bims-unfpre Biomed news
on Unfolded protein response
Issue of 2019‒01‒13
twelve papers selected by
Susan Logue
Apoptosis Research Centre


  1. PLoS One. 2019 ;14(1): e0209824
    Thamsen M, Ghosh R, Auyeung VC, Brumwell A, Chapman HA, Backes BJ, Perara G, Maly DJ, Sheppard D, Papa FR.
      Endoplasmic reticulum stress (ER stress) has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF), a disease of progressive fibrosis and respiratory failure. ER stress activates a signaling pathway called the unfolded protein response (UPR) that either restores homeostasis or promotes apoptosis. The bifunctional kinase/RNase IRE1α is a UPR sensor/effector that promotes apoptosis if ER stress remains high and irremediable (i.e., a "terminal" UPR). Using multiple small molecule inhibitors against IRE1α, we show that ER stress-induced apoptosis of murine alveolar epithelial cells can be mitigated in vitro. In vivo, we show that bleomycin exposure to murine lungs causes early ER stress to activate IRE1α and the terminal UPR prior to development of pulmonary fibrosis. Small-molecule IRE1α kinase-inhibiting RNase attenuators (KIRAs) that we developed were used to evaluate the contribution of IRE1α activation to bleomycin-induced pulmonary fibrosis. One such KIRA-KIRA7-provided systemically to mice at the time of bleomycin exposure decreases terminal UPR signaling and prevents lung fibrosis. Administration of KIRA7 14 days after bleomycin exposure even promoted the reversal of established fibrosis. Finally, we show that KIRA8, a nanomolar-potent, monoselective KIRA compound derived from a completely different scaffold than KIRA7, likewise promoted reversal of established fibrosis. These results demonstrate that IRE1α may be a promising target in pulmonary fibrosis and that kinase inhibitors of IRE1α may eventually be developed into efficacious anti-fibrotic drugs.
    DOI:  https://doi.org/10.1371/journal.pone.0209824
  2. Chem Asian J. 2019 Jan 07.
    Liew LP, Singleton DC, Wong WW, Cheng GJ, Jamieson SMF, Hay M.
      Tumour hypoxia plays an important role in tumour progression and resistance to therapy. Under hypoxia unfolded proteins accumulate in the endoplasmic reticulum (ER) and this stress is relieved through the protein kinase R-like ER kinase (PERK) signalling arm of the unfolded protein response (UPR). Targeting the UPR through PERK kinase inhibitors provides tumour growth inhibition, but also elicits on-mechanism normal tissue toxicity. Hypoxia presents a target for tumour-selective drug delivery using hypoxia-activated prodrugs. We designed and prepared hypoxia-activated prodrugs of modified PERK inhibitors using a 2-nitromidazole bioreductive trigger. The new inhibitors retained PERK kinase inhibitory activity and the corresponding prodrugs were strongly deactivated. The prodrugs were able to undergo fragmentation following radiolytic reduction, or bioreduction in HCT116 cells, to release their effectors, albeit inefficiently. We examined the effects of the prodrugs on PERK signalling in hypoxic HCT116 cells. This study has identified a 2-substituted nitroimidazole carbamate prodrug with potential to deliver PERK inhibitors in a hypoxia selective manner.
    Keywords:  drug delivery; hypoxia; kinase inhibitor; nitroimidazole; prodrug
    DOI:  https://doi.org/10.1002/asia.201801826
  3. Front Immunol. 2018 ;9 2934
    Gómez-Fernández P, Urtasun A, Paton AW, Paton JC, Borrego F, Dersh D, Argon Y, Alloza I, Vandenbroeck K.
