p38 pathway targets SWI-SNF chromatin-remodeling complex to muscle-specific loci

During skeletal myogenesis, genomic reprogramming toward terminal differentiation is achieved by recruiting chromatin-modifying enzymes to muscle-specific loci(1,2). The relative contribution of extracellular signaling cascades in targeting these enzymes to individual genes is unknown. Here we show that the differentiation-activated p38 pathway(3-5) targets the SWI-SNF chromatin-remodeling complex to myogenic loci. Upon differentiation, p38 kinases were recruited to the chromatin of muscle-regulatory elements. Blockade of p38alpha/beta repressed the transcription of muscle genes by preventing recruitment of the SWI-SNF complex at these elements without affecting chromatin binding of muscle-regulatory factors and acetyltransferases. The SWI-SNF subunit BAF60 could be phosphorylated by p38alpha-beta in vitro, and forced activation of p38alpha/beta in myoblasts by expression of a constitutively active MKK6 (refs. 5-7) promoted unscheduled SWI-SNF recruitment to the myogenin promoter. Conversely, inactivation of SWI-SNF enzymatic subunits abrogated MKK6-dependent induction of muscle gene expression. These results identify an unexpected function of differentiation-activated p38 in converting external cues into chromatin modifications at discrete loci, by selectively targeting SWI-SNF to muscle-regulatory elements.