Metabolic adaptation to glucose limitation in Lung adenocarcinoma : the role of the Hexosamine Pathway and COPII vesicle transport

La vascularisation des tumeurs pulmonaires, hétérogène et peu efficace, génère des zones intra-tumorales pauvres en oxygène et nutriments. Pour survivre à ces conditions délétères, les cellules tumorales doivent s’adapter, mais les mécanismes de leur plasticité métabolique restent mal compris. Ces mécanismes adaptatifs contribuent à augmenter l’agressivité tumorale et la résistance aux traitements. Dans ce travail, en comparant des échantillons appariés tumoraux et non-tumoraux issus de patients, nous montrons que l’adénocarcinome pulmonaire (LUAD) présente une augmentation de la voie de biosynthèse des hexosamines (HBP). La voie HBP une branche métabolique qui utilise le glucose pour produire un sucre nucléotidique important pour les réactions de glycosylation. L’augmentation d’HBP est accompagnée par l’augmentation sélective des constituants des vésicules à COPII qui assurent le transport des protéines et lipides depuis le réticulum endoplasmique vers l’appareil de Golgi. Ces caractéristiques moléculaires sont récapitulées dans des lignées cellulaires de LUAD soumises à une limitation en glucose et leur assurent des fonctions protectrices. Au niveau mécanistique, l’augmentation d’HBP permet de lever un défaut lié à la limitation en glucose, dans l’ajout de résidus mannose sur les N-glycanes greffés aux protéines, dans le réticulum endoplasmique. Cette fonction inattendue de la voie HBP, ainsi que l’augmentation du système COPII, maintient l’expression à la membrane plasmique d’un sous-groupe de glycoprotéines incluant le récepteur pour l’EGF. Ce mécanisme s’oppose à la réduction de la croissance cellulaire indépendante de l’ancrage médiée par l’EGF. En accord avec ces résultats, l’augmentation d’expression de GFAT1, enzyme limitante de la voie HBP, corrèle avec l’activation du récepteur de l’EGF sauvage dans les tissus de patients LUAD. De plus, l’augmentation de la voie HBP et des constituants des COPII permettent de distinguer les LUAD des carcinomes épidermoïdes pulmonaire. Ainsi, nos résultats indiquent que la voie HBP et le système COPII jouent un rôle clé dans l’adaptation des LUAD à la carence nutritionnelle.Human lung tumors contain substantial heterogeneity of perfusion, such that many tumor cells reside in nutrient-and oxygen-poor microenvironments. Accordingly, cancer cells have to adapt for survival, but their metabolic plasticity remain incompletely understood. Notably, the successful adaptation to a harsh microenvironment further increases tumor aggression and resistance to antitumor treatments. In this study, using paired tumor-normal patient samples from non-small cell lung cancer (NSCLC), we found that the lung adenocarcinoma (LUAD) subtype exhibits a distinctive up-regulation of the metabolic hexosamine biosynthetic pathway (HBP), a side-branch pathway from glycolysis that synthesizes a major nucleotide sugar used in cellular glycosylation reactions. The HBP upregulation is accompanied by an increase in Coat protein complex II (COPII) components known to mediate trafficking of protein and lipid cargos from the ER towards the Golgi apparatus. The two molecular features are recapitulated under glucose scarcity, bestowing protective functions to LUAD cell lines. Mechanistically, HBP upregulation rescued a low glucose-induced deficiency of the first mannosylation step in the N-glycan building in the ER, rather than a deficiency in HBP-derived nucleotide sugar. This previously unknown function for the HBP, alongside the increased COPII-dependent transport, rescued the cell surface expression of a subset of glycoproteins, which included the epidermal growth factor receptor (EGFR). This mechanism counterbalanced the loss of the epidermal growth factor receptor (EGFR)-mediated anchorage-independent growth. Accordingly, expression of the HBP rate-limiting enzyme GFAT1 was correlated with wild type EGFR activation in LUAD patient samples. Notably, HBP and COPII upregulation distinguished LUAD from the lung squamous cell carcinoma subtype. Together, our data indicate that HBP and COPII play a key role in the adaptation of LUADs to low nutrient conditions

Modelling cancer metabolism in vitro : current improvements and future challenges

International audienceAdvances in cancer biology over the past decades have revealed that metabolic adaptation of cancer cells is an essential aspect of tumorigenesis. However, recent insights into tumour metabolism in vivo have revealed dissimilarities with results obtained in vitro. This is partly due to the reductionism of in vitro cancer models that struggle to reproduce the complexity of tumour tissues. This review describes some of the discrepancies in cancer cell metabolism between in vitro and in vivo conditions, and presents current methodological approaches and tools used to bridge the gap with the clinically relevant microenvironment. As such, these approaches should generate new knowledge that could be more effectively translated into therapeutic opportunities

ATF4-Dependent NRF2 Transcriptional Regulation Promotes Antioxidant Protection during Endoplasmic Reticulum Stress

