bims-unfpre Biomed News
on Unfolded protein response
Issue of 2021‒06‒20
fifteen papers selected by
Susan Logue
University of Manitoba

  1. PLoS Pathog. 2021 Jun;17(6): e1009644
      Coronavirus infection induces the unfolded protein response (UPR), a cellular signalling pathway composed of three branches, triggered by unfolded proteins in the endoplasmic reticulum (ER) due to high ER load. We have used RNA sequencing and ribosome profiling to investigate holistically the transcriptional and translational response to cellular infection by murine hepatitis virus (MHV), often used as a model for the Betacoronavirus genus to which the recently emerged SARS-CoV-2 also belongs. We found the UPR to be amongst the most significantly up-regulated pathways in response to MHV infection. To confirm and extend these observations, we show experimentally the induction of all three branches of the UPR in both MHV- and SARS-CoV-2-infected cells. Over-expression of the SARS-CoV-2 ORF8 or S proteins alone is itself sufficient to induce the UPR. Remarkably, pharmacological inhibition of the UPR greatly reduced the replication of both MHV and SARS-CoV-2, revealing the importance of this pathway for successful coronavirus replication. This was particularly striking when both IRE1α and ATF6 branches of the UPR were inhibited, reducing SARS-CoV-2 virion release (~1,000-fold). Together, these data highlight the UPR as a promising antiviral target to combat coronavirus infection.
  2. Front Physiol. 2021 ;12 665622
      The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and induces the unfolded protein response (UPR) and other mechanisms to restore ER homeostasis, including translational shutdown, increased targeting of mRNAs for degradation by the IRE1-dependent decay pathway, selective translation of proteins that contribute to the protein folding capacity of the ER, and activation of the ER-associated degradation machinery. When ER stress is excessive or prolonged and these mechanisms fail to restore proteostasis, the UPR triggers the cell to undergo apoptosis. This review also examines the overlooked role of post-translational modifications and their roles in protein processing and effects on ER stress and the UPR. Finally, these effects are examined in the context of lung structure, function, and disease.
    Keywords:  disulfide bonds; endoplasmic reticulum; integrated stress response; lung disease; lung function; post-translational modifications; unfolded protein response
  3. Front Microbiol. 2021 ;12 670874
      Endoplasmic reticulum stress (ER stress) can be induced when cellular protein homeostasis is damaged, and cells can activate the unfolded protein response (UPR) to restore protein homeostasis or induce cell death to facilitate the survival of the whole system. Globally, parasites are a constant threat to human health and are therefore considered a serious public health problem. Parasitic infection can cause ER stress in host cells, and parasites also possess part or all of the UPR under ER stress conditions. In this review, we aim to clarify the role of ER stress pathways and related molecules in parasites for their survival and development, the pathogenesis of parasitosis in hosts, and the artemisinin resistance of Plasmodium, which provides some potential drug design targets to inhibit survival of parasites, relieves pathological damage of parasitosis, and solves the problem of artemisinin resistance.
    Keywords:  drug resistance; drug targets; endoplasmic reticulum stress; parasite; parasitosis
  4. J Am Heart Assoc. 2021 Jun 15. 10(12): e020216
      Background Ischemia/reperfusion injury impairs proteostasis, and triggers adaptive cellular responses, such as the unfolded protein response (UPR), which functions to restore endoplasmic reticulum homeostasis. After cardiac arrest (CA) and resuscitation, the UPR is activated in various organs including the brain. However, the role of the UPR in CA has remained largely unknown. Here we aimed to investigate effects of activation of the ATF6 (activating transcription factor 6) UPR branch in CA. Methods and Results Conditional and inducible sATF6-KI (short-form ATF6 knock-in) mice and a selective ATF6 pathway activator 147 were used. CA was induced in mice by KCl injection, followed by cardiopulmonary resuscitation. We first found that neurologic function was significantly improved, and neuronal damage was mitigated after the ATF6 pathway was activated in neurons of sATF6-KI mice subjected to CA/cardiopulmonary resuscitation. Further RNA sequencing analysis indicated that such beneficial effects were likely attributable to increased expression of pro-proteostatic genes regulated by ATF6. Especially, key components of the endoplasmic reticulum-associated degradation process, which clears potentially toxic unfolded/misfolded proteins in the endoplasmic reticulum, were upregulated in the sATF6-KI brain. Accordingly, the CA-induced increase in K48-linked polyubiquitin in the brain was higher in sATF6-KI mice relative to control mice. Finally, CA outcome, including the survival rate, was significantly improved in mice treated with compound 147. Conclusions This is the first experimental study to determine the role of the ATF6 UPR branch in CA outcome. Our data indicate that the ATF6 UPR branch is a prosurvival pathway and may be considered as a therapeutic target for CA.
