IRE1α Disruption in Triple-Negative Breast Cancer Cooperates with Antiangiogenic Therapy by Reversing ER Stress Adaptation and Remodeling the Tumor Microenvironment

Unraveling the unfolded protein response signature: implications for tumor immune microenvironment heterogeneity and clinical prognosis in stomach cancer

BACKGROUND

Stomach cancer is a leading cause of cancer-related deaths globally due to its high grade and poor response to treatment. Understanding the molecular network driving the rapid progression of stomach cancer is crucial for improving patient outcomes.

METHODS

This study aimed to investigate the role of unfolded protein response (UPR) related genes in stomach cancer and their potential as prognostic biomarkers. RNA expression data and clinical follow-up information were obtained from the TCGA and GEO databases. An unsupervised clustering algorithm was used to identify UPR genomic subtypes in stomach cancer. Functional enrichment analysis, immune landscape analysis, and chemotherapy benefit prediction were conducted for each subtype. A prognostic model based on UPR-related genes was developed and validated using LASSO-Cox regression, and a multivariate nomogram was created. Key gene expression analyses in pan-cancer and in vitro experiments were performed to further investigate the role of the identified genes in cancer progression.

RESULTS

A total of 375 stomach cancer patients were included in this study. Analysis of 113 UPR-related genes revealed their close functional correlation and significant enrichment in protein modification, transport, and RNA degradation pathways. Unsupervised clustering identified two molecular subtypes with significant differences in prognosis and gene expression profiles. Immune landscape analysis showed that UPR may influence the composition of the tumor immune microenvironment. Chemotherapy sensitivity analysis indicated that patients in the C2 molecular subtype were more responsive to chemotherapy compared to those in the C1 molecular subtype. A prognostic signature consisting of seven UPR-related genes was constructed and validated, and an independent prognostic nomogram was developed. The gene IGFBP1, which had the highest weight coefficient in the prognostic signature, was found to promote the malignant phenotype of stomach cancer cells, suggesting its potential as a therapeutic target.

CONCLUSIONS

The study developed a UPR-related gene classifier and risk signature for predicting survival in stomach cancer, identifying IGFBP1 as a key factor promoting the disease's malignancy and a potential therapeutic target. IGFBP1's role in enhancing cancer cell adaptation to endoplasmic reticulum stress suggests its importance in stomach cancer prognosis and treatment.

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.

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.

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.

Endoplasmic reticulum stress and therapeutic strategies in metabolic, neurodegenerative diseases and cancer

The accumulation of unfolded or misfolded proteins within the endoplasmic reticulum (ER), due to genetic determinants and extrinsic environmental factors, leads to endoplasmic reticulum stress (ER stress). As ER stress ensues, the unfolded protein response (UPR), comprising three signaling pathways-inositol-requiring enzyme 1, protein kinase R-like endoplasmic reticulum kinase, and activating transcription factor 6 promptly activates to enhance the ER's protein-folding capacity and restore ER homeostasis. However, prolonged ER stress levels propels the UPR towards cellular demise and the subsequent inflammatory cascade, contributing to the development of human diseases, including cancer, neurodegenerative disorders, and diabetes. Notably, increased expression of all three UPR signaling pathways has been observed in these pathologies, and reduction in signaling molecule expression correlates with decreased proliferation of disease-associated target cells. Consequently, therapeutic strategies targeting ER stress-related interventions have attracted significant research interest. In this review, we elucidate the critical role of ER stress in cancer, metabolic, and neurodegenerative diseases, offering novel therapeutic approaches for these conditions.

Emerging Futuristic Targeted Therapeutics: A Comprising Study Towards a New Era for the Management of TNBC

Triple-negative breast cancer is characterized by high lethality attributed to factors such as chemoresistance, transcriptomic, and genomic heterogeneity, leading to a poor prognosis and limiting available targeted treatment options. While the identification of molecular targets remains pivotal for therapy involving chemo drugs, the current challenge lies in the poor response rates, low survival rates, and frequent relapses. Despite various clinical investigations exploring molecular targeted therapies in conjunction with conventional chemo treatment, the outcomes have been less than optimal. The critical need for more effective therapies underscores the urgency to discover potent novel treatments, including molecular and immune targets, as well as emerging strategies. This review provides a comprehensive analysis of conventional treatment approaches and explores emerging molecular and immune-targeted therapeutics, elucidating their mechanisms to address the existing obstacles for a more effective management of triple-negative breast cancer.

Brucea javanica derived exosome-like nanovesicles deliver miRNAs for cancer therapy

Triple-negative breast cancer (TNBC) is characterized by complex heterogeneity, high recurrence and metastasis rates, and short overall survival, owing to the lack of endocrine and targeted receptors, which necessitates chemotherapy as the major treatment regimen. Exosome-like nanovesicles derived from medicinal plants have shown great potential as novel biotherapeutics for cancer therapy by delivering their incorporated nucleic acids, especially microRNAs (miRNAs), to mammalian cells. In this study, we isolated exosome-like nanovesicles derived from B. javanica (BF-Exos) and investigated their influence and underlying molecular mechanisms in TNBC. We found that BF-Exos delivered 10 functional miRNAs to 4T1 cells, significantly retarding the growth and metastasis of 4T1 cells by regulating the PI3K/Akt/mTOR signaling pathway and promoting ROS/caspase-mediated apoptosis. Moreover, BF-Exos were shown to inhibit the secretion of vascular endothelial growth factor, contributing to anti-angiogenesis in the tumor microenvironment. In vivo, BF-Exos inhibited tumor growth, metastasis, and angiogenesis in breast tumor mouse models, while maintaining high biosafety. Overall, BF-Exos are considered promising nanoplatforms for the delivery of medicinal plant-derived nucleic acids, with great potential to be developed into novel biotherapeutics for the treatment of TNBC.

