Inhibition of IRE1 RNase activity modulates the tumor cell secretome and enhances response to chemotherapy

G protein-coupled estrogen receptor reduces the breast cancer cell survival by regulating the IRE1α/miR-17-5p/TXNIP pathway

This study aimed to explore whether GPER can induce the UPR response in the SKBR3 cell line through ER and IREα activation, and to assess whether this response leads to cell survival or cell death. Additionally, the study sought to evaluate the impact of this response on cell behaviors such as apoptosis, migration, and drug resistance. To activate the UPR and induce ER stress, we treated the MCF10A cell line with 0.5 µg/ml TUN for 24 and 48 h. The expression levels of XBP-1 and C/EBP homology protein (CHOP) genes (ER stress markers) were measured using the qRT-PCR technique. The MCF10A + TUN cell line was used as a positive control. To determine the optimal doses of G1 and tamoxifen (TAM), we evaluated GPER expression using qRT-PCR analysis. Cells were then treated with various doses of G1 (1000 nM), G15 (1000 nM), and TAM (2000 nM), both individually and in combination (G1 + G15, TAM + G15, G1 + TAM), for 24 and 48 h. We measured the expression of GPER, IRE1α, MiR-17-5p, TXNIP, ABCB1, and ABCC1 genes. Apoptosis was assessed via flow cytometry, and cell migration was examined using the wound-healing assay. Our results demonstrated that GPER activation by G1 and TAM significantly increased IRE1α expression in SKBR3 cells. This activation, through its RIDD activity, cleaved miR-17-5p and initiated the UPR death response. The upregulation of the TXNIP gene expression enhanced apoptosis and chemotherapy sensitivity while decreasing cell migration. Interestingly, these effects were notably reversed by G15 treatment. In summary, the GPER/IRE1α/miR-17-5p/TXNIP axis plays a key role in the UPR pro-death response, promoting programmed cell death, reducing migration, and decreasing drug resistance in SKBR3 cells.

XBP1: A key regulator in breast cancer development and treatment

X-box binding protein 1 (XBP1), as a transcription factor, plays pivotal role in unfolded protein response (UPR), which is activated in response to endoplasmic reticulum (ER) stress to restore ER homeostasis. IRE1α/XBP1 pathway is a key component of UPR, and the expression levels of XBP1 can dictate the fate of cells under ER stress, either promoting survival or driving apoptosis. High expression of XBP1 in breast tumors is closely associated with poor prognosis. The paper elucidates the biological functions of XBP1 and its involvement in UPR, while also surveying the latest research on how XBP1 influences immunity, metabolism, apoptosis, angiogenesis, and the invasive and migratory behaviors of breast cancer cells. Moreover, it contemplates the potential of XBP1 as a therapeutic target for breast cancer treatment.

The Role of ER Stress and the Unfolded Protein Response in Cancer

Dysregulation of protein synthesis, folding, and secretion leads to endoplasmic reticulum (ER) stress, triggering the unfolded protein response (UPR). While the UPR is essential for cell survival under stress, its chronic activation in cancer cells supports tumorigenesis, metastasis, and chemoresistance by enabling cellular adaptation to hypoxia, nutrient deprivation, and oxidative stress. This review provides a comprehensive overview of the roles of key UPR mediators - binding immunoglobulin protein (BiP), protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6) - in cancer progression and therapy resistance. Furthermore, it discusses strategies to target UPR pathways, including small molecule inhibitors, gene therapies, natural compounds, and combination therapies, while it evaluates their preclinical and clinical relevance. Finally, it explores how modulating UPR signaling can overcome therapeutic resistance, improve immunotherapy outcomes, and reshape the tumor microenvironment. This review emphasizes the promise of UPR-targeted approaches in enhancing the efficacy of current cancer treatments and achieving better patient outcomes.

Unraveling UPR-mediated intercellular crosstalk: Implications for immunotherapy resistance mechanisms

Endoplasmic reticulum (ER) is the critical organelle that regulates essential cellular processes, including protein synthesis, folding, and post-translational modification, as well as lipid metabolism and calcium homeostasis. Disruption in ER homeostasis leads to a condition known as ER stress, characterized by the accumulation of misfolded or unfolded proteins. This triggers the unfolded protein response (UPR), an adaptive pathway mediated by three ER-resident sensors: inositol-requiring enzyme 1α (IRE1α), protein kinase R-like ER kinase (PERK), and activating transcription factor 6 (ATF6). Increasing evidence highlights sustained UPR activation in malignant and immune cells within the tumor microenvironment (TME), which promotes tumor progression and metastasis while simultaneously impairing antitumor immunity. This review explores how UPR-driven intercellular signaling influences immunotherapy resistance, focusing on the alterations occurring in tumor cells as well as in the surrounding immune environment. By providing insights into these mechanisms, we aim to highlight the therapeutic potential of targeting the UPR pathways in modulating cancer immunity.

Elucidating the interaction between MTDH, an oncoprotein with UPR signalling molecule IRE1α under cellular stress

IRE1α (inositol-requiring enzyme type 1) is one of the primary sensor arms of UPR signalling pathway with special ability to detect unfolded/misfolded proteins in the ER lumen. It is a bifunctional protein with kinase and endoribonuclease activity, playing a crucial role in managing ER stress. The C-terminal domain of IRE1α, facing towards the cytosol, acts as a scaffold for various effector proteins to regulate IRE1α activity. Our previous mass spectroscopic studies has revealed Metadherin (MTDH) as one of the binding partner of IRE1α. MTDH is an oncoprotein implicated in cancer metastasis and survival, affecting various cell signalling pathways to drive cancer progression. The presence of this protein in the immune complex in our IRE1α driven immunoprecipitation experiments of stressed cells was significant as the UPR is believed to facilitate cell apoptosis during prolonged stress, which is compromised in cancerous cells to allow metastasis. This prompted us to study and explore the interaction between the two proteins IRE1α and MTDH, a positive interaction pointing to a cross talk between the homeostatic and metastatic signalling pathways. Various experiments, including co-immunoprecipitation, Yeast-two Hybrid assay, and bioinformatics analyses established a positive interaction between IRE1α and MTDH supporting the argument that these proteins interact and might influence IRE1α's role in cellular stress response.

Mapping Dynamic Protein Clustering with AIEgen-Active Chemigenetic Probe

Protein clustering/disassembling is a fundamental process in biomolecular condensates, playing a crucial role in cell fate decision and cellular homeostasis. However, the inherent features of protein clustering, especially for its reversible behavior and subtle microenvironment variation, present significant hurdles in probe chemistry for tracking protein clustering dynamics. Herein, we report a bilateral-tailored chemigenetic probe, in which an "amphiphilic" aggregate-induced emission luminogen (AIEgen) QMSO3Cl is covalently conjugated to a protein tag that is genetically fused to protein-of-interest (POI). Prior to target POI, the "amphiphilic" AIE-active QMSO3Cl achieves a completely dark state in both aqueous biological environment and lipophilic organelles, thereby ensuring an ultra-low intrinsic background interference. Upon reaching POI, the combination of synthetic molecule and genetically encoded protein allows for protein clustering-dependent ultra-sensitive response, with a substantial lighting-up fluorescence (67.5-fold) as protein transitions from disassembling to clustering state. Such ultra-high signal-to-noise ratio enables to monitor the dynamic and fate of inositol requiring enzyme 1 (IRE1) clustering/disassembling under both acute and chronic endoplasmic reticulum (ER) stress in living cells. For the first time, we have demonstrated the use of chemigenetic probe to reveal therapy-induced ER stress and screen drugs in a three-dimensional scenario: microviscosity change, clustering dynamic, and cluster morphology. This chemigenetic probe design strategy would greatly facilitate the advancement of mapping protein dynamics in cell homeostasis and medicine research.

A nonenzymatic dependency on inositol-requiring enzyme 1 controls cancer cell cycle progression and tumor growth

Endoplasmic-reticulum resident inositol-requiring enzyme 1α (IRE1) supports protein homeostasis via its cytoplasmic kinase-RNase module. Known cancer dependency on IRE1 entails its enzymatic activation of the transcription factor XBP1s and of regulated RNA decay. We discovered surprisingly that some cancer cell lines require IRE1 but not its enzymatic activity. IRE1 knockdown but not enzymatic IRE1 inhibition or XBP1 disruption attenuated cell cycle progression and tumor growth. IRE1 silencing led to activation of TP53 and CDKN1A/p21 in conjunction with increased DNA damage and chromosome instability, while decreasing heterochromatin as well as DNA and histone H3K9me3 methylation. Immunoelectron microscopy detected some endogenous IRE1 protein at the nuclear envelope. Thus, cancer cells co-opt IRE1 either enzymatically or nonenzymatically, which has significant implications for IRE1's biological role and therapeutic targeting.

