Endoplasmic Reticulum Stress Is Involved in Cochlear Cell Apoptosis in a Cisplatin-Induced Ototoxicity Rat Model

Endoplasmic reticulum (ER) stress arises when excessive improperly folded proteins accumulate in the ER lumen. When ER stress occurs, the unfolded protein response (UPR) is subsequently activated to restore ER proteostasis. However, severe ER stress leads to apoptosis. Recent studies have suggested that cisplatin cytotoxicity may be related to ER stress. The purpose of this study was to determine whether ER stress participates in cochlear cell apoptosis in a cisplatin-induced ototoxicity rat model and to also determine the possible relationship between ER stress and hearing loss. Our results revealed that treatment with cisplatin upregulated the expression of active caspase-12 in cochlear cells, which is indicative of cisplatin-induced activation of ER-specific apoptosis. Increased expression of C/EBP homologous protein (CHOP) and cleaved caspase-9 suggested a close relationship between severe ER stress and mitochondria-dependent apoptosis in the cochlear cells of cisplatin-treated rats. In addition, we found that tauroursodeoxycholic acid (TUDCA), a promoter of ER proteostasis, had a protective effect on cisplatin-induced hearing loss. These results demonstrate that ER stress is involved in the cisplatin-induced apoptosis of cochlear cells in vivo.

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BCL-2 family member BOK promotes apoptosis in response to endoplasmic reticulum stress

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1421063112 ◽

2015 ◽

Vol 112 (23) ◽

pp. 7201-7206 ◽

Cited By ~ 67

Author(s):

Marcos A. Carpio ◽

Michael Michaud ◽

Wenping Zhou ◽

Jill K. Fisher ◽

Loren D. Walensky ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Brefeldin A ◽

B Cell Lymphoma ◽

Apoptotic Response ◽

Apoptotic Pathway ◽

Multiple Organs ◽

Induced Apoptosis ◽

The Unfolded Protein Response

B-cell lymphoma 2 (BCL-2) ovarian killer (BOK) is a BCL-2 family protein with high homology to the multidomain proapoptotic proteins BAX and BAK, yet Bok−/− and even Bax−/−Bok−/− and Bak−/−Bok−/− mice were reported to have no overt phenotype or apoptotic defects in response to a host of classical stress stimuli. These surprising findings were interpreted to reflect functional compensation among the BAX, BAK, and BOK proteins. However, BOK cannot compensate for the severe apoptotic defects of Bax−/−Bak−/− mice despite its widespread expression. Here, we independently developed Bok−/− mice and found that Bok−/− cells are selectively defective in their response to endoplasmic reticulum (ER) stress stimuli, consistent with the predominant subcellular localization of BOK at the ER. Whereas Bok−/− mouse embryonic fibroblasts exposed to thapsigargin, A23187, brefeldin A, DTT, geldanamycin, or bortezomib manifested reduced activation of the mitochondrial apoptotic pathway, the death response to other stimuli such as etoposide, staurosporine, or UV remained fully intact. Multiple organs in Bok−/− mice exhibited resistance to thapsigargin-induced apoptosis in vivo. Although the ER stress agents activated the unfolded protein response, both ATF4 and CHOP activation were diminished in Bok−/− cells and mice. Importantly, BAX and BAK were unable to compensate for the defective apoptotic response to ER stress observed in SV40-transformed and primary Bok−/− cells, and in vivo. These findings support a selective and distinguishing role for BOK in regulating the apoptotic response to ER stress, revealing—to our knowledge—the first bona fide apoptotic defect linked to Bok deletion.

