bims-unfpre Biomed News
on Unfolded protein response
Issue of 2019–02–24
sixteen papers selected by
Susan Logue, Apoptosis Research Centre
  1. Binding to an unusual inactive kinase conformation by highly selective inhibitors of inositol-requiring enzyme 1α kinase-endoribonuclease.
  2. Degradation of Blos1 mRNA by IRE1 repositions lysosomes and protects cells from stress.
  3. Adaptive endoplasmic reticulum stress signalling via IRE1α-XBP1 preserves self-renewal of haematopoietic and pre-leukaemic stem cells.
  4. IRE1α maintains HSC stemness under ER-stress.
  5. VEGF-A promotes angiogenesis after acute myocardial infarction through increasing ROS production and enhancing ER stress-mediated autophagy.
  6. Simultaneous polychromatic flow cytometric detection of multiple forms of regulated cell death.
  7. Peptide Targeting of an Intracellular Receptor of the Secretory Pathway.
  8. Endoplasmic Reticulum Stress and Unfolded Protein Response in Breast Cancer: The Balance between Apoptosis and Autophagy and Its Role in Drug Resistance.
  9. Endoplasmic Reticulum Stress in Tauopathies: Contrasting Human Brain Pathology with Cellular and Animal Models.
  10. The potential contribution of stromal cell-derived factor 2 (SDF2) in endoplasmic reticulum stress response in severe preeclampsia and labor-onset.
  11. Endoplasmic reticulum proteostasis control and gastric cancer.
  12. RADIATION INDUCES EIF2AK3/PERK AND ERN1/IRE1 MEDIATED PRO-SURVIVAL AUTOPHAGY.
  13. Inhibition of the hexosamine biosynthesis pathway potentiates cisplatin cytotoxicity by decreasing BiP expression in non-small cell lung cancer cells.
  14. Feedback-Driven Mechanisms between Microtubules and the Endoplasmic Reticulum Instruct Neuronal Polarity.
  15. Possible involvement of 4-hydroxy-2-nonenal in the pathogenesis of leptin resistance in obesity.
  16. Gambogic acid triggers vacuolization-associated cell death in cancer cells via disruption of thiol proteostasis.
  1. J Med Chem. 2019 Feb 19.
    Binding to an unusual inactive kinase conformation by highly selective inhibitors of inositol-requiring enzyme 1α kinase-endoribonuclease.
    Giampiero Colombano, John J Caldwell, Thomas Peter Matthews, Chitra Bhatia, Amar Joshi, Tatiana McHardy, Ngai Yi Mok, Yvette Newbatt, Lisa Pickard, Jade Strover, Somaieh Hedayat, Michael Ian Walton, Stephanie Myers, Alan Morenc Jones, Harry Saville, Craig McAndrew, Rosemary Burke, Suzanne Eccles, Faith Davies, Richard Bayliss, Ian Collins.
      A series of imidazo[1,2-b]pyridazin-8-amine kinase inhibitors was discovered to allosterically inhibit the endoribonuclease function of the dual kinase-endoribonuclease inositol-requiring enzyme 1α (IRE1α), a key component of the unfolded protein response in mammalian cells and a potential drug target in multiple human diseases. Inhibitor optimization gave compounds with high kinome selectivity that prevented endoplasmic reticulum stress-induced IRE1α oligomerization and phosphorylation, and inhibited endoribonuclease activity in human cells. X-ray crystallography showed the inhibitors to bind to a previously unreported and unusually disordered conformation of the IRE1α kinase domain that would be incompatible with back-to-back dimerization of the IRE1α protein and activation of the endoribonuclease function. These findings increase the repertoire of known IRE1α protein conformations and can guide the discovery of highly selective ligands for the IRE1α kinase site that allosterically inhibit the endoribonuclease.