    Keywords:  ER stress; ER‐associated degradation; RNA‐Seq; brain ischemia; neuroprotection; transgenic mice
  5. Front Cell Dev Biol. 2021 ;9 674103
      The oxidative modification of the major cholesterol carrying lipoprotein, oxLDL, is a biomarker as well as a pathological factor in cardiovascular diseases (CVD), type 2 diabetes mellitus (T2DM), obesity and other metabolic diseases. Perturbed cellular homeostasis due to physiological, pathological and pharmacological factors hinder the proper functioning of the endoplasmic reticulum (ER), which is the major hub for protein folding and processing, lipid biosynthesis and calcium storage, thereby leading to ER stress. The cellular response to ER stress is marked by a defensive mechanism called unfolded protein response (UPR), wherein the cell adapts strategies that favor survival. Under conditions of excessive ER stress, when the survival mechanisms fail to restore balance, UPR switches to apoptosis and eliminates the defective cells. ER stress is a major hallmark in metabolic syndromes such as diabetes, non-alcoholic fatty liver disease (NAFLD), neurological and cardiovascular diseases. Though the pathological link between oxLDL and ER stress in cardiovascular diseases is well-documented, its involvement in other diseases is still largely unexplored. This review provides a deep insight into the common mechanisms in the pathogenicity of diseases involving oxLDL and ER stress as key players. In addition, the potential therapeutic intervention of the targets implicated in the pathogenic processes are also explored.
    Keywords:  ER stress sensors; HDL; UPR arm; human disease; oxidized LDL; therapy
  6. Front Endocrinol (Lausanne). 2021 ;12 671724
      Aims/hypothesis: Recurrent hypoglycaemia (RH) is a major side-effect of intensive insulin therapy for people with diabetes. Changes in hypoglycaemia sensing by the brain contribute to the development of impaired counterregulatory responses to and awareness of hypoglycaemia. Little is known about the intrinsic changes in human astrocytes in response to acute and recurrent low glucose (RLG) exposure.Methods: Human primary astrocytes (HPA) were exposed to zero, one, three or four bouts of low glucose (0.1 mmol/l) for three hours per day for four days to mimic RH. On the fourth day, DNA and RNA were collected. Differential gene expression and ontology analyses were performed using DESeq2 and GOseq, respectively. DNA methylation was assessed using the Infinium MethylationEPIC BeadChip platform.
    Results: 24 differentially expressed genes (DEGs) were detected (after correction for multiple comparisons). One bout of low glucose exposure had the largest effect on gene expression. Pathway analyses revealed that endoplasmic-reticulum (ER) stress-related genes such as HSPA5, XBP1, and MANF, involved in the unfolded protein response (UPR), were all significantly increased following low glucose (LG) exposure, which was diminished following RLG. There was little correlation between differentially methylated positions and changes in gene expression yet the number of bouts of LG exposure produced distinct methylation signatures.
    Conclusions/interpretation: These data suggest that exposure of human astrocytes to transient LG triggers activation of genes involved in the UPR linked to endoplasmic reticulum (ER) stress. Following RLG, the activation of UPR related genes was diminished, suggesting attenuated ER stress. This may be a consequence of a successful metabolic adaptation, as previously reported, that better preserves intracellular energy levels and a reduced necessity for the UPR.
