The kinetics of p53 activation versus cyclin E accumulation underlies the relationship between the spindle-assembly checkpoint and the postmitotic checkpoint.
Although cells can exit mitotic block aberrantly by mitotic slippage, they are prevented from becoming tetraploids by a p53-dependent postmitotic checkpoint. Intriguingly, disruption of the spindle-assembly checkpoint also compromises the postmitotic checkpoint. The precise mechanism of the interplay between these two pivotal checkpoints is not known. We found that after prolonged nocodazole exposure, the postmitotic checkpoint was facilitated by p53. We demonstrated that although disruption of the mitotic block by a MAD2-binding protein promoted slippage, it did not influence the activation of p53. Both p53 and its downstream target p21(CIP1/WAF1) were activated at the same rate irrespective of whether the spindle-assembly checkpoint was enforced or not. The accelerated S phase entry, as reflected by the premature accumulation of cyclin E relative to the activation of p21(CIP1/WAF1), is the reason for the uncoupling of the postmitotic checkpoint. In support of this hypothesis, forced premature mitotic exit with a specific CDK1 inhibitor triggered DNA replication without affecting the kinetics of p53 activation. Finally, replication after checkpoint bypass was boosted by elevating the level of cyclin E. These observations indicate that disruption of the spindle-assembly checkpoint does not directly influence p53 activation, but the shortening of the mitotic arrest allows cyclin E-CDK2 to be activated before the accumulation of p21(CIP1/WAF1). These data underscore the critical relationship between the spindle-assembly checkpoint and the postmitotic checkpoint in safeguarding chromosomal stability.
Chan
Ying Wai
YW
Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong.
On
Kin Fan
KF
Chan
Wan Mui
WM
Wong
Winnie
W
Siu
Ho On
HO
Hau
Pok Man
PM
Poon
Randy Y C
RY
D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D043171:Chromosomal Instability / Q000187:drug effects / Q000502:physiology; D002877:Chromosomes, Human / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D064246:Mad2 Proteins; D015739:Nocodazole / Q000494:pharmacology; D011123:Polyploidy; D012097:Repressor Proteins / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000502:physiology*; D008941:Spindle Apparatus / Q000378:metabolism*; D050257:Tubulin Modulators / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
C493956:CDKN1A protein, human; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D012097:Repressor Proteins; C495901:TP53 protein, human; D050257:Tubulin Modulators; D016159:Tumor Suppressor Protein p53; D016203:CDC2 Protein Kinase; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D015739:Nocodazole