bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019‒09‒29
nine papers selected by
Susan Logue
University of Manitoba

  1. Genes Dev. 2019 Sep 26.
    Xiao Y, Hill MC, Li L, Deshmukh V, Martin TJ, Wang J, Martin JF.
      Cardiac fibroblasts (CFs) respond to injury by transitioning through multiple cell states, including resting CFs, activated CFs, and myofibroblasts. We report here that Hippo signaling cell-autonomously regulates CF fate transitions and proliferation, and non-cell-autonomously regulates both myeloid and CF activation in the heart. Conditional deletion of Hippo pathway kinases, Lats1 and Lats2, in uninjured CFs initiated a self-perpetuating fibrotic response in the adult heart that was exacerbated by myocardial infarction (MI). Single cell transcriptomics showed that uninjured Lats1/2 mutant CFs spontaneously transitioned to a myofibroblast cell state. Through gene regulatory network reconstruction, we found that Hippo-deficient myofibroblasts deployed a network of transcriptional regulators of endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) consistent with elevated secretory activity. We observed an expansion of myeloid cell heterogeneity in uninjured Lats1/2 CKO hearts with similarity to cells recovered from control hearts post-MI. Integrated genome-wide analysis of Yap chromatin occupancy revealed that Yap directly activates myofibroblast cell identity genes, the proto-oncogene Myc, and an array of genes encoding pro-inflammatory factors through enhancer-promoter looping. Our data indicate that Lats1/2 maintain the resting CF cell state through restricting the Yap-induced injury response.
    Keywords:  cell state transitions; epigenomics; fibrosis; hippo signaling; macrophages; myocardial infarction; myofibroblast; single-cell RNA-seq; tissue homeostasis
  2. FEBS J. 2019 Sep 24.
    Anand AA, Walter P.
      The integrated stress response regulates protein synthesis under conditions of stress. Phosphorylation of translation initiation factor eIF2 by stress-sensing kinases converts eIF2 from substrate to competitive inhibitor of its dedicated nucleotide exchange factor, eIF2B, arresting translation. A drug-like molecule called ISRIB reverses the effects of eIF2 phosphorylation and restores translation by targeting eIF2B. When administered to mice, ISRIB enhances cognition and limits cognitive decline due to brain injury. To determine ISRIB's mechanism of action we solved an atomic structure of ISRIB bound to the human eIF2B decamer. We found that ISRIB acts as a molecular staple, pinning together tetrameric subcomplexes of eIF2B along the assembly path to a fully-active, decameric enzyme. In this Structural Snapshot, we discuss ISRIB's mechanism, its ability to rescue disease mutations in eIF2B and conservation of the enzyme and ISRIB binding pocket.
    Keywords:  ISRIB; cognition; eIF2B; integrated stress response; translation; unfolded protein response
  3. Cell Death Dis. 2019 Sep 27. 10(10): 725
    Sarkar Bhattacharya S, Thirusangu P, Jin L, Roy D, Jung D, Xiao Y, Staub J, Roy B, Molina JR, Shridhar V.
      The metabolic signatures of cancer cells are often associated with elevated glycolysis. Pharmacological (PFK158 treatment) and genetic inhibition of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a critical control point in the glycolytic pathway, decreases glucose uptake, ATP production, and lactate dehydrogenase activity and arrests malignant pleural mesothelioma (MPM) cells in the G0/G1 phase to induce cell death. To overcome this nutrient stress, inhibition of PFKFB3 activity led to an escalation in endoplasmic reticulum (ER) activity and aggravated ER stress mostly by upregulating BiP and GADD153 expression and activation of the endocytic Rac1-Rab5-Rab7 pathway resulting in a unique form of cell death called "methuosis" in both the sarcomatoid (H28) and epithelioid (EMMeso) cells. Transmission electron microscopy (TEM) analysis showed the formation of nascent macropinocytotic vesicles, which rapidly coalesced to form large vacuoles with compromised lysosomal function. Both immunofluorescence microscopy and co-immunoprecipitation analyses revealed that upon PFKFB3 inhibition, two crucial biomolecules of each pathway, Rac1 and Calnexin interact with each other. Finally, PFK158 alone and in combination with carboplatin-inhibited tumorigenesis of EMMeso xenografts in vivo. Since most cancer cells exhibit an increased glycolytic rate, these results provide evidence for PFK158, in combination with standard chemotherapy, may have a potential in the treatment of MPM.
  4. Nat Cell Biol. 2019 Sep 23.
    Lim CY, Davis OB, Shin HR, Zhang J, Berdan CA, Jiang X, Counihan JL, Ory DS, Nomura DK, Zoncu R.