    DOI:  https://doi.org/10.1021/acs.jmedchem.8b01721
  2. J Cell Biol. 2019 Feb 20. pii: jcb.201809027. [Epub ahead of print]
    Degradation of Blos1 mRNA by IRE1 repositions lysosomes and protects cells from stress.
    Donghwi Bae, Kristin A Moore, Jessica M Mella, Samantha Y Hayashi, Julie Hollien.
      Cells respond to stress in the ER by initiating the widely conserved unfolded protein response. Activation of the ER transmembrane nuclease IRE1 leads to the degradation of specific mRNAs, but how this pathway affects the ability of cells to recover from stress is not known. Here, we show that degradation of the mRNA encoding biogenesis of lysosome-related organelles 1 subunit 1 (Blos1) leads to the repositioning of late endosomes (LEs)/lysosomes to the microtubule-organizing center in response to stress in mouse cells. Overriding Blos1 degradation led to ER stress sensitivity and the accumulation of ubiquitinated protein aggregates, whose efficient degradation required their independent trafficking to the cell center and the LE-associated endosomal sorting complexes required for transport. We propose that Blos1 regulation by IRE1 promotes LE-mediated microautophagy of protein aggregates and protects cells from their cytotoxic effects.
    DOI:  https://doi.org/10.1083/jcb.201809027
  3. Nat Cell Biol. 2019 Feb 18.
    Adaptive endoplasmic reticulum stress signalling via IRE1α-XBP1 preserves self-renewal of haematopoietic and pre-leukaemic stem cells.
    Lu Liu, Meiling Zhao, Xi Jin, Gina Ney, Kevin B Yang, Fanglue Peng, Jin Cao, Takao Iwawaki, Juan Del Valle, Xi Chen, Qing Li.
      Over their lifetime, long-term haematopoietic stem cells (HSC) are exposed to a variety of stress conditions that they must endure. Many stresses, such as infection/inflammation, reactive oxygen species, nutritional deprivation and hypoxia, activate unfolded protein response signalling, which induces either adaptive changes to resolve the stress or apoptosis to clear the damaged cell. Whether unfolded-protein-response signalling plays any role in HSC regulation remains to be established. Here, we report that the adaptive signalling of the unfolded protein response, IRE1α-XBP1, protects HSCs from endoplasmic reticulum stress-induced apoptosis. IRE1α knockout leads to reduced reconstitution of HSCs. Furthermore, we show that oncogenic N-RasG12D activates IRE1α-XBP1, through MEK-GSK3β, to promote HSC survival under endoplasmic reticulum stress. Inhibiting IRE1α-XBP1 abolished N-RasG12D-mediated survival under endoplasmic reticulum stress and diminished the competitive advantage of NrasG12D HSCs in transplant recipients. Our studies illuminate how the adaptive endoplasmic reticulum stress response is advantageous in sustaining self-renewal of HSCs and promoting pre-leukaemic clonal dominance.
    DOI:  https://doi.org/10.1038/s41556-019-0285-6
  4. Nat Cell Biol. 2019 Feb 18.
    IRE1α maintains HSC stemness under ER-stress.
    Marina Scheller-Wendorff, Carsten Müller-Tidow.
      
    DOI:  https://doi.org/10.1038/s41556-019-0295-4
  5. J Cell Physiol. 2019 Feb 21.
    VEGF-A promotes angiogenesis after acute myocardial infarction through increasing ROS production and enhancing ER stress-mediated autophagy.
    Jiang Zou, Qin Fei, Hui Xiao, Hao Wang, Ke Liu, Meidong Liu, Huali Zhang, Xianzhong Xiao, Kangkai Wang, Nian Wang.
