Tam S W, Schlegel R
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115.
Cell Growth Differ. 1992 Nov;3(11):811-7.
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.
在正常情况下，哺乳动物细胞在存在未复制或受损DNA时不会启动有丝分裂。我们在此报告，星形孢菌素，一种肿瘤促进剂和强效蛋白激酶抑制剂，能够使有丝分裂与DNA复制的完成脱钩，并克服DNA损伤诱导的G2期延迟。停滞在S期的叙利亚仓鼠（BHK）成纤维细胞在低至1 ng/ml的浓度下就会发生早熟有丝分裂，在50 ng/ml时活性最高。组蛋白H1激酶活性增加到正常有丝分裂细胞中发现水平的约二分之一。在星形孢菌素处理期间抑制蛋白质合成可阻断早熟有丝分裂并抑制组蛋白H1激酶活性的增加。在异步生长的细胞中，星形孢菌素短暂增加有丝分裂指数和组蛋白H1激酶活性，但不会诱导S期细胞发生早熟有丝分裂，这表明需要S期停滞。星形孢菌素还绕过了在存在受损DNA时阻止有丝分裂开始的细胞周期检查点。当在γ射线照射后立即暴露于50 ng/ml的星形孢菌素时，γ射线导致的有丝分裂起始延迟会降低。这些发现表明，星形孢菌素对蛋白质磷酸化的抑制作用可以克服BHK细胞中有丝分裂起始的两个重要检查点。
