bims-unfpre Biomed News
on Unfolded protein response
Issue of 2021‒03‒21
ten papers selected by
Susan Logue
University of Manitoba

  1. Nat Commun. 2021 03 16. 12(1): 1684
      Heart failure with preserved ejection fraction (HFpEF) is now the dominant form of heart failure and one for which no efficacious therapies exist. Obesity and lipid mishandling greatly contribute to HFpEF. However, molecular mechanism(s) governing metabolic alterations and perturbations in lipid homeostasis in HFpEF are largely unknown. Here, we report that cardiomyocyte steatosis in HFpEF is coupled with increases in the activity of the transcription factor FoxO1 (Forkhead box protein O1). FoxO1 depletion, as well as over-expression of the Xbp1s (spliced form of the X-box-binding protein 1) arm of the UPR (unfolded protein response) in cardiomyocytes each ameliorates the HFpEF phenotype in mice and reduces myocardial lipid accumulation. Mechanistically, forced expression of Xbp1s in cardiomyocytes triggers ubiquitination and proteasomal degradation of FoxO1 which occurs, in large part, through activation of the E3 ubiquitin ligase STUB1 (STIP1 homology and U-box-containing protein 1) a novel and direct transcriptional target of Xbp1s. Our findings uncover the Xbp1s-FoxO1 axis as a pivotal mechanism in the pathogenesis of cardiometabolic HFpEF and unveil previously unrecognized mechanisms whereby the UPR governs metabolic alterations in cardiomyocytes.
  2. Am J Physiol Gastrointest Liver Physiol. 2021 Mar 17.
      BACKGROUND/AIMS: Liver injury and the Unfolded Protein Response (UPR) are tightly linked, but their relationship differs with cell-type and injurious stimuli. UPR initiation promotes hepatic stellate cell (HSC) activation and fibrogenesis, but the underlying mechanisms are unclear. Despite the complexity and overlap downstream of UPR transducers IRE1α, ATF6α, and PERK, previous research in HSCs primarily focused on IRE1α. Here, we interrogated the fibrogenic role of ATF6α or PERK in vitro and HSC-specific UPR signaling in vivo.METHODS/RESULTS: Overexpression of ATF6α, but not the PERK effector ATF4, promoted HSC activation and fibrogenic gene transcription in immortalized HSCs. Furthermore, ATF6α inhibition through Ceapin-A7, or Atf6a deletion, disrupted TGFβ-mediated activation of primary hHSCs or mHSCs respectively. We interrogated the fibrogenic role of ATF6α in vivo through conditional HSC-specific Atf6a deletion. Atf6aHSCΔ/Δ mice displayed reduced fibrosis and HSC activation following bile-duct ligation (BDL) or CCl4-induced injury. The Atf6aHSCΔ/Δ phenotype differed from HSC-specific Ire1a deletion, as Ire1aHSCΔ/Δ mice showed reduced fibrogenic gene transcription no changes in fibrosis compared to Ire1afl/fl mice following BDL. Interestingly, ATF6α signaling increased in Ire1aΔ/Δ HSCs, while IRE1α signaling was upregulated in Atf6aΔ/Δ HSCs. Finally, we asked whether co-deletion of Arf6a and Ire1a additively limits fibrosis. Unexpectedly, fibrosis worsened in Atf6aHSCΔ/ΔIre1aHSCΔ/Δ mice following BDL, and Atf6aΔ/ΔIre1aΔ/Δ mHSCs showed increased fibrogenic gene transcription.
    CONCLUSIONS: ATF6α and IRE1α individually promote fibrogenic transcription in HSCs and ATF6α drives fibrogenesis in vivo. Unexpectedly, disruption of both pathways sensitizes the liver to fibrogenesis, suggesting that fine-tuned UPR signaling is critical for regulating HSC activation and fibrogenesis.
