Knockout of Vdac1 activates hypoxia-inducible factor through reactive oxygen species generation and induces tumor growth by promoting metabolic reprogramming and inflammation

BACKGROUND: Mitochondria are more than just the powerhouse of cells; they dictate if a cell dies or survives. Mitochondria are dynamic organelles that constantly undergo fusion and fission in response to environmental conditions. We showed previously that mitochondria of cells in a low oxygen environment (hypoxia) hyperfuse to form enlarged or highly interconnected networks with enhanced metabolic efficacy and resistance to apoptosis. Modifications to the appearance and metabolic capacity of mitochondria have been reported in cancer. However, the precise mechanisms regulating mitochondrial dynamics and metabolism in cancer are unknown. Since hypoxia plays a role in the generation of these abnormal mitochondria, we questioned if it modulates mitochondrial function. The mitochondrial outer-membrane voltage-dependent anion channel 1 (VDAC1) is at center stage in regulating metabolism and apoptosis. We demonstrated previously that VDAC1 was post-translationally C-terminal cleaved not only in various hypoxic cancer cells but also in tumor tissues of patients with lung adenocarcinomas. Cells with enlarged mitochondria and cleaved VDAC1 were also more resistant to chemotherapy-stimulated cell death than normoxic cancer cells. RESULTS: Transcriptome analysis of mouse embryonic fibroblasts (MEF) knocked out for Vdac1 highlighted alterations in not only cancer and inflammatory pathways but also in the activation of the hypoxia-inducible factor-1 (HIF-1) signaling pathway in normoxia. HIF-1α was stable in normoxia due to accumulation of reactive oxygen species (ROS), which decreased respiration and glycolysis and maintained basal apoptosis. However, in hypoxia, activation of extracellular signal-regulated kinase (ERK) in combination with maintenance of respiration and increased glycolysis counterbalanced the deleterious effects of enhanced ROS, thereby allowing Vdac1 (-/-) MEF to proliferate better than wild-type MEF in hypoxia. Allografts of RAS-transformed Vdac1 (-/-) MEF exhibited stabilization of both HIF-1α and HIF-2α, blood vessel destabilization, and a strong inflammatory response. Moreover, expression of Cdkn2a, a HIF-1-target and tumor suppressor gene, was markedly decreased. Consequently, RAS-transformed Vdac1 (-/-) MEF tumors grew faster than wild-type MEF tumors. CONCLUSIONS: Metabolic reprogramming in cancer cells may be regulated by VDAC1 through vascular destabilization and inflammation. These findings provide new perspectives into the understanding of VDAC1 in the function of mitochondria not only in cancer but also in inflammatory diseases

A Dialogue between the Hypoxia-Inducible Factor and the Tumor Microenvironment

The hypoxia-inducible factor is the key protein responsible for the cellular adaptation to low oxygen tension. This transcription factor becomes activated as a result of a drop in the partial pressure of oxygen, to hypoxic levels below 5% oxygen, and targets a panel of genes involved in maintenance of oxygen homeostasis. Hypoxia is a common characteristic of the microenvironment of solid tumors and, through activation of the hypoxia-inducible factor, is at the center of the growth dynamics of tumor cells. Not only does the microenvironment impact on the hypoxia-inducible factor but this factor impacts on microenvironmental features, such as pH, nutrient availability, metabolism and the extracellular matrix. In this review we discuss the influence the tumor environment has on the hypoxia-inducible factor and outline the role of this factor as a modulator of the microenvironment and as a powerful actor in tumor remodeling. From a fundamental research point of view the hypoxia-inducible factor is at the center of a signaling pathway that must be deciphered to fully understand the dynamics of the tumor microenvironment. From a translational and pharmacological research point of view the hypoxia-inducible factor and its induced downstream gene products may provide information on patient prognosis and offer promising targets that open perspectives for novel “anti-microenvironment” directed therapies

The role of the hypoxia-inducible factor in tumor metabolism growth and invasion.

Oxygen deprivation leading to hypoxia is a common feature of solid tumours. Under these conditions a signalling pathway involving a key oxygen-response regulator termed the hypoxia-inducible factor (HIF) is switched on. HIF is a transcription factor that, in hypoxia, drives the induction or repression of a myriad of genes controlling multiple cell functions such as angiogenesis, metabolism, invasion/metastasis and apoptosis/survival. Thus, the level of oxygen in a cell dictates the molecular response of cells through modulation of gene expression. Here we review the central role of HIF in cancer progression through the tumour response to hypoxia. Within this context the following aspects will be discussed: i) the mechanism by which oxygen deprivation inhibits two oxygen-sensor hydroxylases, thereby releasing the alpha subunit of HIF from programmed destruction by the ubiquitin-proteasome system and from a lock on its transcriptional activity; ii) the way in which the bi-transcriptional activity of HIF-alpha, which is regulated by the interplay between an oxygen-sensor attenuator and co-activators, determines the repertoire of gene expression; and iii) the role that HIF plays in tumour metabolism, in particular in glycolysis, and consequent acidification of the microenvironment, which influences both cell survival and cell death. Finally, the direct link of HIF to tumourigenesis and metastasis will be investigated and approaches for fighting tumour progression through a better understanding of HIF-mediated modulation of tumour metabolism and cell death will be considered