A risk signature based on endoplasmic reticulum stress-associated genes predicts prognosis and immunity in pancreatic cancer

Introduction: The involvement of endoplasmic reticulum (ER) stress in cancer biology is increasingly recognized, yet its role in pancreatic cancer (PC) remains unclear. This study aims to elucidate the impact of ER stress on prognosis and biological characteristics in PC patients. Methods: A bioinformatic analysis was conducted using RNA-seq data and clinicopathological information from PC patients in the TCGA and ICGC databases. The ER stress-associated gene sets were extracted from MSigDB. ER stress-associated genes closely linked with overall survival (OS) of PC patients were identified via log-rank test and univariate Cox analysis, and further narrowed by LASSO method. A risk signature associated with ER stress was formulated using multivariate Cox regression and assessed through Kaplan-Meier curves, receiver operating characteristic (ROC) analyses, and Harrell's concordance index. External validation was performed with the ICGC cohort. The single-sample gene-set enrichment analysis (ssGSEA) algorithm appraised the immune cell infiltration landscape. Results: Worse OS in PC patients with high-risk signature score was observed. Multivariate analysis underscored our ER stress-associated signature as a valuable and independent predictor of prognosis. Importantly, these results based on TCGA were further validated in ICGC dataset. In addition, our risk signature was closely associated with homeostasis, protein secretion, and immune regulation in PC patients. In particular, PC microenvironment in the high-risk cluster exhibited a more immunosuppressive status. At last, we established a nomogram model by incorporating the risk signature and clinicopathological parameters, which behaves better in predicting prognosis of PC patients. Discussion: This comprehensive molecular analysis presents a new predictive model for the prognosis of PC patients, highlighting ER stress as a potential therapeutic target. Besides, the findings indicate that ER stress can have effect modulating PC immune responses.

Dual RNase activity of IRE1 as a target for anticancer therapies

The unfolded protein response (UPR) is a cellular mechanism that protects cells during stress conditions in which there is an accumulation of misfolded proteins in the endoplasmic reticulum (ER). UPR activates three signaling pathways that function to alleviate stress conditions and promote cellular homeostasis and cell survival. During unmitigated stress conditions, however, UPR activation signaling changes to promote cell death through apoptosis. Interestingly, cancer cells take advantage of this pathway to facilitate survival and avoid apoptosis even during prolonged cell stress conditions. Here, we discuss different signaling pathways associated with UPR and focus specifically on one of the ER signaling pathways activated during UPR, inositol-requiring enzyme 1α (IRE1). The rationale is that the IRE1 pathway is associated with cell fate decisions and recognized as a promising target for cancer therapeutics. Here we discuss IRE1 inhibitors and how they might prove to be an effective cancer therapeutic.

Tube geometry controls protein cluster conformation and stability on the endoplasmic reticulum surface

The endoplasmic reticulum (ER), a cellular organelle that forms a cell-spanning network of tubes and sheets, is an important location of protein synthesis and folding. When the ER experiences sustained unfolded protein stress, IRE1 proteins embedded in the ER membrane activate and assemble into clusters as part of the unfolded protein response (UPR). We use kinetic Monte Carlo simulations to explore IRE1 clustering dynamics on the surface of ER tubes. While initially growing clusters are approximately round, once a cluster is sufficiently large a shorter interface length can be achieved by 'wrapping' around the ER tube. A wrapped cluster can grow without further interface length increases. Relative to wide tubes, narrower tubes enable cluster wrapping at smaller cluster sizes. Our simulations show that wrapped clusters on narrower tubes grow more rapidly, evaporate more slowly, and require a lower protein concentration to grow compared to equal-area round clusters on wider tubes. These results suggest that cluster wrapping, facilitated by narrower tubes, could be an important factor in the growth and stability of IRE1 clusters and thus impact the persistence of the UPR, connecting geometry to signaling behavior. This work is consistent with recent experimental observations of IRE1 clusters wrapped around narrow tubes in the ER network.

Association of cyclooxygenase-2 expression with endoplasmic reticulum stress and autophagy in triple-negative breast cancer

Cyclooxygenase-2 plays a role in oncogenesis and its overexpression is associated with triple-negative breast cancer. However, the mechanisms whereby cyclooxygenase-2 contribute to breast cancer are complex and not well understood. Cyclooxygenase-2 overexpression causes hypoxia, oxidative stress, and endoplasmic reticulum stress. The aim of this study is to investigate the correlations among cyclooxygenase-2 expression, endoplasmic reticulum stress-associated molecules, and autophagy-associated molecules in triple-negative breast cancer. Surgical specimens from two cohorts of triple-negative breast cancer patients without neoadjuvant systemic therapy were analyzed: cohorts 1 and 2 consisted of 218 cases from 2004 to 2006 and 221 cases from 2007 to 2009, respectively. Specimens were evaluated by immunohistochemical examination of cyclooxygenase-2, endoplasmic reticulum stress markers, and autophagy markers expression using tissue microarrays. Cyclooxygenase-2 was overexpressed in 29.8% and 23.9% of cases in cohorts 1 and 2, respectively; and it was positively correlated with two out of three endoplasmic reticulum stress-associated molecules (XBP1, p = 0.025 and p = 0.003 in cohort 1 and cohort 2, respectively; PERK, p < 0.001 in both cohorts). Cyclooxygenase-2 was also positively correlated with two out of three autophagy markers (p62, p = 0.002 and p = 0.003 in cohort 1 and cohort 2, respectively; beclin1, p < 0.001 in both cohorts). Although cyclooxygenase-2 was not an independent prognostic factor for distant metastasis free survival and overall survival, its expression was associated with the expression of endoplasmic reticulum stress and autophagy molecules in triple-negative breast cancer.

