bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒03‒15
eleven papers selected by
Susan Logue
University of Manitoba

  1. EMBO J. 2020 Mar 09. e103841
    Yu J, Li T, Liu Y, Wang X, Zhang J, Wang X, Shi G, Lou J, Wang L, Wang CC, Wang L.
      Accumulated unfolded proteins in the endoplasmic reticulum (ER) trigger the unfolded protein response (UPR) to increase ER protein folding capacity. ER proteostasis and UPR signaling need to be regulated in a precise and timely manner. Here, we identify phosphorylation of protein disulfide isomerase (PDI), one of the most abundant and critical folding catalysts in the ER, as an early event during ER stress. The secretory pathway kinase Fam20C phosphorylates Ser357 of PDI and responds rapidly to various ER stressors. Phosphorylation of Ser357 induces an open conformation of PDI and turns it from a "foldase" into a "holdase", which is critical for preventing protein misfolding in the ER. Phosphorylated PDI also binds to the lumenal domain of IRE1α, a major UPR signal transducer, and attenuates excessive IRE1α activity. Importantly, PDI-S359A knock-in mice display enhanced IRE1α activation and liver damage under acute ER stress. We conclude that the Fam20C-PDI axis constitutes a post-translational response to maintain ER proteostasis and plays a vital role in protecting against ER stress-induced cell death.
    Keywords:  Fam20C; IRE1α; endoplasmic reticulum; phosphorylation; protein disulfide isomerase
  2. Cell. 2020 Mar 03. pii: S0092-8674(20)30161-6. [Epub ahead of print]
    Liang JR, Lingeman E, Luong T, Ahmed S, Muhar M, Nguyen T, Olzmann JA, Corn JE.
      Selective autophagy of organelles is critical for cellular differentiation, homeostasis, and organismal health. Autophagy of the ER (ER-phagy) is implicated in human neuropathy but is poorly understood beyond a few autophagosomal receptors and remodelers. By using an ER-phagy reporter and genome-wide CRISPRi screening, we identified 200 high-confidence human ER-phagy factors. Two pathways were unexpectedly required for ER-phagy. First, reduced mitochondrial metabolism represses ER-phagy, which is opposite of general autophagy and is independent of AMPK. Second, ER-localized UFMylation is required for ER-phagy to repress the unfolded protein response via IRE1α. The UFL1 ligase is brought to the ER surface by DDRGK1 to UFMylate RPN1 and RPL26 and preferentially targets ER sheets for degradation, analogous to PINK1-Parkin regulation during mitophagy. Our data provide insight into the cellular logic of ER-phagy, reveal parallels between organelle autophagies, and provide an entry point to the relatively unexplored process of degrading the ER network.
    Keywords:  CRISPR; ER-phagy; UFMylation; autophagy; endoplasmic reticulum; genome-wide screen; organelle turnover; oxidative phosphorylation; post-translational modification
  3. Front Microbiol. 2020 ;11 193
    Bitencourt TA, Lang EAS, Sanches PR, Peres NTA, Oliveira VM, Fachin AL, Rossi A, Martinez-Rossi NM.
      The ability of fungi to sense environmental stressors and appropriately respond is linked to secretory system functions. The dermatophyte infection process depends on an orchestrated signaling regulation that triggers the transcription of genes responsible for adherence and penetration of the pathogen into host-tissue. A high secretion system is activated to support the host-pathogen interaction and assures maintenance of the dermatophyte infection. The gateway of secretion machinery is the endoplasmic reticulum (ER), which is the primary site for protein folding and transport. Current studies have shown that ER stress that affects adaptive responses is primarily regulated by UPR and supports fungal pathogenicity; this has been assessed for yeasts and Aspergillus fumigatus, in regard to how these fungi cope with host environmental stressors. Fungal UPR consists of a transmembrane kinase sensor (Ire1/IreA) and a downstream target Hac1/HacA. The active form of Hac is achieved via non-spliceosomal intron removal promoted by endonuclease activity of Ire1/IreA. Here, we assessed features of HacA and its involvement in virulence and susceptibility in Trichophyton rubrum. Our results showed that exposure to antifungals and ER-stressing agents initiated the activation of HacA from T. rubrum. Interestingly, the activation occurs when a 20 nt fragment is removed from part of the exon-2 and part of intron-2, which in turn promotes the arisen of the DNA binding site motif and a dimer interface domain. Further, we found changes in the cell wall and cellular membrane composition in the ΔhacA mutant as well as an increase in susceptibility toward azole and cell wall disturbing agents. Moreover, the ΔhacA mutant presented significant defects in important virulence traits like thermotolerance and growth on keratin substrates. For instance, the development of the ΔhacA mutant was impaired in co-culture with keratinocytes or human nail fragments. Changes in the pro-inflammatory cytokine release were verified for the ΔhacA mutant during the co-culture assay, which might be related to differences in pathogen-associated molecular patterns (PAMPs) in the cell wall. Together, these results suggested that HacA is an integral part of T. rubrum physiology and virulence, implying that it is an important molecular target for antidermatophytic therapy.
