bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019‒04‒21
eight papers selected by
Susan Logue
University of Manitoba

  1. Sci Adv. 2019 Apr;5(4): eaaw0025
    Simic MS, Moehle EA, Schinzel RT, Lorbeer FK, Halloran JJ, Heydari K, Sanchez M, Jullié D, Hockemeyer D, Dillin A.
      Somatic cells can be reprogrammed into pluripotent stem cells using the Yamanaka transcription factors. Reprogramming requires both epigenetic landscape reshaping and global remodeling of cell identity, structure, basic metabolic processes, and organelle form and function. We hypothesize that variable regulation of the proteostasis network and its influence upon the protein-folding environment within cells and their organelles is responsible for the low efficiency and stochasticity of reprogramming. We find that the unfolded protein response of the endoplasmic reticulum (UPRER), the mitochondrial UPR, and the heat shock response, which ensure proteome quality during stress, are activated during reprogramming. The UPRER is particularly crucial, and its ectopic, transient activation, genetically or pharmacologically, enhances reprogramming. Last, stochastic activation of the UPRER predicts reprogramming efficiency in naïve cells. Thus, the low efficiency and stochasticity of cellular reprogramming are due partly to the inability to properly initiate the UPRER to remodel the ER and its proteome.
  2. Apoptosis. 2019 Apr 15.
    Mielczarek-Lewandowska A, Sztiller-Sikorska M, Osrodek M, Czyz M, Hartman ML.
      Outcomes of melanoma patient treatment remain unsatisfactory despite accessibility of oncoprotein-targeting drugs and immunotherapy. Here, we reported that 17-aminogeldanamycin more potently activated caspase-3/7 in BRAFV600E melanoma cells than geldanamycin, another inhibitor of heat shock protein 90 (HSP90). 17-aminogeldanamycin alleviated self-triggered compensatory increase in HSP70 mRNA level and induced endoplasmic reticulum (ER) stress, which was followed by selective diminution of cytoprotective IRE1α-XBP1s pathway activity of unfolded protein response (UPR), inhibition of ERK1/2 activity and induction of apoptosis. Concomitantly, ATF6/p50 level and expression of PERK-dependent genes, CHOP and BIM, remained unaltered. This might result from an inframe deletion in EIF2AK3 leading to a PERKL21del variant revealed by whole-exome sequencing in melanoma cell lines. 17-aminogeldanamycin exhibited similar activity in NRASQ61R melanoma cells that harbored a heterozygous inactivating variant of NAD(P)H:quinone oxidoreductase 1 (NQO1P187S). In addition, 17-aminogeldanamycin acted cooperatively with trametinib (an inhibitor of MEK1/2) and vemurafenib (an inhibitor of BRAFV600E) in induction of apoptosis in melanoma cell lines as evidenced by in-cell caspase-3/7 activation and PARP cleavage that occurred earlier compared with either drug used alone. As trametinib and vemurafenib did not significantly affect HSP70 and GRP78 transcript levels, cooperation of MEK/BRAFV600E inhibitors and 17-aminogeldanamycin might result from a concurrent inhibition of the RAS/RAF/MEK/ERK cascade and IRE1α-dependent signaling, and cell-intrinsic ER homeostasis can determine the extent of the drug cooperation. Our study indicates that 17-aminogeldanamycin takes several advantages compared with other HSP90-targeting compounds, and can complement activity of BRAF/MEK inhibitors in melanoma cells of different genetic subtypes.
    Keywords:  17-aminogeldanamycin; Endoplasmic reticulum stress; HSP90 inhibitors; IRE-1α; Melanoma; Targeted therapy
  3. FEBS Lett. 2019 Apr 19.
    Guerra-Moreno A, Ang J, Welsch H, Jochem M, Hanna J.
      In the unfolded protein response (UPR), Ire1 activates Hac1 to coordinate the transcription of hundreds of genes to mitigate ER stress. Recent work in C. elegans suggests that oxidative stress inhibits this canonical Ire1 signaling pathway, activating instead an anti-oxidant stress response. We sought to determine whether this novel mode of UPR function also existed in yeast, where Ire1 has been best characterized. We show that the yeast UPR is also subject to inhibition by oxidative stress. Inhibition is mediated by a single evolutionarily conserved cysteine, and affects both luminal and membrane pathways of Ire1 activation. In yeast, Ire1 appears dispensable for resistance to oxidative stress and, therefore, the physiologic significance of this pathway remains to be demonstrated. This article is protected by copyright. All rights reserved.
