bims-ershed Biomed News
on ER Stress in Health and Diseases
Issue of 2023–05–14
six papers selected by
Matías Eduardo González Quiroz, Worker’s Hospital
  1. Activation of XBP1 but not ATF6α rescues heart failure induced by persistent ER stress in medaka fish.
  2. Activation of the PERK branch of the unfolded protein response during production reduces specific productivity in CHO cells via downregulation of PDGFRa and IRE1a signaling.
  3. SARS-CoV-2 Nonstructural Proteins 3 and 4 tune the Unfolded Protein Response.
  4. Targeting XBP1 mRNA splicing sensitizes glioblastoma to chemotherapy.
  5. Protein quality control and aggregation in the endoplasmic reticulum: From basic to bedside.
  6. Endoplasmic reticulum in oocytes: spatiotemporal distribution and function.
  1. Life Sci Alliance. 2023 Jul;pii: e202201771. [Epub ahead of print]6(7):
    Activation of XBP1 but not ATF6α rescues heart failure induced by persistent ER stress in medaka fish.
    Byungseok Jin, Tokiro Ishikawa, Makoto Kashima, Rei Komura, Hiromi Hirata, Tetsuya Okada, Kazutoshi Mori.
      The unfolded protein response is triggered in vertebrates by ubiquitously expressed IRE1α/β (although IRE1β is gut-specific in mice), PERK, and ATF6α/β, transmembrane-type sensor proteins in the ER, to cope with ER stress, the accumulation of unfolded and misfolded proteins in the ER. Here, we burdened medaka fish, a vertebrate model organism, with ER stress persistently from fertilization by knocking out the AXER gene encoding an ATP/ADP exchanger in the ER membrane, leading to decreased ATP concentration-mediated impairment of the activity of Hsp70- and Hsp90-type molecular chaperones in the ER lumen. ER stress and apoptosis were evoked from 4 and 6 dpf, respectively, leading to the death of all AXER-KO medaka by 12 dpf because of heart failure (medaka hatch at 7 dpf). Importantly, constitutive activation of IRE1α signaling-but not ATF6α signaling-rescued this heart failure and allowed AXER-KO medaka to survive 3 d longer, likely because of XBP1-mediated transcriptional induction of ER-associated degradation components. Thus, activation of a specific pathway of the unfolded protein response can cure defects in a particular organ.
    DOI:  https://doi.org/10.26508/lsa.202201771
  2. Biotechnol Prog. 2023 May 10. e3354
    Activation of the PERK branch of the unfolded protein response during production reduces specific productivity in CHO cells via downregulation of PDGFRa and IRE1a signaling.
    Brian M Castellano, Danming Tang, Scot Marsters, Cynthia Lam, Peter Liu, Christopher M Rose, Wendy Sandoval, Avi Ashkenazi, Brad Snedecor, Shahram Misaghi.
      During the course of biopharmaceutical production, heterologous protein expression in Chinese hamster ovary (CHO) cells imposes a high proteostatic burden that requires cellular adaptation. To mitigate such burden, cells utilize the unfolded protein response (UPR), which increases endoplasmic reticulum (ER) capacity to accommodate elevated rates of protein synthesis and folding. In this study, we show that during production the UPR regulates growth factor signaling to modulate growth and protein synthesis. Specifically, the protein kinase R-like ER kinase (PERK) branch of the UPR is responsible for transcriptional down-regulation of platelet-derived growth factor receptor alpha (PDGFRa) and attenuation of the IRE1-alpha (IRE1a) branch of the UPR. PERK knockout (KO) cell lines displayed reduced growth and viability due to higher rates of apoptosis despite having stabilized PDGFRa levels. Knocking out PERK in an apoptosis impaired (Bax/Bak double KO) antibody-expressing cell line prevented apoptotic cell death and revealed that apoptosis was likely triggered by increased ER stress and reactive oxygen species levels in the PERK KO hosts. Our findings suggest that attenuation of IRE1a and PDGFRa signaling by the PERK branch of the UPR reduces ER protein folding capacity and hence specific productivity of CHO cells in order to mitigate UPR and prevent apoptotic cell death. Last, Bax/Bak/PERK triple KO CHO cell lines displayed 2-3 folds higher specific productivity and titer (up to 8 g/L), suggesting that modulation of PERK signaling during production processes can greatly improve specific productivity in CHO cells.
    Keywords:  Chinese hamster ovary; UPR; apoptosis; bioprocess; fed-batch; growth factor receptor
    DOI:  https://doi.org/10.1002/btpr.3354
  3. bioRxiv. 2023 Apr 24. pii: 2023.04.22.537917. [Epub ahead of print]
    SARS-CoV-2 Nonstructural Proteins 3 and 4 tune the Unfolded Protein Response.
    Jonathan P Davies, Athira Sivadas, Katherine R Keller, Richard J H Wojcikiewicz, Lars Plate.
      Coronaviruses (CoV), including SARS-CoV-2, modulate host proteostasis pathways during infection through activation of stress-responsive signaling pathways such as the Unfolded Protein Response (UPR). The UPR regulates protein translation, increases protein folding capacity and enhances endoplasmic reticulum (ER) biogenesis to alleviate ER stress caused by accumulation of misfolded proteins. CoVs depend on host machinery to generate large amounts of viral protein and manipulate ER-derived membranes to form double-membrane vesicles (DMVs), which serve as replication sites, making the UPR a key host pathway for CoVs to hijack. Despite the importance of CoV nonstructural proteins (nsps) in mediating replication, little is known about the role of nsps in modulating the UPR. We characterized the impact of SARS-CoV-2 nsp4, which is a key driver of DMV formation, on the UPR using quantitative proteomics. We find nsp4 preferentially activates the ATF6 and PERK branches of the UPR. Previously, we found an N-terminal truncation of nsp3 (nsp3.1) can suppress pharmacological activation of the ATF6 pathway. To determine how nsp3.1 and nsp4 might tune the UPR in concert, both proteins were co-expressed demonstrating that nsp3.1 does not suppress nsp4-mediated ATF6 activation but does suppress PERK activation. A meta-analysis of SARS-CoV-2 infection proteomics data reveals a time-dependent activation of PERK protein markers early in infection, which subsequently fades. This temporal regulation suggests a role for nsps tuning the PERK pathway to attenuate host translation beneficial for viral replication while avoiding later apoptotic signaling caused by chronic PERK activation. This work furthers our understanding of CoV-host proteostasis interactions and identifies potential areas to target for anti-viral therapies.