A novel IRE1 kinase inhibitor for adjuvant glioblastoma treatment

Inositol-requiring enzyme 1 (IRE1) is a major mediator of the unfolded protein response (UPR), which is activated upon endoplasmic reticulum (ER) stress. Tumor cells experience ER stress due to adverse microenvironmental cues, a stress overcome by relying on IRE1 signaling as an adaptive mechanism. Herein, we report the discovery of structurally new IRE1 inhibitors identified through the structural exploration of its kinase domain. Characterization in in vitro and in cellular models showed that they inhibit IRE1 signaling and sensitize glioblastoma (GB) cells to the standard chemotherapeutic, temozolomide (TMZ). Finally, we demonstrate that one of these inhibitors, Z4P, permeates the blood-brain barrier (BBB), inhibits GB growth, and prevents relapse in vivo when administered together with TMZ. The hit compound disclosed herein satisfies an unmet need for targeted, non-toxic IRE1 inhibitors and our results support the attractiveness of IRE1 as an adjuvant therapeutic target in GB.

In silico analysis reveals PRDX4 as a prognostic and oncogenic marker in renal papillary cell carcinoma

BACKGROUND

Alterations in the tumor microenvironment leads to the accumulation of reactive oxygen species (ROS). When in low levels, ROS act as a signaling molecule and contribute to tumor cell proliferation whereas its elevation results in oxidative stress and eventually cell death. It is known that antioxidant systems regulate the ROS levels and thus cell fate. Among these systems, peroxiredoxins (PRDXs) were found to be upregulated in various cancers. However their exact contribution to carcinogenesis is not yet clear.

AIM

Herein, the expression pattern and prognostic value of PRDXs were explored in cancer setting by using in silico analysis tools and publicly available datasets.

RESULTS

Pan-cancer analysis revealed that PRDXs are differentially expressed in normal and tumor tissues. Further analysis showed that higher PRDX4 levels was associated with poor prognosis and clinicopathological and histological features associated with a more aggressive renal papillary cell carcinoma (KIRP) profile. Hypoxia, ER stress and protein folding were shown to be pathways positively correlated with PRDX4 levels. Furthermore, PRDX4 was found to be strong regulator of protein homeostasis. Kaplan-Meier analysis revealed that PRDX4 is a potent prognostic marker in Type 2 KIRP and this might be due to increased ER stress and oxidative stress levels in this subtype.

CONCLUSIONS

The data suggest that PRDX4 can be used as a prognostic marker for KIRP patients. Its association with more aggressive tumor characteristics also underlines that it might be used for targeted therapy.

Unfolded protein response and angiogenesis in malignancies

Cellular stress, arising from accumulation of unfolded proteins, occurs frequently in rapidly proliferating cancer cells. This cellular stress, in turn, activates the unfolded protein response (UPR), an interconnected set of signal transduction pathways that alleviate the proteostatic stress. The UPR is implicated in cancer cell survival and proliferation through upregulation of pro-tumorigenic pathways that ultimately promote malignant metabolism and neoangiogenesis. Here, we reviewed mechanisms of signaling crosstalk between the UPR and angiogenesis pathways, as well as transmissible ER stress and the role in tumor growth and development. To characterize differences in UPR and UPR-mediated angiogenesis in malignancy, we employed a data mining approach using patient tumor data from The Cancer Genome Atlas (TCGA). The analysis of TCGA revealed differences in UPR between malignant samples versus their non-malignant counterparts.

Loss of ATF6α in a human carcinoma cell line is compensated not by its paralogue ATF6β but by sustained activation of the IRE1 and PERK arms for tumor growth in nude mice

To survive poor nutritional conditions, tumor cells activate the unfolded protein response, which is composed of the IRE1, PERK, and ATF6 arms, to maintain the homeostasis of the endoplasmic reticulum, where secretory and transmembrane proteins destined for the secretory pathway gain their correct three-dimensional structure. The requirement of the IRE1 and PERK arms for tumor growth in nude mice is established. Here we investigated the requirement for the ATF6 arm, which consists of ubiquitously expressed ATF6α and ATF6β, by constructing ATF6α-knockout (KO), ATF6β-KO, and ATF6α/β-double KO (DKO) in HCT116 cells derived from human colorectal carcinoma. Results showed that these KO cells grew similarly to wild-type (WT) cells in nude mice, contrary to expectations from our analysis of ATF6α-KO, ATF6β-KO, and ATF6α/β-DKO mice. We then found that the loss of ATF6α in HCT116 cells resulted in sustained activation of the IRE1 and PERK arms in marked contrast to mouse embryonic fibroblasts, in which the loss of ATF6α is compensated for by ATF6β. Although IRE1-KO in HCT116 cells unexpectedly did not affect tumor growth in nude mice, IRE1-KO HCT116 cells with ATF6α knockdown grew significantly more slowly than WT or IRE1-KO HCT116 cells. These results have unraveled the situation-dependent differential compensation strategies of ATF6α.

