Endoplasmic Reticulum Stress Research Articles

Betacoronaviruses Differentially Activate the Integrated Stress Response to Optimize Viral Replication in Lung-Derived Cell Lines

The betacoronavirus genus contains five of the seven human coronaviruses, making it a particularly critical area of research to prepare for future viral emergence. We utilized three human betacoronaviruses, one from each subgenus—HCoV-OC43 (embecovirus), SARS-CoV-2 (sarbecovirus), and MERS-CoV (merbecovirus)—, to study betacoronavirus interactions with the PKR-like ER kinase (PERK) pathway of the integrated stress response (ISR)/unfolded protein response (UPR). The PERK pathway becomes activated by an abundance of unfolded proteins within the endoplasmic reticulum (ER), leading to phosphorylation of eIF2α and translational attenuation. We demonstrate that MERS-CoV, HCoV-OC43, and SARS-CoV-2 all activate PERK and induce responses downstream of p-eIF2α, while only SARS-CoV-2 induces detectable p-eIF2α during infection. Using a small molecule inhibitor of eIF2α dephosphorylation, we provide evidence that MERS-CoV and HCoV-OC43 maximize viral replication through p-eIF2α dephosphorylation. Interestingly, genetic ablation of growth arrest and DNA damage-inducible protein (GADD34) expression, an inducible protein phosphatase 1 (PP1)-interacting partner targeting eIF2α for dephosphorylation, did not significantly alter HCoV-OC43 or SARS-CoV-2 replication, while siRNA knockdown of the constitutive PP1 partner, constitutive repressor of eIF2α phosphorylation (CReP), dramatically reduced HCoV-OC43 replication. Combining GADD34 knockout with CReP knockdown had the maximum impact on HCoV-OC43 replication, while SARS-CoV-2 replication was unaffected. Overall, we conclude that eIF2α dephosphorylation is critical for efficient protein production and replication during MERS-CoV and HCoV-OC43 infection. SARS-CoV-2, however, appears to be insensitive to p-eIF2α and, during infection, may even downregulate dephosphorylation to limit host translation.

Transcription factor EB (TFEB) activity increases resistance of TNBC stem cells to metabolic stress

Breast cancer stem cells (CSCs) are difficult to therapeutically target, but continued efforts are critical given their contribution to tumor heterogeneity and treatment resistance in triple-negative breast cancer. CSC properties are influenced by metabolic stress, but specific mechanisms are lacking for effective drug intervention. Our previous work on TFEB suggested a key function in CSC metabolism. Indeed, TFEB knockdown (KD) inhibited mammosphere formation in vitro and tumor initiation/growth in vivo. These phenotypic effects were accompanied by a decline in CD44high/CD24lowcells. Glycolysis inhibitor 2-deoxy-D-glucose (2-DG) induced TFEB nuclear translocation, indicative of TFEB transcriptional activity. TFEB KD blunted, whereas TFEB (S142A) augmented 2-DG–driven unfolded protein response (UPR) mediators, notably BiP/HSPA5 and CHOP. Like TFEB KD, silencing BiP/HSPA5 inhibited CSC self-renewal, suggesting that TFEB augments UPR-related survival. Further studies showed that TFEB KD attenuated 2-DG–directed autophagy, suggesting a mechanism whereby TFEB protects CSCs against 2-DG–induced stress. Our data indicate that TFEB modulates CSC metabolic stress response via autophagy and UPR. These findings reveal the novel role of TFEB in regulating CSCs during metabolic stress in triple-negative breast cancer.