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Novel targets for endoplasmic reticulum stress-induced apoptosis in B-CLL

Blood ◽

10.1182/blood-2010-03-275628 ◽

2010 ◽

Vol 116 (15) ◽

pp. 2713-2723 ◽

Cited By ~ 53

Author(s):

Emanuela Rosati ◽

Rita Sabatini ◽

Giuliana Rampino ◽

Filomena De Falco ◽

Mauro Di Ianni ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Cell Apoptosis ◽

Ex Vivo ◽

Lymphocytic Leukemia ◽

Minor Role ◽

Caspase 8 ◽

Caspase 9 ◽

Cytochrome C Release ◽

Induced Apoptosis

Abstract A better understanding of apoptotic signaling in B-chronic lymphocytic leukemia (B-CLL) cells may help to define new therapeutic strategies. This study investigated endoplasmic reticulum (ER) stress signaling in spontaneous apoptosis of B-CLL cells and whether manipulating ER stress increases their apoptosis. Results show that a novel ER stress-triggered caspase cascade, initiated by caspase-4 and involving caspase-8 and -3, plays an important role in spontaneous B-CLL cell apoptosis. ER stress-induced apoptosis in B-CLL cells also involves CHOP/GADD153 up-regulation, increased JNK1/2 phosphorylation, and caspase-8–mediated cleavage of Bap31 to Bap20, known to propagate apoptotic signals from ER to mitochondria. In ex vivo B-CLL cells, some apoptotic events associated with mitochondrial pathway also occur, including mitochondrial cytochrome c release and caspase-9 processing. However, pharmacologic inhibition studies show that caspase-9 plays a minor role in B-CLL cell apoptosis. ER stress also triggers survival signals in B-CLL cells by increasing BiP/GRP78 expression. Manipulating ER signaling by siRNA down-regulation of BiP/GRP78 or treating B-CLL cells with 2 well-known ER stress-inducers, tunicamycin and thapsigargin, increases their apoptosis. Overall, our findings show that ER triggers an essential pathway for B-CLL cell apoptosis and suggest that genetic and pharmacologic manipulation of ER signaling could represent an important therapeutic strategy.

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Protective role of Gipie, a Girdin family protein, in endoplasmic reticulum stress responses in endothelial cells

Molecular Biology of the Cell ◽

10.1091/mbc.e10-08-0724 ◽

2011 ◽

Vol 22 (6) ◽

pp. 736-747 ◽

Cited By ~ 18

Author(s):

Etsushi Matsushita ◽

Naoya Asai ◽

Atsushi Enomoto ◽

Yoshiyuki Kawamoto ◽

Takuya Kato ◽

...

Keyword(s):

Endothelial Cells ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Stress Responses ◽

Protective Role ◽

Jnk Pathway ◽

Interacting Protein ◽

Family Protein ◽

Induced Apoptosis ◽

The Unfolded Protein Response

Continued exposure of endothelial cells to mechanical/shear stress elicits the unfolded protein response (UPR), which enhances intracellular homeostasis and protect cells against the accumulation of improperly folded proteins. Cells commit to apoptosis when subjected to continuous and high endoplasmic reticulum (ER) stress unless homeostasis is maintained. It is unknown how endothelial cells differentially regulate the UPR. Here we show that a novel Girdin family protein, Gipie (78 kDa glucose-regulated protein [GRP78]-interacting protein induced by ER stress), is expressed in endothelial cells, where it interacts with GRP78, a master regulator of the UPR. Gipie stabilizes the interaction between GRP78 and the ER stress sensor inositol-requiring protein 1 (IRE1) at the ER, leading to the attenuation of IRE1-induced c-Jun N-terminal kinase (JNK) activation. Gipie expression is induced upon ER stress and suppresses the IRE1-JNK pathway and ER stress-induced apoptosis. Furthermore we found that Gipie expression is up-regulated in the neointima of carotid arteries after balloon injury in a rat model that is known to result in the induction of the UPR. Thus our data indicate that Gipie/GRP78 interaction controls the IRE1-JNK signaling pathway. That interaction appears to protect endothelial cells against ER stress-induced apoptosis in pathological contexts such as atherosclerosis and vascular endothelial dysfunction.

