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In Arabidopsis thaliana, the High-Affinity Transport System (HATS) for root NO3 - uptake depends mainly on four NRT2 transporters, namely NRT2.1, NRT2.2, NRT2.4 and NRT2.5. The HATS is the target of many regulations to coordinate nitrogen (N) acquisition with the N status of the plant and with carbon (C) assimilation through photosynthesis. At the molecular level, C and N signaling pathways have been shown to control gene expression of the NRT2 transporters. Although several regulators of these transporters have been identified in response to either N or C signals, the response of NRT2 genes expression to the interaction of these signals has never been specifically investigated and the underlying molecular mechanisms remain largely unknown. To address this question we used an original systems biology approach to model a regulatory gene network targeting NRT2.1, NRT2.2, NRT2.4 and NRT2.5 in response to N/C signals. Our systems analysis of the data highlighted the potential role of three putative transcription factors, TGA3, MYC1 and bHLH093. Functional analysis of mutants combined with yeast one hybrid experiments confirmed that all 3 transcription factors are regulators of NRT2.4 or NRT2.5 in response to N or C signals.

Tumours rely on external amino acids (AA) uptake to maintain their exacerbated metabolism and proliferation. To optimize AA uptake, tumors overexpress key carriers such as the multifunctional CD98/LAT 1 heterodimer. CD98 (SLC3A2) acts as a co-receptor of β integrins and enhances signaling that promotes cellular migration and invasion. LAT1 (SLC7A5) is responsible for the transport of essential AA. Previous studies have suggested that the CD98/integrin axis of the complex is essential for tumour growth, while LAT1 activity is dispensible. However, the increased nutritional requirements of tumor cells led us to hypothesize that the proliferative advantage given by this complex is in fact supported by the AA transporter activity of LAT1 and not by the CD98/integrin activity. In this context, I have shown that genetic or pharmacological invalidation of LAT1 in various tumor cell lines leads to a complete removal of the sodium-independent leucine transport. This leads to a loss of AA homeostasis with activation of the GCN2 stress pathway, inhibition of mTORC1 and supression of tumour growth. In addition, genetic invalidation of CD98 did not result in any detectable phenotype. However, inhibition of the residual activity of LAT1 in CD98 knockout cells is sufficient to abolish their tumorigenicity. Thus, my results clearly demonstrate the fundamental role of LAT1 in tumour growth and advocate the pharmacology development of LAT1 transporter inhibitors as very promising anticancer agents.; Dans le but de maintenir leur métabolisme et leur prolifération exacerbée, les tumeurs sont dépendantes d’un apport accru en acides aminés. Afin d'optimiser cet apport, les tumeurs surexpriment certains transporteurs clés tels que l'hétérodimère multifonctionnel CD98/LAT1. CD98 (SLC3A2) agit comme co-récepteur des intégrines β et amplifie leur signalisation régulant ainsi la migration et l'adhésion cellulaire. La protéine LAT1 (SLC7A5) est quant à elle responsable du transport des acides aminés (AA) essentiels. Des études antérieures ont suggéré que la fonction CD98/intégrines du complexe est essentielle à la croissance tumorale, alors que LAT1 aurait un rôle mineur dans ce contexte. Cependant, les besoins nutritifs accrus des cellules tumorales nous ont conduit à émettre l’hypothèse contraire selon laquelle l’avantage prolifératif donné par ce complexe serait en réalité supporté par l’activité du transporteur LAT1 et non pas par l’interaction CD98/intégrine. Dans ce contexte, j’ai montré que l’invalidation génétique ou pharmacologique de LAT1 dans différentes lignées tumorales entraine une suppression totale du transport de la leucine, sodium-indépendant. Ceci entrainant une perte d’homéostasie des AA avec l’activation de la voie de stress GCN2, l’inhibition de mTORC1 et la suppression de la croissance tumorale. De plus, l’invalidation génétique de CD98 ne s’est traduite par aucun phénotype visible. Cependant, la suppression de l'activité résiduelle de LAT1 de ces cellules est suffisante pour abolir leur potentiel tumoral. Ainsi, mes résultats démontrent le rôle clé de LAT1 dans la croissance tumorale en faisant ainsi une cible thérapeutique prometteuse.

