Ferguson Bridget E, Oh Dennis H
Department of Dermatology, University of California-San Francisco, San Francisco VA Medical Center, San Francisco, California 94121, USA.
Cancer Res. 2005 Oct 1;65(19):8723-9. doi: 10.1158/0008-5472.CAN-05-1457.
The p53 tumor suppressor protein is important for many cellular responses to DNA damage in mammalian cells, but its role in regulating DNA repair in human keratinocytes is undefined. We compared the nucleotide excision repair (NER) response of human fibroblasts and keratinocytes deficient in p53. Fibroblasts expressing human papillomavirus 16 E6 oncoprotein had impaired repair of UV radiation-induced cyclobutane pyrimidine dimers in association with reduced levels of p53 and XPC, which is involved in DNA damage recognition. In contrast, keratinocytes expressing E6 alone or concurrently with the E7 oncoprotein, while possessing reduced levels of p53 but normal levels of XPC, continued to repair pyrimidine dimers as efficiently as control cells with normal p53 levels. Despite preservation of DNA repair, E6 and E6/E7 keratinocytes were hypersensitive to UV radiation. E6 fibroblasts exhibited markedly reduced basal and induced levels of mRNA encoding DDB2, another protein implicated in early events in global NER. In contrast, E6 or E6/E7 keratinocytes possessed basal DDB2 mRNA levels that were not significantly altered relative to control cells, although little induction occurred following UV radiation. Intact global NER was also confirmed in SCC25 cells possessing inactivating mutations in p53 as well as in cells treated with pifithrin-alpha, a chemical inhibitor of p53 that decreased sensitivity of cells to UV radiation. Collectively, these results indicate that human keratinocytes, unlike fibroblasts, do not require p53 to maintain basal global NER activity, but p53 may still be important in mediating inducible responses following DNA damage.
p53肿瘤抑制蛋白对哺乳动物细胞中许多DNA损伤的细胞反应至关重要，但其在调节人类角质形成细胞DNA修复中的作用尚不清楚。我们比较了p53缺陷的人类成纤维细胞和角质形成细胞的核苷酸切除修复（NER）反应。表达人乳头瘤病毒16 E6癌蛋白的成纤维细胞，其紫外线辐射诱导的环丁烷嘧啶二聚体修复受损，同时p53和参与DNA损伤识别的XPC水平降低。相比之下，单独表达E6或与E7癌蛋白同时表达的角质形成细胞，虽然p53水平降低但XPC水平正常，其嘧啶二聚体的修复效率仍与p53水平正常的对照细胞一样高。尽管DNA修复得以保留，但E6和E6/E7角质形成细胞对紫外线辐射高度敏感。E6成纤维细胞中编码DDB2（另一种参与全局NER早期事件的蛋白）的mRNA基础水平和诱导水平显著降低。相比之下，E6或E6/E7角质形成细胞的DDB2 mRNA基础水平与对照细胞相比无显著变化，尽管紫外线辐射后诱导作用很小。在p53发生失活突变的SCC25细胞以及用pifithrin-α（一种p53化学抑制剂，可降低细胞对紫外线辐射的敏感性）处理的细胞中，也证实了完整的全局NER。总体而言，这些结果表明，与成纤维细胞不同，人类角质形成细胞维持基础全局NER活性不需要p53，但p53在介导DNA损伤后的诱导反应中可能仍然很重要。
