Histone deacetylase inhibitors induce the expression of tumor suppressor genes Per1 and Per2 in human gastric cancer cells.

Period circadian regulator (Per)1 and Per2 genes are involved in the molecular mechanism of the circadian clock, and exhibit tumor suppressor properties. Several studies have reported a decreased expression of Per1, Per2 and Per3 genes in different types of cancer and cancer cell lines. Promoter methylation downregulates Per1, Per2 or Per3 expression in myeloid leukemia, breast, lung, and other cancer cells; whereas histone deacetylase inhibitors (HDACi) upregulate Per1 or Per3 expression in certain cancer cell lines. However, the transcriptional regulation of Per1 and Per2 in cancer cells by chromatin modifications is not fully understood. The present study aimed to determine whether HDACi regulate Per1 and Per2 expression in gastric cancer cell lines, and to investigate changes in chromatin modifications in response to HDACi. Treatment of KATO III and NCI-N87 human gastric cancer cells with sodium butyrate (NaB) or Trichostatin A (TSA) induced Per1 and Per2 mRNA expression in a dose-dependent manner. Chromatin immunoprecipitaion assays revealed that NaB and TSA decreased lysine 9 trimethylation on histone H3 (H3K9me3) at the Per1 promoter. TSA, but not NaB increased H3K9 acetylation at the Per2 promoter. It was also observed that binding of Sp1 and Sp3 to the Per1 promoter decreased following NaB treatment, whereas Sp1 binding increased at the Per2 promoter of NaB- and TSA-treated cells. In addition, Per1 promoter is not methylated in KATO III cells, while Per2 promoter was methylated, although NaB, TSA, and 5-Azacytidine do not change the methylated CpGs analyzed. In conclusion, HDACi induce Per1 and Per2 expression, in part, through mechanisms involving chromatin remodeling at the proximal promoter of these genes; however, other indirect mechanisms triggered by these HDACi cannot be ruled out. These findings reveal a previously unappreciated regulatory pathway between silencing of Per1 gene by H3K9me3 and upregulation of Per2 by HDACi in cancer cells.