    Keywords:  Ire1; arsenic; cysteine; oxidative stress; unfolded protein response
  4. PLoS Genet. 2019 Apr 17. 15(4): e1008069
    Volpi VG, Ferri C, Fregno I, Del Carro U, Bianchi F, Scapin C, Pettinato E, Solda T, Feltri ML, Molinari M, Wrabetz L, D'Antonio M.
      In the peripheral nervous system (PNS) myelinating Schwann cells synthesize large amounts of myelin protein zero (P0) glycoprotein, an abundant component of peripheral nerve myelin. In humans, mutations in P0 cause the demyelinating Charcot-Marie-Tooth 1B (CMT1B) neuropathy, one of the most diffused genetic disorders of the PNS. We previously showed that several mutations, such as the deletion of serine 63 (P0-S63del), result in misfolding and accumulation of P0 in the endoplasmic reticulum (ER), with activation of the unfolded protein response (UPR). In addition, we observed that S63del mouse nerves display the upregulation of many ER-associated degradation (ERAD) genes, suggesting a possible involvement of this pathway in the clearance of the mutant P0. In ERAD in fact, misfolded proteins are dislocated from the ER and targeted for proteasomal degradation. Taking advantage of inducible cells that express the ER retained P0, here we show that the P0-S63del glycoprotein is degraded via ERAD. Moreover, we provide strong evidence that the Schwann cell-specific ablation of the ERAD factor Derlin-2 in S63del nerves exacerbates both the myelin defects and the UPR in vivo, unveiling a protective role for ERAD in CMT1B neuropathy. We also found that lack of Derlin-2 affects adult myelin maintenance in normal nerves, without compromising their development, pinpointing ERAD as a previously unrecognized player in preserving Schwann cells homeostasis in adulthood. Finally, we provide evidence that treatment of S63del peripheral nerve cultures with N-Acetyl-D-Glucosamine (GlcNAc), known to enhance protein quality control pathways in C.elegans, ameliorates S63del nerve myelination ex vivo. Overall, our study suggests that potentiating adaptive ER quality control pathways might represent an appealing strategy to treat both conformational and age-related PNS disorders.
  5. Curr Opin Cell Biol. 2019 Apr 16. pii: S0955-0674(19)30017-1. [Epub ahead of print]59 40-49
    Henne M.
      Sterols and fatty acids (FAs) are essential lipids that play fundamental roles in membrane dynamics and cellular homeostasis. Synthesized at the endoplasmic reticulum (ER) and cytoplasm, trafficked by proteins, and stored in lipid droplets (LDs), much work has been conducted examining how these lipids are shuttled from one location to another. Recent work has highlighted the importance of inter-organelle crosstalk in the regulation of sterol and FA homeostasis. In particular, three organelles-lysosomes, LDs, and the ER network-function together to regulate sterol subcellular distribution and utilization. This tri-organelle crosstalk also drives adaptions to stress and protects against FA-induced lipotoxicity. Here, we highlight recent work revealing how this unique organelle trio function together. We also discuss how LDs can modulate lysosome signaling to control growth, autophagy, and ER homeostasis.
  6. J Biol Chem. 2019 Apr 17. pii: jbc.RA119.007997. [Epub ahead of print]
    Molinaro R, Mukherjee T, Flick R, Philpott DJ, Girardin SE.
      NOD1 and NOD2 are intracellular sensors of bacterial peptidoglycan that belong to the Nod-like receptor (NLR) family of innate immune proteins. In addition to their role as direct bacterial sensors, it was proposed that NOD proteins could detect endoplasmic reticulum (ER) stress induced by thapsigargin, an inhibitor of the sarcoplasmic or endoplasmic reticulum calcium ATPase family (SERCA) that pumps Ca2+ into the ER, resulting in pro-inflammatory signalling. Here, we confirm that thapsigargin induces NOD-dependent pro-inflammatory signalling in epithelial cells. However, the effect was specific to thapsigargin, as tunicamycin and the subtilase cytotoxin SubAB from Shiga toxigenic Escherichia coli, which induce ER stress by other mechanisms, did not induce cytokine expression. The calcium ionophore A23187 also induced NOD-dependent signalling, and calcium chelators demonstrated a role for both intracellular and extracellular calcium in mediating thapsigargin-induced and NOD-dependent pro-inflammatory signalling, in part through the activation of plasma membrane-associated calcium release-activated channels (CRACs). Moreover, our results demonstrate that both endocytosis and the addition of serum to the cell culture medium were required for thapsigargin-mediated NOD activation. Finally, we analyzed cell culture grade fetal calf serum as well as serum from laboratory mice by high-pressure liquid chromatography and mass spectrometry, and identified the presence of various peptidoglycan fragments. We propose that cellular perturbations that affect intracellular Ca2+ can trigger internalization of peptidoglycan trace contaminants found in culture serum, thereby stimulating pro-inflammatory signalling. The presence of peptidoglycan in animal serum suggests that a homeostatic function of NOD signalling may have been previously overlooked.
