Kubbutat M H, Vousden K H
ABL Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21702, USA.
Mol Cell Biol. 1997 Jan;17(1):460-8. doi: 10.1128/MCB.17.1.460.
The p53 tumor suppressor protein is activated in cells in response to DNA damage and prevents the replication of cells sustaining genetic damage by inducing a cell cycle arrest or apoptosis. Activation of p53 is accompanied by stabilization of the protein, resulting in accumulation to high levels within the cell. p53 is normally degraded through the proteasome following ubiquitination, although the mechanisms which regulate this proteolysis in normal cells and how the p53 protein becomes stabilized following DNA damage are not well understood. We show here that p53 can also be a substrate for cleavage by the calcium-activated neutral protease, calpain, and that a preferential site for calpain cleavage exists within the N terminus of the p53 protein. Treatment of cells expressing wild-type p53 with an inhibitor of calpain resulted in the stabilization of the p53 protein. By contrast, in vitro or in vivo degradation mediated by human papillomavirus E6 protein was unaffected by the calpain inhibitor, indicating that the stabilization did not result from inhibition of the proteasome. These results suggest that calpain cleavage plays a role in regulating p53 stability.
p53肿瘤抑制蛋白在细胞中因DNA损伤而被激活，并通过诱导细胞周期停滞或凋亡来阻止遭受基因损伤的细胞进行复制。p53的激活伴随着该蛋白的稳定，导致其在细胞内积累至高水平。p53通常在泛素化后通过蛋白酶体降解，尽管在正常细胞中调节这种蛋白水解的机制以及DNA损伤后p53蛋白如何变得稳定尚不清楚。我们在此表明，p53也可以是钙激活中性蛋白酶（钙蛋白酶）的切割底物，并且在p53蛋白的N末端存在一个钙蛋白酶切割的优先位点。用钙蛋白酶抑制剂处理表达野生型p53的细胞导致p53蛋白的稳定。相比之下，人乳头瘤病毒E6蛋白介导的体外或体内降解不受钙蛋白酶抑制剂的影响，这表明这种稳定不是由蛋白酶体抑制导致的。这些结果表明，钙蛋白酶切割在调节p53稳定性中起作用。
