Regulation of Melanocyte Differentiation by SWI/SNF Chromatin Remodeling Enzymes

描述（由申请人提供）：皮肤黑色素细胞提供主要的生理防御紫外线辐射（UVR）的破坏性影响，但它们可以转化为黑色素瘤，这是最致命的皮肤癌形式。小眼症转录因子（MITF）是黑素细胞分化的主要调控因子，激活对黑色素合成和黑素细胞功能重要的基因表达。MITF也调节黑色素瘤的致瘤性。α -促黑素细胞激素（1-MSH）促进黑素细胞分化，保护细胞免受紫外线辐射引起的损伤。重要的是，1-MSH激活的基因表达是通过涉及MITF的转录机制介导的。然而，细胞分化过程中的转录激活和对许多环境线索的响应需要表观遗传变化，将压抑的染色质结构转化为转录允许的构象。MITF在抑制性染色质结构中激活转录的机制尚不清楚。更好地了解MITF介导的转录激活的表观遗传机制将使我们能够调节黑色素合成和黑素细胞功能的其他方面，从而设计旨在预防和治疗皮肤癌的策略。SWI/SNF酶是一种多亚基复合物，以ATP依赖的方式改变染色质结构，在调节基因表达中发挥重要作用。该复合物的组成部分是干细胞可塑性和分化成多个细胞系所必需的。我们的数据表明，SWI/SNF酶与MITF合作激活黑素细胞特异性基因的表达，并且需要MITF来阻止SWI/SNF依赖性分化途径的激活。这些结果提出了通过MITF介导的1- msh诱导的黑素细胞分化需要SWI/SNF染色质重塑酶的假设。我们将通过(1)阐明调控SWI/SNF酶募集到目标启动子的机制，(2)分析SWI/SNF酶在介导黑素细胞特异性启动子特异性染色质结构变化中的需求来验证这一假设。(3)确定SWI/SNF介导的染色质重塑导致下游组蛋白翻译后修饰调节转录的机制。

DESCRIPTION (provided by applicant): Cutaneous melanocytes provide the major physiological defense against the damaging effects of ultraviolet radiation (UVR) but they can be transformed to melanoma, the most deadly form of skin cancer. Microphthalmia Transcription Factor (MITF) is the master regulator of melanocyte differentiation and activates the expression of genes important for melanin synthesis and melanocyte function. MITF also regulates aspects of melanoma tumorigenicity. The alpha melanocyte stimulating hormone (1-MSH) promotes melanocyte differentiation and protects cells from UVR induced damage. Importantly, 1-MSH activated gene expression is mediated through a transcriptional mechanism involving MITF. However, transcriptional activation during cellular differentiation and in response to many environmental cues requires epigenetic changes that convert repressive chromatin structure to a transcriptionally permissive conformation. The mechanisms by which MITF activates transcription within repressive chromatin structure are unclear. A better understanding of the epigenetic mechanisms underlying MITF mediated transcriptional activation will allow us to modulate melanin synthesis and other aspects of melanocyte function for design of strategies aimed at preventing and treating skin cancer. SWI/SNF enzymes are multi-subunit complexes that alter chromatin structure in an ATP dependent manner and play important roles in regulating gene expression. Components of the complex are required for stem cell plasticity as well as for differentiation into multiple cell lineages. Our data suggest that SWI/SNF enzymes cooperate with MITF to activate expression of melanocyte specific genes and that MITF is required to prevent SWI/SNF dependent activation of a divergent differentiation pathway. These results raise the hypothesis that 1-MSH-induced melanocyte differentiation mediated through MITF requires SWI/SNF chromatin remodeling enzymes. We will test this hypothesis by (1) elucidating the mechanisms that regulate the recruitment of SWI/SNF enzymes to target promoters, (2) analyzing the requirement for SWI/SNF enzymes in mediating specific chromatin structural changes on a melanocyte specific promoter. (3) Determining the mechanisms by which SWI/SNF mediated chromatin remodeling leads to downstream histone posttranslational modifications that regulate transcription. PUBLIC HEALTH RELEVANCE: Melanocytes are cells that synthesize the pigment melanin and play a critical role in protecting skin against ultraviolet radiation. This proposal will investigate the mechanisms by which melanocyte specific gene expression is regulated. A better understanding of this process will allow us to develop more effective strategies for prevention and treatment of pigmentary disorders and skin cancer.