    Keywords:  ER Stress; Endoplasmic Reticulum; Hepatic Fibrosis; Unfolded Protein Response
  3. Cell Mol Biol Lett. 2021 Mar 17. 26(1): 11
      Inositol requiring enzyme 1 alpha (IRE1α) is one of three signaling sensors in the unfolding protein response (UPR) that alleviates endoplasmic reticulum (ER) stress in cells and functions to promote cell survival. During conditions of irrevocable stress, proapoptotic gene expression is induced to promote cell death. One of the three signaling stressors, IRE1α is an serine/threonine-protein kinase/endoribonuclease (RNase) that promotes nonconventional splicing of XBP1 mRNA that is translated to spliced XBP1 (XBP1s), an active prosurvival transcription factor. Interestingly, elevated IRE1α and XBP1s are both associated with poor cancer survival and drug resistance. In this study, we used next-generation sequencing analyses to demonstrate that triazoloacridone C-1305, a microtubule stabilizing agent that also has topoisomerase II inhibitory activity, dramatically decreases XBP1s mRNA levels and protein production during ER stress conditions, suggesting that C-1305 does this by decreasing IRE1α's endonuclease activity.
    Keywords:  ER stress; IRE1α; UPR; XBP1s
  4. Cell Death Dis. 2021 Mar 17. 12(4): 286
      p97/VCP, an evolutionarily concerned ATPase, partakes in multiple cellular proteostatic processes, including the endoplasmic reticulum (ER)-associated protein degradation (ERAD). Elevated expression of p97 is common in many cancers and is often associated with poor survival. Here we report that the levels of p97 positively correlated with the histological grade, tumor size, and lymph node metastasis in breast cancers. We further examined p97 expression in the stem-like cancer cells or cancer stem cells (CSCs), a cell population that purportedly underscores cancer initiation, therapeutic resistance, and recurrence. We found that p97 was consistently at a higher level in the CD44+/CD24-, ALDH+, or PKH26+ CSC populations than the respective non-CSC populations in human breast cancer tissues and cancer cell lines and p97 expression also positively correlated with that of SOX2, another CSC marker. To assess the role of p97 in breast cancers, cancer proliferation, mammosphere, and orthotopic growth were analyzed. Similarly as p97 depletion, two pharmacological inhibitors, which targets the ER-associated p97 or globally inhibits p97's ATPase activity, markedly reduced cancer growth and the CSC population. Importantly, depletion or inhibition of p97 greatly suppressed the proliferation of the ALDH+ CSCs and the CSC-enriched mammospheres, while exhibiting much less or insignificant inhibitory effects on the non-CSC cancer cells. Comparable phenotypes produced by blocking ERAD suggest that ER proteostasis is essential for the CSC integrity. Loss of p97 gravely activated the unfolded protein response (UPR) and modulated the expression of multiple stemness and pluripotency regulators, including C/EBPδ, c-MYC, SOX2, and SKP2, which collectively contributed to the demise of CSCs. In summary, p97 controls the breast CSC integrity through multiple targets, many of which directly affect cancer stemness and are induced by UPR activation. Our findings highlight the importance of p97 and ER proteostasis in CSC biology and anticancer therapy.
  5. Cancer Med. 2021 Mar 20.
      The protein disulphide isomerase (PDI) gene family is a large, diverse group of enzymes recognised for their roles in disulphide bond formation within the endoplasmic reticulum (ER). PDI therefore plays an important role in ER proteostasis, however, it also shows involvement in ER stress, a characteristic recognised in multiple disease states, including cancer. While the exact mechanisms by which PDI contributes to tumorigenesis are still not fully understood, PDI exhibits clear involvement in the unfolded protein response (UPR) pathway. The UPR acts to alleviate ER stress through the activation of ER chaperones, such as PDI, which act to refold misfolded proteins, promoting cell survival. PDI also acts as an upstream regulator of the UPR pathway, through redox regulation of UPR stress receptors. This demonstrates the pro-protective roles of PDI and highlights PDI as a potential therapeutic target for cancer treatment. Recent research has explored the use of PDI inhibitors with PACMA 31 in particular, demonstrating promising anti-cancer effects in ovarian cancer. This review discusses the properties and functions of PDI family members and focuses on their potential as a therapeutic target for cancer treatment.
