A Novel GLP1 Receptor Interacting Protein ATP6ap2 Regulates Insulin Secretion in Pancreatic Beta Cells

J Biol Chem. 2015 Oct 9;290(41):25045-61. doi: 10.1074/jbc.M115.648592. Epub 2015 Aug 13.


GLP1 activates its receptor, GLP1R, to enhance insulin secretion. The activation and transduction of GLP1R requires complex interactions with a host of accessory proteins, most of which remain largely unknown. In this study, we used membrane-based split ubiquitin yeast two-hybrid assays to identify novel GLP1R interactors in both mouse and human islets. Among these, ATP6ap2 (ATPase H(+)-transporting lysosomal accessory protein 2) was identified in both mouse and human islet screens. ATP6ap2 was shown to be abundant in islets including both alpha and beta cells. When GLP1R and ATP6ap2 were co-expressed in beta cells, GLP1R was shown to directly interact with ATP6ap2, as assessed by co-immunoprecipitation. In INS-1 cells, overexpression of ATP6ap2 did not affect insulin secretion; however, siRNA knockdown decreased both glucose-stimulated and GLP1-induced insulin secretion. Decreases in GLP1-induced insulin secretion were accompanied by attenuated GLP1 stimulated cAMP accumulation. Because ATP6ap2 is a subunit required for V-ATPase assembly of insulin granules, it has been reported to be involved in granule acidification. In accordance with this, we observed impaired insulin granule acidification upon ATP6ap2 knockdown but paradoxically increased proinsulin secretion. Importantly, as a GLP1R interactor, ATP6ap2 was required for GLP1-induced Ca(2+) influx, in part explaining decreased insulin secretion in ATP6ap2 knockdown cells. Taken together, our findings identify a group of proteins that interact with the GLP1R. We further show that one interactor, ATP6ap2, plays a novel dual role in beta cells, modulating both GLP1R signaling and insulin processing to affect insulin secretion.

Keywords: cyclic AMP (cAMP); insulin secretion; receptor; receptor-interacting protein (RIP); yeast two-hybrid.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • CHO Cells
  • Calcium / metabolism
  • Cricetinae
  • Cricetulus
  • Cyclic AMP / metabolism
  • Gene Knockdown Techniques
  • Glucagon-Like Peptide 1 / pharmacology
  • Glucagon-Like Peptide-1 Receptor / metabolism*
  • Humans
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / drug effects
  • Insulin-Secreting Cells / metabolism*
  • Male
  • Mice
  • Protein Binding
  • Proton-Translocating ATPases / deficiency
  • Proton-Translocating ATPases / genetics
  • Proton-Translocating ATPases / metabolism*
  • Receptors, Cell Surface / deficiency
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Vacuolar Proton-Translocating ATPases / deficiency
  • Vacuolar Proton-Translocating ATPases / genetics
  • Vacuolar Proton-Translocating ATPases / metabolism*


  • ATP6AP2 protein, human
  • ATP6AP2 protein, mouse
  • Glucagon-Like Peptide-1 Receptor
  • Insulin
  • Receptors, Cell Surface
  • Glucagon-Like Peptide 1
  • Cyclic AMP
  • Vacuolar Proton-Translocating ATPases
  • Proton-Translocating ATPases
  • Calcium