Structure-guided design of a truncated heterobivalent chemical probe degrader of IRE1α

IRE1α is an ER protein involved in the unfolded protein response (UPR) and dysregulation of the ER stress pathway has been implicated in several diseases. Inhibitors of the cytoplasmic endonuclease or kinase domains of the enzyme have limited utility and targeted degradation would address additional scaffolding functions of the protein. Here, we describe the design and development of IRE1α proteolysis targeting chimeras (PROTACs) based on a lysine-reactive salicylaldehyde RNase inhibitor, and present the structure-activity relationships (SARs) that delivered the first highly selective degraders of a native ER-membrane associated protein. Medicinal chemistry optimization exploited ternary complex computational modelling to inform design, HiBiT-SpyTag IRE1α degradation and NanoBRET cereblon occupancy cell-based assays to generate SARs, and mass spectrometry-based proteomics to assess broad selectivity in an unbiased manner. Merging IRE1α and CRBN ligand chemotypes provided the truncated chimera CPD-2828 with physicochemical properties more akin to an oral molecular glue degrader than a traditional PROTAC.

Identification of hub genes for the diagnosis and prognosis in triple negative breast cancer using transcriptome and differential methylation integration analysis

Introduction: Triple-negative breast cancer (TNBC) is characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression. It is highly invasive and aggressive, making it the subtype of breast cancer with the poorest prognosis. Currently, systemic chemotherapy is the primary treatment option, but targeted therapies remain unavailable. Therefore, there is an urgent need to identify novel biomarkers for the early diagnosis and treatment of TNBC. Methods: We conducted an integrated analysis of transcriptome and methylation data to identify methylation-regulated differentially expressed genes (MDEGs). Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and protein-protein interaction (PPI) network analysis were performed on MDEGs to investigate the impact of hub genes on the diagnosis and prognosis of TNBC. Subsequently, the expression levels and DNA methylation patterns of key genes were validated in the TNBC cell line MDA-MB-231 and the normal breast epithelial cell line MCF-10A using reverse transcription quantitative PCR (RT-qPCR) and quantitative methylation-specific PCR (qMSP). Results: A total of 98 upregulated and 87 downregulated genes were identified through transcriptomic profiling integration analysis. By incorporating methylation data, we further identified 22 genes with high expression of hypomethylation (hypo-MDEGs) and 32 genes with low expression of hypermethylation (hyper-MDEGs). The hypo-MDEGs were primarily involved in nuclear division, organelle fission, spindle formation, chromosome and kinetochore development, and protein binding. KEGG pathway analysis revealed that these genes were enriched in progesterone-mediated oocyte maturation, cell cycle regulation, and oocyte meiosis. Hyper-MDEGs were associated with cell proliferation, hormone response, pain, extracellular matrix composition, and binding to sulfur compounds, heparin, and glycosaminoglycans. PPI network analysis identified seven hub genes-EXO1, KIF11, FOXM1, CENPF, CCNB1, PLK1, and KIF23-which were all significantly overexpressed in TNBC tissues and positively correlated with each other (p < 0.05). Receiver operating characteristic curve analysis showed that the area under the curve (AUC) for all seven genes exceeded 0.9 (p < 0.05), suggesting strong diagnostic potential. Kaplan-Meier survival analysis indicated that KIF11, CCNB1, and PLK1 were associated with a higher hazard ratio (HR > 1, p < 0.05) in TNBC. In vitro validation experiments demonstrated that, compared to MCF-10A cells, MDA-MB-231 cells exhibited higher mRNA expression levels of KIF11, CCNB1, and PLK1, while their DNA methylation levels were lower. Conclusions: This study identified seven hypo-MDEGs, including EXO1, KIF11, FOXM1, CENPF, CCNB1, PLK1, and KIF23, which are involved in the regulation of the cell cycle and mitotic processes and have significant potential as diagnostic biomarkers for TNBC. Notably, elevated expression of KIF11, CCNB1, and PLK1 is associated with poor prognosis in patients with TNBC. These findings contribute to an improved understanding of the epigenetic molecular mechanisms underlying TNBC progression and highlight novel biomarkers that may enhance the accuracy of TNBC diagnosis and provide potential targets for therapeutic intervention.

IRE1 is a promising therapeutic target in pancreatic cancer

[Figure: see text].

NRF-mediated autophagy and UPR: Exploring new avenues to overcome cancer chemo-resistance

The development of chemo-resistance remains a significant hurdle in effective cancer therapy. NRF1 and NRF2, key regulators of redox homeostasis, play crucial roles in the cellular response to oxidative stress, with implications for both tumor growth and resistance to chemotherapy. This study delves into the dualistic role of NRF2, exploring its protective functions in normal cells and its paradoxical support of tumor survival and drug resistance in cancerous cells. We investigate the interplay between the PERK/NRF signaling pathway, ER stress, autophagy, and the unfolded protein response, offering a mechanistic perspective on how these processes contribute to chemoresistance. Our findings suggest that targeting NRF signaling pathways may offer new avenues for overcoming resistance to chemotherapeutic agents, highlighting the importance of a nuanced approach to redox regulation in cancer treatment. This research provides a molecular basis for the development of NRF-targeted therapies, potentially enhancing the efficacy of existing cancer treatments and offering hope for more effective management of resistant tumors.

A review on endoplasmic reticulum-dependent anti-breast cancer activity of herbal drugs: possible challenges and opportunities

Breast cancer (BC) is a major cause of cancer-related mortality across the globe and is especially highly prevalent in females. Based on the poor outcomes and several limitations of present management approaches in BC, there is an urgent need to focus and explore an alternate target and possible drug candidates against the target in the management of BC. The accumulation of misfolded proteins and subsequent activation of unfolded protein response (UPR) alters the homeostasis of endoplasmic reticulum (ER) lumen that ultimately causes oxidative stress in ER. The UPR activates stress-detecting proteins such as IRE1α, PERK, and ATF6, these proteins sometimes may lead to the activation of pro-apoptotic signaling pathways in cancerous cells. The ER stress-dependent antitumor activity could be achieved either through suppressing the adaptive UPR to make cells susceptible to ER stress or by causing chronic ER stress that may lead to triggering of pro-apoptotic signaling pathways. Several herbal drugs trigger ER-dependent apoptosis in BC cells. Therefore, this review discussed the role of fifty-two herbal drugs and their active constituents, focusing on disrupting the balance of the ER within cancer cells. Further, several challenges and opportunities have also been discussed in ER-dependent management in BC.Breast cancer (BC) is a major cause of cancer-related mortality across the globe and is especially highly prevalent in females. Based on the poor outcomes and several limitations of present management approaches in BC, there is an urgent need to focus and explore an alternate target and possible drug candidates against the target in the management of BC. The accumulation of misfolded proteins and subsequent activation of unfolded protein response (UPR) alters the homeostasis of endoplasmic reticulum (ER) lumen that ultimately causes oxidative stress in ER. The UPR activates stress-detecting proteins such as IRE1α, PERK, and ATF6, these proteins sometimes may lead to the activation of pro-apoptotic signaling pathways in cancerous cells. The ER stress-dependent antitumor activity could be achieved either through suppressing the adaptive UPR to make cells susceptible to ER stress or by causing chronic ER stress that may lead to triggering of pro-apoptotic signaling pathways. Several herbal drugs trigger ER-dependent apoptosis in BC cells. Therefore, this review discussed the role of fifty-two herbal drugs and their active constituents, focusing on disrupting the balance of the ER within cancer cells. Further, several challenges and opportunities have also been discussed in ER-dependent management in BC.

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.

The impact of ERN1 endoribonuclease activity inhibition on TOB1, HBEGF, and TWIST1 genes expression in U87MG glioblastoma cells

Objective. It is known that inhibition of the endoplasmic reticulum transmembrane signaling protein (ERN1) suppresses the glioblastoma cells proliferation. The present study aims to investigate the impact of inhibition of ERN1 endoribonuclease and protein kinase activities on the TOB1, HBEGF, and TWIST1 gene expression in U87MG glioblastoma cells with an intent to reveal the role of ERN1 signaling in the regulation of expression of these genes. Methods. The U87MG glioblastoma cells with inhibited ERN1 endoribonuclease (dnrERN1) or both enzymatic activities of ERN1 (endoribonuclease and protein kinase; dnERN1) were used. Cells transfected with empty vector served as controls. Wild-type glioblastoma cells were used for mRNA silencing. The expression level of the TOB1, HBEGF, and TWIST1 genes and microRNA were studied by quantitative RT-PCR. Results. We found that inhibition of ERN1 endoribonuclease activity led to a strong down-regulation of HBEGF gene expression in glioblastoma cells and did not significantly change the expression of TOB1 and TWIST1 genes. At the same time, inhibition of both enzymatic activities of ERN1 strongly increased the expression of the TOB1 gene and down-regulated HBEGF and TWIST1 genes in glioblastoma cells. The expression of TWIST1 gene increased, but HBEGF and TOB1 genes significantly decreased in cells with silencing of ERN1 mRNA by specific siRNA. At the same time, silencing of XBP1 mRNA reduced the expression of HBEGF gene only. In addition, in glioblastoma cells with ERN1 knockdown, the level of miR-96-5p was suppressed, but miR-182-5p was increased and could promote post-transcriptional expression of TWIST1, HBEGF, and TOB1 mRNAs. Conclusion. The results of the present study demonstrate that inhibition of ERN1 strongly up-regulated the expression of the anti-proliferative TWIST1 gene through protein kinase activity of ERN1 and that decreased HBEGF and TOB1 genes expression was also controlled preferentially by ERN1 protein kinase activity. These changes in the expression level of TWIST1, HBEGF, and TOB1 genes may also contribute to ERN1 knockdown-mediated suppression of glioblastoma cells proliferation.

