Role of vitamin D receptor in DNA repair

描述（由申请人提供）：维生素D在改善骨相关代谢以外的各种健康结果方面的作用存在争议。医学研究所最近的一份报告确定了一项主要的研究需要，即研究是否足以在皮肤中进行维生素D光合作用的皮下剂量与额外的风险有关。 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，这是可行的，问是否存在补偿生物机制，可能夫妇维生素D光合作用的DNA修复途径相关的紫外线辐射（UV）。这项研究提案的假设是，在与维生素D光合作用相关的紫外线暴露剂量后，独立于经典维生素D信号传导的维生素D受体（VDR）被上调，以介导细胞反应，限制附带的DNA损伤，从而最大限度地降低皮肤癌风险。为了支持这一假设，我们观察到VDR是一种UV诱导基因，并且VDR敲除小鼠表皮在主要UV光产物的修复中显著受损。这些和其他初步研究表明，VDR可能以不依赖维生素D的方式起作用，具有光保护作用。在目标1中，我们将确定紫外线照射后DNA修复中VDR活性的决定因素。使用小鼠表皮片以及培养的人类和小鼠角质形成细胞，其中VDR是缺乏的，我们将确定是否VDR诱导是一种普遍的反应，以多种形式的DNA损伤，或者如果它是紫外线特异性的。将测量UV诱导的VDR表达对p53家族和生物活性维生素D的依赖性。在目标2中，我们将评估VDR在全球基因组和转录偶联核苷酸切除修复中的作用，通过测定小鼠表皮层和培养的缺乏VDR的小鼠和人角质形成细胞中的DNA修复活性和关键DNA损伤识别蛋白的水平。我们还将检查来自人类和小鼠的紫外线诱导的肿瘤组织，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相关。在这些研究的结论，一个系统的理解应该出现的作用，VDR在响应维生素D光合作用过程中发生的DNA损伤。这些研究与了解皮肤产生维生素D所需的生理补偿有关，并可能为未来的临床研究和阳光照射和保护的公共卫生建议提供信息。

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.