bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒03‒01
eight papers selected by
Susan Logue
University of Manitoba


  1. J Biol Chem. 2020 Feb 27. pii: jbc.RA119.010655. [Epub ahead of print]
    Okamoto Y, Saito T, Tani Y, Toki T, Hasebe A, Koido M, Tomida A.
      As a branch of the unfolded protein response, protein kinase R-like endoplasmic reticulum kinase (PERK) represses global translation in response to endoplasmic reticulum (ER) stress. This pathophysiological condition is associated with the tumor microenvironment in cancer. Previous findings in our lab have suggested that PERK selectively represses translation of some mRNAs, but this possibility awaits additional investigation. In the present study, we show that a stem cell marker protein, leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), is rapidly depleted in colon cancer cells during ER stress, an effect that depended on the PERK-mediated translational repression. Indeed, the PERK inhibition led to the accumulation of premature, underglycosylated forms of LGR5, which were produced only at low levels during proper PERK activation. Unlike the mature LGR5 form, which is constitutively degraded regardless of PERK activation, the underglycosylated LGR5 exhibited a prolonged half-life and accumulated inside the cells without being expressed on the cell surface. We also found that Erb-B2 receptor tyrosine kinase 3 (ERBB3) is subjected to a similar regulated depletion by PERK, whereas epidermal growth factor (EGFR), stress-inducible heat shock protein family A (Hsp70) member 5 (HSPA5), and anterior gradient 2 protein disulfide isomerase family member (AGR2) were relatively insensitive to the PERK-mediated repression of translation. These results indicate that LGR5 and ERBB3 are targets for PERK-mediated translational repression during ER stress.
    Keywords:  colon cancer; endoplasmic reticulum stress (ER stress); eukaryotic initiation factor 2 (eIF2); kinase signaling; leucine-rich repeat-containing G-protein-coupled receptor 5(LGR5); protein kinase R-like ER kinase (PERK); protein stability; protein synthesis; unfolded protein response (UPR)
    DOI:  https://doi.org/10.1074/jbc.RA119.010655
  2. Mol Cancer Res. 2020 Feb 26. pii: molcanres.0673.2019. [Epub ahead of print]
    Yoneda A, Sakai-Sawada K, Minomi K, Tamura Y.
      Heat shock protein 47 (HSP47) is a collagen-specific protein chaperone expressed in fibroblasts, myofibroblasts and stromal cells. HSP47 is also expressed in and involved in growth of cancer cells in which collagen levels are extremely low. However, its role in cancer remains largely unclear. Here, we showed that HSP47 maintains cancer cell growth via the unfolded protein response (UPR), the activation of which is well known to be induced by endoplasmic reticulum (ER) stress. We observed that HSP47 forms a complex with both the UPR transducer inositol-requiring enzyme 1α (IRE1α) and ER chaperone BiP in cancer cells. Moreover, HSP47 silencing triggered dissociation of BiP from IRE1α and IRE1α activation, followed by an increase in the intracellular level of reactive oxygen species (ROS). Increase in ROS induced accumulation of 4-hydroxy-2-nonenal-protein adducts and activated two UPR transducers, PKR-like ER kinase (PERK) and activating transcription factor 6α (ATF6α), resulting in impaired cancer cell growth. Our work indicates that HSP47 expressed in cancer cells relieves the ER stress arising from protein synthesis overload within these cells and tumor environments, such as stress induced by hypoxia, low glucose and pH. We also propose that HSP47 has a biological role that is distinct from its normal function as a collagen-specific chaperone. Implications: HSP47 maintains cancer cell growth by inhibiting IRE1α.
    DOI:  https://doi.org/10.1158/1541-7786.MCR-19-0673
  3. Cells. 2020 Feb 26. pii: E540. [Epub ahead of print]9(3):
    Jaud M, Philippe C, Di Bella D, Tang W, Pyronnet S, Laurell H, Mazzolini L, Rouault-Pierre K, Touriol C.
      During carcinogenesis, almost all the biological processes are modified in one way or another. Among these biological processes affected, anomalies in protein synthesis are common in cancers. Indeed, cancer cells are subjected to a wide range of stresses, which include physical injuries, hypoxia, nutrient starvation, as well as mitotic, oxidative or genotoxic stresses. All of these stresses will cause the accumulation of unfolded proteins in the Endoplasmic Reticulum (ER), which is a major organelle that is involved in protein synthesis, preservation of cellular homeostasis, and adaptation to unfavourable environment. The accumulation of unfolded proteins in the endoplasmic reticulum causes stress triggering an unfolded protein response in order to promote cell survival or to induce apoptosis in case of chronic stress. Transcription and also translational reprogramming are tightly controlled during the unfolded protein response to ensure selective gene expression. The majority of stresses, including ER stress, induce firstly a decrease in global protein synthesis accompanied by the induction of alternative mechanisms for initiating the translation of mRNA, later followed by a translational recovery. After a presentation of ER stress and the UPR response, we will briefly present the different modes of translation initiation, then address the specific translational regulatory mechanisms acting during reticulum stress in cancers and highlight the importance of translational control by ER stress in tumours.