      The human IL22RA2 gene co-produces three protein isoforms in dendritic cells [IL-22 binding protein isoform-1 (IL-22BPi1), IL-22BPi2, and IL-22BPi3]. Two of these, IL-22BPi2 and IL-22BPi3, are capable of neutralizing the biological activity of IL-22. The function of IL-22BPi1, which differs from IL-22BPi2 through an in-frame 32-amino acid insertion provided by an alternatively spliced exon, remains unknown. Using transfected human cell lines, we demonstrate that IL-22BPi1 is secreted detectably, but at much lower levels than IL-22BPi2, and unlike IL-22BPi2 and IL-22BPi3, is largely retained in the endoplasmic reticulum (ER). As opposed to IL-22BPi2 and IL-22BPi3, IL-22BPi1 is incapable of neutralizing or binding to IL-22 measured in bioassay or assembly-induced IL-22 co-folding assay. We performed interactome analysis to disclose the mechanism underlying the poor secretion of IL-22BPi1 and identified GRP78, GRP94, GRP170, and calnexin as main interactors. Structure-function analysis revealed that, like IL-22BPi2, IL-22BPi1 binds to the substrate-binding domain of GRP78 as well as to the middle domain of GRP94. Ectopic expression of wild-type GRP78 enhanced, and ATPase-defective GRP94 mutant decreased, secretion of both IL-22BPi1 and IL-22BPi2, while neither of both affected IL-22BPi3 secretion. Thus, IL-22BPi1 and IL-22BPi2 are bona fide clients of the ER chaperones GRP78 and GRP94. However, only IL-22BPi1 activates an unfolded protein response (UPR) resulting in increased protein levels of GRP78 and GRP94. Cloning of the IL22RA2 alternatively spliced exon into an unrelated cytokine, IL-2, bestowed similar characteristics on the resulting protein. We also found that CD14++/CD16+ intermediate monocytes produced a higher level of IL22RA2 mRNA than classical and non-classical monocytes, but this difference disappeared in immature dendritic cells (moDC) derived thereof. Upon silencing of IL22RA2 expression in moDC, GRP78 levels were significantly reduced, suggesting that native IL22RA2 expression naturally contributes to upregulating GRP78 levels in these cells. The IL22RA2 alternatively spliced exon was reported to be recruited through a single mutation in the proto-splice site of a Long Terminal Repeat retrotransposon sequence in the ape lineage. Our work suggests that positive selection of IL-22BPi1 was not driven by IL-22 antagonism as in the case of IL-22BPi2 and IL-22BPi3, but by capacity for induction of an UPR response.
    Keywords:  GRP78; GRP94; IL-22; IL-22BP; UPR; dendritic cells; exonization; isoform
    DOI:  https://doi.org/10.3389/fimmu.2018.02934
  4. BMC Immunol. 2019 Jan 10. 20(1): 3
    Poe C, Youngblood C, Hodge K, Kemp K.
      BACKGROUND: T cell activation induces ER stress and upregulates Inositol Requiring Enzyme 1 alpha (IRE1α), an activator of the unfolded protein response (UPR) pathway. Inhibition of IRE1α RNase activity in activated CD4+ splenocytes from naïve mice, via treatment of the cells with the commercially available drug 4μ8c upon activation, results in the reduction of the secretion of proteins IL-5, IL-4, and IL-13. Prior to this work, it was unknown if 4μ8c could inhibit TH2 cytokines in established TH2 cells, cells that are crucial in promoting disease in severe asthma.RESULTS: Treatment of a mouse T helper (TH)2 cell line and differentiated human TH2 cells with 4μ8c resulted in inhibition of IL-5, but not IL-4, as measured by ELISA. The reduced cytokine expression was not due to differences in mRNA stability or mRNA levels; it appears to be due to a defect in secretion, as the cells produce cytokines IL-5 as measured by flow cytometry and western blot.
    CONCLUSION: These data suggest that the inhibition of IL-5 was due to post-translational processes. IL-5 promotes chronic, inflammatory asthma, and 4μ8c blocks its expression in T cells in vitro. Future studies will determine if 4μ8c treatment can ameliorate the effects of the cytokine IL-5 in a disease model.
    Keywords:  4μ8c; IL-5; IRE1α; Protein secretion; TH2
    DOI:  https://doi.org/10.1186/s12865-018-0283-7
  5. Blood Adv. 2019 Jan 08. 3(1): 51-62
    Best S, Hashiguchi T, Kittai A, Bruss N, Paiva C, Okada C, Liu T, Berger A, Danilov AV.