Endoplasmic reticulum stress mediates the myeloid-derived immune suppression associated with cancer and infectious disease

Myeloid-derived suppressor cells (MDSCs), which are immature heterogeneous bone marrow cells, have been described as potent immune regulators in human and murine cancer models. The distribution of MDSCs varies across organs and is divided into three subpopulations: granulocytic MDSCs or polymorphonuclear MDSCs (G-MDSCs or PMN-MDSCs), monocytic MDSCs (M-MDSCs), as well as a recently identified early precursor MDSC (eMDSCs) in humans. Activated MDSCs induce the inactivation of NK cells, CD4+, and CD8+ T cells through a variety of mechanisms, thus promoting the formation of tumor immunosuppressive microenvironment. ER stress plays an important protecting role in the survival of MDSC, which aggravates the immunosuppression in tumors. In addition, ferroptosis can promote an anti-tumor immune response by reversing the immunosuppressive microenvironment. This review summarizes immune suppression by MDSCs with a focus on the role of endoplasmic reticulum stress-mediated immune suppression in cancer and infectious disease, in particular leprosy and tuberculosis.

IRE1α overexpression in malignant cells limits tumor progression by inducing an anti-cancer immune response

IRE1α is one of the three ER transmembrane transducers of the Unfolded Protein Response (UPR) activated under endoplasmic reticulum (ER) stress. IRE1α activation has a dual role in cancer as it may be either pro- or anti-tumoral depending on the studied models. Here, we describe the discovery that exogenous expression of IRE1α, resulting in IRE1α auto-activation, did not affect cancer cell proliferation in vitro but resulted in a tumor-suppressive phenotype in syngeneic immunocompetent mice. We found that exogenous expression of IRE1α in murine colorectal and Lewis lung carcinoma cells impaired tumor growth when syngeneic tumor cells were subcutaneously implanted in immunocompetent mice but not in immunodeficient mice. Mechanistically, the in vivo tumor-suppressive effect of overexpressing IRE1α in tumor cells was associated with IRE1α RNAse activity driving both XBP1 mRNA splicing and regulated IRE1-dependent decay of RNA (RIDD). We showed that the tumor-suppressive phenotype upon IRE1α overexpression was characterized by the induction of apoptosis in tumor cells along with an enhanced adaptive anti-cancer immunosurveillance. Hence, our work indicates that IRE1α overexpression and/or activation in tumor cells can limit tumor growth in immunocompetent mice. This finding might point toward the need of adjusting the use of IRE1α inhibitors in cancer treatments based on the predominant outcome of the RNAse activity of IRE1α.

The unfolded protein response (UPR) pathway: the unsung hero in breast cancer management

Tumor cells always have the need to produce an increased amount of proteins in the cells. This elevated amount of proteins increases the pressure on the organelles of the cell such as the endoplasmic reticulum and compels it to increase its protein folding efficiency. However, it is by a matter of fact, that the amount of proteins synthesized outweighs the protein folding capacity of the ER which in turn switches on the UPR pathway by activating the three major molecular sensors and other signaling cascades, which helps in cell survival instead of instant death. However, if this pathway is active for a prolonged period of time the tumor cells heads toward apoptosis. Again, interestingly this is not the same as in case of non- tumorogenic cells. This exhibit a straight natural pathway for tumor cells-specific destruction which has a great implication in today's world where hormone therapies and chemo-therapies are non-effective for various types of breast cancer, a major type being Triple Negative Breast Cancer. Thus a detailed elucidation of the molecular involvement of the UPR pathway in breast cancer may open new avenues for management and attract novel chemotherapeutic targets providing better hopes to patients worldwide.

Cancer cell-intrinsic XBP1 drives immunosuppressive reprogramming of intratumoral myeloid cells by promoting cholesterol production

A hostile microenvironment in tumor tissues disrupts endoplasmic reticulum homeostasis and induces the unfolded protein response (UPR). A chronic UPR in both cancer cells and tumor-infiltrating leukocytes could facilitate the evasion of immune surveillance. However, how the UPR in cancer cells cripples the anti-tumor immune response is unclear. Here, we demonstrate that, in cancer cells, the UPR component X-box binding protein 1 (XBP1) favors the synthesis and secretion of cholesterol, which activates myeloid-derived suppressor cells (MDSCs) and causes immunosuppression. Cholesterol is delivered in the form of small extracellular vesicles and internalized by MDSCs through macropinocytosis. Genetic or pharmacological depletion of XBP1 or reducing the tumor cholesterol content remarkably decreases MDSC abundance and triggers robust anti-tumor responses. Thus, our data unravel the cell-non-autonomous role of XBP1/cholesterol signaling in the regulation of tumor growth and suggest its inhibition as a useful strategy for improving the efficacy of cancer immunotherapy.

X-box binding protein 1 as a key modulator in “healing endothelial cells”, a novel EC phenotype promoting angiogenesis after MCAO

Background

Endothelial cells (ECs) play an important role in angiogenesis and vascular reconstruction in the pathophysiology of ischemic stroke. Previous investigations have provided a profound cerebral vascular atlas under physiological conditions, but have failed to identify new disease-related cell subtypes. We aimed to identify new EC subtypes and determine the key modulator genes.

Methods

Two datasets GSE174574 and GSE137482 were included in the study. Seurat was utilized as the standard quality-control pipeline. UCell was used to calculate single-cell scores to validate cellular identity. Monocle3 and CytoTRACE were utilized in aid of pseudo-time differentiation analysis. CellChat was utilized to infer the intercellular communication pathways. The angiogenesis ability of ECs was validated by MTS, Transwell, tube formation, flow cytometry, and immunofluorescence assays in vitro and in vivo. A synchrotron radiation-based propagation contrast imaging was introduced to comprehensively portray cerebral vasculature.

