Identification of the couple GSK3α/c-Myc as a new regulator of hexokinase II in benzo[a]pyrene-induced apoptosis.

International audienceThe early apoptotic events induced by environmental pollutants with carcinogenic properties are poorly understood. Here, we focus on the early cytotoxic effects of benzo[a]pyrene (B[a]P). In F258 rat hepatic epithelial cells, B[a]P induces intrinsic apoptosis via a mitochondrial dysfunction characterized by the release of hexokinase II (HKII) from the mitochondria. Cancer cells often have an anomalous cell energy metabolism; since HKII dysfunction regulates B[a]P-induced apoptosis in F258 cells, but may also alter cell energy metabolism, HKII release from the mitochondria may represent an important B[a]P-related carcinogenic issue. Thus in the present study, we aimed at deciphering the mechanisms underlying HKII dysfunction upon B[a]P exposure. We show that while glycogen synthase kinase 3 beta (GSK3β) regulated the expression of HKII at the transcriptional level, glycogen synthase kinase 3 alpha (GSK3α) was involved in B[a]P-induced apoptosis via a decrease in c-Myc expression. The reduced level of c-Myc caused the relocation of HKII from the mitochondria to the cytosol, thereby being involved in the formation of reactive oxygen species and apoptosis. In conclusion, we show that the couple GSK3α/c-Myc plays a key role in B[a]P-induced early apoptotic cell signaling via HKII dysfunction

Unprecedented incorporation of α-emitter radioisotope 213Bi into porphyrin chelates with reference to a daughter isotope mediated assistance mechanism.

International audienceFor the first time, α-emitter radioisotope (213)Bi has been incorporated into porphyrin chelates, with rates matching with the short period of the radionuclide. An in situ transmetalation mechanism involving the daughter isotope (209)Pb is expected to boost the (213)Bi radiolabeling process

RIPK1 protects from TNF-α-mediated liver damage during hepatitis

Cell death of hepatocytes is a prominent characteristic in the pathogenesis of liver disease, while hepatolysis is a starting point of inflammation in hepatitis and loss of hepatic function. However, the precise molecular mechanisms of hepatocyte cell death, the role of the cytokines of hepatic microenvironment and the involvement of intracellular kinases, remain unclear. Tumor necrosis factor alpha (TNF-alpha) is a key cytokine involved in cell death or survival pathways and the role of RIPK1 has been associated to the TNF-alpha-dependent signaling pathway. We took advantage of two different deficient mouse lines, the RIPK1 kinase dead knock-in mice (Ripk1K45A) and the conditional knockout mice lacking RIPK1 only in liver parenchymal cells (Ripk1LPC-KO), to characterize the role of RIPK1 and TNF-alpha in hepatitis induced by concanavalin A (ConA). Our results show that RIPK1 is dispensable for liver homeostasis under steady-state conditions but in contrast, RIPK1 kinase activity contributes to caspase-independent cell death induction following ConA injection and RIPK1 also serves as a scaffold, protecting hepatocytes from massive apoptotic cell death in this model. In the Ripk1LPC-KO mice challenged with ConA, TNF-alpha triggers apoptosis, responsible for the observed severe hepatitis. Mechanism potentially involves both TNF-independent canonical NF-kappa B activation, as well as TNF-dependent, but canonical NF-kappa B-independent mechanisms. In conclusion, our results suggest that RIPK1 kinase activity is a pertinent therapeutic target to protect liver against excessive cell death in liver diseases

A role for lipid rafts in the protection afforded by docosahexaenoic acid against ethanol toxicity in primary rat hepatocytes.

International audience: Previously, we demonstrated that eicosapentaenoic acid enhanced ethanol-induced oxidative stress and cell death in primary rat hepatocytes via an increase in membrane fluidity and lipid raft clustering. In this context, another n-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA), was tested with a special emphasis on physical and chemical alteration of lipid rafts. Pretreatment of hepatocytes with DHA reduced significantly ethanol-induced oxidative stress and cell death. DHA protection could be related to an alteration of lipid rafts. Indeed, rafts exhibited a marked increase in membrane fluidity and packing defects leading to the exclusion of a raft protein marker, flotillin. Furthermore, DHA strongly inhibited disulfide bridge formation, even in control cells, thus suggesting a disruption of protein-protein interactions inside lipid rafts. This particular spatial organization of lipid rafts due to DHA subsequently prevented the ethanol-induced lipid raft clustering. Such a prevention was then responsible for the inhibition of phospholipase C-γ translocation into rafts, and consequently of both lysosome accumulation and elevation in cellular low-molecular-weight iron content, a prooxidant factor. In total, the present study suggests that DHA supplementation could represent a new preventive approach for patients with alcoholic liver disease based upon modulation of the membrane structures

TRAIL induces a new necrotic cell death pathway at acidic extracellular pH.

