Extranuclear estrogen receptor-α stimulates NeuroD1 binding to the insulin promoter and favors insulin synthesis

Estrogen receptors (ERs) protect pancreatic islet survival in mice through rapid extranuclear actions. ER alpha also enhances insulin synthesis in cultured islets. Whether ERa stimulates insulin synthesis in vivo and, if so, through which mechanism(s) remain largely unknown. To address these issues, we generated a pancreas-specific ERa knockout mouse (PER alpha KO-/-) using the Cre-loxP strategy and used a combination of genetic and pharmacologic tools in cultured islets and beta cells. Whereas 17 beta-estradiol (E2) treatment up-regulates pancreatic insulin gene and protein content in control ER alpha lox/lox mice, these E2 effects are abolished in PER alpha KO-/- mice. We find that E2-activated ER alpha increases insulin synthesis by enhancing glucose stimulation of the insulin promoter activity. Using a knock-in mouse with a mutated ER alpha eliminating binding to the estrogen response elements (EREs), we show that E2 stimulation of insulin synthesis is independent of the ERE. We find that the extranuclear ER alpha interacts with the tyrosine kinase Src, which activates extracellular signal-regulated kinases(1/2), to increase nuclear localization and binding to the insulin promoter of the transcription factor NeuroD1. This study supports the importance of ERa in beta cells as a regulator of insulin synthesis in vivo.