Min I, Stubbs M C, Strachan G D, Hall D J
Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Int J Oncol. 1998 Sep;13(3):549-55. doi: 10.3892/ijo.13.3.549.
Culture of murine embryonic fibroblasts, but not vascular smooth muscle cells, on a fibronectin matrix significantly shortens their transit time through the S phase of the cell cycle. This shortening corresponds to an increase in both cyclin A protein levels and active cyclin A/cdk2 complex. The increase in cyclin A protein appears due to a translational/post-translational mechanism since there is no increase in cyclin A mRNA following culture of the cells on fibronectin. Treatment of cells cultured on fibronectin with a short pulse of the S phase chemotherapeutic agent camptothecin, resulted in a relative protection from cell death when compared to cells cultured on tissue culture plastic. Thus, while the cells have increased rate of transit through S phase fibronectin-mediated signaling protects the cells from S phase mediated apoptosis. In addition, fibroblasts constitutively expressing a mutant E2F1 transcription factor (E2F1d87) have a lengthened S phase, due to a truncation of the cyclin A/cdk2 binding domain. Culture of these mutant- expressing cells on fibronectin did not shorten their S phase duration in spite of the fact that cyclin A levels and active cyclin A/cdk2 complex were significantly elevated. Thus, although the fibronectin signaling mechanisms culminating in elevated cyclin A were intact in these mutant E2F1 expressing cells, they were insensitive to the effects of this elevated cyclin A. The effect of the mutant E2F1d87 on slowing transit through S phase appears dominant over the effect of elevated cyclin A.
在纤连蛋白基质上培养小鼠胚胎成纤维细胞而非血管平滑肌细胞，会显著缩短它们通过细胞周期S期的时间。这种缩短对应着细胞周期蛋白A蛋白水平和活性细胞周期蛋白A/细胞周期蛋白依赖性激酶2复合物的增加。细胞周期蛋白A蛋白的增加似乎是由于翻译/翻译后机制，因为在纤连蛋白上培养细胞后，细胞周期蛋白A信使核糖核酸没有增加。用S期化疗药物喜树碱短脉冲处理在纤连蛋白上培养的细胞，与在组织培养塑料上培养的细胞相比，可使细胞相对免受细胞死亡。因此，虽然细胞通过S期的速率增加，但纤连蛋白介导的信号传导可保护细胞免受S期介导的细胞凋亡。此外，组成性表达突变型E2F1转录因子（E2F1d87）的成纤维细胞，由于细胞周期蛋白A/细胞周期蛋白依赖性激酶2结合域的截断，其S期延长。尽管细胞周期蛋白A水平和活性细胞周期蛋白A/细胞周期蛋白依赖性激酶2复合物显著升高，但在纤连蛋白上培养这些表达突变体的细胞并没有缩短其S期持续时间。因此，尽管在这些表达突变型E2F1的细胞中，最终导致细胞周期蛋白A升高的纤连蛋白信号传导机制是完整的，但它们对这种升高的细胞周期蛋白A的作用不敏感。突变型E2F1d87对减缓通过S期的作用似乎比升高的细胞周期蛋白A的作用更占主导。
