Hepatocellular carcinoma is one of the most common
cancers worldwide. During
tumorigenesis,
tumor suppressor and
cancer-related genes are commonly silenced by aberrant DNA methylation in their promoter regions.
Zebularine (1-(β-(D)-ribofuranosyl)-1,2-dihydropyrimidin-2-one) acts as an inhibitor of DNA methylation and exhibits chemical stability and minimal cytotoxicity both in vitro and in vivo. In this study, we explore the effect and possible mechanism of action of
zebularine on
hepatocellular carcinoma cell line HepG2. We demonstrate that
zebularine exhibits antitumor activity on HepG2 cells by inhibiting cell proliferation and inducing apoptosis, however, it has little effect on DNA methylation in HepG2 cells. On the other hand,
zebularine treatment downregulated CDK2 and the phosphorylation of
retinoblastoma protein (Rb), and upregulated p21(WAF/CIP1) and p53. We also found that
zebularine treatment upregulated the phosphorylation of p44/42
mitogen-activated protein kinase (MAPK). These results suggest that the p44/42 MAPK pathway plays a role in
zebularine-induced cell-cycle arrest by regulating the activity of p21(WAF/CIP1) and Rb. Furthermore, although the proapoptotic
protein Bax levels were not affected, the antiapoptotic
protein Bcl-2 level was downregulated with
zebularine treatment. In addition, the data in the present study indicate that inhibition of the
double-stranded RNA-dependent
protein kinase (PKR) is involved in inducing apoptosis with
zebularine. These results suggest a novel mechanism of
zebularine-induced cell growth arrest and apoptosis via
a DNA methylation-independent pathway in
hepatocellular carcinoma.