Increased ER Stress and Unfolded Protein Response Activation in Epithelial and Inflammatory Cells in Hypersensitivity Pneumonitis.

Several types of cytotoxic insults disrupt endoplasmic reticulum (ER) homeostasis, cause ER stress, and activate the unfolded protein response (UPR). The role of ER stress and UPR activation in hypersensitivity pneumonitis (HP) has not been described. HP is an immune-mediated interstitial lung disease that develops following repeated inhalation of various antigens in susceptible and sensitized individuals. The aim of this study was to investigate the lung expression and localization of the key effectors of the UPR, BiP/GRP78, CHOP, and sXBP1 in HP patients compared with control subjects. Furthermore, we developed a mouse model of HP to determine whether ER stress and UPR pathway are induced during this pathogenesis. In human control lungs, we observed weak positive staining for BiP in some epithelial cells and macrophages, while sXBP1 and CHOP were negative. Conversely, strong BiP, sXBP1- and CHOP-positive alveolar and bronchial epithelial, and inflammatory cells were identified in HP lungs. We also found apoptosis and autophagy markers colocalization with UPR proteins in HP lungs. Similar results were obtained in lungs from an HP mouse model. Our findings suggest that the UPR pathway is associated with the pathogenesis of HP.

Hepatic IRE1α-XBP1 signaling promotes GDF15-mediated anorexia and body weight loss in chemotherapy.

Platinum-based chemotherapy drugs can lead to the development of anorexia, a detrimental effect on the overall health of cancer patients. However, managing chemotherapy-induced anorexia and subsequent weight loss remains challenging due to limited effective therapeutic strategies. Growth differentiation factor 15 (GDF15) has recently gained significant attention in the context of chemotherapy-induced anorexia. Here, we report that hepatic GDF15 plays a crucial role in regulating body weight in response to chemo drugs cisplatin and doxorubicin. Cisplatin and doxorubicin treatments induce hepatic Gdf15 expression and elevate circulating GDF15 levels, leading to hunger suppression and subsequent weight loss. Mechanistically, selective activation by chemotherapy of hepatic IRE1α-XBP1 pathway of the unfolded protein response (UPR) upregulates Gdf15 expression. Genetic and pharmacological inactivation of IRE1α is sufficient to ameliorate chemotherapy-induced anorexia and body weight loss. These results identify hepatic IRE1α as a molecular driver of GDF15-mediated anorexia and suggest that blocking IRE1α RNase activity offers a therapeutic strategy to alleviate the adverse anorexia effects in chemotherapy.

Specific Knockout of Notch-1 in Macrophages Modulate the Progression of Hepatic Insulin Resistance in HFD Fed Mice via Regulating IRE1α-XBP1 Signals.

OBJECTIVE: To develop an intervention based on Notch-1 signalling pathway blockade by investigating the potential application of the neurogenic locus notch homologue protein 1(Notch-1) signalling pathway as a key regulator of chronic inflammation and adipogenesis in the treatment of hepatic insulin resistance (HIR). STUDY DESIGN: Experimental study. Place and Duration of the Study: Animal Laboratory of the Fourth Hospital of Hebei Medical University, Shijiazhuang, China, from April 2021 to June 2022. METHODOLOGY: HIR models were established in Notch-1WT and Notch-1MAC-KO mice by high fat diet (HFD) for 16 weeks. Haematoxylin and eosin (HE) staining and oil red O (ORO) staining were used to detect inflammatory infiltration and lipid accumulation in each group. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of TNF-α and IL-6. Free fatty acid (FFA) and total cholesterol (TC) were measured with relevant kits. Moreover, real-time quantitative polymerase chain reaction (PCR) was performed to detect the relative expressions of F4/80, Mcp1, and CD11b in hepatic tissues. Mass spectrometry was used to analyse the levels of triglyceride (TG), diacylglycerol (DAG) and conformite europeenne (CE) in liver tissue. Western blotting was used to detect the expression of related proteins. RESULTS: Specific knockdown of Notch-1 in macrophages decreases the relative fluorescence intensity of CD68 and attenuates inflammatory infiltration and lipid degeneration. There was no difference in plasma levels of FFA and TG. Specific knockdown of Notch-1 in macrophages decreases the expression of F4/80, Mcp1, and CD11b, as well as the levels of TG, DAG, CE, IL-6, and TNF-α. CONCLUSION: Specific knockout of Notch-1 in macrophages may reduce HIR by inhibiting the IRE1α-XBP1 signalling pathway. KEY WORDS: Hepatic insulin resistance, Macrophages, Notch-1, IRE1α, XBP1.

