Neuronostatin acts via GPR107 to increase cAMP-independent PKA phosphorylation and proglucagon mRNA accumulation in pancreatic α-cells

Abstract

Neuronostatin (NST) is a recently described peptide that is produced from the somatostatin preprohormone in pancreatic δ-cells. NST has been shown to increase glucagon secretion from primary rat pancreatic islets in low-glucose conditions. Here, we demonstrate that NST increases proglucagon message in α-cells and identify a potential mechanism for NST's cellular activities, including the phosphorylation of PKA following activation of the G protein-coupled receptor, GPR107. GPR107 is abundantly expressed in the pancreas, particularly, in rodent and human α-cells. Compromise of GPR107 in pancreatic α-cells results in failure of NST to increase PKA phosphorylation and proglucagon mRNA levels. We also demonstrate colocalization of GPR107 and NST on both mouse and human pancreatic α-cells. Taken together with our group's observation that NST infusion in conscious rats impairs glucose clearance in response to a glucose challenge and that plasma levels of the peptide are elevated in the fasted compared with the fed or fasted-refed state, these studies support the hypothesis that endogenous NST regulates islet cell function by interacting with GPR107 and initiating signaling in glucagon-producing α-cells.