Results

We successfully identified a novel subtype of EC named “healing EC” that highly expressed pan-EC marker and pro-angiogenic genes but lowly expressed all the arteriovenous markers identified in the vascular single-cell atlas. Further analyses showed its high stemness to differentiate into other EC subtypes and potential to modulate inflammation and angiogenesis via excretion of signal molecules. We therefore identified X-box binding protein 1 (Xbp1) as a key modulator in the healing EC phenotype. In vitro and in vivo experiments confirmed its pro-angiogenic roles under both physiological and pathological conditions. Synchrotron radiation-based propagation contrast imaging further proved that Xbp1 could promote angiogenesis and recover normal vasculature conformation, especially in the corpus striatum and prefrontal cortex under middle cerebral artery occlusion (MCAO) condition.

Conclusions

Our study identified a novel disease-related EC subtype that showed high stemness to differentiate into other EC subtypes. The predicted molecule Xbp1 was thus confirmed as a key modulator that can promote angiogenesis and recover normal vasculature conformation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00399-5.

Endoplasmic reticulum stress targeted therapy for breast cancer

Recurrence, metastasis, and drug resistance are still big challenges in breast cancer therapy. Internal and external stresses have been proven to substantially facilitate breast cancer progression through molecular and systemic mechanisms. For example, endoplasmic reticulum stress (ERS) results in activation of the unfolded protein response (UPR), which are considered an important cellular stress response. More and more reports indicate its key role in protein homeostasis and other diverse functions involved in the process of breast cancer progression. Therefore, therapies targeting the activation of ERS and its downstream signaling pathways are potentially helpful and novel tools to counteract and fight breast cancer. However, recent advances in our understanding of ERS are focused on characterizing and modulating ERS between healthy and disease states, and so little attention has been paid to studying the role and clinical application of targeting ERS in a certain cancer. In this review, we summarize the function and main mechanisms of ERS in different molecular types of breast cancer, and focus on the development of agents targeting ERS to provide new treatment strategies for breast cancer.

Decoding endoplasmic reticulum stress signals in cancer cells and antitumor immunity

The tumor microenvironment (TME) provokes endoplasmic reticulum (ER) stress in malignant cells and infiltrating immune populations. Sensing and responding to ER stress is coordinated by the unfolded protein response (UPR), an integrated signaling pathway governed by three ER stress sensors: activating transcription factor (ATF6), inositol-requiring enzyme 1α (IRE1α), and protein kinase R (PKR)-like ER kinase (PERK). Persistent UPR activation modulates malignant progression, tumor growth, metastasis, and protective antitumor immunity. Hence, therapies targeting ER stress signaling can be harnessed to elicit direct tumor killing and concomitant anticancer immunity. We highlight recent findings on the role of the ER stress responses in onco-immunology, with an emphasis on genetic vulnerabilities that render tumors highly sensitive to therapeutic UPR modulation.

The Role of the Hypoxia-Related Unfolded Protein Response (UPR) in the Tumor Microenvironment

Despite our understanding of the unfolded protein response (UPR) pathways, the crosstalk between the UPR and the complex signaling networks that different cancers utilize for cell survival remains to be, in most cases, a difficult research barrier. A major problem is the constant variability of different cancer types and the different stages of cancer as well as the complexity of the tumor microenvironments (TME). This complexity often leads to apparently contradictory results. Furthermore, the majority of the studies that have been conducted have utilized two-dimensional in vitro cultures of cancer cells that were exposed to continuous hypoxia, and this approach may not mimic the dynamic and cyclic conditions that are found in solid tumors. Here, we discuss the role of intermittent hypoxia, one of inducers of the UPR in the cellular component of TME, and the way in which intermittent hypoxia induces high levels of reactive oxygen species, the activation of the UPR, and the way in which cancer cells modulate the UPR to aid in their survival. Although the past decade has resulted in defining the complex, novel non-coding RNA-based regulatory networks that modulate the means by which hypoxia influences the UPR, we are now just to beginning to understand some of the connections between hypoxia, the UPR, and the TME.

Construction of an endoplasmic reticulum stress-related gene model for predicting prognosis and immune features in kidney renal clear cell carcinoma

Background: Kidney renal clear cell carcinoma (KIRC) is one of the most lethal malignant tumors with a propensity for poor prognosis and difficult treatment. Endoplasmic reticulum (ER) stress served as a pivotal role in the progression of the tumor. However, the implications of ER stress on the clinical outcome and immune features of KIRC patients still need elucidation.

Methods: We identified differentially expressed ER stress-related genes between KIRC specimens and normal specimens with TCGA dataset. Then, we explored the biological function and genetic mutation of ER stress-related differentially expressed genes (DEGs) by multiple bioinformatics analysis. Subsequently, LASSO analysis and univariate Cox regression analysis were applied to construct a novel prognostic model based on ER stress-related DEGs. Next, we confirmed the predictive performance of this model with the GEO dataset and explored the potential biological functions by functional enrichment analysis. Finally, KIRC patients stratified by the prognostic model were assessed for tumor microenvironment (TME), immune infiltration, and immune checkpoints through single-sample Gene Set Enrichment Analysis (ssGSEA) and ESTIMATE analysis.

Results: We constructed a novel prognostic model, including eight ER stress-related DEGs, which could stratify two risk groups in KIRC. The prognostic model and a model-based nomogram could accurately predict the prognosis of KIRC patients. Functional enrichment analysis indicated several biological functions related to the progression of KIRC. The high-risk group showed higher levels of tumor infiltration by immune cells and higher immune scores.

Conclusion: In this study, we constructed a novel prognostic model based on eight ER stress-related genes for KIRC patients, which would help predict the prognosis of KIRC and provide a new orientation to further research studies on personalized immunotherapy in KIRC.

