Ras activation pathways in UVR-induced epidermal transformation

描述(申请人提供)：皮肤鳞状细胞癌(SCC)是西方国家第二常见的诊断恶性肿瘤，由于暴露在太阳紫外线辐射(UVR)和人口老龄化的增加，其发病率正在上升。虽然大多数鳞状细胞癌可以通过手术成功地治疗，但它们仍然是由于疤痕和毁容而导致的显著发病率的原因。更重要的是，有一定比例的肿瘤可能会转移，目前还没有针对这一问题的量身定做的治疗方法。因此，有必要对皮肤鳞状细胞癌的发生、促进和发展的机制有更全面的了解，以便开发预防和治疗这种恶性肿瘤的新方法。鳞状细胞癌的很大一部分表现出蛋白RAS的过度激活；不幸的是，RAS是一个难以捉摸的分子，从药理上来说是抑制的，由于它的多重功能，对于健康的细胞来说，它可能毒性太大，无法抵抗这种抑制。因此，寻找在鳞癌中参与致癌RAS通路的上游和下游元件可能揭示出一个更易于化学预防和治疗的靶点。我们实验室的研究表明，RASGRP1通过激活RAS在皮肤肿瘤发生中发挥作用，并支持细胞外信号增强刺激RASGRP1可能有助于激活RAS的剂量，这是皮肤恶性转化和肿瘤进展所必需的。鉴于UVR是与皮肤鳞状细胞癌最相关的致癌物，本研究的目的是阐明RASGRP1在UVR诱导的肿瘤发生中的潜在作用。采用小鼠模型和体外方法相结合的方法，我们提出了以下目标：(1)确定RASGRP1在角质形成细胞对UVR的急性反应中的作用；(2)利用RASGRP1基因敲除和K5.RasGRP1转基因小鼠模型，确定RASGRP1在UVR诱导的皮肤癌变中的需求。这些综合结果将为我们的假设提供强有力的检验，即RASGRP1是UVR在表皮中致癌所必需的，并为进一步研究针对RASGRP1的新药奠定基础，这些新药可能有助于皮肤鳞状细胞癌的化学预防和治疗。 公共卫生相关性：这项应用研究与皮肤鳞状细胞癌(SCC)相关的分子途径，可能导致预防和治疗的新方法。太阳紫外线辐射(UVR)是皮肤鳞状细胞癌的主要致癌因素，并被认为影响RAS，RAS是一种在皮肤动态平衡中起重要作用的分子。事实上，很大比例的皮肤鳞状细胞癌具有RAS的异常激活；因此，它是癌症治疗的一个有吸引力的分子靶点。不幸的是，RAS不容易下药，因此人们的努力被重新定向到作用于RAS癌基因上游或下游的其他分子。该提案的目的是测试一种新的RAS激活剂-RASGRP1-在UVR诱导的皮肤肿瘤形成中的参与。这些研究得到了我们在角质形成细胞生物学和皮肤鳞状细胞癌小鼠模型上的发现的支持。如果我们的研究成功完成，它们将影响可能导致更好的皮肤癌治疗方法的知识，包括化学预防。

DESCRIPTION (provided by applicant): Cutaneous squamous cell carcinoma (SCC) is the second most common diagnosed malignancy in Western countries, and its incidence is rising due to increased exposure to solar ultraviolet radiation (UVR) and population aging. While most SCC are successfully treated by surgery, they still represents a cause of significant morbidity due to scarring and disfigurement. More importantly, a percentage of tumors can metastasize, for which there are no tailored treatments. Thus, there is a need to gather a more complete understanding of the mechanisms perturbed in the initiation, promotion and progression of cutaneous SCC in order to develop new approaches for prevention and treatment of this malignancy. A large fraction of SCC shows hyperactivation of the protein Ras; unfortunately, Ras is an elusive molecule to inhibit pharmacologically, and due to its multiple functions, it may be too toxic for healthy cells to withstand such inhibition. Thus, finding upstream and downstream elements that participate in the oncogenic Ras pathways in SCC may reveal a more amenable target for chemoprevention and therapy. Studies from our lab have demonstrated a role for RasGRP1 in skin tumorigenesis through its ability to activate Ras, and support the concept that stimulation of RasGRP1 by intensified extracellular signals could contribute to the dosage of activated Ras necessary for malignant transformation and tumor progression in the skin. Given the fact that UVR is the most relevant carcinogen associated to cutaneous SCC, the goal of this proposal is to elucidate the potential participation of RasGRP1 in UVR-induced tumorigenesis. Using a combination of mouse models and in vitro approaches, we proposed the following aims: (1) Define the role of RasGRP1 in the acute response of keratinocytes to UVR, and (2) Determine the requirement for RasGRP1 in UVR-induced skin carcinogenesis, using a RasGRP1 knockout and a K5.RasGRP1 transgenic mouse models. The combined results should provide a strong test for our hypothesis that RasGRP1 is required for the tumorigenic effects of UVR in the epidermis, and set the basis for further studies on new drugs targeted to RasGRP1 that could be useful in chemoprevention and treatment of cutaneous SCC. PUBLIC HEALTH RELEVANCE: This application investigates molecular pathways relevant to cutaneous squamous cell carcinoma (SCC) that could lead to novel approaches for prevention and treatment. The solar UV radiation (UVR) is a major carcinogenic factor in cutaneous SCC and is known to affect Ras, a molecule with important roles in skin homeostasis. In fact, a large proportion of cutaneous SCC possesses aberrant activation of Ras; as such, it represents an attractive molecular target for cancer therapeutics. Unfortunately, Ras is not easily druggable, so efforts have been redirected to other molecules that act upstream or downstream of the Ras oncogene. The goal of the proposal is to test the participation of a novel Ras activator -RasGRP1- in UVR-induced skin tumorigenesis. The studies are supported by our findings on keratinocyte biology and mouse models of cutaneous SCC. If our studies are successfully completed, they will impact the knowledge that could lead to better approaches for treatment in skin cancer, including chemoprevention.