Correlation Between Low Cytoplasmic Expression of XBP1 and the Likelihood of Surviving Hepatocellular Carcinoma.

BACKGROUND/AIM: Our objectives in this study were to (i) evaluate the clinical significance of X-box-binding protein 1 (XBP1) expression in cases of hepatocellular carcinoma (HCC) and (ii) assess the potential of XBP1 to be used as a prognostic biomarker. PATIENTS AND METHODS: The expression of XBP1 protein in 267 HCC tissue specimens was measured using immunohistochemistry in order to characterize the associations among XBP1 expression, clinicopathological factors and survival outcomes. Survival analysis using follow-up data was used to assess the prognostic value of XBP1 in cases of HCC. Immunohistochemistry revealed a significant decrease in cytoplasmic XBP1 protein expression in HCC tumor tissue. RESULTS: Immunoreactivity results showed that low cytoplasmic XBP1 expression was significantly associated with vascular invasion, as well as poor 5-year overall survival and long-term disease-specific (DSS) and disease-free (DFS) survival rates. Kaplan-Meier survival curves further confirmed a significant association between low cytoplasmic XBP1 protein expression and poor DSS and DFS. Univariate and multivariate analyses revealed that XBP1 expression, tumor differentiation, vascular invasion, tumor stage, and the rate of recurrence were linked to DSS, while low cytoplasmic XBP1 expression remained an independent predictor of poor DSS. Our analysis also revealed that XBP1 expression, tumor differentiation, vascular invasion, and T classification were linked to DFS, while low cytoplasmic XBP1 expression remained an independent predictor of poor DFS. CONCLUSION: Low cytoplasmic XBP1 protein expression may play an important role in the pathogenesis of HCC, which suggests that XBP1 could potentially be targeted to benefit therapeutic strategies for HCC.

The IRE1α-XBP1 arm of the unfolded protein response is a host factor activated in SARS-CoV-2 infection.

SARS-CoV-2 infection can cause severe pneumonia, wherein exacerbated inflammation plays a major role. This is reminiscent of the process commonly termed cytokine storm, a condition dependent on a disproportionated production of cytokines. This state involves the activation of the innate immune response by viral patterns and coincides with the biosynthesis of the biomass required for viral replication, which may overwhelm the capacity of the endoplasmic reticulum and drive the unfolded protein response (UPR). The UPR is a signal transduction pathway composed of three branches that is initiated by a set of sensors: inositol-requiring protein 1 (IRE1), protein kinase RNA-like ER kinase (PERK), and activating transcription factor 6 (ATF6). These sensors control adaptive processes, including the transcriptional regulation of proinflammatory cytokines. Based on this background, the role of the UPR in SARS-CoV-2 replication and the ensuing inflammatory response was investigated using in vivo and in vitro models of infection. Mice and Syrian hamsters infected with SARS-CoV-2 showed a sole activation of the Ire1α-Xbp1 arm of the UPR associated with a robust production of proinflammatory cytokines. Human lung epithelial cells showed the dependence of viral replication on the expression of UPR-target proteins branching on the IRE1α-XBP1 arm and to a lower extent on the PERK route. Likewise, activation of the IRE1α-XBP1 branch by Spike (S) proteins from different variants of concern was a uniform finding. These results show that the IRE1α-XBP1 system enhances viral replication and cytokine expression and may represent a potential therapeutic target in SARS-CoV-2 severe pneumonia.