The ERN1 signaling pathway of unfolded protein controls the expression of EDEM1 and its hypoxic regulation in glioblastoma cells

Objective. For the effective growth of malignant tumors, including glioblastoma, the necessary factors involve endoplasmic reticulum (ER) stress, hypoxia, and the availability of nutrients, particularly glucose. The ER degradation enhancing alpha-mannosidase like protein 1 (EDEM1) is involved in ER-associated degradation (ERAD) targeting misfolded glycoproteins for degradation in an N-glycan-independent manner. EDEM1 was also identified as a new modulator of insulin synthesis and secretion. The present study aims to investigate the regulation of the EDEM1 gene expression in U87MG glioblastoma cells by hypoxia and glucose or glutamine deprivations depending on the knockdown of ERN1 (endoplasmic reticulum to nucleus signaling 1) with the intent to reveal the role of ERN1 signaling in the regulation of this gene expression and function in tumorigenesis. Methods. The U87MG glioblastoma cells (transfected by an empty vector; control) and ERN1 knockdown cells with inhibited ERN1 endoribonuclease and protein kinase (dnERN1) or only ERN1 endoribonuclease (dnrERN1) were used. Hypoxia was introduced by dimethyloxalylglycine (4 h). For glucose and glutamine deprivations, the cells were exposed to DMEM medium without glucose and glutamine, respectively, for 16 h. The expression level of the EDEM1 gene was studied by quantitative RT-PCR and normalized to the ACTB mRNA. Results. It was found that inhibition of endoribonuclease and protein kinase activities of ERN1 led to down-regulation of EDEM1 gene expression in glioblastoma cells. Moreover, the expression of this gene was also decreased after silencing ERN1 in glioblastoma cells. At the same time, the expression of EDEM1 gene did not significantly change in cells with inhibited ERN1 endoribonuclease only. The expression of the EDEM1 gene was increased under hypoxia in control U87MG cells, but resistant to hypoxia in cells with ERN1 knockdown. Furthermore, the expression of this gene was up-regulated under glucose and glutamine deprivations in control glioblastoma cells. However, the ERN1 knockdown increased the sensitivity of EDEM1 gene expression to glucose and decreased to glutamine deprivations. Conclusion. The results of the present study demonstrate that inhibition of ERN1 down-regulated the expression of the EDEM1 gene through protein kinase activity of ERN1 and that the regulation of this gene expression by hypoxia and nutrient supply, especially glucose, is differently controlled by ERN1 in glioblastoma cells.

Opposing regulation of endoplasmic reticulum retention under stress by ERp44 and PDIA6

Conditions of endoplasmic reticulum (ER) stress reduce protein synthesis by provoking translation regulation, governed by the eIF2α kinase PERK. When PERK is inhibited during ER stress, retention of a selective subset of glycoproteins occurs, a phenomenon we termed selective ER retention (sERr). sERr clients are enriched with tyrosine kinase receptors (RTKs), which form large molecular weight disulfide bonded complexes in the ER. The protein disulfide isomerase ERp44 promotes sERr and increases the size of sERr complexes. Here we show that sERr is reversible upon washout. Pulse chase analyses show that upon recovery, only a small fraction of the sERr complexes disintegrates and contributes to the matured proteins, while most are newly synthesized. Sequential inductions of sERr and washouts demonstrate an accelerated recovery that is dependent on the unfolded protein response transducer IRE1. Since IRE1 regulates the expression level PDIA6, we analyzed its contribution to sERr. We found that PDIA6 and ERp44 constitutively interact by disulfides and have opposite effects on resumed recovery of trafficking following removal of sERr conditions. Deletion of ERp44 accelerates, while deletion of PDIA6 slows down recovery with a minimal effect on total protein synthesis. ERp44 is a primary interactor with sERr clients. When missing, PDIA6 partitions more into sERr complexes. Deletion of the tumor suppressor PTEN, which induces RTK signaling, promoted sERr formation kinetics, and accelerated the recovery, suggesting feedback between RTKs signaling and sERr. This study suggests that sERr, should develop physiologically or pathologically, is counteracted by adaptation responses that involve IRE1 and PDIA6.

IRE1α silences dsRNA to prevent taxane-induced pyroptosis in triple-negative breast cancer

Chemotherapy is often combined with immune checkpoint inhibitor (ICIs) to enhance immunotherapy responses. Despite the approval of chemo-immunotherapy in multiple human cancers, many immunologically cold tumors remain unresponsive. The mechanisms determining the immunogenicity of chemotherapy are elusive. Here, we identify the ER stress sensor IRE1α as a critical checkpoint that restricts the immunostimulatory effects of taxane chemotherapy and prevents the innate immune recognition of immunologically cold triple-negative breast cancer (TNBC). IRE1α RNase silences taxane-induced double-stranded RNA (dsRNA) through regulated IRE1-dependent decay (RIDD) to prevent NLRP3 inflammasome-dependent pyroptosis. Inhibition of IRE1α in Trp53-/- TNBC allows taxane to induce extensive dsRNAs that are sensed by ZBP1, which in turn activates NLRP3-GSDMD-mediated pyroptosis. Consequently, IRE1α RNase inhibitor plus taxane converts PD-L1-negative, ICI-unresponsive TNBC tumors into PD-L1high immunogenic tumors that are hyper-sensitive to ICI. We reveal IRE1α as a cancer cell defense mechanism that prevents taxane-induced danger signal accumulation and pyroptotic cell death.

The mammalian Ire1 inhibitor, 4µ8C, exhibits broad anti-Aspergillus activity in vitro and in a treatment model of fungal keratitis

Objective

The fungal unfolded protein response consists of a two-component relay in which the ER-bound sensor, IreA, splices and activates the mRNA of the transcription factor, HacA. Previously, we demonstrated that hacA is essential for Aspergillus fumigatus virulence in a murine model of fungal keratitis (FK), suggesting the pathway could serve as a therapeutic target. Here we investigate the antifungal properties of known inhibitors of the mammalian Ire1 protein both in vitro and in a treatment model of FK.

Methods

The antifungal activity of Ire1 inhibitors was tested against conidia of several A. fumigatus isolates by a broth microdilution assay and against fungal biofilm by XTT reduction. The influence of 4μ8C on hacA mRNA splicing in A. fumigatus was assessed through gel electrophoresis and qRT-PCR of UPR regulatory genes. The toxicity and antifungal profile of 4μ8C in the cornea was assessed by applying drops to uninfected or A. fumigatus-infected corneas 3 times daily starting 4 hours post-inoculation. Corneas were evaluated daily through slit-lamp imaging and optical coherence tomography, or at endpoint through histology or fungal burden quantification via colony forming units.

Results

Among six Ire1 inhibitors screened, the endonuclease inhibitor 4μ8C displayed the strongest antifungal profile with an apparent fungicidal action. The compound both blocked conidial germination and hyphal metabolism of A. fumigatus Af293 in the same concentration range that blocked hacA splicing and UPR gene induction (60-120 µM). Topical treatment of sham-inoculated corneas with 0.5 and 2.5 mM 4μ8C did not impact corneal clarity, but did transiently inhibit epithelialization of corneal ulcers. Relative to vehicle-treated Af293-infected corneas, treatment with 0.5 and 2.5 mM drug resulted in a 50% and >90% reduction in fungal load, respectively, the latter of which corresponded to an absence of clinical signs of infection or corneal pathology.

Conclusion

The in vitro data suggest that 4μ8C displays antifungal activity against A. fumigatus through the specific inhibition of IreA. Topical application of the compound to the murine cornea can furthermore block the establishment of infection, suggesting this class of drugs can be developed as novel antifungals that improve visual outcomes in FK patients.

Transgelin 2 guards T cell lipid metabolism and antitumour function

Mounting effective immunity against pathogens and tumours relies on the successful metabolic programming of T cells by extracellular fatty acids1-3. Fatty-acid-binding protein 5 (FABP5) has a key role in this process by coordinating the efficient import and trafficking of lipids that fuel mitochondrial respiration to sustain the bioenergetic requirements of protective CD8+ T cells4,5. However, the mechanisms that govern this immunometabolic axis remain unexplored. Here we report that the cytoskeletal organizer transgelin 2 (TAGLN2) is necessary for optimal fatty acid uptake, mitochondrial respiration and anticancer function in CD8+ T cells. TAGLN2 interacts with FABP5 to facilitate its cell surface localization and function in activated CD8+ T cells. Analyses of ovarian cancer specimens revealed that endoplasmic reticulum (ER) stress responses induced by the tumour microenvironment repress TAGLN2 in infiltrating CD8+ T cells, thereby enforcing their dysfunctional state. Restoring TAGLN2 expression in ER-stressed CD8+ T cells increased their lipid uptake, mitochondrial respiration and cytotoxic capacity. Accordingly, chimeric antigen receptor T cells overexpressing TAGLN2 bypassed the detrimental effects of tumour-induced ER stress and demonstrated therapeutic efficacy in mice with metastatic ovarian cancer. Our study establishes the role of cytoskeletal TAGLN2 in T cell lipid metabolism and highlights the potential to enhance cellular immunotherapy in solid malignancies by preserving the TAGLN2-FABP5 axis.

