Induction of ferroptotic death in pancreatic cancer cells : essential role of cysteine and the xCT transporter ; Induction de la mort ferroptotique dans les cellules de cancer pancréatique : rôle essentiel de la cystéine et du transporteur xCT

When compared with normal, non-transformed counterparts, cancer cells exhibit a modified proliferation profile, supported by intensified metabolic activity. Consequently, this leads to greater requirements of the cancer cells for nutrients, but also for antioxidant defence that can counteract increased production of reactive oxygen species (ROS) as a necessary by-product of the metabolism. Cysteine is an amino acid with a dual function within the cell. Indeed, in addition to its proteogenic role like all the other 21 amino acids, cysteine plays an important role in the antioxidant functions of the cell. Namely, cysteine is a rate-limiting amino acid for synthesis of the major redox molecule of the cell: the glutathione (GSH). GSH serves as a reducing equivalent for many antioxidant enzymes, including large family of peroxidases (glutathione peroxidases, GPx), such as GPx4 that ensures the reduction of lipid peroxides in the membrane compartment of the cell. The maintenance of an intracellular cysteine level is done by a set of incompletely characterized transporters, among which the best known is xCT – the transporter of the oxidized form of cysteine (cystine). This transporter is part of a minimal set' of transporters overexpressed in the majority of cancers, together with LAT1 and ASCT1/2. A disbalance in the intracellular cysteine and glutathione homeostasis leads to disturbed cellular redox status, an accumulation of lipid peroxides, and finall to a recently described non-apoptotic type of cell death named ferroptosis. In this thesis, we initially investigated the impact of a genetic invalidation (CRISPR-Cas9) of the xCT transporter on different pancreatic ductal adenocarcinoma (PDAC) cell lines. The resulting xCT-KO cells exhibit nutrient stress with an activation of the GCN2/ATF4 pathway and an inhibition of general protein synthesis via mTORC1 suppresion. In addition, these cells undergo ferroptosis unless alternative source of cysteine (N-acetylcysteine, NAC) is added. Indeed, the depletion of glutathione in these cells induces a notable accumulation of lipid peroxides, thus compromising the membrane integrity of cells. Therefore, according to the data, the xCT/cysteine/GSH/GPx4 axis seems crucial for ferroptotic cell death in PDAC cells. Subsequently, in the second part of this thesis, we look at the role played by glutathione in the occurrence of ferroptosis, independently of intracellular cysteine. For this we invalidated the catalytic subunit of the gene responsible for its biosynthesis, γ-Glutamate Cysteine Ligase (GCLC). These GCLC-KO cells also undergo cell death