Role of vitamin D receptor in DNA repair

描述(申请人提供)：维生素D在改善除骨骼相关代谢以外的各种健康后果方面的作用存在争议。医学研究所最近的一份报告指出，一项重大研究需要研究皮肤中足以进行维生素D光合作用的亚红斑剂量是否与患上糖尿病的额外风险有关 皮肤癌。由于正常人皮肤癌的潜伏期很长，临床试验不太可能在不久的将来解决这个问题。然而，询问是否存在可能将维生素D光合作用耦合到与紫外线(UV)相关的DNA修复途径的补偿生物学机制是可行的。这项研究的假设是，在紫外线暴露与维生素D光合作用相关的剂量后，不依赖于典型的维生素D信号的维生素D受体(VDR)被上调，以介导细胞反应，从而限制附带的DNA损伤，从而将皮肤癌的风险降至最低。为了支持这一假说，我们观察到VDR是一个紫外线诱导基因，并且VDR基因敲除的小鼠表皮在修复主要紫外光产物的过程中显著受损。这些和其他初步研究表明，VDR可能以一种不依赖维生素D的方式发挥作用，具有光保护作用。在目标1中，我们将确定紫外线后DNA修复中VDR活性的决定因素。利用小鼠的表皮片以及培养的缺乏VDR的人和小鼠角质形成细胞，我们将确定VDR的诱导是对多种形式的DNA损伤的普遍反应，还是紫外线特异性的。紫外线诱导的VDR表达对P53家族和生物活性维生素D的依赖性将被测量。在目标2中，我们将通过检测缺乏VDR的小鼠表皮细胞和培养的小鼠和人角质形成细胞的DNA修复活性和关键DNA损伤识别蛋白的水平，来评估VDR在全球基因组和转录偶联核苷酸切除修复中的作用。我们还将研究紫外线诱导的人类和小鼠的肿瘤组织，以将VDR与关键DNA修复蛋白的水平相关联，并对关键的肿瘤抑制基因进行突变分析，以测试VDR丢失是否与异常突变表型有关。在这些研究的结论中，应该会出现对VDR在应对维生素D光合作用过程中造成的DNA损伤所起的作用的系统理解。这些研究对了解皮肤在产生维生素D时所需的生理补偿是相关的，并可能为未来的临床研究和公共卫生建议提供阳光照射和防护的信息。

DESCRIPTION (provided by applicant): The role of vitamin D in ameliorating various health outcomes other than bone-related metabolism is controversial. A recent Institute of Medicine report identified as a major research need studies that address whether the sub-erythemal doses sufficient for vitamin D photosynthesis in the skin are associated with an additional risk of skin cancer. Due to the lengthy latency of skin cancers in normal humans, it is unlikely that clinical trials can address this issue in the near future. However, it is feasible to ask whether compensatory biological mechanisms exist that might couple vitamin D photosynthesis to the DNA repair pathways relevant for ultraviolet radiation (UV). The hypothesis of this research proposal is that, following doses of UV exposure associated with vitamin D photosynthesis, vitamin D receptor (VDR) independent of canonical vitamin D signaling is upregulated to mediate cellular responses that limit the collateral DNA damage incurred, thus minimizing skin cancer risk. In support of the hypothesis, we have observed that VDR is a UV- inducible gene, and that VDR knockout mouse epidermis is significantly impaired in the repair of the major UV photoproducts. These and other preliminary studies suggest that VDR, likely acting in a vitamin D-independent manner, is photoprotective. In Aim 1, we will identify the determinants of VDR activity in DNA repair following UV. Using mouse epidermal sheets as well as cultured human and mouse keratinocytes in which VDR is deficient, we will determine if VDR induction is a general response to multiple forms of DNA damage, or if it is UV-specific. The dependence of UV-induced VDR expression on the p53 family and on biologically active vitamin D will be measured. In Aim 2, we will assess VDR's role in both global genomic and transcription-coupled nucleotide excision repair by assaying DNA repair activity and levels of key DNA damage recognition proteins in mouse epidermal sheets and cultured mouse and human keratinocytes lacking VDR. We will also examine UV-induced tumor tissue from humans and mice to correlate VDR with levels of key DNA repair proteins as well as perform a mutational analysis on key tumor suppressor genes to test if VDR loss is associated with an abnormal mutator phenotype. At the conclusion of these studies, a systematic understanding should emerge of the role that VDR plays in the response to DNA damage incurred during vitamin D photosynthesis. These studies are relevant for understanding the physiological compensations required of skin in producing vitamin D and may inform future clinical studies and public health recommendations for sun exposure and protection.