CREB Promotes Beta Cell Gene Expression by Targeting Its Coactivators to Tissue-Specific Enhancers

Abstract

CREB mediates effects of cyclic AMP on cellular gene expression. Ubiquitous CREB target genes are induced following recruitment of CREB and its coactivators to promoter proximal binding sites. We found that CREB stimulates the expression of pancreatic beta cell-specific genes by targeting CBP/p300 to promoter-distal enhancer regions. Subsequent increases in histone acetylation facilitate recruitment of the coactivators CRTC2 and BRD4, leading to release of RNA polymerase II over the target gene body. Indeed, CREB-induced hyperacetylation of chromatin over superenhancers promoted beta cell-restricted gene expression, which is sensitive to inhibitors of CBP/p300 and BRD4 activity. Neurod1 appears critical in establishing nucleosome-free regions for recruitment of CREB to beta cell-specific enhancers. Deletion of a CREB-Neurod1-bound enhancer within the Lrrc10b-Syt7 superenhancer disrupted the expression of both genes and decreased beta cell function. Our results demonstrate how cross talk between signal-dependent and lineage-determining factors promotes the expression of cell-type-specific gene programs in response to extracellular cues.

Keywords: BRD4; CBP; CREB; CRTC2; NeuroD1; PKA; beta cell; cAMP; insulin.