Le mésothéliome pleural est un cancer de la plèvre provoqué principalement par linhalation de fibres damiante. Nous avons émis lhypothèse que la dérégulation de lexpression génique est un paramètre important du développement de cette maladie. Or, les histones désacétylases (HDACs) peuvent jouer le rôle de répresseur transcriptionnel en modifiant la conformation de la chromatine. Dans ce contexte, nous avons étudié lactivité anticancéreuse du valproate, un inhibiteur dHDAC, en combinaison avec différents types de traitements utilisés en chimiothérapie. Nous avons démontré leffet synergique entre la chimiothérapie et le valproate dans des lignées cellulaires et dans des biopsies isolées à partir de patients. Nous avons étudié les processus impliqués dans lapoptose et révélé limplication des caspases, des espèces oxygéno-réactives et le rôle important de la protéine Bid. Nous avons ensuite réalisé une étude transcriptomique par microdamiers dans le but de mieux caractériser les mécanismes impliqués. Enfin, nous avons démontré lefficacité du valproate dans un modèle préclinique murin. Ces recherches ont permis la mise en place dun essai clinique de deuxième ligne sur des patients réfractaires à une première chimiothérapie.

Besides playing its structural function in cellular membranes, ceramide has been recognized as a bioactive signalling molecule playing roles in the regulation of cell growth, differentiation, senescence and programmed cell death. Apoptosis can be induced in cancer cells by elevation of endogenous ceramide levels in response to a variety of apoptotic stimuli such as cytokines (TNF, IL-1), death receptor ligands (Fas ligand), heat stress, oxidative stress, chemotherapeutic agents, and ionizing or ultraviolet radiation. It was shown that use of exogenous cell-permeable short-chain ceramide can also promote apoptotic pathways in cancer cells. Several studies have attempted to further define the specific role of ceramide in cell death. However, the mechanisms by which ceramide mediates antiproliferative pathways or inhibits prosurvival effects are not yet well-defined. So, we investigated the signalling pathways triggered by exogenously-supplied natural long chain ceramide, especially C16-ceramide, to better understand how this messenger induces its biological effects in cancer cells. We first showed that C16-ceramide induced a decrease in viability of adenocarcinoma cells (HCT116), partly due to apoptosis. Using two-dimensional differential in-gel electrophoresis (2D-DIGE) proteomic approach, we identified new proteins involved notably in cell proliferation, apoptosis, protein transport and transcriptional regulation in response to exogenous C16-ceramide. Among them, the death promoting factor Btf (Bcl-2-associated transcription factor) was found to be involved in the ceramide-dependent pro-apoptotic signalling pathway. Indeed, Btf-depleted colon cancer cells were found to be more resistant to death triggered by C16-ceramide. Transfection of GFP-Btf expression plasmid up-regulated p53 and BAX protein levels whereas pBcl-2 and Mdm2 expression were down-regulated. Furthermore, we identified a new signalling pathway specifically induced by C16-ceramide, depending on Btf and leading to down-regulation of the Mdm2 protein expression and MDM2 promoter activity. Thus, we provided new information on molecular mechanisms involved in the ceramide-mediated cell death. Then, we investigated the regulation of Emerin expression and its post-translational modifications induced by ceramide. We found that cAMP-dependent protein kinase A (PKA) could be involved in the C16-ceramide induced-Emerin phosphorylation. However, we did not demonstrate the interaction between Btf and phosphorylated-Emerin upon ceramide treatment. Nevertheless, we showed that one of the pathway induced by ceramide implies Emerin and leads to down-regulation of the MDM2 promoter activity. We also hypothesized that GCL (germ-cell-less) could be an intermediate in the Emerin-Mdm2 pathway triggered by C16-ceramide. Furthermore, we showed that Emerin-depleted cells were not more sensitive to apoptosis induced by C16-ceramide. These results should allow us to further explore the potential functions of Emerin in a ceramide-dependent pathway.