Ras activation pathways in UVR-induced epidermal transformation

描述（由申请人提供）：皮肤鳞状细胞癌（SCC）是西方国家第二常见的恶性肿瘤，由于太阳紫外线辐射（UVR）的增加和人口老龄化，其发病率正在上升。虽然大多数SCC可以通过手术成功治疗，但由于疤痕和毁容，它们仍然是导致严重发病率的原因。更重要的是，一定比例的肿瘤会发生转移，目前还没有专门的治疗方法。因此，有必要更全面地了解皮肤鳞状细胞癌发生、促进和发展的机制，以便开发预防和治疗这种恶性肿瘤的新方法。大部分SCC表现出Ras蛋白的过度活化；不幸的是，Ras是一种难以从药理学上抑制的分子，由于其多种功能，它可能对健康细胞的毒性太大，无法承受这种抑制。因此，在SCC中发现参与致癌Ras通路的上游和下游元件可能会揭示一个更合适的化学预防和治疗靶点。我们实验室的研究已经证明RasGRP1通过激活Ras的能力在皮肤肿瘤发生中发挥作用，并支持通过强化细胞外信号刺激RasGRP1可能有助于皮肤恶性转化和肿瘤进展所需的激活Ras剂量的概念。鉴于UVR是与皮肤SCC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参与。通过小鼠模型和体外方法的结合，我们提出了以下目标：(1)确定RasGRP1在角化细胞对UVR的急性反应中的作用；(2)通过敲除RasGRP1和K5来确定RasGRP1在UVR诱导的皮肤癌发生中的需求。RasGRP1转基因小鼠模型。综合研究结果将有力地验证我们的假设，即UVR在表皮的致瘤作用需要RasGRP1，并为进一步研究针对RasGRP1的新药奠定基础，这些药物可能有助于皮肤SCC的化学预防和治疗。

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.