Targeting IRE1α reprograms the tumor microenvironment and enhances anti-tumor immunity in prostate cancer

Unfolded protein response (UPR) is a central stress response pathway that is hijacked by tumor cells for their survival. Here, we find that IRE1α signaling, one of the canonical UPR arms, is increased in prostate cancer (PCa) patient tumors. Genetic or small molecule inhibition of IRE1α in syngeneic mouse PCa models and an orthotopic model decreases tumor growth. IRE1α ablation in cancer cells potentiates interferon responses and activates immune system related pathways in the tumor microenvironment (TME). Single-cell RNA-sequencing analysis reveals that targeting IRE1α in cancer cells reduces tumor-associated macrophage abundance. Consistently, the small molecule IRE1α inhibitor MKC8866, currently in clinical trials, reprograms the TME and enhances anti-PD-1 therapy. Our findings show that IRE1α signaling not only promotes cancer cell growth and survival but also interferes with anti-tumor immunity in the TME. Thus, targeting IRE1α can be a promising approach for improving anti-PD-1 immunotherapy in PCa.

High-grade serous ovarian cancer development and anti-PD-1 resistance is driven by IRE1α activity in neutrophils

High-grade serious ovarian cancer (HGSOC) is an aggressive malignancy that remains refractory to current immunotherapies. While advanced stage disease has been extensively studied, the cellular and molecular mechanisms that promote early immune escape in HGSOC remain largely unexplored. Here, we report that primary HGSO tumors program neutrophils to inhibit T cell anti-tumor function by activating the endoplasmic reticulum (ER) stress sensor IRE1α. We found that intratumoral neutrophils exhibited overactivation of ER stress response markers compared with their counterparts at non-tumor sites. Selective deletion of IRE1α in neutrophils delayed primary ovarian tumor growth and extended the survival of mice with HGSOC by enabling early T cell-mediated tumor control. Notably, loss of IRE1α in neutrophils sensitized tumor-bearing mice to PD-1 blockade, inducing HGSOC regression and long-term survival in ~ 50% of the treated hosts. Hence, neutrophil-intrinsic IRE1α facilitates early adaptive immune escape in HGSOC and targeting this ER stress sensor might be used to unleash endogenous and immunotherapy-elicited immunity that controls metastatic disease.

The Role of Endoplasmic Reticulum Stress on Reducing Recombinant Protein Production in Mammalian Cells

Therapeutic recombinant protein production relies on industrial scale culture of mammalian cells to produce active proteins in quantities sufficient for clinical use. The combination of stresses from industrial cell culture environment and recombinant protein production can overwhelm the protein synthesis machinery in the endoplasmic reticulum (ER). This leads to a buildup of improperly folded proteins which induces ER stress. Cells respond to ER stress by activating the Unfolded Protein Response (UPR). To restore proteostasis, ER sensor proteins reduce global protein synthesis and increase chaperone protein synthesis, and if that is insufficient the proteins are degraded. If proteostasis is still not restored, apoptosis is initiated. Increasing evidence suggests crosstalk between ER proteostasis and DNA damage repair (DDR) pathways. External factors (e.g., metabolites) from the cellular environment as well as internal factors (e.g., transgene copy number) can impact genome stability. Failure to maintain genome integrity reduces cell viability and in turn protein production. This review focuses on the association between ER stress and processes that affect protein production and secretion. The processes mediated by ER stress, including inhibition of global protein translation, chaperone protein production, degradation of misfolded proteins, DNA repair, and protein secretion, impact recombinant protein production. Recombinant protein production can be reduced by ER stress through increased autophagy and protein degradation, reduced protein secretion, and reduced DDR response.

The activation of the G-protein-coupled estrogen receptor promotes the aggressiveness of MDA-MB231 cells by targeting the IRE1α/TXNIP pathway

Background and purpose

This study investigated modulating the G protein-coupled estrogen receptor (GPER) on the IRElα/TXNIP pathway and its role in drug resistance in MDA-MB231 cells.

Experimental approach

To determine the optimal concentrations of G1 and 4-hydroxytamoxifen (TAM), GPER expression and ERK1/2 phosphorylation were analyzed using qRT-PCR and western blotting, respectively. Cells were treated with individual concentrations of G1 (1000 nM), G15 (1000 nM), and TAM (2000 nM), as well as combinations of these treatments (G1 + G15, TAM + G15, and G1 + TAM) for 24 and 48 h. The expression levels of GPER, IRE1α, miR-17-5p, TXNIP, ABCB1, and ABCC1 genes and TXNIP protein expression were evaluated. Finally, apoptosis and cell migration were examined using flow cytometry and the wound-healing assay, respectively.

Findings/Results

Activating GPER with its specific agonist G1 and TAM significantly increased IRE1α levels in MDA-MB231 cells. IRE1α through splicing XBP1 led to unfolded protein response. In addition, decreased TXNIP gene and protein expression reduced apoptosis, increased migration, and upregulated the genes associated with drug resistance.

Conclusion and implication

Our investigation revealed that blocking the GPER/IRE1α/TXNIP pathway in MDA-MB231 cells could enhance treatment efficacy and improve chemotherapy responsiveness. The distinct unfolded protein response observed in MDA-MB231 cells may stem from the unique characteristics of these cells, which lack receptors for estrogen, progesterone, and HER2/neu hormones, possessing only the GPER receptor (ER-/PR-/HER2-/GPER+). This study introduced a new pathway in TNBC cells, indicating that targeting GPER could be crucial in comprehensive therapeutic strategies in TNBC cells.

Knockdown of ERN1 disturbs the expression of phosphoserine aminotransferase 1 and related genes in glioblastoma cells

BACKGROUND

Endoplasmic reticulum stress and synthesis of serine are essential for tumor growth, but the mechanism of their interaction is not clarified yet. The overarching goal of this work was to investigate the impact of ERN1 (endoplasmic reticulum to nucleus signaling 1) inhibition on the expression of serine synthesis genes in U87MG glioblastoma cells concerning the suppression of cell proliferation.

METHODS

Wild type U87MG glioblastoma cells and their clones with overexpression of transgenes dnERN1 (without cytoplasmic domain of ERN1) and dnrERN1 (with mutation in endoribonuclease of ERN1), and empty vector (as control) were used. The silencing of ERN1 and XBP1 was also used to inhibition of ERN1 and its function. Gene expression was measured by qPCR.

RESULTS

We show that the expression of PSAT1 and several other related to serine synthesis genes is suppressed in cells with ERN1 inhibition by dissimilar mechanisms: PHGDH gene through ERN1 protein kinase, because its expression was resistant to inhibition of ERN1 endoribonuclease, but ATF4 gene via endoribonuclease of ERN1. However, in the control of PSAT1 and PSPH genes both enzymatic activities of ERN1 signaling protein are involved. At the same time, ERN1 knockdown strongly increased SHMT1 expression, which controls serine metabolism and enhances the proliferation and invasiveness of glioma cells. The level of microRNAs, which have binding sites in PSAT1, SHMT1, and PSPH mRNAs, was also changed in cells harboring dnERN1 transgene. Inhibition of ERN1 suppressed cell proliferation and enzymatic activity of PHGDH, a rate-limiting enzyme for serine synthesis.

CONCLUSION

Changes in the expression of phosphoserine aminotransferase 1 and other genes related to serine synthesis are mediated by diverse ERN1-dependent mechanisms and contributed to suppressed proliferation and enhanced invasiveness of ERN1 knockdown glioblastoma cell.

Microcystin-LR Regulates Interaction between Tumor Cells and Macrophages via the IRE1α/XBP1 Signaling Pathway to Promote the Progression of Colorectal Cancer

Microcystin-LR (MC-LR), a cyanobacterial toxin, is a potent carcinogen implicated in colorectal cancer (CRC) progression. However, its impact on the tumor microenvironment (TME) during CRC development remains poorly understood. This study investigates the interaction between tumor cells and macrophages mediated by MC-LR within the TME and its influence on CRC progression. CRC mice exposed to MC-LR demonstrated a significant transformation from adenoma to adenocarcinoma. The infiltration of macrophages increased, and the IRE1α/XBP1 pathway was activated in CRC cells after MC-LR exposure, influencing macrophage M2 polarization under co-culture conditions. Additionally, hexokinase 2 (HK2), a downstream target of the IRE1α/XBP1 pathway, was identified, regulating glycolysis and lactate production. The MC-LR-induced IRE1α/XBP1/HK2 axis enhanced lactate production in CRC cells, promoting M2 macrophage polarization. Furthermore, co-culturing MC-LR-exposed CRC cells with macrophages, along with the IRE1α/XBP1 pathway inhibitor 4μ8C and the hexokinase inhibitor 2-DG, suppressed M2 macrophage-induced CRC cell migration, clonogenicity, and M2 macrophage polarization. This study elucidates the mechanism by which MC-LR-mediated interactions through the IRE1α/XBP1 pathway promote CRC progression, highlighting potential therapeutic targets.

