bims-unfpre 2022-06-26 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2022–06–26
eight papers selected by
Susan Logue, University of Manitoba

Live imaging of the co-translational recruitment of XBP1 mRNA to the ER and its processing by diffuse, non-polarized IRE1α.
Endoplasmic reticulum stress activates human IRE1α through reversible assembly of inactive dimers into small oligomers.
The epithelial-specific ER stress sensor ERN2/IRE1β enables host-microbiota crosstalk to affect colon goblet cell development.
Functional role of the ER stress transducer IRE1α in CF airway epithelial inflammation.
UFL1 alleviates ER stress and apoptosis stimulated by LPS via blocking the ferroptosis pathway in human granulosa-like cells.
Gold Nanorods Induce Endoplasmic Reticulum Stress and Autocrine Inflammatory Activation in Human Neutrophils.
Neuronal microRNAs safeguard ER Ca2+ homeostasis and attenuate the unfolded protein response upon stress.
The Unfolded Protein Response Sensor PERK Mediates Stiffness-Dependent Adaptation in Glioblastoma Cells.

Elife. 2022 Jun 22. pii: e75580. [Epub ahead of print]11

Live imaging of the co-translational recruitment of XBP1 mRNA to the ER and its processing by diffuse, non-polarized IRE1α.

Silvia Gómez-Puerta, Roberto Ferrero, Tobias Hochstoeger, Ivan Zubiri, Jeffrey Chao, Tomás Aragón, Franka Voigt.

  Endoplasmic reticulum (ER) to nucleus homeostatic signaling, known as the unfolded protein response (UPR), relies on the non-canonical splicing of XBP1 mRNA. The molecular switch that initiates splicing is the oligomerization of the ER stress sensor and UPR endonuclease IRE1α (inositol-requiring enzyme 1 alpha). While IRE1α can form large clusters that have been proposed to function as XBP1 processing centers on the ER, the actual oligomeric state of active IRE1α complexes as well as the targeting mechanism that recruits XBP1 to IRE1α oligomers remains unknown. Here, we have developed a single-molecule imaging approach to monitor the recruitment of individual XBP1 transcripts to the ER surface. Using this methodology, we confirmed that stable ER association of unspliced XBP1 mRNA is established through HR2 (hydrophobic region 2)-dependent targeting and relies on active translation. In addition, we show that IRE1α-catalyzed splicing mobilizes XBP1 mRNA from the ER membrane in response to ER stress. Surprisingly, we find that XBP1 transcripts are not recruited into large IRE1α clusters, which are only observed upon overexpression of fluorescently tagged IRE1α during ER stress. Our findings support a model where ribosome-engaged, immobilized XBP1 mRNA is processed by small IRE1α assemblies that could be dynamically recruited for processing of mRNA transcripts on the ER.

Keywords:  ER; IRE1; XBP1; cell biology; human; imaging; single-molecule; unfolded protein response

DOI:  https://doi.org/10.7554/eLife.75580
Elife. 2022 Jun 22. pii: e74342. [Epub ahead of print]11

Endoplasmic reticulum stress activates human IRE1α through reversible assembly of inactive dimers into small oligomers.

Vladislav Belyy, Iratxe Zuazo-Gaztelu, Andrew Alamban, Avi Ashkenazi, Peter Walter.

  Protein folding homeostasis in the endoplasmic reticulum (ER) is regulated by a signaling network, termed the unfolded protein response (UPR). Inositol-requiring enzyme 1 (IRE1) is an ER membrane-resident kinase/RNase that mediates signal transmission in the most evolutionarily conserved branch of the UPR. Dimerization and/or higher-order oligomerization of IRE1 are thought to be important for its activation mechanism, yet the actual oligomeric states of inactive, active, and attenuated mammalian IRE1 complexes remain unknown. We developed an automated two-color single-molecule tracking approach to dissect the oligomerization of tagged endogenous human IRE1 in live cells. In contrast to previous models, our data indicate that IRE1 exists as a constitutive homodimer at baseline and assembles into small oligomers upon ER stress. We demonstrate that the formation of inactive dimers and stress-dependent oligomers is fully governed by IRE1's lumenal domain. Phosphorylation of IRE1's kinase domain occurs more slowly than oligomerization and is retained after oligomers disassemble back into dimers. Our findings suggest that assembly of IRE1 dimers into larger oligomers specifically enables trans-autophosphorylation, which in turn drives IRE1's RNase activity.

