Centrosome-associated Chk1 prevents premature activation of cyclin-B-Cdk1 kinase.
Entry into mitosis occurs after activation of Cdk1, resulting in chromosome condensation in the nucleus and centrosome separation, as well as increased microtubule nucleation activity in the cytoplasm. The active cyclin-B1-Cdk1 complex first appears at the centrosome, suggesting that the centrosome may facilitate the activation of mitotic regulators required for the commitment of cells to mitosis. However, the signalling pathways involved in controlling the initial activation of Cdk1 at the centrosome remain largely unknown. Here, we show that human Chk1 kinase localizes to interphase, but not mitotic, centrosomes. Chemical inhibition of Chk1 resulted in premature centrosome separation and activation of centrosome-associated Cdk1. Forced immobilization of kinase-inactive Chk1 to centrosomes also resulted in premature Cdk1 activation. Conversely, under such conditions wild-type Chk1 impaired activation of centrosome-associated Cdk1, thereby resulting in DNA endoreplication and centrosome amplification. Activation of centrosomal Cdk1 in late prophase seemed to be mediated by cytoplasmic Cdc25B, whose activity is controlled by centrosome-associated Chk1. These results suggest that centrosome-associated Chk1 shields centrosomal Cdk1 from unscheduled activation by cytoplasmic Cdc25B, thereby contributing to proper timing of the initial steps of cell division, including mitotic spindle formation.
Danish Cancer Society, Institute of Cancer Biology, Department of Cell Cycle and Cancer, Strandboulevarden 49, DK-2100 Copenhagen Ø, Denmark.
Alwin
A
Krämer
Niels
N
Mailand
Claudia
C
Lukas
Randi G
RG
Syljuåsen
Christopher J
CJ
Wilkinson
Erich A
EA
Nigg
Jiri
J
Bartek
Jiri
J
Lukas
D016203:CDC2 Protein Kinase / Q000378:metabolism / Q000502:physiology; D018797:Cell Cycle Proteins / Q000502:physiology; D002455:Cell Division; D002460:Cell Line; D018385:Centrosome / Q000201:enzymology*; D000071877:Checkpoint Kinase 1; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D016213:Cyclins / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007399:Interphase; D018613:Microscopy, Confocal; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D008941:Spindle Apparatus; D020687:cdc25 Phosphatases / Q000502:physiology
C534699:CCNB1 protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D016213:Cyclins; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D016203:CDC2 Protein Kinase; C517008:CDC25B protein, human; D020687:cdc25 Phosphatases