      Cholesterol activates the master growth regulator, mTORC1 kinase, by promoting its recruitment to the surface of lysosomes by the Rag guanosine triphosphatases (GTPases). The mechanisms that regulate lysosomal cholesterol content to enable mTORC1 signalling are unknown. Here, we show that oxysterol binding protein (OSBP) and its anchors at the endoplasmic reticulum (ER), VAPA and VAPB, deliver cholesterol across ER-lysosome contacts to activate mTORC1. In cells lacking OSBP, but not other VAP-interacting cholesterol carriers, the recruitment of mTORC1 by the Rag GTPases is inhibited owing to impaired transport of cholesterol to lysosomes. By contrast, OSBP-mediated cholesterol trafficking drives constitutive mTORC1 activation in a disease model caused by the loss of the lysosomal cholesterol transporter, Niemann-Pick C1 (NPC1). Chemical and genetic inactivation of OSBP suppresses aberrant mTORC1 signalling and restores autophagic function in cellular models of Niemann-Pick type C (NPC). Thus, ER-lysosome contacts are signalling hubs that enable cholesterol sensing by mTORC1, and targeting the sterol-transfer activity of these signalling hubs could be beneficial in patients with NPC.
  5. Cells. 2019 Sep 12. pii: E1071. [Epub ahead of print]8(9):
    Fan Y, Simmen T.
      The past decade has seen the emergence of endoplasmic reticulum (ER) chaperones as key determinants of contact formation between mitochondria and the ER on the mitochondria-associated membrane (MAM). Despite the known roles of ER-mitochondria tethering factors like PACS-2 and mitofusin-2, it is not yet entirely clear how they mechanistically interact with the ER environment to determine mitochondrial metabolism. In this article, we review the mechanisms used to communicate ER redox and folding conditions to the mitochondria, presumably with the goal of controlling mitochondrial metabolism at the Krebs cycle and at the electron transport chain, leading to oxidative phosphorylation (OXPHOS). To achieve this goal, redox nanodomains in the ER and the interorganellar cleft influence the activities of ER chaperones and Ca2+-handling proteins to signal to mitochondria. This mechanism, based on ER chaperones like calnexin and ER oxidoreductases like Ero1α, controls reactive oxygen production within the ER, which can chemically modify the proteins controlling ER-mitochondria tethering, or mitochondrial membrane dynamics. It can also lead to the expression of apoptotic or metabolic transcription factors. The link between mitochondrial metabolism and ER homeostasis is evident from the specific functions of mitochondria-ER contact site (MERC)-localized Ire1 and PERK. These functions allow these two transmembrane proteins to act as mitochondria-preserving guardians, a function that is apparently unrelated to their functions in the unfolded protein response (UPR). In scenarios where ER stress cannot be resolved via the activation of mitochondrial OXPHOS, MAM-localized autophagosome formation acts to remove defective portions of the ER. ER chaperones such as calnexin are again critical regulators of this MERC readout.
    Keywords:  ER-phagy; autophagy; chaperones; endoplasmic reticulum; mitochondria; redox
  6. Cell Metab. 2019 Sep 17. pii: S1550-4131(19)30495-4. [Epub ahead of print]
    Chen S, Henderson A, Petriello M, Romano KA, Gearing M, Miao J, Schell M, Sandoval-EspinolaEspinola WJ, Tao J, Sha B, Graham M, Crooke R, Kleinridders A, Balskus EP, Rey FE, Morris A, Biddinger SB.
      The gut-microbe-derived metabolite trimethylamine N-oxide (TMAO) is increased by insulin resistance and associated with several sequelae of metabolic syndrome in humans, including cardiovascular, renal, and neurodegenerative disease. The mechanism by which TMAO promotes disease is unclear. We now reveal the endoplasmic reticulum stress kinase PERK (EIF2AK3) as a receptor for TMAO: TMAO binds to PERK at physiologically relevant concentrations; selectively activates the PERK branch of the unfolded protein response; and induces the transcription factor FoxO1, a key driver of metabolic disease, in a PERK-dependent manner. Furthermore, interventions to reduce TMAO, either by manipulation of the gut microbiota or by inhibition of the TMAO synthesizing enzyme, flavin-containing monooxygenase 3, can reduce PERK activation and FoxO1 levels in the liver. Taken together, these data suggest TMAO and PERK may be central to the pathogenesis of the metabolic syndrome.
    Keywords:  EIF2AK3; FoxO1; PERK; diabetes; endoplasmic reticulum stress; insulin signaling; metabolomics; trimethylamine N-oxide
  7. Cancers (Basel). 2019 Sep 20. pii: E1407. [Epub ahead of print]11(10):
    Aydin Y, Kurt R, Song K, Lin D, Osman H, Youngquist B, Scott JW, Shores NJ, Thevenot P, Cohen A, Dash S.