The modulation of autophagy and unfolded protein response by ent-kaurenoid derivative CPUK02 in human colorectal cancer cells.

BACKGROUND: CPUK02 (15-Oxosteviol benzyl ester) is a semi-synthetic derivative of stevioside known for its anticancer effects. It has been reported that the natural compound of stevioside and its associated derivatives enhances the sensitivity of cancer cells to conventional anti-cancer agents by inducing endoplasmic reticulum (ER) stress. In response to ER stress, autophagy and unfolded protein responses (UPR) are activated to restore cellular homeostasis. Consequently, the primary aim of this study is to investigate the impact of CPUK02 treatment on UPR and autophagy markers in two colorectal cancer cell lines. METHODS: HCT116 and SW480 cell lines were treated with various concentrations of CPUK02 for 72 h. The expression levels of several proteins and enzymes were evaluated to investigate the influence of CPUK02 on autophagy and UPR pathways. These include glucose-regulated protein 78 (GRP78), Inositol-requiring enzyme 1-α (IRE1-α), spliced X-box binding protein 1 (XBP-1 s), protein kinase R-like ER kinase (PERK), C/EBP homologous protein (CHOP), Beclin-1, P62 and Microtubule-associated protein 1 light chain 3 alpha (LC3ßII). The evaluation was conducted using western blotting and quantitative real-time PCR techniques. RESULTS: The results obtained indicate that the treatment with CPUK02 reduced the expression of UPR markers, including GRP78 and IRE1-α at protein levels and XBP-1 s, PERK, and CHOP at mRNA levels in both HCT116 and SW480 cell lines. Furthermore, CPUK02 also influenced autophagy by decreasing Beclin-1 and increasing P62 and LC3ßII at mRNA levels in both HCT116 and SW480 treated cells. CONCLUSIONS: The study findings suggest CPUK02 may exert its cytotoxic effects by inhibiting UPR and autophagy flux in colorectal cancer cells.

Transcriptomics analysis of LINC02202/XBP1 axis in melanoma: Implications for drug targeting and PD-1 monoclonal antibody efficacy.

Malignant melanoma (MM) is a highly aggressive and deadly form of skin cancer, primarily caused by recurrence and metastasis. Therefore, it is crucial to investigate the regulatory mechanisms underlying melanoma recurrence and metastasis. Our study has identified a potential targeted regulatory relationship between LINC02202, miR-526b-3p and XBP1 in malignant melanoma. Through the regulation of the miR-526b-3p/XBP1 signalling pathway, LINC02202 may play a role in tumour progression and immune infiltration and inhibiting the expression of LINC02202 can increase the efficacy of immunotherapy for melanoma. Our findings shed light on the impact of LINC02202/XBP1 on the phenotype and function of malignant melanoma cells. Furthermore, this study provides a theoretical foundation for the development of novel immunotherapy strategies for malignant melanoma.

Inhibition of keloid fibroblast proliferation by artesunate is mediated by targeting the IRE1α/XBP1 signaling pathway and decreasing TGF-ß1.

