Role of the aryl hydrocarbon receptor in ultraviolet-B radiation-induced DNA damage responses and skin carcinogenesis

紫外线B（UVB）辐射被表皮细胞的DNA吸收导致形成致突变DNA光产物，特别是环丁烷嘧啶二聚体（CPD），其对皮肤癌的发生起关键作用。在最初的研究中，我们鉴定了芳烃受体（aryl hydrocarbon receptor，AHR），它是一种配体激活的UVB敏感的转录因子，可以抑制这些早期的防御机制，从而对UVB辐射的遗传毒性效应产生了重要的影响。50%）。而AHR的抑制导致加速CPD修复后早期UVB曝光和增强细胞凋亡在以后的时间点，UVB照射角质形成细胞与AHR激动剂治疗引起相反的effects.In更新proposal，我们将评估AHR影响NER活性的机制。对这一过程的透彻理解是重要的，特别是关于我们以前的结果，表明AHR激动剂几乎完全抑制UVB诱导的CPD的修复。通过进行体外实验，以及与SKH-1小鼠的致癌性研究，我们将测试的假设，即紫外线相关的AHR激动剂，如多环芳烃，通过加强UVB引发的鳞状细胞癌（SCC）的发展共同致癌。这些研究的结果对于每天暴露于两种压力因素的个体特别具有临床相关性，因此具有SCC发展的高风险，例如道路工和屋顶工。 来自先前实验的进一步结果提供了证据，AHR抑制增强了SCC细胞对遗传毒性细胞抑制剂的凋亡易感性。因此，我们将了解AHR配体促进致命DNA双链断裂修复的分子机制，从而有助于SCC细胞的凋亡抗性。将进行体外机制研究和小鼠异种移植研究，以检验SCC细胞中AHR的药理学抑制增加共同应用的遗传毒性细胞抑制剂的疗效的假设。如果这是真的，这将为SCC的局部化疗开辟新的机会。例如，与AHR拮抗剂的共同治疗将允许减少副作用丰富的化学治疗剂的剂量而不影响临床反应。拟议的研究项目是临床相关性，因为它的目的是表征AHR依赖的过程在健康皮肤暴露于遗传毒性的环境因素，以及在细胞抑制剂治疗的SCC。因此，该项目的结果不仅对预防而且对皮肤SCC的治疗都很重要。

Absorbance of ultraviolet B (UVB) radiation by the DNA of epidermal cells results in the formation of mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPD), which critically contribute to skin carcinogenesis. The most important protective mechanisms against the genotoxic effects of UVB radiation are nucleotide excision repair (NER) and apoptosis.In the initial grant, we identified the aryl hydrocarbon receptor (AHR), a ligand-activated and UVB-sensitive transcription factor, to repress these early defense mechanisms, thereby critically contributing (approx. 50%) to photocarcinogenesis in mice. Whereas an inhibition of AHR led to accelerated CPD repair early after UVB exposure and enhanced apoptosis at later time points, treatment of UVB-irradiated keratinocytes with AHR agonists caused opposite effects.In the renewal proposal, we will assess the mechanism by which AHR influences NER activity. A thorough understanding of this process is important, in particular with regards to our previous results, showing that AHR agonists nearly completely inhibited the repair of UVB-induced CPDs. By conducting in vitro experiments as well as a carcinogenesis study with SKH-1 mice, we will test the hypothesis that exposure-relevant AHR agonists, such as polycyclic aromatic hydrocarbons, act co-carcinogenic by enforcing the development of UVB-initiated squamous cell carcinomas (SCC). The results of these studies are in particular of clinical relevance for individuals that are daily exposed to both stress factors and thus are at high risk for SCC development, such as roadmen and roofers. Further results from previous experiments provide evidence that AHR inhibition enhances the apoptosis susceptibility of SCC cells to genotoxic cytostatics. Hence, we will understand the molecular mechanisms by which AHR ligands facilitate the repair of lethal DNA double-strand breaks and thereby contribute to apoptosis resistance of SCC cells. Mechanistic in vitro studies and a mouse xenograft study will be conducted to test the hypothesis that a pharmacological inhibition of AHR in SCC cells increases the efficacy of co-applied genotoxic cytostatics. If this turns out to be true, it would open up new opportunities for the topical chemotherapy of SCC. Co-treatment with AHR antagonists would, for instance, allow to reduce the dose of side-effect-rich chemotherapeutics without affecting the clinical response. The proposed research project is of clinical relevance as it aims to characterize AHR-dependent processes in healthy skin exposed to genotoxic environmental factors, as well as in cytostatic-treated SCC. Hence, the results of this project are not only important for prevention but also for the therapy of cutaneous SCC.