bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒03‒29
seven papers selected by
Susan Logue
University of Manitoba

  1. Biochem Biophys Res Commun. 2020 Mar 18. pii: S0006-291X(20)30506-4. [Epub ahead of print]
    Yamamoto T, Endo J, Kataoka M, Matsuhashi T, Katsumata Y, Shirakawa K, Isobe S, Moriyama H, Goto S, Shimanaka Y, Kono N, Arai H, Shinmura K, Fukuda K, Sano M.
      Overloading of the saturated fatty acid (SFA) palmitate induces cardiomyocyte death. The purpose of this study is to elucidate signaling pathways contributing to palmitate-induced cardiomyocyte death. Palmitate-induced cardiomyocyte death was induced in Toll-like receptor 2/4 double-knockdown cardiomyocytes to a similar extent as wild-type cardiomyocytes, while cardiomyocyte death was canceled out by triacsin C, a long-chain acyl-CoA synthetase inhibitor. These results indicated that palmitate induced cytotoxicity after entry and conversion into palmitoyl-CoA. Palmitoyl-CoA is not only degraded by mitochondrial oxidation but also taken up as a component of membrane phospholipids. Palmitate overloading causes cardiomyocyte membrane fatty acid (FA) saturation, which is associated with the activation of endoplasmic reticulum (ER) unfolded protein response (UPR) signaling. We focused on the ER UPR signaling as a possible mechanism of cell death. Palmitate loading activates the UPR signal via membrane FA saturation, but not via unfolded protein overload in the ER since the chemical chaperone 4-phenylbutyrate failed to suppress palmitate-induced ER UPR. The mammalian UPR relies on three ER stress sensors named inositol requiring enzyme-1 (IRE1), PKR-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6). Palmitate loading activated only IRE1 and PERK. Knockdown of PERK did not affect palmitate-induced cardiomyocyte death, while knockdown of IRE1 suppressed palmitate-induced cardiomyocyte death. However, knockdown of X-box binding protein 1 (XBP1), the downstream effector of IRE1, did not affect palmitate-induced cardiomyocyte death. These results were validated by pharmacological inhibitor experiments. In conclusion, we identified that palmitate-induced cardiomyocyte death was triggered by IRE1-mediated signaling independent of XBP1.
    Keywords:  Endoplasmic reticulum stress; Membrane fatty acid composition; Monounsaturated fatty acid; Saturated fatty acid
  2. Stroke. 2020 Mar 26. STROKEAHA120029071
    Wang YC, Li X, Shen Y, Lyu J, Sheng H, Paschen W, Yang W.
      Background and Purpose- Ischemic stroke impairs endoplasmic reticulum (ER) function, causes ER stress, and activates the unfolded protein response. The unfolded protein response consists of 3 branches controlled by ER stress sensor proteins, which include PERK (protein kinase RNA-like ER kinase). Activated PERK phosphorylates eIF2α (eukaryotic initiation factor 2 alpha), resulting in inhibition of global protein synthesis. Here, we aimed to clarify the role of the PERK unfolded protein response branch in stroke. Methods- Neuron-specific and tamoxifen-inducible PERK conditional knockout (cKO) mice were generated by cross-breeding Camk2a-CreERT2 with Perkf/f mice. Transient middle cerebral artery occlusion was used to induce stroke. Short- and long-term stroke outcomes were evaluated. Protein synthesis in the brain was assessed using a surface-sensing-of-translation approach. Results- After tamoxifen-induced deletion of Perk in forebrain neurons was confirmed in PERK-cKO mice, PERK-cKO and control mice were subjected to transient middle cerebral artery occlusion and 3 days or 3 weeks recovery. PERK-cKO mice had larger infarcts and worse neurological outcomes compared with control mice, suggesting that PERK-induced eIF2α phosphorylation and subsequent suppression of translation protects neurons from ischemic stress. Indeed, better stroke outcomes were observed in PERK-cKO mice that received postischemic treatment with salubrinal, which can restore the ischemia-induced increase in phosphorylated eIF2α in these mice. Finally, our data showed that post-treatment with salubrinal improved functional recovery after stroke. Conclusions- Here, we presented the first evidence that postischemic suppression of translation induced by PERK activation promotes recovery of neurological function after stroke. This confirms and further extends our previous observations that recovery of ER function impaired by ischemic stress critically contributes to stroke outcome. Therefore, future research should include strategies to improve stroke outcome by targeting unfolded protein response branches to restore protein homeostasis in neurons.
