Cavβ3 regulates Ca2+-signalling and insulin expression in pancreatic β-cells in a cell-autonomous manner

Abstract

<p>Voltage-gated Ca<sup>2+</sup> (Cav) channels consist of a pore-forming Cavα1 subunit and auxiliary Cavα2-δ and Cavβ subunits. In fibroblasts, Cavβ3, independent of its role as a Cav subunit, reduces the sensitivity to low concentrations of inositol-1,4,5-trisphosphate (IP3). Similarly, Cavβ3 could affect cytosolic [Ca<sup>2+</sup>] in pancreatic β-cells. Here, we deleted the Cavβ3-encoding gene <i>Cacnb3</i> in insulin-secreting rat β-(Ins-1) cells using CRISPR/Cas9. These cells were used as controls to investigate the role of Cavβ3 on Ca<sup>2+</sup>-signalling, glucose-induced insulin secretion (GIIS), Cav-channel activity and gene expression in wild-type cells in which Cavβ3 and the IP3-receptor were co-immunoprecipitated. Transcript and protein profiling revealed significantly increased levels of insulin transcription factor Mafa, CaMKIV, neuroendocrine convertase1 (Pcsk1) and nitric oxide synthase-1 (NOS-1) in Cavβ3-KO cells. In the absence of Cavβ3, Cav-currents were not altered. In contrast, CREB activity, the amount of MAFA protein and GIIS, the extent of IP3-dependent Ca<sup>2+</sup> release and the frequency of Ca<sup>2+</sup>-oscillations were increased. These processes were decreased by the Cavβ3 protein in a concentration-dependent manner. Our study shows that Cavβ3 interacts with the IP3-receptor in isolated β-cells, controls IP3-dependent Ca<sup>2+</sup>-signalling independently of Cav channel functions, and thereby regulates insulin expression and its glucose-dependent release in a cell-autonomous manner.</p>