scholarly journals Reticulon proteins modulate autophagy of the endoplasmic reticulum in maize endosperm

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Xiaoguo Zhang ◽  
Xinxin Ding ◽  
Richard Scott Marshall ◽  
Julio Paez-Valencia ◽  
Patrick Lacey ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Lipid Droplets ◽  
Autophagic Flux ◽  
Dependent Manner ◽  
Maize Endosperm ◽  
Transmembrane Segments ◽  
C Terminus ◽  
Er Homeostasis ◽  
Dose Dependent

Reticulon (Rtn) proteins shape tubular domains of the endoplasmic reticulum (ER), and in some cases are autophagy receptors for selective ER turnover. We have found that maize Rtn1 and Rtn2 control ER homeostasis and autophagic flux in endosperm aleurone cells, where the ER accumulates lipid droplets and synthesizes storage protein accretions metabolized during germination. Maize Rtn1 and Rtn2 are expressed in the endosperm, localize to the ER, and re-model ER architecture in a dose-dependent manner. Rtn1 and Rtn2 interact with Atg8a using four Atg8-interacting motifs (AIMs) located at the C-terminus, cytoplasmic loop, and within the transmembrane segments. Binding between Rtn2 and Atg8 is elevated upon ER stress. Maize rtn2 mutants display increased autophagy and up-regulation of an ER stress-responsive chaperone. We propose that maize Rtn1 and Rtn2 act as receptors for autophagy-mediated ER turnover, and thus are critical for ER homeostasis and suppression of ER stress.

scholarly journals Melatonin-Mediated Intracellular Insulin during 2-Deoxy-d-glucose Treatment Is Reduced through Autophagy and EDC3 Protein in Insulinoma INS-1E Cells

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Han Sung Kim ◽  
Tae-Young Han ◽  
Yeong-Min Yoo
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Metabolic Pathways ◽  
Mtor Inhibitor ◽  
Glucose Deprivation ◽  
Dependent Manner ◽  
Insulin Production ◽  
Insulin Synthesis ◽  
Dose Dependent ◽  
Rat Insulinoma

2-DG triggers glucose deprivation without altering other nutrients or metabolic pathways and then activates autophagy via activation of AMPK and endoplasmic reticulum (ER) stress. We investigated whether 2-DG reduced intracellular insulin increased by melatonin via autophagy/EDC3 in insulinoma INS-1E cells. p-AMPK and GRP78/BiP level were significantly increased by 2-DG in the presence/absence of melatonin, but IRE1αlevel was reduced in 2-DG treatment. Levels of p85α, p110, p-Akt (Ser473, Thr308), and p-mTOR (Ser2481) were also significantly reduced by 2-DG in the presence/absence of melatonin. Mn-SOD increased with 2-DG plus melatonin compared to groups treated with/without melatonin alone. Bcl-2 was decreased and Bax increased with 2-DG plus melatonin. LC3II level increased with 2-DG treatment in the presence/absence of melatonin. Intracellular insulin production increased in melatonin plus 2-DG but reduced in treatment with 2-DG with/without melatonin. EDC3 was increased by 2-DG in the presence/absence of melatonin. Rapamycin, an mTOR inhibitor, increased GRP78/BiP and EDC3 levels in a dose-dependent manner and subsequently resulted in a decrease in intracellular production of insulin. These results suggest that melatonin-mediated insulin synthesis during 2-DG treatment involves autophagy and EDC3 protein in rat insulinoma INS-1E cells and subsequently results in a decrease in intracellular production of insulin.

scholarly journals ATP6AP2 functions as a V-ATPase assembly factor in the endoplasmic reticulum

2018 ◽  
Vol 29 (18) ◽  
pp. 2156-2164 ◽  
Author(s):  
Maria Clara Guida ◽  
Tobias Hermle ◽  
Laurie A. Graham ◽  
Virginie Hauser ◽  
Margret Ryan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Planar Cell Polarity ◽  
Transmembrane Protein ◽  
Type I ◽  
Genetic Studies ◽  
C Terminus ◽  
Assembly Factor ◽  
Pcp Signaling ◽  
Er Homeostasis

ATP6AP2 (also known as the [pro]renin receptor) is a type I transmembrane protein that can be cleaved into two fragments in the Golgi apparatus. While in Drosophila ATP6AP2 functions in the planar cell polarity (PCP) pathway, recent human genetic studies have suggested that ATP6AP2 could participate in the assembly of the V-ATPase in the endoplasmic reticulum (ER). Using a yeast model, we show here that the V-ATPase assembly factor Voa1 can functionally be replaced by Drosophila ATP6AP2. This rescue is even more efficient when coexpressing its binding partner ATP6AP1, indicating that these two proteins together fulfill Voa1 functions in higher organisms. Structure–function analyses in both yeast and Drosophila show that proteolytic cleavage is dispensable, while C-terminus-dependent ER retrieval is required for ATP6AP2 function. Accordingly, we demonstrate that both overexpression and lack of ATP6AP2 causes ER stress in Drosophila wing cells and that the induction of ER stress is sufficient to cause PCP phenotypes. In summary, our results suggest that full-length ATP6AP2 contributes to the assembly of the V-ATPase proton pore and that impairment of this function affects ER homeostasis and PCP signaling.

