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诊断恶性肿瘤，由于太阳紫外线辐射（UVR）暴露的增加和人口老龄化，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治疗，但由于疤痕和毁容，它们仍然是导致严重发病的原因。更重要的是，一定比例的肿瘤会发生转移，而目前还没有专门的治疗方法。因此，需要更全面地了解皮肤鳞状细胞癌的发生、促进和进展的机制，以便开发预防和治疗这种恶性肿瘤的新方法。大部分 SCC 显示 Ras 蛋白过度激活；不幸的是，Ras 是一种难以捉摸的药理学抑制分子，并且由于其多种功能，它对于健康细胞来说可能毒性太大而无法承受这种抑制。因此，寻找参与 SCC 致癌 Ras 途径的上游和下游元件可能会揭示一个更适合化学预防和治疗的靶点。我们实验室的研究证明 RasGRP1 通过激活 Ras 的能力在皮肤肿瘤发生中发挥作用，并支持这样的观点：通过增强的细胞外信号刺激 RasGRP1 可能有助于皮肤恶性转化和肿瘤进展所需的激活 Ras 的剂量。鉴于 UVR 是与皮肤鳞状细胞癌最相关的致癌物，本提案的目标是阐明 RasGRP1 在 UVR 诱导的肿瘤发生中的潜在参与。通过结合小鼠模型和体外方法，我们提出了以下目标：(1) 定义 RasGRP1 在角质形成细胞对 UVR 的急性反应中的作用，以及 (2) 使用 RasGRP1 敲除和 K5.RasGRP1 转基因小鼠模型确定 RasGRP1 在 UVR 诱导的皮肤癌发生中的需求。综合结果应该为我们的假设提供强有力的检验，即 RasGRP1 是 UVR 在表皮中的致瘤作用所必需的，并为进一步研究针对 RasGRP1 的新药物奠定基础，这些新药物可用于化学预防和治疗皮肤鳞状细胞癌。 公共健康相关性：本申请研究了与皮肤鳞状细胞癌 (SCC) 相关的分子途径，可能会带来新的预防和治疗方法。太阳紫外线辐射 (UVR) 是皮肤鳞状细胞癌的主要致癌因素，并且已知会影响 Ras（一种在皮肤稳态中发挥重要作用的分子）。事实上，很大一部分皮肤鳞状细胞癌具有Ras的异常激活；因此，它代表了癌症治疗的一个有吸引力的分子靶点。不幸的是，Ras 不易药物化，因此人们将努力转向作用于 Ras 癌基因上游或下游的其他分子。该提案的目标是测试新型 Ras 激活剂 RasGRP1 在 UVR 诱导的皮肤肿瘤发生中的参与。这些研究得到了我们对角质形成细胞生物学和皮肤鳞状细胞癌小鼠模型的研究结果的支持。如果我们的研究成功完成，它们将影响知识，从而导致更好的皮肤癌治疗方法，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.