bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019‒07‒28
twelve papers selected by
Susan Logue
University of Manitoba

  1. J Biol Chem. 2019 Jul 23. pii: jbc.RA119.008857. [Epub ahead of print]
    Claes Z, Jonkhout M, Crespillo-Casado A, Bollen M.
      The aminoguanidine compound robenidine is widely used as an antibiotic for the control of coccidiosis, a protozoal infection in poultry and rabbits. Interestingly, robenidine is structurally similar to guanabenz analogs, which currently undergo clinical trials as cytoprotective agents for the management of neurodegenerative diseases. Here, we show that robenidine and guanabenz to a similar degree protect cells from a tunicamycin-induced unfolded protein response (UPR). Both compounds also reduced the tumor necrosis factor alpha (TNFα)-induced activation of NFκB. The cytoprotective effects of guanabenz (analogs) have previously been explained by their ability to maintain eukaryotic translation initiation factor 2 subunit alpha (eIF2α) phosphorylation by allosterically inhibiting protein phosphatase PP1:PPP1R15A. However, using a novel split-luciferase based protein-protein interaction assay, we demonstrate here that neither robenidine nor guanabenz disrupt the interaction between PPP1R15A and either PP1 or eIF2α in intact cells. Moreover, both drugs also inhibited the UPR in cells that expressed a non-phosphorylatable mutant (Ser51Ala) of eIF2α. Our results identify robenidine as a PP1:PPP1R15A-independent cytoprotective compound that holds potential for the management of protein misfolding-associated diseases.
    Keywords:  bioluminescence; biosensor; cell proliferation; drug action; endoplasmic reticulum stress (ER stress); enzyme inhibitor; eukaryotic initiation factor 2 (eIF2); guanabenz; neurodegenerative disease; protein phosphatase; protein phosphatase 1 (PP1); protein phosphatase 1 regulatory subunit 15A (PPP1R15A); robenidine; unfolded protein response (UPR)
  2. Curr Genet. 2019 Jul 25.
    Chadwick SR, Fazio EN, Etedali-Zadeh P, Genereaux J, Duennwald ML, Lajoie P.
      Progressive impairment of proteostasis and accumulation of toxic misfolded proteins are associated with the cellular aging process. Here, we employed chronologically aged yeast cells to investigate how activation of the unfolded protein response (UPR) upon accumulation of misfolded proteins in the endoplasmic reticulum (ER) affects lifespan. We found that cells lacking a functional UPR display a significantly reduced chronological lifespan, which contrasts previous findings in models of replicative aging. We find exacerbated UPR activation in aged cells, indicating an increase in misfolded protein burden in the ER during the course of aging. We also observed that caloric restriction, which promotes longevity in various model organisms, extends lifespan of UPR-deficient strains. Similarly, aging in pH-buffered media extends lifespan, albeit independently of the UPR. Thus, our data support a role for caloric restriction and reduced acid stress in improving ER homeostasis during aging. Finally, we show that UPR-mediated upregulation of the ER chaperone Kar2 and functional ER-associated degradation (ERAD) are essential for proper aging. Our work documents the central role of secretory protein homeostasis in chronological aging in yeast and highlights that the requirement for a functional UPR can differ between post-mitotic and actively dividing eukaryotic cells.
    Keywords:  Chronological aging; Endoplasmic reticulum stress; Protein misfolding; Unfolded protein response; Yeast
  3. J Biol Chem. 2019 Jul 26. pii: jbc.RA119.008353. [Epub ahead of print]
    Xia Z, Wu S, Wei X, Liao Y, Yi P, Liu Y, Liu J, Liu J.