Advances in siRNA Drug Delivery Strategies for Targeted TNBC Therapy

Among breast cancers, triple-negative breast cancer (TNBC) has been recognized as the most aggressive type with a poor prognosis and low survival rate. Targeted therapy for TNBC is challenging because it lacks estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Chemotherapy, radiation therapy, and surgery are the common therapies for TNBC. Although TNBC is prone to chemotherapy, drug resistance and recurrence are commonly associated with treatment failure. Combination therapy approaches using chemotherapy, mAbs, ADC, and antibody-siRNA conjugates may be effective in TNBC. Recent advances with siRNA-based therapy approaches are promising for TNBC therapy with better prognosis and reduced mortality. This review discusses advances in nanomaterial- and nanobiomaterial-based siRNA delivery platforms for TNBC therapy exploring targeted therapy approaches for major genes, proteins, and TFs upregulated in TNBC tumors, which engage in molecular pathways associated with low TNBC prognosis. Bioengineered siRNA drugs targeting one or several genes simultaneously can downregulate desired genes, significantly reducing disease progression.

High-grade serous ovarian cancer development and anti-PD-1 resistance is driven by IRE1α activity in neutrophils

High-grade serous ovarian cancer (HGSOC) is an aggressive malignancy that remains refractory to current immunotherapies. While advanced stage disease has been extensively studied, the cellular and molecular mechanisms that promote early immune escape in HGSOC remain largely unexplored. Here we report that primary HGSO tumors program neutrophils to inhibit T cell anti-tumor function by activating the endoplasmic reticulum (ER) stress sensor IRE1α. We found that intratumoral neutrophils exhibited overactivation of ER stress response markers compared with their counterparts at non-tumor sites. Selective deletion of IRE1α in neutrophils delayed primary ovarian tumor growth and extended the survival of mice with HGSOC by enabling early T cell-mediated tumor control. Notably, loss of IRE1α in neutrophils sensitized tumor-bearing mice to PD-1 blockade, inducing HGSOC regression and long-term survival in ∼50% of treated hosts. Hence, neutrophil-intrinsic IRE1α facilitates early adaptive immune escape in HGSOC and targeting this ER stress sensor might be used to unleash endogenous and immunotherapy-elicited immunity that controls metastatic disease.

Inhibition of ERN1 affects the expression of TGIF1 and other homeobox gene expressions in U87MG glioblastoma cells

BACKGROUND

The ERN1 (endoplasmic reticulum to nucleus signaling 1) pathway plays an important role in the regulation of gene expression in glioblastoma, but molecular mechanism has not yet been fully elucidated. The aim of this study was to evaluate the relative relevance of ERN1 activity as a kinase in comparison to its endoribonuclease activity in the regulation of homeobox gene expression.

METHODS

Two sublines of U87MG glioblastoma cells with different ways of ERN1 inhibition were used: dnERN1 (overexpressed transgene without protein kinase and endoribonuclease) and dnrERN1 (overexpressed transgene with mutation in endoribonuclease). ERN1 suppression was also done using siRNA for ERN1. Silencing of XBP1 mRNA by specific siRNA was used for suppression of ERN1 endoribonuclease function mediated by XBP1s. The expression levels of homeobox genes and microRNAs were evaluated by qPCR.

RESULTS

The expression of TGIF1 and ZEB2 genes was downregulated in both types of glioblastoma cells with inhibition of ERN1 showing the ERN1 endoribonuclease-dependent mechanism of their regulation. However, the expression of PBX3 and PRPRX1 genes did not change significantly in dnrERN1 glioblastoma cells but was upregulated in dnERN1 cells indicating the dependence of these gene expressions on the ERN1 protein kinase. At the same time, the changes in PAX6 and PBXIP1 gene expressions introduced in glioblastoma cells by dnrERN1 and dnERN1 were different in direction and magnitude indicating the interaction of ERN1 protein kinase and endoribonuclease activities in regulation of these gene expressions. The impact of ERN1 and XBP1 silencing on the expression of studied homeobox genes is similar to that observed in dnERN1 and dnrERN1 glioblastoma cells, correspondingly.

CONCLUSION

The expression of TGIF1 and other homeobox genes is dependent on the ern1 signaling pathways by diverse mechanisms because inhibition of ERN1 endoribonuclease and both ERN1 enzymatic activities had dissimilar impacts on the expression of most studied genes showing that ERN1 protein kinase plays an important role in controlling homeobox gene expression associated with glioblastoma cell invasion.

XBP1s activates METTL3/METTL14 for ER-phagy and paclitaxel sensitivity regulation in breast cancer

Cancer cells employ the unfolded protein response (UPR) or induce autophagy, especially selective removal of certain ER domains via reticulophagy (termed ER-phagy), to mitigate endoplasmic reticulum (ER) stress for ER homeostasis when encountering microenvironmental stress. N6-methyladenosine (m6A) is one of the most abundant epitranscriptional modifications and plays important roles in various biological processes. However, the molecular mechanism of m6A modification in the ER stress response is poorly understood. In this study, we first found that ER stress could dramatically elevate m6A methylation levels through XBP1s-dependent transcriptional upregulation of METTL3/METTL14 in breast cancer (BC) cells. Further MeRIP sequencing and relevant validation results confirmed that ER stress caused m6A methylation enrichment on target genes for ER-phagy. Mechanistically, METTL3/METTL14 increased ER-phagy machinery formation by promoting m6A modification of the ER-phagy regulators CALCOCO1 and p62, thus enhancing their mRNA stability. Of note, we further confirmed that the chemotherapeutic drug paclitaxel (PTX) could induce ER stress and increase m6A methylation for ER-phagy. Furthermore, the combination of METTL3/METTL14 inhibitors with PTX demonstrated a significant synergistic therapeutic effect in both BC cells and xenograft mice. Thus, our data built a novel bridge on the crosstalk between ER stress, m6A methylation and ER-phagy. Most importantly, our work provides novel evidence of METTL3 and METTL14 as potential therapeutic targets for PTX sensitization in breast cancer.

Navigating the landscape of the unfolded protein response in CD8+ T cells

Endoplasmic reticulum stress occurs due to large amounts of misfolded proteins, hypoxia, nutrient deprivation, and more. The unfolded protein is a complex intracellular signaling network designed to operate under this stress. Composed of three individual arms, inositol-requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor-6, the unfolded protein response looks to resolve stress and return to proteostasis. The CD8+ T cell is a critical cell type for the adaptive immune system. The unfolded protein response has been shown to have a wide-ranging spectrum of effects on CD8+ T cells. CD8+ T cells undergo cellular stress during activation and due to environmental insults. However, the magnitude of the effects this response has on CD8+ T cells is still understudied. Thus, studying these pathways is important to unraveling the inner machinations of these powerful cells. In this review, we will highlight the recent literature in this field, summarize the three pathways of the unfolded protein response, and discuss their roles in CD8+ T cell biology and functionality.

N6-methyladenosine modified TGFB2 triggers lipid metabolism reprogramming to confer pancreatic ductal adenocarcinoma gemcitabine resistance

Gemcitabine resistance is a major obstacle to the effectiveness of chemotherapy in pancreatic ductal adenocarcinoma (PDAC). Therefore, new strategies are needed to sensitize cancer cells to gemcitabine. Here, we constructed gemcitabine-resistant PDAC cells and analyzed them with RNA-sequence. Employing an integrated approach involving bioinformatic analyses from multiple databases, TGFB2 is identified as a crucial gene in gemcitabine-resistant PDAC and is significantly associated with poor gemcitabine therapeutic response. The patient-derived xenograft (PDX) model further substantiates the gradual upregulation of TGFB2 expression during gemcitabine-induced resistance. Silencing TGFB2 expression can enhance the chemosensitivity of gemcitabine against PDAC. Mechanistically, TGFB2, post-transcriptionally stabilized by METTL14-mediated m6A modification, can promote lipid accumulation and the enhanced triglyceride accumulation drives gemcitabine resistance by lipidomic profiling. TGFB2 upregulates the lipogenesis regulator sterol regulatory element binding factor 1 (SREBF1) and its downstream lipogenic enzymes via PI3K-AKT signaling. Moreover, SREBF1 is responsible for TGFB2-mediated lipogenesis to promote gemcitabine resistance in PDAC. Importantly, TGFB2 inhibitor imperatorin combined with gemcitabine shows synergistic effects in gemcitabine-resistant PDAC PDX model. This study sheds new light on an avenue to mitigate PDAC gemcitabine resistance by targeting TGFB2 and lipid metabolism and develops the potential of imperatorin as a promising chemosensitizer in clinical translation.

The inositol-requiring enzyme 1 (IRE1) endoplasmic reticulum stress pathway promotes MDA-MB-231 cell survival and renewal in response to the aryl-ureido fatty acid CTU

Current treatment options for triple-negative breast cancer (TNBC) are limited to toxic drug combinations of low efficacy. We recently identified an aryl-substituted fatty acid analogue, termed CTU, that effectively killed TNBC cells in vitro and in mouse xenograft models in vivo without producing toxicity. However, there was a residual cell population that survived treatment. The present study evaluated the mechanisms that underlie survival and renewal in CTU-treated MDA-MB-231 TNBC cells. RNA-seq profiling identified several pro-inflammatory signaling pathways that were activated in treated cells. Increased expression of cyclooxygenase-2 and the cytokines IL-6, IL-8 and GM-CSF was confirmed by real-time RT-PCR, ELISA and Western blot analysis. Increased self-renewal was confirmed using the non-adherent, in vitro colony-forming mammosphere assay. Neutralizing antibodies to IL-6, IL-8 and GM-CSF, as well as cyclooxygenase-2 inhibition suppressed the self-renewal of MDA-MB-231 cells post-CTU treatment. IPA network analysis identified major NF-κB and XBP1 gene networks that were activated by CTU; chemical inhibitors of these pathways and esiRNA knock-down decreased the production of pro-inflammatory mediators. NF-κB and XBP1 signaling was in turn activated by the endoplasmic reticulum (ER)-stress sensor inositol-requiring enzyme 1 (IRE1), which mediates the unfolded protein response. Co-treatment with an inhibitor of IRE1 kinase and RNase activities, decreased phospho-NF-κB and XBP1s expression and the production of pro-inflammatory mediators. Further, IRE1 inhibition also enhanced apoptotic cell death and prevented the activation of self-renewal by CTU. Taken together, the present findings indicate that the IRE1 ER-stress pathway is activated by the anti-cancer lipid analogue CTU, which then activates secondary self-renewal in TNBC cells.

