Postdoctoral fellow, Emory University
Investigation of the mechanisms by which agonists and transcriptional coactivators activate LRH-1
Liver receptor homolog 1 is an orphan nuclear hormone receptor that regulates diverse biological processes, including metabolism, proliferation, and the resolution of endoplasmic reticulum stress. LRH-1 has great potential as a therapeutic target for metabolic diseases and cancer but development of LRH-1 modulators has been difficult. Chemical scaffolds exist that are capable of activating LRH-1, however the mechanisms of activation are unknown. X-ray crystallography and other structural methods are used to explore receptor-ligand interactions associated with LRH-1 activation by a set of related agonists with similar efficacies but dramatically different binding modes. Molecular dynamics simulations elucidate the important roles of pi-stacking and polar interactions in mediating differing binding modes, and subsequently different mechanisms of action for the two agonists. A network of conserved water molecules near the ligand-binding site, important for activation by both agonists, is explored. Additionally, the mechanism of LRH-1 coactivation by Peroxisome proliferator-activated gamma coactivator 1-a (PGC1α), a coactivator for LRH-1, is explored in comparison with Nuclear Receptor Coactivator-2 (Tif2). LRH-1 binds PGC1α with higher affinity than Tif2. Molecular dynamics reveal that PGC1a induces correlated atomic motion throughout the activation function surface of LRH-1, while Tif2 induces weaker signaling at the activation function surface, instead promoting allosteric signaling from the Helix 6/b-sheet region of LRH-1. This work i) reveals complexities associated with LRH-1 agonist development, ii) offers insight into rational design strategies, and iii) Illuminates strategies for selective therapeutic targeting of PGC1α dependent LRH1 signaling pathways.
Abstract: Liver receptor homolog 1 (NR5A2, LRH-1) is an orphan nuclear hormone receptor that regulates diverse biological processes, including metabolism, proliferation, and the resolution of endoplasmic reticulum stress. While preclinical and cellular studies demonstrate that LRH-1 has great potential as a therapeutic target for metabolic diseases and cancer, development of LRH-1 modulators has been difficult. Recently, systematic modifications to one of the few known chemical scaffolds capable of activating LRH-1 failed to improve efficacy substantially. Moreover, mechanisms through which LRH-1 is activated by synthetic ligands are entirely unknown. Here, we use x-ray crystallography and other structural methods to explore conformational changes and receptor-ligand interactions associated with LRH-1 activation by a set of related agonists. Unlike phospholipid (PL) LRH-1 ligands, these agonists bind deep in the pocket and do not interact with residues near the mouth, nor do they expand the pocket like PLs. Unexpectedly, two closely related agonists with similar efficacies (GSK8470 and RJW100) exhibit completely different binding modes. The dramatic repositioning is influenced by a differential ability to establish stable, face-to-face π-π-stacking with LRH-1 residue H390, as well as by a novel polar interaction mediated by the RJW100 hydroxyl group. The differing binding modes result in distinct mechanisms of action for the two agonists. Finally, we identify a network of conserved water molecules near the ligand-binding site that are important for activation by both agonists. This work reveals a previously unappreciated complexity associated with LRH-1 agonist development and offers insights into rational design strategies.
Pub.: 30 Sep '16, Pinned: 28 Jun '17