A sequential treatment of depsipeptide followed by 5-azacytidine enhances Gadd45beta expression in hepatocellular carcinoma cells.

BACKGROUND DNA methylation can influence histone modification and gene expression. The growth-arrest DNA damage inducible gene 45beta (Gadd45beta) has been reported as a potential diagnostic marker for aggressive hepatocellular carcinoma. In this study, the synergistic effect of the histone deacetylase inhibitor depsipeptide and the DNA methyltransferase inhibitor 5-azacytidine on the Gadd45beta gene expression in human liver cells was examined. MATERIALS AND METHODS The effects of depsipeptide and 5-azacytidine in CL-48, HepG2 and Hep3B cells were examined by PCR, cell viability test, Western blot and chromatin immunoprecipitation assay. RESULTS Two microM depsipeptide reactivated Gadd45beta gene expression considerably within 4 h in HepG2 cells, but not in CL-48 or Hep3B cells. Up to 10 microM 5-azacytidine had no reactivation effect on Gadd45beta. A sequential treatment of depsipeptide+5-azacytidine (but not 5-azacytidine+depsipeptide) exhibited a synergistic effect on Gadd45beta gene reactivation in the HepG2 cells. CONCLUSION The results show for the first time that histone acetylation in sequence with hypermethylation can override transcriptional repression. Our results provide a novel insight into the epigenetics-based strategy for treating human liver cancer.