bims-unfpre Biomed News
on Unfolded protein response
Issue of 2021‒07‒04
fifteen papers selected by
Susan Logue
University of Manitoba

  1. Elife. 2021 Jun 28. pii: e64977. [Epub ahead of print]10
      Molecular chaperones, such as Hsp70, prevent proteotoxicity and maintain homeostasis. This is perhaps most evident in cancer cells, which overexpress Hsp70 and thrive even when harboring high levels of misfolded proteins. To define the response to proteotoxic challenges, we examined adaptive responses in breast cancer cells in the presence of an Hsp70 inhibitor. We discovered that the cells bin into distinct classes based on inhibitor sensitivity. Strikingly, the most resistant cells have higher autophagy levels, and autophagy was maximally activated only in resistant cells upon Hsp70 inhibition. In turn, resistance to compromised Hsp70 function required the integrated stress response transducer, GCN2, which is commonly associated with amino acid starvation. In contrast, sensitive cells succumbed to Hsp70 inhibition by activating PERK. These data reveal an unexpected route through which breast cancer cells adapt to proteotoxic insults and position GCN2 and autophagy as complementary mechanisms to ensure survival when proteostasis is compromised.
    Keywords:  cell biology; human
  2. J Cell Biol. 2021 Aug 02. pii: e202011078. [Epub ahead of print]220(8):
      The ER is a key organelle of membrane biogenesis and crucial for the folding of both membrane and secretory proteins. Sensors of the unfolded protein response (UPR) monitor the unfolded protein load in the ER and convey effector functions for maintaining ER homeostasis. Aberrant compositions of the ER membrane, referred to as lipid bilayer stress, are equally potent activators of the UPR. How the distinct signals from lipid bilayer stress and unfolded proteins are processed by the conserved UPR transducer Ire1 remains unknown. Here, we have generated a functional, cysteine-less variant of Ire1 and performed systematic cysteine cross-linking experiments in native membranes to establish its transmembrane architecture in signaling-active clusters. We show that the transmembrane helices of two neighboring Ire1 molecules adopt an X-shaped configuration independent of the primary cause for ER stress. This suggests that different forms of stress converge in a common, signaling-active transmembrane architecture of Ire1.
  3. J Parkinsons Dis. 2021 Jun 19.
      Parkinson's disease (PD) pathology involves progressive degeneration and death of vulnerable dopamine neurons in the substantia nigra. Extensive axonal arborisation and distinct functions make this type of neurons particularly sensitive to homeostatic perturbations, such as protein misfolding and Ca2 + dysregulation. Endoplasmic reticulum (ER) is a cell compartment orchestrating protein synthesis and folding, as well as synthesis of lipids and maintenance of Ca2 +-homeostasis in eukaryotic cells. When misfolded proteins start to accumulate in ER lumen the unfolded protein response (UPR) is activated. UPR is an adaptive signalling machinery aimed at relieving of protein folding load in the ER. When UPR is chronic, it can either boost neurodegeneration and apoptosis or cause neuronal dysfunctions. We have recently discovered that mesencephalic astrocyte-derived neurotrophic factor (MANF) exerts its prosurvival action in dopamine neurons and in animal model of PD through the direct binding to UPR sensor inositol-requiring protein 1 alpha (IRE1α) and attenuation of UPR. In line with this, UPR targeting resulted in neuroprotection and neurorestoration in various preclinical PD animal models. Therefore, growth factors (GFs), possessing both neurorestorative activity and restoration of protein folding capacity are attractive as drug candidates for PD treatment especially their blood-brain barrier penetrating analogs and small molecule mimetics. In this review, we discuss ER stress as a therapeutic target to treat PD; we summarize the existing preclinical data on the regulation of ER stress for PD treatment. In addition, we point out the crucial aspects for successful clinical translation of UPR-regulating GFs and new prospective in GFs-based treatments of PD, focusing on ER stress regulation.