    Keywords:  dermatophytes; endoplasmic reticulum; host-pathogen interaction; mycoses; secretory system; unfolded protein response
  4. Cancers (Basel). 2020 Mar 06. pii: E613. [Epub ahead of print]12(3):
    Pham DV, Raut PK, Pandit M, Chang JH, Katila N, Choi DY, Jeong JH, Park PH.
      Adiponectin, an adipokine predominantly derived from adipose tissue, exhibits potent antitumor properties in breast cancer cells. However, its mechanisms of action remain elusive. Inflammasomes-intracellular multimeric protein complexes-modulate cancer cell growth in a complicated manner, as well as playing a role in the innate immune system. Herein, we examined the potential role of inflammasomes in the antitumor activity of adiponectin and found that globular adiponectin (gAcrp) significantly suppressed inflammasomes activation in breast cancer cells both in vitro and in vivo conditions, as determined by decreased expression of inflammasomes components, including NOD-like receptor pyrin domain-containing protein 3 (NLRP3) and the apoptosis-associated speck-like protein containing a CARD (ASC), and inhibition of interleukin-1β and caspase-1 activation. Treatment with pharmacological inhibitors of inflammasomes caused decrease in cell viability, apoptosis induction, and G0/G1 cell cycle arrest, suggesting that inflammasomes activation is implicated in the growth of breast cancer cells. In addition, treatment with gAcrp generated essentially similar results to those of inflammasomes inhibitors, further indicating that suppression of breast cancer cell growth by gAcrp is mediated via modulation of inflammasomes. Mechanistically, gAcrp suppressed inflammasomes activation through sestrin2 (SESN2) induction, liver kinase B1 (LKB-1)-dependent AMP-activated protein kinase (AMPK) phosphorylation, and alleviation of endoplasmic reticulum (ER) stress. Taken together, these results demonstrate that gAcrp inhibits growth of breast cancer cells by suppressing inflammasomes activation, at least in part, via SESN2 induction and AMPK activation-dependent mechanisms.
    Keywords:  Adiponectin; Breast cancer; Inflammasomes; Sestrin2
  5. FEBS J. 2020 Mar 13.
    Kwon MY, Hwang N, Back SH, Lee SJ, Perrella MA, Chung SW.
      ER (endoplasmic reticulum) stress-induced cell death of VSMCs (vascular smooth muscle cells) is extensively involved in atherosclerotic plaque stabilization. We previously reported that NOD2 (nucleotide-binding oligomerization domain protein 2) participated in vascular homeostasis and tissue injury. However, the role and underlying mechanisms of NOD2 remain unknown in ER stress-induced cell death of VSMC during vascular diseases, including advanced atherosclerosis. Here, we report that NOD2 specifically interacted with ER stress sensor- ATF6 (activating transcription factor 6) and suppressed the expression of proapoptotic transcription factor CHOP (C/EBP homologous protein) during ER stress. CHOP-positive cells were increased in neointimal lesions after femoral artery injury in NOD2-deficient mice. In particular, a NOD2 ligand, MDP, and overexpression of NOD2 decreased CHOP expression in wild-type VSMCs. NOD2 interacted with an ER stress sensor molecule, ATF6, and acted as a negative regulator for ATF6 activation and its downstream target molecule, CHOP, that regulates ER stress-induced apoptosis. Moreover, NOD2 deficiency promoted disruption of advanced atherosclerotic lesions and CHOP expression in NOD2-/- ApoE-/- mice. Our findings indicate an unsuspected critical role for NOD2 in ER stress-induced cell death.