      Proangiogenesis is generally regarded as an effective approach for treating ischemic heart disease. Vascular endothelial growth factor (VEGF)-A is a strong and essential proangiogenic factor. Reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, and autophagy are implicated in the process of angiogenesis. This study is designed to clarify the regulatory mechanisms underlying VEGF-A, ROS, ER stress, autophagy, and angiogenesis in acute myocardial infarction (AMI). A mouse model of AMI was successfully established by occluding the left anterior descending coronary artery. Compared with the sham-operated mice, the microvessel density, VEGF-A content, ROS production, expression of vascular endothelial cadherin, positive expression of 78 kDa glucose-regulated protein/binding immunoglobulin protein (GRP78/Bip), and LC3 puncta in CD31-positive endothelial cells of the ischemic myocardium were overtly elevated. Moreover, VEGF-A exposure predominantly increased the expression of beclin-1, autophagy-related gene (ATG) 4, ATG5, inositol-requiring enzyme-1 (IRE-1), GRP78/Bip, and LC3-II/LC3-I as well as ROS production in the human umbilical vein endothelial cells (HUVECs) in a dose and time-dependent manner. Both beclin-1 small interfering RNA and 3-methyladenine treatment predominantly mitigated VEGF-A-induced tube formation and migration of HUVECs, but they failed to elicit any notable effect on VEGF-A-increased expression of GRP78/Bip. Tauroursodeoxycholic acid not only obviously abolished VEGF-A-induced increase of IRE-1, GRP78/Bip, beclin-1 expression, and LC3-II/LC3-I, but also negated VEGF-A-induced tube formation and migration of HUVECs. Furthermore, N-acetyl- l-cysteine markedly abrogated VEGF-A-increased ROS production, IRE-1, GRP78/Bip, beclin-1 expression, and LC3-II/LC3-I in the HUVECs. Taken together, our data demonstrated that increased spontaneous production of VEGF-A may induce angiogenesis after AMI through initiating ROS-ER stress-autophagy axis in the vascular endothelial cells.
    Keywords:  ER stress; ROS; VEGF-A; angiogenesis; autophagy
    DOI:  https://doi.org/10.1002/jcp.28395
  6. Apoptosis. 2019 Feb 20.
    Simultaneous polychromatic flow cytometric detection of multiple forms of regulated cell death.
    D Bergamaschi, A Vossenkamper, W Y J Lee, P Wang, E Bochukova, G Warnes.
      Currently the study of Regulated Cell Death (RCD) processes is limited to the use of lysed cell populations for Western blot analysis of each separate RCD process. We have previously shown that intracellular antigen flow cytometric analysis of RIP3, Caspase-3 and cell viability dye allowed the determination of levels of apoptosis (Caspase-3+ ve/RIP3- ve), necroptosis (RIP3Hi + ve/Caspase-3- ve) and RIP1-dependent apoptosis (Caspase-3+ ve/RIP3+ ve) in a single Jurkat cell population. The addition of more intracellular markers allows the determination of the incidence of parthanatos (PARP), DNA Damage Response (DDR, H2AX), H2AX hyper-activation of PARP (H2AX/PARP) autophagy (LC3B) and ER stress (PERK), thus allowing the identification of 124 sub-populations both within live and dead cell populations. Shikonin simultaneously induced Jurkat cell apoptosis and necroptosis the degree of which can be shown flow cytometrically together with the effects of blockade of these forms of cell death by zVAD and necrostatin-1 have on specific RCD populations including necroptosis, early and late apoptosis and RIP1-dependent apoptosis phenotypes in live and dead cells. Necrostatin-1 and zVAD was shown to modulate levels of shikonin induced DDR, hyper-action of PARP and parthanatos in the four forms of RCD processes analysed. LC3B was up-regulated by combined treatment of zVAD with chloroquine which also revealed that DNA damage was reduced in live cells but enhanced in dead cells indicating the role of autophagy in maintaining cell health. This approach to RCD research should be a great advance to understanding the mechanisms of drugs and their effects upon RCD populations.
    Keywords:  Apoptosis; Autophagy; DNA damage response; Flow cytometry; Hyper-activation of PARP; Necroptosis; Parthanatos; RIP1-dependent apoptosis; Regulated cell death
    DOI:  https://doi.org/10.1007/s10495-019-01528-w
  7. Biochemistry. 2019 Feb 22.
    Peptide Targeting of an Intracellular Receptor of the Secretory Pathway.