Tumours rely on external amino acids (AA) uptake to maintain their exacerbated metabolism and proliferation. To optimize AA uptake, tumors overexpress key carriers such as the multifunctional CD98/LAT 1 heterodimer. CD98 (SLC3A2) acts as a co-receptor of β integrins and enhances signaling that promotes cellular migration and invasion. LAT1 (SLC7A5) is responsible for the transport of essential AA. Previous studies have suggested that the CD98/integrin axis of the complex is essential for tumour growth, while LAT1 activity is dispensible. However, the increased nutritional requirements of tumor cells led us to hypothesize that the proliferative advantage given by this complex is in fact supported by the AA transporter activity of LAT1 and not by the CD98/integrin activity. In this context, I have shown that genetic or pharmacological invalidation of LAT1 in various tumor cell lines leads to a complete removal of the sodium-independent leucine transport. This leads to a loss of AA homeostasis with activation of the GCN2 stress pathway, inhibition of mTORC1 and supression of tumour growth. In addition, genetic invalidation of CD98 did not result in any detectable phenotype. However, inhibition of the residual activity of LAT1 in CD98 knockout cells is sufficient to abolish their tumorigenicity. Thus, my results clearly demonstrate the fundamental role of LAT1 in tumour growth and advocate the pharmacology development of LAT1 transporter inhibitors as very promising anticancer agents., Dans le but de maintenir leur métabolisme et leur prolifération exacerbée, les tumeurs sont dépendantes d’un apport accru en acides aminés. Afin d'optimiser cet apport, les tumeurs surexpriment certains transporteurs clés tels que l'hétérodimère multifonctionnel CD98/LAT1. CD98 (SLC3A2) agit comme co-récepteur des intégrines β et amplifie leur signalisation régulant ainsi la migration et l'adhésion cellulaire. La protéine LAT1 (SLC7A5) est quant à elle responsable du transport des acides aminés (AA) essentiels. Des études antérieures ont suggéré que la fonction CD98/intégrines du complexe est essentielle à la croissance tumorale, alors que LAT1 aurait un rôle mineur dans ce contexte. Cependant, les besoins nutritifs accrus des cellules tumorales nous ont conduit à émettre l’hypothèse contraire selon laquelle l’avantage prolifératif donné par ce complexe serait en réalité supporté par l’activité du transporteur LAT1 et non pas par l’interaction CD98/intégrine. Dans ce contexte, j’ai montré que l’invalidation génétique ou pharmacologique de LAT1 dans différentes lignées tumorales entraine une suppression totale du transport de la leucine, sodium-indépendant. Ceci entrainant une perte d’homéostasie des AA avec l’activation de la voie de stress GCN2, l’inhibition de mTORC1 et la suppression de la croissance tumorale. De plus, l’invalidation génétique de CD98 ne s’est traduite par aucun phénotype visible. Cependant, la suppression de l'activité résiduelle de LAT1 de ces cellules est suffisante pour abolir leur potentiel tumoral. Ainsi, mes résultats démontrent le rôle clé de LAT1 dans la croissance tumorale en faisant ainsi une cible thérapeutique prometteuse.

Peut-on orienter le transfert membranaire des nutriments par une limitation de l'ingestion ou un apport en fibres dans l'aliment ?

Membrane potential generation via malate/lactate exchange catalyzed by the malate carrier (MleP) of Lactococcus lactis, together with the generation of a pH gradient via decarboxylation of malate to lactate in the cytoplasm, is a typical example of a secondary proton motive force-generating system, The mleP gene was cloned, sequenced, and expressed in a malolactic fermentation-deficient L. lactis strain. Functional analysis revealed the same properties as observed in membrane vesicles of a malolactic fermentation-positive strain. MleP belongs to a family of secondary transporters in which the citrate carriers from Leuconostoc mesenteroides (CitP) and Klebsiella pneumoniae (CitS) ass; found also. CitP, but not CitS, is also involved in membrane potential generation via electrogenic citrate/lactate exchange, MleP, CitP, and CitS were analyzed for their substrate specificity, The 2-hydroxycarboxylate motif R1R2COHCOOH, common to the physiological substrates, was found to be essential for transport although same 2-oxocarboxylates could be transported to a lesser extent. Clear differences ill substrate specificity among the transporters were observed because of different tolerances toward the R substituents at the C2 atom, Both MleP and CitP transport a broad range of 2-hydroxycarboxylates with R substituents ranging in size from two hydrogen atoms (glycolate) to acetyl and methyl groups (citromalate) for MleP and two acetyl groups (citrate) for CitP. CitS was much less tolerant and transported only citrate and at a low rats citromalate. The substrate specificities are discussed in the context of the physiological function of the transporters.