TRANSFERT DE GENE PAR UN VECTEUR NON VIRAL COMPOSE D'UNE SEQUENCE DE CIBLAGE DES INTEGRINES ET D'UN LIPOSOME CATIONIQUE (EFFICACITE ET DEVENIR INTRACELLULAIRE)

UN DES BUTS DE LA THERAPIE GENIQUE EST D'INTRODUIRE DANS UNE CELLULE UN GENE-MEDICAMENT AFIN DE CORRIGER UN DYSFONCTIONNEMENT DE SON PROGRAMME GENETIQUE. CETTE NOUVELLE THERAPEUTIQUE NECESSITE, LA PLUPART DU TEMPS, LA MISE AU POINT D'UNE VECTORISATION AFIN DE TRANSPORTER CE GENE-MEDICAMENT DANS LA CELLULE. NOUS AVONS AINSI MONTRE, DANS UN MODELE DE CELLULES TRACHEALES HUMAINES, UNE AUGMENTATION SPECIFIQUE D'UN FACTEUR 10 DE L'EXPRESSION D'UN PLASMIDE (ADNP) CODANT POUR LE GENE RAPPORTEUR LUCIFERASE LORSQUE CELUI-CI EST CONDENSE PAR UN PEPTIDE CYCLIQUE SPECIFIQUE DES INTEGRINES, COMPRENANT UNE SEQUENCE POLYLYSINE-ARG-GLY-ASP (K 1 6RGD). L'ADDITION D'UN LIPIDE CATIONIQUE AU COMPLEXE ADNP:K 1 6RGD PERMET D'OBTENIR DES NIVEAUX D'EXPRESSION COMPARABLES A CEUX OBTENUS AVEC UN ADENOVIRUS, EN AMELIORANT L'EFFICACITE DU VECTEUR D'UN FACTEUR 30. CE LIPOPOLYPLEXE (ADNP:K 1 6RGD : LIPIDE) PENETRE DANS LA CELLULE PAR ENDOCYTOSE MEDIEE PAR LES INTEGRINES, IMPLIQUANT LES PUITS RECOUVERTS DE CLATHRINE. L'AUGMENTATION DE L'EXPRESSION DU GENE RAPPORTEUR LUCIFERASE, EN PRESENCE DU LIPIDE, EST CORRELEE AVEC UNE AUGMENTATION DU PASSAGE DE L'ADNP DANS LES ENDOSOMES/LYSOSOMES, UNE DIMINUTION DE L'EXOCYTOSE DE L'ADNP ET UN MEILLEUR TRANSFERT NUCLEAIRE. LE TRAFIC INTRACELLULAIRE NECESSITE UNE FUSION ENDOSOMALE ET UN ENVIRONNEMENT VESICULAIRE ACIDE EST BENEFIQUE A L'EFFICACITE DU VECTEUR LIPIDIQUE. LE PASSAGE DE L'ADNP A TRAVERS L'ENVELOPPE NUCLEAIRE SERAIT UN MECANISME ACTIF IMPLIQUANT LES PORES NUCLEAIRES ET NE NECESSITANT PAS L'APPORT D'ELEMENTS CYTOSOLIQUES. LE LIPOPOLYPLEXE PEUT TRANSFECTER DES CELLULES QUIESCENTES MAIS SON ACTIVITE EST MULTIPLIEE PAR QUATRE SUR DES CELLULES EN MITOSE. DES ETUDES IN VIVO CHEZ LA SOURIS NOUS ONT PERMIS D'ETABLIR QUE L'HEMOGLOBINE MASQUAIT LA DETECTION DE L'ACTIVITE LUCIFERASE. UNE PERFUSION APPROPRIEE DES ORGANES PERMETTANT D'EXTRAIRE L'HEMOGLOBINE S'IMPOSE ALORS, AFIN DE DETERMINER L'EXPRESSION IN VIVO DU GENE RAPPORTEUR LUCIFERASE. CES TRAVAUX PARTICIPENT A L'AMELIORATION DES CONNAISSANCES DEVANT PERMETTRE A TERME, UNE OPTIMISATION DES VECTEURS NON VIRAUX NECESSAIRE A L'OBTENTION D'ESSAIS CLINIQUES CONCLUANTS.PARIS-BIUSJ-Thèses (751052125) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

The hypoxia-inducible factor and tumor progression along the angiogenic pathway.

