title: Plk1 phosphorylation of Orc2 promotes DNA replication under conditions of stress.
abstract: Polo-like kinase 1 (Plk1) plays pivotal roles in mitosis; however, little is known about its function in S phase. In this study, we show that inhibition of Plk1 impairs DNA replication and results in slow S-phase progression in cultured cancer cells. We have identified origin recognition complex 2 (Orc2), a member of the DNA replication machinery, as a Plk1 substrate and have shown that Plk1 phosphorylates Orc2 at Ser188 in vitro and in vivo. Furthermore, Orc2-S188 phosphorylation is enhanced when DNA replication is under challenge induced by ultraviolet, hydroxyurea, gemcitabine, or aphidicolin treatment. Cells expressing the unphosphorylatable mutant (S188A) of Orc2 had defects in DNA synthesis under stress, suggesting that this phosphorylation event is critical to maintain DNA replication under stress. To dissect the mechanism pertinent to this observation, we showed that Orc2-S188 phosphorylation associates with DNA replication origin and that cells expressing Orc2-S188A mutant fail to maintain the functional pre-replicative complex (pre-RC) under DNA replication stress. Furthermore, the intra-S-phase checkpoint is activated in Orc2-S188A-expressing cells to cause delay of S-phase progress. Our study suggests a novel role of Plk1 in facilitating DNA replication under conditions of stress to maintain genomic integrity.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Song
authors.forename: X Shawn
authors.initials: XS
authors.lastname: Liu
authors.forename: Korbin
authors.initials: K
authors.lastname: Davis
authors.forename: Xiaoqi
authors.initials: X
authors.lastname: Liu
mesh_terms: D020816:Amino Acid Motifs; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D004261:DNA Replication; D042822:Genomic Instability; D006801:Humans; D051738:Origin Recognition Complex / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D016196:S Phase; D059807:S Phase Cell Cycle Checkpoints; D013312:Stress, Physiological; D000097869:Polo-Like Kinase 1
chemical_list: D018797:Cell Cycle Proteins; D051738:Origin Recognition Complex; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D000097869:Polo-Like Kinase 1; C497224:ORC2 protein, human