Differential effects of two HDAC inhibitors with distinct concomitant DNA hypermethylation or hypomethylation in breast cancer cells
DNA methylation and histone acetylation are the two important epigenetic phenomena that control the status of X-chromosome inactivation (XCI), a process of dosage compensation in mammals resulting in active X chromosome (Xa) and inactive X chromosome (Xi) in females. While DNA methyltransferases (DNMTs) are known to maintain the DNA hypermethylation of Xi, it remains to be determined how one or a few of 18 known histone deacetylases (HDACs) contribute(s) to Xi maintenance. Herein we found that HDAC1/2/4/6 were overexpressed in breast cancer cells, MDA-MB-231, with Xa/Xa status compared to normal breast epithelial cells, MCF10A, with Xa/Xi status. Inhibition of these overexpressed HDACs with two different drugs, sodium butyrate (SB) and Trichostatin A (TSA), caused surprisingly distinct effects on global DNA methylation: hypermethylation and hypomethylation, respectively, as well as distinct effects on a repressing histone mark H3K27me3 for heterochromatin and an active mark H3K56ac for DNA damage. Surveying three DNMTs through immunoblot analyses for insights revealed the up- or down-regulation of DNMT3A upon drug treatments in a concentration-dependent manner. These results correlated with the decreased XIST and increased TSIX expression in MDA-MB 231 as a possible mechanism of Xi loss and were reversed with SB treatment. Further RNA-seq analysis indicated differential gene expression correlating with the promoter methylation status of a few genes. Collectively, our results demonstrate a crosstalk between HDACs and DNMTs and the novel involvement of HDACs in skewed Xi in breast cancer.