Limitation of individual folding resources in the ER leads to outcomes distinct from the unfolded protein response

Journal of Cell Science (Impact Factor: 5.43). 08/2012; 125(20). DOI: 10.1242/jcs.108928
Source: PubMed


ER stress leads to upregulation of multiple folding and quality control components, known as the unfolded protein response (UPR). Glucose Regulated Proteins 78 and 94 (GRP78/BiP and GRP94) are often upregulated coordinately as part of this homeostatic response. Given that ER chaperones have distinct sets of clients, we asked how cells respond to ablation of individual chaperones. The cellular responses to silencing BiP, GRP94, HSP47, PDIA6 and OS-9, were distinct. When BiP was silenced, a widespread UPR was observed, but when GRP94 was either inhibited or depleted by RNAi, the expression of only some genes, notably BiP and protein disulfide isomerase A6 (PDIA6) was induced. Silencing of HSP47 or OS-9 did not lead to any compensatory induction of other genes. The selective response to GRP94 depletion was distinct from a typical ER stress response, both because other UPR target genes were not affected and because the canonical UPR signaling branches were not activated. The response to silencing of GRP94 did not preclude further UPR induction when chemical stress was imposed. Importantly, re-expression of wild-type GRP94 in the silenced cells prevented the up-regulation of BiP and PDIA6, while re-expression of an ATPase-deficient GRP94 mutant did not, indicating that cells monitor the state of activity of GRP94. These findings suggest that cells are able to distinguish among folding resources and generate distinct responses.

Download full-text


Available from: Davide Eletto
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The endoplasmic reticulum is a major compartment of protein biogenesis in the cell, dedicated to production of secretory, membrane and organelle proteins. The secretome has distinct structural and post-translational characteristics, since folding in the ER occurs in an environment that is distinct in terms of its ionic composition, dynamics and requirements for quality control. The folding machinery in the ER therefore includes chaperones and folding enzymes that introduce, monitor and react to disulfide bonds, glycans, and fluctuations of luminal calcium. We describe the major chaperone networks in the lumen and discuss how they have distinct modes of operation that enable cells to accomplish highly efficient production of the secretome. This article is part of a Special Issue entitled:Functional and structural diversity of endoplasmic reticulum.
    Preview · Article · Mar 2013 · Biochimica et Biophysica Acta
  • [Show abstract] [Hide abstract]
    ABSTRACT: AB5 toxins are key virulence factors found in a range of pathogenic bacteria. AB5 toxins consist of two components: a pentameric B subunit that targets eukaryotic cells by binding to glycans located on the cell surface and a catalytic A subunit that disrupts host cellular function following internalization. To date, the A subunits of AB5 toxins either have RNA-N-glycosidase, ADP-ribosyltransferase or serine protease activity. However, it has been suggested that a novel AB5 toxin produced by clinical isolates of Escherichia coli and Citrobacter freundii has an A subunit with metalloproteinase activity. Here, the expression, purification and crystallization of this novel AB5 toxin from E. coli (EcxAB) and the collection of X-ray data to 1.9 Å resolution are reported.
    No preview · Article · Aug 2013 · Acta Crystallographica Section F Structural Biology and Crystallization Communications
  • [Show abstract] [Hide abstract]
    ABSTRACT: The response to endoplasmic reticulum (ER) stress relies on activation of unfolded protein response (UPR) sensors, and the outcome of the UPR depends on the duration and strength of signal. Here, we demonstrate a mechanism that attenuates the activity of the UPR sensor inositol-requiring enzyme 1α (IRE1α). A resident ER protein disulfide isomerase, PDIA6, limits the duration of IRE1α activity by direct binding to cysteine 148 in the lumenal domain of the sensor, which is oxidized when IRE1 is activated. PDIA6-deficient cells hyperrespond to ER stress with sustained autophosphorylation of IRE1α and splicing of XBP1 mRNA, resulting in exaggerated upregulation of UPR target genes and increased apoptosis. In vivo, PDIA6-deficient C. elegans exhibits constitutive UPR and fails to complete larval development, a program that normally requires the UPR. Thus, PDIA6 activity provides a mechanism that limits UPR signaling and maintains it within a physiologically appropriate range.
    No preview · Article · Feb 2014 · Molecular cell
Show more