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Modulation de la sensibilité à TRAIL (TNF-a-related apoptosis-inducing ligand) par le glutathion et le pH

Ce travail de thèse montre le rôle du glutathion (GSH) et du pH dans la sensibilité des cellules cancéreuses à la mort cellulaire induite par TRAIL (TNF-a-related apoptosis-inducing ligand). La diminution du taux intracellulaire de GSH par la buthionine-sulfoximine (BSO) augmente la sensibilité des cellules humaines d'adénocarcinome colique HT29 et d'hépatocarcinome HepG2 à l'apoptose induite par l'association de TRAIL avec le cisplatine ou le 5-fluoro-uracile. L'expression de la protéine Bcl-2 reste un facteur de résistance même en présence de BSO. Les hépatocytes humains ne sont sensibles qu'à la combinaison TRAIL/cisplatine. Par ailleurs la diminution du pH extracellulaire à une valeur comparable à celle observée au niveau des tumeurs (pH 6.5), sensibilise les cellules cancéreuses mais pas les hépatocytes humains à une mort cellulaire nécrotique dépendante des récepteurs de mort, TRAIL-R1 et TRAIL-R2, des caspases et de la protéine kinase RIP (Receptor-Interacting-Protein).RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Rôle des caractéristiques membranaires et du récepteur de mort Fas dans l apoptose induite par le cisplatine

Le cisplatine, agent anti-cancéreux utilisé dans le traitement des tumeurs solides, induit la mort des cellules cancéreuses via la formation d adduits à l ADN. Toutefois, ces lésions ne suffisent pas à expliquer sa cytotoxicité et la membrane plasmique pourrait être une autre cible du cisplatine. L objectif de ce travail était de déterminer le rôle des caractéristiques membranaires (radeaux lipidiques et fluidité) en relation avec l échangeur Na+/H+ NHE1, la sphingomyélinase acide et le récepteur de mort Fas dans l apoptose induite par le cisplatine dans une lignée cancéreuse colique humaine. Nous avons montré que le cisplatine inhibe précocement NHE1, conduisant à une acidification intracellulaire qui favoriserait l activation de la sphingomyélinase acide entraînant la production de céramide membranaire, l augmentation de la fluidité membranaire, l agrégation des radeaux lipidiques en plateformes de signalisation, la redistribution du récepteur de mort Fas dans ces radeaux lipidiques, et finalement la réorganisation des filaments d actine et la mort des cellules. Ces événements membranaires sont précoces et indépendants de la formation d adduits à l ADN. Cette étude a permis d identifier la cascade des évènements membranaires dans l apoptose induite par le cisplatine et a révélé de nouvelles cibles de cet agent anti-cancéreux qui, dès lors qu elles seraient dérégulées, pourraient conduire à une chimiorésistance des cellules cancéreuses.Cisplatin, an anticancer agent widely used in treatment of solid tumors, induces cancer cell death through the formation of DNA adducts. However, these lesions are not sufficient to explain cisplatin cytotoxicity and plasma membrane could be an other important target of this agent. The aim of my work was to determine the role of membrane properties (lipid rafts and membrane fluidity) in relation with Na+/H+ exchanger-1 NHE1, acid sphingomyelinase and Fas death receptor in cisplatin-induced cell death in human colon cancer cell line. We have shown that cisplatin induces a rapid inhibition of NHE1, leading to intracellular acidification which favors acid sphingomyelinase activation, membrane ceramide generation, membrane fluidification, lipid raft aggregation, Fas death receptor redistribution into rafts, actin cytoskeleton reorganization and apoptosis. These early membrane events are independent of DNA adducts formation. This study revealed new targets of cisplatin. A disregulation of these targets could induce cancer cells chemoresistance.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Vecteur recombinant pour la production et la sécrétion de séquences d'acides aminés d'intérêt par les bactéries propioniques et ses applications.

La présente invention concerne un vecteur recombinant pour l'expression et la sécrétion, par une bactérie propionique, d'une ou plusieurs séquences d'acides aminés d'intérêt, ledit vecteur comprenant au moins : - sous le contrôle d'au moins un promoteur approprié, - au moins une séquence nucléotidique codant un peptide signal de bactérie propionique et, en fusion traductionnelle avec celle-ci, - une ou plusieurs séquences nucléotidiques codant la ou lesdites séquences d'acides aminés d'intérêt. L'invention s'intéresse également aux utilisations d'un tel vecteur dans le domaine pharmaceutique ou pour la production à grande échelle de peptides ou protéines d'intérêt