    Keywords:  ER stress; human primary astrocytes; recurrent low glucose; transcriptome (RNA-seq); unfolded protein response
  7. Front Cell Dev Biol. 2021 ;9 683940
      Bladder cancer is a common malignant tumor of the urinary system. Despite recent advances in treatments such as local or systemic immunotherapy, chemotherapy, and radiotherapy, the high metastasis and recurrence rates, especially in muscle-invasive bladder cancer (MIBC), have led to the evaluation of more targeted and personalized approaches. A fundamental understanding of the tumorigenesis of bladder cancer along with the development of therapeutics to target processes and pathways implicated in bladder cancer has provided new avenues for the management of this disease. Accumulating evidence supports that the tumor microenvironment (TME) can be shaped by and reciprocally act on tumor cells, which reprograms and regulates tumor development, metastasis, and therapeutic responses. A hostile TME, caused by intrinsic tumor attributes (e.g., hypoxia, oxidative stress, and nutrient deprivation) or external stressors (e.g., chemotherapy and radiation), disrupts the normal synthesis and folding process of proteins in the endoplasmic reticulum (ER), culminating in a harmful situation called ER stress (ERS). ERS is a series of adaptive changes mediated by unfolded protein response (UPR), which is interwoven into a network that can ultimately mediate cell proliferation, apoptosis, and autophagy, thereby endowing tumor cells with more aggressive behaviors. Moreover, recent studies revealed that ERS could also impede the efficacy of anti-cancer treatment including immunotherapy by manipulating the TME. In this review, we discuss the relationship among bladder cancer, ERS, and TME; summarize the current research progress and challenges in overcoming therapeutic resistance; and explore the concept of targeting ERS to improve bladder cancer treatment outcomes.
    Keywords:  bladder cancer; endoplasmic reticulum stress; therapeutic target; tumor microenvironment; unfolded protein response
  8. J Proteome Res. 2021 Jun 14.
      Epithelial-mesenchymal transition (EMT) plays a critical role in airway injury, repair, and structural remodeling. IκB kinase (IKK)-NFκB signaling regulates late EMT-associated gene expression. However, IKK-mediated mesenchymal transition occurs earlier than NFκB/RelA subunit-dependent EMT gene expression, leading us to investigate the hypothesis that IKK plays an independent mechanism in transforming growth factor-β (TGFβ)-induced EMT. Time-resolved dissection of early proteome and phosphoproteome changes in response to TGFβ and a specific IKK inhibitor, BMS-345541, revealed that IKK regulates cascades of 23 signaling pathways essential in EMT, including TGFβ signaling, p38 mitogen associate protein kinase (MAPK), Toll receptor signaling, and integrin pathways. We identified early IKK-dependent phosphorylation of core regulatory proteins in essential EMT signaling cassettes, including ATF2, JUN, NFKB1/p105, and others. Interestingly, we found that IKKβ directly complexes with and phosphorylates the spliced X-box-binding protein 1 (XBP1s). XBP1s is an arm of the unfolded protein response (UPR) that activates the hexosamine biosynthetic pathway (HBP), a pathway that mediates protein N-glycosylation and survival from ER stress-induced apoptosis in EMT. We found that inhibition of IKK activity abolishes the phosphorylation of XBP1-T48, blocks XBP1s nuclear translocation, and inhibits the activation of HBP. Our study elucidates a previously unrecognized IKKβ-XBP1s-HBP crosstalk pathway that couples inflammation and glucose metabolic reprogramming in ETM. Because XBP1-HBP controls N-glycosylation of the extracellular matrix (ECM) in EMT, this novel IKKβ-XBP1-HBP pathway may contain therapeutic targets whose inhibition could prevent ECM remodeling in lung fibrosis or other airway remodeling diseases.
    Keywords:  IκB kinase-NFκB; N-glycosylation; epithelial−mesenchymal transition; extracellular matrix; hexosamine biosynthetic pathway; proteomics; unfolded protein response
  9. Sci Rep. 2021 Jun 15. 11(1): 12574
      Human neutrophils constitutively express high amounts of arginase-1, which depletes arginine from the surrounding medium and downregulates T-cell activation. Here, we have found that neutrophil arginase-1, released from activated human neutrophils or dead cells, induced apoptosis in cancer cells through an endoplasmic reticulum (ER) stress pathway. Silencing of PERK in cancer cells prevented the induction of ER stress and apoptosis. Arginase inhibitor Nω-hydroxy-nor-arginine inhibited apoptosis and ER stress response induced by conditioned medium from activated neutrophils. A number of tumor cell lines, derived from different tissues, were sensitive to neutrophil arginase-1, with pancreatic, breast, ovarian and lung cancer cells showing the highest sensitivity. Neutrophil-released arginase-1 and arginine deprivation potentiated the antitumor action against pancreatic cancer cells of the ER-targeted antitumor alkylphospholipid analog edelfosine. Our study demonstrates the involvement of neutrophil arginase-1 in cancer cell killing and highlights the importance and complex role of neutrophils in tumor surveillance and biology.
