Ubp-M Serine 552 Phosphorylation By Cyclin-dependent Kinase 1 Regulates Cell Cycle Progression

Ubiquitination and deubiquitination are very important epigenetical modulations.We identified Ubp-M as a histone H2A deubiquitinase that regulates cell cycle progression and gene expression.In previous study,Ubp-M is phosphorylated at the onset of mitosis and dephosphorylated during the metaphase/anaphase transition.It was not clear how phosphorylation regulates the function of Ubp-M,which sites can be phosphorylated in Ubp-M and what kind of kinase catalyzes Ubp-M phosphorylation.Reserches indicated that cyclin-dependent kinasel(CDK)which regulates cell cycle processtion,may phosphorylate Ubp-M,because Ubp-M is phosphorylated in mitosis when CDKl regulates cell cycle with kinase activity.In our studies,mass spectrometry analysis confirmed Ubp-M is phosphorylated at 4 sites,but Serine 552 is the major site.In vitro and in vivo assays demonstrated that CDKI/cyclin B kinase is responsible for Ubp-M S552P.To further study the function of Ubp-M S552P,we purified wild type FLAG-Ubp-M and two Ubp-M mutants S552A and S552E.Importantly,our study revealed that Ubp-M S552P is not required for Ubp-M in vitro deubiquitination activity and in vivo gene expression regulation;instead,our studies specifically link Ubp-M S552P to cell proliferation and cell cycle G2/M phase progression.In addition,Ubp-M S552P regulates interaction between Ubp-M and nuclear export receptor CRM1.As cells prepare to enter M phase,cytoplasmic cycle B/CDK kinase is activated and phosphorylates Ubp-M S552.S552P is not required to deubiquitinase activity and gene expression regulation,but regulates cell proliferation and cell cycle progression.S552P disrupts Ubp-M interaction with CRM1,allowing Ubp-M to be retained in the nucleus and deubiquitinate nucleosomal uH2A,which is required for chromosome condensation and cell cycle progression.