Keywords:  IRE1; UPR; cell biology; endoplasmic reticulum; human; molecular biophysics; single-molecule; stress signaling; structural biology

DOI:  https://doi.org/10.7554/eLife.74342
J Clin Invest. 2022 Jun 21. pii: e153519. [Epub ahead of print]

The epithelial-specific ER stress sensor ERN2/IRE1β enables host-microbiota crosstalk to affect colon goblet cell development.

Michael J Grey, Heidi De Luca, Doyle V Ward, Irini Am Kreulen, Katlynn Bugda Gwilt, Sage E Foley, Jay R Thiagarajah, Beth A McCormick, Jerrold R Turner, Wayne I Lencer.

  Epithelial cells lining mucosal surfaces of the gastrointestinal and respiratory tracts uniquely express ERN2/IRE1β, a paralogue of the most evolutionarily conserved endoplasmic reticulum stress sensor ERN1/IRE1α. How ERN2 functions at the host-environment interface and why a second paralogue evolved remain incompletely understood. Using conventionally raised and germ-free Ern2-/- mice, we found that ERN2 was required for microbiota-induced goblet cell maturation and mucus barrier assembly in the colon. This occurred only after colonization of the alimentary tract with normal gut microflora, which induced Ern2 expression. ERN2 acted by splicing Xbp1 mRNA to expand ER function and prevent ER stress in goblet cells. Although ERN1 can also splice Xbp1 mRNA, it did not act redundantly to ERN2 in this context. By regulating assembly of the colon mucus layer, ERN2 further shaped the composition of the gut microbiota. Mice lacking Ern2 had a dysbiotic microbial community that failed to induce goblet cell development and increased susceptibility to colitis when transferred into germ-free wild type mice. These results show that ERN2 evolved at mucosal surfaces to mediate crosstalk between gut microbes and the colonic epithelium required for normal homeostasis and host defense.

Keywords:  Cell stress; Gastroenterology; Inflammatory bowel disease

DOI:  https://doi.org/10.1172/JCI153519
Curr Opin Pharmacol. 2022 Jun 21. pii: S1471-4892(22)00085-6. [Epub ahead of print]65 102258

Functional role of the ER stress transducer IRE1α in CF airway epithelial inflammation.

Carla M P Ribeiro, Emily A Hull-Ryde.

Excessive and chronic airway inflammation associated with increased morbidity and mortality is a hallmark of cystic fibrosis (CF) airway disease. Previous studies underscored the role of endoplasmic reticulum (ER) signaling in CF airway inflammatory responses. In this review we discuss 1) how airway inflammation induces ER stress-triggered activation of the unfolded protein response and 2) the functional importance of the ER stress transducer inositol requiring enzyme 1α (IRE1α) in CF airway epithelial inflammatory responses. We also briefly review the current understanding of IRE1α activation and the development of small molecules aimed at modulating IRE1α kinase and RNase activities. Inhibition of IRE1α kinase and RNase may be considered as a novel therapeutic strategy to ameliorate the robust inflammatory status of CF airways.

DOI: https://doi.org/10.1016/j.coph.2022.102258
Cell Stress Chaperones. 2022 Jun 21.

UFL1 alleviates ER stress and apoptosis stimulated by LPS via blocking the ferroptosis pathway in human granulosa-like cells.