Identification of critical endoplasmic reticulum stress-related genes in advanced atherosclerotic plaque

Atherosclerosis (AS) is the principal pathological cause of atherosclerotic cardiovascular diseases. Chronic endoplasmic reticulum stress (ERS) has been implicated in AS aetiopathogenesis, but the underlying molecular interactions remain unclear. This study aims to identify the molecular mechanisms of ERS in AS pathogenesis to inform innovative diagnostic approaches and therapeutic targets for managing AS. GSE28829 and GSE43292—human early and advanced carotid atherosclerotic tissue samples—were obtained from the Gene Expression Omnibus database. Endoplasmic reticulum stress-related genes (ERSRGs) were obtained from GeneCards. Differential gene expression and weighted gene co-expression network analyses were conducted to identify genes associated with atherosclerosis, and intersection with ER-related genes revealed three ERSRGs (i.e. CTSB, LYN, and CYBB) associated with advanced atherosclerotic plaque. These three ERSRGs exhibited associations with various immune cells. Additionally, the three ERSRGs were upregulated in human atherosclerotic tissues, mouse models of progressive atherosclerotic lesions, and in vitro macrophage models. In conclusion, this study identified CTSB, LYN, and CYBB as potentially critical ERSRGs associated with advanced atherosclerotic plaque, demonstrating their good diagnostic utility and offering novel insights into the potential pathobiology of AS progression, paving the way for exploring innovative therapeutic targets.

A Novel Approach for In Vitro Testing and Hazard Evaluation of Nanoformulated RyR2-Targeting siRNA Drugs Using Human PBMCs

Nucleic acid (NA)-based drugs are promising therapeutics agents. Beyond efficacy, addressing safety concerns—particularly those specific to this class of drugs—is crucial. Here, we propose an in vitro approach to screen for potential adverse off-target effects of NA-based drugs. Human peripheral blood mononuclear cells (PBMCs), purified from buffy coats of healthy donors, were used to investigate the ability of NA-drugs to trigger toxicity pathways and inappropriate immune stimulation. PBMCs were selected for their ability to represent potential human responses, given their likelihood of interacting with administered drugs. As proof of concept, a small interfering RNA (siRNA) targeting Ryanodine Receptor mRNA (RyR2) identified by the Italian National Center for Gene Therapy and Drugs based on RNA Technology as a potential therapeutic target for dominant catecholaminergic polymorphic ventricular tachycardia, was selected. This compound and its scramble were formulated within a calcium phosphate nanoparticle-based delivery system. Positive controls for four toxicity pathways were identified through literature review, each associated with a specific type of cellular stress: oxidative stress (tert-butyl hydroperoxide), mitochondrial stress (rotenone), endoplasmic reticulum stress (thapsigargin), and autophagy (rapamycin). These controls were used to define specific mRNA signatures triggered in PBMCs, which were subsequently used as indicators of off-target effects. To assess immune activation, the release of pro-inflammatory cytokines (interleukin-6, interleukin-8, tumor necrosis factor-α, and interferon-γ) was measured 24 h after exposure. The proposed approach provides a rapid and effective screening method for identifying potential unintended effects in a relevant human model, which also allows to address gender effects and variability in responses.

Involvement of p38 MAPK and MAPKAPK2 in promoting cell death and the inflammatory response to ischemic stress associated with necrotic glioblastoma

The association of necrosis in tumors with poor prognosis implies a potential tumor-promoting role. However, the mechanisms underlying cell death in this context and how damaged tissue contributes to tumor progression remain unclear. Here, we identified p38 mitogen-activated protein kinases (p38 MAPK, a.k.a. p38) as a key player in promoting cell death and the inflammatory response to ischemic stress associated with necrotic tumors. We found that glioblastoma (GBM) cells expressing patient-derived Kirsten rat sarcoma (KRAS) or phosphoinositide-3-kinase (PI3K) active mutants showed enhanced cell death under ischemia-mimetic conditions in vitro and were more likely to develop into necrotic tumors in vivo. Cell death in both settings depended on p38, which is also required for tumor progression driven by KRAS or PI3K. Under ischemia-mimetic conditions, GBM cells undergo reactive oxygen species (ROS)-dependent cell death. Gene expression in these cells recapitulated multiple features observed in peri-necrotic tumors from patient GBM. Further studies showed the involvement of a positive feedback loop between the p38-MAPK-activated protein kinase 2 (MAPKAPK2, a.k.a. MK2) signaling axis and the unfolded protein response signaling components activating transcription factor 4 (ATF4) and inositol-requiring enzyme 1 (IRE1α) in driving ischemic tumor cell death. This signaling cascade was further potentiated by RAS or PI3K activation under ischemic conditions, contributing to the inflammatory gene expression response. Therefore, our study suggests that p38 could be targeted to relieve the inflammatory response in necrotic tumors and inhibit GBM progression.

