bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019‒10‒20
fourteen papers selected by
Susan Logue
University of Manitoba


  1. BMB Rep. 2019 Oct 17. pii: 4699. [Epub ahead of print]
    Kwon MY, Hwang N, Lee SJ, Chung SW.
      Nucleotide-binding oligomerization domain protein 2 (NOD2), an intracellular pattern recognition receptor, plays important roles in inflammation and cell death. Previously, we have shown that NOD2 is expressed in vascular smooth muscle cells (VSMCs) and that NOD2 deficiency promotes VSMC proliferation, migration, and neointimal formation after vascular injury. However, its role in endoplasmic reticulum (ER) stress-induced cell death in VSMCs remains unclear. Thus, the objective of this study was to evaluate ER stress-induced viability of mouse primary VSMCs. NOD2 deficiency increased ER stress-induced cell death and expression levels of apoptosis mediators (cleaved caspase-3, Bax, and Bak) in VSMCs in the presence of tunicamycin (TM), an ER stress inducer. In contrast, ER stress-induced cell death and expression levels of apoptosis mediators (cleaved caspase-3, Bax, and Bak) were decreased in NOD2-overexpressed VSMCs. We found that the IRE-1α-XBP1 pathway, one of unfolded protein response branches, was decreased in NOD2-deficient VSMCs and reversed in NOD2-overexpressed VSMCs in the presence of TM. Furthermore, NOD2 deficiency reduced the expression of XBP1 target genes such as GRP78, PDI-1, and Herpud1, thus improving cell survival. Taken together, these data suggest that the induction of ER stress through NOD2 expression can protect against TM-induced cell death in VSMCs. These results may contribute to a new paradigm in vascular homeostasis.
  2. Front Physiol. 2019 ;10 1198
    Gu R, Huang T, Xiao J, Liao Z, Li J, Lan H, Ouyang J, Hu J, Liao H.
      Skeletal muscle repair and systemic inflammation/immune responses are linked to endoplasmic reticulum stress (ER stress) pathways in myopathic muscle, and muscle cells play an active role in muscular immune reactions by exhibiting immunological characteristics under persistent proinflammation stimuli. Whether ER stress affects the intrinsic immunological capacities of myocytes in the inflammatory milieu, as it does to immune cells, and which arms of the unfolded protein response (UPR) mainly participate in these processes remain mostly unknown. We investigated this issue and showed that inflammatory stimuli can induce the activation of the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1α (IRE1α) arms of the UPR in myocytes both in vivo and in vitro. UPR stressor administration reversed the increased IFN-γ-induced expression of the MHC-II molecule H2-Ea, the MHC-I molecule H-2K b , toll-like receptor 3 (TLR3) and some proinflammatory myokines in differentiated primary myotubes in vitro. However, further IRE1α inhibition thoroughly corrected the trend in the UPR stressor-triggered suppression of immunobiological molecules. In IFN-γ-treated myotubes, dramatic p38 MAPK activation was observed under IRE1α inhibitory conditions, and the pharmacological inhibition of p38 reversed the immune molecule upregulation induced by IRE1α inhibition. In parallel, our coculturing system verified that the ovalbumin (OVA) antigen presentation ability of inflamed myotubes to OT-I T cells was enhanced by IRE1α inhibition, but was attenuated by further p38 inhibition. Thus, the present findings demonstrated that p38 MAPK contributes greatly to IRE1α arm-dependent immunobiological suppression in myocytes under inflammatory stress conditions.
    Keywords:  endoplasmic reticulum stress; inositol-requiring enzyme 1α; myotubes; p38 MAPK; unfolded protein responses
    DOI:  https://doi.org/10.3389/fphys.2019.01198
  3. Sci Rep. 2019 Oct 17. 9(1): 14931
    Sanchez CL, Sims SG, Nowery JD, Meares GP.
