Nitric Oxide: An Epigenetic Regulator

Methylation and acetylation of Lysine 9 on Histone 3 (H3K9me2/ac) has been shown to play an important role in the epigenetic regulation of gene expression. The methylation status of H3K9 is regulated by methyltransferases (HMT) and demethylases. Demethylation of these epigenetic marks is performed predominantly by a family of JMJC domain Fe(II)-dependent enzymes which use alpha-ketoglutarate and O2 as substrates. Nitric oxide (•NO), a biological free radical with a similar chemical structure as O2, has been shown by our lab to inhibit the JMJC class of lysine-specific demethylases (KDM) and affect global histone methylation. Here, we will demonstrate that the removal of •NO on MDA-MB-231 can reverse the expression of HMT and KDM caused by •NO exposure. Also, levels of H3K9me2/ac returned to basal level after •NO had been removed from the cellular environment. Furthermore, H3K4mono/di/tri methylation are all shown to be affected by •NO. This study provides important insights on how this endogenously-produced molecule can possibly regulate transcription of genes by changing global methylation and acetylation levels of histones. TETs are dioxygenase enzymes that convert 5-methylcytosine (5mC) containing DNA to 5-hydroxymethylcytosine (5hmC) containing DNA. 5mC has been associated with transcription repression whereas, elevated 5hmC levels are associated with gene activation. TET-mediated conversion of 5mC to 5hmC is considered as an important epigenetic component of transcriptional regulation. Similar to JMJC domain-containing demethylases, TETs are oxygen-dependent and require α-ketoglutarate and Fe(II) for their catalytic activities. In addition to determining the modifications of histones by •NO, we will demonstrate the ability of •NO to inhibit TETs functions and decrease the overall conversion of 5mC to 5hmC. Overall, our study reveals novel roles of •NO in regulating the epigenetics landscape via altering DNA modifications and histone modifications.