    Alina Tirla, Pablo Rivera-Fuentes.
      Numerous peptides serve as natural ligands of intra- and extracellular receptors. The presence of charged amino acids, however, often hinders the membrane-crossing ability of some of these peptides and renders them unsuitable as chemical probes for perturbing or imaging intracellular targets. In this report, we show that addition of a few natural and unnatural amino acids enhances the cellular uptake and intracellular localization of a highly charged Lys-Asp-Glu-Leu (KDEL) peptide to target the corresponding receptor of the secretory pathway. Live-cell imaging experiments revealed that, through interaction with the KDEL receptor, the peptide is delivered to the endoplasmic reticulum (ER), where it accumulates preferentially. The enhanced uptake and selectivity of this peptide make it a good probe for monitoring disruptions in retrograde transport and ER stress in living cells without any genetic modifications.
    DOI:  https://doi.org/10.1021/acs.biochem.9b00029
  8. Int J Mol Sci. 2019 Feb 16. pii: E857. [Epub ahead of print]20(4):
    Endoplasmic Reticulum Stress and Unfolded Protein Response in Breast Cancer: The Balance between Apoptosis and Autophagy and Its Role in Drug Resistance.
    Lorenza Sisinni, Michele Pietrafesa, Silvia Lepore, Francesca Maddalena, Valentina Condelli, Franca Esposito, Matteo Landriscina.
      The unfolded protein response (UPR) is a stress response activated by the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER) and its uncontrolled activation is mechanistically responsible for several human pathologies, including metabolic, neurodegenerative, and inflammatory diseases, and cancer. Indeed, ER stress and the downstream UPR activation lead to changes in the levels and activities of key regulators of cell survival and autophagy and this is physiologically finalized to restore metabolic homeostasis with the integration of pro-death or/and pro-survival signals. By contrast, the chronic activation of UPR in cancer cells is widely considered a mechanism of tumor progression. In this review, we focus on the relationship between ER stress, apoptosis, and autophagy in human breast cancer and the interplay between the activation of UPR and resistance to anticancer therapies with the aim to disclose novel therapeutic scenarios. The hypothesis that autophagy and UPR may provide novel molecular targets in human malignancies is discussed.
    Keywords:  apoptosis; autophagy; breast cancer; drug resistance; endoplasmic reticulum stress; hormone therapy; unfolded protein response
    DOI:  https://doi.org/10.3390/ijms20040857
  9. J Alzheimers Dis. 2019 Feb 11.
    Endoplasmic Reticulum Stress in Tauopathies: Contrasting Human Brain Pathology with Cellular and Animal Models.
    Nadia I Bocai, María S Marcora, Lautaro F Belfiori-Carrasco, Laura Morelli, Eduardo M Castaño.
      The accumulation and spreading of protein tau in the human brain are major features of neurodegenerative disorders known as tauopathies. In addition to several subcellular abnormalities, tau aggregation within neurons seems capable of triggering endoplasmic reticulum (ER) stress and the consequent unfolded protein response (UPR). In metazoans, full activation of a complex ER-UPR network may restore proteostasis and ER function or, if stress cannot be solved, commit cells to apoptosis. Due to these alternative outcomes (survival or death), the pharmacological manipulation of ER-UPR has become the focus of potential therapies in many human diseases, including tauopathies. Here we update and analyze the experimental data from human brain, cellular, and animal models linking tau accumulation and ER-UPR. We further discuss mechanistic aspects and put the ER-UPR into perspective as a possible therapeutic target in this group of diseases.