Unusual Iron-Independent Ferroptosis-like Cell Death Induced by Photoactivation of a Typical Iridium Complex for Hypoxia Photodynamic Therapy.

Ferroptosis is a unique cell death mode that relies on iron and lipid peroxidation (LPO) and is extensively utilized to treat drug-resistant tumor. However, like the other antitumor model, requirement of oxygen limited its application in treating the malignant tumors in anaerobic environments, just as photodynamic therapy, a very promising anticancer therapy. Here, we show that an iridium(III) complex (Ir-dF), which was often used in proton-coupled electron transport (PCET) process, can induce efficient cell death upon photo irradiation, which can be effectively protected by the typical ferroptosis inhibitor Fer-1 but not by the classic iron chelating agents and ROS scavengers. Surprisingly, LPO was further demonstrated to be directly induced by Ir-dF/light activation via PCET, by utilizing a model polyunsaturated fatty acid. Ir-dF was found to be accumulated preferentially in mitochondria and the endoplasmic reticulum (ER), leading to mitochondrial swelling and ER stress accompanied by obvious LPO accumulation and downregulation of the characteristic ferroptosis protein GPX4. More interestingly, Ir-dF was also found to induce photocytotoxicity under hypoxia, and an in vivo experiment further confirmed that Ir-dF can effectively inhibit the growth of tumor under two-photon laser irradiation. Taken together, for the first time, this article introduces a new mechanism of inducing the LPO through a photoactivated PCET process, leading to a ferroptosis-like cell death which is independent of the iron and oxygen. This innovative mechanism holds great potential as a future treatment option for hypoxic malignant tumors and drug-resistant tumors.

A Peptide Nanoregulator Enriched at the Endoplasmic Reticulum for Boosting Fractionated Radiotherapy‐Mediated Antitumor Immune Response

AbstractFractionated radiotherapy (FRT), typically delivering low‐dose radiation of 2 Gy per fraction, has been used as the main clinical treatment regimen for various tumors. However, its therapeutic efficacy is severely hindered by inadequate pro‐immunogenic effect and ionizing radiation‐induced immunosuppression. Herein, a peptide nanoregulator (SPER‐NO‐Ind) is constructed from self‐assembling peptides that can enrich nitric oxide (NO) at the endoplasmic reticulum (ER) and inhibit indoleamine 2,3‐dioxygenase (IDO) to enhance FRT‐mediated antitumor immunity and reinforce treatment outcomes. SPER‐NO‐Ind triggered S‐nitrosylation of the ryanodine receptor by ER‐specific enrichment of NO, triggering the release of Ca2+ within ER and induction of robust ER stress. The combination of 2 Gy γ‐radiation with SPER‐NO‐Ind induced intense immunogenic cell death (ICD) in ER‐stressed 4T1 cells. Furthermore, this nanoregulator inhibited IDO and decreased kynurenine production, reversing FRT‐induced immunosuppressive effects. The combined application of FRT and SPER‐NO‐Ind demonstrated superior efficacy in suppressing breast tumor growth, amplifying abscopal effects, and inhibiting metastasis in mice. The SPER‐NO‐Ind treatment achieved a 40% decrease in the total radiation dose while securing equivalent tumor suppression efficacy. Collectively, the work presents a facile approach to augment the efficacy of fractionated radiotherapy for tumors, opening up a new way to enhance the antitumor immune response of radiotherapy.

MAPK signaling mediated intestinal inflammation induced by endoplasmic reticulum stress and NOD2.

