title: The reversibility of mitotic exit in vertebrate cells.
abstract: A guiding hypothesis for cell-cycle regulation asserts that regulated proteolysis constrains the directionality of certain cell-cycle transitions. Here we test this hypothesis for mitotic exit, which is regulated by degradation of the cyclin-dependent kinase 1 (Cdk1) activator, cyclin B. Application of chemical Cdk1 inhibitors to cells in mitosis induces cytokinesis and other normal aspects of mitotic exit, including cyclin B degradation. However, chromatid segregation fails, resulting in entrapment of chromatin in the midbody. If cyclin B degradation is blocked with a proteasome inhibitor or by expression of non-degradable cyclin B, Cdk inhibitors will nonetheless induce mitotic exit and cytokinesis. However, if after mitotic exit, the Cdk1 inhibitor is washed free from cells in which cyclin B degradation is blocked, the cells can revert back to M phase. This reversal is characterized by chromosome recondensation, nuclear envelope breakdown, assembly of microtubules into a mitotic spindle, and in most cases, dissolution of the midbody, reopening of the cleavage furrow, and realignment of chromosomes at the metaphase plate. These findings demonstrate that proteasome-dependent degradation of cyclin B provides directionality for the M phase to G1 transition.
authors.affiliation: Program in Molecular, Cell and Developmental Biology, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, Oklahoma 73104, USA.
authors.forename: Tamara A
authors.initials: TA
authors.lastname: Potapova
authors.forename: John R
authors.initials: JR
authors.lastname: Daum
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Pittman
authors.forename: Joanna R
authors.initials: JR
authors.lastname: Hudson
authors.forename: Tara N
authors.initials: TN
authors.lastname: Jones
authors.forename: David L
authors.initials: DL
authors.lastname: Satinover
authors.forename: P Todd
authors.initials: PT
authors.lastname: Stukenberg
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Gorbsky
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D019926:Cyclin B / Q000378:metabolism; D048749:Cytokinesis / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D008677:Metaphase / Q000187:drug effects; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D008954:Models, Biological; D015739:Nocodazole / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D014981:Xenopus
chemical_list: D019926:Cyclin B; D005419:Flavonoids; D010880:Piperidines; C077990:alvocidib; D016203:CDC2 Protein Kinase; D046988:Proteasome Endopeptidase Complex; D015739:Nocodazole