Macrophages and tumor-associated macrophages in the senescent microenvironment: From immunosuppressive TME to targeted tumor therapy

In-depth studies of the tumor microenvironment (TME) have helped to elucidate its cancer-promoting mechanisms and inherent characteristics. Cellular senescence, which acts as a response to injury and can the release of senescence-associated secretory phenotypes (SASPs). These SASPs release various cytokines, chemokines, and growth factors, remodeling the TME. This continual development of a senescent environment could be associated with chronic inflammation and immunosuppressive TME. Additionally, SASPs could influence the phenotype and function of macrophages, leading to the recruitment of tumor-associated macrophages (TAMs). This contributes to tumor proliferation and metastasis in the senescent microenvironment, working in tandem with immune regulation, angiogenesis, and therapeutic resistance. This comprehensive review covers the evolving nature of the senescent microenvironment, macrophages, and TAMs in tumor development. We also explored the links between chronic inflammation, immunosuppressive TME, cellular senescence, and macrophages. Moreover, we compiled various tumor-specific treatment strategies centered on cellular senescence and the current challenges in cellular senescence research. This study aimed to clarify the mechanism of macrophages and the senescent microenvironment in tumor progression and advance the development of targeted tumor therapies.

IRE1 endoribonuclease signaling promotes myeloid cell infiltration in glioblastoma

BACKGROUND

Intrinsic or environmental stresses trigger the accumulation of improperly folded proteins in the endoplasmic reticulum (ER), leading to ER stress. To cope with this, cells have evolved an adaptive mechanism named the unfolded protein response (UPR) which is hijacked by tumor cells to develop malignant features. Glioblastoma (GB), the most aggressive and lethal primary brain tumor, relies on UPR to sustain growth. We recently showed that IRE1 alpha (referred to IRE1 hereafter), 1 of the UPR transducers, promotes GB invasion, angiogenesis, and infiltration by macrophage. Hence, high tumor IRE1 activity in tumor cells predicts a worse outcome. Herein, we characterized the IRE1-dependent signaling that shapes the immune microenvironment toward monocytes/macrophages and neutrophils.

METHODS

We used human and mouse cellular models in which IRE1 was genetically or pharmacologically invalidated and which were tested in vivo. Publicly available datasets from GB patients were also analyzed to confirm our findings.

RESULTS

We showed that IRE1 signaling, through both the transcription factor XBP1s and the regulated IRE1-dependent decay controls the expression of the ubiquitin-conjugating E2 enzyme UBE2D3. In turn, UBE2D3 activates the NFκB pathway, resulting in chemokine production and myeloid infiltration in tumors.

CONCLUSIONS

Our work identifies a novel IRE1/UBE2D3 proinflammatory axis that plays an instrumental role in GB immune regulation.

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 (LC3βII). 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 LC3βII 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.

IRE1 signaling increases PERK expression during chronic ER stress

The Unfolded Protein Response (UPR) is an essential cellular process activated by the accumulation of unfolded proteins within the Endoplasmic Reticulum (ER), a condition referred to as ER stress. Three ER anchored receptors, IRE1, PERK and ATF6 act as ER stress sensors monitoring the health of the ER. Upon detection of ER stress, IRE1, PERK and ATF6 initiate downstream signaling pathways collectively referred to as the UPR. The overarching aim of the UPR is to restore ER homeostasis by reducing ER stress, however if that is not possible, the UPR transitions from a pro-survival to a pro-death response. While our understanding of the key signaling pathways central to the UPR is well defined, the same is not true of the subtle signaling events that help fine tune the UPR, supporting its ability to adapt to varying amplitudes or durations of ER stress. In this study, we demonstrate cross talk between the IRE1 and PERK branches of the UPR, wherein IRE1 via XBP1s signaling helps to sustain PERK expression during prolonged ER stress. Our findings suggest cross talk between UPR branches aids adaptiveness thereby helping to support the plasticity of UPR signaling responses.

Endoplasmic reticulum stress responses and epigenetic alterations in arsenic carcinogenesis

Arsenic is a well-known human carcinogen whose environmental exposure via drinking water, food, and air impacts millions of people across the globe. Various mechanisms of arsenic carcinogenesis have been identified, ranging from damage caused by excessive production of free radicals and epigenetic alterations to the generation of cancer stem cells. A growing body of evidence supports the critical involvement of the endoplasmic stress-activated unfolded protein response (UPR) in promoting as well as suppressing cancer development/progression. Various in vitro and in vivo models have also demonstrated that arsenic induces the UPR via activation of the PERK, IRE1α, and ATF6 proteins. In this review, we discuss the mechanisms of arsenic-induced endoplasmic reticulum stress and the role of each UPR pathway in the various cancer types with a focus on the epigenetic regulation and function of the ATF6 protein. The importance of UPR in arsenic carcinogenesis and cancer stem cells is a relatively new area of research that requires additional investigations via various omics-based and computational tools. These approaches will provide interesting insights into the mechanisms of arsenic-induced cancers for prospective target identification and development of novel anti-cancer therapies.

The Tumor Microenvironment: Signal Transduction

In the challenging tumor microenvironment (TME), tumors coexist with diverse stromal cell types. During tumor progression and metastasis, a reciprocal interaction occurs between cancer cells and their environment. These interactions involve ongoing and evolving paracrine and proximal signaling. Intrinsic signal transduction in tumors drives processes such as malignant transformation, epithelial-mesenchymal transition, immune evasion, and tumor cell metastasis. In addition, cancer cells embedded in the tumor microenvironment undergo metabolic reprogramming. Their metabolites, serving as signaling molecules, engage in metabolic communication with diverse matrix components. These metabolites act as direct regulators of carcinogenic pathways, thereby activating signaling cascades that contribute to cancer progression. Hence, gaining insights into the intrinsic signal transduction of tumors and the signaling communication between tumor cells and various matrix components within the tumor microenvironment may reveal novel therapeutic targets. In this review, we initially examine the development of the tumor microenvironment. Subsequently, we delineate the oncogenic signaling pathways within tumor cells and elucidate the reciprocal communication between these pathways and the tumor microenvironment. Finally, we give an overview of the effect of signal transduction within the tumor microenvironment on tumor metabolism and tumor immunity.

Targeting the IRE1α-XBP1s axis confers selective vulnerability in hepatocellular carcinoma with activated Wnt signaling

Liver-specific Ern1 knockout impairs tumor progression in mouse models of hepatocellular carcinoma (HCC). However, the mechanistic role of IRE1α in human HCC remains unclear. In this study, we show that XBP1s, the major downstream effector of IRE1α, is required for HCC cell survival both in vitro and in vivo. Mechanistically, XBP1s transactivates LEF1, a key co-factor of β-catenin, by binding to its promoter. Moreover, XBP1s physically interacts with LEF1, forming a transcriptional complex that enhances classical Wnt signaling. Consistently, the activities of XBP1s and LEF1 are strongly correlated in human HCC and with disease prognosis. Notably, selective inhibition of XBP1 splicing using an IRE1α inhibitor significantly repressed the viability of tumor explants as well as the growth of tumor xenografts derived from patients with distinct Wnt/LEF1 activities. Finally, machine learning algorithms developed a powerful prognostic signature based on the activities of XBP1s/LEF1. In summary, our study uncovers a key mechanistic role for the IRE1α-XBP1s pathway in human HCC. Targeting this axis could provide a promising therapeutic strategy for HCC with hyperactivated Wnt/LEF1 signaling.

IRE1 RNase controls CD95-mediated cell death

Signalling by the Unfolded Protein Response (UPR) or by the Death Receptors (DR) are frequently activated towards pro-tumoral outputs in cancer. Herein, we demonstrate that the UPR sensor IRE1 controls the expression of the DR CD95/Fas, and its cell death-inducing ability. Both genetic and pharmacologic blunting of IRE1 activity increased CD95 expression and exacerbated CD95L-induced cell death in glioblastoma (GB) and Triple-Negative Breast Cancer (TNBC) cell lines. In accordance, CD95 mRNA was identified as a target of Regulated IRE1-Dependent Decay of RNA (RIDD). Whilst CD95 expression is elevated in TNBC and GB human tumours exhibiting low RIDD activity, it is surprisingly lower in XBP1s-low human tumour samples. We show that IRE1 RNase inhibition limited CD95 expression and reduced CD95-mediated hepatic toxicity in mice. In addition, overexpression of XBP1s increased CD95 expression and sensitized GB and TNBC cells to CD95L-induced cell death. Overall, these results demonstrate the tight IRE1-mediated control of CD95-dependent cell death in a dual manner through both RIDD and XBP1s, and they identify a novel link between IRE1 and CD95 signalling.

