Biology subjects

Chevet, E.

Publications and source records attributed to Chevet, E..

11 recordsLinked to original sources

bioRxiv2026

RBM25 selectively stabilizes XBP1s mRNA independently of splicing factor activity

The unfolded protein response (UPR) preserves endoplasmic reticulum (ER) proteostasis through coordinated transcriptional and translational programs that promote adaptation and prevents apoptosis. A central component of this response is the IRE1-XBP1 signaling axis, in which IRE1-mediated unconventional splicing of XBP1 mRNA generates the active transcription factor XBP1s. While the mechanisms governing IRE1 activation and XBP1 splicing have been extensively characterized, the post-transcriptional processes that sustain XBP1s expression remain poorly understood. Here, we identify RNA-binding motif protein 25 (RBM25) as a key post-transcriptional regulator of the UPR that selectively stabilizes spliced XBP1 mRNA during ER stress. RBM25 binds the XBP1s 3' untranslated region and prolongs XBP1s mRNA half-life without affecting unspliced XBP1u transcripts or IRE1-dependent regulated decay (RIDD) targets. Consequently, RBM25 depletion diminishes XBP1 transcriptional output, compromises adaptive UPR signaling, and sensitizes cells to ER stress-induced death across multiple stress paradigms. Together, our findings uncover a previously unrecognized RNA-based regulatory checkpoint that amplifies and sustains XBP1 signaling, thereby tuning the magnitude of the adaptive UPR and cellular survival under proteotoxic stress.

molecular biology↗

bioRxiv2026

STING dampens the unfolded protein response to enable the presentation of self-antigens on MHC-I during inflammation.

A growing body of evidence supports the contribution of the long-lasting adaptive immune system in Parkinsons disease (PD). We showed that the PD-associated protein PINK1 negatively regulates the presentation of mitochondrial antigens (MitAP) on MHC-I molecules. In vivo evidence indicated that MitAP activation in mice, in the absence of PINK1, led to cytotoxic CD8+ T cell stimulation and severe motor impairments, reversible by L-DOPA. We show here that following TLR4 activation, MitAP is engaged through a pathway involving cGAS-STING, which acts as a rheostat to dampen the unfolded protein response (UPR). Without STING, the stress response is amplified, leading to a translational attenuation that inhibits the expression of XBP1s, a transcription factor required for MitAP. STING activity also regulates the repertoire of peptides displayed at the cell surface during inflammation, highlighting a potential role in immunosurveillance. These findings establish STING and the UPR as key immune regulators targetable for therapeutic intervention during autoimmune diseases and PD.

immunology↗

bioRxiv2024

IRE1-dependent GOLIM4 expression controls protein secretion to modulate glioblastoma cell adhesion and migration

One of the main glioblastoma (GB) features is the diffuse migration of the tumor cells within the surrounding brain parenchyma, rendering almost impossible the complete tumor resection and irradiation, leading to inexorable lethal relapse of the disease. In the past years, we demonstrated that IRE1 (hereafter IRE1), one of the Endoplasmic Reticulum (ER) stress sensors, plays a key role in GB biology by impacting on immune infiltration, angiogenesis and tumor cell migration/invasion, all these features being linked to an alteration of protein secretion. In the present study, we investigated if and how IRE1 could regulate the functionality of the secretory machinery in GB cells and identified GOLIM4, a Golgi-associated molecule whose expression is regulated downstream of IRE1 through the transcription of XBP1s. Interestingly, GOLIM4 silencing led to decreased surface expression of multiple molecules including MHC class I molecules, growth factor receptors (PDGFRA and IL13RA2) and proteins involved in cell-cell adhesion (CD44, CD54, NCAM1), adhesion to matrix (ITGB1) or cell migration (CD90) without alteration of their encoding transcripts expression levels. Moreover, GOLIM4 silencing phenotypically affected GB cell-cell adhesion and cell migration in multiple models. Overall, we have described a novel IRE1/XBP1s/GOLIM4 operon that controls the secretion of specific proteins and impacts the tumor aggressiveness. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=100 SRC="FIGDIR/small/619629v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@511636org.highwire.dtl.DTLVardef@18971f6org.highwire.dtl.DTLVardef@98ff81org.highwire.dtl.DTLVardef@ae7189_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2023

LRRK2 regulates the activation of the unfolded protein response and antigen presentation in macrophages during inflammation

While the contribution of inflammation in the pathological process leading to Parkinsons disease (PD) is well established, a growing body of evidence supports a role for the long-lasting adaptive immune system in the disease. We showed that, in inflammatory conditions, the PD-proteins PINK1 and Parkin negatively regulate the presentation of mitochondrial antigens on MHC I molecules, a process referred to as MitAP (Mitochondrial Antigen Presentation). In the absence of PINK1, over-activation of this pathway in antigen-presenting cells (APCs) engages autoimmune mechanisms leading to the establishment of cytotoxic CD8+ T cells. Co-culture of dopaminergic neurons (DNs) with these T cells led to neuronal cell death, suggesting that the MitAP in DNs made them susceptible to T cell-mediated destruction. In the present study, we used a pharmacological and genetic approach to characterize the MitAP pathway at the molecular level. We showed that this antigen presentation pathway is induced in APCs in response to inflammatory signals through the sequential activation of TLR4, cGAS-STING and the Unfolded Protein Response (UPR). A "UPR motif" present on a STING cytoplasmic domain was shown to specifically activate the UPR sensor IRE1. Remarkably, the PD-related protein LRRK2, acted with STING upstream of the UPR to regulate the transition from innate to adaptive immunity, thereby identifying this PD-related protein as a key player in the immune response during inflammation.

