Cavβ3 Regulates Ca2+ Signaling and Insulin Expression in Pancreatic β-Cells in a Cell-Autonomous Manner

Abstract

Voltage-gated Ca2+ (Cav) channels consist of a pore-forming Cava1 subunit and auxiliary Cava2-d and Cavb subunits. In fibroblasts, Cavb3, independent of its role as a Cav subunit, reduces the sensitivity to low concentrations of inositol-1,4,5-trisphosphate (IP3). Similarly, Cavb3 could affect cytosolic calcium concentration ([Ca2+]) in pancreatic b-cells. In this study, we deleted the Cavb3-encoding gene Cacnb3 in insulin-secreting rat b-(Ins-1) cells using CRISPR/Cas9. These cells were used as controls to investigate the role of Cavb3 on Ca2+ signaling, glucoseinduced insulin secretion (GIIS), Cav channel activity, and gene expression in wild-type cells in which Cavb3 and the IP3 receptor were coimmunoprecipitated. Transcript and protein profiling revealed significantly increased levels of insulin transcription factor Mafa, CaMKIV, proprotein convertase subtilisin/kexin type-1, and nitric oxide synthase-1 in Cavb3-knockout cells. In the absence of Cavb3, Cav currents were not altered. In contrast, CREB activity, the amount of MAFA protein and GIIS, the extent of IP3-dependent Ca2+ release and the frequency of Ca2+ oscillations were increased. These processes were decreased by the Cavb3 protein in a concentration-dependent manner. Our study shows that Cavb3 interacts with the IP3 receptor in isolated b-cells, controls IP3-dependent Ca2+-signaling independently of Cav channel functions, and thereby regulates insulin expression and its glucose-dependent release in a cell-autonomous manner.