scholarly journals Zinc Attenuates the Cytotoxicity of Some Stimuli by Reducing Endoplasmic Reticulum Stress in Hepatocytes

2019 ◽  
Vol 20 (9) ◽  
pp. 2192 ◽  
Author(s):  
Masashi Kusanaga ◽  
Shinji Oe ◽  
Noriyoshi Ogino ◽  
Sota Minami ◽  
Koichiro Miyagawa ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Inclusion Body ◽  
Cultured Cells ◽  
Autophagic Flux ◽  
Body Formation ◽  
Excess Copper ◽  
Inclusion Body Formation ◽  
Cellular Integrity ◽  
Er Homeostasis

Zinc is an essential trace element and plays critical roles in cellular integrity and biological functions. Excess copper induced both oxidative stress and endoplasmic reticulum (ER) stress in liver-derived cultured cells. Excess copper also induced impairment of autophagic flux at the step of autophagosome–lysosome fusion, as well as Mallory–Denk body (MDB)-like inclusion body formation. Zinc ameliorated excess copper-induced impairment of autophagic flux and MDB-like inclusion body formation via the maintenance of ER homeostasis. Furthermore, zinc also ameliorated free fatty acid-induced impairment of autophagic flux. These results indicate that zinc may be able to protect hepatocytes from various ER stress-related conditions.

scholarly journals Demethylzeylasteral (T-96) Initiates Extrinsic Apoptosis Against Prostate Cancer cells by Inducing ROS-Mediated ER Stress and Suppressing Autophagic Flux

2021 ◽  
Author(s):  
Dong-Lin Yang ◽  
Ya-jun Zhang ◽  
Liu-jun He ◽  
Chun-sheng Hu ◽  
Li-xia Gao ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Er Stress ◽  
Cancer Cells ◽  
Autophagic Flux ◽  
Dependent Manner ◽  
Mechanistic Investigation ◽  
Potential Applications ◽  
Extrinsic Apoptosis ◽  
Pharmacologically Active

Abstract Demethylzeylasteral (T-96), a pharmacologically active triterpenoid monomer extracted from Tripterygiumwilfordii Hook F (TWHF), has been reported to exhibit anti-neoplastic effect on several types of cancer cells. However,whether it has the anti-tumour capability in human Prostate cancer (CaP)cells and what’s the precise regulatory mechanisms underlying the anti-proliferation effect of T-96 on human CaP. In the current study, T-96 exerted significant cytotoxicity to CaP cells in vitro and induced cell cycle arrest at S-phase in a dose-dependent manner. Furthermore, mechanistic investigation indicated that through inducing endoplasmic reticulum (ER) stress caused by intracellular accumulation of reactive oxygen species (ROS), T-96 significantly promoted autophagy initiation while blocked the autophagic flux and finally caused extrinsic apoptosis in CaP cells, implying that ER stress induced byT-96 initiated caspase dependent apoptosis to inhibit CaP cells. Moreover, as a novel lethal ER stress inducer, T-96 was capable to enhance the sensitivity of CaP cells to chemotherapeutic drug cisplatin. Taken together, our data implied that T-96 is a novel ER stress and autophagy modulator, and has the potential applications for CaP therapy in clinic.

scholarly journals Endoplasmic reticulum stress induces a novel Ca2+ signalling system initiated by Ca2+ microdomains

2020 ◽  
Author(s):  
Constanza Feliziani ◽  
Gonzalo Quasollo ◽  
Deborah Holstein ◽  
Macarena Fernandez ◽  
James C Paton ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Cell Model ◽  
Signal Transduction Pathway ◽  
Unfolded Proteins ◽  
Potent Inducer ◽  
Human Astrocytes ◽  
Receptor Isoforms ◽  
A Cell ◽  
Er Homeostasis

AbstractThe accumulation of unfolded proteins within the Endoplasmic Reticulum (ER) activates a signal transduction pathway termed the unfolded protein response (UPR), which attempts to restore ER homeostasis. If homeostasis cannot be restored, UPR signalling ultimately induces apoptosis. Ca2+ depletion in the ER is a potent inducer of ER stress. Despite the ubiquity of Ca2+ as intracellular messenger, the precise mechanism (s) by which Ca2+ release affects the UPR remains unknown. Use of a genetically encoded Ca2+ indicator (GCamP6) that is tethered to the ER membrane, uncovered novel Ca2+ signalling events initiated by Ca2+ microdomains in human astrocytes under ER stress, as well as in a cell model deficient in all three IP3 Receptor isoforms. Pharmacological and molecular studies indicate that these local events are mediated by translocons. Together, these data reveal the existence of a previously unrecognized mechanism by which stressor-mediated Ca2+ release regulates ER stress.

