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

表皮细胞对紫外线B(UVB)辐射的吸收会导致DNA光产物的突变，特别是环丁烷嘧啶二聚体(CPD)的形成，而环丁烷嘧啶二聚体(CPD)是皮肤癌变的关键因素。针对UVB辐射的遗传毒性效应，最重要的保护机制是核苷酸切除修复(NER)和细胞凋亡。在最初的拨款中，我们确定了芳烃受体(AHR)，一个配体激活的和UVB敏感的转录因子，以抑制这些早期的防御机制，从而发挥关键作用(约.50%)对小鼠的光致癌作用。UVB照射后早期抑制AHR导致CPD修复加速，后期促进细胞凋亡，而AHR激动剂处理UVB照射的角质形成细胞则产生相反的效果。在更新方案中，我们将评估AHR影响NER活性的机制。彻底了解这一过程是很重要的，特别是关于我们之前的结果，表明AHR激动剂几乎完全抑制了UVB诱导的CPD的修复。通过对SKH-1小鼠进行体外实验和致癌研究，我们将检验与暴露相关的AHR激动剂，如多环芳烃，通过促进UVB启动的鳞状细胞癌(SCC)的发展而起协同致癌作用的假设。这些研究的结果对于那些每天都暴露在这两种压力因素下的人，如路工和屋顶工人，具有特别重要的临床意义，因此有发生鳞状细胞癌的高风险。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敏感性。因此，我们将了解AHR配体促进致死性DNA双链断裂修复从而促进SCC细胞抗凋亡的分子机制。体外机制研究和小鼠异种移植研究将被用来验证这样的假设，即药物抑制SCC细胞中的AHR会增加联合应用的遗传毒性细胞抑制剂的疗效。如果这是真的，它将为鳞状细胞癌的局部化疗开辟新的机会。例如，与AHR拮抗剂联合治疗将允许减少副作用丰富的化疗药物的剂量，而不会影响临床反应。这项拟议的研究项目具有临床意义，因为它旨在描述暴露于遗传毒性环境因素的健康皮肤以及细胞抑制剂治疗的SCC中AHR依赖的过程。因此，本项目的研究结果不仅对皮肤鳞状细胞癌的预防具有重要意义，而且对皮肤鳞状细胞癌的治疗也具有重要意义。

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.