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Depuis 2018, le cancer du sein est la forme de cancer la plus répandue chez les femmes au Canada et représente environ 26 % de tous les cas de cancer. Chaque jour, 80 femmes reçoivent un diagnostic de cancer du sein et 15 décèdent de cette maladie. En raison de son hétérogénéité, le cancer du sein est divisé en sous-types, caractérisés par l’expression de récepteurs aux estrogènes (ER), de récepteurs à la progestérone (PR) et de récepteurs du facteur de croissance épidermique humain 2 (HER2), ou son absence. Le cancer du sein triple négatif (TNBC) n’exprime pas ER, PR et HER2 et est connu pour son risque métastatique élevé. Par conséquent, il ne peut pas être ciblé par les thérapies hormonales traditionnelles et la chimiothérapie reste le traitement le plus utilisé pour le moment. Il est donc essentiel de trouver de nouvelles pistes qui pourraient être utilisées comme cibles thérapeutiques dans le traitement du TNBC. Le récepteur nucléaire NR5A2, communément appelé le récepteur hépatique homologue 1 (LRH-1), est un récepteur nucléaire orphelin important dans la régulation de nombreux processus biologiques. Il a déjà été prouvé que LRH-1 favorise la progression de nombreux cancers, dont le TNBC, mais ses mécanismes moléculaires ne sont pas encore bien définis dans ce type de cancer. Afin de déterminer le rôle de LRH-1 dans la progression du TNBC, cette étude s’est concentrée sur l’identification de ses interactions avec des cofacteurs ou des facteurs de transcription pour mieux comprendre comment il régule l’expression des gènes importants dans la progression de ce type de cancer du sein. L’immunoprécipitation de la chromatine suivie du séquençage (ChIP-Seq), réalisée dans le modèle cellulaire MDA-MB-231, a permis d’identifier les régions spécifiques au TNBC qui sont liées par LRH-1. Pour déterminer le potentiel de discussion croisée avec LRH-1, ces régions ont été superposées avec les données ChIP-Seq pour des facteurs déjà connus pour promouvoir le TNBC : JUNB, YAP

The nuclear receptor LRH-1 (Liver Receptor Homolog-1, NR5A2) is a transcription factor that regulates gene expression programs critical for many aspects of metabolism and reproduction. Although LRH-1 is able to bind phospholipids, it is still considered an orphan nuclear receptor (NR) with an unknown regulatory hormone. Our prior cellular and structural studies demonstrated that the signaling phosphatidylinositols PI(4,5)P2 (PIP2) and PI(3,4,5)P3 (PIP3) bind and regulate SF-1 (Steroidogenic Factor-1, NR5A1), a close homolog of LRH-1. Here, we describe the crystal structure of human LRH-1 ligand binding domain (LBD) bound by PIP3 - the first phospholipid with a head group endogenous to mammals. We show that the phospholipid hormone binds LRH-1 with high affinity, stabilizing the receptor LBD. While the hydrophobic PIP3 tails (C16/C16) are buried inside the LRH-1 ligand binding pocket, the negatively charged PIP3 head group is presented on the receptor surface, similar to the phosphatidylinositol binding mode observed in the PIP3-SF-1 structure. Thus, data presented in this work reinforce our earlier findings demonstrating that signaling phosphatidylinositols regulate the NR5A receptors LRH-1 and SF-1.

NR5A2 is a nuclear receptor which regulates the expression of genes involved in cholesterol metabolism, pluripotency maintenance and cell differentiation. It has been recently shown that DLPC, a NR5A2 ligand, prevents liver steatosis and improves insulin sensitivity in mouse models of insulin resistance, an effect that has been associated with changes in glucose and fatty acids metabolism in liver. Because skeletal muscle is a major tissue in clearing glucose from blood, we studied the effect of the activation of NR5A2 on muscle metabolism by using cultures of C2C12, a mouse-derived cell line widely used as a model of skeletal muscle. Treatment of C2C12 with DLPC resulted in increased levels of expression of GLUT4 and also of several genes related to glycolysis and glycogen metabolism. These changes were accompanied by an increased glucose uptake. In addition, the activation of NR5A2 produced a reduction in the oxidation of fatty acids, an effect which disappeared in low-glucose conditions. Our results suggest that NR5A2, mostly by enhancing glucose uptake, switches muscle cells into a state of glucose preference. The increased use of glucose by muscle might constitute another mechanism by which NR5A2 improves blood glucose levels and restores insulin sensitivity.

Liver receptor homolog 1 (nuclear receptor LRH-1, NR5A2) is an essential regulator of gene transcription, critical for maintenance of cell pluripotency in early development and imperative for the proper functions of the liver, pancreas, and intestines during the adult life. Although physiological hormones of LRH-1 have not yet been identified, crystallographic and biochemical studies demonstrated that LRH-1 could bind regulatory ligands and suggested phosphatidylinositols as potential hormone candidates for this receptor. No synthetic antagonists of LRH-1 are known to date. Here, we identify the first small molecule antagonists of LRH-1 activity. Our search for LRH-1 modulators was empowered by screening of 5.2 million commercially available compounds via molecular docking followed by verification of the top-ranked molecules using in vitro direct binding and transcriptional assays. Experimental evaluation of the predicted ligands identified two compounds that inhibit the transcriptional activity of LRH-1 and diminish the expression of the receptor's target genes. Among the affected transcriptional targets are co-repressor SHP (small heterodimer partner) as well as cyclin E1 (CCNE1) and G0S2 genes that are known to regulate cell growth and proliferation. Treatments of human pancreatic (AsPC-1), colon (HT29), and breast adenocarcinoma cells T47D and MDA-MB-468 with the LRH-1 antagonists resulted in the receptor-mediated inhibition of cancer cell proliferation. Our data suggest that specific antagonists of LRH-1 could be used as specific molecular probes for elucidating the roles of the receptor in different types of malignancies.

Fushi tarazu factor-1 (FTZ-F1) genes belong to the nuclear receptor family 5A (NR5A). The distribution pattern of NR5A genes in teleosts suggests that they control functions separate to, or in addition to, those of other vertebrates. In mammals NR5A1 genes, including steroidogenic factor-1 (SF-1), are primarily involved in steroidogenesis. NR5A2 contain the alpha-fetoprotein transcription factor (FTF) genes, which protect mammalian embryos against maternal estrogens, and are involved in cholesterol transfer and metabolism. In this study we have analysed the expression of two Arctic char FTZ-F1 forms belonging to the NR5A2 group. The expression starts during early development and the transcripts are present in embryonic liver/pancreas and gonadal regions. The genes are up-regulated during embryogenesis as the embryo develops towards hatch, as shown by increased mRNA and protein levels. In adult Arctic char the FTZ-F1 forms are primarily located to tissues involved in steroidogenesis as well as cholesterol metabolism. Thus, a division of NR5A into SF-1 (NR5A1) and FTF (NR5A2) specific functions does not appear to have occurred in teleosts.