scholarly journals Activation of Hepatitis B Virus S Promoter by a Cell Type-Restricted IRE1-Dependent Pathway Induced by Endoplasmic Reticulum Stress

2005 ◽  
Vol 25 (17) ◽  
pp. 7522-7533 ◽  
Author(s):  
Zhi-Ming Huang ◽  
Thomas Tan ◽  
Hiderou Yoshida ◽  
Kazutoshi Mori ◽  
Yanjun Ma ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Er Stress ◽  
Transcriptional Activation ◽  
Active Form ◽  
Dominant Negative ◽  
Dependent Manner ◽  
Cell Type ◽  
B Virus

ABSTRACT IRE1-alpha is an integral membrane protein of the endoplasmic reticulum (ER) that is a key sensor in the cellular transcriptional response to stress in the ER. Upon induction of ER stress, IRE1-alpha is activated, resulting in the synthesis of the active form of the transcription factor XBP1 via IRE1-mediated splicing of its mRNA. In this report, we have examined the role of IRE1-alpha and XBP1 in activation of the hepatitis B virus S promoter by ER stress. Cotransfection experiments revealed that overexpression of either IRE1-alpha or XBP1 activated this promoter. Conversely, cotransfected dominant-negative IRE1-alpha or small interfering RNA directed against XBP1 decreased the activation of the S promoter by ER stress, confirming an important role for the IRE1-alpha/XBP1 signaling pathway in activation of the S promoter. However, XBP1 does not bind directly to the S promoter; rather, a novel S promoter-binding complex that does not contain XBP1 is induced in cells undergoing ER stress in an XBP1-dependent manner. This complex, as well as transcriptional activation of the S promoter, is induced by ER stress in hepatocytes but not in fibroblasts, despite the presence of active XBP1 in the latter. Thus, the hepatitis B virus S promoter responds to a novel, cell type-restricted transcriptional pathway downstream of IRE1-alpha and XBP1.

scholarly journals Mdm1 maintains endoplasmic reticulum homeostasis by spatially regulating lipid droplet biogenesis

2019 ◽  
Vol 218 (4) ◽  
pp. 1319-1334 ◽  
Author(s):  
Hanaa Hariri ◽  
Natalie Speer ◽  
Jade Bowerman ◽  
Sean Rogers ◽  
Gang Fu ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
Fatty Acyl ◽  
Nutrient Depletion ◽  
Coenzyme A Ligase ◽  
Response To Stress ◽  
Acyl Coenzyme A ◽  
Er Homeostasis

Lipid droplets (LDs) serve as cytoplasmic reservoirs for energy-rich fatty acids (FAs) stored in the form of triacylglycerides (TAGs). During nutrient stress, yeast LDs cluster adjacent to the vacuole/lysosome, but how this LD accumulation is coordinated remains poorly understood. The ER protein Mdm1 is a molecular tether that plays a role in clustering LDs during nutrient depletion, but its mechanism of function remains unknown. Here, we show that Mdm1 associates with LDs through its hydrophobic N-terminal region, which is sufficient to demarcate sites for LD budding. Mdm1 binds FAs via its Phox-associated domain and coenriches with fatty acyl–coenzyme A ligase Faa1 at LD bud sites. Consistent with this, loss of MDM1 perturbs free FA activation and Dga1-dependent synthesis of TAGs, elevating the cellular FA level, which perturbs ER morphology and sensitizes yeast to FA-induced lipotoxicity. We propose that Mdm1 coordinates FA activation adjacent to the vacuole to promote LD production in response to stress, thus maintaining ER homeostasis.

scholarly journals Endoplasmic Reticulum Stress Mediates Vascular Smooth Muscle Cell Calcification via Increased Release of Grp78-Loaded Extracellular Vesicles

2020 ◽  
Author(s):  
Malgorzata Furmanik ◽  
Rick van Gorp ◽  
Meredith Whitehead ◽  
Sadia Ahmad ◽  
Jayanta Bordoloi ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Er Stress ◽  
Vascular Calcification ◽  
Bone Mineralization ◽  
Extracellular Vesicle ◽  
Dependent Manner ◽  
The Matrix ◽  
Stress Dependent