    Keywords:  cancer; protein disulphide isomerase; protein disulphide isomerase inhibitors
  6. Plant Physiol. 2021 Mar 15. pii: kiab126. [Epub ahead of print]
      The unfolded protein response (UPR) is a conserved stress adaptive signaling pathway in eukaryotic organisms activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). UPR can be elicited in the course of plant defense, playing important roles in plant-microbe interactions. The major signaling pathways of plant UPR rely on the transcriptional activity of activated forms of ER membrane-associated stress sensors bZIP60 and bZIP28, which are transcription factors that modulate expression of UPR genes. In this study, we report the plant susceptibility factor RTP1 (Resistance to Phytophthora parasitica 1) is involved in ER stress sensing and rtp1-mediated resistance against P. parasitica is synergistically regulated with UPR, as demonstrated by the simultaneous strong induction of UPR and ER stress-associated immune genes in Arabidopsis thaliana rtp1 mutant plants during infection by P. parasitica. We further demonstrate RTP1 contributes to stabilization of the ER membrane-associated bZIP60 and bZIP28 through manipulating the bifunctional protein kinase/ribonuclease IRE1-mediated bZIP60 splicing activity and interacting with bZIP28. Consequently, we find rtp1bzip60 and rtp1bzip28 mutant plants exhibit compromised resistance accompanied with attenuated induction of ER stress-responsive immune genes and reduction of callose deposition in response to P. parasitica infection. Taken together, we demonstrate RTP1 may exert negative modulating roles in the activation of key UPR regulators bZIP60 and bZIP28, which are required for rtp1-mediated plant resistance to P. parasitica. This facilitates our understanding of the important roles of stress adaptive UPR and ER stress in plant immunity.
    Keywords:  ER stress; Phytophthora parasitica; RTP1; UPR; bZIP28; bZIP60; immunity; susceptibility
  7. Aging (Albany NY). 2021 Mar 10. 13
      Primary open angle glaucoma (POAG) is the leading cause of irreversible blindness. Dysfunction of the trabecular meshwork (TM), resulting in decreased outflow of aqueous humor and increased intraocular pressure (IOP), plays an important role in the pathogenesis of POAG. However, the underlying mechanisms still remain unclear. In this study, we demonstrated that the eIF2-α/ATF4/CHOP branch of unfolded protein response (UPR) was activated in human trabecular meshwork cells (HTMCs) upon tert-butyl hydroperoxide (TBHP) exposure. Inhibition of ATF4 ameliorated TBHP-induced apoptosis and inflammatory cytokine production, while ectopic expression of ATF4 increased the expression of endothelial leukocyte adhesion molecule (ELAM)-1 and IL-8 in HTMCs. Furthermore, we found that ATF4 inhibition reduced tunicamycin-induced caspase-3 activation, ROS production, ELAM-1 expression, and HTMCs phagocytosis impairment. By an in vivo study in mice, we showed that overexpression of ATF4 in the TM induced C/EBP homologous protein (CHOP) expression and TM cells apoptosis, contributing to inflammatory cytokine production, and probably IOP elevation. More importantly, upregulation of ATF4 and CHOP, and colocalization of ATF4 with ELAM-1 were found in the TM of POAG patients. These results suggest that ATF4 is a critical mediator of oxidative stress and ER stress-induced TM cell dysfunction and apoptosis in POAG.