BACKGROUND: Keloid is a benign hyperplastic dermatosis with high recurrence rate and complex pathogenesis. There is no universally effective treatment yet. New therapies and elucidation of pathogenesis are urgently required. AIMS: To explore the function of IRE1α/XBP1 in keloid fibroblasts and to investigate the potential mechanism of artesunate in inhibiting keloid hyperplasia. METHODS: Human keloid fibroblasts (KFs) were cultured, and the expressions of XBP1 and TGF-ß1 were detected by immunohistochemistry. The expression of IRE1 was interfered with through cell transfection and the effects of IRE1 interference on cell proliferation and the cell cycle were assessed using MTS, colony formation assays, and flow cytometry. Detection of the expressions of XBP1 and TGF-ß1 by qRT-PCR and Western blot. Then artesunate was applied to a subset of the cells, and its effects on cell viability and the expression of related proteins using the same methods. RESULTS: The IRE1α/XBP1 pathway was activated in KFs. Knocking out the gene IRE1α can inhibit the expression of TGF-ß1, in addition, the cell viability and cell cycle progression of KFs were also significantly affected. After artesunate treatment, there was a remarkable reduction in cell proliferation. Meanwhile, the cell cycle of KFs treated with artesunate was blocked in G1 phase.After upregulating the expression of IRE1α and treating KFs with artesunate, both cell cycle and proliferation showed inhibitory effects, and related proteins also exhibited suppressed expression. CONCLUSIONS: The IRE1α/XBP1 pathway is activated in keloid, and inhibiting the expression of this pathway can affect the cell proliferation activity. In addition, artesunate also has a significant effect on fibroblast proliferation, and the IRE1α/XBP1 pathway may participate in this process. These findings suggest that IRE1α/XBP1 signal pathway may be a potential target for scar treatment, and artesunate could also be a powerful candidate for keloid treatment.

Mechanism of Qili Qiangxin Capsule for Heart Failure Based on miR133a-Endoplasmic Reticulum Stress.

OBJECTIVE: To investigate the pharmacological mechanism of Qili Qiangxin Capsule (QLQX) improvement of heart failure (HF) based on miR133a-endoplasmic reticulum stress (ERS) pathway. METHODS: A left coronary artery ligation-induced HF after myocardial infarction model was used in this study. Rats were randomly assigned to the sham group, the model group, the QLQX group [0.32 g/(kg·d)], and the captopril group [2.25 mg/(kg·d)], 15 rats per group, followed by 4 weeks of medication. Cardiac function such as left ventricular ejection fraction (EF), fractional shortening (FS), left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), the maximal rate of increase of left ventricular pressure (+dp/dt max), and the maximal rate of decrease of left ventricular pressure (-dp/dt max) were monitored by echocardiography and hemodynamics. Hematoxylin and eosin (HE) and Masson stainings were used to visualize pathological changes in myocardial tissue. The mRNA expression of miR133a, glucose-regulated protein78 (GRP78), inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6), X-box binding protein1 (XBP1), C/EBP homologous protein (CHOP) and Caspase 12 were detected by RT-PCR. The protein expression of GRP78, p-IRE1/IRE1 ratio, cleaved-ATF6, XBP1-s (the spliced form of XBP1), CHOP and Caspase 12 were detected by Western blot. TdT-mediated dUTP nick-end labeling (TUNEL) staining was used to detect the rate of apoptosis. RESULTS: QLQX significantly improved cardiac function as evidenced by increased EF, FS, LVSP, +dp/dt max, -dp/dt max, and decreased LVEDP (P<0.05, P<0.01). HE staining showed that QLQX ameliorated cardiac pathologic damage to some extent. Masson staining indicated that QLQX significantly reduced collagen volume fraction in myocardial tissue (P<0.01). Results from RT-PCR and Western blot showed that QLQX significantly increased the expression of miR133a and inhibited the mRNA expressions of GRP78, IRE1, ATF6 and XBP1, as well as decreased the protein expressions of GRP78, cleaved-ATF6 and XBP1-s and decreased p-IRE1/IRE1 ratio (P<0.05, P<0.01). Further studies showed that QLQX significantly reduced the expression of CHOP and Caspase12, resulting in a significant reduction in apoptosis rate (P<0.05, P<0.01). CONCLUSION: The pharmacological mechanism of QLQX in improving HF is partly attributed to its regulatory effect on the miR133a-IRE1/XBP1 pathway.

Hypoxia-activated XBP1s recruits HDAC2-EZH2 to engage epigenetic suppression of ΔNp63α expression and promote breast cancer metastasis independent of HIF1α.

