Entry into mitosis without Cdc2 kinase activation.
Mouse FT210 cells at 39 degreesC cannot enter mitosis but arrest in G2 phase, because they lack Cdc2 kinase activity as a result of a temperature-sensitive lesion in the cdc2 gene. Incubation of arrested cells with the protein phosphatase 1 and 2A inhibitor okadaic acid induces morphologically normal chromosome condensation. We now show that okadaic acid also induces two other landmark events of early mitosis, nuclear lamina depolymerization and centrosome separation, in the absence of Cdc2 kinase activity. Okadaic acid-induced entry into mitosis is accompanied by partial activation of Cdc25C and may be prevented by tyrosine phosphatase inhibitors and by the protein kinase inhibitor staurosporine, suggesting that Cdc25C and kinases distinct from Cdc2 are required for these mitotic events. Using in-gel assays, we show that a 45-kDa protein kinase normally activated at mitosis is also activated by okadaic acid independently of Cdc2 kinase. The 45-kDa kinase can utilize GTP, is stimulated by spermine and is inhibited by heparin. These properties are characteristic of the kinase CK2, but immunoprecipitation studies indicate that it is not CK2. The data underline the importance of a tyrosine phosphatase, possibly Cdc25C, and of kinases other than Cdc2 in the structural changes the cell undergoes at mitosis, and indicate that entry into mitosis involves the activation of multiple kinases working in concert with Cdc2 kinase.
Gowdy
P M
PM
Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z3.
Anderson
H J
HJ
Roberge
M
M
D000818:Animals; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002875:Chromosomes / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016195:G2 Phase / Q000502:physiology; D034882:Lamins; D008325:Mammary Neoplasms, Experimental; D051379:Mice; D008870:Microtubules / Q000737:chemistry / Q000201:enzymology; D008938:Mitosis / Q000502:physiology*; D009685:Nuclear Envelope / Q000737:chemistry / Q000201:enzymology; D009687:Nuclear Proteins / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000201:enzymology; D020687:cdc25 Phosphatases
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D034882:Lamins; D009687:Nuclear Proteins; D019319:Okadaic Acid; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases; D019311:Staurosporine