Zhu Q, Wani M A, El-Mahdy M, Wani G, Wani A A
Department of Radiology, The Ohio State University, Columbus, Ohio, USA.
Mol Carcinog. 2000 Aug;28(4):215-24.
The increase in the p53 activity in response to DNA damage is thought to be one of the important mechanisms by which p53 contributes to transcriptional activation of p21(wafl), mdm2, and other downstream regulatory genes. To investigate the p53 response to ultraviolet (UV) type of DNA damage, p53 protein level, its transcriptional activity and in vivo ubiquitination were compared in repair-proficient normal human fibroblasts (NHFs) and repair-deficient xeroderma pigmentosum (XP) group A and group C (XP-C) fibroblasts subsequent to irradiation with UV light. Accumulation of p53 protein level was observed with increasing UV doses in all the cell lines; however, discordance between p53 and p21(waf1) and mdm2 levels was observed in NHF and XP-A cells. Induction of p21(waf1) and mdm2 was inhibited by UV irradiation, requiring higher doses in NHF and lower doses in XP-A cells. However, inhibition of p21(waf1) and mdm2 induction was not observed in XP-C cells. Ubiquitin-p53 conjugates could be detected in irradiated or unirradiated NHF and XP-A cells but not in XP-C cells irradiated with 30 and 50 J/m(2) UV light. Using a p53 reporter assay, p53 transcriptional activities were found to be induced by 10 J/m(2) UV exposure and dramatically inhibited with increasing UV doses in NHF cells. Compared with repair-proficient NHF cells, UV inhibition of p53 transcriptional activity was relatively more sensitive in XP-A cells but resistant in XP-C cells. These results indicate that DNA damage by UV, in addition to inducing p53, acts as a trigger for inhibition of p53 transcriptional activity. Overall, recognition of DNA damage links both p53 induction and p53 degradation to DNA repair mechanisms.
p53活性因DNA损伤而增加，被认为是p53促进p21（wafl）、mdm2及其他下游调控基因转录激活的重要机制之一。为研究p53对紫外线（UV）所致DNA损伤的反应，在用紫外线照射后，比较了修复功能正常的正常人成纤维细胞（NHFs）以及修复缺陷的着色性干皮病（XP）A组和C组（XP-C）成纤维细胞中p53蛋白水平、其转录活性及体内泛素化情况。在所有细胞系中，随着紫外线剂量增加均观察到p53蛋白水平的积累；然而，在NHF和XP-A细胞中观察到p53与p21（waf1）及mdm2水平不一致。紫外线照射抑制了p21（waf1）和mdm2的诱导，NHF细胞需要更高剂量，而XP-A细胞需要更低剂量。然而，在XP-C细胞中未观察到对p21（waf1）和mdm2诱导的抑制。在照射或未照射的NHF和XP-A细胞中均可检测到泛素-p53缀合物，但在用30和50 J/m(2)紫外线照射的XP-C细胞中未检测到。使用p53报告基因检测法，发现10 J/m(2)紫外线照射可诱导NHF细胞中p53转录活性，且随着紫外线剂量增加而显著抑制。与修复功能正常的NHF细胞相比，紫外线对p53转录活性的抑制在XP-A细胞中相对更敏感，而在XP-C细胞中具有抗性。这些结果表明，紫外线造成的DNA损伤除了诱导p53外，还作为抑制p53转录活性的触发因素。总体而言，对DNA损伤的识别将p53诱导和p53降解都与DNA修复机制联系起来。
