title: Site-specific phosphorylation of MCM4 during the cell cycle in mammalian cells.
abstract: MCM4, a subunit of a putative replicative helicase, is phosphorylated during the cell cycle, at least in part by cyclin-dependent kinases (CDK), which play a central role in the regulation of DNA replication. However, detailed characterization of the phosphorylation of MCM4 remains to be performed. We examined the phosphorylation of human MCM4 at Ser3, Thr7, Thr19, Ser32, Ser54, Ser88 and Thr110 using anti-phosphoMCM4 sera. Western blot analysis of HeLa cells indicated that phosphorylation of MCM4 at these seven sites can be classified into two groups: (a) phosphorylation that is greatly enhanced in the G2 and M phases (Thr7, Thr19, Ser32, Ser54, Ser88 and Thr110), and (b) phosphorylation that is firmly detected during interphase (Ser3). We present data indicating that phosphorylation at Thr7, Thr19, Ser32, Ser88 and Thr110 in the M phase requires CDK1, using a temperature-sensitive mutant of mouse CDK1, and phosphorylation at sites 3 and 32 during interphase requires CDK2, using a dominant-negative mutant of human CDK2. Based on these results and those from in vitro phosphorylation of MCM4 with CDK2/cyclin A, we discuss the kinases responsible for MCM4 phosphorylation. Phosphorylated MCM4 detected using anti-phospho sera exhibited different affinities for chromatin. Studies on the nuclear localization of chromatin-bound MCM4 phosphorylated at sites 3 and 32 suggested that they are not generally colocalized with replicating DNA. Unexpectedly, MCM4 phosphorylated at site 32 was enriched in the nucleolus through the cell cycle. These results suggest that phosphorylation of MCM4 has several distinct and site-specific roles in the function of MCM during the mammalian cell cycle.
authors.affiliation: Mitsubishi Kagaku Institute of Life Sciences, Tokyo, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Komamura-Kohno
authors.forename: Kumiko
authors.initials: K
authors.lastname: Karasawa-Shimizu
authors.forename: Takako
authors.initials: T
authors.lastname: Saitoh
authors.forename: Michio
authors.initials: M
authors.lastname: Sato
authors.forename: Fumio
authors.initials: F
authors.lastname: Hanaoka
authors.forename: Shoji
authors.initials: S
authors.lastname: Tanaka
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ishimi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism*; D019925:Cyclin A / Q000502:physiology; D051357:Cyclin-Dependent Kinase 2 / Q000502:physiology*; D004265:DNA Helicases / Q000037:antagonists & inhibitors*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008322:Mammals / Q000378:metabolism; D051379:Mice; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7; D008938:Mitosis; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D017385:Sequence Homology
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D019925:Cyclin A; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051357:Cyclin-Dependent Kinase 2; D004265:DNA Helicases; C099243:MCM4 protein, human; C103258:MCM6 protein, human; C101624:MCM7 protein, human; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7