title: Phosphorylation of minichromosome maintenance protein 7 (MCM7) by cyclin/cyclin-dependent kinase affects its function in cell cycle regulation.
abstract: MCM7 is one of the subunits of the MCM2-7 complex that plays a critical role in DNA replication initiation and cell proliferation of eukaryotic cells. After forming the pre-replication complex (pre-RC) with other components, the MCM2-7 complex is activated by DDK/cyclin-dependent kinase to initiate DNA replication. Each subunit of the MCM2-7 complex functions differently under regulation of various kinases on the specific site, which needs to be investigated in detail. In this study, we demonstrated that MCM7 is a substrate of cyclin E/Cdk2 and can be phosphorylated on Ser-121. We found that the distribution of MCM7-S121A is different from wild-type MCM7 and that the MCM7-S121A mutant is much less efficient to form a pre-RC complex with MCM3/MCM5/cdc45 compared with wild-type MCM7. By using the Tet-On inducible HeLa cell line, we revealed that overexpression of wild-type MCM7 but not MCM7-S121A can block S phase entry, suggesting that an excess of the pre-RC complex may activate the cell cycle checkpoint. Further analysis indicates that the Chk1 pathway is activated in MCM7-overexpressed cells in a p53-dependent manner. We performed experiments with the human normal cell line HL-7702 and also observed that overexpression of MCM7 can cause S phase block through checkpoint activation. In addition, we found that MCM7 could also be phosphorylated by cyclin B/Cdk1 on Ser-121 both in vitro and in vivo. Furthermore, overexpression of MCM7-S121A causes an obvious M phase exit delay, which suggests that phosphorylation of MCM7 on Ser-121 in M phase is very important for a proper mitotic exit. These data suggest that the phosphorylation of MCM7 on Ser-121 by cyclin/Cdks is involved in preventing DNA rereplication as well as in regulation of the mitotic exit.
authors.affiliation: Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wei
authors.forename: Junhui
authors.initials: J
authors.lastname: Li
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: D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D064168:Minichromosome Maintenance Complex Component 7; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: C113571:CDC45 protein, human; D018797:Cell Cycle Proteins; D019927:Cyclin E; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C101624:MCM7 protein, human; D064168:Minichromosome Maintenance Complex Component 7
keywords: Cell Cycle; Cell Signaling; Cyclin-dependent kinase (CDK); Cyclins; MCM7; Phosphorylation