Staurosporine overrides checkpoints for mitotic onset in BHK cells.
Under normal conditions, mammalian cells will not initiate mitosis in the presence of either unreplicated or damaged DNA. We report here that staurosporine, a tumor promoter and potent protein kinase inhibitor, can uncouple mitosis from the completion of DNA replication and override DNA damage-induced G2 delay. Syrian hamster (BHK) fibroblasts that were arrested in S phase underwent premature mitosis at concentrations as low as 1 ng/ml, with maximum activity seen at 50 ng/ml. Histone H1 kinase activity was increased to approximately one-half the level found in normal mitotic cells. Inhibition of protein synthesis during staurosporine treatment blocked premature mitosis and suppressed the increase in histone H1 kinase activity. In asynchronously growing cells, staurosporine transiently increased the mitotic index and histone H1 kinase activity but did not induce S phase cells to undergo premature mitosis, indicating a requirement for S phase arrest. Staurosporine also bypassed the cell cycle checkpoint that prevents the onset of mitosis in the presence of damaged DNA. The delay in mitotic onset resulting from gamma radiation was reduced when irradiation was followed immediately by exposure to 50 ng/ml of staurosporine. These findings indicate that inhibition of protein phosphorylation by staurosporine can override two important checkpoints for the initiation of mitosis in BHK cells.
Tam
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Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115.
Schlegel
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D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D006224:Cricetinae; D016213:Cyclins / Q000378:metabolism; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects; D007668:Kidney; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D008647:Mesocricetus; D008938:Mitosis / Q000187:drug effects* / Q000528:radiation effects; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D019311:Staurosporine; D013268:Stimulation, Chemical
D000470:Alkaloids; D016213:Cyclins; D016203:CDC2 Protein Kinase; D016200:Maturation-Promoting Factor; D019311:Staurosporine