Jingyi Li, Xiangting Tang, Xueer Tu, Zhe Jin, Hao Dong, Qi Yang, Ting Yao, Zezheng Pan.

  Ubiquitin-like modifier 1 ligating enzyme 1 (UFL1) is a unique E3 ligase of the UFMylation system. Recent studies have shown that this enzyme plays a crucial role in the processes of endoplasmic reticulum stress (ER stress) and apoptosis. Lipopolysaccharide (LPS) can cause injury to ovarian granule cells and hinder follicular development by triggering ER stress and apoptosis. Our study aimed to investigate the mechanism by which UFL1 alleviates ER stress and apoptosis caused by LPS in human granulosa-like cells (KGNs). In this study, we found that the protein levels of UFL1 were increased obviously under LPS stimulation in KGNs and that ER stress and apoptosis were further aggravated when UFL1 was knocked down; in contrast, these events were rescued when UFL1 was overexpressed. Next, we showed that the levels of ferroptosis-related proteins were relatively altered, accompanied by the accumulation of reactive oxygen species (ROS) and Fe2+, following the inhibition of UFL1 expression. In contrast, the overexpression of UFL1 reversed the ferroptosis process by regulating the P53/SLC7A11 (solute carrier family 7, member 11, SLC7A11) system and autophagy in response to LPS stimulation. Furthermore, apoptosis and ER stress in KGNs are rescued by the administration of the ferroptosis inhibitor ferrostatin-1 (Fer-1). Collectively, our research demonstrated a new mechanism for UFL1 that can alleviate ER stress and apoptosis stimulated by LPS; this occurred via the regulation of the ferroptosis pathway in KGNs and may provide a new strategy for research in the field of reproduction.

Keywords:  Apoptosis; ER stress; Ferroptosis; UFL1

DOI:  https://doi.org/10.1007/s12192-022-01284-y
ACS Nano. 2022 Jun 23.

Gold Nanorods Induce Endoplasmic Reticulum Stress and Autocrine Inflammatory Activation in Human Neutrophils.

Ronja Schirrmann, Michael Erkelenz, Kim Lamers, Oliver Sritharan, Milen Nachev, Bernd Sures, Sebastian Schlücker, Sven Brandau.

  Gold nanorods (AuNRs) are promising agents for diverse biomedical applications such as drug and gene delivery, bioimaging, and cancer treatment. Upon in vivo application, AuNRs quickly interact with cells of the immune system. On the basis of their strong intrinsic phagocytic activity, polymorphonuclear neutrophils (PMNs) are specifically equipped for the uptake of particulate materials such as AuNRs. Therefore, understanding the interaction of AuNRs with PMNs is key for the development of safe and efficient therapeutic applications. In this study, we investigated the uptake, intracellular processing, and cell biological response induced by AuNRs in PMNs. We show that uptake of AuNRs mainly occurs via phagocytosis and macropinocytosis with rapid deposition of AuNRs in endosomes within 5 min. Within 60 min, AuNR uptake induced an unfolded protein response (UPR) along with induction of inositol-requiring enzyme 1 α (IREα) and features of endoplasmic reticulum (ER) stress. This early response was followed by a pro-inflammatory autocrine activation loop that involves LOX1 upregulation on the cell surface and increased secretion of IL8 and MMP9. Our study provides comprehensive mechanistic insight into the interaction of AuNRs with immune cells and suggests potential targets to limit the unwanted immunopathological activation of PMNs during application of AuNRs.

Keywords:  ER stress; IL8; LOX1; gold nanorods; neutrophils

DOI:  https://doi.org/10.1021/acsnano.2c03586
Cell Mol Life Sci. 2022 Jun 21. 79(7): 373

Neuronal microRNAs safeguard ER Ca2+ homeostasis and attenuate the unfolded protein response upon stress.

Maria Paschou, Panagiota Papazafiri, Chrysanthi Charalampous, Michael Zachariadis, Skarlatos G Dedos, Epaminondas Doxakis.