      In many diseases, misfolded proteins accumulate within the endoplasmic reticulum (ER), leading to ER stress. In response, the cell initiates the unfolded protein response (UPR) to reestablish homeostasis. Additionally, in response to ER stress, various cell types mount an inflammatory response involving interleukin (IL)-6. While IL-6 has been widely studied, the impact of ER stress on other members of the IL-6 cytokine family, including oncostatin (OSM), IL-11, ciliary neurotrophic factor (CNTF), and leukemia inhibitor factor (LIF) remains to be elucidated. Here, we have examined the expression of the IL-6 family cytokines in response to pharmacologically-induced ER stress in astrocytes and macrophages, which express IL-6 in response to ER stress through different mechanisms. Our findings indicate that, in astrocytes, ER stress regulates mRNA expression of the IL-6 family of cytokines that is, in part, mediated by PKR-like ER kinase (PERK) and Janus kinase (JAK) 1. Additionally, in astrocytes, CNTF expression was suppressed through a PERK-dependent mechanism. Macrophages display a different profile of expression of the IL-6 family that is largely independent of PERK. However, IL-6 expression in macrophages was dependent on JAK signaling. Overall, this study demonstrates the cell-specific and differential mechanisms controlling expression of the IL-6 family of cytokines in response to ER stress.
    DOI:  https://doi.org/10.1038/s41598-019-51481-6
  4. Dis Model Mech. 2019 Oct 18. pii: dmm.040741. [Epub ahead of print]
    Itzhak DN, Sacco F, Nagaraj N, Tyanova S, Mann M, Murgia M.
      The unfolded protein response (UPR) involves extensive proteome remodeling in many cellular compartments. So far, a comprehensive analysis has been missing due to technological limitations. Here we employ Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC)-based proteomics to quantify over 6200 proteins at increasing concentrations of tunicamycin in HeLa cells. We further compare the effects of tunicamycin (5 ug/ml) to those of thapsigargin (1 µM) and DTT (2mM), both activating the UPR through different mechanisms. The systematic quantification of the proteome-wide expression changes following proteostatic stress is a resource for the scientific community, which enables the discovery of novel players involved in the pathophysiology of the broad range of disorders linked to proteostasis. We identified 38 proteins not previously linked to the UPR, whose expression increases, of which 15 likely remediate ER stress, and the remainder may contribute to pathological outcomes. Unexpectedly, there are few strongly downregulated proteins, despite expression of the pro-apoptotic transcription factor CHOP, suggesting that IRE1-dependent mRNA decay (RIDD) has a limited contribution to ER-stress mediated cell death in our system.
    Keywords:  Endoplasmic Reticulum stress; Proteomics; SILAC; Tunicamycin; Unfolded Protein Response
    DOI:  https://doi.org/10.1242/dmm.040741
  5. J Biol Chem. 2019 Oct 17. pii: jbc.RA119.009128. [Epub ahead of print]
    Pierce M, Vengsarkar D, McLaughlin JE, Kahn JN, Tumer NE.
      Ricin undergoes retrograde transport to the endoplasmic reticulum (ER) and ricin toxin A chain (RTA) enters the cytosol from the ER. Previous reports indicated that RTA inhibits activation of the unfolded protein response (UPR) in yeast and in mammalian cells. Both precursor (preRTA) and mature form of RTA (mRTA) inhibited splicing of HAC1u (u for uninduced) mRNA, suggesting that UPR inhibition occurred on the cytosolic face of the ER. Here we examined the role of ribosome binding and depurination activity on inhibition of the UPR using mRTA mutants. An active site mutant with very low depurination activity, which bound ribosomes as wild type RTA, did not inhibit HAC1u mRNA splicing. A ribosome binding mutant, which showed reduced binding to ribosomes, but retained depurination activity inhibited HAC1u mRNA splicing. This mutant allowed separation of the UPR inhibition by RTA from cytotoxicity because it reduced the rate of depurination. Ribosome binding mutant inhibited the UPR without affecting IRE1 oligomerization or cleavage of HAC1u mRNA at the splice site junctions.  Inhibition of the UPR correlated with the depurination level, suggesting that ribosomes play a role in splicing of HAC1u mRNA. We show that HAC1u mRNA is associated with ribosomes and does not get processed on depurinated ribosomes thereby inhibiting the UPR. These results demonstrate that RTA inhibits HAC1u mRNA splicing through its depurination activity on the ribosome without directly affecting IRE1 oligomerization or the splicing reaction and provide evidence that IRE1 recognizes HAC1u mRNA that is associated with ribosomes.