Hypoxia is a hallmark of cancer development. However, the molecular mechanisms by which hypoxia promotes tumor metastasis are not fully understood. In this study, we demonstrate that hypoxia promotes breast cancer metastasis through suppression of ΔNp63α in a HIF1α-independent manner. We show that hypoxia-activated XBP1s forms a stable repressor protein complex with HDAC2 and EZH2 to suppress ΔNp63α transcription. Notably, H3K27ac is predominantly occupied on the ΔNp63 promoter under normoxia, while H3K27me3 on the promoter under hypoxia. We show that XBP1s binds to the ΔNp63 promoter to recruit HDAC2 and EZH2 in facilitating the switch of H3K27ac to H3K27me3. Pharmacological inhibition or the knockdown of either HDAC2 or EZH2 leads to increased H3K27ac, accompanied by the reduced H3K27me3 and restoration of ΔNp63α expression suppressed by hypoxia, resulting in inhibition of cell migration. Furthermore, the pharmacological inhibition of IRE1α, but not HIF1α, upregulates ΔNp63α expression in vitro and inhibits tumor metastasis in vivo. Clinical analyses reveal that reduced p63 expression is correlated with the elevated expression of XBP1, HDAC2, or EZH2, and is associated with poor overall survival in human breast cancer patients. Together, these results indicate that hypoxia-activated XBP1s modulates the epigenetic program in suppression of ΔNp63α to promote breast cancer metastasis independent of HIF1α and provides a molecular basis for targeting the XBP1s/HDAC2/EZH2-ΔNp63α axis as a putative strategy in the treatment of breast cancer metastasis.

Expression and Clinical Significance of IRE1-XBP1s, p62, and Caspase-3 in Colorectal Cancer Patients.

Background: Three main cell signaling pathways including the endoplasmic reticulum stress (ERS) response, autophagy, and apoptosis play critical roles in both cell survival and death. They were found to crosstalk with one another during tumorigenesis and cancer progression. This study aimed to investigate the expression of the spliced form of X-box binding protein 1 (XBP1s), p62, and caspase-3, as the essential biomarkers of ERS, autophagy, and apoptosis in patients with colorectal cancer (CRC), as well as the correlation between their expression and clinicopathological data. Methods: This retrospective study was conducted on formalin-fixed paraffin-embedded (FFPE) blocks, which were collected from patients and their tumor margins, from the tumor bank of Imam Khomeini Hospital (Tehran, Iran) from 2017 to 2019. Tissue microarray (TMA) was used to measure the XBP1s, p62, and caspase-3 biomarkers. Data were analyzed using SPSS software version 20, and P≤0.05 was considered statistically significant. Results: Evaluating the total of 91 patients, a significant relationship was found between XBP1s expression and TNM stage (P=0.003), primary tumor (pT) (P=0.054), and the degree of differentiation (P=0.006); and between caspase-3 with pT (P=0.004), and lymphovascular invasion (P=0.02). However, no significant correlation was found between p62 and clinicopathological data. Furthermore, a positive relationship between XBP1s and p62 was confirmed (correlation coefficient: 22.2% and P=0.05). Conclusion: Our findings indicated that XBP1s could be considered as a target for therapy in personalized medicine.

Psychological stress to ovalbumin peptide-specific T-cell receptor transgenic mice impairs the suppressive ability of type 1 regulatory T cell.

Numerous diseases of the immune system can be traced back to the malfunctioning of the regulatory T cells. The aetiology is unclear. Psychological stress can cause disruption to the immune regulation. The synergistic effects of psychological stress and immune response on immune regulation have yet to be fully understood. The intention of this study is to analyse the interaction between psychological stress and immune responses and how it affects the functional status of type 1 regulatory T (Tr1) cells. In this study, ovalbumin peptide T-cell receptor transgenic mice were utilised. Mice were subjected to restraint stress to induce psychological stress. An airway allergy murine model was established, in which a mouse strain with RING finger protein 20 (Rnf20)-deficient CD4+ T cells were used. The results showed that concomitant exposure to restraint stress and immune response could exacerbate endoplasmic reticulum stress in Tr1 cells. Corticosterone was responsible for the elevated expression of X-box protein-1 (XBP1) in mouse Tr1 cells after exposure to both restraint stress and immune response. XBP1 mediated the effects of corticosterone on inducing Rnf20 in Tr1 cells. The reduction of the interleukin-10 expression in Tr1 cells was facilitated by Rnf20. Inhibition of Rnf20 alleviated experimental airway allergy by restoring the immune regulatory ability of Tr1 cells. In conclusion, the functions of Tr1 cells are negatively impacted by simultaneous exposure to psychological stress and immune response. Tr1 cells' immune suppressive functions can be restored by inhibiting Rnf20, which has the translational potential for the treatment of diseases of the immune system.