    Keywords:  ATF6; CHOP; ER stress; NOD2; VSMCs
  6. Nat Commun. 2020 Mar 11. 11(1): 1304
    Mahameed M, Boukeileh S, Obiedat A, Darawshi O, Dipta P, Rimon A, McLennan G, Fassler R, Reichmann D, Karni R, Preisinger C, Wilhelm T, Huber M, Tirosh B.
      The integrated stress response (ISR) converges on eIF2α phosphorylation to regulate protein synthesis. ISR is activated by several stress conditions, including endoplasmic reticulum (ER) stress, executed by protein kinase R-like endoplasmic reticulum kinase (PERK). We report that ER stress combined with ISR inhibition causes an impaired maturation of several tyrosine kinase receptors (RTKs), consistent with a partial block of their trafficking from the ER to the Golgi. Other proteins mature or are secreted normally, indicating selective retention in the ER (sERr). sERr is relieved upon protein synthesis attenuation and is accompanied by the generation of large mixed disulfide bonded complexes, including ERp44. sERr was pharmacologically recapitulated by combining the HIV-protease inhibitor nelfinavir with ISRIB, an experimental drug that inhibits ISR. Nelfinavir/ISRIB combination is highly effective to inhibit the growth of RTK-addicted cell lines and hepatocellular (HCC) cells in vitro and in vivo. Thus, pharmacological sERr can be utilized as a modality for cancer treatment.
  7. Curr Biol. 2020 Mar 09. pii: S0960-9822(20)30203-7. [Epub ahead of print]
    Ly S, Lee DA, Strus E, Prober DA, Naidoo N.
      Sleep is a cross-species phenomenon whose evolutionary and biological function remain poorly understood. Clinical and animal studies suggest that sleep disturbance is significantly associated with disruptions in protein homeostasis-or proteostasis-in the brain, but the mechanism of this link has not been explored. In the cell, the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) pathway modulates proteostasis by transiently inhibiting protein synthesis in response to proteostatic stress. In this study, we examined the role of the PERK pathway in sleep regulation and provide the first evidence that PERK signaling is required to regulate normal sleep in both vertebrates and invertebrates. We show that pharmacological inhibition of PERK reduces sleep in both Drosophila and zebrafish, indicating an evolutionarily conserved requirement for PERK in sleep. Genetic knockdown of PERK activity also reduces sleep in Drosophila, whereas PERK overexpression induces sleep. Finally, we demonstrate that changes in PERK signaling directly impact wake-promoting neuropeptide expression, revealing a mechanism through which proteostatic pathways can affect sleep and wake behavior. Taken together, these results demonstrate that protein synthesis pathways like PERK could represent a general mechanism of sleep and wake regulation and provide greater insight into the relationship between sleep and proteostasis.
    Keywords:  Drosophila; ER stress; PERK; protein synthesis; protein translation; proteostasis; sleep; unfolded protein response; zebrafish
  8. Nat Chem Biol. 2020 Mar 09.
    Origel Marmolejo CA, Bachhav B, Patibandla SD, Yang AL, Segatori L.
      Gene expression in mammalian cells results from coordinated protein-driven processes guided by diverse mechanisms of regulation, including protein-protein interactions, protein localization, DNA modifications and chromatin rearrangement. Regulation of gene expression is particularly important in stress-response pathways. To address the need to monitor chromosomal gene expression generating a readily detectable signal output that recapitulates gene expression dynamics, we developed a gene signal amplifier platform that links transcriptional and post-translational regulation of a fluorescent output to the expression of a chromosomal target gene. We generated a multiplex reporter system for monitoring markers of the unfolded protein response, a complex signal transduction pathway that remodels gene expression in response to proteotoxic stress in the endoplasmic reticulum. By recapitulating the transcriptional and translational control mechanisms underlying the expression of a target gene with high sensitivity, this platform provides a technology for monitoring gene expression with superior sensitivity and dynamic resolution.
