A sequential treatment of depsipeptide followed by 5-azacytidine enhances Gadd45β expression in hepatocellular carcinoma cells

Background: DNA methylation can influence histone modification and gene expression. The growth-arrest DNA damage inducible gene 45β (Gadd45β) 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 Gadd45β 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 μM depsipeptide reactivated Gadd45β gene expression considerably within 4 h in HepG2 cells, but not in CL-48 or Hep3B cells. Up to 10 μM 5-azacytidine had no reactivation effect on Gadd45β. A sequential treatment of depsipeptide+5-azacytidine (but not 5-azacytidine+depsipeptide) exhibited a synergistic effect on Gadd45β 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.