Inhibitory phosphorylation of cyclin-dependent kinase 1 as a compensatory mechanism for mitosis exit.
The current paradigm states that exit from mitosis is triggered by the ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C) acting in concert with an activator called CDC20. While this has been well established for a number of systems, the evidence of a critical role of CDC20 in somatic cells is not unequivocal. In this study, we reexamined whether mitotic exit can occur properly after CDC20 is depleted. Using single-cell analysis, we found that CDC20 depletion with small interfering RNAs (siRNAs) significantly impaired the degradation of APC/C substrates and delayed mitotic exit in various cancer cell lines. The recruitment of cyclin B1 to the core APC/C was defective after CDC20 downregulation. Nevertheless, CDC20-depleted cells were still able to complete mitosis, albeit requiring twice the normal time. Intriguingly, a high level of cyclin-dependent kinase 1 (CDK1)-inhibitory phosphorylation was induced during mitotic exit in CDC20-depleted cells. The expression of an siRNA-resistant CDC20 rescued both the mitotic exit delay and the CDK1-inhibitory phosphorylation. Moreover, the expression of a nonphosphorylatable CDK1 mutant or the downregulation of WEE1 and MYT1 abolished mitotic exit in CDC20-depleted cells. These findings indicate that, in the absence of sufficient APC/C activity, an alternative mechanism that utilized the classic inhibitory phosphorylation of CDK1 could mediate mitotic exit.
Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong.
Jeremy P H
JP
Chow
Randy Y C
RY
Poon
Hoi Tang
HT
Ma
D000705:Anaphase; D064173:Anaphase-Promoting Complex-Cyclosome; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D056744:Cyclin B1 / Q000378:metabolism; D019610:Cytoprotection; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D006367:HeLa Cells; D006801:Humans; D008853:Microscopy; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013379:Substrate Specificity; D059008:Time-Lapse Imaging; D014157:Transcription Factors / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism
D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; D056744:Cyclin B1; D004268:DNA-Binding Proteins; C078341:MYT1 protein, human; D009687:Nuclear Proteins; D014157:Transcription Factors; C577488:CDC20 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D011505:Protein-Tyrosine Kinases; C499349:WEE1 protein, human; D016203:CDC2 Protein Kinase
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