Lu Y, Yamagishi N, Yagi T, Takebe H
Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Japan.
Oncogene. 1998 Feb 12;16(6):705-12. doi: 10.1038/sj.onc.1201585.
Human colorectal tumor cell lines were established which express wildtype p21 or p21 with a mutation at codon 46 (Cys) or 140 (Gly) on IPTG treatment (LacSwitch). The IPTG-induced wildtype p21 bound to CDK2 and PCNA and inhibited CDK activity in the cells and reduced cell growth rate; whereas, both IPTG-induced mutated p21 proteins neither bound to CDK2 nor affected the CDK activity but did bind to PCNA, and they did not affect the cell growth rate. Wildtype p21 suppressed apoptosis and enhanced survival of X-ray-irradiated or adriamycin-treated cells; but, mutated p21 neither suppressed apoptosis nor affected cell survival. When cells were treated with mimosine, a p53-independent p21-inducer, or butyrolactone I, a specific inhibitor of CDK, cellular endogenous p21 was induced and X-ray or adriamycin-induced apoptosis was blocked. These results suggest that CDK-binding or CDK-inhibitory activity of p21 is required to prevent apoptosis, i.e., CDK is required for apoptosis in human tumor cells.
建立了人结肠直肠肿瘤细胞系，这些细胞系在异丙基-β-D-硫代半乳糖苷（IPTG）处理（LacSwitch）下表达野生型p21或密码子46（半胱氨酸）或140（甘氨酸）发生突变的p21。IPTG诱导的野生型p21与细胞周期蛋白依赖性激酶2（CDK2）和增殖细胞核抗原（PCNA）结合，抑制细胞中的CDK活性并降低细胞生长速率；而IPTG诱导的两种突变型p21蛋白既不与CDK2结合，也不影响CDK活性，但确实与PCNA结合，并且它们不影响细胞生长速率。野生型p21抑制X射线照射或阿霉素处理的细胞的凋亡并提高其存活率；但是，突变型p21既不抑制凋亡也不影响细胞存活。当用含羞草碱（一种不依赖p53的p21诱导剂）或丁内酯I（一种CDK特异性抑制剂）处理细胞时，细胞内源性p21被诱导，并且X射线或阿霉素诱导的凋亡被阻断。这些结果表明，p21的CDK结合或CDK抑制活性是预防凋亡所必需的，即CDK是人类肿瘤细胞凋亡所必需的。
