RFX6 Regulates Insulin Secretion by Modulating Ca2+ Homeostasis in Human β Cells

Development and function of pancreatic beta cells involve the regulated activity of specific transcription factors. RFX6 is a transcription factor essential for mouse beta cell differentiation that is mutated in monogenic forms of neonatal diabetes. However, the expression and functional roles of RFX6 in human beta cells, especially in pathophysiological conditions, are poorly explored. We demonstrate the presence of RFX6 in adult human pancreatic endocrine cells. Using the recently developed human beta cell line EndoC-beta H2, we show that RFX6 regulates insulin gene transcription, insulin content, and secretion. Knockdown of RFX6 causes downregulation of Ca2+-channel genes resulting in the reduction in L-type Ca2+-channel activity that leads to suppression of depolarization-evoked insulin exocytosis. We also describe a previously unreported homozygous missense RFX6 mutation (p.V506G) that is associated with neonatal diabetes, which lacks the capacity to activate the insulin promoter and to increase Ca2+-channel expression. Our data therefore provide insights for understanding certain forms of neonatal diabetes.