Population pharmacokinetic model for oral ORIN1001 in Chinese patients with advanced solid tumors

Background: ORIN1001, a first-in-class oral IRE1-α endoribonuclease inhibitor to block the activation of XBP1, is currently in clinical development for inhibiting tumor growth and enhancing the effect of chemical or targeted therapy. Early establishment of a population pharmacokinetic (PopPK) model could characterize the pharmacokinetics (PK) of ORIN1001 and evaluate the effects of individual-specific factors on PK, which will facilitate the future development of this investigational drug. Methods: Non-linear mixed effect model was constructed by Phoenix NLME software, utilizing the information from Chinese patients with advanced solid tumors in a phase I clinical trial (Register No. NCT05154201). Statistically significant PK covariates were screened out by a stepwise process. The final model, after validating by the goodness-of-fit plots, non-parametric bootstrap, visual predictive check and test of normalized prediction distribution errors, was further applied to simulate and evaluate the impact of covariates on ORIN1001 exposure at steady state up to 900 mg per day as a single agent. Results: A two-compartment model with first-order absorption (with lag-time)/elimination was selected as the best structural model. Total bilirubin (TBIL) and lean body weight (LBW) were considered as the statistically significant covariates on clearance (CL/F) of ORIN1001. They were also confirmed to exert clinically significant effects on ORIN1001 steady-state exposure after model simulation. The necessity of dose adjustments based on these two covariates remains to be validated in a larger population. Conclusion: The first PopPK model of ORIN1001 was successfully constructed, which may provide some important references for future research.

Cellular and molecular antiproliferative effects in 2D monolayer and 3D-cultivated HT-29 cells treated with zerumbone

Zerumbone (ZER) is a phytochemical isolated from plants of the Zingiberaceae family. Numerous studies have demonstrated its diverse pharmacological properties, particularly its potent antitumorigenic activity. This study aimed to assess the antiproliferative effects of ZER on HT-29 cells cultivated in both two-dimensional (2D) monolayer and three-dimensional (3D) spheroid culture systems. The evaluation of growth (size), cell death, and cell cycle arrest in 3D spheroid HT-29 cells was correlated with mRNA expression data. Treatment of 2D cells revealed that ZER exhibited cytotoxicity at concentrations above 30 µM, and an IC50 of 83.54 µM (24-h post-ZER treatment) effectively suppressed cell migration. In the 3D model, ZER induced an increase in spheroid volume over a 72-h period attributed to disaggregation and reconfiguration of characteristic zones. Analysis of cell death demonstrated a significant rise in apoptotic cells after 24 h of ZER treatment, along with cell cycle arrest in the G1 phase. Furthermore, ZER treatment resulted in alterations in mRNA expression, affecting key signaling pathways involved in cell death (BCL2 and BBC3), endoplasmic reticulum stress (ERN1), DNA damage (GADD45A), cell cycle regulation (CDKN1A, NFKB1, MYC, and TP53), and autophagy (BECN1 and SQSTM1). These findings suggested that ZER holds promise as a potential candidate for the development of novel anticancer agents that can modulate crucial cell signaling pathways. Additionally, the use of the 3D culture system proved to be a valuable tool in our investigation.

Protein-rich foods, sea foods, and gut microbiota amplify immune responses in chronic diseases and cancers - Targeting PERK as a novel therapeutic strategy for chronic inflammatory diseases, neurodegenerative disorders, and cancer

The endoplasmic reticulum (ER) is a cellular organelle that is physiologically responsible for protein folding, calcium homeostasis, and lipid biosynthesis. Pathological stimuli such as oxidative stress, ischemia, disruptions in calcium homeostasis, and increased production of normal and/or folding-defective proteins all contribute to the accumulation of misfolded proteins in the ER, causing ER stress. The adaptive response to ER stress is the activation of unfolded protein response (UPR), which affect a wide variety of cellular functions to maintain ER homeostasis or lead to apoptosis. Three different ER transmembrane sensors, including PKR-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme-1 (IRE1), are responsible for initiating UPR. The UPR involves a variety of signal transduction pathways that reduce unfolded protein accumulation by boosting ER-resident chaperones, limiting protein translation, and accelerating unfolded protein degradation. ER is now acknowledged as a critical organelle in sensing dangers and determining cell life and death. On the other hand, UPR plays a critical role in the development and progression of several diseases such as cardiovascular diseases (CVD), metabolic disorders, chronic kidney diseases, neurological disorders, and cancer. Here, we critically analyze the most current knowledge of the master regulatory roles of ER stress particularly the PERK pathway as a conditional danger receptor, an organelle crosstalk regulator, and a regulator of protein translation. We highlighted that PERK is not only ER stress regulator by sensing UPR and ER stress but also a frontier sensor and direct senses for gut microbiota-generated metabolites. Our work also further highlighted the function of PERK as a central hub that leads to metabolic reprogramming and epigenetic modification which further enhanced inflammatory response and promoted trained immunity. Moreover, we highlighted the contribution of ER stress and PERK in the pathogenesis of several diseases such as cancer, CVD, kidney diseases, and neurodegenerative disorders. Finally, we discuss the therapeutic target of ER stress and PERK for cancer treatment and the potential novel therapeutic targets for CVD, metabolic disorders, and neurodegenerative disorders. Inhibition of ER stress, by the development of small molecules that target the PERK and UPR, represents a promising therapeutic strategy.

Understanding the prion-like behavior of mutant p53 proteins in triple-negative breast cancer pathogenesis: The current therapeutic strategies and future directions

Breast cancer (BC) is viewed as a significant public health issue and is the primary cause of cancer-related deaths among women worldwide. Triple-negative breast cancer (TNBC) is a particularly aggressive subtype that predominantly affects young premenopausal women. The tumor suppressor p53 playsa vital role in the cellular response to DNA damage, and its loss or mutations are commonly present in many cancers, including BC. Recent evidence suggests that mutant p53 proteins can aggregate and form prion-like structures, which may contribute to the pathogenesis of different types of malignancies, such as BC. This review provides an overview of BC molecular subtypes, the epidemiology of TNBC, and the role of p53 in BC development. We also discuss the potential implications of prion-like aggregation in BC and highlight future research directions. Moreover, a comprehensive analysis of the current therapeutic approaches targeting p53 aggregates in BC treatment is presented. Strategies including small molecules, chaperone inhibitors, immunotherapy, CRISPR-Cas9, and siRNA are discussed, along with their potential benefits and drawbacks. The use of these approaches to inhibit p53 aggregation and degradation represents a promising target for cancer therapy. Future investigations into the efficacy of these approaches against various p53 mutations or binding to non-p53 proteins should be conducted to develop more effective and personalized therapies for BC treatment.

Identification of the unfolded protein response pathway as target for radiosensitization in pancreatic cancer

BACKGROUND AND PURPOSE

Due to the high intrinsic radioresistance of pancreatic ductal adenocarcinoma (PDAC), radiotherapy (RT) is only beneficial in 30% of patients. Therefore, this study aimed to identify targets to improve the efficacy of RT in PDAC.

MATERIALS AND METHODS

Alamar Blue proliferation and colony formation assay (CFA) were used to determine the radioresponse of a cohort of 38 murine PDAC cell lines. A gene set enrichment analysis was performed to reveal differentially expressed pathways. CFA, cell cycle distribution, γH2AX FACS analysis, and Caspase 3/7 SYTOX assay were used to examine the effect of a combination treatment using KIRA8 as an IRE1α-inhibitor and Ceapin-A7 as an inhibitor against ATF6.

RESULTS

The unfolded protein response (UPR) was identified as a pathway highly expressed in radioresistant cell lines. Using the IRE1α-inhibitor KIRA8 or the ATF6-inhibitor Ceapin-A7 in combination with radiation, a radiosensitizing effect was observed in radioresistant cell lines, but no substantial alteration of the radioresponse in radiosensitive cell lines. Mechanistically, increased apoptosis by KIRA8 in combination with radiation and a cell cycle arrest in the G1 phase after ATF6 inhibition and radiation have been observed in radioresistant cell lines.

CONCLUSION

So, our data show evidence that the UPR is involved in radioresistance of PDAC. Increased apoptosis and a G1 cell cycle arrest seem to be responsible for the radiosensitizing effect of UPR inhibition. These findings are supportive for developing novel combination treatment concepts in PDAC to overcome radioresistance.