Platelets induce endoplasmic reticulum stress in macrophages in vitro.

BACKGROUND: Endoplasmic reticulum (ER) stress is a key feature of lipid-laden macrophages and contributes to the development of atherosclerotic plaques. Blood platelets are known to interact with macrophages and fine-tune effector functions such as inflammasome activation and phagocytosis. However, the effect of platelets on ER stress induction is unknown. OBJECTIVES: The objective of this study is to elucidate the potential of platelets in regulating ER stress in macrophages in vitro. METHODS: Bone marrow-derived macrophages and RAW 264.7 cells were incubated with isolated murine platelets, and ER stress and inflammation markers were determined by reverse transcription-quantitative polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay. ER morphology was investigated by electron microscopy. Cell viability, lipid accumulation, and activation were measured by flow cytometry. To gain mechanistic insights, coincubation experiments were performed with platelet decoys/releasates as well as lipopolysaccharide, blocking antibodies, and TLR4 inhibitors. RESULTS: Coincubation of platelets and macrophages led to elevated levels of ER stress markers (BIP, IRE1α, CHOP, and XBP1 splicing) in murine and human macrophages, which led to a pronounced enlargement of the ER. Macrophage ER stress was accompanied by increased release of proinflammatory cytokines and intracellular lipid accumulation, but not cell death. Platelet decoys, but not platelet releasates or lysate from other cells, phenocopied the effect of platelets. Blocking TLR4 inhibited inflammatory activation of macrophages but did not affect ER stress induction by platelet coincubation. CONCLUSION: To our knowledge, this study is the first to demonstrate that platelets induce ER stress and unfolded protein response in macrophages by heat-sensitive membrane proteins, independent of inflammatory activation of macrophages.

Methylparaben induces hepatic glycolipid metabolism disorder by activating the IRE1α-XBP1 signaling pathway in male mice.

Methylparaben (MP), a preservative widely used in daily supplies, exists in both the environment and the human body. However, the potential health risks posed by MP remain unclear. This study aimed to unravel the mechanisms by which MP disrupts glucose and lipid homeostasis. For this, we administered MP to mice and observed changes in glucose and lipid metabolism. MP exposure led to hyperglycemia, hyperlipidemia, visceral organ injury, and hepatic lipid accumulation. RNA sequencing results from mice livers indicated a close association between MP exposure and endoplasmic reticulum (ER) stress, inflammatory response, and glucose and lipid homeostasis. Western blotting and quantitative reverse transcription-polymerase chain reaction revealed that MP activated ER stress, particularly the inositol-requiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) pathway, which further promoted the activation of the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. The activation of these pathways phosphorylated insulin receptor substrate-1 (IRS1) (ser 307), resulting in decreased phosphorylation of protein kinase B (Akt) (ser 473), leading to insulin resistance. Additionally, MP exposure promoted lipogenesis through ER stress. To explore potential remedies, we administered the ER stress inhibitor 4-phenylbutyric acid (4-PBA) and the IRE1α-XBP1 pathway inhibitor toyocamycin to mice, both of which protected against metabolic disorders and organ injury caused by MP. These findings suggest that MP induces disruptions in glucose and lipid metabolism through ER stress, primarily through the IRE1α-XBP1 pathway.

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.

Hepatocellular carcinoma cell-derived exosomal miR-21-5p promotes the polarization of tumor-related macrophages (TAMs) through SP1/XBP1 and affects the progression of hepatocellular carcinoma.