ARHGEF2/EDN1 pathway participates in ER stress-related drug resistance of hepatocellular carcinoma by promoting angiogenesis and malignant proliferation

Endoplasmic reticulum (ER) stress is widely involved in the drug resistance of hepatocellular carcinoma (HCC), but the mechanism of ER stress-induced drug resistance involves multiple signaling pathways that cannot be fully explained. Exploring genes associated with ER stress could yield a novel therapeutic target for ER stress-induced drug resistance. By analyzing RNA-sequencing, ATAC-sequencing, and Chip-sequencing data of Tunicamycin (TM)-treated or untreated HCC cells, we found that Rho guanine nucleotide exchange factor 2 (ARHGEF2) is upregulated in HCC cells with ER stress. ARHGEF2 plays an active role in tumor malignant progression. Notwithstanding, no research has been done on the link between ER stress and ARHGEF2. The function of ARHGEF2 as a novel downstream effector of ER stress in the angiogenesis and treatment resistance of HCC was revealed in this work. ARHGEF2 overexpression was linked to malignant development and a poor prognosis in HCC. ER stress stimulates the expression of ARHGEF2 through upregulation of ZNF263. Elevated ARHGEF2 accelerates HCC angiogenesis via the EDN1 pathway, enhances HCC cell proliferation and tumor growth both in vitro and in vivo, and contributes to ER stress-related treatment resistance. HCC cell growth was more inhibited when ARHGEF2 knockdown was paired with targeted medicines. Collectively, we uncovered a previously hidden mechanism where ARHGEF2/EDN1 pathway promotes angiogenesis and participates in ER stress-related drug resistance in HCC.

Endoplasmic Reticulum Stress-Related Signature Predicts Prognosis and Drug Response in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common type of kidney cancer. The maximum number of deaths associated with kidney cancer can be attributed to ccRCC. Disruption of cellular proteostasis results in endoplasmic reticulum (ER) stress, which is associated with various aspects of cancer. It is noteworthy that the role of ER stress in the progression of ccRCC remains unclear. We classified 526 ccRCC samples identified from the TCGA database into the C1 and C2 subtypes by consensus clustering of the 295 ER stress-related genes. The ccRCC samples belonging to subtype C2 were in their advanced tumor stage and grade. These samples were characterized by poor prognosis and malignancy immune microenvironment. The upregulation of the inhibitory immune checkpoint gene expression and unique drug sensitivity were also observed. The differentially expressed genes between the two clusters were explored. An 11-gene ER stress-related prognostic risk model was constructed following the LASSO regression and Cox regression analyses. In addition, a nomogram was constructed by integrating the clinical parameters and risk scores. The calibration curves, ROC curves, and DCA curves helped validate the accuracy of the prediction when both the TCGA dataset and the external E-MTAB-1980 dataset were considered. Moreover, we analyzed the differentially expressed genes common to the E-MTAB-1980 and TCGA datasets to screen out new therapeutic compounds. In summary, our study can potentially help in the comprehensive understanding of ER stress in ccRCC and serve as a reference for future studies on novel prognostic biomarkers and treatments.

The cell-line-derived subcutaneous tumor model in preclinical cancer research

Tumor-bearing experimental animals are essential for preclinical cancer drug development. A broad range of tumor models is available, with the simplest and most widely used involving a tumor of mouse or human origin growing beneath the skin of a mouse: the subcutaneous tumor model. Here, we outline the different types of in vivo tumor model, including some of their advantages and disadvantages and how they fit into the drug-development process. We then describe in more detail the subcutaneous tumor model and key steps needed to establish it in the laboratory, namely: choosing the mouse strain and tumor cells; cell culture, preparation and injection of tumor cells; determining tumor volume; mouse welfare; and an appropriate experimental end point. The protocol leads to subcutaneous tumor growth usually within 1-3 weeks of cell injection and is suitable for those with experience in tissue culture and mouse experimentation.

Targeting autophagy increases the efficacy of proteasome inhibitor treatment in multiple myeloma by induction of apoptosis and activation of JNK

Background

The therapeutic armamentarium in multiple myeloma has been significantly broadened by proteasome inhibitors, highly efficient means in controlling of multiple myeloma. Despite the developments of therapeutic regimen in treatment of multiple myeloma, still the complete remission requires a novel therapeutic strategy with significant difference in outcomes. Proteasome inhibitors induce autophagy and ER stress, both pivotal pathways for protein homeostasis. Recent studies showed that the IRE1α-XBP1 axis of the unfolded protein response (UPR) is up-regulated in multiple myeloma patients. In addition, XBP1 is crucial for the maintenance of viability of acute lymphoblastic leukemia (ALL).

Results

We analyzed the efficacy of targeting IRE1α-XBP1 axis and autophagy in combination with proteasome inhibitor, ixazomib in treatment of multiple myeloma. In this present study, we first show that targeting the IRE1α-XBP1 axis with small molecule inhibitors (STF-083010, A106) together with the ixazomib induces cell cycle arrest with an additive cytotoxic effect in multiple myeloma. Further, we examined the efficacy of autophagy inhibitors (bafilomycin A, BAF and chloroquine, CQ) together with ixazomib in multiple myeloma and observed that this combination treatment synergistically reduced cell viability in multiple myeloma cell lines (viable cells Ixa: 51.8 ± 3.3, Ixa + BAF: 18.3 ± 7.2, Ixa + CQ: 38.4 ± 3.7) and patient-derived multiple myeloma cells (Ixa: 59.6 ± 4.4, Ixa + CQ: 7.0 ± 2.1). We observed, however, that this combined strategy leads to activation of stress-induced c-Jun N-terminal kinase (JNK). Cytotoxicity mediated by combined proteasome and autophagy inhibition was reversed by addition of the specific JNK inhibitor JNK-In-8 (viable cells: Ixa + BAF: 11.6 ± 7.0, Ixa + BAF + JNK-In-8: 30.9 ± 6.1).

