Kashiwagi M, Ohba M, Watanabe H, Ishino K, Kasahara K, Sanai Y, Taya Y, Kuroki T
Institute of Molecular Oncology, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
Oncogene. 2000 Dec 14;19(54):6334-41. doi: 10.1038/sj.onc.1204028.
PKC is activated on the cell membrane by phospholipids, thereby transducing signals to intracellular pathways. We provide here another function of PKC, namely, regulating cell cycle by interaction with the cyclin E/cdk2/p21 complex. Among the 10 isoforms of PKC, PKCeta is predominantly expressed in squamous cell epithelia and induces terminal differentiation of keratinocytes. PKCeta that is endogenously expressed or overexpressed was found to associate with the cyclin E/cdk2/p21 complex in keratinocytes of mice and humans. Requirement of a possible adaptor protein to the binding was suggested by the reconstitution of PKCeta and the cyclin E/cdk2/p21 complex which were prepared from human keratinocytes or Sf9 insect cells. Colocalization of PKCeta with cdk2 and cyclin E was observed in the cytoplasm, particularly in the perinuclear region. p21 was phosphorylated in the complex in a PKC-activator dependent manner. Association of PKCeta with cdk2 resulted in marked inhibition of cdk2-kinase activity when measured by phosphorylation of Rb. Dominant negative PKCeta associated with the cyclin E/cdk2/p21 complex, but caused a little inhibition of cdk2 kinase activity. Among the known regulatory mechanisms of cdk2 activity, dephosphorylation of Thr160 was demonstrated. Oncogene (2000) 19, 6334 - 6341.
蛋白激酶C（PKC）在细胞膜上被磷脂激活，从而将信号转导至细胞内途径。我们在此提供PKC的另一个功能，即通过与细胞周期蛋白E/周期蛋白依赖性激酶2（cdk2）/p21复合物相互作用来调节细胞周期。在PKC的10种同工型中，PKCη主要在鳞状上皮细胞中表达，并诱导角质形成细胞的终末分化。发现在小鼠和人类角质形成细胞中，内源性表达或过表达的PKCη与细胞周期蛋白E/cdk2/p21复合物相关联。由人角质形成细胞或Sf9昆虫细胞制备的PKCη与细胞周期蛋白E/cdk2/p21复合物的重组表明，可能需要一种衔接蛋白来实现这种结合。在细胞质中，特别是在核周区域，观察到PKCη与cdk2和细胞周期蛋白E共定位。在该复合物中，p21以PKC激活剂依赖性方式被磷酸化。当通过Rb的磷酸化来测量时，PKCη与cdk2的结合导致cdk2激酶活性受到显著抑制。显性负性PKCη与细胞周期蛋白E/cdk2/p21复合物相关联，但对cdk2激酶活性的抑制作用较小。在已知的cdk2活性调节机制中，已证实苏氨酸160的去磷酸化。《癌基因》（2000年）第19卷，6334 - 6341页。