    Keywords:  RNA processing; RNA splicing; endoplasmic reticulum stress (ER stress); ribosomal ribonucleic acid (rRNA) (ribosomal RNA); ribosome; ribosome-inactivating protein (RIP); unfolded protein response (UPR)
    DOI:  https://doi.org/10.1074/jbc.RA119.009128
  6. Virology. 2019 Sep 26. pii: S0042-6822(19)30277-6. [Epub ahead of print]539 1-10
    Cao L, Xue M, Chen J, Shi H, Zhang X, Shi D, Liu J, Huang L, Wei Y, Liu C, Feng L.
      Endoplasmic reticulum (ER) stress is associated with numerous mammalian diseases, especially viral diseases. Porcine parvovirus (PPV) is the causative agent of reproductive failure in swine. Here, we observed that the PPV infection of porcine kidney 15 and porcine testis cells resulted in the activation of ER stress sensors mediated by protein kinase R-like ER kinase (PERK), but not inositol-requiring enzyme 1 and activating transcription factor 6 (ATF6). ER stress activation obviously blocked PPV replication. Depletion of proteins, such as PERK, eukaryotic initiation factor 2, and ATF4, by small interfering RNA significantly enhanced PPV replication. Moreover, the pro-apoptotic factor C/EBP homologous protein was identified a key factor in the inhibition of PPV replication. These data demonstrate that PPV infection activates ER stress through the PERK signaling pathway and that ER stress inhibits further PPV replication by promoting apoptosis.
    Keywords:  Apoptotic cell death; Endoplasmic reticulum stress; Porcine parvovirus; Protein kinase R-like ER kinase pathway; Unfolded protein response
    DOI:  https://doi.org/10.1016/j.virol.2019.09.012
  7. Elife. 2019 10 15. pii: e49577. [Epub ahead of print]8
    Perlaza K, Toutkoushian H, Boone M, Lam M, Iwai M, Jonikas MC, Walter P, Ramundo S.
      In response to proteotoxic stress, chloroplasts communicate with the nuclear gene expression system through a chloroplast unfolded protein response (cpUPR). We isolated Chlamydomonas reinhardtii mutants that disrupt cpUPR signaling and identified a gene encoding a previously uncharacterized cytoplasmic protein kinase, termed Mars1-for mutant affected in chloroplast-to-nucleus retrograde signaling-as the first known component in cpUPR signal transmission. Lack of cpUPR induction in MARS1 mutant cells impaired their ability to cope with chloroplast stress, including exposure to excessive light. Conversely, transgenic activation of cpUPR signaling conferred an advantage to cells undergoing photooxidative stress. Our results indicate that the cpUPR mitigates chloroplast photodamage and that manipulation of this pathway is a potential avenue for engineering photosynthetic organisms with increased tolerance to chloroplast stress.
    Keywords:  cell biology; chlamydomonas reinhardtii; chloroplast-to-nucleus signaling; genetics; genomics; organellar protein homeostasis; photoprotection
    DOI:  https://doi.org/10.7554/eLife.49577
  8. ACS Chem Biol. 2019 Oct 14.
    Feldman HC, Vidadala VN, Potter ZE, Papa FR, Backes BJ, Maly DJ.
      The dual kinase endoribonuclease IRE1 is a master regulator of cell fate decisions in cells experiencing endoplasmic reticulum (ER) stress. In mammalian cells, there are two paralogs of IRE1: IRE1α and IRE1β. While IRE1α has been extensively studied, much less is understood about IRE1β and its role in signaling. In addition, whether the regulation of IRE1β's enzymatic activities varies compared to IRE1α is not known. Here, we show that the RNase domain of IRE1β is enzymatically active and capable of cleaving an XBP1 RNA mini-substrate in vitro. Using ATP-competitive inhibitors, we find that, like IRE1α, there is an allosteric relationship between the kinase and RNase domains of IRE1β. This allowed us to develop a novel toolset of both paralog specific and dual-IRE1α/β kinase inhibitors that attenuate RNase activity (KIRAs). Using sequence alignments of IRE1α and IRE1β, we propose a model for paralog-selective inhibition through interactions with nonconserved residues that differentiate the ATP-binding pockets of IRE1α and IRE1β.