Endoplasmic reticulum (ER) stress is crucially involved in inflammatory bowel disease (IBD), but the mechanisms remain incompletely understood. This study aimed to elucidate how ER stress promotes inflammation in IBD. ER stress marker Grp78 and NOD2 in colon tissues of Crohn's disease (CD) patients and IBD model mice were detected by immunohistochemical analysis. THP-1 cells were exposed to ER stress and the expression of NOD2 and inflammatory cytokines was detected by PCR. We found that ER stress markers Grp78 and NOD2 were upregulated in intestinal tissues of CD patients and in THP-1 cells exposed to ER stress. ER stress inhibitor reduced Grp78 and NOD2 expression in colitis model mice and alleviated colitis. ER stress inducer cooperated with NOD2 ligand MDP to upregulate TNF-α, IL-8 and IL-1β, and activate MAPK signaling in THP-1 cells. Moreover, inhibitors of MAPK signaling led to the downregulation of IL-1β, IL-8 and TNF-α in THP-1 cells stimulated by ER stress inducer and MDP. In conclusion, ER stress upregulates NOD2 and promotes inflammation in IBD, at least partially due to the activation of MAPK pathway.

Investigation of the Mesencephalic Astrocyte Derived Neurotrophic Factor-Endoplasmic Reticulum Stress Pathway in Mood Disorders.

Bipolar disorder (BD) has been associated with impaired cellular resilience. Recent studies have shown abnormalities in the unfolded protein response (UPR) in BD. The UPR is the cellular response to endoplasmic reticulum (ER) stress. Mesencephalic astrocyte-derived neurotrophic factor (MANF), a trophic factor, decreases ER stress by modulating the UPR. The objective of this study is to investigate the MANF-ER stress pathway in BD and major depressive disorder (MDD) compared to healthy controls (HC). MANF protein concentration and MANF and GRP78 gene expression were assessed in peripheral blood from individuals with BD, MDD and HC (protein: 40 BD, 55 MDD, 55 HC; gene expression: 52 BD, 61 MDD, 69 HC). MANF protein and gene expression along with GRP78 gene expression were also analyzed in postmortem brain tissue (20 BD, 20 MDD, 19 HC). MANF protein was quantified using an ELISA assay while quantitative polymerase chain reaction was used for MANF and GRP78 gene expression. Peripheral MANF protein levels were reduced in individuals with BD in a depressive state compared to controls (p=0.031) and euthymic BD participants (p=0.013). No significant differences in MANF or GRP78 gene expression were observed in BD irrespective of mood state, or MDD compared to HC (all p>0.05). No differences were observed regarding MANF/GRP78 protein or gene expression levels in postmortem tissue (p>0.05). Individuals with BD who were in an acute depressive phase were found to have reduced peripheral MANF levels potentially signifying abnormal UPR and supporting the notion that BD is associated with increased ER stress.

Small protein ERSP encoded by LINC02870 promotes triple negative breast cancer progression via IRE1α/XBP1s activation.

Clinical treatment options for triple-negative breast cancer (TNBC) are currently limited to chemotherapy because of a lack of effective therapeutic targets. Recent evidence suggests that long noncoding RNAs (lncRNAs) encode bioactive peptides or proteins, thereby playing noncanonical yet significant roles in regulating cellular processes. However, the potential of lncRNA-translated products in cancer progression remains largely unknown. In this study, we identified a previously undocumented small protein encoded by the lncRNA LINC02870. This protein is localized at the endoplasmic reticulum (ER) and participates in ER stress, thus, we named it the endoplasmic reticulum stress protein (ERSP). ERSP was highly expressed in TNBC tissues, and elevated LINC02870 content was correlated with poor prognosis in TNBC patients. Loss of ERSP inhibited TNBC growth and metastasis both in vitro and in vivo. The pro-oncogenic effects of ERSP could be attributed to its selective activation of the IRE1α/XBP1s branch. ERSP enhances the unfolded protein response (UPR) by interacting with XBP1s, facilitating the nuclear accumulation of XBP1s, thereby promoting the expression of ER stress-related genes. These findings highlight the regulatory role of the lncRNA-encoded protein ERSP in ER stress and suggest that it is a potential therapeutic target for TNBC.

Targeting P21-Activated Kinase 2 as a Novel Therapeutic Approach to Mitigate Endoplasmic Reticulum Stress in Heart Failure With Preserved Ejection Fraction.

