Baf60a Mediates Interactions Between The Microphthalmia-Associated Transcription Factor And The Brg1-Containing Swi/Snf Complex During Melanocyte Differentiation

SWI/SNF chromatin remodeling enzymes are multisubunit complexes that contain one of two catalytic subunits, BRG1 or BRM and 9-11 additional subunits called BRG1 or BRM-associated factors (BAFs). BRG1 interacts with the microphthalmia-associated transcription factor (MITF) and is required for melanocyte development in vitro and in vivo. The subunits of SWI/SNF that mediate interactions between BRG1 and MITF have not been elucidated. Three mutually exclusive isoforms of a 60-kDa subunit (BAF60A, B, or C) often facilitate interactions with transcription factors during lineage specification. We tested the hypothesis that a BAF60 subunit promotes interactions between MITF and the BRG1-containing SWI/SNF complex. We found that MITF can physically interact with BAF60A, BAF60B, and BAF60C. The interaction between MITF and BAF60A required the basic helix-loop-helix domain of MITF. Recombinant BAF60A pulled down recombinant MITF, suggesting that the interaction can occur in the absence of other SWI/SNF subunits and other transcriptional regulators of the melanocyte lineage. Depletion of BAF60A in differentiating melanoblasts inhibited melanin synthesis and expression of MITF target genes. MITF promoted BAF60A recruitment to melanocyte-specific promoters, and BAF60A was required to promote BRG1 recruitment and chromatin remodeling. Thus, BAF60A promotes interactions between MITF and the SWI/SNF complex and is required for melanocyte differentiation.