  10. Sci Rep. 2021 Jun 17. 11(1): 12759
      Diabetes mellitus (DM) has profound effects on the female mammalian reproductive system, and early embryonic development, reducing female reproductive outcomes and inducing developmental programming in utero. However, the underlying cellular and molecular mechanisms remain poorly defined. Accumulating evidence implicates endoplasmic reticulum (ER)-stress with maternal DM associated pathophysiology. Yet the direct pathologies and causal events leading to ovarian dysfunction and altered early embryonic development have not been determined. Here, using an in vivo mouse model of Type 1 DM and in vitro hyperglycaemia-exposure, we demonstrate the activation of ER-stress within adult ovarian tissue and pre-implantation embryos. In diabetic ovaries, we show that the unfolded protein response (UPR) triggers an apoptotic cascade by the co-activation of Caspase 12 and Cleaved Caspase 3 transducers. Whereas DM-exposed early embryos display differential ER-associated responses; by activating Chop in within embryonic precursors and Caspase 12 within placental precursors. Our results offer new insights for understanding the pathological effects of DM on mammalian ovarian function and early embryo development, providing new evidence of its mechanistic link with ER-stress in mice.
  11. Front Cell Dev Biol. 2021 ;9 670435
      The unfolded protein response (UPR) plays important roles in various cells that have a high demand for protein folding, which are involved in the process of cell differentiation and development. Here, we separately knocked down the three sensors of the UPR in myoblasts and found that PERK knockdown led to a marked transformation in myoblasts from a fusiform to a rounded morphology, which suggests that PERK is required for early myoblast differentiation. Interestingly, knocking down PERK induced reprogramming of C2C12 myoblasts into stem-like cells by altering the miRNA networks associated with differentiation and stemness maintenance, and the PERK-ATF4 signaling pathway transactivated muscle differentiation-associated miRNAs in the early stage of myoblast differentiation. Furthermore, we identified Ppp1cc as a direct target gene of miR-128 regulated by the PERK signaling pathway and showed that its repression is critical for a feedback loop that regulates the activity of UPR-associated signaling pathways, leading to cell migration, cell fusion, endoplasmic reticulum expansion, and myotube formation during myoblast differentiation. Subsequently, we found that the RNA-binding protein ARPP21, encoded by the host gene of miR-128-2, antagonized miR-128 activity by competing with it to bind to the 3' untranslated region (UTR) of Ppp1cc to maintain the balance of the differentiation state. Together, these results reveal the crucial role of PERK signaling in myoblast maintenance and differentiation and identify the mechanism underlying the role of UPR signaling as a major regulator of miRNA networks during early differentiation of myoblasts.
    Keywords:  C2C12 (mouse skeletal myoblasts); PERK signaling; differentiation; microRNA network; myoblasts
  12. EMBO J. 2021 Jun 16. e108812
      The cytosolic NOD1 and NOD2 pattern recognition receptors are typically known as sensors of bacterial peptidoglycan fragments. A new study in this issue links NOD1/2 activation with ER homeostasis through the bioactive metabolite sphingosine-1-phosphate (S1P).