Heart failure with preserved ejection fraction (HFpEF) is linked to prolonged endoplasmic reticulum (ER) stress. P21-activated kinase 2 (Pak2) facilitates a protective ER stress response. This study explores the mechanism and role of Pak2 in HFpEF pathology. The HFpEF mouse model was established using a high-fat diet combined with the nitric oxide synthase inhibitor Nω-Nitro-l-arginine methyl ester (high-fat diet+Nω-Nitro-l-arginine methyl ester). The model exhibited the typical characteristics of HFpEF (cardiac hypertrophy, diastolic dysfunction with preserved systolic function, and lung edema) as determined by echocardiography and hemodynamic analysis. Terminal deoxynucleotidyl transferase dUTP nick end labeling and dihydroethidium staining results showed that cell death and reactive oxygen species generation were higher in the high-fat diet+Nω-Nitro-l-arginine methyl ester-treated group. Transmission electron microscopy revealed disruption of the ER subcellular structures in the HFpEF mouse model, while western blot analysis confirmed reduced Pak2 phosphorylation and impaired inositol-requiring enzyme 1/X-box binding protein 1 splicing ER stress response signaling. Furthermore, H9c2 cells subjected to the palmitic acid-mediated metabolic stress developed temporal changes in unfolded protein response proteins and Pak2 activity. The inositol requiring enzyme 1/X-box binding protein 1 splicing branch of unfolded protein response was impaired earlier than other branches. Overexpression of Pak2 by adenovirus in H9c2 cells sustained the activation of inositol requiring enzyme 1/X-box binding protein 1 splicing. Pak2 deficiency in the mouse heart accelerated the HFpEF progression, and this phenomenon occurred as early as 10 weeks in Pak2 cardiomyocyte-specific knockout mice. Conversely, adeno-associated virus serotype 9-mediated Pak2 overexpression mitigated HFpEF symptoms, underscoring its protective role against HFpEF progression. Pak2 prevents HFpEF progression, exerting cardioprotective effects against ER stress. These insights underscore the therapeutic value of Pak2 in HFpEF.

Artificial enforcement of the unfolded protein response (UPR) reduces disease features in multiple preclinical models of ALS/FTD.

Amyotrophic lateral sclerosis (ALS) and fronto-temporal dementia (FTD) are part of a spectrum of diseases that share several causative genes, resulting in a combinatory of motor and cognitive symptoms and abnormal protein aggregation. Multiple unbiased studies have revealed that proteostasis impairment at the level of the endoplasmic reticulum (ER) is a transversal pathogenic feature of ALS/FTD. The transcription factor XBP1s is a master regulator of the unfolded protein response (UPR), the main adaptive pathway to cope with ER stress. Here we provide evidence of suboptimal activation of the UPR in ALS/FTD models under experimental ER stress. To artificially engage the UPR, we intracerebroventricularly administrated adeno-associated viruses (AAV) to express the active form of XBP1 (XBP1s) in the nervous system of ALS/FTD models. XBP1s expression improved motor performance and extended life span of mutant SOD1 mice, associated with reduced protein aggregation. AAV-XBP1s administration also attenuated disease progression in models of TDP-43 and C9orf72 pathogenesis. Proteomic profiling of spinal cord tissue revealed that XBP1s overexpression improved proteostasis and modulated the expression of a cluster of synaptic and cell morphology proteins. Our results suggest that strategies to improve ER proteostasis may serve as a pan-therapeutic strategy to treat ALS/FTD.

Noncanonical UPR factor CREB3L2 drives immune evasion of triple-negative breast cancer through Hedgehog pathway modulation in T cells.

