The Important Role Of UHRF1/DNMT1 Stability Regulation In DNA Methylation Maintenance

The precise inheritance of DNA methylation during cell division is important for cell function and cell fate.DNA methylation homeostasis regulation is a hot topic in the field of epigenetics.DNMT1 and UHRF1 are important factors for DNA methylation,but how UHRF1 and DNMT1 are regulated remains to be fully investigated.Previous studies indicated that the protein levels of histone methyltransferase SET8 and UHRF1 show an opposite change in the process of cell cycle.In this study,we found that histone methyltransferase SET8 can regulate the protein stability of UHRF1.SET8 catalyzes the methylation of UHRF1 at K385,which in turn promotes the ubiquitination of UHRF1 at K500,leading to the ubiquitination-dependent degradation of UHRF1.In contrast,lysine demethylase LSD1 can remove the methylation modification of UHRF1 and stabilize UHRF1 protein.We also found that,similar to UHRF1,the protein stability of DNMT1 is also oppositely regulated by SET8 and LSD1.Further studies showed that SET8 protein negatively controls DNA methylation by promoting ubiquitination and degradation of DNMT1 and UHRF1.On the contrary,LSD1 positively control DNA methylation by stabilizing DNMT1 and UHRF1.Moreover,we found that the down-regulation of UHRF1 by SET8 in G2/M p Hase is important for accurate regulation of DNA methylation in G2/M p Hase.Based on our findings that methylation modification can regulate the stability of UHRF1 and DNMT1 and DNA methylation,we investigated if the intracellular methyl donor S-adenosyl methionine(SAM)affects the protein stability of UHRF1 and DNMT1.We found that the intracellular SAM concentration was negatively correlated with the protein stability of UHRF1 and DNMT1.Importantly,we found that changes in SAM level only moderately affect the global level of DNA methylation,due to the existence of the negative regulation of UHRF1/DNMT1 by SAM.In summary,we have identified a SET8-mediated,methylation-dependent regulation of UHRF1 and DNMT1 protein stability and elucidated the underlying mechanism for UHRF1.We also demonstrate that this methylation-dependent stablility control of UHRF1 and DNMT1 can be used by cell to sense the changing levels of SAM to maintain DNA methylation homeostasis.