    Keywords:  ER stress; translation initiation; uORF; unfolded protein response (UPR), IRES
    DOI:  https://doi.org/10.3390/cells9030540
  4. J Exp Clin Cancer Res. 2020 Feb 28. 39(1): 44
    Xu H, Liu P, Yan Y, Fang K, Liang D, Hou X, Zhang X, Wu S, Ma J, Wang R, Li T, Piao H, Meng S.
      BACKGROUND: FK506-binding protein 9 (FKBP9) is amplified in high-grade gliomas (HGGs). However, the roles and mechanism(s) of FKBP9 in glioma are unknown.METHODS: The expression of FKBP9 in clinical glioma tissues was detected by immunohistochemistry (IHC). The correlation between FKBP9 expression levels and the clinical prognosis of glioma patients was examined by bioinformatic analysis. Glioblastoma (GBM) cell lines stably depleted of FKBP9 were established using lentiviruses expressing shRNAs against FKBP9. The effects of FKBP9 on GBM cells were determined by cell-based analyses, including anchorage-independent growth, spheroid formation, transwell invasion assay, confocal microscopy, immunoblot (IB) and coimmunoprecipitation assays. In vivo tumor growth was determined in both chick chorioallantoic membrane (CAM) and mouse xenograft models.
    RESULTS: High FKBP9 expression correlated with poor prognosis in glioma patients. Knockdown of FKBP9 markedly suppressed the malignant phenotype of GBM cells in vitro and inhibited tumor growth in vivo. Mechanistically, FKBP9 expression induced the activation of p38MAPK signaling via ASK1. Furthermore, ASK1-p38 signaling contributed to the FKBP9-mediated effects on GBM cell clonogenic growth. In addition, depletion of FKBP9 activated the IRE1α-XBP1 pathway, which played a role in the FKBP9-mediated oncogenic effects. Importantly, FKBP9 expression conferred GBM cell resistance to endoplasmic reticulum (ER) stress inducers that caused FKBP9 ubiquitination and degradation.
    CONCLUSIONS: Our findings suggest an oncogenic role for FKBP9 in GBM and reveal FKBP9 as a novel mediator in the IRE1α-XBP1 pathway.
    Keywords:  Endoplasmic reticulum (ER) stress; FK506-binding protein 9; Glioma; IRE1α-XBP1; Unfolded protein response (UPR)
    DOI:  https://doi.org/10.1186/s13046-020-1541-0
  5. J Biol Chem. 2020 Feb 26. pii: jbc.RA119.011766. [Epub ahead of print]
    Moilanen A, Ruddock LW.
      Protein maturation in the endoplasmic reticulum (ER) depends on a fine balance between oxidative protein folding and quality control mechanisms, which together ensure high-capacity export of properly folded proteins from the ER. Oxidative protein folding needs to be regulated to avoid hyperoxidation. The folding capacity of the ER is regulated by the unfolded protein response (UPR) and ER-associated degradation (ERAD). The UPR is triggered by unfolded protein stress and leads to up-regulation of cellular components such as chaperones and folding catalysts. These components relieve stress by increasing folding capacity and up-regulating ERAD components that remove non-native proteins. Although oxidative protein folding and the UPR/ERAD pathways each are well understood, very little is known about any direct cross-talk between them. In this study, we carried out comprehensive in vitro activity and binding assays, indicating that the oxidative protein folding relay formed by ER oxidoreductin 1 (Ero1) and protein disulfide isomerase (PDI) can be inactivated by a feedback inhibition mechanism involving unfolded proteins and folding intermediates when their levels exceed the folding capacity of the system. This mechanism allows client proteins to remain mainly in the reduced state and thereby minimizes potential futile oxidation-reduction cycles and may also enhance ERAD, which requires reduced protein substrates. Relief from excess levels of non-native proteins by increasing the levels of folding factors removed the feedback inhibition. These results reveal regulatory cross-talk between the oxidative protein folding and UPR and ERAD pathways.
    Keywords:  ER oxidoreductin (Ero1); disulfide; endoplasmic-reticulum-associated protein degradation (ERAD); feedback inhibition; hyperoxidation; oxidative folding; protein disulfide isomerase; protein misfolding; regulation; unfolded protein response (UPR)
    DOI:  https://doi.org/10.1074/jbc.RA119.011766
  6. Stem Cell Res. 2020 Feb 12. pii: S1873-5061(20)30036-2. [Epub ahead of print]43 101732
    Kim JS, Hwang SI, Ryu JL, Hong HS, Lee JM, Lee SM, Jin X, Han C, Kim JH, Han J, Lee MR, Woo DH.
