Lee Hunjoo, Zeng Shelya X, Lu Hua
Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon 97239, USA.
J Biol Chem. 2006 Sep 15;281(37):26876-83. doi: 10.1074/jbc.M605366200. Epub 2006 Jun 27.
It was previously reported that low doses, but not high doses, of UV trigger the Skp2-mediated proteasomal degradation of the cyclin-dependent kinase inhibitor p21 in mammalian cells. Here we show that both UV-C and UV-B lead to decrease of p21 protein, but not mRNA, level in a dose-dependent fashion in all of six human cell lines and five mouse cell lines tested. Also, high doses of UV reduce the half-life of p21. High doses, but not low doses, of UV induced p21 degradation in both skp2-proficient and -deficient murine embryonic fibroblast cells. UV-induced p21 reduction was rescued by proteasome inhibitors in all human and mouse cell lines tested. Neither a caspase inhibitor nor small interfering RNA against skp2 had an effect on the UV-induced p21 decrease, suggesting that this p21 degradation pathway may not involve caspases, or Skp2. Finally, UV did not induce p21 ubiquitination but still induced its degradation when the E1-activating enzyme was inactivated in an E1 temperature-sensitive mouse embryonic fibroblast cell line. Altogether, these results demonstrate that UV induces p21 degradation through an Skp2 and ubiquitin-independent pathway.
先前有报道称，低剂量而非高剂量的紫外线可触发哺乳动物细胞中细胞周期蛋白依赖性激酶抑制剂p21的Skp2介导的蛋白酶体降解。在此我们表明，在测试的所有六种人类细胞系和五种小鼠细胞系中，UV-C和UV-B均以剂量依赖性方式导致p21蛋白水平降低，但不影响mRNA水平。此外，高剂量的紫外线会缩短p21的半衰期。高剂量而非低剂量的紫外线在Skp2表达正常和缺失的小鼠胚胎成纤维细胞中均诱导p21降解。在所有测试的人类和小鼠细胞系中，蛋白酶体抑制剂均可挽救紫外线诱导的p21减少。半胱天冬酶抑制剂和针对Skp2的小干扰RNA均对紫外线诱导的p21减少无影响，这表明该p21降解途径可能不涉及半胱天冬酶或Skp2。最后，在E1温度敏感的小鼠胚胎成纤维细胞系中，当E1激活酶失活时，紫外线不会诱导p21泛素化，但仍会诱导其降解。总之，这些结果表明紫外线通过Skp2和泛素非依赖性途径诱导p21降解。
