bims-unfpre Biomed news
on Unfolded protein response
Issue of 2019‒03‒17
eleven papers selected by
Susan Logue
Apoptosis Research Centre

  1. Elife. 2019 Mar 13. pii: e43244. [Epub ahead of print]8
    Schmidt RM, Schessner JP, Borner GH, Schuck S.
      Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.
    Keywords:  Rpn4 regulon; S. cerevisiae; cell biology; endoplasmic reticulum stress; proteasome biogenesis; protein degradation; unfolded protein response
  2. Elife. 2019 Mar 14. pii: e41168. [Epub ahead of print]8
    Vitale M, Bakunts A, Orsi A, Lari F, Tadè L, Danieli A, Rato C, Valetti C, Sitia R, Raimondi A, Christianson JC, van Anken E.
      How endoplasmic reticulum (ER) stress leads to cytotoxicity is ill-defined. Previously we showed that HeLa cells readjust homeostasis upon proteostatically driven ER stress, triggered by inducible bulk expression of secretory immunoglobulin M heavy chain (μs) thanks to the unfolded protein response (UPR; Bakunts et al., 2017). Here we show that conditions that prevent that an excess of the ER resident chaperone (and UPR target gene) BiP over µs is restored lead to µs-driven proteotoxicity, i.e. abrogation of HRD1-mediated ER-associated degradation (ERAD), or of the UPR, in particular the ATF6α branch. Such conditions are tolerated instead upon removal of the BiP-sequestering first constant domain (CH1) from µs. Thus, our data define proteostatic ER stress to be a specific consequence of inadequate BiP availability, which both the UPR and ERAD redeem.
    Keywords:  BiP/GRP78; ER stress; cell biology; chaperones; endoplasmic reticulum; human; proteotoxicity; unfolded protein response
  3. Biol Cell. 2019 Mar 12.
    Martinez A, Lopez N, Gonzalez C, Hetz C.
      Parkinson's disease is the second most common neurodegenerative disorder, leading to the progressive decline of motor control due to the loss of dopaminergic neurons in the substantia nigra pars compacta. At the molecular level, Parkinson's disease share common molecular signatures with most neurodegenerative diseases including the accumulation of misfolded proteins in the brain. Alteration in the buffering capacity of the proteostasis network during aging is proposed as one of the triggering steps leading to abnormal protein aggregation in this disease, highlighting disturbances in the function of the endoplasmic reticulum (ER). The ER is the main subcellular compartment involved in protein folding and quality control. ER stress triggers a signaling reaction known as the unfolded protein response (UPR), which aims restoring proteostasis through the induction of adaptive programs or the activation of cell death programs when damage is chronic and cannot be repaired. Here we overview most evidence linking altered mechanisms leading to ER stress in Parkinson´s disease. Strategies to target specific components of the UPR to alleviate ER stress using small molecules and gene therapy are highlighted. This article is protected by copyright. All rights reserved.
    Keywords:  Endoplasmic reticulum; Parkinson's disease; Proteostasis; Unfolded Protein Response; α-Synuclein
  4. Hepatology. 2019 Mar 10.
    Liu J, Fan L, Yu H, Zhang J, He Y, Feng D, Wang F, Li X, Liu Q, Li Y, Guo Z, Gao B, Wei W, Wang H, Sun G.
