Sunlight-Related Steps in Human Skin Cancer

描述(申请人提供)：我们的长期目标是了解阳光中的紫外线辐射是如何导致皮肤癌的。在之前的资助期间，我们从生物物理事件发展到组织水平，将DNA光产物与阳光诱导的p53和PTCH肿瘤抑制基因突变联系起来，将p53与紫外线诱导的细胞凋亡和紫外线驱动的突变型角质形成细胞的克隆性增殖联系起来。现在，我们更密切地关注紫外线诱导细胞凋亡的分子机制的一个新方面。我们最近发现，p53；E2fl双基因敲除小鼠恢复了对紫外线诱导的细胞凋亡(以及它们的抗癌能力)的熟练程度，这与p53基因敲除的缺陷形成了鲜明对比。我们假设：a)P53不是细胞凋亡的重要触发因素，而是调节由其自身的UV诱导信号触发的“直接UV-凋亡途径”，b)P53通过对抗B2fl的基础抑制而上调这一途径。因此，P53；E2FL双敲除是研究直接紫外线凋亡途径的独特试剂，而不会因同时紫外线对其调节装置的影响而产生并发症。本研究的目的是：1)确定直接UV-凋亡途径；2)鉴定其P53-E2f1调节因子；3)鉴定在直接途径中触发UV-凋亡的信号。这些实验将阐明紫外线辐射--由此推断，阳光--诱导皮肤细胞凋亡的分子途径。将系统分成两个部分，每个部分都需要一个单独的紫外线信号，一个“直接”操作部分和它的P53-E2FL调节装置，也可能解决紫外线信号中损伤对DNA、RNA和膜受体的相对贡献。在临床水平上，了解E2fl的机制可能为规避P53相关的癌症治疗耐药奠定基础。

DESCRIPTION (provided by applicant): Our long-term aim is to understand how the ultraviolet radiation in sunlight causes skin cancer. In previous grant periods we progressed from biophysical events to the tissue level, linking DNA photoproducts to sunlight-induced mutations in the p53 and PTCH tumor suppressor genes, and p53 to UV-induced apoptosis and UV-driven clonal expansion ofp53-mutant keratinocytes. Now, we focus more closely on a novel aspect of the molecular mechanism of UV-induced apoptosis. We recently found that p53;E2fl double knockout mice regain their proficiency for UV-induced apoptosis (as well as their cancer resistance), in striking contrast to the defect in p53 knockouts. We hypothesize that: a) P53 is not an essential trigger of apoptosis, but instead regulates a "direct UV-apoptosis pathway" that is triggered by its own UV induction signal, b) P53 upregulates this pathway by opposing basal suppression by B2fl. The p53; E2fl double knockout is thus a unique reagent for studying the direct UV apoptosis pathway without complications from simultaneous UV effects on its regulatory apparatus. The present Aims seek to: i) identify the direct UV-apoptosis pathway; ii) characterize its P53-E2fl regulator; and iii) characterize the signal that triggers UV-apoptosis in the direct pathway. These experiments will clarify the molecular pathway through which UV radiation -- and, by inference, sunlight -- induces apoptosis in skin cells. Dividing the system into two parts each needing a separate UV signal, a "direct" operating part and its P53-E2fl regulatory apparatus, may also resolve the relative contributions of damage to DNA, RNA, and membrane receptors in UV signaling. At a clinical level, understanding the E2fl mechanism may lay the basis for circumventing p53-related resistance to cancer therapy.