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Oleate attenuates palmitate-induced endoplasmic reticulum stress and apoptosis in placental trophoblasts

Reproduction ◽

10.1530/rep-16-0576 ◽

2017 ◽

Vol 153 (4) ◽

pp. 369-380 ◽

Cited By ~ 11

Author(s):

Bryanne N Colvin ◽

Mark S Longtine ◽

Baosheng Chen ◽

Maria Laura Costa ◽

D Michael Nelson

Keyword(s):

Fatty Acids ◽

Endoplasmic Reticulum ◽

Er Stress ◽

Maternal Blood ◽

Dietary Fatty Acids ◽

Obese Women ◽

Villous Trophoblast ◽

The Unfolded Protein Response

Pre-pregnancy obesity is increasingly common and predisposes pregnant women and offspring to gestational diabetes, pre-eclampsia, fetal growth abnormalities and stillbirth. Obese women exhibit elevated levels of the two most common dietary fatty acids, palmitate and oleate, and the maternal blood containing these nutrients bathes the surface of trophoblasts of placental villi in vivo. We test the hypothesis that the composition and concentration of free fatty acids modulate viability and function of primary human villous trophoblasts in culture. We found that palmitate increases syncytiotrophoblast death, specifically by caspase-mediated apoptosis, whereas oleate does not cause enhanced cell death. Importantly, exposure to both fatty acids in equimolar amounts yielded no increase in death or apoptosis, suggesting that oleate can protect syncytiotrophoblasts from palmitate-induced death. We further found that palmitate, but not oleate or oleate with palmitate, increases endoplasmic reticulum (ER) stress, signaling through the unfolded protein response, and yielding CHOP-mediated induction of apoptosis. Finally, we show that oleate or oleate plus palmitate both lead to increased lipid droplets in syncytiotrophoblasts, whereas palmitate does not. The data show palmitate is toxic to human syncytiotrophoblasts, through the induction of ER stress and apoptosis mediated by CHOP, whereas oleate is not toxic, abrogates palmitate toxicity and induces fat accumulation. We speculate that our in vitro results offer pathways by which the metabolic milieu of the obese pregnant woman can yield villous trophoblast dysfunction and sub-optimal placental function.

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p31 Deficiency Influences Endoplasmic Reticulum Tubular Morphology and Cell Survival

Molecular and Cellular Biology ◽

10.1128/mcb.01089-08 ◽

2009 ◽

Vol 29 (7) ◽

pp. 1869-1881 ◽

Cited By ~ 19

Author(s):

Takefumi Uemura ◽

Takashi Sato ◽

Takehiro Aoki ◽

Akitsugu Yamamoto ◽

Tetsuya Okada ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Nuclear Translocation ◽

Marked Change ◽

Conditional Knockout ◽

Induced Apoptosis ◽

Factor C ◽

Er Membrane

ABSTRACT p31, the mammalian orthologue of yeast Use1p, is an endoplasmic reticulum (ER)-localized soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) that forms a complex with other SNAREs, particularly syntaxin 18. However, the role of p31 in ER function remains unknown. To determine the role of p31 in vivo, we generated p31 conditional knockout mice. We found that homozygous deletion of the p31 gene led to early embryonic lethality before embryonic day 8.5. Conditional knockout of p31 in brains and mouse embryonic fibroblasts (MEFs) caused massive apoptosis accompanied by upregulation of ER stress-associated genes. Microscopic analysis showed vesiculation and subsequent enlargement of the ER membrane in p31-deficient cells. This type of drastic disorganization in the ER tubules has not been demonstrated to date. This marked change in ER structure preceded nuclear translocation of the ER stress-related transcription factor C/EBP homologous protein (CHOP), suggesting that ER stress-induced apoptosis resulted from disruption of the ER membrane structure. Taken together, these results suggest that p31 is an essential molecule involved in the maintenance of ER morphology and that its deficiency leads to ER stress-induced apoptosis.

