Levedakou E N, Kaufmann W K, Alcorta D A, Galloway D A, Paules R S
National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Cancer Res. 1995 Jun 15;55(12):2500-2.
We have previously reported that the immediate G2 checkpoint delay of normal human fibroblasts in response to ionizing radiation is correlated with inhibition of p34CDC2/cyclin B kinase activity. Here, we observed increased amounts of the cyclin-dependent protein kinase inhibitor p21CIP1 associated with p34CDC2/cyclin B protein complexes from irradiated normal human fibroblasts. Since wild-type p53 function is not required for the early G2 checkpoint response to ionizing radiation, we investigated whether a p53-independent induction of p21CIP1 was required for the G2 checkpoint. Early passage human fibroblasts expressing the E6 oncoprotein of human papilloma virus-type 16 (NHF4 E6) were analyzed. It has been demonstrated earlier than inactivation of wild-type p53 function in these cells by E6 protein does not alter their intact early G2 checkpoint response to gamma-rays. p21CIP1 was found to be undetectable in p34CDC2/cyclin B protein complexes and in total extracts from the E6-expressing cells, with or without exposure to ionizing radiation. These data indicate that p21CIP1 is not required for the immediate G2 checkpoint response and is not induced by a p53-independent pathway in G2 phase following exposure to gamma-rays.
我们之前报道过，正常人类成纤维细胞对电离辐射的即时G2期检查点延迟与p34CDC2/细胞周期蛋白B激酶活性的抑制相关。在此，我们观察到来自受辐照正常人类成纤维细胞的与p34CDC2/细胞周期蛋白B蛋白复合物相关的细胞周期蛋白依赖性蛋白激酶抑制剂p21CIP1的量增加。由于野生型p53功能对于电离辐射的早期G2期检查点反应并非必需，我们研究了G2期检查点是否需要p21CIP1的p53非依赖性诱导。对表达人乳头瘤病毒16型（NHF4 E6）E6癌蛋白的早期传代人类成纤维细胞进行了分析。之前已经证明，这些细胞中E6蛋白使野生型p53功能失活不会改变它们对γ射线完整的早期G2期检查点反应。在表达E6的细胞的p34CDC2/细胞周期蛋白B蛋白复合物和总提取物中，无论是否暴露于电离辐射，均未检测到p21CIP1。这些数据表明，p21CIP1对于即时G2期检查点反应并非必需，且在暴露于γ射线后的G2期不会由p53非依赖性途径诱导产生。