    Keywords:  Parkinson’s disease; cerebral dopamine neurotrophic factor; endoplasmic reticulum stress; growth factors; mesencephalic astrocyte-derived neurotrophic factor; unfolded protein response
  4. EMBO Rep. 2021 Jun 30. e52905
      Planarians are able to stand long periods of starvation by maintaining adult stem cell pools and regenerative capacity. The molecular pathways that are needed for the maintenance of regeneration during starvation are not known. Here, we show that down-regulation of chaperonin TRiC/CCT subunits abrogates the regeneration capacity of planarians during starvation, but TRiC/CCT subunits are dispensable for regeneration in fed planarians. Under starvation, they are required to maintain mitotic fidelity and for blastema formation. We show that TRiC subunits modulate the unfolded protein response (UPR) and are required to maintain ATP levels in starved planarians. Regenerative defects in starved CCT-depleted planarians can be rescued by either chemical induction of mild endoplasmic reticulum stress, which leads to induction of the UPR, or by the supplementation of fatty acids. Together, these results indicate that CCT-dependent UPR induction promotes regeneration of planarians under food restriction.
    Keywords:  ER stress; chaperonin; hematopoietic stem cell; planarian; starvation
  5. Front Aging Neurosci. 2021 ;13 682633
      Immune surveillance is an essential process that safeguards the homeostasis of a healthy brain. Among the increasing diversity of immune cells present in the central nervous system (CNS), microglia have emerged as a prominent leukocyte subset with key roles in the support of brain function and in the control of neuroinflammation. In fact, impaired microglial function is associated with the development of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Interestingly, these pathologies are also typified by protein aggregation and proteostasis dysfunction at the level of the endoplasmic reticulum (ER). These processes trigger activation of the unfolded protein response (UPR), which is a conserved signaling network that maintains the fidelity of the cellular proteome. Remarkably, beyond its role in protein folding, the UPR has also emerged as a key regulator of the development and function of immune cells. However, despite this evidence, the contribution of the UPR to immune cell homeostasis, immune surveillance, and neuro-inflammatory processes remains largely unexplored. In this review, we discuss the potential contribution of the UPR in brain-associated immune cells in the context of neurodegenerative diseases.
    Keywords:  ER stress; UPR; immune system; inflammation; microglia; neurodegeneration; neuroinflammation; protein misfolding
  6. Metabolites. 2021 Jun 26. pii: 422. [Epub ahead of print]11(7):
      The endoplasmic reticulum (ER) is a complex, multifunctional organelle of eukaryotic cells and responsible for the trafficking and processing of nearly 30% of all human proteins. Any disturbance to these processes can cause ER stress, which initiates an adaptive mechanism called unfolded protein response (UPR) to restore ER functions and homeostasis. Mitochondrial ATP production is necessary to meet the high energy demand of the UPR, while the molecular mechanisms of ER to mitochondria crosstalk under such stress conditions remain mainly enigmatic. Thus, better understanding the regulation of mitochondrial bioenergetics during ER stress is essential to combat many pathologies involving ER stress, the UPR, and mitochondria. This article investigates the role of Sigma-1 Receptor (S1R), an ER chaperone, has in enhancing mitochondrial bioenergetics during early ER stress using human neuroblastoma cell lines. Our results show that inducing ER stress with tunicamycin, a known ER stressor, greatly enhances mitochondrial bioenergetics in a time- and S1R-dependent manner. This is achieved by enhanced ER Ca2+ leak directed towards mitochondria by S1R during the early phase of ER stress. Our data point to the importance of S1R in promoting mitochondrial bioenergetics and maintaining balanced H2O2 metabolism during early ER stress.
    Keywords:  ER Ca2+ leak; ER stress; UPR; mitochondrial Ca2+; mitochondrial bioenergetics; mitochondrial metabolism; sigma-1 receptor