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Endoplasmic reticulum stress as target for treatment of hearing loss

STEMedicine ◽

10.37175/stemedicine.v1i3.21 ◽

2020 ◽

Vol 1 (3) ◽

pp. e21

Author(s):

Yanfei Wang ◽

Zhigang Xu

Keyword(s):

Endoplasmic Reticulum ◽

Hearing Loss ◽

Er Stress ◽

Protein Biosynthesis ◽

Unfolded Proteins ◽

Unfolded Protein ◽

Global Protein Synthesis ◽

Acquired Hearing Loss ◽

The Unfolded Protein Response ◽

Protein Response

The endoplasmic reticulum (ER) plays pivotal roles in coordinating protein biosynthesis and processing. Under ER stress, when excessive misfolded or unfolded proteins are accumulated in the ER, the unfolded protein response (UPR) is activated. The UPR blocks global protein synthesis while activates chaperone expression, eventually leading to the alleviation of ER stress. However, prolonged UPR induces cell death. ER stress has been associated with various types of diseases. Recently, increasing evidences suggest that ER stress and UPR are also involved in hearing loss. In the present review, we will discuss the role of ER stress in hereditary hearing loss as well as acquired hearing loss. Moreover, we will discuss the emerging ER stress-based treatment of hearing loss. Further investigations are warranted to understand the mechanisms in detail how ER stress contributes to hearing loss, which will help us develop better ER stress-related treatments.

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The endocannabinoid 2-arachidonoylglycerol promotes endoplasmic reticulum stress in placental cells

Reproduction ◽

10.1530/rep-19-0539 ◽

2020 ◽

Vol 160 (2) ◽

pp. 171-180 ◽

Cited By ~ 1

Author(s):

Marta Almada ◽

Lia Costa ◽

Bruno Fonseca ◽

Patrícia Alves ◽

Jorge Braga ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Cannabinoid Receptor ◽

Initiation Factor ◽

Parp Cleavage ◽

Ros Generation ◽

Placental Development ◽

Induced Apoptosis ◽

The Unfolded Protein Response ◽

Er Homeostasis

Proliferation, differentiation and apoptosis of trophoblast cells are required for normal placental development. Impairment of those processes may lead to pregnancy-related diseases. Disruption of endoplasmic reticulum (ER) homeostasis has been associated with several reproductive pathologies including recurrent pregnancy loss and preeclampsia. In the unfolded protein response (UPR), specific ER-stress signalling pathways are activated to restore ER homeostasis, but if the adaptive response fails, apoptosis is triggered. Protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1) and Activating transcription factor 6 (ATF6) are central players in UPR and in ER-stress-induced apoptosis, as well as downstream transcription factors, as C/EBP homologous protein (CHOP). Our previous studies have shown that the endocannabinoid 2-arachidonoylglycerol (2-AG) modulates trophoblast cell turnover. Nevertheless, the role of ER-stress on 2-AG induced apoptosis and cannabinoid signalling in trophoblast has never been addressed. In this work, we used BeWo cells and human primary cytotrophoblasts isolated from term-placenta. The expression of ER-stress markers was analysed by qRT-PCR and Western blotting. ROS generation was assessed by fluorometric methods, while apoptosis was detected by the evaluation of caspase -3/-7 activities and Poly (ADP-ribose) polymerase (PARP) cleavage. Our findings indicate that 2-AG is able to induce ER-stress and apoptosis. Moreover, the eukaryotic initiation factor 2 (eIF2α)/CHOP pathway involved in ER-stress-induced apoptosis is triggered through a mechanism dependent on cannabinoid receptor CB2 activation. The results bring novel insights on the importance of ER-stress and cannabinoid signalling on 2-AG mechanisms of action in placenta.

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The Drosophila metallopeptidase superdeath decouples apoptosis from the activation of the ER stress response

10.1101/620492 ◽

2019 ◽

Cited By ~ 1

Author(s):

Rebecca A.S. Palu ◽

Clement Y. Chow

Keyword(s):

