1. Cell Biology
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Endoplasmic reticulum tubules limit the size of misfolded protein condensates

  1. Smriti Parashar
  2. Ravi Chidambaram
  3. Shuliang Chen
  4. Christina R Liem
  5. Eric Griffis
  6. Gerard G Lambert
  7. Nathan C Shaner
  8. Matthew Wortham
  9. Jesse C Hay
  10. Susan Ferro-Novick  Is a corresponding author
  1. University of California, San Diego, United States
  2. University of Montana, United States
Research Article
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Cite this article as: eLife 2021;10:e71642 doi: 10.7554/eLife.71642

Abstract

The endoplasmic reticulum (ER) is composed of sheets and tubules. Here we report that the COPII coat subunit, SEC24C, works with the long form of the tubular ER-phagy receptor, RTN3, to target dominant-interfering mutant proinsulin Akita puncta to lysosomes. When the delivery of Akita puncta to lysosomes was disrupted, large puncta accumulated in the ER. Unexpectedly, photobleach analysis indicated that Akita puncta behaved as condensates and not aggregates, as previously suggested. Akita puncta enlarged when either RTN3 or SEC24C were depleted, or when ER sheets were proliferated by either knocking out Lunapark or overexpressing CLIMP63. Other ER-phagy substrates that are segregated into tubules behaved like Akita, while a substrate (type I procollagen) that is degraded by the ER-phagy sheets receptor, FAM134B, did not. Conversely, when ER tubules were augmented in Lunapark knock-out cells by overexpressing reticulons, ER-phagy increased and the number of large Akita puncta were reduced. Our findings imply that segregating cargos into tubules has two beneficial roles. First, it localizes mutant misfolded proteins, the receptor and SEC24C to the same ER domain. Second, physically restraining condensates within tubules, before they undergo ER-phagy, prevents them from enlarging and impacting cell health.

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All data generated or analyzed during this study are included in the manuscript and supporting files.

Article and author information

Author details

  1. Smriti Parashar

    Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Ravi Chidambaram

    Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Shuliang Chen

    Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Christina R Liem

    Division of Biological Sciences, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Eric Griffis

    Nikon Imaging Center, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Gerard G Lambert

    Department of Neurosciences, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. Nathan C Shaner

    Department of Neurosciences, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  8. Matthew Wortham

    Department of Neurosciences, University of California, San Diego, San Diego, United States
    Competing interests
    The authors declare that no competing interests exist.
  9. Jesse C Hay

    Division of Biological Sciences and Center for Structural & Functional Neuroscience, University of Montana, Missoula, United States
    Competing interests
    The authors declare that no competing interests exist.
  10. Susan Ferro-Novick

    Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, United States
    For correspondence
    sfnovick@ucsd.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8714-7352

Funding

National Institute of General Medical Sciences (5R35GM131681)

  • Susan Ferro-Novick

National Science Foundation (1707352)

  • Nathan C Shaner

The Pathways in Biological Science Graduate Training Program

  • Christina R Liem

National Institute of Neurological Disorders and Stroke (RO1NS117440)

  • Susan Ferro-Novick

National Institute of Diabetes and Digestive and Kidney Diseases (R01DK068471)

  • Matthew Wortham

National Institute of General Medical Sciences (2R15GM106323)

  • Jesse C Hay

National Institute of General Medical Sciences (R01GM109984)

  • Nathan C Shaner

National Institute of General Medical Sciences (R01GM121944)

  • Nathan C Shaner

National Institute of Neurological Disorders and Stroke (U01NS099709)

  • Nathan C Shaner

National Eye Institute (R21EY030716)

  • Nathan C Shaner

National Institute of Neurological Disorders and Stroke (U01NS113294)

  • Nathan C Shaner

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

Reviewing Editor

  1. Randy Schekman, Howard Hughes Medical Institute, University of California, Berkeley, United States

Publication history

  1. Received: June 25, 2021
  2. Accepted: August 31, 2021
  3. Accepted Manuscript published: September 1, 2021 (version 1)

Copyright

© 2021, Parashar 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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