Effects of Histone Deacetylase Inhibitors on Modulating H3K4 Methylation Marks - A Novel Cross-Talk Mechanism between Histone-Modifying Enzymes.

A recent study reports that histone deacetylase (HDAC) inhibitors, AR42 and MS- 275, upregulated H3K4 methylation marks in prostate cancer cells, leading to transcriptional activation of genes including those associated with roles in tumor suppression and cell differentiation (1). Evidence suggests that the crosstalk between histone deacetylation and histone H3K4 methylation is attributable to the ability of these HDAC inhibitors to repress the JARID1 family of histone H3 lysine 4 demethylases (H3K4DMs), including RBP2, PLU-1, SMCX, and LSD1, through the downregulation of Sp1 expression. This demonstrates the complexity of the functional roles of HDACs in the regulation of histone modifications as well as the activation of epigenetically silenced gene expression. Equally important is the ability of HDAC inhibitors to transcriptionally suppress H3K4DM gene expression which has therapeutic implications, in that several H3K4DMs such as LSD1 and PLU-1 have been implicated in the pathogenesis of many types of malignancies.