Post-translational Regulation of the Type III Inositol 1,4,5-Trisphosphate Receptor by miRNA-506

The type III isoform of the inositol 1,4,5-trisphosphate receptor (InsP 3 R3) is apically localized and triggers Ca 2+ waves and secretion in a number of polarized epithelia. However, nothing is known about epigenetic regulation of this InsP3R isoform. We investigated miRNA regulation of InsP 3 R3 in primary bile duct epithelia (cholangiocytes) and in the H69 cholangiocyte cell line, because the role of InsP 3 R3 in cholangiocyte Ca 2+ signaling and secretion is well established and because loss of InsP 3 R3 from cholangiocytes is responsible for the impairment in bile secretion that occurs in a number of liver diseases. Analysis of the 3′-UTR of human InsP 3 R3 mRNA revealed two highly conserved binding sites for miR-506. Transfection of miR-506 mimics into cell lines expressing InsP 3 R3–3′UTR-luciferase led to decreased reporter activity, whereas co-transfection with miR-506 inhibitors led to enhanced activity. Reporter activity was abrogated in isolated mutant proximal or distal miR-506 constructs in miR-506-transfected HEK293 cells. InsP 3 R3 protein levels were decreased by miR-506 mimics and increased by inhibitors, and InsP 3 R3 expression was markedly decreased in H69 cells stably transfected with miR-506 relative to control cells. miR-506-H69 cells exhibited a fibrotic signature. In situ hybridization revealed elevated miR-506 expression in vivo in human-diseased cholangiocytes. Histamine-induced, InsP 3 -mediated Ca 2+ signals were decreased by 50% in stable miR-506 cells compared with controls. Finally, InsP 3 R3-mediated fluid secretion was significantly decreased in isolated bile duct units transfected with miR-506, relative to control IBDU. Together, these data identify miR-506 as a regulator of InsP 3 R3 expression and InsP 3 R3-mediated Ca 2+ signaling and secretion.Inositol 1,4,5-trisphosphate receptor (InsP 3 R3) is critical to secretion in a number of epithelia and its expression is lost in secretory disorders. Results miR-506 down-regulates InsP 3 R3 expression and impairs Ca 2+ signaling and secretion. Conclusion Post-translational regulation of InsP 3 R3 expression by miR-506 might contribute to disease phenotype. Significance Restoring InsP 3 R3 expression by use of anti-miR-506 therapy might be beneficial in a variety of secretory disorders.