G9a Regulates Degradation of the DNMT Family through their Methylation-Dependent Ubiquitination

Abstract

Histone H3K9 methyl transferase G9a plays a key role in transcriptional repression via the increase of H3K9 methylation for recruiting the repressor complex. G9a is reported to associate with DNMT1, DNMT3a, and DNMT3b. A previous study reported that G9a methylates DNMT3a on K44 site, however, DNMT3a2, which doesn’t have K44 site, is still methylated by G9a. G9a methylates DNMT3a2 and DNMT3b directly. G9a expression increases DNMT3a2 and DNMT3b degradation through their ubiquitination. The treatment of the G9a/GLP inhibitor UNC0638 and G9a knockdown by pGreenPuro G9a as a shRNA decrease DNMT3a degradation and increases DNA methylation levels. Moreover, the expressions of G9a and GLP increase DNMT3a ubiquitination compared to the control, indicating that DNMT3a degradation is dependent on methyltransferase activity. UHRF1 and DCAF1, E3 ligases containing the methyl recognition domains, are responsible for methylated DNMT3a2 degradation. Collectively, DNMT3a2 and DNMT3b methylated by G9a are degraded by UHRF1 and DCAF1 through methylation-dependent ubiquitination. Therefore, G9a regulates DNA methylation by UHRF1 and DCAF1-mediated DNMT3a/3b degradation.