    Keywords:  animals; mice; neurons; neuroprotection; proteostasis
  3. Oncotarget. 2020 Mar 17. 11(11): 956-968
    Dafflon C, Gaulis S, Barys L, Kapur K, Cornacchione V, Schukur L, Bergling S, Traggiai E, Jansky S, Hellmann L, Engstler BS, Kerr G, de Weck A, Ruddy DA, Naumann U, Stauffer F, Gaul C, Lin Y, Billy E, Weiss A, Hofmann F, Ito M, Tiedt R.
      The histone 3 lysine 79 (H3K79) methyltransferase (HMT) DOT1L is known to play a critical role for growth and survival of MLL-rearranged leukemia. Serendipitous observations during high-throughput drug screens indicated that the use of DOT1L inhibitors might be expandable to multiple myeloma (MM). Through pharmacologic and genetic experiments, we could validate that DOT1L is essential for growth and viability of a subset of MM cell lines, in line with a recent report from another team. In vivo activity against established MM xenografts was observed with a novel DOT1L inhibitor. In order to understand the molecular mechanism of the dependency in MM, we examined gene expression changes upon DOT1L inhibition in sensitive and insensitive cell lines and discovered that genes belonging to the endoplasmic reticulum (ER) stress pathway and protein synthesis machinery were specifically suppressed in sensitive cells. Whole-genome CRISPR screens in the presence or absence of a DOT1L inhibitor revealed that concomitant targeting of the H3K4me3 methyltransferase SETD1B increases the effect of DOT1L inhibition. Our results provide a strong basis for further investigating DOT1L and SETD1B as targets in MM.
    Keywords:  DOT1L; epigenetics; histone methylation; multiple myeloma; unfolded protein response
  4. Plant Physiol. 2020 Mar 23. pii: pp.01488.2019. [Epub ahead of print]
    Yu CY, Kanehara K.
      Phosphoinositides function as lipid signals in plant development and stress tolerance by binding with partner proteins. We previously reported that Arabidopsis (Arabidopsis thaliana) phosphoinositide-specific phospholipase C2 (PLC2) functions in the endoplasmic reticulum (ER) stress response. However, the underlying molecular mechanisms of how phosphoinositides act in the ER stress response remain elusive. Here, we report that a phosphoinositide-binding protein, SMALLER TRICHOMES WITH VARIABLE BRANCHES (SVB), is involved in the ER stress tolerance. SVB contains a DUF538 domain with unknown function; orthologs are exclusively found in Viridiplantae (green plants). We established that SVB is ubiquitously expressed in plant tissues and is localized to the ER, Golgi apparatus, prevacuolar compartment, and plasma membranes. The knockout mutants of svb showed enhanced tolerance to ER stress, which was genetically complemented by transducing genomic SVB. SVB showed time-dependent induction after tunicamycin-induced ER stress, which depended on IRE1 and bZIP60 but not bZIP17 and bZIP28 in the unfolded protein response (UPR). A protein-lipid overlay assay showed specific binding of SVB to phosphatidylinositol 3,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. SVB is therefore suggested to be the plant-specific phosphoinositide-binding protein whose expression is controlled by the UPR through the IRE1-bZIP60 pathway in Arabidopsis.
  5. J Biol Chem. 2020 Mar 23. pii: jbc.RA120.012525. [Epub ahead of print]
    Kapoor A, Chen CG, Iozzo RV.
      Endorepellin, the C-terminal fragment of the heparan sulfate proteoglycan perlecan, influences various signaling pathways in endothelial cells by binding to VEGFR2. In this study, we discovered that soluble endorepellin activates the canonical stress signaling pathway  consisting of PERK, eIF2α, ATF4 and GADD45α. Specifically, endorepellin evoked transient activation of VEGFR2 which in turn phosphorylated PERK at Thr980. Subsequently, PERK phosphorylated eIF2αat Ser51, thereby upregulating its downstream effector proteins ATF4 and GADD45a. RNAi-mediated knockdown of PERK or  eIF2α abrogated the endorepellin-mediated upregulation of GADD45α, the ultimate effector protein of this stress signaling cascade. To functionally validate these findings, we utilized an ex vivo model of angiogenesis. Exposure of the aortic rings embedded in 3D fibrillar collagen to recombinant endorepellin for 2-4 h activated PERK and induced GADD45a vis-à-vis vehicle-treated counterparts. Similar effects were obtained with the established cellular stress inducer tunicamycin. Notably, chronic exposure of aortic rings to endorepellin for 7-9 days markedly suppressed vessel sprouting, an angiostatic effect that was rescued by blocking PERK kinase activity.  Our findings unravel a mechanism by which an extracellular matrix protein evokes stress signaling in endothelial cells that leads to angiostasis.
