Chronic Hepatitis B virus (HBV) infection is linked to development of hepatocellular carcinoma (HCC). The HBV X protein (pX) is implicated in HCC pathogenesis acting as a weak oncogene or a co-factor in hepatocarcinogenesis. pX induces DNA re-replication, DNA damage and partial polyploidy in a poorly differentiated, immortalized hepatocyte cell line. In this study, we employed sorted, pX-induced polyploid cells to investigate their growth and oncogenic transformation potential, over the course of 70 cell doublings. Immediately after live cell-sorting, nearly 40% of pX-induced polyploid cells undergo apoptosis, while 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, indicative of oncogenic transformation. 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 shown to be elevated in human HCC, including HBV-HCC. One of these genes is the mitotic kinase Polo-like kinase 1 (Plk1). Oncogenic transformation is suppressed in the absence of pX expression, and significantly, by inhibition of Plk1. These results identify Plk1 as crucial in pX-mediated oncogenic transformation.