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Unfolded protein response (UPR) is a complex cellular mechanism induced upon ER stress caused by various environmental factors. Single spanning signal transducers of UPR were reported to recognise also lipid-induced ER stress. Studies of these transducers, namely PERK and IRE1 uncovered that they can sense change in membrane properties and activate themselves by clustering. Moreover, signal transducer IRE1 retained ability to sense changes in the membrane properties with TMD exchanged for a polyLeu α-helix. It was thus unclear what mechanism drives lipid-induced UPR via IRE1. We employed model membrane system in form of LUVs, where properties of membranes can be readily altered by specific lipid composition. As a simplified model of the UPR signal transducers in the ER, synthetic transmembrane peptides with polyLeu core were used. Dynamic light scattering (DLS) has been used for qualitative and semi-quantitative analysis of LUVs. Clustering of synthetic peptides was determined by time resolved anisotropy of fluorescence. DLS results demonstrate successful formation of vesicles with a desired size in all planned composition. On the contrary to the studies in living cells, the presence of cholesterol or palmitic acid in model membranes did not induce the aggregation of transmembrane peptides....

Le domaine transmembranaire des récepteurs membranaires est aujourd’hui considéré comme essentiel dans l’activation et la régulation des voies de signalisation sous-jacentes. Ceci est tout particulièrement le cas pour neuropiline-1 et -2 (NRP1/2), et ErbB2, trois récepteurs impliqués dans la croissance tumorale. Notre laboratoire a initialement démontré qu’un peptide ciblant le domaine transmembrane du récepteur NRP1, bloque l’oligomérisation de ce récepteur et provoque ainsi l’inhibition de la prolifération/migration des cellules tumorales et l’angiogenèse in vivo. L’objectif principal de ce travail de thèse était d’élargir cette stratégie aux récepteurs membranaires NRP2 et ErbB2, et ce, dans le contexte du cancer du sein. Mes travaux montrent que ces peptides inhibent la pousse tumorale et les métastases associées dans différents modèles de cancer du sein. Les effets anti-tumoraux peuvent s’expliquer par les propriétés anti-angiogéniques et anti-prolifératives des peptides démontrées in vitro et in vivo. J’ai également disséqué le mécanisme d’action du peptide ErbB2 et montré que le peptide inhibiteur de NRP2 induit des effets secondaires rédhibitoires (promotion des métastases osseuses). Dans l’ensemble, mes recherches valident le potentiel thérapeutique de cette stratégie peptidique et renforce l’idée d’un développement clinique de ces composés. D’une terre inconnue à une terre d’espoir, le cœur de la membrane est incontestablement une nouvelle source d’inspiration pour le développement des médicaments de demain. / The role of transmembrane domains (TMD) in membrane receptor activation and regulation is nowadays appearing as a key step of cell signaling. This has been indeed evaluated for neuropilin-1 and -2 (NRP1/2) and ErbB2 receptors, three membrane receptors whose signaling has clearly been implicated in tumorigenesis. Our team had demonstrated that a synthetic peptide blocking the transmembrane domain of NRP1 blocked NRP1-dependent signaling leading to the inhibition of glioma cell proliferation/migration and tumor associated angiogenesis in vivo. The major goal of this thesis project was to extend this novel strategy to NRP2 and ErbB2 in the breast cancer context. Thus, I was able to demonstrate for the first time that the use of peptides, inhibiting the TMD of these receptors, was able to inhibit tumor growth and related metastases in vivo, in three different breast cancer mouse models that I have developed in the laboratory. These results were supported by in vitro experiments demonstrating anti-proliferative and anti-angiogenic properties of these peptides. Besides, I was able to dissect the mechanism of action of the peptide targeting ErbB2 receptor in vitro and in vivo, and I provided data excluding NRP2 as a target because of an unexpected promotion of bone metastasis. Altogether, my data offer convincing evidences to further develop MTP-ErbB2 and MTP-NRP1 peptides as novel therapeutic compounds for patients suffering metastatic cancers. From terra incognita to the exploration of a world of hope, the heart of the membrane is becoming a new promising estate for drug design.

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