Regulation of Melanocyte Differentiation by SWI/SNF Chromatin Remodeling Enzymes

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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.