title: Prolonged arrest of mammalian cells at the G1/S boundary results in permanent S phase stasis.
abstract: Mammalian cells in culture normally enter a state of quiescence during G1 following suppression of cell cycle progression by senescence, contact inhibition or terminal differentiation signals. We find that mammalian fibroblasts enter cell cycle stasis at the onset of S phase upon release from prolonged arrest with the inhibitors of DNA replication, hydroxyurea or aphidicolin. During arrest typical S phase markers remain present, and G0/G1 inhibitory signals such as p21(WAF1) and p27 are absent. Cell cycle stasis occurs in T-antigen transformed cells, indicating that p53 and pRB inhibitory circuits are not involved. While no DNA replication is evident in arrested cells, nuclei isolated from these cells retain measurable competence for in vitro replication. MCM proteins are required to license replication origins, and are put in place in nuclei in G1 and excluded from chromatin by the end of replication to prevent rereplication of the genome. Strikingly, MCM proteins are strongly depleted from chromatin during prolonged S phase arrest, and their loss may underlie the observed cell cycle arrest. S phase stasis may thus be a 'trap' in which cells otherwise competent for S phase have lost a key component required for replication and thus can neither go forward nor retreat to G1 status.
authors.affiliation: Institut de Biologie Structurale J-P Ebel (CEA-CNRS), 41 rue Jules Horowitz, 38027 Grenoble Cedex 1, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Borel
authors.forename: Françoise B
authors.initials: FB
authors.lastname: Lacroix
authors.forename: Robert L
authors.initials: RL
authors.lastname: Margolis
mesh_terms: D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects / Q000235:genetics*; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000378:metabolism* / Q000648:ultrastructure; D005333:Fetus; D005347:Fibroblasts; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D064126:Minichromosome Maintenance Complex Component 3; D064148:Minichromosome Maintenance Complex Component 4; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D016196:S Phase / Q000187:drug effects / Q000235:genetics*; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C103706:CDC6 protein, human; C493956:CDKN1A protein, human; C467199:CDT1 protein, human; C493958:Cdkn1a protein, rat; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C066470:MCM3 protein, human; D009687:Nuclear Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016590:Aphidicolin; D004247:DNA; C099243:MCM4 protein, human; D064126:Minichromosome Maintenance Complex Component 3; D064148:Minichromosome Maintenance Complex Component 4; D015739:Nocodazole; D006918:Hydroxyurea