      Hypoxia occurs in many human solid tumors and activates multiple cellular adaptive response pathways, including the unfolded protein response (UPR) in the endoplasmic reticulum (ER). Wnt/β-catenin signaling plays a critical role in tumorigenesis, and β-catenin has been shown to enhance hypoxia-inducible factor 1α (HIF1α)-activated gene expression, thereby supporting cell survival during hypoxia. However, the molecular interplay between hypoxic ER stress, Wnt/β-catenin signaling, and HIF1α-mediated gene regulation during hypoxia remains incompletely understood. Here, we report that hypoxic ER stress reduces β-catenin stability, which, in turn, enhances the activity of spliced X-box-binding protein 1 (XBP1s), a transcription factor and signal transducer of the UPR, in HIF1α-mediated hypoxic responses. We observed that in the RKO colon cancer cell line, which possesses a Wnt-stimulated β-catenin signaling cascade, increased ER stress during hypoxia is accompanied by a reduction in LDL receptor-related protein 6 (LRP6), and this reduction in LRP6 decreased β-catenin accumulation and impaired Wnt/β-catenin signaling. Of note, β-catenin interacted with both XBP1s and HIF1α, suppressing XBP1s-mediated augmentation of HIF1α target genes expression. Furthermore, Wnt stimulation or β-catenin overexpression blunted XBP1s-mediated cell survival under hypoxia. Together, these results reveal an unanticipated role for the Wnt/β-catenin pathway in hindering hypoxic UPR-mediated responses that increase cell survival. Our findings suggest that the molecular cross-talks between hypoxic ER stress, LRP6/β-catenin signaling, and the HIF1α pathway may represent an unappreciated mechanism that enables some tumor subtypes to survival and grow in hypoxic conditions.
    Keywords:  Wnt signaling; X-box binding protein 1 (XBP1); cancer biology; endoplasmic reticulum stress (ER stress); hypoxia-inducible factor (HIF)
  4. PLoS One. 2019 ;14(7): e0219978
    Yoon SB, Park YH, Choi SA, Yang HJ, Jeong PS, Cha JJ, Lee S, Lee SH, Lee JH, Sim BW, Koo BS, Park SJ, Lee Y, Kim YH, Hong JJ, Kim JS, Jin YB, Huh JW, Lee SR, Song BS, Kim SU.
      X-box binding protein 1 (XBP1) mRNA processing plays a crucial role in the unfolded protein response (UPR), which is activated in response to endoplasmic reticulum (ER) stress. Upon accumulation of the UPR-converted XBP1 mRNA splicing from an unspliced (u) XBP1 (inactive) isoform to the spliced (s) XBP1 (active) isoform, inositol-requiring enzyme 1 α (IRE1α) removes a 26-nucleotide intron from uXBP1 mRNA. Recent studies have reported the assessment of ER stress by examining the ratio of sXBP1 to uXBP1 mRNA (s/uXBP1 ratio) via densitometric analysis of PCR bands relative to increased levels of sXBP1 to uXBP1 using a housekeeping gene for normalization. However, this measurement is visualized by gel electrophoresis, making it very difficult to quantify differences between the two XBP1 bands and complicating data interpretation. Moreover, most commonly used housekeeping genes display an unacceptably high variable expression pattern of the s/uXBP1 ratio under different experimental conditions, such as various phases of development and different cell types, limiting their use as internal controls. For a more quantitative determination of XBP1 splicing activity, we measured the expression levels of total XBP1 (tXBP1: common region of s/uXBP1) and sXBP1 via real-time PCR using specific primer sets. We also designed universal real-time PCR primer sets capable of amplifying a portion of each u/s/tXBP1 mRNA that is highly conserved in eukaryotes, including humans, monkeys, cows, pigs, and mice. Therefore, we provide a more convenient and easily approachable quantitative real-time PCR method that can be used in various research fields to assess ER stress.
  5. EMBO J. 2019 Jul 22. e102743
    Fass D.
      ATF6 is a major signal transducer for cellular reprogramming in response to protein mis-folding in the endoplasmic reticulum. However, the mechanism by which ATF6 senses unfolded proteins and becomes activated is not yet known. In this issue of The EMBO Journal, Oka et al show that ERp18, a single-domain member of the protein disulfide isomerase family, interacts preferentially with ATF6 under stress conditions and regulates ATF6 transport to the Golgi apparatus. Furthermore, ERp18 impacts the ATF6 cleavage product generated in the Golgi, ultimately determining whether or not ATF6 becomes a functional transcription factor and induces the unfolded protein response.
  6. Sci Rep. 2019 Jul 25. 9(1): 10783
    Lenin R, Nagy PG, Jha KA, Gangaraju R.