BACKGROUND: Tumor-associated macrophages (TAMs) have unique functions in the development of hepatocellular carcinoma (HCC). The tumor microenvironment is in a complex state in chronic disease. As a major participant in tumor-associated inflammation, TAMs have a unique effect on promoting tumor cell proliferation, angiogenesis and immunosuppression. The in-depth study of TAMs has important scientific and clinical value and provides new ideas for the treatment of cancer. METHODS: Bioinformatics analysis, dual-luciferase reporter assays, RT-qPCR and clinical samples were used to analyze the potential mechanism of the miR-21-5p/SP1/XBP1 molecular axis in HCC. In this study, miR-21-5p was highly expressed in HCC exosomes compared with normal hepatocyte exosomes, and HCC exosomes containing miR-21-5p promoted the proliferation and migration of HCC cells and inhibited cell apoptosis. In addition, this treatment promoted the M2 polarization of macrophages, induced the expression of transcription factor-specific protein 1 (SP1), and inhibited the expression of X-box binding protein 1 (XBP1). However, these expression trends were reversed after inhibition of miR-21-5p expression in exosomes of hepatoma cells, and the effects of exosomal miR-21-5p were partially restored after overexpression of SP1. Animal experiments also verified that exosomal miR-21-5p in HCC cells affected the expression level of the SP1/XBP1 protein and promoted M2 polarization of TAMs. CONCLUSION: Exosomal miR-21-5p in HCC cells can affect the development of HCC cells by regulating SP1/XBP1 and promoting the M2 polarization of TAMs, thereby affecting the adverse prognostic response of HCC patients.

Innate IRE1α-XBP1 activation by viral single-stranded RNA and its influence on lung cytokine production during SARS-CoV-2 pneumonia.

The utilization of host-cell machinery during SARS-CoV-2 infection can overwhelm the protein-folding capacity of the endoplasmic reticulum and activate the unfolded protein response (UPR). The IRE1α-XBP1 arm of the UPR could also be activated by viral RNA via Toll-like receptors. Based on these premises, a study to gain insight into the pathogenesis of COVID-19 disease was conducted using nasopharyngeal exudates and bronchioloalveolar aspirates. The presence of the mRNA of spliced XBP1 and a high expression of cytokine mRNAs were observed during active infection. TLR8 mRNA showed an overwhelming expression in comparison with TLR7 mRNA in bronchioloalveolar aspirates of COVID-19 patients, thus suggesting the presence of monocytes and monocyte-derived dendritic cells (MDDCs). In vitro experiments in MDDCs activated with ssRNA40, a synthetic mimic of SARS-CoV-2 RNA, showed induction of XBP1 splicing and the expression of proinflammatory cytokines. These responses were blunted by the IRE1α inhibitor MKC8866, the TLR8 antagonist CU-CPT9a, and knockdown of TLR8 receptor. In contrast, the IRE1α-XBP1 activator IXA4 enhanced these responses. Based on these findings, the TLR8/IRE1α system seems to play a significant role in the induction of the proinflammatory cytokines associated with severe COVID-19 disease and might be a druggable target to control cytokine storm.

Angiotensin II type-2 receptor attenuates liver fibrosis progression by suppressing IRE1α-XBP1 pathway.

The renin-angiotensin system (RAS) has been recognized as a crucial contributor to the development of liver fibrosis, and AT2R, an essential component of RAS, is involved in the progression of liver fibrosis. However, the underlying mechanisms by which AT2R modulates liver fibrosis remain elusive. Here, we report that AT2R was induced to be highly expressed during the progression of liver fibrosis, and the elevated AT2R attenuates liver fibrosis by suppressing IRE1α-XBP1 pathway. In this study, we found that AT2R is not expressed in the no cirrhotic adult liver, but is induced expression during liver fibrosis in both cirrhotic patients and fibrotic mice models. Upregulated AT2R inhibits the activation and proliferation of hepatic stellate cells (HSCs). In addition, our study showed that during liver fibrosis, AT2R deletion increased the dimerization activation of IRE1α and promoted XBP1 splicing, and the spliced XBP1s could promote their transcription by binding to the AT2R promoter and repress the IRE1α-XBP1 axis, forming an AT2R-IRE1α-XBP1 negative feedback loop. Importantly, the combination treatment of an AT2R agonist and an endoplasmic reticulum stress (ER stress) alleviator significantly attenuated liver fibrosis in a mouse model of liver fibrosis. Therefore, we conclude that the AT2R-IRE1α signaling pathway can regulate the progression of liver fibrosis, and AT2R is a new potential therapeutic target for treating liver fibrosis.