International audienceEndoplasmic reticulum (ER) stress generates reactive oxygen species (ROS) that induce apoptosis if left unabated. To limit oxidative insults, the ER stress PKR-like endoplasmic reticulum Kinase (PERK) has been reported to phosphorylate and activate nuclear factor erythroid 2-related factor 2 (NRF2). Here, we uncover an alternative mechanism for PERK-mediated NRF2 regulation in human cells that does not require direct phosphorylation. We show that the activation of the PERK pathway rapidly stimulates the expression of NRF2 through activating transcription factor 4 (ATF4). In addition, NRF2 activation is late and largely driven by reactive oxygen species (ROS) generated during late protein synthesis recovery, contributing to protecting against cell death. Thus, PERK-mediated NRF2 activation encompasses a PERK-ATF4-dependent control of NRF2 expression that contributes to the NRF2 protective response engaged during ER stress-induced ROS production

Pemetrexed Hinders Translation Inhibition upon Low Glucose in Non-Small Cell Lung Cancer Cells

International audienceGenetic alterations in non-small cell lung cancers (NSCLC) stimulate the generation of energy and biomass to promote tumor development. However, the efficacy of the translation process is finely regulated by stress sensors, themselves often controlled by nutrient availability and chemotoxic agents. Yet, the crosstalk between therapeutic treatment and glucose availability on cell mass generation remains understudied. Herein, we investigated the impact of pemetrexed (PEM) treatment, a first-line agent for NSCLC, on protein synthesis, depending on high or low glucose availability. PEM treatment drastically repressed cell mass and translation when glucose was abundant. Surprisingly, inhibition of protein synthesis caused by low glucose levels was partially dampened upon co-treatment with PEM. Moreover, PEM counteracted the elevation of the endoplasmic reticulum stress (ERS) signal produced upon low glucose availability, providing a molecular explanation for the differential impact of the drug on translation according to glucose levels. Collectively, these data indicate that the ERS constitutes a molecular crosstalk between microenvironmental stressors, contributing to translation reprogramming and proteostasis plasticity

A non-canonical role of ELN protects from cellular senescence by limiting iron-dependent regulation of gene expression

International audienceThe ELN gene encodes tropoelastin which is used to generate elastic fibers that insure proper tissue elasticity. Decreased amounts of elastic fibers and/or accumulation of bioactive products of their cleavage, named elastokines, are thought to contribute to aging. Cellular senescence, characterized by a stable proliferation arrest and by the senescence-associated secretory phenotype (SASP), increases with aging, fostering the onset and progression of age-related diseases and overall aging, and has so far never been linked with elastin. Here, we identified that decrease in ELN either by siRNA in normal human fibroblasts or by knockout in mouse embryonic fibroblasts results in premature senescence. Surprisingly this effect is independent of elastic fiber degradation or elastokines production, but it relies on the rapid increase in HMOX1 after ELN downregulation. Moreover, the induction of HMOX1 depends on p53 and NRF2 transcription factors, and leads to an increase in iron, further mediating ELN downregulation-induced senescence. Screening of iron-dependent DNA and histones demethylases revealed a role for histone PHF8 demethylase in mediating ELN downregulation-induced senescence. Collectively, these results unveil a role for ELN in protecting cells from cellular senescence through a non-canonical mechanism involving a ROS/HMOX1/iron accumulation/PHF8 histone demethylase pathway reprogramming gene expression towards a senescence program

The hexosamine pathway and coat complex II promote malignant adaptation to nutrient scarcity

International audienceThe glucose-requiring hexosamine biosynthetic pathway (HBP), which produces UDP-N-acetylglucosamine for glycosylation reactions, promotes lung adenocarcinoma (LUAD) progression. However, lung tumor cells often reside in low-nutrient microenvironments, and whether the HBP is involved in the adaptation of LUAD to nutrient stress is unknown. Here, we show that the HBP and the coat complex II (COPII) play a key role in cell survival during glucose shortage. HBP up-regulation withstood low glucose-induced production of proteins bearing truncated N-glycans, in the endoplasmic reticulum. This function for the HBP, alongside COPII up-regulation, rescued cell surface expression of a subset of glycoproteins. Those included the epidermal growth factor receptor (EGFR), allowing an EGFR-dependent cell survival under low glucose in anchorage-independent growth. Accordingly, high expression of the HBP rate-limiting enzyme GFAT1 was associated with wild-type EGFR activation in LUAD patient samples. Notably, HBP and COPII up-regulation distinguished LUAD from the lung squamous-cell carcinoma subtype, thus uncovering adaptive mechanisms of LUAD to their harsh microenvironment

Identification of a miRNA multi-targeting therapeutic strategy in glioblastoma

Abstract Glioblastoma (GBM) is a deadly and the most common primary brain tumor in adults. Due to their regulation of a high number of mRNA transcripts, microRNAs (miRNAs) are key molecules in the control of biological processes and are thereby promising therapeutic targets for GBM patients. In this regard, we recently reported miRNAs as strong modulators of GBM aggressiveness. Here, using an integrative and comprehensive analysis of the TCGA database and the transcriptome of GBM biopsies, we identified three critical and clinically relevant miRNAs for GBM, miR-17-3p, miR-222, and miR-340. In addition, we showed that the combinatorial modulation of three of these miRNAs efficiently inhibited several biological processes in patient-derived GBM cells of all these three GBM subtypes (Mesenchymal, Proneural, Classical), induced cell death, and delayed tumor growth in a mouse tumor model. Finally, in a doxycycline-inducible model, we observed a significant inhibition of GBM stem cell viability and a significant delay of orthotopic tumor growth. Collectively, our results reveal, for the first time, the potential of miR-17-3p, miR-222 and miR-340 multi-targeting as a promising therapeutic strategy for GBM patients