Bai Jingxiang, Cederbaum Arthur I
Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, New York, New York 10029, USA.
J Biol Chem. 2003 Feb 14;278(7):4660-7. doi: 10.1074/jbc.M206273200. Epub 2002 Dec 4.
Oxidants such as H(2)O(2) play a role in the toxicity of certain DNA-damaging agents, a process that often involves the tumor suppressor p53. H(2)O(2) is rapidly degraded by catalase, which protects cells against oxidant injury. To study the effect of catalase on apoptosis induced by DNA-damaging agents, HepG2 cells were infected with adenovirus containing the cDNA of catalase (Ad-Cat). Forty-eight hours after infection, catalase protein and activity was increased 7-10-fold compared with control cells infected with Ad-LacZ. After treatment with Vp16 or mitomycin C, control cells underwent apoptosis in a p53-dependent manner; however, overexpression of catalase inhibited this apoptosis. Basal levels as well as Vp16- or mitomycin C-stimulated levels of p53 and p21 protein were decreased in the catalase-overexpressing cells as compared with control cells; however, p53 mRNA levels were not decreased by catalase. There was no difference in p53 protein synthesis between catalase-overexpressing cells and control cells. However, pulse-chase experiments indicated that p53 protein degradation was enhanced in the catalase-overexpressing cells. Proteasome inhibitors but not calpeptin prevented the catalase-mediated decrease of p53 content. Whereas Vp16 increased, catalase overexpression decreased the phosphorylation of p53. The protein phosphatase inhibitor okadaic acid did not prevent the catalase-mediated down-regulation of p53 or phosphorylated p53. These results demonstrate that catalase protects HepG2 cells from apoptosis induced by DNA-damaging agents in association with decreasing p53 phosphorylation; the latter may lead to an acceleration in the degradation of p53 protein by the proteasome complex. This suggests that the level of catalase may play a critical role in cell-induced resistance to the effects of anti-cancer drugs which up-regulate p53.
诸如过氧化氢（H₂O₂）之类的氧化剂在某些DNA损伤剂的毒性作用中发挥作用，这一过程通常涉及肿瘤抑制因子p53。过氧化氢酶可迅速降解H₂O₂，从而保护细胞免受氧化损伤。为了研究过氧化氢酶对DNA损伤剂诱导的细胞凋亡的影响，将含过氧化氢酶cDNA的腺病毒（Ad-Cat）感染HepG2细胞。感染48小时后，与感染Ad-LacZ的对照细胞相比，过氧化氢酶蛋白和活性增加了7至10倍。在用Vp16或丝裂霉素C处理后，对照细胞以p53依赖的方式发生凋亡；然而，过氧化氢酶的过表达抑制了这种凋亡。与对照细胞相比，过氧化氢酶过表达细胞中p53和p21蛋白的基础水平以及Vp16或丝裂霉素C刺激后的水平均降低；然而，过氧化氢酶并未降低p53 mRNA水平。过氧化氢酶过表达细胞与对照细胞之间的p53蛋白合成没有差异。然而，脉冲追踪实验表明，过氧化氢酶过表达细胞中p53蛋白的降解增强。蛋白酶体抑制剂而非钙蛋白酶抑制剂可阻止过氧化氢酶介导的p53含量降低。虽然Vp16可增加p53磷酸化，但过氧化氢酶过表达可降低p53磷酸化。蛋白磷酸酶抑制剂冈田酸不能阻止过氧化氢酶介导的p53或磷酸化p53的下调。这些结果表明，过氧化氢酶通过降低p53磷酸化来保护HepG2细胞免受DNA损伤剂诱导的凋亡；后者可能导致蛋白酶体复合物加速p53蛋白的降解。这表明过氧化氢酶水平可能在细胞对上调p53的抗癌药物作用的诱导抗性中起关键作用。