  Ca2+ is a critical mediator of neurotransmitter release, synaptic plasticity, and gene expression, but also excitotoxicity. Ca2+ signaling and homeostasis are coordinated by an intricate network of channels, pumps, and calcium-binding proteins, which must be rapidly regulated at all expression levels. Τhe role of neuronal miRNAs in regulating ryanodine receptors (RyRs) and inositol 1,4,5-triphosphate receptors (IP3Rs) was investigated to understand the underlying mechanisms that modulate ER Ca2+ release. RyRs and IP3Rs are critical in mounting and propagating cytosolic Ca2+ signals by functionally linking the ER Ca2+ content, while excessive ER Ca2+ release via these receptors is central to the pathophysiology of a wide range of neurological diseases. Herein, two brain-restricted microRNAs, miR-124-3p and miR-153-3p, were found to bind to RyR1-3 and IP3R3 3'UTRs, and suppress their expression at both the mRNA and protein level. Ca2+ imaging studies revealed that overexpression of these miRNAs reduced ER Ca2+ release upon RyR/IP3R activation, but had no effect on [Ca2+]i under resting conditions. Interestingly, treatments that cause excessive ER Ca2+ release decreased expression of these miRNAs and increased expression of their target ER Ca2+ channels, indicating interdependence of miRNAs, RyRs, and IP3Rs in Ca2+ homeostasis. Furthermore, by maintaining the ER Ca2+ content, miR-124 and miR-153 reduced cytosolic Ca2+ overload and preserved protein-folding capacity by attenuating PERK signaling. Overall, this study shows that miR-124-3p and miR-153-3p fine-tune ER Ca2+ homeostasis and alleviate ER stress responses.

Keywords:  Calcium; Inositol 1,4,5-triphosphate receptor; Ryanodine receptor; Unfolded protein response; miR-124; miR-153

DOI:  https://doi.org/10.1007/s00018-022-04398-9
Int J Mol Sci. 2022 Jun 10. pii: 6520. [Epub ahead of print]23(12):

The Unfolded Protein Response Sensor PERK Mediates Stiffness-Dependent Adaptation in Glioblastoma Cells.

Mohammad Khoonkari, Dong Liang, Marina Trombetta Lima, Tjitze van der Land, Yuanke Liang, Jianwu Sun, Amalia Dolga, Marleen Kamperman, Patrick van Rijn, Frank A E Kruyt.

  Glioblastoma multiforme (GBM) is the most aggressive brain tumor in adults. In addition to genetic causes, the tumor microenvironment (TME), including stiffening of the extracellular matrix (ECM), is a main driver of GBM progression. Mechano-transduction and the unfolded protein response (UPR) are essential for tumor-cell adaptation to harsh TME conditions. Here, we studied the effect of a variable stiff ECM on the morphology and malignant properties of GBM stem cells (GSCs) and, moreover, examined the possible involvement of the UPR sensor PERK herein. For this, stiffness-tunable human blood plasma (HBP)/alginate hydrogels were generated to mimic ECM stiffening. GSCs showed stiffness-dependent adaptation characterized by elongated morphology, increased proliferation, and motility which was accompanied by F-Actin cytoskeletal remodeling. Interestingly, in PERK-deficient GSCs, stiffness adaptation was severely impaired, which was evidenced by low F-Actin levels, the absence of F-Actin remodeling, and decreased cell proliferation and migration. This impairment could be linked with Filamin-A (FLN-A) expression, a known interactor of PERK, which was strongly reduced in PERK-deficient GSCs. In conclusion, we identified a novel PERK/FLNA/F-Actin mechano-adaptive mechanism and found a new function for PERK in the cellular adaptation to ECM stiffening.

Keywords:  PERK; extracellular matrix stiffening; glioblastoma; mechanical stress; tumor microenvironment; unfolded protein response

DOI:  https://doi.org/10.3390/ijms23126520