    Keywords:  Dementia; endoplasmic reticulum stress; tau proteins; tauopathies; unfolded protein response
    DOI:  https://doi.org/10.3233/JAD-181021
  10. Biochim Biophys Acta Mol Basis Dis. 2019 Feb 15. pii: S0925-4439(19)30012-2. [Epub ahead of print]
    The potential contribution of stromal cell-derived factor 2 (SDF2) in endoplasmic reticulum stress response in severe preeclampsia and labor-onset.
    Aline R Lorenzon-Ojea, Hong Wa Yung, Graham J Burton, Estela Bevilacqua.
      Endoplasmic reticulum (ER) stress occurs when the protein folding machinery in the cell is unable to cope with newly synthesized proteins, which results in an accumulation of misfolded proteins in the ER lumen. In response, the cell activates a cellular signaling pathway known as the Unfolded Protein Response (UPR), aiming to restore cellular homeostasis. Activation and exacerbation of the UPR have been described in several human pathologies, including cancer and neurological disorders, and in some gestational diseases such as preeclampsia and gestational diabetes. This review explores the participation of stromal cell-derived factor 2 (SDF2) in UPR pathways, shows new information and discusses its exacerbation regarding protein expression in severe preeclampsia and labor, both of which are associated with ER stress.
    Keywords:  Labor; Placenta; Preeclampsia; SDF2; Trophoblast; UPR
    DOI:  https://doi.org/10.1016/j.bbadis.2019.01.012
  11. Cancer Lett. 2019 Feb 15. pii: S0304-3835(19)30054-0. [Epub ahead of print]
    Endoplasmic reticulum proteostasis control and gastric cancer.
    Yu Wang, Kai Wang, Yang Jin, Xia Sheng.
      The endoplasmic reticulum (ER) is the primary organelle responsible for the synthesis, modification, folding and secretion of proteins, especially in specialized secretory cells. It also contributes to the maintenance of cellular functions, such as Ca2+ storage, lipogenesis, gluconeogenesis, and organelle biogenesis. Cellular stress conditions, such as glucose deprivation, hypoxia and disturbance of Ca2+ homeostasis, may increase the risk of protein misfolding and perturb proteostasis. This activates ER stress and triggers the unfolded protein response (UPR), leading to either the restoration of homeostasis or cell death. ER stress and UPR have been shown to play crucial roles in the pathogenesis, progression and treatment response of various cancers. In gastric cancer (GC), one of the most aggressive cancer types, critical functions of ER stress signaling have also started to emerge. Herein, we summarize the current knowledge linking ER stress and UPR to GC; we also discuss the possible nodes of therapeutic intervention and propose directions of future research.
    Keywords:  ER proteostasis; UPR; gastric cancer; therapeutic targeting
    DOI:  https://doi.org/10.1016/j.canlet.2019.01.034
  12. Autophagy. 2019 Feb 17.
    RADIATION INDUCES EIF2AK3/PERK AND ERN1/IRE1 MEDIATED PRO-SURVIVAL AUTOPHAGY.
    Madhuri Chaurasia, Swapnil Gupta, Asmita Das, B S Dwarakanath, Anne Simonsen, Kulbhushan Sharma.
      Cellular effects of ionizing radiation include oxidative damage to macromolecules, unfolded protein response (UPR) and metabolic imbalances. Oxidative stress and UPR have been shown to induce macroautophagy/autophagy in a context-dependent manner and are crucial factors in determining the fate of irradiated cells. However, an in-depth analysis of the relationship between radiation-induced damage and autophagy has not been explored. In the present study, we investigated the relationship between radiation-induced oxidative stress, UPR and autophagy in murine macrophage cells. A close association was observed between radiation-induced oxidative burst, UPR and induction of autophagy, with the possible involvement of EIF2AK3/PERK (eukaryotic translation initiation factor 2 alpha kinase 3) and ERN1/IRE1 (endoplasmic reticulum [ER] to nucleus signaling 1). Inhibitors of either UPR or autophagy reduced the cell survival indicating the importance of these processes after radiation exposure. Moreover, modulation of autophagy affected lethality in the whole body of irradiated C57BL/6 mouse. These findings indicate that radiation-induced autophagy is a pro-survival response initiated by oxidative stress and mediated by EIF2AK3 and ERN1.
