title: DNA methyltransferase inhibitor zebularine inhibits human hepatic carcinoma cells proliferation and induces apoptosis.
abstract: 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.
authors: Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan. nakamura-kz@ncchd.go.jp
authors: Kazuaki
authors: K
authors: Nakamura
authors: Kazuko
authors: K
authors: Aizawa
authors: Kazuhiko
authors: K
authors: Nakabayashi
authors: Natsuko
authors: N
authors: Kato
authors: Junji
authors: J
authors: Yamauchi
authors: Kenichiro
authors: K
authors: Hata
authors: Akito
authors: A
authors: Tanoue
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors*; D019175:DNA Methylation / Q000187:drug effects*; D056945:Hep G2 Cells; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D010766:Phosphorylation
chemical_list: D000970:Antineoplastic Agents; D003562:Cytidine; C009131:pyrimidin-2-one beta-ribofuranoside; D004248:DNA (Cytosine-5-)-Methyltransferases; D020169:Caspases