Epigenetic modulation by green tea in prevention of photocarcinogenesis

描述（由申请人提供）：在美国，人类皮肤过度暴露于太阳紫外线（UV）辐射是黑色素瘤和非黑色素瘤皮肤癌发展的主要病因，非黑色素瘤皮肤癌是最常见的皮肤恶性肿瘤。尽管表观遗传机制与uvb诱导的皮肤癌发生有关，但其机制尚未得到充分表征。重要的是，表观遗传机制是潜在可逆的，并且代表了预防uvb诱导的皮肤恶性肿瘤发展的有吸引力的目标。我们现在已经产生了初步数据，表明小鼠皮肤长期暴露于紫外线辐射会诱导表观遗传改变，包括：DNA超甲基化，DNA甲基转移酶（Dnmt）活性增加，组蛋白去乙酰化增加，这些改变可能导致小鼠皮肤中肿瘤抑制基因的沉默。此外，我们还观察到一种无毒的植物化学物质可能通过抑制表观遗传机制来防止光致癌。我们之前已经证明，在小鼠的饮用水中添加绿茶多酚（GTPs, 0.2%, w/v）可以显著抑制紫外线诱导的皮肤肿瘤的发生（肿瘤小鼠的百分比）和肿瘤的多样性。我们现在已经产生了初步数据，表明在小鼠饮用水中给予GTPs可以抑制uvb诱导的皮肤DNA超甲基化和Dnmt活性。基于我们的初步数据，我们提出了一个创新的假设，即皮肤暴露于紫外线辐射会导致DNA超甲基化，从而导致光致癌过程中关键肿瘤抑制基因的表观遗传沉默。我们还假设gtp通过预防与紫外线辐射相关的表观遗传改变，至少在一定程度上阻止了紫外线诱导的皮肤肿瘤的发展。我们的长期目标是充分验证这一假设。这个探索性R21应用程序的目的是验证和扩展我们使用SKH-1无毛小鼠模型的初步结果，以便生成研究设计所需的数据，这些数据将严格测试小鼠和人类皮肤的中心假设，并为观察到的数据建立分子基础。因此，我们提出了两个互补的特定目的：(1)确定GTPs是否通过抑制uvb暴露的皮肤和肿瘤中uvb诱导的DNA超甲基化和Dnmt活性来抑制光致癌作用；(2)确定GTPs在光致癌过程中调控关键肿瘤抑制因子的表观遗传调节剂的分子机制。使用人角质形成细胞和表观遗传调节药物的体外分析将用于验证使用小鼠模型生成的数据。这项研究的结果将为光致癌的表观遗传机制提供新的认识，并表明gtp是否通过抑制这些反应来发挥其皮肤癌化学预防作用。我们解决了一个主要的公共卫生问题，因为人类皮肤过度暴露于太阳紫外线辐射是美国黑色素瘤和非黑色素瘤皮肤癌发展的主要病因。拟议的研究将提供有关uvb诱导的致癌作用的关键新数据，并将确定绿茶可能起到预防/纠正紫外线诱导的缺陷的机制。使用绿茶多酚作为膳食补充剂的新策略的发展可能有助于降低人类患皮肤癌的风险。全世界都对绿茶作为人类癌症化学预防剂感兴趣，因为绿茶是一种无毒、价格合理、受欢迎的饮料，对许多器官都有效。

DESCRIPTION (provided by applicant): Overexposure of the human skin to solar ultraviolet (UV) radiation is the major etiologic factor for the development of melanoma and non-melanoma skin cancers in the United States, with the non-melanoma skin cancer being the most common cutaneous malignancy. Although epigenetic mechanisms have been implicated in UVB-induced skin carcinogenesis, the mechanisms have not been fully characterized. Importantly, epigenetic mechanisms are potentially reversible and represent attractive targets for the prevention of the development of UVB-induced cutaneous malignancies. We have now generated preliminary data that indicate that chronic exposure of the mouse skin to UV radiation induces epigenetic alterations which include: DNA hypermethylation, increases in DNA methyltransferase (Dnmt) activity, and increases in histone de-acetylation and that these alterations may lead to the silencing of tumor suppressor genes in mouse skin. Furthermore, we have made the unique observation that a non-toxic phytochemical may act to prevent photocarcinogenesis through inhibition of epigenetic mechanisms. We had demonstrated previously that administration of green tea polyphenols (GTPs, 0.2%, w/v) in drinking water of mice significantly inhibits UV- induced skin tumor development in terms of tumor incidence (% mice with tumors) and tumor multiplicity. We have now generated preliminary data that suggest that administration of GTPs in drinking water of mice inhibits UVB-induced DNA hypermethylation and Dnmt activity in the skin. Based on our preliminary data, we have formulated the innovative hypothesis that exposure of the skin to UV radiation results in the DNA hypermethylation which leads to epigenetic silencing of key tumor suppressor genes during photocarcinogenesis. We also hypothesize that GTPs prevent UV-induced skin tumor development, at least in part, through the prevention of epigenetic alterations associated with UV radiation. Our long- term goal is to fully test this hypothesis. The objectives of this exploratory R21 application are to verify and extend our preliminary results using the SKH-1 hairless mouse model in order to generate the data necessary for the design of studies that will rigorously test the central hypothesis in mouse and human skin and establish the molecular basis for the observed data. Thus, we propose two complementary Specific Aims: (1) To determine whether inhibition of photocarcinogenesis by GTPs is mediated through inhibition of UVB-induced DNA hypermethylation and Dnmt activity in UVB-exposed skin and tumors, and (2) To determine the molecular mechanisms by which GTPs control epigenetic modulators which regulate key tumor suppressors during photocarcinogenesis. In vitro analyses using human keratinocytes and epigenetic modulating drugs will be used to verify the data generated using the mouse model. The results obtained from this study will generate new knowledge concerning the identity of the epigenetic mechanisms involved in photocarcinogenesis and should indicate whether GTPs exert their skin cancer chemopreventive effects by inhibiting these responses. We address a major public health concern as overexposure of the human skin to solar UV radiation is the major etiologic factor for the development of melanoma and non-melanoma skin cancers in the United States. The proposed studies will provide critical new data concerning UVB-induced carcinogenesis and will identify mechanisms by which green tea may act to prevent/correct UV-induced deficiencies. The development of new strategies using green tea polyphenols as a dietary supplement may help to reduce the risk of skin cancer in humans. There is world-wide interest in green tea as a cancer chemopreventive agent for humans as it is a non-toxic, affordable, popular beverage and is effective in a wide range of organs. PUBLIC HEALTH RELEVANCE: Chronic exposure of the skin to solar ultraviolet (UV) radiation induces multiple adverse effects including the risk of skin cancer development. The epigenetic modifications that occur in DNA play a significant role in the regulation of gene expression and lead to the development of cancers. In the current application, we will determine the molecular mechanism of epigenetic changes which leads to epigenetic silencing of key tumor suppressor genes during photocarcinogenesis. We will also determine whether administration of green tea polyphenols in drinking water of mice prevents photocarcinogenesis in mice through the inhibition of UVB- induced epigenetic alterations and silencing of tumor suppressor genes.