    Keywords:  Autophagy; EIF2AK3/PERK; ER stress; ERN1/IRE1; oxidative stress; radiation exposure
    DOI:  https://doi.org/10.1080/15548627.2019.1582973
  13. Mol Carcinog. 2019 Feb 20.
    Inhibition of the hexosamine biosynthesis pathway potentiates cisplatin cytotoxicity by decreasing BiP expression in non-small cell lung cancer cells.
    Wenshu Chen, Kieu Chinh Do, Bryanna Saxton, Shuguang Leng, Piotr Filipczak, Mathewos Tessema, Steven A Belinsky, Yong Lin.
      Platinum anticancer agents are essential components in chemotherapeutic regimens for non-small cell lung cancer (NSCLC) patients ineligible for targeted therapy. However, platinum-based regimens have reached a plateau of therapeutic efficacy; therefore, it is critical to implement novel approaches for improvement. The hexosamine biosynthesis pathway (HBP), which produces amino-sugar N-acetyl-glucosamine (GlcNAc) for protein glycosylation, is important for protein function and cell survival. Here we show a beneficial effect by combination of cisplatin with HBP inhibition. Expression of glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme of HBP, was increased in NSCLC cell lines and tissues. Pharmacological inhibition of GFAT activity or knockdown of GFAT impaired cell proliferation and exerted a synergistic or additive cytotoxicity to the cells treated with cisplatin. Mechanistically, GFAT positively regulated the expression of binding immunoglobulin protein (BiP; also known as glucose-regulated protein 78, GRP78), an endoplasmic reticulum chaperone involved in unfolded protein response. Suppressing GFAT activity resulted in downregulation of BiP that activated inositol-requiring enzyme 1α (IRE1α), a sensor protein of unfolded protein response, and exacerbated cisplatin-induced cell apoptosis. These data identify GFAT-mediated HBP as a target for improving platinum-based chemotherapy for NSCLC. This article is protected by copyright. All rights reserved.
    Keywords:  binding immunoglobulin protein; cisplatin; glutamine:fructose-6-phosphate amidotransferase; hexosamine biosynthesis pathway; non-small cell lung cancer
    DOI:  https://doi.org/10.1002/mc.22992
  14. Neuron. 2019 Feb 13. pii: S0896-6273(19)30057-1. [Epub ahead of print]
    Feedback-Driven Mechanisms between Microtubules and the Endoplasmic Reticulum Instruct Neuronal Polarity.
    Ginny G Farías, Amélie Fréal, Elena Tortosa, Riccardo Stucchi, Xingxiu Pan, Sybren Portegies, Lena Will, Maarten Altelaar, Casper C Hoogenraad.
      Establishment of neuronal polarity depends on local microtubule (MT) reorganization. The endoplasmic reticulum (ER) consists of cisternae and tubules and, like MTs, forms an extensive network throughout the entire cell. How the two networks interact and control neuronal development is an outstanding question. Here we show that the interplay between MTs and the ER is essential for neuronal polarity. ER tubules localize within the axon, whereas ER cisternae are retained in the somatodendritic domain. MTs are essential for axonal ER tubule stabilization, and, reciprocally, the ER is required for stabilizing and organizing axonal MTs. Recruitment of ER tubules into one minor neurite initiates axon formation, whereas ER retention in the perinuclear area or disruption of ER tubules prevent neuronal polarization. The ER-shaping protein P180, present in axonal ER tubules, controls axon specification by regulating local MT remodeling. We propose a model in which feedback-driven regulation between the ER and MTs instructs neuronal polarity.
