Le catabolisme exacerbé du glucose et de la glutamine est actuellement reconnu comme une caractéristique des cellules cancéreuses, qui leur procure un avantage prolifératif via la production et l’accumulation de plusieurs métabolites au niveau du microenvironnement. Parmi ces métabolites, l’acide lactique représente une molécule de signalisation clé, favorisant la migration et les métastases. Mon projet de thèse s’inscrit dans le contexte d’une étude du métabolisme glycolytique associé aux cellules tumorales à division rapide. Durant ce projet, nous nous sommes intéressés à la caractérisation génétique et fonctionnelle des transporteurs MCT (MonoCarboxylate Transporters) 1 et 4, qui sont des symporteurs H+/lactate dont l’expression membranaire et la fonctionnalité requièrent la liaison avec une protéine chaperonne : CD147/BASIGINE (BSG). Afin de mieux explorer la physiologie des complexes MCT/BSG, et valider le ciblage de l’export d’acide lactique comme une nouvelle approche anti-cancer, nous avons développé une stratégie visant à invalider le gène BSG et/ou MCT4, en utilisant la technologie des Zinc Finger Nucleases (ZFN), dans des lignées cellulaires cancéreuses humaines de côlon, poumon et glioblastome. D’abord, nous avons démontré, que l’effet pro-tumoral majeur de BSG est lié à son action directe sur la stabilisation des MCTs au niveau des tumeurs glycolytiques et non pas à la production des metalloprotéases. Ensuite, nous avons démontré pour la première fois que l’inhibition concomitante de MCT1 et MCT4 est nécessaire pour induire une baisse significative de la tumorigénécité in vivo. / Enhanced glucose and glutamine catabolism has become a recognized feature of cancer cells, leading to accumulation of metabolites in the tumour microenvironment, which offers growth advantages to tumours. Among these metabolites is emerging as a key signalling molecule that plays a pivotal role in cancer cell migration and metastasis. In this thesis, we focused on the genetic and functional characterization of monocarboxylate transporters (MCT) 1 and 4, which are H+/lactate symporters that require an interaction with an ancillary protein, CD147/BASIGIN (BSG), for their plasma membrane expression and function. To further explore the physiology of MCT/BSG complexes and validate the blockade of lactic acid export as an anti-cancer strategy, we designed experiments using Zinc Finger Nuclease mediated BSG and/or MCT4 gene knockouts in human colon adenocarcinoma, lung carcinoma and glioblastoma cell lines. First of all, we demonstrated that the major protumoural action of BSG is to control the energetics of glycolytic tumours via MCT1/4 activity and not to produce matrix metalloproteases. Second, we showed for the first time that combined inhibition of both MCT1 and MCT4 transporters is required to achieve a significant reduction in the tumour growth in vivo. Moreover, our findings reported that disruption of the BSG gene dramatically reduced the plasma membrane expression and lactate transport activity of both MCT1 and MCT4, leading to increased accumulation of intracellular pools of lactic and pyruvic acids, decreased intracellular pH and reduced rate of glycolysis.

Toll-like receptors (TLRs) are a major group of pattern recognition receptors expressed on the surface of immune cells that recognize molecular patterns associated with all classes of pathogenic microorganisms. TLR4 recognizes the lipopolysaccharide component of Gram-negative bacterial cell walls and is the only TLR known to induce signaling through both the MyD88 and TRIF pathways. Basigin, a ubiquitous cell adhesion molecule, is a member of the immunoglobulin superfamily that has the ability to influence cell signaling mediated by the MyD88 and TRIF pathways, the same signaling pathways induced by the TLR4 receptor protein. Analysis of the Basigin protein sequence indicates the presence of a hydrophilic glutamate residue within the hydrophobic transmembrane domain, but no consensus binding sites for MyD88 or TRIF. The purpose of this study was to determine if Basigin uses TLR4 for signal transduction. It is hypothesized that Basigin interacts with TLR4 and that the glutamate residue plays a role in the interaction. Enzyme-linked immunosorbent binding assays were performed using endogenous TLR4 and recombinant Basigin proteins. These analyses demonstrated that binding of Basigin to TLR4 was significantly greater than that of the control protein and that the glutamate residue in the Basigin transmembrane domain does play a role in the interaction between Basigin and TLR4 as well as many hydrophobic residues in the Basigin transmembrane domain. The data suggest that Basigin interacts with TLR4 to influence signaling cascades using MyD88 and TRIF.