    Keywords:  Angiogenesis; GADD45; PERK; angiogenesis; eIF2alpha; endothelial cell; proteoglycan; signal transduction; stress response; stress signaling
  6. Front Physiol. 2020 ;11 177
    Ding HR, Tang ZT, Tang N, Zhu ZY, Liu HY, Pan CY, Hu AY, Lin YZ, Gou P, Yuan XW, Cai JH, Dong CL, Wang JL, Ren HZ.
      Aim: The pathogenesis of non-alcoholic fatty liver disease is currently unclear, however, lipid accumulation leading to endoplasmic reticulum stress appears to be pivotal in the process. At present, FOXO1 is known to be involved in NAFLD progression. The relationship between necroptosis and non-alcoholic steatohepatitis has been of great research interest more recently. However, whether FOXO1 regulates ER stress and necroptosis in mice fed with a high fat diet is not clear. Therefore, in this study we analyzed the relationship between non-alcoholic steatohepatitis, ER stress, and necroptosis.Main Methods: Male C57BL/6J mice were fed with an HFD for 14 weeks to induce non-alcoholic steatohepatitis. ER stress and activation of necroptosis in AML12 cells were evaluated after inhibition of FOXO1 in AML12 cells. In addition, mice were fed with AS1842856 for 14 weeks. Liver function and lipid accumulation were measured, and further, ER stress and necroptosis were evaluated by Western Blot and Transmission Electron Microscopy.
    Key Findings: Mice fed with a high fat diet showed high levels of FOXO1, accompanying activation of endoplasmic reticulum stress and necroptosis. Further, sustained PA stimulation caused ER stress and necroptosis in AML12 cells. At the same time, protein levels of FOXO1 increased significantly. Inhibition of FOXO1 with AS1842856 alleviated ER stress and necroptosis. Additionally, treatment of mice with a FOXO1 inhibitor ameliorated liver function after they were fed with a high fat diet, displaying better liver condition and lighter necroptosis.
    Significance: Inhibition of FOXO1 attenuates ER stress and necroptosis in a mouse model of non-alcoholic steatohepatitis.
    Keywords:  FOXO1; NAFLD (non alcoholic fatty liver disease); endoplasmic reticulum stress; necroptosis; non-alcoholic steatohepatitis
  7. iScience. 2020 Mar 07. pii: S2589-0042(20)30154-1. [Epub ahead of print]23(3): 100970
    Okumura F, Fujiki Y, Oki N, Osaki K, Nishikimi A, Fukui Y, Nakatsukasa K, Kamura T.
      The UGA codon signals protein translation termination, but it can also be translated into selenocysteine (Sec, U) to produce selenocysteine-containing proteins (selenoproteins) by dedicated machinery. As Sec incorporation can fail, Sec-containing longer and Sec-lacking shorter proteins co-exist. Cul2-type ubiquitin ligases were recently shown to destabilize such truncated proteins; however, which ubiquitin ligase targets truncated proteins for degradation remained unclear. We report that the Cul5-type ubiquitin ligase KLHDC1 targets truncated SELENOS, a selenoprotein, for proteasomal degradation. SELENOS is involved in endoplasmic reticulum (ER)-associated degradation, which is linked to reactive oxygen species (ROS) production, and the knockdown of KLHDC1 in U2OS cells decreased ER stress-induced cell death. Knockdown of SELENOS increased the cell population with lower ROS levels. Our findings reveal that, in addition to Cul2-type ubiquitin ligases, KLHDC1 is involved in the elimination of truncated oxidoreductase-inactive SELENOS, which would be crucial for maintaining ROS levels and preventing cancer development.
    Keywords:  Cancer; Cell Biology; Molecular Biology