International audienceThe hypoxia-inducible factor (HIF) is a transcription factor that plays a key role in the response of cells to oxygen levels. HIF is a heterodimer of alpha- and beta-subunits where the alpha-subunit is translated constitutively but has a very short half-life under normal oxygen concentrations. Negative regulation of the half-life and activity of the alpha-subunit is dependent on its posttranslational hydroxylation by hydroxylases that are dependent on oxygen for activity. Thus under low oxygen (hypoxic) conditions the hydroxylases are inactive and the alpha-subunit is stable and able to interact with the beta-subunit to bind and induce transcription of target genes. Hypoxic conditions are encountered in development and in disease states such as cancer. Tumors that have outstripped their blood supply become hypoxic and express high levels of HIF. HIF in turn targets genes that induce survival, glycolysis, and angiogenesis, a form of neovascularization, which ensures the tumor with a continued supply of oxygen and nutrients for further growth

La régulation de HIF-1α (Hypoxia-Inducible Factor-1α) : un air nouveau dans le domaine de l’hypoxie

L’angiogenèse, le processus conduisant à la formation de nouveaux vaisseaux sanguins à partir du réseau vasculaire préexistant, est finement régulée. La compréhension des mécanismes qui contrôlent son activité devrait permettre de nouvelles avancées dans le traitement de maladies comme le cancer ou dans le cas de désordres ischémiques. Dans le cas du cancer, la prolifération rapide des cellules tumorales induit une baisse de la concentration en oxygène ou hypoxie au cœur de la tumeur. Ce stress va servir de signal pour activer l’angiogenèse. Les vaisseaux sanguins qui irriguent la tumeur permettent d’une part la progression de la croissance tumorale via l’apport de nutriments, et d’autre part la formation de métastases. Le facteur HIF-1 (Hypoxia-Inducible Factor-1) joue un rôle crucial dans ce processus. HIF-1 est un hétérodimère constitué des sous-unités α et β. HIF-1α, stabilisé sous hypoxie, se transloque dans le noyau où il va pouvoir se dimériser avec la sous-unité HIF-1β pour activer ses gènes cibles. Parmi ces gènes, on retrouve le vegf (Vascular Endothelial Growth Factor) un facteur de croissance clé dans le processus de formation des vaisseaux sanguins. La protéine HIF-1α subit de multiples modifications post-traductionnelles dont les rôles exacts ne sont pas encore à ce jour totalement élucidés, mais qui sont la base de la régulation de la réponse des cellules à l’hypoxie. Dans cette revue, nous exposerons tout particulièrement les nombreuses modifications post-traductionnelles qui régulent l’activité de la protéine HIF-1α

Signalling via the hypoxia-inducible factor-1alpha requires multiple posttranslational modifications.

International audienceCellular hypoxia, a local decrease in the oxygen concentration below normal (21%) atmospheric concentrations, occurs in both physiological and pathological situations. The transcriptional complex Hypoxia-Inducible Factor-1 (HIF-1) is the key player in the signalling pathway that controls the hypoxic response of mammalian cells. Tight regulation of this response involves posttranslational modification of the alpha subunit of HIF-1. Hydroxylation, ubiquitination, acetylation, S-nitrosation and phosphorylation have been shown to determine its half-life and/or transcriptional activity. The precise spatio-temporal occurrence of these multiple modifications is still not fully understood but is dependent on the microenvironment and determines the driving force of variable cellular responses

ARDent about acetylation and deacetylation in hypoxia signalling

Copyright © 2006 Elsevier Ltd All rights reserved.Given the key role that the α subunit of the αβ heterodimeric transcription factor hypoxia-inducible factor-1 (HIF-1) has in tumourigenesis, and in particular in angiogenesis, a full understanding of its regulation is crucial to the development of cancer therapeutics. Posttranslational acetylation and deacetylation of this subunit by an acetyltransferase called Arrest-defective-1 (ARD1) and by different histone deacetylases (HDACs), respectively, has been suggested as a mechanism. However, conflicting data bring into question the foundations of this mechanism and at present it is not clear what the precise role of these proteins is with respect to HIF. Nonetheless, the observation that small-molecule inhibitors of HDACs have anti-angiogenic activity suggests that acetylation and deacetylation of HIF or HIF modifiers represents a potential target in cancer therapy.Rebecca Bilton, Eric Trottier, Jacques Pouysségur and M. Christiane Brahimi-Hornhttp://www.sciencedirect.com/science/journal/0962892