Conclusion

In this study we showed that combined inhibition of autophagy and the proteasome synergistically induces cell death in multiple myeloma. Hence, we consider the implication of pharmaceutical inhibition of autophagy together with proteasome inhibition and UPR-directed therapy as promising novel in vitro treatment strategy against multiple myeloma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09775-y.

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

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

Antigen-derived peptides engage the ER stress sensor IRE1α to curb dendritic cell cross-presentation

Dendritic cells (DCs) promote adaptive immunity by cross-presenting antigen-based epitopes to CD8⁺ T cells. DCs process internalized protein antigens into peptides that enter the endoplasmic reticulum (ER), bind to major histocompatibility type I (MHC-I) protein complexes, and are transported to the cell surface for cross-presentation. DCs can exhibit activation of the ER stress sensor IRE1α without ER stress, but the underlying mechanism remains obscure. Here, we show that antigen-derived hydrophobic peptides can directly engage ER-resident IRE1α, masquerading as unfolded proteins. IRE1α activation depletes MHC-I heavy-chain mRNAs through regulated IRE1α-dependent decay (RIDD), curtailing antigen cross-presentation. In tumor-bearing mice, IRE1α disruption increased MHC-I expression on tumor-infiltrating DCs and enhanced recruitment and activation of CD8⁺ T cells. Moreover, IRE1α inhibition synergized with anti–PD-L1 antibody treatment to cause tumor regression. Our findings identify an unexpected cell-biological mechanism of antigen-driven IRE1α activation in DCs, revealing translational potential for cancer immunotherapy.

Regulated IRE1α-dependent decay (RIDD)-mediated reprograming of lipid metabolism in cancer

IRE1α is constitutively active in several cancers and can contribute to cancer progression. Activated IRE1α cleaves XBP1 mRNA, a key step in production of the transcription factor XBP1s. In addition, IRE1α cleaves select mRNAs through regulated IRE1α-dependent decay (RIDD). Accumulating evidence implicates IRE1α in the regulation of lipid metabolism. However, the roles of XBP1s and RIDD in this process remain ill-defined. In this study, transcriptome and lipidome profiling of triple negative breast cancer cells subjected to pharmacological inhibition of IRE1α reveals changes in lipid metabolism genes associated with accumulation of triacylglycerols (TAGs). We identify DGAT2 mRNA, encoding the rate-limiting enzyme in TAG biosynthesis, as a RIDD target. Inhibition of IRE1α, leads to DGAT2-dependent accumulation of TAGs in lipid droplets and sensitizes cells to nutritional stress, which is rescued by treatment with the DGAT2 inhibitor PF-06424439. Our results highlight the importance of IRE1α RIDD activity in reprograming cellular lipid metabolism.

IRE1α cleaves several mRNAs upon accumulation of misfolded proteins. Here the authors show that active IRE1α cleaves DGAT2 mRNA encoding the rate-limiting enzyme in the synthesis of triacylglycerols, suggesting a role of IRE1α in reprogramming lipid metabolism in cancer cells.

Endoplasmic reticulum stress in airway hyperresponsiveness

Airway hyperresponsiveness(AHR) is a major clinical phenomenon in lung diseases (asthma, COPD and pulmonary fibrosis) and not only a high-risk factor for perioperative airway spasm leading to hypoxaemia, haemodynamic instability and even "silent lung", but also a potential risk for increased mortality from underlying diseases (e.g. asthma, COPD). Airway reactivity is closely linked to airway inflammation, remodelling and increased mucus secretion, and endoplasmic reticulum stress is an important mechanism for the development of these pathologies. This review, therefore, focuses on the effects of endoplasmic reticulum stress on the immune cells involved in airway hyperreactivity (epithelial cells, dendritic cells, eosinophils and neutrophils) in inflammation and mucus & sputum secretion; and on the differentiation and remodelling of airway smooth muscle cells and epithelial cells. The aim is to clarify the mechanisms associated with endoplasmic reticulum stress in airway hyperresponsiveness and to find new ideas and methods for the prevention of airway hyperresponsiveness in the perioperative period.

Cellular stress responses and metabolic reprogramming in cancer progression and dormancy

Recurrent disease after prolonged cancer dormancy is a major cause of cancer associated mortality, yet many of the mechanisms that are engaged to initiate dormancy as well as later recurrence remain incompletely understood. It is known that cancer cells initiate adaptation mechanisms to adapt tightly regulated cellular processes to non-optimal growth environments; Recent investigations have begun to elucidate the contribution of these mechanisms to malignant progression, with intriguing studies now defining cellular stress as a key contributor to the development and maintenance of cancer dormancy. This review will focus on our current understanding of stress responses facilitating malignant cell adaptation and metabolic reprogramming to establish cancer dormancy.

Decoding non-canonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1α

Inositol requiring enzyme 1 (IRE1) mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, in mammals RIDD seems to target only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1α-controlled mRNAs in human cells, we identify not only canonical endomotif-containing RIDD substrates, but also targets without such motifs-degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1α displays two basic endoribonuclease modalities: highly specific, endomotif-directed cleavage, minimally requiring dimers; and more promiscuous, endomotif-independent processing, requiring phospho-oligomers. An oligomer-deficient IRE1α mutant fails to support RIDDLE in vitro and in cells. Our results advance current mechanistic understanding of the UPR.

