bims-unfpre 2023-12-17 papers

Issue of 2023–12–17
six papers selected by
Susan Logue, University of Manitoba

Cell Rep. 2023 Dec 05. pii: S2211-1247(23)01552-8. [Epub ahead of print]42(12): 113540

The ER stress sensor IRE1 interacts with STIM1 to promote store-operated calcium entry, T cell activation, and muscular differentiation.

Amado Carreras-Sureda, Xin Zhang, Loann Laubry, Jessica Brunetti, Stéphane Koenig, Xiaoxia Wang, Cyril Castelbou, Claudio Hetz, Yong Liu, Maud Frieden, Nicolas Demaurex.

Store-operated Ca2+ entry (SOCE) mediated by stromal interacting molecule (STIM)-gated ORAI channels at endoplasmic reticulum (ER) and plasma membrane (PM) contact sites maintains adequate levels of Ca2+ within the ER lumen during Ca2+ signaling. Disruption of ER Ca2+ homeostasis activates the unfolded protein response (UPR) to restore proteostasis. Here, we report that the UPR transducer inositol-requiring enzyme 1 (IRE1) interacts with STIM1, promotes ER-PM contact sites, and enhances SOCE. IRE1 deficiency reduces T cell activation and human myoblast differentiation. In turn, STIM1 deficiency reduces IRE1 signaling after store depletion. Using a CaMPARI2-based Ca2+ genome-wide screen, we identify CAMKG2 and slc105a as SOCE enhancers during ER stress. Our findings unveil a direct crosstalk between SOCE and UPR via IRE1, acting as key regulator of ER Ca2+ and proteostasis in T cells and muscles. Under ER stress, this IRE1-STIM1 axis boosts SOCE to preserve immune cell functions, a pathway that could be targeted for cancer immunotherapy.

Keywords: CP: Cell biology; CP: Immunology; CRISPR screening; CaMPARI; ER stress; IRE1; SOCE; STIM1; T cells; calcium; muscle

DOI: https://doi.org/10.1016/j.celrep.2023.113540

J Autoimmun. 2023 Dec 09. pii: S0896-8411(23)00161-0. [Epub ahead of print]142 103152

Loss of function of XBP1 splicing activity of IRE1α favors B cell tolerance breakdown.

Anti-nuclear antibodies are the hallmark of autoimmune diseases such as systemic lupus erythematosus (SLE) and scleroderma. However, the molecular mechanisms of B cell tolerance breakdown in these pathological contexts are poorly known. The study of rare familial forms of autoimmune diseases could therefore help to better describe common biological mechanisms leading to B cell tolerance breakdown. By Whole-Exome Sequencing, we identified a new heterozygous mutation (p.R594C) in ERN1 gene, encoding IRE1α (Inositol-Requiring Enzyme 1α), in a multiplex family with several members presenting autoantibody-mediated autoimmunity. Using human cell lines and a knock-in (KI) transgenic mouse model, we showed that this mutation led to a profound defect of IRE1α ribonuclease activity on X-Box Binding Protein 1 (XBP1) splicing. The KI mice developed a broad panel of autoantibodies, however in a subclinical manner. These results suggest that a decrease of spliced form of XBP1 (XBP1s) production could contribute to B cell tolerance breakdown and give new insights into the function of IRE1α which are important to consider for the development of IRE1α targeting strategies.

Keywords: Autoimmunity; Breakdown of tolerance; IRE1α; Unfolded protein response

DOI: https://doi.org/10.1016/j.jaut.2023.103152

Cancer Gene Ther. 2023 Dec 12.

SPRTN is involved in hepatocellular carcinoma development through the ER stress response.

Anja Batel, Mirjana Polović, Mateo Glumac, Oliver Šuman, Stipislav Jadrijević, Bernarda Lozić, Marija Petrović, Bobana Samardžija, Nicholas J Bradshaw, Karlo Skube, Vinko Palada, Mislav Acman, Ivana Marinović Terzić.

Endoplasmic reticulum (ER) stress, prompted by the accumulation of misfolded or unfolded proteins, triggers the activation of the unfolded protein response (UPR) pathway to restore ER homeostasis. This stress response is implicated in the development of hepatocellular carcinoma (HCC). A biallelic mutation in SPRTN is currently the only known single-gene mutation implicated in the early onset of HCC. However, the exact mechanism linking SPRTN mutations to HCC remains unclear. In our study, we analyzed SPRTN and UPR in 21 human HCC tissue samples using RT-qPCR, immunoblot, and immunohistochemistry. We found alterations in the expression levels of SPRTN and UPR-related genes and proteins in HCC samples. The impact of SPRTN on the ER stress response was assessed in SPRTN-depleted HepG2 cells through RNA sequencing, pull-down assay, comet assay, and mitotic index calculation. We demonstrated that SPRTN interacts with the UPR sensor GRP78. Furthermore, we observed a decrease in SPRTN levels during ER stress, and increased sensitivity to ER stress in SPRTN-depleted cells. These findings suggest an essential role for SPRTN in the ER stress response and provide new insights into HCC pathogenesis. This newly discovered function of SPRTN could significantly enhance our understanding and treatment of HCC.

DOI: https://doi.org/10.1038/s41417-023-00708-w

Prog Retin Eye Res. 2023 Dec 11. pii: S1350-9462(23)00070-8. [Epub ahead of print] 101231

The endoplasmic reticulum: Homeostasis and crosstalk in retinal health and disease.

Sarah X Zhang, Josh J Wang, Christopher R Starr, Eun-Jin Lee, Sophia Park, Assylbek Zhylkibayev, Andy Medina, Jonathan H Lin, Marina Gorbatyuk.

