Endoplasmic reticulum tubules limit the size of misfolded protein condensates
- University of California, San Diego, United States
- University of Montana, United States
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.
Data availability
All data generated or analyzed during this study are included in the manuscript and supporting files.
Article and author information
Author details
Susan Ferro-Novick
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.
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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Endoplasmic reticulum tubules limit the size of misfolded protein condensates
eLife 10:e71642.
https://doi.org/10.7554/eLife.71642
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