  7. J Neurosci Res. 2021 Jul 01.
      Glutamate excitotoxicity and endoplasmic reticulum (ER) recently have been found to be instrumental in the pathogenesis of various neurodegenerative diseases. However, the paucity of literature deciphering the inter-linkage among glutamate receptors, behavioral alterations, and ER demands thorough exploration. Reckoning the aforesaid concerns, a prospective study was outlined to delineate the influence of ER stress inhibition via 4-phenylbutyric acid (PBA) on α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) excitotoxicity-induced behavioral aspects and possible ER stress-glutamate linkage. Male SD rats were randomly divided into four groups namely sham (surgical control+vehicle, group 1), AMPA-induced excitotoxic group 2 receive a single intra-hippocampal injection of 10 mM AMPA, group 3 received AMPA along with PBA (i.p, 100 mg/kg body weight) for 15 days, and group 4 received PBA alone. Behavioral analyses were performed prior to the sacrifice of animals and hippocampus was extracted thereafter for further analysis. AMPA-induced excitotoxicity exhibited significant impairment of locomotion as well as cognitive functions. The levels of neurotransmitters such as dopamine, homo vanillic acid (HVA), norepinephrine, and serotonin were reduced accompanied by reduced expression of GLUR1 and GLUR4 (glutamate receptor) as well as loss of neurons in different layers of hippocampus. ER stress markers were upregulated upon AMPA excitotoxicity. However, chemical chaperone PBA supplementation remarkably mitigated the behavioral alterations along with expression of glutamate and ER stress intermediates/markers in AMPA excitotoxic animals. Therefore, the present exploration convincingly emphasizes the significance of ER stress and its inhibition via PBA in combating cognitive impairment as well as improving locomotion in excitotoxic animals.
    Keywords:  ER stress; RRID:AB_10715096; RRID:AB_2119991; RRID:AB_2230863; RRID:AB_2293243; RRID:AB_2687626; RRID:AB_2810998; RRID:AB_395198; RRID:AB_629532; RRID:RGD_70508; RRID:SCR_002798; RRID:SCR_003073; RRID:SCR_014289; behavioral alterations; excitotoxicity; glutamate receptors; hippocampus
  8. Biomedicines. 2021 Jun 02. pii: 635. [Epub ahead of print]9(6):
      Breast cancer (BC) is the second most frequent cause of death among women. Representing a complex and heterogeneous type of cancer, its occurrence is attributed by both genetic (gene mutations, e.g., BRCA1, BRCA2) and non-genetic (race, ethnicity, etc.) risk factors. The effectiveness of available treatment regimens (small molecules, cytotoxic agents, and inhibitors) decreased due to their poor penetration across biological barriers, limited targeting, and rapid body clearance along with their effect on normal resident cells of bone marrow, gastrointestinal tract, and hair follicles. This significantly reduced their clinical outcomes, which led to an unprecedented increase in the number of cases worldwide. Nanomedicine, a nano-formulation of therapeutics, emerged as a versatile delivering module for employment in achieving the effective and target specific delivery of pharmaceutical payloads. Adoption of nanotechnological approaches in delivering therapeutic molecules to target cells ensures not only reduced immune response and toxicity, but increases the stability of therapeutic entities in the systemic circulation that averts their degradation and as such increased extravasations and accumulation via enhanced permeation and the retention (EPR) effect in target tissues. Additionally, nanoparticle (NP)-induced ER stress, which enhances apoptosis and autophagy, has been utilized as a combative strategy in the treatment of cancerous cells. As nanoparticles-based avenues have been capitalized to achieve better efficacy of the new genera of therapeutics with enhanced specificity and safety, the present study is aimed at providing the fundamentals of BC, nanotechnological modules (organic, inorganic, and hybrid) employed in delivering different therapeutic molecules, and mechanistic insights of nano-ER stress induced apoptosis and autophagy with a perspective of exploring this avenue for use in the nano-toxicological studies. Furthermore, the current scenario of USA FDA approved nano-formulations and the future perspective of nanotechnological based interventions to overcome the existing challenges are also discussed.
