Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import into the nucleus

  1. Akira Takano
  2. Takuya Kajita
  3. Makoto Mochizuki
  4. Toshiya Endo
  5. Tohru Yoshihisa  Is a corresponding author
  1. Nagoya University, Japan
  2. University of Hyogo, Japan

Abstract

tRNAs are unique among various RNAs in that they shuttle between the nucleus and the cytoplasm, and their localization is regulated by nutrient conditions. Although nuclear export of tRNAs has been well documented, the import machinery is poorly understood. Here, we identified Ssa2p, a major cytoplasmic Hsp70 in Saccharomyces cerevisiae, as a tRNA-binding protein whose deletion compromises nuclear accumulation of tRNAs upon nutrient starvation. Ssa2p recognizes several structural features of tRNAs through its nucleotide-binding domain, but prefers loosely-folded tRNAs, suggesting that Ssa2p has a chaperone-like activity for RNAs. Ssa2p also binds Nup116, one of the yeast nucleoporins. Sis1p and Ydj1p, cytoplasmic co-chaperones for Ssa proteins, were also found to contribute to the tRNA import. These results unveil a novel function of the Ssa2p system as a tRNA carrier for nuclear import by a novel mode of substrate recognition. Such Ssa2p-mediated tRNA import likely contributes to quality control of cytosolic tRNAs.

Article and author information

Author details

  1. Akira Takano

    Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
    Competing interests
    The authors declare that no competing interests exist.
  2. Takuya Kajita

    Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
    Competing interests
    The authors declare that no competing interests exist.
  3. Makoto Mochizuki

    Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
    Competing interests
    The authors declare that no competing interests exist.
  4. Toshiya Endo

    Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan
    Competing interests
    The authors declare that no competing interests exist.
  5. Tohru Yoshihisa

    Graduate School of Life Science, University of Hyogo, Kobe, Japan
    For correspondence
    tyoshihi@sci.u-hyogo.ac.jp
    Competing interests
    The authors declare that no competing interests exist.

Copyright

© 2015, Takano 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

  • 2,239
    views
  • 536
    downloads
  • 21
    citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.

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. Akira Takano
  2. Takuya Kajita
  3. Makoto Mochizuki
  4. Toshiya Endo
  5. Tohru Yoshihisa
(2015)
Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import into the nucleus
eLife 4:e04659.
https://doi.org/10.7554/eLife.04659

Share this article

https://doi.org/10.7554/eLife.04659

Further reading

    1. Cell Biology
    2. Immunology and Inflammation
    Alejandro Rosell, Agata Adelajda Krygowska ... Esther Castellano Sanchez
    Research Article

    Macrophages are crucial in the body’s inflammatory response, with tightly regulated functions for optimal immune system performance. Our study reveals that the RAS–p110α signalling pathway, known for its involvement in various biological processes and tumourigenesis, regulates two vital aspects of the inflammatory response in macrophages: the initial monocyte movement and later-stage lysosomal function. Disrupting this pathway, either in a mouse model or through drug intervention, hampers the inflammatory response, leading to delayed resolution and the development of more severe acute inflammatory reactions in live models. This discovery uncovers a previously unknown role of the p110α isoform in immune regulation within macrophages, offering insight into the complex mechanisms governing their function during inflammation and opening new avenues for modulating inflammatory responses.

    1. Cell Biology
    Affiong Ika Oqua, Kin Chao ... Alejandra Tomas
    Research Article

    G protein-coupled receptors (GPCRs) are integral membrane proteins which closely interact with their plasma membrane lipid microenvironment. Cholesterol is a lipid enriched at the plasma membrane with pivotal roles in the control of membrane fluidity and maintenance of membrane microarchitecture, directly impacting on GPCR stability, dynamics, and function. Cholesterol extraction from pancreatic beta cells has previously been shown to disrupt the internalisation, clustering, and cAMP responses of the glucagon-like peptide-1 receptor (GLP-1R), a class B1 GPCR with key roles in the control of blood glucose levels via the potentiation of insulin secretion in beta cells and weight reduction via the modulation of brain appetite control centres. Here, we unveil the detrimental effect of a high cholesterol diet on GLP-1R-dependent glucoregulation in vivo, and the improvement in GLP-1R function that a reduction in cholesterol synthesis using simvastatin exerts in pancreatic islets. We next identify and map sites of cholesterol high occupancy and residence time on active vs inactive GLP-1Rs using coarse-grained molecular dynamics (cgMD) simulations, followed by a screen of key residues selected from these sites and detailed analyses of the effects of mutating one of these, Val229, to alanine on GLP-1R-cholesterol interactions, plasma membrane behaviours, clustering, trafficking and signalling in INS-1 832/3 rat pancreatic beta cells and primary mouse islets, unveiling an improved insulin secretion profile for the V229A mutant receptor. This study (1) highlights the role of cholesterol in regulating GLP-1R responses in vivo; (2) provides a detailed map of GLP-1R - cholesterol binding sites in model membranes; (3) validates their functional relevance in beta cells; and (4) highlights their potential as locations for the rational design of novel allosteric modulators with the capacity to fine-tune GLP-1R responses.