Endoplasmic reticulum stress inhibits 3D Matrigel-induced vasculogenic mimicry of breast cancer cells via TGF-β1/Smad2/3 and β-catenin signaling

Endoplasmic reticulum (ER) stress is a cellular stress condition involving disturbance in the folding capacity of the ER caused by endogenous and exogenous factors. ER stress signaling pathways affect tumor malignant growth, angiogenesis and progression, and promote the antitumor effects of certain drugs. However, the impact of ER stress on the vasculogenic mimicry (VM) phenotype of cancer cells has not been well addressed. VM is a phenotype that mimics vasculogenesis by forming patterned tubular networks, which are related to stemness and aggressive behaviors of cancer cells. In this study, we used tunicamycin (TM), the unfolded protein response (UPR)-activating agent, to induce ER stress in aggressive triple-negative MDA-MB-231 breast cancer cells, which exhibit a VM phenotype in 3D Matrigel cultures. TM-induced ER stress was able to inhibit the VM phenotype. In addition to the tumor spheroid phenotype observed upon inhibiting the VM phenotype, we observed alterations in glycosylation of integrin β1, loss of VE-cadherin and a decrease in stem cell marker Bmi-1. Further study revealed decreased activated transforming growth factor β1, Smad2/3, Phospho-Smad2 and β-catenin. β-Catenin knockdown markedly inhibited the VM phenotype and resulted in the loss of VE-cadherin. The data suggest that the activation of ER stress inhibited VM phenotype formation of breast cancer cells via both the transforming growth factor β1/Smad2/3 and β-catenin signaling pathways. The discovery of prospective regulatory mechanisms involved in ER stress and VM in breast cancer could lead to more precisely targeted therapies that inhibit vessel formation and affect tumor progression.

Structural and molecular bases to IRE1 activity modulation

The Unfolded Protein response is an adaptive pathway triggered upon alteration of endoplasmic reticulum (ER) homeostasis. It is transduced by three major ER stress sensors, among which the Inositol Requiring Enzyme 1 (IRE1) is the most evolutionarily conserved. IRE1 is an ER-resident type I transmembrane protein exhibiting an ER luminal domain that senses the protein folding status and a catalytic kinase and RNase cytosolic domain. In recent years, IRE1 has emerged as a relevant therapeutic target in various diseases including degenerative, inflammatory and metabolic pathologies and cancer. As such several drugs altering IRE1 activity were developed that target either catalytic activity and showed some efficacy in preclinical pathological mouse models. In this review, we describe the different drugs identified to target IRE1 activity as well as their mode of action from a structural perspective, thereby identifying common and different modes of action. Based on this information we discuss on how new IRE1-targeting drugs could be developed that outperform the currently available molecules.

Endoplasmic reticulum stress signals in the tumour and its microenvironment

Protein handling, modification and folding in the endoplasmic reticulum (ER) are tightly regulated processes that determine cell function, fate and survival. In several tumour types, diverse oncogenic, transcriptional and metabolic abnormalities cooperate to generate hostile microenvironments that disrupt ER homeostasis in malignant and stromal cells, as well as infiltrating leukocytes. These changes provoke a state of persistent ER stress that has been demonstrated to govern multiple pro-tumoural attributes in the cancer cell while dynamically reprogramming the function of innate and adaptive immune cells. Aberrant activation of ER stress sensors and their downstream signalling pathways have therefore emerged as key regulators of tumour growth and metastasis as well as response to chemotherapy, targeted therapies and immunotherapy. In this Review, we discuss the physiological inducers of ER stress in the tumour milieu, the interplay between oncogenic signalling and ER stress response pathways in the cancer cell and the profound immunomodulatory effects of sustained ER stress responses in tumours.

Identification of BRaf-Sparing Amino-Thienopyrimidines with Potent IRE1α Inhibitory Activity

Amino-quinazoline BRaf kinase inhibitor 2 was identified from a library screen as a modest inhibitor of the unfolded protein response (UPR) regulating potential anticancer target IRE1α. A combination of crystallographic and conformational considerations were used to guide structure-based attenuation of BRaf activity and optimization of IRE1α potency. Quinazoline 6-position modifications were found to provide up to 100-fold improvement in IRE1α cellular potency but were ineffective at reducing BRaf activity. A salt bridge contact with Glu651 in IRE1α was then targeted to build in selectivity over BRaf which instead possesses a histidine in this position (His539). Torsional angle analysis revealed that the quinazoline hinge binder core was ill-suited to accommodate the required conformation to effectively reach Glu651, prompting a change to the thienopyrimidine hinge binder. Resulting analogues such as 25 demonstrated good IRE1α cellular potency and imparted more than 1000-fold decrease in BRaf activity.

Pharmacological Targeting of IRE1 in Cancer

IRE1α (inositol requiring enzyme 1 alpha) is one of the main transducers of the unfolded protein response (UPR). IRE1α plays instrumental protumoral roles in several cancers, and high IRE1α activity has been associated with poorer prognoses. In this context, IRE1α has been identified as a potentially relevant therapeutic target. Pharmacological inhibition of IRE1α activity can be achieved by targeting either the kinase domain or the RNase domain. Herein, the recent advances in IRE1α pharmacological targeting is summarized. We describe the identification and optimization of IRE1α inhibitors as well as their mode of action and limitations as anticancer drugs. The potential pitfalls and challenges that could be faced in the clinic, and the opportunities that IRE1α modulating strategies may present are discussed.