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

Flora Brozzi1, Sophie Lajus, Frederique Diraison

  • 1Centre for Research in Biomedicine, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom.

Molecular Biology of the Cell
|September 21, 2012
PubMed

Insights

Myosin- and Rab-interacting protein (MyRIP) does not directly link to myosin Va in pancreatic beta cells. MyRIP facilitates hormone secretion by interacting with myosin Va only when cAMP levels are elevated.

Area of Science:

  • Cell Biology
  • Endocrinology
  • Molecular Biology

Background:

  • Myosin- and Rab-interacting protein (MyRIP) is involved in hormone secretion.
  • Its precise role in secretory granule (SG) transport and secretion, particularly its interaction with myosin Va (MyoVa), remains unclear.
  • Pancreatic beta cells utilize the brain isoform of MyoVa (BR-MyoVa) for SG transport.

Purpose of the Study:

  • To investigate the role of MyRIP in BR-MyoVa-dependent SG transport and secretion in pancreatic beta cells.
  • To elucidate the mechanism by which MyRIP influences hormone secretion, especially in response to glucose and incretin hormones.

Main Methods:

  • In vitro pull-down assays
  • Coimmunoprecipitation studies
  • Colocalization studies
  • Small interfering RNA (siRNA) knockdown of MyRIP
  • Analysis of rabphilin-3A (Rph-3A) phosphorylation using mutants.

Main Results:

  • MyRIP does not interact with BR-MyoVa in basal conditions of glucose-stimulated pancreatic beta cells.
  • Incretin hormones increase cAMP, leading to MyRIP phosphorylation and its subsequent interaction with BR-MyoVa.
  • MyRIP knockdown inhibited Rph-3A phosphorylation and reduced cAMP-mediated hormone secretion.
  • Rph-3A phosphorylation is crucial for enhanced hormone release upon PKA activation.

Conclusions:

  • MyRIP does not directly link BR-MyoVa to SGs in basal conditions.
  • MyRIP forms a functional complex with BR-MyoVa on SGs only when cAMP levels are elevated.
  • MyRIP facilitates hormone secretion by promoting the phosphorylation of SG-associated proteins under high cAMP conditions.

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