    Keywords:  ER cisternae; ER tubules; ER-shaping proteins; MT-driven motors; axon specification; endoplasmic reticulum; microtubule dynamics; microtubules; neuronal polarity; neurons
    DOI:  https://doi.org/10.1016/j.neuron.2019.01.030
  15. Am J Physiol Cell Physiol. 2019 Feb 21.
    Possible involvement of 4-hydroxy-2-nonenal in the pathogenesis of leptin resistance in obesity.
    Toru Hosoi, Ayaka Kuwamura, Mina Thon, Kyoji Tsuchio, Amer Ali Abd El-Hafeez, Koichiro Ozawa.
      Insensitivity to the anti-obesity hormone, leptin, has been suggested to be involved in the pathogenesis of obesity. However, the pathological mechanisms underlying the development of leptin resistance are not well understood. This study aimed to examine the pathological mechanisms of leptin resistance in obesity. In the present study, we found that 4-hydroxy-2-nonenal (4-HNE), an aldehyde, may be involved in the development of leptin resistance. The SH-SY5Y-Ob-Rb human neuroblastoma cell line, transfected to stably express the Ob-Rb leptin receptor, was treated with 4-HNE and leptin-induced signal transduction was analysed. We found that 4-HNE dose- and time-dependently inhibited leptin-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation, a major anti-obesity signal of leptin. On the other hand, 4-HNE did not affect tyrosine phosphorylation of broad cellular proteins, suggesting that the inhibitory effect may be selective to leptin signalling. Mechanistically, 4-HNE induced the eukaryotic initiation factor 2 α (eIF2α) -C/EBP-homologous protein (CHOP) arm of endoplasmic reticulum stress signalling, which may be involved in the pathogenesis of leptin resistance. Overall, these results suggest that 4-HNE may partly affect ER stress-induced unfolded protein response (UPR) signalling and may be involved in the pathogenesis of leptin resistance.
    Keywords:  4-hydroxy-2-nonenal; endoplasmic reticulum stress; leptin resistance; obesity; signal transducer and activator of transcription 3
    DOI:  https://doi.org/10.1152/ajpcell.00080.2018
  16. Cell Death Dis. 2019 Feb 22. 10(3): 187
    Gambogic acid triggers vacuolization-associated cell death in cancer cells via disruption of thiol proteostasis.
    Min Ji Seo, Dong Min Lee, In Young Kim, Dongjoo Lee, Min-Koo Choi, Joo-Youn Lee, Seok Soon Park, Seong-Yun Jeong, Eun Kyung Choi, Kyeong Sook Choi.
      Gambogic acid (GA), a xanthonoid extracted from the resin of the tree, Garcinia hanburyi, was recently shown to exert anticancer activity in multiple studies, but the underlying action mechanism remains unclear. Here, we show that GA induces cancer cell death accompanied by vacuolation in vitro and in vivo. This GA-induced vacuolation in various cancer cells was derived from dilation of the endoplasmic reticulum (ER) and mitochondria, and was blocked by cycloheximide. These findings suggest that GA kills cancer cells by inducing paraptosis, a vacuolization-associated cell death. We found that megamitochondria formation, which arose from the fusion of swollen mitochondria, preceded the fusion of ER-derived vacuoles. GA-induced proteasomal inhibition was found to contribute to the ER dilation and ER stress seen in treated cancer cells, and megamitochondria formation was followed by mitochondrial membrane depolarization. Interestingly, GA-induced paraptosis was effectively blocked by various thiol-containing antioxidants, and this effect was independent of ROS generation. We observed that GA can react with cysteinyl thiol to form Michael adducts, suggesting that the ability of GA to covalently modify the nucleophilic cysteinyl groups of proteins may cause protein misfolding and subsequent accumulation of misfolded proteins within the ER and mitochondria. Collectively, our findings show that disruption of thiol proteostasis and subsequent paraptosis may critically contribute to the anti-cancer effects of GA.
    DOI:  https://doi.org/10.1038/s41419-019-1360-4
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