immunology↗

bioRxiv2022

Integrative analysis of genomic and transcriptomic alterations of AGR2 and AGR3 in cancer

The AGR2 and AGR3 genes have been shown by numerous groups to be functionally associated to adenocarcinoma progression and metastasis. We explore in this paper the data available in databases concerning genomic and transcriptomic features concerning these two genes: the NCBI dbSNP database was used to explore the presence and roles of constitutional SNPs, and the NCI, CCLE and TCGA databases were used to explore somatic mutations and copy number variations (CNVs), as well as mRNA expression of these genes in human cancer cell lines and tumours. Relationships of AGR2/3 expression with whole genome mRNA expression and cancer features (i.e. mutations and CNVs of oncogenes and tumour suppressor genes [TSG]) were established using CCLE and TCGA databases. In addition, the CCLE data concerning CRISPR gene extinction screens (Achilles project) were explored concerning these two genes and a panel of oncogenes and TSG. We observed that no functional polymorphism or recurrent mutation could be detected in AGR2 or AGR3. The expression of these genes was positively correlated with the expression of epithelial genes and inversely correlated with that of mesenchymal genes. It was also significantly associated with several cancer features, such as TP53 or SMAD4 mutations, depending on the gene and the cancer type. The CRISPR screens revealed in addition the absence of cell fitness modification upon gene extinction, in contrast to oncogenes (cell fitness decrease) and TSG (cell fitness increase). Overall, these explorations revealed that AGR2 and AGR3 proteins appear as common non-genetic evolutionary factors in the process of human tumorigenesis.

cancer biology↗

bioRxiv2021

Anterior Gradient-2 (AGR2) overexpression in colon cancer: a potential prognostic biomarker

BackgroundColon cancer is one of the most common leading causes of death worldwide. Prognostic at an early stage is an efficient way to decrease mortality. The Endoplasmic Reticulum (ER)-resident protein anterior gradient-2 (AGR2), a Protein Disulfide Isomerase (PDI) is highly expressed in various tumours and is involved in tumour-associated processes. This study aims at examining the expression of AGR2 protein in colon cancer. MethodsAGR2 protein expression was determined using immunohistochemistry on tissue samples issued from a cohort of 82 colorectal carcinomas. ResultsAGR2 protein expression was significantly higher in tumours than in adjacent nontumour controls. AGR2 expression subgroup analyses indicated that AGR2 low expression in colon cancer patients was significantly associated with worse overall survival. Mucinous colon cancers exhibited higher AGR2 expression levels than non-mucinous cancers. Additionally, tumours with microsatellite instability (MSI) were characterised by a strong upregulation of AGR2 mRNA and protein expression despite an absence of MLH1/MSH2 mutations. ConclusionsOur findings indicate that high AGR2 protein expression is correlated with longer patient survival and that AGR2 overexpression is associated with MSI tumours and could represent an MSI biomarker. Overall, AGR2 might serve as a biomarker to stratify colon tumours and to contribute to the prognosis of colon cancer patients.

cancer biology↗

bioRxiv2021

p97/VCP induces GLI1 to control XBP1-dependent endoplasmic reticulum stress transcriptional response

Upon accumulation of improperly folded proteins in the ER, an adaptive pathway named the UPR is triggered to restore ER homeostasis. The induction of stress genes controlling ER dynamics is a condition sine qua non for an effective UPR. Although this requirement has been extensively characterized, the transcriptional mechanism underlying this process remains in part elucidated. Here, we show that p97/VCP, an AAA+ ATPase known to modulate ER stress-induced gene expression, dynamically interacts with RUVBL2 and the mSin3A-HDAC1/2 complex. Further analysis of the mechanism defined a novel interplay between the aforementioned molecules and the transcription factor USF2 to control expression of GLI1, a primary effector of Hedgehog (Hh) signaling. Under basal conditions, GLI1 is repressed by RUVBL2-mSin3A-HDAC1/2 while upon ER stress GLI1 is induced through a mechanism requiring p97/VCP-mediated extraction of the repressor complex. Further analysis showed that GLI1 cooperate with ATF6f to activate the expression of XBP1, a transcription factor regulating the expression of genes controlling cellular stress response, under ER conditions. Overall, our work demonstrates that p97/VCP orchestrates the activation of GLI1 upon ER stress in a Hh ligand-independent fashion and defines the interplay between the newly identified p97/VCP-mSin3A-HDAC1/2 complex and the transcription factor USF2 as an essential player in this process.

