Ravitz M J, Yan S, Herr K D, Wenner C E
Department of Biochemistry, Roswell Park Cancer Institute, Buffalo, New York 14263.
Cancer Res. 1995 Apr 1;55(7):1413-6.
Transforming growth factor (TGF-beta)-stimulated induction of DNA synthesis is preceded by the activation of cyclin E/cyclin-dependent kinase (cdk)2 kinase in late G1 in C3H 10T1/2 mouse fibroblasts. TGF-beta has no effect on the steady-state level of cdk4, while having only a modest inductive effect on cyclin D1 expression. TGF-beta stimulation does, however, lead to the striking down-regulation of p27Kip1 expression during G1 in a manner consistent with the timing of cyclin E-cdk2 activation. Coimmunoprecipitation analysis reveals that the amount of p27Kip1 in complexes with the cdk2 catalytic subunit is drastically reduced at the time in late G1 when cyclin E-cdk2 activity is maximal. These data indicate that cyclin E-cdk2 is inhibited by p27Kip1 in the growth-arrested state and that TGF-beta relieves this inhibition by down-regulating the steady-state level of the p27Kip1 inhibitor protein, thus reducing the level of inhibitor present in complexes with cdk2.
在C3H 10T1/2小鼠成纤维细胞中，转化生长因子（TGF-β）刺激诱导的DNA合成之前，在G1晚期会激活细胞周期蛋白E/细胞周期蛋白依赖性激酶（cdk）2激酶。TGF-β对cdk4的稳态水平没有影响，而对细胞周期蛋白D1的表达只有适度的诱导作用。然而，TGF-β刺激确实会导致在G1期p27Kip1表达显著下调，其方式与细胞周期蛋白E-cdk2激活的时间一致。免疫共沉淀分析显示，在G1晚期细胞周期蛋白E-cdk2活性最大时，与cdk2催化亚基结合的复合物中p27Kip1的量急剧减少。这些数据表明，在生长停滞状态下，细胞周期蛋白E-cdk2被p27Kip1抑制，而TGF-β通过下调p27Kip1抑制蛋白的稳态水平来解除这种抑制，从而降低与cdk2结合的复合物中抑制剂的水平。
