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.

Citation

Brozzi, F., Lajus, S., Diraison, F., Rajatileka, S., Hayward, K., Regazzi, R., …Varadi, A. (2012). MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway. Molecular Biology of the Cell, 23(22), 4444-4455. https://doi.org/10.1091/mbc.E12-05-0369

• 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