MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway

Flora Brozzi, Sophie Lajus, Frederique Diraison, Shavanthi Rajatileka, Katy Hayward, Romano Regazzi, Elek Molnar, Aniko Varadi*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)4444-4455
Number of pages12
JournalMolecular Biology of the Cell
Volume23
Issue number22
Early online date19 Sep 2012
DOIs
Publication statusPublished - 15 Nov 2012

Keywords

  • PROTEIN-KINASE-A
  • PANCREATIC BETA-CELL
  • CHANNEL-INDEPENDENT PATHWAY
  • INSULIN-SECRETION
  • MYOSIN VA
  • B-CELLS
  • RABPHILIN PHOSPHORYLATION
  • PLASMA-MEMBRANE
  • BINDING-PROTEIN
  • EXOCYST COMPLEX

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