      Alterations in the ubiquitin proteasome system (UPS) leave malignant cells in heightened cellular stress, making them susceptible to proteasome inhibition. However, given the limited efficacy of proteasome inhibitors in non-Hodgkin lymphoma (NHL), novel approaches to target the UPS are needed. Here, we show that TAK-243, the first small-molecule inhibitor of the ubiquitin activating enzyme (UAE) to enter clinical development, disrupts all ubiquitin signaling and global protein ubiquitination in diffuse large B-cell lymphoma (DLBCL) cells, thereby inducing endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). Activation of the ER stress response protein kinase R (PKR)-like ER kinase and phosphorylation of eukaryotic translation initiator factor 2α led to upregulation of the proapoptotic molecule C/EBP homologous protein and cell death across a panel of DLBCL cell lines independent of cell of origin. Concurrently, targeting UAE led to accumulation of Cdt1, a replication licensing factor, leading to DNA rereplication, checkpoint activation, and cell cycle arrest. MYC oncoprotein sensitized DLBCL cells to UAE inhibition; engineered expression of MYC enhanced while genetic MYC knockdown protected from TAK-243-induced apoptosis. UAE inhibition demonstrated enhanced ER stress and UPR and increased potency compared with bortezomib in DLBCL cell lines. In vivo treatment with TAK-243 restricted the growth of xenografted DLBCL tumors, accompanied by reduced cell proliferation and apoptosis. Finally, primary patient-derived DLBCL cells, including those expressing aberrant MYC, demonstrated susceptibility to UAE inhibition. In sum, targeting UAE may hold promise as a novel therapeutic approach in NHL.
    DOI:  https://doi.org/10.1182/bloodadvances.2018026880
  6. Sci Rep. 2019 Jan 11. 9(1): 66
    De Santi M, Baldelli G, Diotallevi A, Galluzzi L, Schiavano GF, Brandi G.
      Autophagy is a cellular mechanism by which cells degrade intracellular components in lysosomes, maintaining cellular homeostasis. It has been hypothesized that autophagy could have a role in cancer prevention through the elimination of damaged proteins and organelles; this could explain epidemiological evidence showing the chemopreventive properties of the autophagy-inducer metformin. In this study, we analyzed the autophagy-related effect of metformin in both cancer initiation and progression in non-tumorigenic cells. We also analyzed the induction of tumorigenesis in autophagy-deficient cells, and its correlation with the ER stress. Our results showed that metformin induced massive cell death in preneoplastic JB6 Cl 41-5a cells treated with tumor promoter (phorbol) and in NIH/3T3 treated with H2O2. Inhibiting autophagy with wortmannin or ATG7 silencing, the effect of metformin decreased, indicating an autophagy-related cytotoxic activity under stress conditions. We also found an induction of tumorigenesis in ATG7-silenced NIH/3T3 cell clone (3T3-619C3 cells), but not in wild-type and in scrambled transfected cells, and an upregulation of unfolded protein response (UPR) markers in 3T3-619C3 cells treated with H2O2. These findings suggest that autophagic cell death could be considered as a new mechanism by which eliminate damaged cells, representing an attractive strategy to eliminate potential tumorigenic cells.
    DOI:  https://doi.org/10.1038/s41598-018-37247-6
  7. J Exp Clin Cancer Res. 2019 Jan 08. 38(1): 8
    Li Z, Zhang L, Gao M, Han M, Liu K, Zhang Z, Gong Z, Xing L, Shi X, Lu K, Gao H.
      BACKGROUND: Xanthoangelol (XAG) was reported to exhibit antitumor properties in several cancer. However, the specific anti-tumor activity of XAG in human hepatocellular carcinoma (HCC) and the relevant mechanisms are not known.METHODS: The effects of XAG on HCC cell proliferation and apoptosis were respectively examined by CCK-8 assay and Annexin V-FITC/PI apoptosis kit. Western blotting was conducted to detect the expression of proteins. The effect of XAG on the development of acidic vesicle organelles was assessed using acridine orange staining. mRFP-GFP-LC3 adenovirus was used to transfect HCC cells and the formation of autolysosome was detected using a confocal microscope.