    Keywords:  activating transcription factor 4; endoplasmic reticulum stress; oxidative stress; primary open angle glaucoma; trabecular meshwork
  8. Virus Res. 2021 Mar 16. pii: S0168-1702(21)00053-8. [Epub ahead of print] 198346
      Avian reovirus (ARV) infection induced apoptosis in vitro and vivo; nevertheless, the intracellular molecular mechanisms have not been sufficiently revealed. In the previous studies, there have been shown that cellular apoptosis caused by ARV were related with GRP78/IRE1/XBP1 pathway. Protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6) are core molecules in unfold protein response (UPR) and play critical role in ER stress related apoptosis, as well as downstream regulation factors, as Caspase-12 and C/EBP homologous protein (CHOP). In this study, we investigated with a focus on the contribution of UPR related signal pathways in the mechanism of ARV mediated apoptosis. Our results showed that the key molecules of UPR pathways proteins, ATF6, PERK and IRE1 as well as Caspase-12 and cleaved-Caspase-3 expression significant increased both in transcript and protein level in ARV infected cultured Vero cells. In the same time, the ARV induces apoptosis was observed by flow cytometric analysis. Further study revealed that when inhibit the UPR effect by 4PBA pretreated or knockdown of ATF6 by lentivirus mediated shRNA abolished the activation effect of UPR, Caspase-12, cleaved-Caspase-3 activation, as well as the apoptosis induction by ARV infection. The present study provides mechanistic insights into that UPR particular ATF6 played critical roles and works upstream of caspase in the process of cellular apoptosis induced by ARV infection.
    Keywords:  ATF6; apoptosis; avian reovirus; unfold protein response
  9. Nat Aging. 2021 Feb;1(2): 165-178
      Organisms respond to mitochondrial stress by activating multiple defense pathways including the mitochondrial unfolded protein response (UPRmt). However, how UPRmt regulators are orchestrated to transcriptionally activate stress responses remains largely unknown. Here we identified CBP-1, the worm ortholog of the mammalian acetyltransferases CBP/p300, as an essential regulator of the UPRmt, as well as mitochondrial stress-induced immune response, reduction of amyloid-β aggregation and lifespan extension in Caenorhabditis elegans. Mechanistically, CBP-1 acts downstream of histone demethylases, JMJD-1.2/JMJD-3.1, and upstream of UPRmt transcription factors including ATFS-1, to systematically induce a broad spectrum of UPRmt genes and execute multiple beneficial functions. In mouse and human populations, transcript levels of CBP/p300 positively correlate with UPRmt transcripts and longevity. Furthermore, CBP/p300 inhibition disrupts, while forced expression of p300 is sufficient to activate, the UPRmt in mammalian cells. These results highlight an evolutionarily conserved mechanism that determines mitochondrial stress response, and promotes health and longevity through CBP/p300.
  10. Biochem Biophys Res Commun. 2021 Mar 16. pii: S0006-291X(21)00399-5. [Epub ahead of print]552 30-36
      Alpha-1 acid glycoprotein (AGP) is a major acute-phase protein that is involved in drug/ligand binding and regulation of immune response. In response to inflammation, AGP secretion from the liver increases, resulting in elevated concentration of plasma AGP. AGP exhibits multiple N-glycosylation sites, and thus, is highly glycosylated. Although AGP glycosylation is considered to affect its functions, the significance of AGP glycosylation for its secretion is unclear. In this study, we investigated the effects of AGP glycosylation using glycosylation-deficient mouse AGP mutants lacking one, four, or all five N-glycosylation sites. Furthermore, we examined the effects of endoplasmic reticulum (ER) stress-inducing reagents, including tunicamycin and thapsigargin, which induce ER stress in an N-glycosylation-dependent and -independent manner, respectively. Here, we found that glycosylation deficiency and ER stress induce a little or no effect on AGP secretion. Conversely, thapsigargin significantly suppressed AGP secretion in glycosylation-independent manner. These findings indicate that AGP secretion is regulated via thapsigargin-sensitive pathway that might be further controlled by the intracellular calcium concentrations.
    Keywords:  Alpha 1-acid glycoprotein; Endoplasmic reticulum stress; N-Glycosylation; Thapsigargin; Tunicamycin