    Keywords:  ER stress; breast cancer; nanomedicine; nanotechnology; therapeutics
  9. Cells. 2021 Jun 09. pii: 1446. [Epub ahead of print]10(6):
      Both calcium-independent phospholipase A2 beta (iPLA2β) and endoplasmic reticulum (ER) stress regulate important pathophysiological processes including inflammation, calcium homeostasis and apoptosis. However, their roles in ischemic heart disease are poorly understood. Here, we show that the expression of iPLA2β is increased during myocardial ischemia/reperfusion (I/R) injury, concomitant with the induction of ER stress and the upregulation of cell death. We further show that the levels of iPLA2β in serum collected from acute myocardial infarction (AMI) patients and in samples collected from both in vivo and in vitro I/R injury models are significantly elevated. Further, iPLA2β knockout mice and siRNA mediated iPLA2β knockdown are employed to evaluate the ER stress and cell apoptosis during I/R injury. Additionally, cell surface protein biotinylation and immunofluorescence assays are used to trace and locate iPLA2β. Our data demonstrate the increase of iPLA2β augments ER stress and enhances cardiomyocyte apoptosis during I/R injury in vitro and in vivo. Inhibition of iPLA2β ameliorates ER stress and decreases cell death. Mechanistically, iPLA2β promotes ER stress and apoptosis by translocating to ER upon myocardial I/R injury. Together, our study suggests iPLA2β contributes to ER stress-induced apoptosis during myocardial I/R injury, which may serve as a potential therapeutic target against ischemic heart disease.
    Keywords:  ER stress; apoptosis; iPLA2β; ischemia/reperfusion injury; lysophosphatidylcholine; translocation
  10. Redox Biol. 2021 Jun 18. pii: S2213-2317(21)00208-1. [Epub ahead of print]45 102049
      Mitochondrial dysfunction is a fundamental challenge in septic cardiomyopathy. Mitophagy and the mitochondrial unfolded protein response (UPRmt) are the predominant stress-responsive and protective mechanisms involved in repairing damaged mitochondria. Although mitochondrial homeostasis requires the coordinated actions of mitophagy and UPRmt, their molecular basis and interactive actions are poorly understood in sepsis-induced myocardial injury. Our investigations showed that lipopolysaccharide (LPS)-induced sepsis contributed to cardiac dysfunction and mitochondrial damage. Although both mitophagy and UPRmt were slightly activated by LPS in cardiomyocytes, their endogenous activation failed to prevent sepsis-mediated myocardial injury. However, administration of urolithin A, an inducer of mitophagy, obviously reduced sepsis-mediated cardiac depression by normalizing mitochondrial function. Interestingly, this beneficial action was undetectable in cardiomyocyte-specific FUNDC1 knockout (FUNDC1CKO) mice. Notably, supplementation with a mitophagy inducer had no impact on UPRmt, whereas genetic ablation of FUNDC1 significantly upregulated the expression of genes related to UPRmt in LPS-treated hearts. In contrast, enhancement of endogenous UPRmt through oligomycin administration reduced sepsis-mediated mitochondrial injury and myocardial dysfunction; this cardioprotective effect was imperceptible in FUNDC1CKO mice. Lastly, once UPRmt was inhibited, mitophagy-mediated protection of mitochondria and cardiomyocytes was partly blunted. Taken together, it is plausible that endogenous UPRmt and mitophagy are slightly activated by myocardial stress and they work together to sustain mitochondrial performance and cardiac function. Endogenous UPRmt, a downstream signal of mitophagy, played a compensatory role in maintaining mitochondrial homeostasis in the case of mitophagy inhibition. Although UPRmt activation had no negative impact on mitophagy, UPRmt inhibition compromised the partial cardioprotective actions of mitophagy. This study shows how mitophagy modulates UPRmt to attenuate inflammation-related myocardial injury and suggests the potential application of mitophagy and UPRmt targeting in the treatment of myocardial stress.
    Keywords:  FUN14 domain-containing 1; Inflammation; Mitochondrial unfolded protein response; Mitophagy; Septic cardiomyopathy
  11. Biol Open. 2021 May 15. pii: bio058613. [Epub ahead of print]10(5):
      A dramatic rise of infections with antibiotic-resistant bacterial pathogens continues to challenge the healthcare field due to the lack of effective treatment regimes. As such, there is an urgent need to develop new antimicrobial agents that can combat these multidrug-resistant superbugs. Mitochondria are central regulators of metabolism and other cellular functions, including the regulation of innate immunity pathways involved in the defense against infection. The mitochondrial unfolded protein response (UPRmt) is a stress-activated pathway that mitigates mitochondrial dysfunction through the regulation of genes that promote recovery of the organelle. In the model organism Caenorhabditis elegans, the UPRmt also mediates an antibacterial defense program that combats pathogen infection, which promotes host survival. We sought to identify and characterize antimicrobial effectors that are regulated during the UPRmt. From our search, we discovered that the antimicrobial peptide CNC-4 is upregulated during this stress response. CNC-4 belongs to the caenacin family of antimicrobial peptides, which are predominantly found in nematodes and are known to have anti-fungal properties. Here, we find that CNC-4 also possesses potent antimicrobial activity against a spectrum of bacterial species and report on its characterization.
