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

ABSTRACT: 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-1? 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-1? and HIF-2?, 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.

SUBMITTER: Brahimi-Horn MC

PROVIDER: S-EPMC4551760 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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

Brahimi-Horn M Christiane MC Giuliano Sandy S Saland Estelle E Lacas-Gervais Sandra S Sheiko Tatiana T Pelletier Joffrey J Bourget Isabelle I Bost Frédéric F Féral Chloé C Boulter Etienne E Tauc Michel M Ivan Mircea M Garmy-Susini Barbara B Popa Alexandra A Mari Bernard B Sarry Jean-Emmanuel JE Craigen William J WJ Pouysségur Jacques J Mazure Nathalie M NM

Cancer & metabolism 20150826

<h4>Background</h4>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 ...[more]

PMID: 26322231

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Project description:Excessive production of mitochondrial reactive oxygen species (ROS) is a central mechanism for the development of diabetes complications. Recently, hypoxia has been identified to play an additional pathogenic role in diabetes. In this study, we hypothesized that ROS overproduction was secondary to the impaired responses to hypoxia due to the inhibition of hypoxia-inducible factor-1 (HIF-1) by hyperglycemia. The ROS levels were analyzed in the blood of healthy subjects and individuals with type 1 diabetes after exposure to hypoxia. The relation between HIF-1, glucose levels, ROS production and its functional consequences were analyzed in renal mIMCD-3 cells and in kidneys of mouse models of diabetes. Exposure to hypoxia increased circulating ROS in subjects with diabetes, but not in subjects without diabetes. High glucose concentrations repressed HIF-1 both in hypoxic cells and in kidneys of animals with diabetes, through a HIF prolyl-hydroxylase (PHD)-dependent mechanism. The impaired HIF-1 signaling contributed to excess production of mitochondrial ROS through increased mitochondrial respiration that was mediated by Pyruvate dehydrogenase kinase 1 (PDK1). The restoration of HIF-1 function attenuated ROS overproduction despite persistent hyperglycemia, and conferred protection against apoptosis and renal injury in diabetes. We conclude that the repression of HIF-1 plays a central role in mitochondrial ROS overproduction in diabetes and is a potential therapeutic target for diabetic complications. These findings are timely since the first PHD inhibitor that can activate HIF-1 has been newly approved for clinical use. This work was supported by grants from the Swedish Research Council, Stockholm County Research Council, Stockholm Regional Research Foundation, Bert von Kantzows Foundation, Swedish Society of Medicine, Kung Gustaf V:s och Drottning Victorias Frimurarestifelse, Karolinska Institute's Research Foundations, Strategic Research Programme in Diabetes, and Erling-Persson Family Foundation for S-B.C.; grants from the Swedish Research Council and Swedish Heart and Lung Foundation for T.A.S.; and ERC consolidator grant for M.M.

Project description:Mitochondria are subcellular organelles that are more than just the powerhouse of cells, they also dictate if a cell dies or survives. The mitochondrial outer-membrane voltage-dependent anion channel 1 (VDAC1) has been shown to play a crucial role in metabolism and apoptosis, however its involvement in ischemic pathologies and cancer is not clear. Transcriptome analysis of Vdac1-/- mouse embryonic fibroblasts (MEF) highlighted cancer and inflammation as top diesases but also activation of the HIF-1 signaling pathway in normoxia. HIF-1α protein was stable due to ROS accumulation that decreased respiration and glycolysis and maintained basal apoptosis. However, in hypoxia increased activation of ERK in combination with maintenance of respiration and increased glycolysis counterbalanced the deleterious effects of ROS, thereby allowing Vdac1-/- MEF to proliferate better than wild-type MEF. Xenografts of RAS-transformed Vdac1-/- MEF in mice showed stabilization of both HIF-1α and HIF-2α which led to blood vessel destabilization and a strong inflammatory response. Moreover, expression of Cdkn2a, a HIF-1-target and tumor suppressor gene, was strongly decreased. Consequently RAS-transformed Vdac1-/- MEF tumors grew faster than wild-type MEF tumors. These findings provide new perspectives into the understanding of VDAC1 in the function of mitochondria not only in cancer but also in inflammatory diseases. Profiling of VDAC1-/- and wild-type (Wt) Mouse Embryonic Fibroblasts (MEFs) was performed using whole genome mouse microarrays. in normoxic or hypoxic conditions. MEF (Wt and Vdac1-/-) were incubated in normoxia (Nx, ie: 20% O2) or hypoxia (Hx, ie: 1% O2) for 72h and then lysed prior to RNA isolation, labelling and hybridization on microarrays. One color experiment with 2 biological replicates (marked 1 or 2) of the 4 experimental conditions. One condition (MEF WT Nx2) has been removed from the statistical analysis after microarray quality check due to high background. Total of 7 samples.

Dataset Information

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

Publications

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

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