    DOI:  https://doi.org/10.1021/acschembio.9b00482
  9. J Biol Chem. 2019 Oct 17. pii: jbc.RA119.009603. [Epub ahead of print]
    Hanafusa K, Wada I, Hosokawa N.
      Molecular chaperones facilitate protein folding by associating with nascent polypeptides, thereby preventing protein misfolding and aggregation. Endoplasmic reticulum (ER) chaperone BiP, the sole HSP70 chaperone in the ER, is regulated by HSP40 chaperones, including ER-resident protein ERdj3 (DNAJB11). ERdj3 lacks an ER retrieval signal, is secreted under ER stress conditions, and functions as a chaperone in the extracellular space, but how its secretion is regulated remains unclear. We recently showed that ERdj3 forms a complex with ER-resident stromal cell-derived factor 2 (SDF2) and SDF2L1 (SDF2-like protein 1) and thereby prevents protein aggregation during the BiP chaperone cycle. However, the contribution of the ERdj3-SDF2L1 complex to protein quality control is poorly understood. Here, we analyzed the intracellular localization and chaperone activity of ERdj3 in complex with SDF2L1. We found that ERdj3 was retained in the ER by associating with SDF2/SDF2L1. In vitro analyses revealed that the ERdj3 dimer incorporated two SDF2L1 molecules; otherwise, ERdj3 alone formed a homotetramer. The ERdj3-SDF2L1 complex suppressed ER protein aggregation, and this suppression did not require substrate transfer to BiP. The ERdj3-SDF2L1 complex inhibited aggregation of denatured glutathione S-transferase (GST) in vitro and maintained GST in a soluble oligomeric state. Both in cellulo and in vitro, the chaperone activities of the ERdj3-SDF2L1 complex were higher than those of ERdj3 alone. These findings suggest that, under normal conditions, ERdj3 functions as an ER chaperone in complex with SDF2/SDF2L1, but is secreted into the extracellular space when it cannot form this complex.
    Keywords:  ER quality control; ERdj3/DNAJB11; GRP78; SDF2-like protein 1 (SDF2L1); chaperone; chaperone DnaJ (DnaJ); endoplasmic reticulum (ER); immunoglobulin heavy chain-binding protein (BiP); protein aggregation; protein homeostasis; secretion; stromal cell derived factor 2 (SDF2); unfolded protein response (UPR)
    DOI:  https://doi.org/10.1074/jbc.RA119.009603
  10. Front Cell Dev Biol. 2019 ;7 198
    Andersohn A, Garcia MI, Fan Y, Thompson MC, Akimzhanov AM, Abdullahi A, Jeschke MG, Boehning D.
      Chronic ER stress occurs when protein misfolding in the Endoplasmic reticulum (ER) lumen remains unresolved despite activation of the unfolded protein response. We have shown that traumatic injury such as a severe burn leads to chronic ER stress in vivo leading to systemic inflammation which can last for more than a year. The mechanisms linking chronic ER stress to systemic inflammatory responses are not clear. Here we show that induction of chronic ER stress leads to the release of known and novel damage-associated molecular patterns (DAMPs). The secreted DAMPs are aggregated and markedly protease resistant. ER stress-derived DAMPs activate dendritic cells (DCs) which are then capable of polarizing naïve T cells. Our findings indicate that induction of chronic ER stress may lead to the release of hyperstable DAMPs into the circulation resulting in persistent systemic inflammation and adverse outcomes.
    Keywords:  DAMP; ER stress; burn; cytokine; damage-associated molecular pattern; dendritic cell; inflammation; trauma
    DOI:  https://doi.org/10.3389/fcell.2019.00198
  11. Front Plant Sci. 2019 ;10 1192
    Zeng Y, Li B, Zhang W, Jiang L.