Endoplasmic Reticulum ◽

Drosophila Melanogaster ◽

Stress Response ◽

Er Stress ◽

Unfolded Protein ◽

Er Stress Response ◽

Membrane Bound ◽

Induced Apoptosis ◽

The Unfolded Protein Response ◽

Protein Response

ABSTRACTEndoplasmic reticulum (ER) stress-induced apoptosis is a primary cause and modifier of degeneration in a number of genetic disorders. Understanding how genetic variation between individuals influences the ER stress response and subsequent activation of apoptosis could improve individualized therapies and predictions of outcomes for patients. In this study, we find that the uncharacterized, membrane-bound metallopeptidase CG14516 in Drosophila melanogaster, which we rename as SUPpressor of ER stress-induced DEATH (superdeath), plays a role in modifying ER stress-induced apoptosis. We demonstrate that loss of superdeath reduces apoptosis and degeneration in the Rh1G69D model of ER stress through the JNK signaling cascade. This effect on apoptosis occurs without altering the activation of the unfolded protein response (IRE1 and PERK), suggesting that the beneficial pro-survival effects of this response are intact. Furthermore, we show that superdeath functions epistatically upstream of CDK5, a known JNK-activated pro-apoptotic factor in this model of ER stress. We demonstrate that superdeath is not only a modifier of this particular model, but functions as a general modifier of ER stress-induced apoptosis across different tissues and ER stresses. Finally, we present evidence of Superdeath localization to the endoplasmic reticulum membrane. While similar in sequence to a number of human metallopeptidases found in the plasma membrane and ER membrane, its localization suggests that superdeath is orthologous to ERAP1/2 in humans. Together, this study provides evidence that superdeath is a link between stress in the ER and activation of cytosolic apoptotic pathways.SIGNIFICANCE STATEMENTGenetic diseases display a great deal of variability in presentation, progression, and overall outcomes. Much of this variability is caused by differences in genetic background among patients. One process that commonly modifies degenerative disease is the endoplasmic reticulum (ER) stress response. Understanding the genetic sources of variation in the ER stress response could improve individual diagnosis and treatment decisions. In this study, we characterized one such modifier in Drosophila melanogaster, the membrane-bound metallopeptidase CG14516 (superdeath). Loss of this enzyme suppresses a model of ER stress-induced degeneration by reducing cell death without altering the beneficial activation of the unfolded protein response. Our findings make superdeath and its orthologues attractive therapeutic targets in degenerative disease.

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Role of ERO1-α–mediated stimulation of inositol 1,4,5-triphosphate receptor activity in endoplasmic reticulum stress–induced apoptosis

The Journal of Cell Biology ◽

10.1083/jcb.200904060 ◽

2009 ◽

Vol 186 (6) ◽

pp. 783-792 ◽

Cited By ~ 326

Author(s):

Gang Li ◽

Marco Mongillo ◽

King-Tung Chin ◽

Heather Harding ◽

David Ron ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Calcium Release ◽

Loss Of Function ◽

Ip3 Receptor ◽

Calcium Dependent ◽

Insulin Resistant ◽

Stressed Cells ◽

Induced Apoptosis

Endoplasmic reticulum (ER) stress–induced apoptosis is involved in many diseases, but the mechanisms linking ER stress to apoptosis are incompletely understood. Based on roles for C/EPB homologous protein (CHOP) and ER calcium release in apoptosis, we hypothesized that apoptosis involves the activation of inositol 1,4,5-triphosphate (IP3) receptor (IP3R) via CHOP-induced ERO1-α (ER oxidase 1 α). In ER-stressed cells, ERO1-α is induced by CHOP, and small interfering RNA (siRNA) knockdown of ERO1-α suppresses apoptosis. IP3-induced calcium release (IICR) is increased during ER stress, and this response is blocked by siRNA-mediated silencing of ERO1-α or IP3R1 and by loss-of-function mutations in Ero1a or Chop. Reconstitution of ERO1-α in Chop−/− macrophages restores ER stress–induced IICR and apoptosis. In vivo, macrophages from wild-type mice but not Chop−/− mice have elevated IICR when the animals are challenged with the ER stressor tunicamycin. Macrophages from insulin-resistant ob/ob mice, another model of ER stress, also have elevated IICR. These data shed new light on how the CHOP pathway of apoptosis triggers calcium-dependent apoptosis through an ERO1-α–IP3R pathway.

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