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

Brozzi, F; Lajus, Sophie; Diraison, Frederique; Rajatileka, Shavanthi; Hayward, K; Regazzi, Romano; Molnar, E; Varadi, Aniko

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.

• Journal Article Type: Article
• Publication Date: Sep 19, 2012
• Journal: Molecular Biology of the Cell
• Publisher: American Society for Cell Biology
• Peer Reviewed: Peer Reviewed
• Volume: 23
• Issue: 22
• Pages: 4444-4455
• DOI: https://doi.org/10.1091/mbc.E12-05-0369
• Keywords: myosin- and rab-interacting protein (MyRIP), pancreatic beta cells, secretory granules, cAMP-PKA pathway
• Public URL: https://uwe-repository.worktribe.com/output/943765
• Publisher URL: http://dx.doi.org/10.1091/mbc.E12-05-0369