      The endoplasmic reticulum (ER) is the starting point for protein secretion and lipid biosynthesis in eukaryotes. ER homeostasis is precisely regulated by the unfolded protein response (UPR) to alleviate stress, involving both transcriptional and translational regulators. Autophagy is an intracellular self-eating process mediated by the double-membrane structure autophagosome for the degradation of cytosolic components and damaged organelles to regenerate nutrient supplies under nutrient-deficient or stress conditions. A recent study has revealed that besides serving as a membrane source for phagophore formation, the ER is also tightly regulated under stress conditions by a distinct type of autophagosome, namely ER-phagy. ER-phagy has been characterized with receptors clearly identified in mammals and yeast, yet relatively little is known about plant ER-phagy and its receptors. Here, we will summarize our current knowledge of ER-phagy in yeast and mammals and highlight recent progress in plant ER-phagy studies, pointing towards a possible interplay between ER-phagy and ER homeostasis under ER stress responses (ERSRs) in plants.
    Keywords:  ER stress responses; ER-phagy; IRE1; autophagy; unfolded protein response
    DOI:  https://doi.org/10.3389/fpls.2019.01192
  12. J Cell Physiol. 2019 Oct 14.
    Huang D, Jiang Y.
      MAP kinase phosphatase 1 (MKP1) has been identified as an antiapoptotic protein via sustaining mitochondrial function. However, the role of MKP1 in neuroinflammation has not been fully understood. The aim of this study is to figure out the influence of MKP1 in lipopolysaccharide (LPS)-treated microglia BV-2 cells and investigate whether MKP1 reduces BV-2 cell death via modulating endoplasmic reticulum (ER) stress and mitochondrial dysfunction. The results of this study demonstrated that MKP1 was rapidly downregulated after exposure to LPS. However, the transfection of MKP1 adenovirus could reverse cell viability and attenuate LPS-mediated BV-2 cell apoptosis. Mechanistically, MKP1 overexpression alleviated ER stress and corrected LPS-induced calcium overloading. Besides, MKP1 adenovirus transfection also reversed mitochondrial bioenergetics, maintained mitochondrial membrane potential, and blocked mitochondria-initiated apoptosis signals. Furthermore, we found that MKP1 overexpression is associated with inactivation of mitogen-activated protein kinase-c-Jun N-terminal kinase (MAPK-JNK) pathway. Interestingly, the activation of MAPK-JNK pathway could abolish the protective effects of MKP1 on BV-2 cells survival and mitochondrial function in the presence of LPS. Altogether, our results identified MKP1 as a primary defender of neuroinflammation via modulating ER stress and mitochondrial function in a manner dependent on MAPK-JNK pathway. These findings may open a new window for the treatment of neuroinflammation in the clinical setting.
    Keywords:  BV-2 cells; ER stress; LPS; MKP1; mitochondrial damage; neuroinflammation
    DOI:  https://doi.org/10.1002/jcp.29308
  13. Cell Calcium. 2019 Oct 10. pii: S0143-4160(19)30168-X. [Epub ahead of print]84 102101
    Filadi R, Pizzo P.
      Inter-organelle communication represents a booming topic in cell biology research, with endoplasmic reticulum (ER)-mitochondria coupling playing the lion's share. In a recent work, Bartok and colleagues found that inositol trisphosphates receptors (IP3Rs), in addition to their well-known involvement in ER-mitochondria Ca2+ transfer, are endowed with structural properties at organelles' interface.
    DOI:  https://doi.org/10.1016/j.ceca.2019.102101
  14. Elife. 2019 10 15. pii: e51430. [Epub ahead of print]8
    Kessler F, Longoni P.
      A genetic screen has identified the first signaling component of the unfolded protein response in chloroplasts.
    Keywords:  cell biology; cell signaling; chlamydomonas reinhardtii; chloroplast; genetics; genomics; organelles; photoprotection; protein homeostasis
    DOI:  https://doi.org/10.7554/eLife.51430