Scheffner M, Huibregtse J M, Vierstra R D, Howley P M
Laboratory of Tumor Virus Biology, National Cancer Institute, Bethesda, Maryland 20892.
Cell. 1993 Nov 5;75(3):495-505. doi: 10.1016/0092-8674(93)90384-3.
The ubiquitin-dependent proteolytic pathway plays a major role in selective protein degradation. Ubiquitination of proteins requires the sequential action of the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzymes (E2), and in some cases ubiquitin-protein ligases (E3s). The oncogenic human papillomavirus (HPV) types 16 and 18 utilize this cellular proteolytic system to target the tumor suppressor protein p53. The HPV E6 oncoprotein binds to a cellular protein of 100 kd, termed E6-associated protein (E6-AP). The E6-E6-AP complex specifically interacts with p53, resulting in the rapid ubiquitin-dependent degradation of p53. Here we report the purification and identification of the factors necessary for the E6-E6-AP-mediated ubiquitination of p53. The ubiquitination of p53 requires the E1 enzyme and a novel E2 in mammalian cells, while E3 activity is conferred by the E6-E6-AP complex. Furthermore, E6-AP appears to have ubiquitin-protein ligase activity in the absence of E6.
泛素依赖性蛋白水解途径在选择性蛋白质降解中起主要作用。蛋白质的泛素化需要泛素激活酶（E1）、泛素结合酶（E2）以及在某些情况下泛素-蛋白质连接酶（E3）的顺序作用。致癌性人乳头瘤病毒（HPV）16型和18型利用这种细胞蛋白水解系统靶向肿瘤抑制蛋白p53。HPV E6癌蛋白与一种100kd的细胞蛋白结合，称为E6相关蛋白（E6-AP）。E6-E6-AP复合物特异性地与p53相互作用，导致p53迅速发生泛素依赖性降解。在此我们报告了E6-E6-AP介导的p53泛素化所需因子的纯化和鉴定。p53的泛素化在哺乳动物细胞中需要E1酶和一种新型E2，而E3活性由E6-E6-AP复合物赋予。此外，在没有E6的情况下，E6-AP似乎具有泛素-蛋白质连接酶活性。