cancer biology↗

bioRxiv2021

SARS-CoV2 envelop proteins reshape the serological responses of COVID-19 patients

The SARS-CoV-2 pandemic has elicited a unique international mobilization of the scientific community to better understand this coronavirus and its associated disease and to develop efficient tools to combat infection. Similar to other coronavirae, SARS-CoV-2 hijacks the host cell complex secretory machinery to produce properly folded viral proteins that will compose the nascent virions; including Spike, Envelope and Membrane proteins, the most exposed membrane viral proteins to the host immune system. Antibody response is part of the anti-viral immune arsenal that infected patients develop to fight viral particles in the body. Herein, we investigate the immunogenic potential of Spike (S), Envelope (E) and Membrane (M) proteins using a human cell-based system to mimic membrane insertion and N-glycosylation. We show that both S and M proteins elicit the production of specific IgG, IgM and IgA in SARS-CoV-2 infected patients. Elevated Ig responses were observed in COVID+ patients with moderate and severe forms of the disease. Finally, when SARS-CoV-2 Spike D614 and G614 variants were compared, reduced Ig binding was observed with the Spike G614 variant. Altogether, this study underlines the needs for including topological features in envelop proteins to better characterize the serological status of COVID+ patients, points towards an unexpected immune response against the M protein and shows that our assay could represent a powerful tool to test humoral responses against actively evolving SARS-CoV-2 variants and vaccine effectiveness.

cell biology↗

bioRxiv2020

Protein homeostasis imprinting across evolution

Protein homeostasis (a.k.a. proteostasis) is associated with the primary functions of life, and therefore with evolution. However, it is unclear how the cellular proteostasis machines have evolved to adjust the protein biogenesis needs to environmental constraints. Herein, we describe a novel computational approach, based on semantic network analysis, to evaluate proteostasis differentiation during evolution. We show that the molecular components of the proteostasis network (PN) are reliable metrics to deconvolute the life forms into Archaea, Bacteria and Eukarya and to assess the evolution rates among species. Topological properties of semantic graphs were used as new criteria to evaluate PN complexity of 93 Eukarya, 250 Bacteria and 62 Archaea, thus representing a novel strategy for taxonomic classification. This functional analysis provides information about species divergence and pointed towards taxonomic clades that evolved faster than others. Kingdom-specific PN were identified, suggesting that PN complexity correlates evolution. Through the analysis of gene conservation, we found that the gains or losses that occurred throughout PN evolution revealed a dichotomy within both the PN conserved modules and within kingdom-specific modules. Since the PN is implicated in cell fitness, aging and disease onset, it could be used as a new metric to tackle mechanisms underlying gain-of-functions, and their biological ramifications.

bioinformatics↗

bioRxiv2020

Reflux of Endoplasmic Reticulum proteins to the cytosol yields inactivation of tumor suppressors

In the past decades many studies reported Endoplasmic Reticulum (ER) resident proteins to localize to the cytosol but the mechanisms by which this occurs and whether these proteins exert cytosolic functions remain unknown. We found that select ER luminal proteins accumulate in the cytosol of glioblastoma cells isolated from mouse and human tumors. In cultured cells ER protein reflux to the cytosol occurs upon proteostasis perturbation. As such we investigated whether refluxed proteins gain new functions in the cytosol thus providing advantage to tumor cells. Using the ER luminal protein AGR2 as a model, we showed that it is refluxed to the cytosol where it binds and inhibits the tumor suppressor p53. We named this phenomenon ER to Cytosol Signaling (ERCYS) as an ER surveillance mechanism conserved in Eukaryotes to relieve the ER from its contents upon stress and to provide selective advantage to tumor cells through gain-of-cytosolic functions.

cell biology↗

bioRxiv2019

Constitutive IRE1α signaling maintains glioblastoma cell differentiation

Endoplasmic Reticulum (ER) proteostasis control and the Unfolded Protein Response (UPRER) have been shown to contribute to tumor development and aggressiveness. As such, the UPRER sensor IRE1 (referred to as IRE1 hereafter) is a major regulator of glioblastoma (GBM) development and is an appealing therapeutic target. To document IRE1 suitability as an antineoplastic pharmacological target, we investigated how this protein contributed to GBM cell reprogramming, a property involved in treatment resistance and disease recurrence. Probing the IRE1 activity molecular signature on transcriptome datasets of human tumors, showed that high IRE1 activity correlated with low expression of the main GBM stemness transcription factors SOX2, SALL2, POU3F2 and OLIG2. Henceforth, this phenotype was pharmacologically and genetically recapitulated in immortalized and primary GBM cell lines as well as in mouse models. We demonstrated that constitutive activation of the IRE1/XBP1/miR148a signaling axis repressed the expression of SOX2 and led to maintenance of a differentiation phenotype in GBM cells. Our results describe a novel role for IRE1 signaling in maintaining differentiated tumor cell state and highlight opportunities of informed IRE1 modulation utility in GBM therapy.

cancer biology↗