      Endoplasmic reticulum (ER) stress promotes tumor cell escape from immunosurveillance. However, the underlying mechanisms remain unknown. We hypothesized that ER stress induces hepatocellular carcinoma (HCC) cells to release exosomes, which attenuate antitumor immunity by modulating the expression of programmed death ligand 1 (PD-L1) on macrophages. In this study, we demonstrated that expression of several ER stress markers (glucose-regulated protein 78 [GRP78], activating transcription factor 6 [ATF6], PKR-like endoplasmic reticulum kinase [PERK], inositol-requiring enzyme 1α [IRE1α]) was up-regulated in HCC tissues and negatively correlated with the overall survival and clinicopathological scores in HCC patients. Expression of ER stress-related proteins positively correlated with cluster of differentiation 68-positive (CD68+ ) macrophage recruitment and PD-L1 expression in HCC tissues. High-throughput sequencing analysis identified microRNA (miRNA/miR)-23a-3p as one of the most abundant miRNAs in exosomes derived from the ER stress inducer tunicamycin treated HCC cells (Exo-TM). miR-23a-3p levels in HCC tissues negatively correlated with overall survival. Treatment with Exo-TM up-regulated the expression of PD-L1 in macrophages in vitro and in vivo. Bioinformatics analysis suggests that miR-23a-3p regulates PD-L1 expression through the phosphatase and tensin homolog (PTEN)- phosphoinositide-4,5-bisphosphate 3-kinase (PI3K)-protein kinase B (AKT) pathway. This notion was confirmed by in vitro transfection and co-culture experiments, which revealed that miR-23a-3p inhibited PTEN expression and subsequently elevated phosphorylated AKT and PD-L1 expression in macrophages. Finally, co-culture of T cells with Exo-TM-stimulated macrophages decreased CD8+ T-cell ratio and interleukin-2 production but increased T-cell apoptosis in vitro. CONCLUSION: ER-stressed HCC cells release exosomes to up-regulate PD-L1expression in macrophages, which subsequently inhibits T-cell function via an exosome miR-23a-PTEN-AKT pathway. Our findings provide a new insight into the mechanism how tumor cells escape from antitumor immunity. This article is protected by copyright. All rights reserved.
    Keywords:  endoplasmic reticulum stress; exosome; hepatocellular carcinoma; macrophage; microRNA
  5. EMBO Mol Med. 2019 Mar 12. pii: e9736. [Epub ahead of print]
    Hamczyk MR, Villa-Bellosta R, Quesada V, Gonzalo P, Vidak S, Nevado RM, Andrés-Manzano MJ, Misteli T, López-Otín C, Andrés V.
      Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder caused by progerin, a mutant lamin A variant. HGPS patients display accelerated aging and die prematurely, typically from atherosclerosis complications. Recently, we demonstrated that progerin-driven vascular smooth muscle cell (VSMC) loss accelerates atherosclerosis leading to premature death in apolipoprotein E-deficient mice. However, the molecular mechanism underlying this process remains unknown. Using a transcriptomic approach, we identify here endoplasmic reticulum stress (ER) and the unfolded protein responses as drivers of VSMC death in two mouse models of HGPS exhibiting ubiquitous and VSMC-specific progerin expression. This stress pathway was also activated in HGPS patient-derived cells. Targeting ER stress response with a chemical chaperone delayed medial VSMC loss and inhibited atherosclerosis in both progeria models, and extended lifespan in the VSMC-specific model. Our results identify a mechanism underlying cardiovascular disease in HGPS that could be targeted in patients. Moreover, these findings may help to understand other vascular diseases associated with VSMC death, and provide insight into aging-dependent vascular damage related to accumulation of unprocessed toxic forms of lamin A.
    Keywords:  aging; endoplasmic reticulum stress; progeria; unfolded protein response; vascular smooth muscle cell
  6. Cancers (Basel). 2019 Mar 13. pii: E357. [Epub ahead of print]11(3):
    Sansalone L, Veliz EA, Myrthil NG, Stathias V, Walters W, Torrens II, Schürer SC, Vanni S, Leblanc RM, Graham RM.
      Glioblastoma (GBM) has a dismal prognosis and successful elimination of GBM stem cells (GSCs) is a high-priority as these cells are responsible for tumor regrowth following therapy and ultimately patient relapse. Natural products and their derivatives continue to be a source for the development of effective anticancer drugs and have been shown to effectively target pathways necessary for cancer stem cell self-renewal and proliferation. We generated a series of curcumin inspired bis-chalcones and examined their effect in multiple patient-derived GSC lines. Of the 19 compounds synthesized, four analogs robustly induced GSC death in six separate GSC lines, with a half maximal inhibitory concentration (IC50) ranging from 2.7⁻5.8 μM and significantly reduced GSC neurosphere formation at sub-cytotoxic levels. Structural analysis indicated that the presence of a methoxy group at position 3 of the lateral phenylic appendages was important for activity. Pathway and drug connectivity analysis of gene expression changes in response to treatment with the most active bis-chalcone 4j (the 3,4,5 trimethoxy substituted analog) suggested that the mechanism of action was the induction of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) mediated cell death. This was confirmed by Western blot analysis in which 4j induced robust increases in CHOP, p-jun and caspase 12. The UPR is believed to play a significant role in GBM pathogenesis and resistance to therapy and as such represents a promising therapeutic target.
