Mechanisms of Carcinogenesis

描述（由申请人提供）：暴露于紫外光，特别是紫外光B (UVB波长，290-320 nm）已知是皮肤癌发展的主要致病因素。紫外线引起组织损伤的确切机制尚不清楚。有研究表明，UVB在皮肤中产生的细胞毒性活性氧中间体可诱导DNA损伤，从而导致癌症。在这方面，我们已经发现UVB光在不需要完整细胞的过程中快速刺激培养中的小鼠和人角质形成细胞产生氢过氧化物。与生长中的角质形成细胞相比，在钙分化的角质形成细胞中产生更大量的氢过氧化物。使用角质形成细胞的匀浆进行的纯化研究已经鉴定了负责响应UVB光在细胞中产生过氧化氢的主要蛋白质。这种UVB光/过氧化物生成活性需要氧气，并通过热变性消除。出乎意料的是，序列分析鉴定出这种蛋白质是过氧化氢酶， 负责细胞内过氧化氢降解为氧气和水。我们 观察到过氧化氢酶响应于UVB光产生活性氧中间体，这与该酶的公知抗氧化功能是高度不同的。我们的研究结果表明，3-氨基-I，2，4-三唑或叠氮化物抑制过氧化氢酶的过氧化氢代谢活性显著增强了UVB光产生氢过氧化物的能力，这为我们的假设提供了直接支持，即过氧化氢酶可能是UVB光诱导的角质形成细胞氧化应激和DNA损伤的重要介质。为了验证这一假设，我们将描述过氧化氢酶在UVB光和过氧化氢酶介导的应激反应中产生氧化剂的特征。我们还将使用小鼠皮肤模型评估过氧化氢酶在UVB光诱导的致癌作用中的作用。我们提出的研究将为UVB光诱导皮肤DNA损伤的机制以及过氧化氢酶在UVB光诱导的皮肤癌中的作用提供重要的见解。

DESCRIPTION (provided by applicant): Exposure to ultraviolet light, in particular, ultraviolet light B (UVB, wavelengths, 290-320 nm) is known to be a major causative factor in the development of skincancer. The precise mechanisms by which ultraviolet light induces tissue damage are not clear. It hasbeen suggested that cytotoxic reactive oxygen intermediates generated by UVB light in the skin induce DNA damage leading to cancer. In this regard, we have discovered that UVB light rapidly stimulates the production of hydroperoxides by mouse and human keratinocytes in culture in a process that does not require intact cells. Greater amounts of hydroperoxides are produced in calcium-differentiated keratinocytes when compared to growing keratinocytes. Purification studies using homogenates of keratinocytes have identified a major protein responsible for generating hydrogen peroxide in the cells in response to UVB light. This UVB light/peroxide generating activity requires oxygen and is eliminated by heat denaturation. Unexpectedly, sequence analysis identified this protein as catalase, an enzyme responsible for the degradation of intracellular hydrogen peroxide to oxygen and water. Our observations that, in response to UVB light, catalase generates reactive oxygen intermediates is highly divergent from the well known antioxidant functions of this enzyme. Our findings that inhibition of the hydrogen peroxide metabolizing activity of catalase with 3-amino-I ,2, 4-trizole or azide markedly enhances the ability of UVB light to generate hydroperoxides provides direct support for our hypothesis that catalase is potentially an important mediator of UVB light-induced oxidative stress and DNA damage in keratinocytes. To test this hypothesis, we will characterize the production of oxidants by catalase in response to UVB light and the catalase-mediated stress response in both growing and differentiated keratinocytes. We will also evaluate the role of catalase in UVB light-induced carcinogenesis using the mouse skin model. Our proposed studies will provide important insights into the mechanisms by which UVB light induces DNA damage in the skin as well as the role of catalase in UVB light-induced skin cancer.