      Increased O-GlcNAcylation, a well-known post-translational modification of proteins causally linked to various detrimental cellular functions in pathological conditions including diabetic retinopathy (DR). Previously we have shown that endothelial activation induced by inflammation and hyperglycemia results in the endoplasmic reticulum (ER) stress-mediated intercellular junction alterations accompanied by visual deficits in a tie2-TNF-α transgenic mouse model. In this study, we tested the hypothesis that increased ER stress via O-GlcNAcylation of VE-Cadherin likely contribute to endothelial permeability. We show that ER stress leads to GRP78 translocation to the plasma membrane, increased O-GlcNAcylation of proteins, particularly VE-Cadherin resulting in a defective complex partnering leading to the loss of retinal endothelial barrier integrity and increased transendothelial migration of monocytes. We further show an association of GRP78 with the VE-Cadherin under these conditions. Interestingly, cells exposed to ER stress inhibitor, tauroursodeoxycholic acid partially mitigated all these effects. Our findings suggest an essential role for ER stress and O-GlcNAcylation in altering the endothelial barrier function and reveal a potential therapeutic target in the treatment of DR.
  7. Cell. 2019 Jul 25. pii: S0092-8674(19)30741-X. [Epub ahead of print]178(3): 521-535.e23
    Dvela-Levitt M, Kost-Alimova M, Emani M, Kohnert E, Thompson R, Sidhom EH, Rivadeneira A, Sahakian N, Roignot J, Papagregoriou G, Montesinos MS, Clark AR, McKinney D, Gutierrez J, Roth M, Ronco L, Elonga E, Carter TA, Gnirke A, Melanson M, Hartland K, Wieder N, Hsu JC, Deltas C, Hughey R, Bleyer AJ, Kmoch S, Živná M, Barešova V, Kota S, Schlondorff J, Heiman M, Alper SL, Wagner F, Weins A, Golub TR, Lander ES, Greka A.
      Intracellular accumulation of misfolded proteins causes toxic proteinopathies, diseases without targeted therapies. Mucin 1 kidney disease (MKD) results from a frameshift mutation in the MUC1 gene (MUC1-fs). Here, we show that MKD is a toxic proteinopathy. Intracellular MUC1-fs accumulation activated the ATF6 unfolded protein response (UPR) branch. We identified BRD4780, a small molecule that clears MUC1-fs from patient cells, from kidneys of knockin mice and from patient kidney organoids. MUC1-fs is trapped in TMED9 cargo receptor-containing vesicles of the early secretory pathway. BRD4780 binds TMED9, releases MUC1-fs, and re-routes it for lysosomal degradation, an effect phenocopied by TMED9 deletion. Our findings reveal BRD4780 as a promising lead for the treatment of MKD and other toxic proteinopathies. Generally, we elucidate a novel mechanism for the entrapment of misfolded proteins by cargo receptors and a strategy for their release and anterograde trafficking to the lysosome.
    Keywords:  COP vesicles; ER stress; Golgi apparatus; cargo receptor; endoplasmic reticulum; epithelial cells; kidney; organoids; secretory pathway; unfolded protein response
  8. Cell Rep. 2019 Jul 23. pii: S2211-1247(19)30858-7. [Epub ahead of print]28(4): 1050-1062.e6
    Lan J, Rollins JA, Zang X, Wu D, Zou L, Wang Z, Ye C, Wu Z, Kapahi P, Rogers AN, Chen D.
      Reduced mRNA translation delays aging, but the underlying mechanisms remain underexplored. Mutations in both DAF-2 (IGF-1 receptor) and RSKS-1 (ribosomal S6 kinase/S6K) cause synergistic lifespan extension in C. elegans. To understand the roles of translational regulation in this process, we performed polysomal profiling and identified translationally regulated ribosomal and cytochrome c (CYC-2.1) genes as key mediators of longevity. cyc-2.1 knockdown significantly extends lifespan by activating the intestinal mitochondrial unfolded protein response (UPRmt), mitochondrial fission, and AMP-activated kinase (AMPK). The germline serves as the key tissue for cyc-2.1 to regulate lifespan, and germline-specific cyc-2.1 knockdown non-autonomously activates intestinal UPRmt and AMPK. Furthermore, the RNA-binding protein GLD-1-mediated translational repression of cyc-2.1 in the germline is important for the non-autonomous activation of UPRmt and synergistic longevity of the daf-2 rsks-1 mutant. Altogether, these results illustrate a translationally regulated non-autonomous mitochondrial stress response mechanism in the modulation of lifespan by insulin-like signaling and S6K.
    Keywords:  AMPK; C. elegans; UPR(mt); aging; daf-2 rsks-1; germline; mRNA translation
  9. Proc Natl Acad Sci U S A. 2019 Jul 22. pii: 201818830. [Epub ahead of print]
    Lee S, Wang W, Hwang J, Namgung U, Min KT.