    Keywords:  bis-chalcones; brain tumor; cancer stem cell; curcumin; endoplasmic reticulum stress; glioblastoma multiforme; glioblastoma stem cell; unfolded protein response
  7. Cancers (Basel). 2019 Mar 08. pii: E338. [Epub ahead of print]11(3):
    Bahar E, Kim JY, Yoon H.
      Cancers cells have the ability to develop chemotherapy resistance, which is a persistent problem during cancer treatment. Chemotherapy resistance develops through different molecular mechanisms, which lead to modification of the cancer cells signals needed for cellular proliferation or for stimulating an immune response. The endoplasmic reticulum (ER) is an important organelle involved in protein quality control, by promoting the correct folding of protein and ER-mediated degradation of unfolded or misfolded protein, namely, ER-associated degradation. Disturbances of the normal ER functions causes an accumulation of unfolded or misfolded proteins in the ER lumen, resulting in a condition called "ER stress (ERS)." ERS triggers the unfolded protein response (UPR)-also called the ERS response (ERSR)-to restore homeostasis or activate cell death. Although the ERSR is one emerging potential target for chemotherapeutics to treat cancer, it is also critical for chemotherapeutics resistance, as well. However, the detailed molecular mechanism of the relationship between the ERSR and tumor survival or drug resistance remains to be fully understood. In this review, we aim to describe the most vital molecular mechanism of the relationship between the ERSR and chemotherapy resistance. Moreover, the review also discusses the molecular mechanism of ER stress-mediated apoptosis on cancer treatments.
    Keywords:  cancer; chemotherapy resistance; endoplasmic reticulum; endoplasmic reticulum stress response
  8. Elife. 2019 Mar 15. pii: e42262. [Epub ahead of print]8
    Cherry PD, Peach SE, Hesselberth JR.
      In the unfolded protein response (UPR), stress in the endoplasmic reticulum (ER) activates a large transcriptional program to increase ER folding capacity. During the budding yeast UPR, Ire1 excises an intron from the HAC1 mRNA and the exon products of cleavage are ligated, and the translated protein induces hundreds of stress-response genes. Using cells with mutations in RNA repair and decay enzymes, we show that phosphorylation of two different HAC1 splicing intermediates is required for their degradation by the 5'→3' exonuclease Xrn1 to enact opposing effects on the UPR. We also found that ligated but 2'-phosphorylated HAC1 mRNA is cleaved, yielding a decay intermediate with both 5'- and 2'-phosphates at its 5'-end that inhibit 5'→3' decay and suggesting that Ire1 degrades incompletely processed HAC1. These decay events expand the scope of RNA-based regulation in the budding yeast UPR and have implications for the control of the metazoan UPR.
    Keywords:  S. cerevisiae; chromosomes; gene expression
  9. Sci Rep. 2019 Mar 13. 9(1): 4330
    Gonen N, Sabath N, Burge CB, Shalgi R.
      The UPR (Unfolded Protein Response) is a well-orchestrated response to ER protein folding and processing overload, integrating both transcriptional and translational outputs. Its three arms in mammalian cells, the PERK translational response arm, together with the ATF6 and IRE1-XBP1-mediated transcriptional arms, have been thoroughly investigated. Using ribosome footprint profiling, we performed a deep characterization of gene expression programs involved in the early and late ER stress responses, within WT or PERK -/- Mouse Embryonic Fibroblasts (MEFs). We found that both repression and activation gene expression programs, affecting hundreds of genes, are significantly hampered in the absence of PERK. Specifically, PERK -/- cells do not show global translational inhibition, nor do they specifically activate early gene expression programs upon short exposure to ER stress. Furthermore, while PERK -/- cells do activate/repress late ER-stress response genes, the response is substantially weaker. Importantly, we highlight a widespread PERK-dependent repression program, consisting of ER targeted proteins, including transmembrane proteins, glycoproteins, and proteins with disulfide bonds. This phenomenon occurs in various different cell types, and has a major translational regulatory component. Moreover, we revealed a novel interplay between PERK and the XBP1-ATF6 arms of the UPR, whereby PERK attenuates the expression of a specific subset of XBP1-ATF6 targets, further illuminating the complexity of the integrated ER stress response.