ER exit in physiology and disease

The biosynthetic secretory pathway is comprised of multiple steps, modifications and interactions that form a highly precise pathway of protein trafficking and secretion, that is essential for eukaryotic life. The general outline of this pathway is understood, however the specific mechanisms are still unclear. In the last 15 years there have been vast advancements in technology that enable us to advance our understanding of this complex and subtle pathway. Therefore, based on the strong foundation of work performed over the last 40 years, we can now build another level of understanding, using the new technologies available. The biosynthetic secretory pathway is a high precision process, that involves a number of tightly regulated steps: Protein folding and quality control, cargo selection for Endoplasmic Reticulum (ER) exit, Golgi trafficking, sorting and secretion. When deregulated it causes severe diseases that here we categorise into three main groups of aberrant secretion: decreased, excess and altered secretion. Each of these categories disrupts organ homeostasis differently, effecting extracellular matrix composition, changing signalling events, or damaging the secretory cells due to aberrant intracellular accumulation of secretory proteins. Diseases of aberrant secretion are very common, but despite this, there are few effective therapies. Here we describe ER exit sites (ERES) as key hubs for regulation of the secretory pathway, protein quality control and an integratory hub for signalling within the cell. This review also describes the challenges that will be faced in developing effective therapies, due to the specificity required of potential drug candidates and the crucial need to respect the fine equilibrium of the pathway. The development of novel tools is moving forward, and we can also use these tools to build our understanding of the acute regulation of ERES and protein trafficking. Here we review ERES regulation in context as a therapeutic strategy.

Different binding modalities of quercetin to inositol-requiring enzyme 1 of S. cerevisiae and human lead to opposite regulation

The flavonoid Quercetin (Qe) was identified as an activator of Inositol-requiring enzyme 1 (IRE1) in S. cerevisiae (scIre1p), but its impact on human IRE1 (hIRE1) remains controversial due to the absence of a conserved Qe binding site. We have explored the binding modes and effect of Qe on both scIre1p and hIRE1 dimers using in silico and in vitro approaches. The activation site in scIre1p stably accommodates both Qe and its derivative Quercitrin (Qi), thus enhancing the stability of the RNase pocket. However, the corresponding region in hIRE1 does not bind any of the two molecules. Instead, we show that both Qe and Qi block the RNase activity of hIRE1 in vitro, with sub-micromolar IC50 values. Our results provide a rationale for why Qe is an activator in scIre1p but a potent inhibitor in hIRE1. The identification of a new allosteric site in hIRE1 opens a promising window for drug development and UPR modulation.

Endoplasmic reticulum stress-dependent regulation of the expression of serine hydroxymethyltransferase 2 in glioblastoma cells

Objective. Serine hydroxymethyltransferase (SHMT2) plays a multifunctional role in mitochondria (folate-dependent tRNA methylation, translation, and thymidylate synthesis). The endoplasmic reticulum stress, hypoxia, and glucose and glutamine supply are significant factors of malignant tumor growth including glioblastoma. Previous studies have shown that the knockdown of the endoplasmic reticulum to nucleus signaling 1 (ERN1) pathway of endoplasmic reticulum stress strongly suppressed glioblastoma cell proliferation and modified the sensitivity of these cells to hypoxia and glucose or glutamine deprivations. The present study aimed to investigate the regulation of the SHMT2 gene in U87MG glioblastoma cells by ERN1 knockdown, hypoxia, and glucose or glutamine deprivations with the intent to reveal the role of ERN1 signaling in sensitivity of this gene expression to hypoxia and nutrient supply. Methods. The control U87MG glioblastoma cells (transfected by an empty vector) and ERN1 knockdown cells with inhibited ERN1 endoribonuclease and protein kinase (dnERN1) or only ERN1 endoribonuclease (dnrERN1) were used. Hypoxia was introduced by dimethyloxalylglycine (500 ng/ml for 4 h). For glucose and glutamine deprivations, cells were exposed in DMEM without glucose and glutamine, respectively for 16 h. RNA was extracted from cells and reverse transcribed. The expression level of the SHMT2 gene was studied by real-time qPCR and normalized to ACTB. Results. It was found that inhibition of ERN1 endoribonuclease and protein kinase in glioblastoma cells led to a down-regulation of SHMT2 gene expression in U87MG cells. At the same time, the expression of this gene did not significantly change in cells with inhibited ERN1 endoribonuclease, but tunicamycin strongly increased its expression. Moreover, the expression of the SHMT2 gene was not affected in U87MG cells after silencing of XBP1. Hypoxia up-regulated the expression level of the SHMT2 gene in both control and ERN1 knockdown U87MG cells. The expression of this gene was significantly up-regulated in glioblastoma cells under glucose and glutamine deprivations and ERN1 knockdown significantly increased the sensitivity of the SHMT2 gene to these nutrient deprivation conditions. Conclusion. The results of the present study demonstrate that the expression of the SHMT2 gene responsible for serine metabolism and formation of folate one-carbon is controlled by ERN1 protein kinase and induced by hypoxia as well as glutamine and glucose deprivation conditions in glioblastoma cells and reflects the ERN1-mediated reprogramming of sensitivity this gene expression to nutrient deprivation.

Inhibition of signaling protein ERN1 increases the sensitivity of serine synthesis gene expressions to glucose and glutamine deprivations in U87MG glioblastoma cells

Objective. Glucose and glutamine supply as well as serine synthesis and endoplasmic reticulum (ER) stress are important factors of glioblastoma growth. Previous studies showed that the knockdown of ERN1 (ER to nucleus signaling 1) suppressed glioblastoma cell proliferation and modified the sensitivity of numerous gene expressions to nutrient deprivations. The present study is aimed to investigate the impact of glucose and glutamine deprivations on the expression of serine synthesis genes in U87MG glioblastoma cells in relation to ERN1 knockdown with the intent to reveal the role of ERN1 signaling pathway on the ER stress-dependent regulation of these gene expressions. Clarification of the regulatory mechanisms of serine synthesis is a great significance for glioblastoma therapy. Methods. The control U87MG glioblastoma cells (transfected by empty vector) and ERN1 knockdown cells (transfected by dominant-negative ERN1) were exposed under glucose and glutamine deprivation conditions for 16 h. RNA was extracted from cells and reverse transcribed. The expression level of PHGDH (phosphoglycerate dehydrogenase), PSAT1 (phosphoserine amino-transferase 1), PSPH (phosphoserine phosphatase), ATF4 (activating transcription factor 4), and SHMT1 (serine hydroxymethyltransferase 1) genes was studied by real-time qPCR and normalized to ACTB. Results. It was found that the expression level of genes responsible for serine synthesis such as PHGDH, PSAT1, PSPH, and transcription factor ATF4 was up-regulated in U87MG glioblastoma cells under glucose and glutamine deprivations. Furthermore, inhibition of ERN1 significantly enhances the impact of glucose and especially glutamine deprivations on these gene expressions. At the same time, the expression of the SHMT1 gene, which is responsible for serine conversion to glycine, was down-regulated in both nutrient deprivation conditions with more significant changes in ERN1 knockdown glioblastoma cells. Conclusion. Taken together, the results of present study indicate that the expression of genes responsible for serine synthesis is sensitive to glucose and glutamine deprivations in gene-specific manner and that suppression of ERN1 signaling significantly modifies the impact of both glucose and glutamine deprivations on PHGDH, PSAT1, PSPH, ATF4, and SHMT1 gene expressions and reflects the ERN1-mediated genome reprograming introduced by nutrient deprivation condition.

ERN1 knockdown modifies the hypoxic regulation of homeobox gene expression in U87MG glioblastoma cells

OBJECTIVE.

Homeobox genes play an important role in health and disease including oncogenesis. The present investigation aimed to study ERN1-dependent hypoxic regulation of the expression of genes encoding homeobox proteins MEIS (zinc finger E-box binding homeobox 2) and LIM homeobox 1 family, SPAG4 (sperm associated antigen 4) and NKX3-1 (NK3 homeobox 1) in U87MG glioblastoma cells in response to inhibition of ERN1 (endoplasmic reticulum to nucleus signaling 1) for evaluation of their possible significance in the control of glioblastoma growth.

METHODS.

The expression level of homeobox genes was studied in control (transfected by vector) and ERN1 knockdown U87MG glioblastoma cells under hypoxia induced by dimethyloxalylglycine (0.5 mM for 4 h) by quantitative polymerase chain reaction and normalized to ACTB.

RESULTS.

It was found that hypoxia down-regulated the expression level of LHX2, LHX6, MEIS2, and NKX3-1 genes but up-regulated the expression level of MEIS1, LHX1, MEIS3, and SPAG4 genes in control glioblastoma cells. At the same time, ERN1 knockdown of glioblastoma cells significantly modified the sensitivity of all studied genes to a hypoxic condition. Thus, ERN1 knockdown of glioblastoma cells removed the effect of hypoxia on the expression of MEIS1 and LHX1 genes, but increased the sensitivity of MEIS2, LHX2, and LHX6 genes to hypoxia. However, the expression of MEIS3, NKX3-1, and SPAG4 genes had decreased sensitivity to hypoxia in ERN1 knockdown glioblastoma cells. Moreover, more pronounced changes under the conditions of ERN1 inhibition were detected for the pro-oncogenic gene SPAG4.

CONCLUSION.

The results of the present study demonstrate that hypoxia affected the expression of homeobox genes MEIS1, MEIS2, MEIS3, LHX1, LHX2, LHX6, SPAG4, and NKX3-1 in U87MG glioblastoma cells in gene-specific manner and that the sensitivity of all studied genes to hypoxia condition is mediated by ERN1, the major pathway of the endoplasmic reticulum stress signaling, and possibly contributed to the control of glioblastoma growth. A fundamentally new results of this work is the establishment of the fact regarding the dependence of hypoxic regulation of SPAG4 gene expression on ER stress, in particular ERN1, which is associated with suppression of cell proliferation and tumor growth.