title: MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway.
abstract: Myosin- and Rab-interacting protein (MyRIP), which belongs to the protein kinase A (PKA)-anchoring family, is implicated in hormone secretion. However, its mechanism of action is not fully elucidated. Here we investigate the role of MyRIP in myosin Va (MyoVa)-dependent secretory granule (SG) transport and secretion in pancreatic beta cells. These cells solely express the brain isoform of MyoVa (BR-MyoVa), which is a key motor protein in SG transport. In vitro pull-down, coimmunoprecipitation, and colocalization studies revealed that MyRIP does not interact with BR-MyoVa in glucose-stimulated pancreatic beta cells, suggesting that, contrary to previous notions, MyRIP does not link this motor protein to SGs. Glucose-stimulated insulin secretion is augmented by incretin hormones, which increase cAMP levels and leads to MyRIP phosphorylation, its interaction with BR-MyoVa, and phosphorylation of the BR-MyoVa receptor rabphilin-3A (Rph-3A). Rph-3A phosphorylation on Ser-234 was inhibited by small interfering RNA knockdown of MyRIP, which also reduced cAMP-mediated hormone secretion. Demonstrating the importance of this phosphorylation, nonphosphorylatable and phosphomimic Rph-3A mutants significantly altered hormone release when PKA was activated. These data suggest that MyRIP only forms a functional protein complex with BR-MyoVa on SGs when cAMP is elevated and under this condition facilitates phosphorylation of SG-associated proteins, which in turn can enhance secretion.
authors.affiliation: Centre for Research in Biomedicine, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom.
authors.forename: Flora
authors.initials: F
authors.lastname: Brozzi
authors.forename: Sophie
authors.initials: S
authors.lastname: Lajus
authors.forename: Frederique
authors.initials: F
authors.lastname: Diraison
authors.forename: Shavanthi
authors.initials: S
authors.lastname: Rajatileka
authors.forename: Katy
authors.initials: K
authors.lastname: Hayward
authors.forename: Romano
authors.initials: R
authors.lastname: Regazzi
authors.forename: Elek
authors.initials: E
authors.lastname: Molnár
authors.forename: Anikó
authors.initials: A
authors.lastname: Váradi
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024701:Myosin Type V / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: C521067:MYRIP protein, mouse; C513082:Myo5a protein, mouse; D033921:Vesicular Transport Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D005947:Glucose