    Keywords:  Antimicrobial peptide; CNC-4; Caenacins; Innate immunity; Mitochondria; Mitochondrial UPR; Stress response
  12. Cells. 2021 Jun 30. pii: 1642. [Epub ahead of print]10(7):
      Autophagy, apoptosis, and the unfolded protein response (UPR) are fundamental biological processes essential for manifold cellular functions in health and disease. Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal pulmonary disorder associated with aging that has limited therapies, reflecting our incomplete understanding. We conducted an observational study linking molecular markers of cell stress response pathways (UPR: BiP, XBP1; apoptosis: cleaved caspase-3; autophagy: LC3β) in lung tissues from IPF patients and correlated the expression of these protein markers to each subject's lung function measures. We hypothesized that changes in lung tissue expression of apoptosis, autophagy, and UPR markers correlate with lung function deficits in IPF. The cell stress markers BiP, XBP1, LC3β puncta, and cleaved caspase-3 were found to be elevated in IPF lungs compared to non-IPF lungs, and, further, BiP and cleaved caspase-3 co-localized in IPF lungs. Considering lung function independently, we observed that increased XBP1, BiP, and cleaved caspase-3 were each associated with reduced lung function (FEV1, FVC, TLC, RV). However, increased lung tissue expression of LC3β puncta was significantly associated with increased diffusion capacity (DLCO), an indicator of alveolar-capillary membrane function. Similarly, the co-localization of UPR (XBP1, BiP) and autophagy (LC3β puncta) markers was positively correlated with increased lung function (FEV1, FVC, TLC, DLCO). However, the presence of LC3β puncta can indicate either autophagy flux inhibition or activation. While the nature of our observational cross-sectional study design does not allow conclusions regarding causal links between increased expression of these cell stress markers, lung fibrosis, and lung function decline, it does provide some insights that are hypothesis-generating and suggests that within the milieu of active UPR, changes in autophagy flux may play an important role in determining lung function. Further research is necessary to investigate the mechanisms linking UPR and autophagy in IPF and how an imbalance in these cell stress pathways can lead to progressive fibrosis and loss of lung function. We conclude by presenting five testable hypotheses that build on the research presented here. Such an understanding could eventually lead to the development of much-needed therapies for IPF.
    Keywords:  apoptosis; autophagy; endoplasmic reticulum stress; idiopathic pulmonary fibrosis; lung fibrosis; lung function; lung physiology; pulmonary function test; unfolded protein response
  13. Cancers (Basel). 2021 Jun 26. pii: 3195. [Epub ahead of print]13(13):
      The protein quality control network, including autophagy, the proteasome and the unfolded protein response (UPR), is triggered by stress and is overactive in acquired antiestrogen therapy resistance. We show for the first time that the aggresome load correlates with apoptosis and is increased in antiestrogen-sensitive cells compared to endocrine-resistant variants. LC-MS/MS analysis of the aggregated proteins obtained after 4OH-tamoxifen and Fulvestrant treatment identified proteins with essential function in protein quality control in antiestrogen-sensitive cells, but not in resistant variants. These include the UPR modulators RTCB and PDIA6, as well as many proteasome proteins such as PSMC2 and PSMD11. RTCB is a tRNA and XBP1 ligase and its aggregation induced by antiestrogens correlated with impaired XBP1s expression in sensitive cells. Knock down of RTCB was sufficient to restore sensitivity to tamoxifen in endocrine-resistant cells and increased the formation of aggresomes, leading to apoptotic cell death. Analysis of primary human breast cancer samples and their metastases appearing after endocrine treatment showed that RTCB is only localized to aggresomes in the primary tumors, while total aggresomes, including aggregated RTCB, were significantly reduced in the metastases. Therefore, different protein aggregation patterns may indicate loss of function of essential proteins resulting in enhanced protein aggregation that can be used to identify antiestrogen-resistant breast cancer cells and improve the response to antiestrogenic therapy.