    Keywords:  NOD1; NOD2; Nod-like receptor (NLR); calcium intracellular release; cell biology; cell signaling; endoplasmic reticulum stress (ER stress); innate immunity
  7. J Biol Chem. 2019 Apr 18. pii: jbc.RA118.005804. [Epub ahead of print]
    Chawsheen HA, Jiang H, Ying Q, Ding N, Thapa P, Wei Q.
      Sulfiredoxin (Srx) reduces hyperoxidized 2-cysteine-containing peroxiredoxins (Prxs) and protects cells against oxidative stress. Previous studies have shown that Srx is highly expressed in primary specimens of lung cancer patients and plays a pivotal role in lung tumorigenesis and cancer progression. However, the oncogenic mechanisms of Srx in cancer are incompletely understood. In this study, we found that Srx knockdown sensitizes lung cancer cells to endoplasmic reticulum (ER)-stress induced cell death. Through mass spectrometry (MS) analysis, we determined that Srx forms a complex with the ER-resident protein thioredoxin domain-containing protein 5 (TXNDC5). Using reciprocal co-immunoprecipitation, immunofluorescence imaging, subcellular fractionation, and domain-mapping assays with site-specific mutagenesis and purified recombinant proteins, we further characterized the Srx-TXNDC5 interaction. In response to ER-stress but not to oxidative stress, Srx exhibits an increased association with TXNDC5, facilitating the retention of Srx in the ER. Of note, TXNDC5 knockdown in lung cancer cells inhibited cell proliferation and repressed anchorage-independent colony formation and migration, but increased cell invasion and activation of mitogen-activated protein kinases. Using immunohistochemical staining, we demonstrate that TXNDC5 is highly expressed in patient-derived lung cancer specimens. Bioinformatics analysis of publicly available datasets revealed that those with high Srx levels have significantly shorter survival and that those with high TXNDC5 levels have longer survival. We conclude that the cellular levels of Srx and TXNDC5 may be useful as biomarkers to predict the survival of individuals with lung cancer.
    Keywords:  antioxidant; enzyme mechanism; oxidative stress; protein disulfide isomerase; protein-protein interaction; proteomics; pulmonary carcinoma; sulfiredoxin; thioredoxin-domain containing 5; tumorigenesis
  8. PLoS Pathog. 2019 Apr 18. 15(4): e1007734
    Pinter N, Hach CA, Hampel M, Rekhter D, Zienkiewicz K, Feussner I, Poehlein A, Daniel R, Finkernagel F, Heimel K.
      The corn smut fungus Ustilago maydis requires the unfolded protein response (UPR) to maintain homeostasis of the endoplasmic reticulum (ER) during the biotrophic interaction with its host plant Zea mays (maize). Crosstalk between the UPR and pathways controlling pathogenic development is mediated by protein-protein interactions between the UPR regulator Cib1 and the developmental regulator Clp1. Cib1/Clp1 complex formation results in mutual modification of the connected regulatory networks thereby aligning fungal proliferation in planta, efficient effector secretion with increased ER stress tolerance and long-term UPR activation in planta. Here we address UPR-dependent gene expression and its modulation by Clp1 using combinatorial RNAseq/ChIPseq analyses. We show that increased ER stress resistance is connected to Clp1-dependent alterations of Cib1 phosphorylation, protein stability and UPR gene expression. Importantly, we identify by deletion screening of UPR core genes the signal peptide peptidase Spp1 as a novel key factor that is required for establishing a compatible biotrophic interaction between U. maydis and its host plant maize. Spp1 is dispensable for ER stress resistance and vegetative growth but requires catalytic activity to interfere with the plant defense, revealing a novel virulence specific function for signal peptide peptidases in a biotrophic fungal/plant interaction.