A functional link between the co-translational protein translocation pathway and the UPR

  1. Rachel Plumb
  2. Zai-Rong Zhang
  3. Suhila Appathurai
  4. Malaiyalam Mariappan  Is a corresponding author
  1. Yale School of Medicine, United States

Abstract

Upon endoplasmic reticulum (ER) stress, the transmembrane endoribonuclease Ire1α performs mRNA cleavage reactions to increase the ER folding capacity. It is unclear how the low abundant Ire1α efficiently finds and cleaves the majority of mRNAs at the ER membrane. Here, we reveal that Ire1α forms a complex with the Sec61 translocon to cleave its mRNA substrates. We show that Ire1α's key substrate, XBP1u mRNA, is recruited to the Ire1α-Sec61 translocon complex through its nascent chain, which contains a pseudo-transmembrane domain to utilize the signal recognition particle (SRP)-mediated pathway. Depletion of SRP, the SRP receptor or the Sec61 translocon in cells leads to reduced Ire1α-mediated splicing of XBP1u mRNA. Furthermore, mutations in Ire1α that disrupt the Ire1α-Sec61 complex causes reduced Ire1α-mediated cleavage of ER-targeted mRNAs. Thus, our data suggest that the UPR is coupled with the co-translational protein translocation pathway to maintain protein homeostasis in the ER during stress conditions.

Article and author information

Author details

  1. Rachel Plumb

    Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Zai-Rong Zhang

    Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Suhila Appathurai

    Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Malaiyalam Mariappan

    Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, West Haven, United States
    For correspondence
    malaiyalam.mariappan@yale.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Reid Gilmore, University of Massachusetts Medical School, United States

Publication history

  1. Received: March 11, 2015
  2. Accepted: May 19, 2015
  3. Accepted Manuscript published: May 20, 2015 (version 1)
  4. Version of Record published: June 5, 2015 (version 2)

Copyright

© 2015, Plumb 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.

Metrics

  • 4,478
    Page views
  • 1,213
    Downloads
  • 57
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, Scopus, PubMed Central.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Rachel Plumb
  2. Zai-Rong Zhang
  3. Suhila Appathurai
  4. Malaiyalam Mariappan
(2015)
A functional link between the co-translational protein translocation pathway and the UPR
eLife 4:e07426.
https://doi.org/10.7554/eLife.07426
  1. Further reading

Further reading

    1. Biochemistry and Chemical Biology
    2. Cell Biology
    Hidehiko Okuma, Jeffrey M Hord ... Kevin P Campbell
    Research Advance

    Dystroglycan (DG) requires extensive post-translational processing and O-glycosylation to function as a receptor for extracellular matrix (ECM) proteins containing laminin-G-like (LG) domains. Matriglycan is an elongated polysaccharide of alternating xylose (Xyl) and glucuronic acid (GlcA) that binds with high-affinity to ECM proteins with LG-domains and is uniquely synthesized on α-dystroglycan (α-DG) by like-acetylglucosaminyltransferase-1 (LARGE1). Defects in the post-translational processing or O-glycosylation of α-DG that result in a shorter form of matriglycan reduce the size of α-DG and decrease laminin binding, leading to various forms of muscular dystrophy. Previously, we demonstrated that Protein O-Mannose Kinase (POMK) is required for LARGE1 to generate full-length matriglycan on α-DG (~150-250 kDa) (Walimbe et al., 2020). Here, we show that LARGE1 can only synthesize a short, non-elongated form of matriglycan in mouse skeletal muscle that lacks the DG N-terminus (α-DGN), resulting in a ~100-125 kDa α-DG. This smaller form of α-DG binds laminin and maintains specific force but does not prevent muscle pathophysiology, including reduced force production after eccentric contractions or abnormalities in the neuromuscular junctions. Collectively, our study demonstrates that α-DGN, like POMK, is required for LARGE1 to extend matriglycan to its full mature length on α-DG and thus prevent muscle pathophysiology.

    1. Biochemistry and Chemical Biology
    2. Microbiology and Infectious Disease
    Abhinay Ramaprasad, Paul-Christian Burda ... Michael J Blackman
    Research Article Updated

    The malaria parasite Plasmodium falciparum synthesizes significant amounts of phospholipids to meet the demands of replication within red blood cells. De novo phosphatidylcholine (PC) biosynthesis via the Kennedy pathway is essential, requiring choline that is primarily sourced from host serum lysophosphatidylcholine (lysoPC). LysoPC also acts as an environmental sensor to regulate parasite sexual differentiation. Despite these critical roles for host lysoPC, the enzyme(s) involved in its breakdown to free choline for PC synthesis are unknown. Here, we show that a parasite glycerophosphodiesterase (PfGDPD) is indispensable for blood stage parasite proliferation. Exogenous choline rescues growth of PfGDPD-null parasites, directly linking PfGDPD function to choline incorporation. Genetic ablation of PfGDPD reduces choline uptake from lysoPC, resulting in depletion of several PC species in the parasite, whilst purified PfGDPD releases choline from glycerophosphocholine in vitro. Our results identify PfGDPD as a choline-releasing glycerophosphodiesterase that mediates a critical step in PC biosynthesis and parasite survival.