    Keywords:  antiestrogen resistance; breast cancer; estrogen receptors; protein aggregation; tRNA-splicing ligase RTCB homolog (RTCB)
  14. Cell Death Dis. 2021 Jun 28. 12(7): 657
      Subcellular organelles communicate with each other to regulate function and coordinate responses to changing cellular conditions. The physical-functional coupling of the endoplasmic reticulum (ER) with mitochondria allows for the direct transfer of Ca2+ between organelles and is an important avenue for rapidly increasing mitochondrial metabolic activity. As such, increasing ER-mitochondrial coupling can boost the generation of ATP that is needed to restore homeostasis in the face of cellular stress. The mitochondrial unfolded protein response (mtUPR) is activated by the accumulation of unfolded proteins in mitochondria. Retrograde signaling from mitochondria to the nucleus promotes mtUPR transcriptional responses aimed at restoring protein homeostasis. It is currently unknown whether the changes in mitochondrial-ER coupling also play a role during mtUPR stress. We hypothesized that mitochondrial stress favors an expansion of functional contacts between mitochondria and ER, thereby increasing mitochondrial metabolism as part of a protective response. Hela cells were treated with doxycycline, an antibiotic that inhibits the translation of mitochondrial-encoded proteins to create protein disequilibrium. Treatment with doxycycline decreased the abundance of mitochondrial encoded proteins while increasing expression of CHOP, C/EBPβ, ClpP, and mtHsp60, markers of the mtUPR. There was no change in either mitophagic activity or cell viability. Furthermore, ER UPR was not activated, suggesting focused activation of the mtUPR. Within 2 h of doxycycline treatment, there was a significant increase in physical contacts between mitochondria and ER that was distributed throughout the cell, along with an increase in the kinetics of mitochondrial Ca2+ uptake. This was followed by the rise in the rate of oxygen consumption at 4 h, indicating a boost in mitochondrial metabolic activity. In conclusion, an early phase of the response to doxycycline-induced mitochondrial stress is an increase in mitochondrial-ER coupling that potentiates mitochondrial metabolic activity as a means to support subsequent steps in the mtUPR pathway and sustain cellular adaptation.
  15. Cell Death Dis. 2021 Jun 30. 12(7): 659
      Cellular stress can lead to several human disease pathologies due to aberrant cell death. The p53 family (tp53, tp63, and tp73) and downstream transcriptional apoptotic target genes (PUMA/BBC3 and NOXA/PMAIP1) have been implicated as mediators of stress signals. To evaluate the importance of key stress response components in vivo, we have generated zebrafish null alleles in puma, noxa, p53, p63, and p73. Utilizing these genetic mutants, we have deciphered that the apoptotic response to genotoxic stress requires p53 and puma, but not p63, p73, or noxa. We also identified a delayed secondary wave of genotoxic stress-induced apoptosis that is p53/puma independent. Contrary to genotoxic stress, ER stress-induced apoptosis requires p63 and puma, but not p53, p73, or noxa. Lastly, the oxidative stress-induced apoptotic response requires p63, and both noxa and puma. Our data also indicate that while the neural tube is poised for apoptosis due to genotoxic stress, the epidermis is poised for apoptosis due to ER and oxidative stress. These data indicate there are convergent as well as unique molecular pathways involved in the different stress responses. The commonality of puma in these stress pathways, and the lack of gross or tumorigenic phenotypes with puma loss suggest that a inhibitor of Puma may have therapeutic application. In addition, we have also generated a knockout of the negative regulator of p53, mdm2 to further evaluate the p53-induced apoptosis. Our data indicate that the p53 null allele completely rescues the mdm2 null lethality, while the puma null completely rescues the mdm2 null apoptosis but only partially rescues the phenotype. Indicating Puma is the key mediator of p53-dependent apoptosis. Interestingly the p53 homozygous null zebrafish develop tumors faster than the previously described p53 homozygous missense mutant zebrafish, suggesting the missense allele may be hypomorphic allele.