title: p21-Mediated nuclear retention of cyclin B1-Cdk1 in response to genotoxic stress.
abstract: G2 arrest of cells suffering DNA damage in S phase is crucial to avoid their entry into mitosis, with the concomitant risks of oncogenic transformation. According to the current model, signals elicited by DNA damage prevent mitosis by inhibiting both activation and nuclear import of cyclin B1-Cdk1, a master mitotic regulator. We now show that normal human fibroblasts use additional mechanisms to block activation of cyclin B1-Cdk1. In these cells, exposure to nonrepairable DNA damage leads to nuclear accumulation of inactive cyclin B1-Cdk1 complexes. This nuclear retention, which strictly depends on association with endogenous p21, prevents activation of cyclin B1-Cdk1 by Cdc25 and Cdk-activating kinase as well as its recruitment to the centrosome. In p21-deficient normal human fibroblasts and immortal cell lines, cyclin B1 fails to accumulate in the nucleus and could be readily detected at the centrosome in response to DNA damage. Therefore, in normal cells, p21 exerts a dual role in mediating DNA damage-induced cell cycle arrest and exit before mitosis. In addition to blocking pRb phosphorylation, p21 directly prevents mitosis by inactivating and maintaining the inactive state of mitotic cyclin-Cdk complexes. This, with subsequent degradation of mitotic cyclins, further contributes to the establishment of a permanent G2 arrest.
authors.affiliation: CRBM-Centre National de la Recherche Scientifique FRE 2593, 34293 Montpellier, France.
authors.forename: Fabienne Baus
authors.initials: FB
authors.lastname: Charrier-Savournin
authors.forename: Marie-Thérèse
authors.initials: MT
authors.lastname: Château
authors.forename: Véronique
authors.initials: V
authors.lastname: Gire
authors.forename: John
authors.initials: J
authors.lastname: Sedivy
authors.forename: Jacques
authors.initials: J
authors.lastname: Piette
authors.forename: Vjekoslav
authors.initials: V
authors.lastname: Dulic
mesh_terms: D016203:CDC2 Protein Kinase / Q000737:chemistry / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D019926:Cyclin B / Q000737:chemistry / Q000378:metabolism*; D056744:Cyclin B1; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004249:DNA Damage / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D008938:Mitosis; D008954:Models, Biological; D046912:Multiprotein Complexes; D010766:Phosphorylation; D011485:Protein Binding; D020687:cdc25 Phosphatases / Q000378:metabolism
chemical_list: C534699:CCNB1 protein, human; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D050759:Cyclin-Dependent Kinase Inhibitor p21; D046912:Multiprotein Complexes; D016203:CDC2 Protein Kinase; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases