bims-unfpre 2023-06-11 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2023–06–11
eleven papers selected by
Susan Logue, University of Manitoba

A cytosolic surveillance mechanism activates the mitochondrial UPR.
mTORC1 inhibition impairs activation of the unfolded protein response and induces cell death during ER stress in cardiomyocytes.
Architecture and dynamics of a desmosome-endoplasmic reticulum complex.
Rescue of proteotoxic stress and neurodegeneration by the Zn 2+ transporter ZIP7.
The role of protein phosphatase 2A (PP2A) in the unfolded protein response (UPR) of plants.
ATF4 regulates mitochondrial content, morphology, and function in differentiating skeletal muscle myotubes.
The acyltransferase Gpc1 is both a target and an effector of the unfolded protein response (UPR) in Saccharomyces cerevisiae.
PERK/ATF3-Reduced ER Stress on high potassium environment in the suppression of tumor ferroptosis.
Early and late chaperone intervention therapy boosts XBP1s and ADAM10, restores proteostasis, and rescues learning in Alzheimer's Disease mice.
Exposure to environmental concentrations of glyphosate induces cardiotoxicity through cellular senescence and reduced cell proliferation capacity.
Endoplasmic reticulum stress in diabetic kidney disease: adaptation and apoptosis after three UPR pathways.

Nature. 2023 Jun 07.

A cytosolic surveillance mechanism activates the mitochondrial UPR.

F X Reymond Sutandy, Ines Gößner, Georg Tascher, Christian Münch.

The mitochondrial unfolded protein response (UPRmt) is essential to safeguard mitochondria from proteotoxic damage by activating a dedicated transcriptional response in the nucleus to restore proteostasis1,2. Yet, it remains unclear how the information on mitochondria misfolding stress (MMS) is signalled to the nucleus as part of the human UPRmt (refs. 3,4). Here, we show that UPRmt signalling is driven by the release of two individual signals in the cytosol-mitochondrial reactive oxygen species (mtROS) and accumulation of mitochondrial protein precursors in the cytosol (c-mtProt). Combining proteomics and genetic approaches, we identified that MMS causes the release of mtROS into the cytosol. In parallel, MMS leads to mitochondrial protein import defects causing c-mtProt accumulation. Both signals integrate to activate the UPRmt; released mtROS oxidize the cytosolic HSP40 protein DNAJA1, which leads to enhanced recruitment of cytosolic HSP70 to c-mtProt. Consequently, HSP70 releases HSF1, which translocates to the nucleus and activates transcription of UPRmt genes. Together, we identify a highly controlled cytosolic surveillance mechanism that integrates independent mitochondrial stress signals to initiate the UPRmt. These observations reveal a link between mitochondrial and cytosolic proteostasis and provide molecular insight into UPRmt signalling in human cells.

DOI: https://doi.org/10.1038/s41586-023-06142-0
Am J Physiol Heart Circ Physiol. 2023 Jun 09.

mTORC1 inhibition impairs activation of the unfolded protein response and induces cell death during ER stress in cardiomyocytes.

Christoph Hofmann, Zoe Löwenthal, Marjan Aghajani, Randal J Kaufman, Hugo A Katus, Norbert Frey, Christopher C Glembotski, Mirko Völkers, Shirin Doroudgar.

  The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of protein synthesis that senses and responds to a variety of stimuli to coordinate cellular metabolism with environmental conditions. To ensure that protein synthesis is inhibited during unfavorable conditions, translation is directly coupled to the sensing of cellular protein homeostasis. Thus, translation is attenuated during endoplasmic reticulum (ER) stress by direct inhibition of the mTORC1 pathway. However, residual mTORC1 activity is maintained during prolonged ER stress which is thought to be involved in translational reprogramming and adaption to ER stress. By analyzing the dynamics of mTORC1 regulation during ER stress, we unexpectedly found that mTORC1 is transiently activated in cardiomyocytes within minutes at the onset of ER stress before being inhibited during chronic ER stress. This dynamic regulation of mTORC1 appears to be mediated, at least in part, by ATF6, as its activation was sufficient to induce the biphasic control of mTORC1. We further showed that protein synthesis remains dependent on mTORC1 throughout the ER stress response and that mTORC1 activity is essential for posttranscriptional induction of several unfolded protein response elements. Pharmacological inhibition of mTORC1 increased cell death during ER stress, indicating that the mTORC1 pathway serves adaptive functions during ER stress in cardiomyocytes potentially by controlling the expression of the protective unfolded protein response.

Keywords:  ATF6; ER stress; cardiomyocytes; cell death; mTORC1

DOI:  https://doi.org/10.1152/ajpheart.00682.2022
Nat Cell Biol. 2023 Jun 08.

Architecture and dynamics of a desmosome-endoplasmic reticulum complex.

COSEM Project Team

The endoplasmic reticulum (ER) forms a dynamic network that contacts other cellular membranes to regulate stress responses, calcium signalling and lipid transfer. Here, using high-resolution volume electron microscopy, we find that the ER forms a previously unknown association with keratin intermediate filaments and desmosomal cell-cell junctions. Peripheral ER assembles into mirror image-like arrangements at desmosomes and exhibits nanometre proximity to keratin filaments and the desmosome cytoplasmic plaque. ER tubules exhibit stable associations with desmosomes, and perturbation of desmosomes or keratin filaments alters ER organization, mobility and expression of ER stress transcripts. These findings indicate that desmosomes and the keratin cytoskeleton regulate the distribution, function and dynamics of the ER network. Overall, this study reveals a previously unknown subcellular architecture defined by the structural integration of ER tubules with an epithelial intercellular junction.

DOI: https://doi.org/10.1038/s41556-023-01154-4
bioRxiv. 2023 May 22. pii: 2023.05.22.541645. [Epub ahead of print]

Rescue of proteotoxic stress and neurodegeneration by the Zn 2+ transporter ZIP7.

Xiaoran Guo, Morgan Mutch, Alba Yurani Torres, Maddalena Nano, Drew McDonald, Zijing Chen, Craig Montell, Wei Dai, Denise J Montell.

Proteotoxic stress drives numerous degenerative diseases. In response to misfolded proteins, cells adapt by activating the unfolded protein response (UPR), including endoplasmic reticulum-associated protein degradation (ERAD). However persistent stress triggers apoptosis. Enhancing ERAD is a promising therapeutic approach for protein misfolding diseases. From plants to humans, loss of the Zn 2+ transporter ZIP7 causes ER stress, however the mechanism is unknown. Here we show that ZIP7 enhances ERAD and that cytosolic Zn 2+ is limiting for deubiquitination of client proteins by the Rpn11 Zn 2+ metalloproteinase as they enter the proteasome in Drosophila and human cells. ZIP7 overexpression rescues defective vision caused by misfolded rhodopsin in Drosophila. Thus ZIP7 overexpression may prevent diseases caused by proteotoxic stress, and existing ZIP inhibitors may be effective against proteasome-dependent cancers.
One-Sentence Summary: Zn 2+ transport from the ER to the cytosol promotes deubiquitination and proteasomal degradation of misfolded proteins and prevents blindness in a fly neurodegeneration model.

DOI: https://doi.org/10.1101/2023.05.22.541645
Biochem Biophys Res Commun. 2023 May 26. pii: S0006-291X(23)00695-2. [Epub ahead of print]670 94-101

The role of protein phosphatase 2A (PP2A) in the unfolded protein response (UPR) of plants.

Ki Seong Ko, Jae Yong Yoo, Bich Ngoc Vu, Young Eun Lee, Ha Na Choi, Yoo Na Lee, Wahyu Indra Duwi Fanata, Rikno Harmoko, Woo Sik Chung, Jong Chan Hong, Kyun Oh Lee.

  Protein phosphatase 2A (PP2A) is a key regulator of plant growth and development, but its role in the endoplasmic reticulum (ER) stress response remains elusive. In this study, we investigated the function of PP2A under ER stress using loss-of-function mutants of ROOTS CURL of NAPHTHYLPHTHALAMIC ACID1 (RCN1), a regulatory A1 subunit isoform of Arabidopsis PP2A. RCN1 mutants (rcn1-1 and rcn1-2) exhibited reduced sensitivity to tunicamycin (TM), an inhibitor of N-linked glycosylation and inducer of unfolded protein response (UPR) gene expression, resulting in less severe effects compared to wild-type plants (Ws-2 and Col-0). TM negatively impacted PP2A activity in Col-0 plants but did not significantly affect rcn1-2 plants. Additionally, TM treatment did not influence the transcription levels of the PP2AA1(RCN1), 2, and 3 genes in Col-0 plants. Cantharidin, a PP2A inhibitor, exacerbated growth defects in rcn1 plants and alleviated TM-induced growth inhibition in Ws-2 and Col-0 plants. Furthermore, cantharidin treatment mitigated TM hypersensitivity in ire1a&b and bzip28&60 mutants. These findings suggest that PP2A activity is essential for an efficient UPR in Arabidopsis.

Keywords:  Cantharidin; ER stress; PP2A; RCN1; UPR

DOI:  https://doi.org/10.1016/j.bbrc.2023.05.106
Am J Physiol Cell Physiol. 2023 Jun 05.

ATF4 regulates mitochondrial content, morphology, and function in differentiating skeletal muscle myotubes.

Jonathan M Memme, Victoria C Sanfrancesco, David A Hood.

  Mitochondrial function is widely recognized as a major determinant of health, emphasizing the importance of understanding the mechanisms promoting mitochondrial quality in various tissues. Recently, the mitochondrial unfolded protein response (UPRmt) has come into focus as a modulator of mitochondrial homeostasis, particularly in stress conditions. In muscle, the necessity for ATF4 and its role in regulating mitochondrial quality control (MQC) has yet to be determined. We overexpressed (OE) and knocked down ATF4 in C2C12 myoblasts, differentiated them to myotubes for 5 days, and subjected them to acute (ACA) or chronic (CCA) contractile activity. ATF4 mediated myotube formation through the regulated expression of myogenic factors, mainly Myc and MyoD, and supressed mitochondrial biogenesis basally through PGC-1a. However, our data also show that ATF4 expression levels are directly related to mitochondrial fusion and dynamics, UPRmt activation, as well as lysosomal biogenesis and autophagy. Thus, ATF4 promoted enhanced mitochondrial networking, protein handling, and capacity for clearance of dysfunctional organelles under stress conditions, despite lower levels of mitophagy flux with OE. Indeed, we found that ATF4 promoted the formation of a smaller pool of high functioning mitochondria that are more responsive to contractile activity, have higher oxygen consumption rates and lower reactive oxygen species levels. These data provide evidence that ATF4 is both necessary and sufficient for mitochondrial quality control and adaptation during both differentiation and contractile activity, thus advancing the current understanding of ATF4 beyond its canonical functions, to include the regulation of mitochondrial morphology, lysosomal biogenesis and mitophagy in muscle cells.

Keywords:  ATF4; mitochondrial quality control; mitochondrial unfolded protein response; mitophagy and lysosomal biogenesis; skeletal muscle C2C12

DOI:  https://doi.org/10.1152/ajpcell.00080.2023
J Biol Chem. 2023 Jun 01. pii: S0021-9258(23)01912-9. [Epub ahead of print] 104884

The acyltransferase Gpc1 is both a target and an effector of the unfolded protein response (UPR) in Saccharomyces cerevisiae.

Victoria Lee Hrach, William R King, Laura D Nelson, Shane Conklin, John A Pollock, Jana Patton-Vogt.

  The unfolded protein response (UPR) is sensitive to proteotoxic and membrane bilayer stress, both of which are sensed by the ER protein Ire1. When activated, Ire1 splices HAC1 mRNA, producing a transcription factor that targets genes involved in proteostasis and lipid metabolism, among others. The major membrane lipid phosphatidylcholine (PC) is subject to phospholipase-mediated deacylation, producing glycerophosphocholine (GPC), followed by reacylation of GPC through the PC deacylation/reacylation pathway (PC-DRP). The reacylation events occur via a two-step process catalyzed first by the GPC acyltransferase Gpc1, followed by acylation of the lyso-PC molecule by Ale1. However, whether Gpc1 is critical for ER bilayer homeostasis is unclear. Using an improved method for C14-choline-GPC radiolabeling, we first show that loss of Gpc1 results in abrogation of PC synthesis through PC-DRP and that Gpc1 colocalizes with the ER. We then probe the role of Gpc1 as both a target and an effector of the UPR. Exposure to the UPR-inducing compounds tunicamycin, DTT, and canavanine results in a Hac1-dependent increase in GPC1 message. Further, cells lacking Gpc1 exhibit increased sensitivity to those proteotoxic stressors. Inositol limitation, known to induce the UPR via bilayer stress, also induces GPC1 expression. Finally, we show that loss of GPC1 induces the UPR. A gpc1Δ mutant displays upregulation of the UPR in strains expressing a mutant form of Ire1 that is unresponsive to unfolded proteins, indicating that bilayer stress is responsible for the observed upregulation. Collectively, our data indicate an important role for Gpc1 in yeast ER bilayer homeostasis.

Keywords:  Gpc1; Ire1; acyltransferase; glycerophosphocholine; lipid remodeling; lysophosphatidylcholine; membrane bilayer stress; phosphatidylcholine; phospholipid metabolism; unfolded protein response; yeast

DOI:  https://doi.org/10.1016/j.jbc.2023.104884
J Cancer. 2023 ;14(8): 1336-1349

PERK/ATF3-Reduced ER Stress on high potassium environment in the suppression of tumor ferroptosis.

Xufeng Pu, Li Li, Zhenhui Chen, Aihua Gong, Jiao Lei, Lirong Zhang, Hsiang-I Tsai.

Potassium (K+) is a vital intracellular cation. In the human body, it regulates membrane potential, electrical excitation, protein synthesis, and cell death. Recent studies revealed that dying cancer cells release potassium into the tumor microenvironment (TME), thereby influencing cell survival-related events. Several investigations reported that potassium channels and high potassium levels influence apoptosis. Increasing extracellular potassium and inhibiting K+ efflux channels significantly block the apoptotic machinery. However, it is unknown whether a high-potassium environment also affects other types of cell death such as ferroptosis. In the present study, cell counting kit (CCK-8), colony formation ability, and 5-ethynyl-2'-deoxyuridine (EdU) assays demonstrated that a high-potassium environment reverses erastin-induced ferroptosis. RNA sequencing (RNA-Seq) and Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO) analyses indicated that high potassium levels attenuated the unfolded protein response that is characteristic of endoplasmic reticulum (ER) stress. The ER transmembrane proteins PRKR-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6) are recognized as ER stress sensors. Here, the PERK blocker GSK2606414 significantly rescued ferroptosis. The present work also disclosed that the ER-related gene activating transcription factor 3 (ATF3) played a vital role in regulating ferroptosis in a high-potassium environment. The foregoing results revealed the roles of potassium and the TME in cancer cell ferroptosis and provided a potential clinical therapeutic strategy for cancer.

DOI: https://doi.org/10.7150/jca.83556
bioRxiv. 2023 May 24. pii: 2023.05.23.541973. [Epub ahead of print]

Early and late chaperone intervention therapy boosts XBP1s and ADAM10, restores proteostasis, and rescues learning in Alzheimer's Disease mice.

Jennifer M Hafycz, Ewa Strus, Nirinjini N Naidoo.

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is pervasive among the aging population. Two distinct phenotypes of AD are deficits in cognition and proteostasis, including chronic activation of the unfolded protein response (UPR) and aberrant Aβ production. It is unknown if restoring proteostasis by reducing chronic and aberrant UPR activation in AD can improve pathology and cognition. Here, we present data using an APP knock-in mouse model of AD and several protein chaperone supplementation paradigms, including a late-stage intervention. We show that supplementing protein chaperones systemically and locally in the hippocampus reduces PERK signaling and increases XBP1s, which is associated with increased ADAM10 and decreased Aβ42. Importantly, chaperone treatment improves cognition which is correlated with increased CREB phosphorylation and BDNF. Together, this data suggests that chaperone treatment restores proteostasis in a mouse model of AD and that this restoration is associated with improved cognition and reduced pathology.
One-sentence summary: Chaperone therapy in a mouse model of Alzheimer's disease improves cognition by reducing chronic UPR activity.

DOI: https://doi.org/10.1101/2023.05.23.541973
Ecotoxicol Environ Saf. 2023 Jun 06. pii: S0147-6513(23)00616-4. [Epub ahead of print]261 115112

Exposure to environmental concentrations of glyphosate induces cardiotoxicity through cellular senescence and reduced cell proliferation capacity.

Jian Lu, Cheng Zhang, Weiguo Wang, Wenping Xu, Weidong Chen, Liming Tao, Zhong Li, Yang Zhang, Jiagao Cheng.

  Glyphosate (GLY), the preeminent herbicide utilized globally, is known to be exposed to the environment and population on a chronic basis. Exposure to GLY and the consequent health risks are alarming public health problems that are attracting international attention. However, the cardiotoxicity of GLY has been a matter of dispute and uncertainty. Here, AC16 cardiomyocytes and zebrafish were exposed to GLY. This study found that low concentrations of GLY lead to morphological enlargement of AC16 human cardiomyocytes, indicating a senescent state. The increased expression of P16, P21, and P53 following exposure to GLY demonstrated that GLY causes senescence in AC16. Moreover, it was mechanistically confirmed that GLY-induced senescence in AC16 cardiomyocytes was produced by ROS-mediated DNA damage. In terms of in vivo cardiotoxicity, GLY decreased the proliferative capacity of cardiomyocytes in zebrafish through the notch signaling pathway, resulting in a reduction of cardiomyocytes. It was also found that GLY caused zebrafish cardiotoxicity associated with DNA damage and mitochondrial damage. KEGG analysis after RNA-seq shows a significant enrichment of protein processing pathways in the endoplasmic reticulum (ER) after GLY exposure. Importantly, GLY induced ER stress in AC16 cells and zebrafish by activating PERK-eIF2α-ATF4 pathway. Our study has thus provided the first novel insights into the mechanism underlying GLY-induced cardiotoxicity. Furthermore, our findings emphasize the need for increased attention to the potential cardiotoxic effects of GLY.

Keywords:  AC16; Cardiomyocyte proliferation; Endoplasmic reticulum; Glyphosate; Senescence

DOI:  https://doi.org/10.1016/j.ecoenv.2023.115112
Apoptosis. 2023 Jun 07.

Endoplasmic reticulum stress in diabetic kidney disease: adaptation and apoptosis after three UPR pathways.

Ruijing Zhang, Che Bian, Jing Gao, Huiwen Ren.

  Diabetes kidney disease (DKD) is one of the common chronic microvascular complications of diabetes, which has become the most important cause of modern chronic kidney disease beyond chronic glomerulonephritis. The endoplasmic reticulum is one of the largest organelles, and endoplasmic reticulum stress (ERS) is the basic mechanism of metabolic disorder in all organs and tissues. Under the stimulation of stress-induced factors, the endoplasmic reticulum, as a trophic receptor, regulates adaptive and apoptotic ERS through molecular chaperones and three unfolded protein reaction (UPR) pathways, thereby regulating diabetic renal damage. Therefore, three pathway factors have different expressions in different sections of renal tissues. This study deeply discussed the specific reagents, animals, cells, and clinical models related to ERS in DKD, and reviewed ERS-related three pathways on DKD with glomerular filtration membrane, renal tubular reabsorption, and other pathological lesions of different renal tissues, as well as the molecular biological mechanisms related to the balance of adaption and apoptosis by searching and sorting out MeSH subject words from PubMed database.

Keywords:  Diabetes; Diabetic kidney disease; Endoplasmic reticulum stress; Kidney

DOI:  https://doi.org/10.1007/s10495-023-01858-w