    RESULTS: Mechanistically, XAG promotes HCC cell death through triggering intrinsic apoptosis pathway, not extrinsic apoptotic pathway. Furthermore, XAG treatment induced autophagy in Bel 7402 and SMMC 7721 cells, as evidenced by an increase in autophagy-associated proteins, including LC3B-II, Beclin-1, and Atg5. Interestingly, inhibition of autophagy with 3-MA, Bafilomycin A1 (Baf A1), or siRNA targeting Atg5 effectively enhanced the apoptotic cell ratio in XAG-treated cells, indicating that protective effect of autophagy induced by XAG in HCC. Moreover, autophagy induced by XAG was mediated by activating endoplasmic reticulum stress (ERS), along with administration of XAG, the expression levels of ERS-associated proteins, including CHOP, GRP78, ATF6, p-eIF2α, IRE1α, and cleaved caspase-12 were significantly increased in HCC cells. Meanwhile, suppressing ERS with chemical chaperones (TUDCA) or CHOP shRNA could effectively abrogate the autophagy-inducing effect of XAG, and increase the apoptotic cell death. Further mechanistic studies showed that ERS-induced autophagy in XAG-treated cells was mediated by activation of JNK/c-jun pathway. XAG treatment resulted in the increase of p-JNK and p-c-jun, while suppressing ERS with TUDCA or CHOP shRNA could effectively reverse it. Meanwhile, SP600125, a JNK inhibitor, effectively reversed XAG-induced protective autophagy and enhanced cell apoptosis in XAG-treated HCC cells. In vivo results demonstrated that XAG exerts potent antitumor properties with low toxicity.
    CONCLUSIONS: Collectively, these results suggested that XAG could be served as a promising candidate for the treatment and prevention of HCC.
    Keywords:  Apoptosis; Autophagy; ER stress; HCC; XAG
    DOI:  https://doi.org/10.1186/s13046-018-1012-z
  8. Front Genet. 2018 ;9 658
    Chen C, Zhong Y, Wang JJ, Yu Q, Plafker K, Plafker S, Zhang SX.
      Normal function of the retinal pigment epithelium (RPE) is essential for maintaining the structural integrity of retinal photoreceptors and the visual process. Sustained oxidative damage of the RPE due to aging and other risk factors contributes to the development of age-related macular degeneration (AMD). The transcription factor NF-E2-related factor 2 (Nrf2) is a central regulator of cellular antioxidant and detoxification responses. Enhancing Nrf2 function protects RPE cells from oxidation-related apoptosis and cell death. Previously, we demonstrated that Nrf2 activation can be induced by endoplasmic reticulum (ER) stress; however, the mechanisms are not fully understood. In the present study, we examined the role of X box-binding protein 1 (XBP1), an ER stress-inducible transcription factor, in regulation of Nrf2 in the RPE. We found that RPE-specific XBP1 conditional knockout (cKO) mice exhibit a significant reduction in Nrf2 mRNA and protein levels, along with decreased expression of major Nrf2 target genes, in the RPE/choroid complex. Using primary RPE cells isolated from XBP1 cKO mice and human ARPE-19 cell line, we confirmed that loss of XBP1 gene or pharmacological inhibition of XBP1 splicing drastically reduces Nrf2 levels in the RPE. Conversely, overexpression of spliced XBP1 results in a modest but significant increase in cytosolic and nuclear Nrf2 protein levels without affecting the transcription of Nrf2 gene. Moreover, induction of ER stress by tunicamycin and thapsigargin markedly increases Nrf2 expression, which is abolished in cells pretreated with XBP1 splicing inhibitors 4μ8C and quinotrierixin. Mechanistic studies indicate that quinotrierixin reduces Nrf2 expression likely through inhibition of protein translation. Finally, we demonstrate that overexpression of Nrf2 protected RPE cells against oxidative injury but appeared to be insufficient to rescue from XBP1 deficiency-induced cell death. Taken together, our results indicate that XBP1 modulates Nrf2 activity in RPE cells and that XBP1 deficiency contributes to oxidative injury of the RPE.
    Keywords:  NF-E2-related factor 2; X-box binding protein 1; cell death; endoplasmic reticulum stress; oxidative stress; retinal pigment epithelium
    DOI:  https://doi.org/10.3389/fgene.2018.00658
  9. J Cell Physiol. 2019 Jan 12.
    Yu Y, Xia X, Li H, Zhang Y, Zhou X, Jiang H.