Objective: Vascular calcification is common among aging populations and mediated by vascular smooth muscle cells (VSMCs). The endoplasmic reticulum (ER) is involved in protein folding and ER stress has been implicated in bone mineralization. The role of ER stress in VSMC-mediated calcification is less clear. Approach and Results: mRNA expression of the ER stress markers PERK (PKR (protein kinase RNA)-like ER kinase), ATF (activating transcription factor) 4, ATF6, and Grp78 was detectable in human vessels with levels of PERK decreased in calcified plaques compared to healthy vessels. Protein deposition of Grp78/Grp94 was increased in the matrix of calcified arteries. Induction of ER stress accelerated human primary VSMC-mediated calcification, elevated expression of some osteogenic markers (Runx2, Osterix, ALP, BSP, and OPG), and decreased expression of SMC markers. ER stress potentiated extracellular vesicle (EV) release via SMPD3. EVs from ER stress-treated VSMCs showed increased Grp78 levels and calcification. Electron microscopy confirmed the presence of Grp78/Grp94 in EVs. siRNA knock-down of Grp78 decreased calcification. Warfarin-induced Grp78 and ATF4 expression in rat aortas and VSMCs and increased calcification in an ER stress-dependent manner via increased EV release. Conclusions: ER stress induces vascular calcification by increasing release of Grp78-loaded EVs. Our results reveal a novel mechanism of action of warfarin, involving increased EV release via the PERK-ATF4 pathway, contributing to calcification. This study is the first to show that warfarin induces ER stress and to link ER stress to cargo loading of EVs.

scholarly journals Development of a pH-responsive polymersome inducing endoplasmic reticulum stress and autophagy blockade

2020 ◽  
Vol 6 (31) ◽  
pp. eabb8725 ◽  
Author(s):  
Funeng Xu ◽  
Xilin Li ◽  
Xuehui Huang ◽  
Jingmei Pan ◽  
Yi Wang ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Tumor Metastasis ◽  
Focal Adhesions ◽  
Matrix Metalloproteinase 2 ◽  
Autophagic Flux ◽  
Ph Responsive ◽  
Ph Response ◽  
Function Mechanism ◽  
Inhibit Tumor Metastasis

Autophagy is involved in the occurrence and development of tumors. Here, a pH-responsive polymersome codelivering hydroxychloroquine (HCQ) and tunicamycin (Tuni) drugs is developed to simultaneously induce endoplasmic reticulum (ER) stress and autophagic flux blockade for achieving an antitumor effect and inhibiting tumor metastasis. The pH response of poly(β-amino ester) and HCQ synergistically deacidifies the lysosomes, thereby blocking the fusion of autophagosomes and lysosomes and lastly blocking autophagic flux. The function mechanism of regulating autophagy was systematically investigated on orthotopic luciferase gene–transfected, 4T1 tumor–bearing BALB/c mice through Western blot and immunohistochemistry analyses. The Tuni triggers ER stress to regulate the PERK/Akt signaling pathway to increase the autophagic level. The “autophagic stress” generated by triggering ER stress–induced autophagy and blocking autophagic flux is effective against tumors. The reduced expression of matrix metalloproteinase-2 due to ER stress and reduced focal adhesions turnover due to the blockade of autophagic flux synergistically inhibit tumor metastasis.

scholarly journals The PERK-Dependent Molecular Mechanisms as a Novel Therapeutic Target for Neurodegenerative Diseases

2020 ◽  
Vol 21 (6) ◽  
pp. 2108 ◽  
Author(s):  
Wioletta Rozpędek-Kamińska ◽  
Natalia Siwecka ◽  
Adam Wawrzynkiewicz ◽  
Radosław Wojtczak ◽  
Dariusz Pytel ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Neurodegenerative Diseases ◽  
Er Stress ◽  
Molecular Mechanisms ◽  
Treatment Strategies ◽  
Stress Conditions ◽  
World Population ◽  
Dependent Manner ◽  
Age Related ◽  
The Unfolded Protein Response

Higher prevalence of neurodegenerative diseases is strictly connected with progressive aging of the world population. Interestingly, a broad range of age-related, neurodegenerative diseases is characterized by a common pathological mechanism—accumulation of misfolded and unfolded proteins within the cells. Under certain circumstances, such protein aggregates may evoke endoplasmic reticulum (ER) stress conditions and subsequent activation of the unfolded protein response (UPR) signaling pathways via the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent manner. Under mild to moderate ER stress, UPR has a pro-adaptive role. However, severe or long-termed ER stress conditions directly evoke shift of the UPR toward its pro-apoptotic branch, which is considered to be a possible cause of neurodegeneration. To this day, there is no effective cure for Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), or prion disease. Currently available treatment approaches for these diseases are only symptomatic and cannot affect the disease progression. Treatment strategies, currently under detailed research, include inhibition of the PERK-dependent UPR signaling branches. The newest data have reported that the use of small-molecule inhibitors of the PERK-mediated signaling branches may contribute to the development of a novel, ground-breaking therapeutic approach for neurodegeneration. In this review, we critically describe all the aspects associated with such targeted therapy against neurodegenerative proteopathies.

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