  13. Aging Cell. 2021 Jun 15. e13382
      Hematopoietic stem cells (HSCs) reside in a quiescent niche to reserve their capacity of self-renewal. Upon hematopoietic injuries, HSCs enter the cell cycle and encounter protein homeostasis problems caused by accumulation of misfolded proteins. However, the mechanism by which protein homeostasis influences HSC function and maintenance remains poorly understood. Here, we show that C/EBP homologous protein (CHOP), demonstrated previously to induces cell death upon unfolded protein response (UPR), plays an important role in HSCs regeneration. CHOP-/- mice showed normal hematopoietic stem and progenitor cell frequencies in steady state. However, when treated with 5-FU, CHOP deficiency resulted in higher survival rates, associated with an increased number of HSCs and reduced level of apoptosis. In serial competitive transplantation experiments, CHOP-/- HSCs showed a dramatic enhancement of repopulation ability and a reduction of protein aggresomes. Mechanistically, CHOP deletion causes reduced ATF3 expression and further leads to decreased protein aggregation and ROS. In addition, CHOP-/- HSCs exhibited an increased resistance to IR-induced DNA damage and improved HSCs homeostasis and function in telomere dysfunctional (G3Terc-/- ) mice. In summary, these findings disclose a new role of CHOP in the regulation of the HSCs function and homeostasis through reducing ATF3 and ROS signaling.
    Keywords:  ATF3; C/EBP homologous protein; ROS; apoptosis; hematopoietic stem cell function
  14. Proc Natl Acad Sci U S A. 2021 Jun 22. pii: e2025299118. [Epub ahead of print]118(25):
      Proteome-wide profiling of protein phosphorylation has been widely used to reveal the underlying mechanism of diverse cellular signaling events. Yet, characterizing subcellular phosphoproteome with high spatial-temporal resolution has remained challenging. Herein, we developed a subcellular-specific uncaging-assisted biotinylation and mapping of phosphoproteome (SubMAPP) strategy to monitor the phosphorylation dynamics of subcellular proteome in living cells and animals. Our method capitalizes on the genetically encoded bioorthogonal decaging strategy, which enables the rapid activation of subcellular localized proximity labeling biotin ligase through either light illumination or small-molecule triggers. By further adopting an integrated orthogonal pull-down strategy with quantitative mass spectrometry, SubMAPP allowed for the investigation of subcellular phosphoproteome dynamics, revealing the altered phosphorylation patterns of endoplasmic reticulum (ER) luminal proteins under ER stress. Finally, we further expanded the scope of the SubMAPP strategy to primary neuron culture and living mice.
    Keywords:  bioorthogonal decaging; proximal labeling; subcellular phosphoproteome
  15. Cell Death Dis. 2021 Jun 17. 12(7): 626
      Acinar cell injury and the inflammatory response are critical bioprocesses of acute pancreatitis (AP). We investigated the role and underlying mechanism of sulfiredoxin-1 (Srxn1) in AP. Mild AP was induced by intraperitoneal injection of cerulein and severe AP was induced by partial duct ligation with cerulein stimulation or intraperitoneal injection of L-arginine in mice. Acinar cells, neutrophils, and macrophages were isolated. The pancreas was analyzed by histology, immunochemistry staining, and TUNEL assays, and the expression of certain proteins and RNAs, cytokine levels, trypsin activity, and reactive oxygen species (ROS) levels were determined. Srxn1 was inhibited by J14 or silenced by siRNA, and overexpression was introduced by a lentiviral vector. Transcriptomic analysis was used to explore the mechanism of Srxn1-mediated effects. We also evaluated the effect of adeno-associated virus (AAV)-mediated overexpression of Srxn1 by intraductal administration and the protection of AP. We found that Srxn1 expression was upregulated in mild AP but decreased in severe AP. Inhibition of Srxn1 increased ROS, histological score, the release of trypsin, and inflammatory responses in mice. Inhibition of Srxn1 expression promoted the production of ROS and induced apoptosis, while overexpression of Srxn1 led to the opposite results in acinar cells. Furthermore, inhibition of Srxn1 expression promoted the inflammatory response by accumulating and activating M1 phenotype macrophages and neutrophils in AP. Mechanistically, ROS-induced ER stress and activation of Cathepsin B, which converts trypsinogen to trypsin, were responsible for the Srxn1 inhibition-mediated effects on AP. Importantly, we demonstrated that AAV-mediated overexpression of Srxn1 attenuated AP in mice. Taken together, these results showed that Srxn1 is a protective target for AP by attenuating acinar injury and inflammation through the ROS/ER stress/Cathepsin B axis.