Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis

Abstract

Regulated exocytosis establishes a narrow fusion pore as initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of polypeptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in diabetes and neurodegenerative disease. Here we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation restricts and slows fusion pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- (Rapgef4-/-) mice. Consistently, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 receptor agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.

Data availability

Source data file has been provided for Fig 7. All raw data are available on the Dryad Digital Repository (https://doi.org/10.5061/dryad.6b604g8).

The following data sets were generated

Article and author information

Author details

  1. Alenka Guček

    Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4453-1498
  2. Nikhil R Gandasi

    Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
    Competing interests
    The authors declare that no competing interests exist.
  3. Muhmmad Omar-Hmeadi

    Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8893-7348
  4. Marit Bakke

    Department of Biomedicine, University of Bergen, Bergen, Norway
    Competing interests
    The authors declare that no competing interests exist.
  5. Stein O Døskeland

    Department of Biomedicine, University of Bergen, Bergen, Norway
    Competing interests
    The authors declare that no competing interests exist.
  6. Anders Tengholm

    Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4508-0836
  7. Sebastian Barg

    Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
    For correspondence
    sebastian.barg@mcb.uu.se
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4661-5724

Funding

Swedish Research Council (2014-02575)

  • Anders Tengholm
  • Sebastian Barg

Norwegian Research Council

  • Marit Bakke

Helse-Bergen

  • Marit Bakke

Olga Jönssons stipend

  • Alenka Guček

P O Zetterlingsstiftelse

  • Alenka Guček

Swedish Research Council (2017-00956)

  • Anders Tengholm
  • Sebastian Barg

Swedich Research Council (2018-02871)

  • Anders Tengholm
  • Sebastian Barg

European Foundation for the Study of Diabetes

  • Anders Tengholm
  • Sebastian Barg

Diabetes Wellness Network Sweden

  • Anders Tengholm
  • Sebastian Barg

Swedish Diabetes Society

  • Anders Tengholm
  • Sebastian Barg

Swedish Society for Medical Research

  • Nikhil R Gandasi

Hjärnfonden

  • Sebastian Barg

NovoNordisk

  • Nikhil R Gandasi
  • Anders Tengholm
  • Sebastian Barg

Family Ernfors Foundation

  • Alenka Guček
  • Anders Tengholm
  • Sebastian Barg

European Foundation for the Study of Diabetes

  • Nikhil R Gandasi
  • Anders Tengholm
  • Sebastian Barg

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Axel T Brunger, Stanford University, United States

Ethics

Animal experimentation: This study was performed in strict accordance with European and Swedish legislation, fundamental ethical principles and approved by the Regional Ethics Board Uppsala (license number 31, 1-32).

Version history

  1. Received: September 5, 2018
  2. Accepted: April 28, 2019
  3. Accepted Manuscript published: May 17, 2019 (version 1)
  4. Accepted Manuscript updated: May 20, 2019 (version 2)
  5. Version of Record published: June 10, 2019 (version 3)

Copyright

© 2019, Guček et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Alenka Guček
  2. Nikhil R Gandasi
  3. Muhmmad Omar-Hmeadi
  4. Marit Bakke
  5. Stein O Døskeland
  6. Anders Tengholm
  7. Sebastian Barg
(2019)
Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis
eLife 8:e41711.
https://doi.org/10.7554/eLife.41711

Share this article

https://doi.org/10.7554/eLife.41711

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