  9. J Pathol. 2020 Mar 13.
    Anspach L, Tsaryk R, Seidmann L, Unger RE, Jayasinghe C, Simiantonaki N, Kirkpatrick CJ, Pröls F.
      Spontaneously regressing infantile haemangiomas and aggressive angiosarcomas are vascular tumours with excessive angiogenesis. When analysing haemangiomas and angiosarcomas immunohistochemically with respect to their chaperone profiles we found that angiosarcomas have significantly elevated protein levels of BiP and PERK with concomitant attenuated IRE1α levels while haemangioma tissue exhibits the same pattern as embryonal skin tissue. We show that BiP is essential for the maintenance of VEGFR2 protein, which is expressed in endothelium of both tumour types. When studying the effects of BiP, the IRE1α/Xbp1 -, and PERK/ATF4-signalling pathways on migration and tube-forming potential of endothelial cells we show that downregulation of BiP, as well as inhibition of the kinase activity of IRE1α, inhibit in vitro angiogenesis. Downregulation of PERK levels promotes Xbp1 splicing in ER-stressed cells, indicating that in angiosarcoma the elevated PERK levels might result in high levels of unspliced Xbp1, which have been reported to promote cell proliferation and increase tumour malignancy. The data presented in this study revealed that besides BiP or PERK, the kinase domain of IRE1α and Xbp1 could be potential targets for the development of novel therapeutic approaches for treating angiosarcomas and to control tumour angiogenesis. This article is protected by copyright. All rights reserved.
    Keywords:  VEGFR2; angiosarcoma; chaperone; crosstalk; haemangioma; tumour angiogenesis; unfolded protein response
  10. Biol Methods Protoc. 2018 ;3(1): bpy003
    Ishikawa K, Kobayashi Y, Wakabayashi Y, Watanabe S, Semba K.
      We devised a versatile vector system for efficient isolation of reporter cells responding to a certain condition of interest. This system combines nontoxic GAL4-UAS and piggyBac transposon systems, allowing application to mammalian cells and improved expression of a fluorescent reporter protein for cell sorting. Case studies under conditions of c-MYC gene induction or endoplasmic reticulum (ER) stress with thapsigargin on mouse or human cell lines confirmed easy and efficient isolation of responsive reporter cells. Sequence analyses of the integrated loci of the thapsigargin-responsive clones identified responsive genes including BiP and OSBPL9. OSBPL9 is a novel ER stress-responsive gene and we confirmed that endogenous mRNA expression of OSBPL9 is upregulated by thapsigargin, and is repressed by IRE1α inhibitors, 4μ8C and toyocamycin, but not significantly by a PERK inhibitor, GSK2656157. These results demonstrate that this approach can be used to discover novel genes regulated by any stimuli without the need for microarray analysis, and that it can concomitantly produce reporter cells without identification of stimuli-responsive promoter/enhancer elements. Therefore, this system has a variety of benefits for basic and clinical research.
    Keywords:  gene mining; reporter cell; transposon; trap vector
  11. PLoS Biol. 2020 Mar;18(3): e3000296
    Park S, Jang A, Bouret SG.
      The steady increase in the prevalence of obesity and associated type II diabetes mellitus is a major health concern, particularly among children. Maternal obesity represents a risk factor that contributes to metabolic perturbations in the offspring. Endoplasmic reticulum (ER) stress has emerged as a critical mechanism involved in leptin resistance and type 2 diabetes in adult individuals. Here, we used a mouse model of maternal obesity to investigate the importance of early life ER stress in the nutritional programming of this metabolic disease. Offspring of obese dams developed glucose intolerance and displayed increased body weight, adiposity, and food intake. Moreover, maternal obesity disrupted the development of melanocortin circuits associated with neonatal hyperleptinemia and leptin resistance. ER stress-related genes were up-regulated in the hypothalamus of neonates born to obese mothers. Neonatal treatment with the ER stress-relieving drug tauroursodeoxycholic acid improved metabolic and neurodevelopmental deficits and reversed leptin resistance in the offspring of obese dams.