From actinic keratosis to invasive squamous cell carcinoma: Impact of AHR and p27KIP1 on malignant transformation

近年来，皮肤鳞状细胞癌（SCC）的发病率稳步上升。发展这种恶性肿瘤的最重要的危险因素是长期暴露于紫外线（UV）辐射。大多数SCC是由光化性角化病（AK）引起的，这是一种主要发生在阳光照射的皮肤区域的癌前前兆。有趣的是，只有一小部分AK发展为侵袭性SCC。驱动这一恶性转化过程的潜在分子机制尚不清楚。在光致癌的背景下，我们已经证明，芳烃受体（AHR），一种在表皮细胞中被氨基酸色氨酸的光产物激活的转录因子，调节暴露于uvb的角化细胞中DNA损伤依赖的反应。具体来说，AHR通过调节肿瘤抑制因子p27KIP1的细胞内定位和蛋白水平来抑制DNA修复和细胞凋亡（p27）。对皮外肿瘤的研究表明，p27在细胞质中的错误定位可诱导迁移、侵袭等过程，从而促进恶性转化。进一步的初步数据表明，促炎细胞因子抑制ahr激活色氨酸光产物的代谢，从而放大AHR-p27轴的激活。在当前的项目中，我们将测试炎症微环境促进AHR激动剂的积累以及随后在这种情况下致癌AHR-p27轴的激活的假设。因此，AK细胞失去接触抑制，运动性增强，侵袭性增强，最终转化为恶性SCC细胞。为了验证我们的工作假设，我们将研究1.)炎症介质（如TNFα）对CYP1A酶活性的抑制是否足以诱导或扩增AK细胞中AHR依赖的信号通路，2.)炎症介质存在下AHR的激活导致细胞质错定位和/或p27蛋白的蛋白水解，3.)AHR-p27轴的激活诱导AK细胞在体外和体内的恶性转化。4)比较免疫/组织学染色和RNAseq分析（细胞，异种移植小鼠模型，临床样本）使我们能够识别ak特异性预后特征。本研究项目的总体目的是鉴定和验证AHR-p27轴作为化学预防措施降低癌前AK转换率的分子靶点。

The incidence of cutaneous squamous cell carcinomas (SCC) has been increasing steadily for years. The most important risk factor for the development of this malignancy is the chronic exposure to ultraviolet (UV) radiation. The majority of SCC arises from actinic keratosis (AK), a precancerous precursor which predominantly occurs on sun-exposed skin areas. Interestingly, only a small percentage of AK develops into invasive SCC. The underlying molecular mechanisms driving this process of malignant transformation are not well understood. In the context of photocarcinogenesis, we have shown that the aryl hydrocarbon receptor (AHR), a transcription factor, which is activated in epidermal cells by photoproducts of the amino acid tryptophan, regulates DNA damage-dependent responses in UVB-exposed keratinocytes. Specifically, AHR inhibits both DNA repair and apoptosis by modulating the intracellular localization and the protein level of the tumor suppressor p27KIP1 (p27). Studies on extracutaneous cancers revealed that a mislocalization of p27 in the cytoplasm induced migration, invasion and other processes, which contribute to the malignant transformation. Further preliminary data indicate that proinflammatory cytokines inhibit the metabolism of AHR-activating tryptophan photoproducts, thereby amplifying the activation of the AHR-p27 axis. In the current project, we will test the hypothesis that an inflammatory micromilieu fosters the accumulation of AHR agonists and the subsequent activation of the, in this context, oncogenic AHR-p27 axis. As a result, AK cells lose their contact inhibition, enhance their motility and grow invasive, finally leading to their transformation into malignant SCC cells. In order to test our working hypothesis, we will investigate whether 1.) an inhibition of CYP1A enzyme activity by inflammatory mediators, such as TNFα, is sufficient to induce or amplify AHR-dependent signaling pathways in AK cells, 2.) an activation of AHR in the presence of inflammatory mediators results in a cytosolic mislocalization and/or proteolysis of the p27 protein, 3.) an activation of the AHR-p27 axis induces the malignant transformation of AK cells in vitro and in vivo, and 4.) comparative immune-/histological staining and RNAseq analyses (cells, xenograft mouse model, clinical samples) enable us to identify AK-specific prognostic signatures. The overall aim of this research project is to identify and validate the AHR-p27 axis as a molecular target for chemopreventive measures to reduce the transformation rate of premalignant AK.