  10. Cell Rep. 2019 Mar 12. pii: S2211-1247(19)30236-0. [Epub ahead of print]26(11): 3087-3099.e11
    Yücel SS, Stelzer W, Lorenzoni A, Wozny M, Langosch D, Lemberg MK.
      Unspliced XBP1 mRNA encodes XBP1u, the transcriptionally inert variant of the unfolded protein response (UPR) transcription factor XBP1s. XBP1u targets its mRNA-ribosome-nascent-chain-complex to the endoplasmic reticulum (ER) to facilitate UPR activation and prevents overactivation. Yet, its membrane association is controversial. Here, we use cell-free translocation and cellular assays to define a moderately hydrophobic stretch in XBP1u that is sufficient to mediate insertion into the ER membrane. Mutagenesis of this transmembrane (TM) region reveals residues that facilitate XBP1u turnover by an ER-associated degradation route that is dependent on signal peptide peptidase (SPP). Furthermore, the impact of these mutations on TM helix dynamics was assessed by residue-specific amide exchange kinetics, evaluated by a semi-automated algorithm. Based on our results, we suggest that SPP-catalyzed intramembrane proteolysis of TM helices is not only determined by their conformational flexibility, but also by side-chain interactions near the scissile peptide bond with the enzyme's active site.
    Keywords:  ERAD; GxGD aspartic intramembrane protease; HO1; SPP; XBP1u; exosite; regulated intramembrane proteolysis; subsite; transmembrane helix dynamics
  11. Biochem Biophys Res Commun. 2019 Mar 07. pii: S0006-291X(19)30366-3. [Epub ahead of print]
    Ohe K, Tanaka T, Horita Y, Harada Y, Yamasaki T, Abe I, Tanabe M, Nomiyama T, Kobayashi K, Enjoji M, Yanase T.
      The recently discovered circular RNAs (circRNAs) are mostly formed by back-splicing where the downstream 5' splice site splices to the upstream 3' splice site by conventional pre-mRNA splicing. These circRNAs regulate gene expression by acting as sponges for micro-RNAs or RNA-binding proteins. Here we show that the NR5A1 (previously called Ad4BP or SF-1) gene which is exclusively expressed in the adrenal cortex and steroidogenic tissue can form atypical circRNAs by unconventional splicing. Two stem loops with inositol-requiring protein-1α (IRE1α) cleavage sites are connected by an IRE1α cleavage site to form a circRNA (circIRE RNA). From total RNA of normal human adrenal cortex, we detected a circIRE RNA with connected ends by IRE1α cleavage sites in exon 6 and exon 1 (circIRE NR5A1 ex6-1 RNA). circIRE NR5A1 ex6-1 RNA was not detected in the adrenocortical cancer cell line, H295R. When IRE1α was expressed in H295R cells a different circIRE NR5A1 RNA connecting IRE1-cleavage sites in exon 7 and exon 1 was detected (circIRE NR5A1 ex7-1 RNA). The expression of this circIRE RNA was inhibited by the IRE1 inhibitor 1, STF-083010, implicating that it was formed via the ER stress pathway, where IRE1α is a major factor. This is the first report of this type of circular RNA connected by IRE1-cleavage sites found to be expressed in mammalian cells in a tissue-specific manner. To our surprise, the concomitant expression of NR5A1 was increased by IRE1α implicating that NR5A1 was not subjected to IRE1-dependent decay of mRNA (RIDD) but rather activating a transcriptional regulatory network to cope with ER stress in steroidogenic tissue reminiscent to XBP1 in other tissue. We believe this is the first report of such tissue-specific transcriptional cascade responding to ER stress as well as the novel finding of circular RNAs connected by IRE1α cleavage sites expressed in mammalian tissue.
    Keywords:  Adrenal cortex; Circular RNA; NR5A1