title: Phosphorylation of MCM3 protein by cyclin E/cyclin-dependent kinase 2 (Cdk2) regulates its function in cell cycle.
abstract: MCM2-7 proteins form a stable heterohexamer with DNA helicase activity functioning in the DNA replication of eukaryotic cells. The MCM2-7 complex is loaded onto chromatin in a cell cycle-dependent manner. The phosphorylation of MCM2-7 proteins contributes to the formation of the MCM2-7 complex. However, the regulation of specific MCM phosphorylation still needs to be elucidated. In this study, we demonstrate that MCM3 is a substrate of cyclin E/Cdk2 and can be phosphorylated by cyclin E/Cdk2 at Thr-722. We find that the MCM3 T722A mutant binds chromatin much less efficiently when compared with wild type MCM3, suggesting that this phosphorylation site is involved in MCM3 loading onto chromatin. Interestingly, overexpression of MCM3, but not MCM3 T722A mutant, inhibits the S phase entry, whereas it does not affect the exit from mitosis. Knockdown of MCM3 does not affect S phase entry and progression, indicating that a small fraction of MCM3 is sufficient for normal S phase completion. These results suggest that excess accumulation of MCM3 protein onto chromatin may inhibit DNA replication. Other studies indicate that excess of MCM3 up-regulates the phosphorylation of CHK1 Ser-345 and CDK2 Thr-14. These data reveal that the phosphorylation of MCM3 contributes to its function in controlling the S phase checkpoint of cell cycle in addition to the regulation of formation of the MCM2-7 complex.
authors.affiliation: Center for Molecular Immunology, Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Junhui
authors.initials: J
authors.lastname: Li
authors.forename: Min
authors.initials: M
authors.lastname: Deng
authors.forename: Qian
authors.initials: Q
authors.lastname: Wei
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Tong
authors.forename: Xin
authors.initials: X
authors.lastname: Ye
mesh_terms: D019943:Amino Acid Substitution; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D002843:Chromatin / Q000235:genetics / Q000378:metabolism*; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D064126:Minichromosome Maintenance Complex Component 3; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011494:Protein Kinases / Q000096:biosynthesis / Q000235:genetics; D016196:S Phase / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D019927:Cyclin E; D004268:DNA-Binding Proteins; C066470:MCM3 protein, human; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D064126:Minichromosome Maintenance Complex Component 3