The endoplasmic reticulum (ER) is the largest intracellular organelle carrying out a broad range of important cellular functions including protein biosynthesis, folding, and trafficking, lipid and sterol biosynthesis, carbohydrate metabolism, and calcium storage and gated release. In addition, the ER makes close contact with multiple intracellular organelles such as mitochondria and the plasma membrane to actively regulate the biogenesis, remodeling, and function of these organelles. Therefore, maintaining a homeostatic and functional ER is critical for the survival and function of cells. This vital process is implemented through well-orchestrated signaling pathways of the unfolded protein response (UPR). The UPR is activated when misfolded or unfolded proteins accumulate in the ER, a condition known as ER stress, and functions to restore ER homeostasis thus promoting cell survival. However, prolonged activation or dysregulation of the UPR can lead to cell death and other detrimental events such as inflammation and oxidative stress; these processes are implicated in the pathogenesis of many human diseases including retinal disorders. In this review manuscript, we discuss the unique features of the ER and ER stress signaling in the retina and retinal neurons and describe recent advances in the research to uncover the role of ER stress signaling in neurodegenerative retinal diseases including age-related macular degeneration, inherited retinal degeneration, achromatopsia and cone diseases, and diabetic retinopathy. In some chapters, we highlight the complex interactions between the ER and other intracellular organelles focusing on mitochondria and illustrate how ER stress signaling regulates common cellular stress pathways such as autophagy. We also touch upon the integrated stress response in retinal degeneration and diabetic retinopathy. Finally, we provide an update on the current development of pharmacological agents targeting the UPR response and discuss some unresolved questions and knowledge gaps to be addressed by future research.

Keywords: Autophagy; Diabetic retinopathy; Endoplasmic reticulum; Integrated stress response; Mitochondria; Protein homeostasis; Retina; Retinal degeneration; Unfolded protein response

DOI: https://doi.org/10.1016/j.preteyeres.2023.101231

Biochim Biophys Acta Biomembr. 2023 Dec 09. pii: S0005-2736(23)00144-X. [Epub ahead of print] 184262

Bilayer tension-induced clustering of the UPR sensor IRE1.

Md Zobayer Hossain, Wylie Stroberg.

The endoplasmic reticulum acts as a protein quality control center where a range of chaperones and foldases facilitates protein folding. IRE1 is a sensory transmembrane protein that transduces signals of proteotoxic stress by forming clusters and activating a cellular program called the unfolded protein response (UPR). Recently, membrane thickness variation due to membrane compositional changes have been shown to drive IRE1 cluster formation, activating the UPR even in the absence of proteotoxic stress. Here, we demonstrate a direct relationship between bilayer tension and UPR activation based on IRE1 dimer stability. The stability of the IRE1 dimer in a (50%DOPC-50%POPC) membrane at different applied bilayer tensions was analyzed via molecular dynamics simulations. The potential of mean force for IRE1 dimerization predicts a higher concentration of IRE1 dimers for both tensed and compressed ER membranes. This study shows that IRE1 may be a mechanosensitive membrane protein and establishes a direct biophysical relationship between bilayer tension and UPR activation.

Keywords: IRE1; Lipid bilayer stress; Mechanosensitivity; Membrane tension; Molecular dynamics; Unfolded protein response

DOI: https://doi.org/10.1016/j.bbamem.2023.184262

Am J Physiol Lung Cell Mol Physiol. 2023 Dec 12.

Molecular Mechanisms Underlying TNFα Induced Mitochondrial Fragmentation in Human Airway Smooth Muscle Cells.

Debanjali Dasgupta, Sanjana Mahadev Bhat, Claire Creighton, Catherin Cortes, Philippe F Delmotte, Gary C Sieck.

Tumor necrosis factor α (TNFa), a proinflammatory cytokine, plays a significant role in mediating the effects of acute inflammation in response to allergens, pollutants, and respiratory infections. Previously, we showed that acute exposure to TNFa induces mitochondrial fragmentation in human airway smooth muscle (hASM) cells, which is associated with increased expression of dynamin-related protein 1 (DRP1). Phosphorylation of DRP1 at serine 616 (pDRP1S616) promotes its translocation and binding to the outer mitochondrial membrane (OMM) and mediates mitochondrial fragmentation. Previously, we reported that TNFa exposure triggers protein unfolding and triggers an endoplasmic reticulum (ER) stress response involving phosphorylation of inositol-requiring enzyme 1α (pIRE1a) at serine 724 (pIRE1aS724) and subsequent splicing of X-box binding protein 1 (XBP1s) in hASM cells. We hypothesize that TNFa-mediated activation of the pIRE1aS724/XBP1s ER stress pathway in hASM cells transcriptionally activates genes that encode kinases responsible for pDRP1S616 phosphorylation. Using 3-D confocal imaging of MitoTracker green-labeled mitochondria, we found that TNFa treatment for 6 h induces mitochondrial fragmentation in hASM cells. We also confirmed that 6 h TNFa treatment activates the pIRE1a/XBP1s ER stress pathway. Using in silico analysis and ChIP assay, we showed that CDK1 and CDK5, kinases involved in the phosphorylation of pDRP1S616, are transcriptionally targeted by XBP1s. TNFa treatment increased the binding affinity of XBP1s on the promoter regions of CDK1 and CDK5, and this was associated with an increase in pDRP1S616 and mitochondria fragmentation. This study reveals a new underlying molecular mechanism for TNFa-induced mitochondrial fragmentation in hASM cells.

Keywords: Airway smooth muscle; DRP1 phosphorylation; ER stress; airway inflammation; mitochondrial fragmentation

DOI: https://doi.org/10.1152/ajplung.00198.2023