      Rhodopsin mutations are associated with the autosomal-dominant form of retinitis pigmentosa (RP). Here we report simultaneous occurrence of RP associated with bilateral nanophthalmos and acute angle-closure glaucoma in patient with a new mutation in rhodopsin (R135W). ARPE-19 cells were transfected with myc-tagged wild-type (WT) and R135W rhodopsin constructs. The half-life of WT and R135W rhodopsin was analyzed via cycloheximide chase analysis. We found that R135W rhodopsin was accumulated in the endoplasmic reticulum (ER) and induced unfolded protein response (UPR) and apoptosis. Moreover, chaperone HSP70 alleviated ER stress and prevented apoptosis induced by R135W rhodopsin by attenuating UPR signaling. These findings reveal the novel pathogenic mechanism of RP and suggest that chaperone HSP70 has potential therapeutic significance for RP.
    Keywords:  HSP70; apoptosis; endoplasmic reticulum; mutation; retinitis pigmentosa; rhodopsin; unfolded protein response
    DOI:  https://doi.org/10.1002/jcp.28100
  10. Trends Immunol. 2019 Jan 03. pii: S1471-4906(18)30227-8. [Epub ahead of print]
    Song M, Cubillos-Ruiz JR.
      Protective anti-tumor immune responses are mediated by effector molecules that enable successful elimination of malignant cells. As the site where transmembrane and secreted proteins are generated, the endoplasmic reticulum (ER) of immune cells plays a key role in this process. Recent studies have indicated that adverse conditions within tumors perturb ER homeostasis in infiltrating immune cells, which can impede the development of effective anti-cancer immunity. Here, we describe how the tumor microenvironment induces ER stress in immune cells, and discuss the detrimental consequences of persistent ER stress responses in intratumoral immune populations. We also explore the concept of targeting ER stress responses to reinvigorate endogenous anti-tumor immunity and enhance the efficacy of various forms of cancer immunotherapy.
    Keywords:  ER stress; cancer; immune cells; immunotherapy; tumor microenvironment; unfolded protein response
    DOI:  https://doi.org/10.1016/j.it.2018.12.001
  11. Cancers (Basel). 2019 Jan 09. pii: E66. [Epub ahead of print]11(1):
    Guang MHZ, Kavanagh EL, Dunne LP, Dowling P, Zhang L, Lindsay S, Bazou D, Goh CY, Hanley C, Bianchi G, Anderson KC, O'Gorman P, McCann A.
      Despite significant advances in cancer diagnostics and therapeutics the majority of cancer unfortunately remains incurable, which has led to continued research to better understand its exceptionally diverse biology. As a result of genomic instability, cancer cells typically have elevated proteotoxic stress. Recent appreciation of this functional link between the two secondary hallmarks of cancer: aneuploidy (oxidative stress) and proteotoxic stress, has therefore led to the development of new anticancer therapies targeting this emerging "Achilles heel" of malignancy. This review highlights the importance of managing proteotoxic stress for cancer cell survival and provides an overview of the integral role proteostasis pathways play in the maintenance of protein homeostasis. We further review the efforts undertaken to exploit proteotoxic stress in multiple myeloma (as an example of a hematologic malignancy) and triple negative breast cancer (as an example of a solid tumor), and give examples of: (1) FDA-approved therapies in routine clinical use; and (2) promising therapies currently in clinical trials. Finally, we provide new insights gleaned from the use of emerging technologies to disrupt the protein secretory pathway and repurpose E3 ligases to achieve targeted protein degradation.
    Keywords:  autophagy; chemoresistance; multiple myeloma; proteasome; protein quality control; proteotoxic stress; triple negative breast cancer; unfolded protein response
    DOI:  https://doi.org/10.3390/cancers11010066
  12. Cold Spring Harb Perspect Biol. 2019 Jan 07. pii: a033944. [Epub ahead of print]
    Naresh NU, Haynes CM.
      The mitochondrial proteome encompasses more than a thousand proteins, which are encoded by the mitochondrial and nuclear genomes. Mitochondrial biogenesis and network health relies on maintenance of protein import pathways and the protein-folding environment. Cell-extrinsic or -intrinsic stressors that challenge mitochondrial proteostasis negatively affect organellar function. During conditions of stress, cells use impaired protein import as a sensor for mitochondrial dysfunction to activate a stress response called the mitochondrial unfolded protein response (UPRmt). UPRmt activation leads to an adaptive transcriptional program that promotes mitochondrial recovery, metabolic adaptations, and innate immunity. In this review, we discuss the regulation of UPRmt activation as well as its role in maintaining mitochondrial homeostasis in physiological and pathological scenarios.
    DOI:  https://doi.org/10.1101/cshperspect.a033944