The unfolded protein response (UPR) pathway is crucial for tumorigenesis, mainly by regulating cancer cell stress responses and survival. However, whether UPR factors facilitate cell-cell communication between cancer cells and immune cells to drive cancer progression remains unclear. We found that adenosine 3',5'-monophosphate response element-binding protein 3-like protein 2 (CREB3L2), a noncanonical UPR factor, is overexpressed and activated in triple-negative breast cancer, where its cleavage releases a C-terminal fragment that activates the Hedgehog pathway in neighboring CD8+ T cells. The enhanced Hedgehog pathway represses CD8+ T cell activation and inhibits its cytotoxic effects. Consequently, overexpression of CREB3L2 not only promotes tumor growth but also causes resistance to immune checkpoint blockade (ICB). Inhibition of the Hedgehog pathway impedes the growth of CREB3L2-overexpressed tumors and sensitizes them to ICB therapy. In summary, we identified a previously unidentified mechanism by which the UPR pathway dictates cross-talk between cancer cells and immune cells, providing important anticancer therapeutic opportunities.

Bile acid synthesis impedes tumor-specific T cell responses during liver cancer.

The metabolic landscape of cancer greatly influences antitumor immunity, yet it remains unclear how organ-specific metabolites in the tumor microenvironment influence immunosurveillance. We found that accumulation of primary conjugated and secondary bile acids (BAs) are metabolic features of human hepatocellular carcinoma and experimental liver cancer models. Inhibiting conjugated BA synthesis in hepatocytes through deletion of the BA-conjugating enzyme bile acid-CoA:amino acid N-acyltransferase (BAAT) enhanced tumor-specific T cell responses, reduced tumor growth, and sensitized tumors to anti-programmed cell death protein 1 (anti-PD-1) immunotherapy. Furthermore, different BAs regulated CD8+ T cells differently; primary BAs induced oxidative stress, whereas the secondary BA lithocholic acid inhibited T cell function through endoplasmic reticulum stress, which was countered by ursodeoxycholic acid. We demonstrate that modifying BA synthesis or dietary intake of ursodeoxycholic acid could improve tumor immunotherapy in liver cancer model systems.

The pentose phosphate pathway controls oxidative protein folding and prevents ferroptosis in chondrocytes.

Bone lengthening and fracture repair depend on the anabolic properties of chondrocytes that function in an avascular milieu. The limited supply of oxygen and nutrients calls into question how biosynthesis and redox homeostasis are guaranteed. Here we show that glucose metabolism by the pentose phosphate pathway (PPP) is essential for endochondral ossification. Loss of glucose-6-phosphate dehydrogenase in chondrocytes does not affect cell proliferation because reversal of the non-oxidative PPP produces ribose-5-phosphate. However, the decreased NADPH production reduces glutathione recycling, resulting in decreased protection against the reactive oxygen species (ROS) produced during oxidative protein folding. The disturbed proteostasis activates the unfolded protein response and protein degradation. Moreover, the oxidative stress induces ferroptosis, which, together with altered matrix properties, results in a chondrodysplasia phenotype. Collectively, these data show that in hypoxia, the PPP is crucial to produce reducing power that confines ROS generated by oxidative protein folding and thereby controls proteostasis and prevents ferroptosis.

The Role of Endoplasmic Reticulum Stress in Alzheimer's Disease: Molecular Mechanisms and Viral Hypotheses

The Role of Endoplasmic Reticulum Stress in Alzheimer's Disease: Molecular Mechanisms and Viral Hypotheses

Unveiling the molecular mechanisms of recurrent miscarriage through endoplasmic reticulum stress related gene expression

Recurrent miscarriage (RM) is a reproductive disorder affecting couples worldwide. The underlying molecular mechanisms remain elusive, even though emerging evidence has implicated endoplasmic reticulum stress (ERS). We investigated RM- and ERS-related genes to develop a diagnostic model that can enhance predictive ability. We utilized the R package GEO query to extract and process Gene Expression Omnibus data, applying batch correction, normalization, and differential gene expression analysis with limma. ERS-related differentially expressed genes (ERSRGs) were identified through Gene Ontology and Kyoto Encyclopedia of genes and genomes analyses, and their diagnostic potential was assessed. Diagnostic models were developed using logistic regression, support vector machines, and least absolute shrinkage and selection operators, complemented by immune infiltration analysis and regulatory network construction. Integrated analysis revealed 1395 differentially expressed genes (DEGs), including 626 upregulated and 769 downregulated genes. Seventeen ERSRGs were identified. KEAP1 and YIPF5 displayed high diagnostic accuracy (area under the curve [AUC] > 0.9). Gene Ontology and Kyoto Encyclopedia of genes and genomes analyses highlighted the role of ESRDEGs in cellular responses to ERS, protein processing, and apoptosis. Diagnostic models demonstrated robust predictive performance (AUC > 0.9). A molecular interaction was found between RM and the ERS response, and the identified ESRDEGs could serve as potential biomarkers for diagnosis.

