RESUMO
One of the most intriguing features of cell-cycle control is that, although there are multiple cyclin-dependent kinases (CDKs) in higher eukaryotes, a single CDK is responsible for both G1-S and G2-M in yeasts. By leveraging a rapid conditional silencing system in human cell lines, we confirm that CDK1 assumes the role of G1-S CDK in the absence of CDK2. Unexpectedly, CDK1 deficiency does not prevent mitotic entry. Nonetheless, inadequate phosphorylation of mitotic substrates by noncanonical cyclin B-CDK2 complexes does not allow progression beyond metaphase and underscores deleterious late mitotic events, including the uncoupling of anaphase A and B and cytokinesis. Elevation of CDK2 to a level similar to CDK1 overcomes the mitotic defects caused by CDK1 deficiency, indicating that the relatively low concentration of CDK2 accounts for the defective anaphase. Collectively, these results reveal that the difference between G2-M and G1-S CDKs in human cells is essentially quantitative.
Assuntos
Proteína Quinase CDC2/metabolismo , Proliferação de Células , Mitose , Epitélio Pigmentado da Retina/enzimologia , Neoplasias do Colo do Útero/enzimologia , Proteína Quinase CDC2/genética , Ciclina B/genética , Ciclina B/metabolismo , Quinase 2 Dependente de Ciclina/genética , Quinase 2 Dependente de Ciclina/metabolismo , Feminino , Regulação Enzimológica da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Células HeLa , Humanos , Fosforilação , Transdução de Sinais , Neoplasias do Colo do Útero/genética , Neoplasias do Colo do Útero/patologiaRESUMO
Biochemical studies have indicated that p31(comet) and TRIP13 are critical for inactivating MAD2. To address unequivocally whether p31(comet) and TRIP13 are required for mitotic exit at the cellular level, their genes were ablated either individually or together in human cells. Neither p31(comet) nor TRIP13 were absolutely required for unperturbed mitosis. MAD2 inactivation was only partially impaired in p31(comet)-deficient cells. In contrast, TRIP13-deficient cells contained MAD2 exclusively in the C-MAD2 conformation. Our results indicate that although p31(comet) enhanced TRIP13-mediated MAD2 conversion, it was not absolutely necessary for the process. Paradoxically, TRIP13-deficient cells were unable to activate the spindle-assembly checkpoint, revealing that cells lacking the ability to inactivate MAD2 were incapable in mounting a checkpoint response. These results establish a paradigm of the roles of p31(comet) and TRIP13 in both checkpoint activation and inactivation.