      Translocation of the endoplasmic reticulum (ER) and mitochondria to the site of axon injury has been shown to facilitate axonal regeneration; however, the existence and physiological importance of ER-mitochondria tethering in the injured axons are unknown. Here, we show that a protein linking ER to mitochondria, the glucose regulated protein 75 (Grp75), is locally translated at axon injury site following axotomy, and that overexpression of Grp75 in primary neurons increases ER-mitochondria tethering to promote regrowth of injured axons. We find that increased ER-mitochondria tethering elevates mitochondrial Ca2+ and enhances ATP generation, thereby promoting regrowth of injured axons. Furthermore, intrathecal delivery of lentiviral vector encoding Grp75 to an animal with sciatic nerve crush injury enhances axonal regeneration and functional recovery. Together, our findings suggest that increased ER-mitochondria tethering at axonal injury sites may provide a therapeutic strategy for axon regeneration.
    Keywords:  ER; axon regeneration; mitochondria
  10. EMBO J. 2019 Jul 22. e102679
    Fonseca D, Carvalho P.
      Disposal of membrane proteins in the late secretory pathway is thought to be exclusively facilitated by ESCRT-dependent lysosomal degradation. In this issue of The EMBO Journal, Schmidt et al define a previously uncharacterized endosome and Golgi-associated degradation (EGAD) pathway. This pathway, which has remarkable similarities to ERAD in the endoplasmic reticulum, operates in post-ER organelles via the proteasome and contributes to lipid homeostasis in eukaryotic cells.
  11. Eur J Pharmacol. 2019 Jul 17. pii: S0014-2999(19)30505-9. [Epub ahead of print] 172553
    Mohan S, R PRM, Brown L, Ayyappan P, G RK.
      Endoplasmic reticulum (ER) stress, a change in the ER homeostasis, leads to initiation of the unfolded protein response (UPR). The primary functions of the UPR are to restore the ER's physiological activity and coordinate the apoptotic and adaptive responses. Pathophysiological conditions that augment ER stress include hypoxia, misfolded and/or mutated protein accumulation, and high glucose. Prolonged ER stress is a critical factor in the pathogenesis of metabolic syndrome including type 2 diabetes mellitus, cardiovascular diseases, atherosclerosis, obesity, and fatty liver disease. UPR is a complex homeostatic pathway between newly synthesized proteins and their maturation, although the regulatory mechanisms contributing to the misfolded protein response and the possible therapeutic strategies are yet to be clarified. Therefore, a comprehensive understanding of the underlying molecular mechanisms is necessary to develop therapeutic interventions targeting ER stress response. In this review, we discuss the role of ER stress and misfolded protein response signaling in the pathogenesis of metabolic syndrome, highlighting the main functions of UPR components. We have emphasized the use of novel small molecular chemical chaperones, considered as modulators of ER stress. The initial studies with these chemical chaperones are promising, but detailed studies are required to define their efficacy and adverse effects during therapeutic use in humans.
    Keywords:  Cardiovascular diseases; Diabetes; ER stress; Liver; Obesity; Unfolded protein response
  12. Nat Commun. 2019 Jul 26. 10(1): 3349
    Li W, Yang J, Luo L, Jiang M, Qin B, Yin H, Zhu C, Yuan X, Zhang J, Luo Z, Du Y, Li Q, Lou Y, Qiu Y, You J.
      Immunogenic cell death (ICD)-associated immunogenicity can be evoked through reactive oxygen species (ROS) produced via endoplasmic reticulum (ER) stress. In this study, we generate a double ER-targeting strategy to realize photodynamic therapy (PDT) photothermal therapy (PTT) immunotherapy. This nanosystem consists of ER-targeting pardaxin (FAL) peptides modified-, indocyanine green (ICG) conjugated- hollow gold nanospheres (FAL-ICG-HAuNS), together with an oxygen-delivering hemoglobin (Hb) liposome (FAL-Hb lipo), designed to reverse hypoxia. Compared with non-targeting nanosystems, the ER-targeting naosystem induces robust ER stress and calreticulin (CRT) exposure on the cell surface under near-infrared (NIR) light irradiation. CRT, a marker for ICD, acts as an 'eat me' signal to stimulate the antigen presenting function of dendritic cells. As a result, a series of immunological responses are activated, including CD8+ T cell proliferation and cytotoxic cytokine secretion. In conclusion, ER-targeting PDT-PTT promoted ICD-associated immunotherapy through direct ROS-based ER stress and exhibited enhanced anti-tumour efficacy.