    DOI:  https://doi.org/10.1101/2023.04.22.537917
  4. FASEB Bioadv. 2023 May;5(5): 211-220
    Targeting XBP1 mRNA splicing sensitizes glioblastoma to chemotherapy.
    Amiee Dowdell, Mark Marsland, Sam Faulkner, Craig Gedye, James Lynam, Cassandra P Griffin, Joanne Marsland, Chen Chen Jiang, Hubert Hondermarck.
      Glioblastoma (GBM) is the most frequent and deadly primary brain tumor in adults. Temozolomide (TMZ) is the standard systemic therapy in GBM but has limited and restricted efficacy. Better treatments are urgently needed. The role of endoplasmic reticulum stress (ER stress) is increasingly described in GBM pathophysiology. A key molecular mediator of ER stress, the spliced form of the transcription factor x-box binding protein 1 (XBP1s) may constitute a novel therapeutic target; here we report XBP1s expression and biological activity in GBM. Tumor samples from patients with GBM (n = 85) and low-grade glioma (n = 20) were analyzed by immunohistochemistry for XBP1s with digital quantification. XBP1s expression was significantly increased in GBM compared to low-grade gliomas. XBP1s mRNA showed upregulation by qPCR analysis in a panel of patient-derived GBM cell lines. Inhibition of XBP1 splicing using the small molecular inhibitor MKC-3946 significantly reduced GBM cell viability and potentiated the effect of TMZ in GBM cells, particularly in those with methylated O6-methylguanine-DNA methyl transferase gene promoter. GBM cells resistant to TMZ were also responsive to MKC-3946 and the long-term inhibitory effect of MKC-3946 was confirmed by colony formation assay. In conclusion, this data reveals that XBP1s is overexpressed in GBM and contributes to cancer cell growth. XBP1s warrants further investigation as a clinical biomarker and therapeutic target in GBM.
    Keywords:  XBP1s; cancer biomarkers; glioblastoma; therapeutic targets
    DOI:  https://doi.org/10.1096/fba.2022-00141
  5. Front Cell Dev Biol. 2023 ;11 1156152
    Protein quality control and aggregation in the endoplasmic reticulum: From basic to bedside.
    Guofang Chen, Tingyi Wei, Furong Ju, Haisen Li.
      Endoplasmic reticulum (ER) is the largest membrane-bound compartment in all cells and functions as a key regulator in protein biosynthesis, lipid metabolism, and calcium balance. Mammalian endoplasmic reticulum has evolved with an orchestrated protein quality control system to handle defective proteins and ensure endoplasmic reticulum homeostasis. Nevertheless, the accumulation and aggregation of misfolded proteins in the endoplasmic reticulum may occur during pathological conditions. The inability of endoplasmic reticulum quality control system to clear faulty proteins and aggregates from the endoplasmic reticulum results in the development of many human disorders. The efforts to comprehensively understand endoplasmic reticulum quality control network and protein aggregation will benefit the diagnostics and therapeutics of endoplasmic reticulum storage diseases. Herein, we overview recent advances in mammalian endoplasmic reticulum protein quality control system, describe protein phase transition model, and summarize the approaches to monitor protein aggregation. Moreover, we discuss the therapeutic applications of enhancing endoplasmic reticulum protein quality control pathways in endoplasmic reticulum storage diseases.
    Keywords:  ER; ER storage disease; phase transition; protein aggregate; protein quality control
    DOI:  https://doi.org/10.3389/fcell.2023.1156152
  6. J Assist Reprod Genet. 2023 May 12.
    Endoplasmic reticulum in oocytes: spatiotemporal distribution and function.
    Xin Kang, Jing Wang, Liying Yan.
       ENDOPLASMIC RETICULUM IN OOCYTES: The storage and release of calcium ions (Ca2 +) in oocyte maturation and fertilization are particularly noteworthy features of the endoplasmic reticulum (ER). The ER is the largest organelle in the cell composed of rough ER, smooth ER, and nuclear envelope, and is the main site of protein synthesis, transport and folding, and lipid and steroid synthesis. An appropriate calcium signaling response can initiate oocyte development and embryogenesis, and the ER is the central link that initiates calcium signaling. The transition from immature oocytes to zygotes also requires many coordinated organelle reorganizations and changes. Therefore, the purpose of this review is to generalize information on the function, structure, interaction with other organelles, and spatiotemporal localization of the ER in mammalian oocytes. Mechanisms related to maintaining ER homeostasis have been extensively studied in recent years. Resolving ER stress through the unfolded protein response (UPR) is one of them. We combined the clinical problems caused by the ER in in vitro maturation (IVM), and the mechanisms of ER have been identified by single-cell RNA-seq. This article systematically reviews the functions of ER and provides a reference for assisted reproductive technology (ART) research.
    Keywords:  Calcium oscillations; Endoplasmic reticulum (ER); Mitochondria; Oocyte maturation; Stress
    DOI:  https://doi.org/10.1007/s10815-023-02782-3
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