Identification and functional coordination analysis of gene co-expression networks in different tissues of XBP1 cartilage-specific deficient mice.

Abnormal differentiation and proliferation of chondrocytes leads to various diseases related to growth and development. The process of chondrocyte differentiation involves a series of complex cellular and molecular interactions. X-box binding protein 1 (XBP1), an essential molecule of the unfolded protein response (UPR) in Endoplasmic Reticulum (ER) stress, participated in cartilage development and causes other related diseases. We previously reported that XBP1 deficiency in cartilage impacts the function and associated diseases of many different tissues including cartilage. However, how differential expression of genes modulates the roles of cartilage and other tissues when XBP1 is lack of in chondrocytes remains unclear. We aimed to screen for differentially expressed (DE) genes in cartilage, brain, heart, and muscle by high-throughput sequencing in XBP1 cartilage-specific knockout (CKO) mice. Further, gene co-expression networks were constructed by weighted gene co-expression network analysis (WGCNA) algorithm and pivot genes were identified in the above four tissues. Protein detection, Hematoxylin-eosin (HE) staining and immunohistochemistry (IHC) experiments have proved that these differentially co-expressed genes participate in the downstream regulatory pathway of different tissues and affect tissue function.Significantly differentially expressed mRNAs [differentially expressed genes (DEGs)] were identified between XBP1 CKO mice and controls in cartilage, brain, heart, and muscle tissues, including 610, 126, 199 and 219 DEGs, respectively. 39 differentially co-expressed genes were identified in the above four tissues, and they were important pivot genes. Comprehensive analysis discovered that XBP1 deficiency in cartilage influences the difference of co-expressed genes between cartilage and other different tissues. These differentially co-expressed genes participate in downstream regulatory pathways of different tissues and affect tissue functions. Collectively, our conclusions may contribute potential biomarkers and molecular mechanisms for the mutual modulation between cartilage and different tissues and the diagnosis and treatment of diseases caused by abnormalities in different tissues. The analysis also provides meaningful insights for future genetic discoveries.

XBP1 as a novel molecular target to attenuate drug resistance in hepatocellular carcinoma.

INTRODUCTION: Despite improvements in clinical management of hepatocellular carcinoma (HCC), prognosis remains poor with a 5-year survival rate less than 40%. Drug resistance in HCC makes it challenging to treat; therefore, it is imperative to develop new therapeutic strategies. Higher expression of X-box binding protein 1 (XBP1) in tumor cells is highly correlated with poor prognosis. In tumor cells, XBP1 modulates the unfolded protein response (UPR) to restore homeostasis in endoplasmic reticulum. Targeting XBP1 could be a promising therapeutic strategy to overcome HCC resistance and improve the survival rate of patients. AREAS COVERED: This review provides the recent evidence that indicates XBP1 is involved in HCC drug resistance via DNA damage response, drug inactivation, and inhibition of apoptosis. In addition, the potential roles of XBP1 in inducing resistance in HCC cells were highlighted, and we showed how its inhibition could sensitize tumor cells to controlled cell death. EXPERT OPINION: Due to the diversity in molecular mechanism of multidrug-resistance, targeting one specific pathway is inadequate. XBP1 inhibition could be a potential therapeutic target to overcome verity of resistance mechanisms. The main function of this transcription factor in HCC treatment response is an attractive area for further studies and should be discussed more.