Cdc25B cooperates with Cdc25A to induce mitosis but has a unique role in activating cyclin B1-Cdk1 at the centrosome.
Cdc25 phosphatases are essential for the activation of mitotic cyclin-Cdks, but the precise roles of the three mammalian isoforms (A, B, and C) are unclear. Using RNA interference to reduce the expression of each Cdc25 isoform in HeLa and HEK293 cells, we observed that Cdc25A and -B are both needed for mitotic entry, whereas Cdc25C alone cannot induce mitosis. We found that the G2 delay caused by small interfering RNA to Cdc25A or -B was accompanied by reduced activities of both cyclin B1-Cdk1 and cyclin A-Cdk2 complexes and a delayed accumulation of cyclin B1 protein. Further, three-dimensional time-lapse microscopy and quantification of Cdk1 phosphorylation versus cyclin B1 levels in individual cells revealed that Cdc25A and -B exert specific functions in the initiation of mitosis: Cdc25A may play a role in chromatin condensation, whereas Cdc25B specifically activates cyclin B1-Cdk1 on centrosomes.
Lindqvist
Arne
A
Department of Cell and Molecular Biology, Karolinska Institutet, S-171 77 Stockholm, Sweden.
Källström
Helena
H
Lundgren
Andreas
A
Barsoum
Emad
E
Rosenthal
Christina Karlsson
CK
D016203:CDC2 Protein Kinase / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D048750:Cell Nucleus Division / Q000187:drug effects; D018385:Centrosome / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D056744:Cyclin B1; D018844:Cyclin-Dependent Kinases / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000187:drug effects* / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D020687:cdc25 Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology*
D018797:Cell Cycle Proteins; D056744:Cyclin B1; D034741:RNA, Small Interfering; D016203:CDC2 Protein Kinase; D018844:Cyclin-Dependent Kinases; C517004:CDC25A protein, human; C517008:CDC25B protein, human; D020687:cdc25 Phosphatases