The Microphthalmia-associated Transcription Factor Requires SWI/SNF Enzymes to Activate Melanocyte-specific Genes

Abstract

The microphthalmia transcription factor (Mitf) activates melanocyte-specific gene expression, is critical for survival and proliferation of melanocytes during development, and has been described as an oncogene in malignant melanoma. SWI/SNF complexes are ATP-dependent chromatin-remodeling enzymes that play a role in many developmental processes. To determine the requirement for SWI/SNF enzymes in melanocyte differentiation, we introduced Mitf into fibroblasts that inducibly express dominant negative versions of the SWI/SNF ATPases, Brahma or Brahma-related gene 1 (BRG1). These dominant negative SWI/SNF components have been shown to inhibit gene activation events that normally require SWI/SNF enzymes. We found that Mitf-mediated activation of a subset of endogenous melanocyte-specific genes required SWI/SNF enzymes but that cell-cycle regulation occurred independently of SWI/SNF function. Activation of tyrosinase-related protein 1, a melanocyte-specific gene, correlated with SWI/SNF-dependent changes in chromatin accessibility at the endogenous locus. Both BRG1 and Mitf could be localized to the tyrosinase-related protein 1 and tyrosinase promoters by chromatin immunoprecipitation, whereas immunofluorescence and immunoprecipitation experiments indicate that Mitf and BRG1 co-localized in the nucleus and physically interacted. Together these results suggest that Mitf can recruit SWI/SNF enzymes to melanocyte-specific promoters for the activation of gene expression via induced changes in chromatin structure at endogenous loci.