Alleviation of liver fibrosis by inhibiting a non-canonical ATF4-regulated enhancer program in hepatic stellate cells

Liver fibrosis is a critical liver disease that can progress to more severe manifestations, such as cirrhosis, yet no effective targeted therapies are available. Here, we identify that ATF4, a master transcription factor in ER stress response, promotes liver fibrosis by facilitating a stress response-independent epigenetic program in hepatic stellate cells (HSCs). Unlike its canonical role in regulating UPR genes during ER stress, ATF4 activates epithelial-mesenchymal transition (EMT) gene transcription under fibrogenic conditions. HSC-specific depletion of ATF4 suppresses liver fibrosis in vivo. Mechanistically, TGFβ resets ATF4 to orchestrate a unique enhancer program for the transcriptional activation of pro-fibrotic EMT genes. Analysis of human data confirms a strong correlation between HSC ATF4 expression and liver fibrosis progression. Importantly, a small molecule inhibitor targeting ATF4 translation effectively mitigates liver fibrosis. Together, our findings identify a mechanism promoting liver fibrosis and reveal new opportunities for treating this otherwise non-targetable disease.

IRE1α-XBP1 safeguards hematopoietic stem and progenitor cells by restricting pro-leukemogenic gene programs.

Hematopoietic stem cells must mitigate myriad stressors throughout their lifetime to ensure normal blood cell generation. Here, we uncover unfolded protein response stress sensor inositol-requiring enzyme-1α (IRE1α) signaling in hematopoietic stem and progenitor cells (HSPCs) as a safeguard against myeloid leukemogenesis. Activated in part by an NADPH oxidase-2 mechanism, IRE1α-induced X-box binding protein-1 (XBP1) mediated repression of pro-leukemogenic programs exemplified by the Wnt-β-catenin pathway. Transcriptome analysis and genome-wide mapping of XBP1 targets in HSPCs identified an '18-gene signature' of XBP1-repressed β-catenin targets that were highly expressed in acute myeloid leukemia (AML) cases with worse prognosis. Accordingly, IRE1α deficiency cooperated with a myeloproliferative oncogene in HSPCs to cause a lethal AML in mice, while genetic induction of XBP1 suppressed the leukemia stem cell program and activity of patient-derived AML cells. Thus, IRE1α-XBP1 signaling safeguards the integrity of the blood system by restricting pro-leukemogenic programs in HSPCs.

Transmission of unfolded protein response-a regulator of disease progression, severity, and spread in virus infections.

The unfolded protein response (UPR) is a cell-autonomous stress response aimed at restoring homeostasis due to the accumulation of misfolded proteins in the endoplasmic reticulum (ER). Viruses often hijack the host cell machinery, leading to an accumulation of misfolded proteins in the ER. The cell-autonomous UPR is the immediate response of an infected cell to this stress, aiming to restore normal function by halting protein translation, degrading misfolded proteins, and activating signaling pathways that increase the production of molecular chaperones. The cell-non-autonomous UPR involves the spreading of UPR signals from initially stressed cells to neighboring unstressed cells that lack the stressor. Though viruses are known modulators of cell-autonomous UPR, recent advancements have highlighted that cell-non-autonomous UPR plays a critical role in elucidating how local infections cause systemic effects, thereby contributing to disease symptoms and progression. Additionally, by utilizing cell-non-autonomous UPR, viruses have devised novel strategies to establish a pro-viral state, promoting virus spread. This review discusses examples that have broadened the understanding of the role of UPR in virus infections and disease progression by looking beyond cell-autonomous to non-autonomous processes and mechanistic details of the inducers, spreaders, and receivers of UPR signals.