Mechanisms of Carcinogenesis

描述（由申请人提供）：已知暴露于紫外光，特别是紫外光B（UVB，波长范围为290-320 nm的紫外光）是皮肤癌发展的主要致病因素。表皮细胞表达多种通过吸收UVB光起作用的保护性分子。暴露在阳光下的组织也受到解毒和修复酶以及其他抗氧化分子的保护。紫外线引起组织损伤的确切机制尚不清楚。有人认为，UVB光在皮肤中产生的细胞毒性活性氧中间体是导致DNA损伤导致癌症的原因。我们已经发现，UVB光在不需要完整细胞的过程中迅速刺激小鼠和人类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。使用角质形成细胞匀浆的纯化研究鉴定了负责响应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，序列分析将这种蛋白质鉴定为过氧化氢酶，一种已知负责细胞内过氧化氢降解的酶。众所周知，过氧化氢酶也具有过氧化活性，UVB光刺激酶的这种功能。在这方面，我们发现用3-氨基-1，2，4-三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UVB光产生氢过氧化物的能力。我们推测过氧化氢酶是UVB光诱导的角质形成细胞氧化应激和DNA损伤的重要介质。我们的具体目标是确定过氧化氢酶介导的紫外线诱导的氧化应激和DNA损伤的生长和分化的角质形成细胞和评估的作用，在UVB诱导的致癌作用的酶使用小鼠皮肤模型。我们提出的研究将提供紫外线诱导皮肤DNA损伤机制的信息，也应该提供过氧化氢酶在紫外线诱导皮肤癌中的潜在作用的信息。

DESCRIPTION (provided by applicant): Exposure to ultraviolet light, in particular, ultraviolet light B (UVB, ultraviolet light in the wavelengths ranging from 290-320 nm) is known to be a major causative factor in the development of skin cancer. Epidermal cells express a variety of protective molecules that function by absorbing UVB light. Sun exposed tissue is also protected by detoxification and repair enzymes, as well as other antioxidant molecules. The precise mechanisms by which ultraviolet light induces tissue damage are not clear. It has been suggested that cytotoxic reactive oxygen intermediates generated by UVB light in the skin are responsible for causing DNA damage leading to cancer. We have discovered that UVB light rapidly stimulates the production of hydroperoxides by mouse and human keratinocytes 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 identified a major protein responsible for generating hydrogen peroxide in the cells in response to UVB light. This UVB light/peroxide generating activity of requires oxygen and is eliminated by heat denaturation. Unexpectedly, sequence analysis identified this protein as catalase, an enzyme known to be responsible for the degradation of intracellular hydrogen peroxide. It is well recognized that catalase also possesses peroxidatic activity and UVB light stimulates this function of the enzyme. In this regard, we found that inhibition of the hydrogen peroxide metabolizing activity of catalase with 3-amino-1,2, 4-triazole or azide markedly enhanced the ability of UVB light to generate hydroperoxides. We hypothesize that catalase is an important mediator of UVB light-induced oxidative stress and DNA damage in keratinocytes. Our specific aims are to determine if catalase mediates ultraviolet light-induced oxidative stress and DNA damage in growing and differentiated keratinocytes and to evaluate the role of the enzyme in UVB-induced carcinogenesis using the mouse skin model. Our proposed studies will provide information on the mechanisms by which ultraviolet light induces DNA damage in the skin and should also provide information on the potential role of catalase in ultraviolet light induced skin cancer.