Although it was once thought that neurons solely rely on glucose as a substrate for cellular energy production, it is now known that small monocarboxylate molecules, like pyruvate, lactate, and ketone bodies, are also utilized. Monocarboxylates are transported across plasma membranes via facilitated diffusion using a family of transport proteins known as monocarboxylate transporters (MCTs). Four MCTs (MCT1, MCT2, MCT3, and MCT4) are expressed within neural tissues. Expression of the MCTs has been tied to co-expression of a cell adhesion molecule belonging to the Basigin subset of the immunoglobulin superfamily (IgSF). Basigin gene products are known to interact with MCT1 and MCT4 in the mammalian neural retina and this association is essential to support the cellular energy needs of photoreceptors. A previous study indicated that Basigin gene products use hydrophobic amino acids within specific regions of the transmembrane domain to interact with MCT1. In the present study, it is hypothesized that the same amino acids within the transmembrane domain are used to interact with MCT4, but that no association exists with MCT2, which typically interacts with a different member of the IgSF subset. Therefore, the purpose of the present study was to assess the association between Basigin gene products and MCT4, and with MCT2. Recombinant proteins corresponding to the transmembrane domain of Basigin gene products were used in in vitro binding assays with endogenous MCT2 and MCT4 from mouse brain protein lysates. Contrary to the hypothesis, it was determined that the transmembrane domain of Basigin gene products binds to both MCT2 and MCT4 in vitro. Different amino acids within the transmembrane domain of Basigin gene products are used for each association and the pattern is different from that used in the association with MCT1. The data suggest that Basigin plays multiple roles in the nervous system.

Basigin and Embigin are members of the immunoglobulin superfamily that function as cell adhesion molecules. Studies of Basigin null mice revealed reproductive sterility, increased pain sensitivity, and blindness. It is thought that the mechanism causing blindness involves misexpression of monocarboxylate transporter 1 (MCT1) in the absence of Basigin. It is known that the transmembrane domain of Basigin interacts with MCT1. In the absence of Basigin, MCT1 does not localize to the plasma membrane of expressing cells and photoreceptor function is disrupted. Studies of the Basigin null mouse brain suggest that MCT1 is properly expressed, which suggests a separate mechanism causes the increased pain sensitivity in these animals, and also that a different protein directs MCT1 to the plasma membrane of expressing cells in mouse brain. Embigin is known to interact with MCT2 in neurons and with MCT1 in erythrocytes. It is not known, however, if Embigin normally interacts with MCT1 in the mouse brain or if Embigin acts to compensate for the lack of Basigin in the Basigin null animals. Therefore, the purpose of this study was to determine if Embigin normally interacts with MCT1, 2, or 4 in the mouse brain and if so, whether the interaction is similar to that between Basigin and MCT1. Expression of Basigin, Embigin, MCT1, MCT2, and MCT4 in mouse brain was assessed via immunoblotting and immunohistochemical analyses. In addition, recombinant protein probes corresponding to the Embigin transmembrane domain were generated for ELISA binding assays using endogenous mouse brain MCTs. It was determined that the proteins in question are rather ubiquitously expressed throughout the mouse brain, and that the cell adhesion molecules Basigin and Embigin may be co-expressed in the same cells as the MCT2 and MCT4 transporter proteins. In addition, it was determined that the Embigin transmembrane domain does not interact with the MCTs. The data therefore suggest that MCTs do not require Basigin or Embigin for plasma membrane expression in mouse brain.