      Endoplasmic reticulum stress (ER stress) leads an unfolded protein response (UPR) which results in internal cellular responses such as proteostasis and protein clearance. Recently, several reports demonstrated that the ER stress in stem cells could affect their stemness and fates to differentiate into certain lineages. However, the potential for controlling differentiation and function of cells by regulating ER stress needs to be further addressed. Here, we demonstrated that relieving the ER stress in cell cultures enhances the functionalities of hPSC-derived hepatocytes and other hepatic cells to be used in various research fields. Firstly, we found that UPR genes were up-regulated during hepatic differentiation of hPSCs and treatment of ER stress reliever at the hepatic induction stage of the differentiation resulted the enhanced mature marker expressions and glycogen storage of the differentiated hepatocytes. The treatment of ER stress reliever also improved the maintenance of hepatic characteristics in long-term culture of hPSC-derived hepatocytes. Furthermore, relieving ER stress increased the hepatic marker expression and CYP3A4 activity in hepatoma cell lines and human primary hepatocytes. Taken together, our findings indicate that regulating ER stress of in vitro cultured hepatocytes might be a crucial factor for enhancing differentiation, function and maintaining hepatic identity.
    Keywords:  Differentiation; ER stress; Function; Hepatic cells; Pluripotent stem cells
    DOI:  https://doi.org/10.1016/j.scr.2020.101732
  7. Oncogene. 2020 Feb 26.
    Olou AA, King RJ, Yu F, Singh PK.
      The Mucin 1 (MUC1) protein is overexpressed in various cancers and mediates chemotherapy resistance. However, the mechanism is not fully understood. Given that most chemotherapeutic drugs disrupt ER homeostasis as part of their toxicity, and MUC1 expression is regulated by proteins involved in ER homeostasis, we investigated the link between MUC1 and ER homeostasis. MUC1 knockdown in pancreatic cancer cells enhanced unfolded protein response (UPR) signaling and cell death upon ER stress induction. Transcriptomic analysis revealed alterations in the pyrimidine metabolic pathway and cytidine deaminase (CDA). ChIP and CDA activity assays showed that MUC1 occupied CDA gene promoter upon ER stress induction correlating with increased CDA expression and activity in MUC1-expressing cells as compared with MUC1 knockdown cells. Inhibition of either the CDA or pyrimidine metabolic pathway diminished survival in MUC1-expressing cancer cells upon ER stress induction. Metabolomic analysis demonstrated that MUC1-mediated CDA activity corresponded to deoxycytidine to deoxyuridine metabolic reprogramming upon ER stress induction. The resulting increase in deoxyuridine mitigated ER stress-induced cytotoxicity. In addition, given (1) the established roles of MUC1 in protecting cells against reactive oxygen species (ROS) insults, (2) ER stress-generated ROS further promote ER stress and (3) the emerging anti-oxidant property of deoxyuridine, we further investigated if MUC1 regulated ER stress by a deoxyuridine-mediated modulation of ROS levels. We observed that deoxyuridine could abrogate ROS-induced ER stress to promote cancer cell survival. Taken together, our findings demonstrate a novel MUC1-CDA axis of the adaptive UPR that provides survival advantage upon ER stress induction.
    DOI:  https://doi.org/10.1038/s41388-020-1225-4
  8. Dev Cell. 2020 Feb 12. pii: S1534-5807(20)30063-0. [Epub ahead of print]
    Sullivan GP, O'Connor H, Henry CM, Davidovich P, Clancy DM, Albert ML, Cullen SP, Martin SJ.
      Inflammation triggered by infection or cellular necrosis is initiated by a battery of pattern-recognition receptors, such as Toll-like receptors or IL-1 family receptors. Diverse forms of cell stress, such as ER stress or mitochondrial stress, can also promote inflammatory responses that contribute to the chronic inflammation observed in cancer, obesity, and other conditions. However, the molecular mechanisms of cell-stress-induced inflammation are poorly understood. Here, we show that ER stress initiated NF-κB activation and inflammation through transcriptional upregulation and ligand-independent activation of TRAIL receptors. ER-stress-induced TRAIL receptor activation resulted in caspase-8/FADD/RIPK1-dependent NF-κB activation and inflammatory cytokine production. Silencing or deletion of TRAIL receptors, or their downstream effectors caspase-8, FADD, or RIPK1, suppressed ER-stress-induced inflammation. Furthermore, chemotherapeutic stress-induced inflammatory responses were blunted in DR5/TRAIL-R null animals. We propose that, upon ER stress, TRAIL receptors serve as "stress-associated molecular patterns (SAMPs)" coupling ER stress to NF-κB-dependent inflammation.
    Keywords:  DR4; DR5; ER Stress; NF-κB; RIPK1; SAMP; TRAIL; death receptors; inflammation; taxol
    DOI:  https://doi.org/10.1016/j.devcel.2020.01.031