      Hepatitis C virus (HCV) infection compromises the natural defense mechanisms of the liver leading to a progressive end stage disease such as cirrhosis and hepatocellular carcinoma (HCC). The hepatic stress response generated due to viral replication in the endoplasmic reticulum (ER) undergoes a stepwise transition from adaptive to pro-survival signaling to improve host cell survival and liver disease progression. The minute details of hepatic pro-survival unfolded protein response (UPR) signaling that contribute to HCC development in cirrhosis are unknown. This study shows that the UPR sensor, the protein kinase RNA-like ER kinase (PERK), mediates the pro-survival signaling through nuclear factor erythroid 2-related factor 2 (NRF2)-mediated signal transducer and activator of transcription 3 (STAT3) activation in a persistent HCV infection model of Huh-7.5 liver cells. The NRF2-mediated STAT3 activation in persistently infected HCV cell culture model resulted in the decreased expression of hepatocyte nuclear factor 4 alpha (HNF4A), a major liver-specific transcription factor. The stress-induced inhibition of HNF4A expression resulted in a significant reduction of liver-specific microRNA-122 (miR-122) transcription. It was found that the reversal of hepatic adaptive pro-survival signaling and restoration of miR-122 level was more efficient by interferon (IFN)-based antiviral treatment than direct-acting antivirals (DAAs). To test whether miR-122 levels could be utilized as a biomarker of hepatic adaptive stress response in HCV infection, serum miR-122 level was measured among healthy controls, and chronic HCV patients with or without cirrhosis. Our data show that serum miR-122 expression level remained undetectable in most of the patients with cirrhosis (stage IV fibrosis), suggesting that the pro-survival UPR signaling increases the risk of HCC through STAT3-mediated suppression of miR-122. In conclusion, our data indicate that hepatic pro-survival UPR signaling suppresses the liver-specific HNF4A and its downstream target miR-122 in cirrhosis. These results provide an explanation as to why cirrhosis is a risk factor for the development of HCC in chronic HCV infection.
    Keywords:  cirrhosis; endoplasmic reticulum (ER) stress; hepatitis C virus (HCV); hepatocellular carcinoma (HCC); hepatocyte nuclear factor 4 alpha (HNF4A); microRNA-122 (miR-122); nuclear factor erythroid 2-related factor 2 (NRF2); oxidative stress (OS); signal transducer and activator of transcription 3 (STAT3); unfolded protein response (UPR)
  8. PLoS Genet. 2019 Sep;15(9): e1008364
    Liu DC, Eagleman DE, Tsai NP.
      Seizures can induce endoplasmic reticulum (ER) stress, and sustained ER stress contributes to neuronal death after epileptic seizures. Despite the recent debate on whether inhibiting ER stress can reduce neuronal death after seizures, whether and how ER stress impacts neural activity and seizures remain unclear. In this study, we discovered that the acute ER stress response functions to repress neural activity through a protein translation-dependent mechanism. We found that inducing ER stress promotes the expression and distribution of murine double minute-2 (Mdm2) in the nucleus, leading to ubiquitination and down-regulation of the tumor suppressor p53. Reduction of p53 subsequently maintains protein translation, before the onset of translational repression seen during the latter phase of the ER stress response. Disruption of Mdm2 in an Mdm2 conditional knockdown (cKD) mouse model impairs ER stress-induced p53 down-regulation, protein translation, and reduction of neural activity and seizure severity. Importantly, these defects in Mdm2 cKD mice were restored by both pharmacological and genetic inhibition of p53 to mimic the inactivation of p53 seen during ER stress. Altogether, our study uncovered a novel mechanism by which neurons respond to acute ER stress. Further, this mechanism plays a beneficial role in reducing neural activity and seizure severity. These findings caution against inhibition of ER stress as a neuroprotective strategy for seizures, epilepsies, and other pathological conditions associated with excessive neural activity.
  9. Front Pharmacol. 2019 ;10 977
    Amen OM, Sarker SD, Ghildyal R, Arya A.
      Obesity has been implicated as a risk factor for insulin resistance and cardiovascular diseases (CVDs). Although the association between obesity and CVD is a well-established phenomenon, the precise mechanisms remain incompletely understood. This has led to a relative paucity of therapeutic measures for the prevention and treatment of CVD and associated metabolic disorders. Recent studies have shed light on the pivotal role of prolonged endoplasmic reticulum stress (ERS)-initiated activation of the unfolded protein response (UPR), the ensuing chronic low-grade inflammation, and altered insulin signaling in promoting obesity-compromised cardiovascular system (CVS). In this aspect, potential ways of attenuating ERS-initiated UPR signaling seem a promising avenue for therapeutic interventions. We review intersecting role of obesity-induced ERS, chronic inflammation, insulin resistance, and oxidative stress in the discovery of targeted therapy. Moreover, this review highlights the current progress and strategies on therapeutics being explored in preclinical and clinical research to modulate ERS and UPR signaling.
    Keywords:  cardiac dysfunction; endoplasmic reticulum stress; inflammation; insulin resistance; obesity; oxidative stress; unfolded protein response