Liver receptor homolog-1 (LRH-1; NR5A2) is a phospholipid-sensing nuclear receptor (NR) expressed predominantly in the liver, pancreas, and ovaries that plays an important role in metabolic physiologies and pathophysiologies. Specifically, it has been characterized to regulate bile acid metabolism, cholesterol homeostasis, and steroidogenesis, and in turn is involved in various disease states such as type 2 diabetes, atherosclerosis, nonalcoholic fatty liver disease as well as a multitude of cancers. These diseases are all risk factors for metabolic syndrome that affects nearly a third of the US population. This represents a significant health concern as individuals diagnosed with metabolic syndrome have increased risk for developing cardiovascular diseases as well as hepatocellular, gastric, and colon cancers; cancers that have been associated with overexpression of LRH-1. This suggests LRH-1 to be a promising therapeutic target for such metabolic diseases and cancers. However, a lack of a wholistic understanding of the receptors regulatory mechanism presents a significant limitation to the success of LRH-1 as a therapeutic target. Similar to other nuclear receptors, LRH-1's activity is tightly regulated via a multitude of pathways including cellular localization, ligand binding, DNA binding, post-translational modifications, and coregulator interactions. Cellular localization is central to these pathways as it determines the receptors milieu and thus available interacting partners. While, multiple nuclear localization signals and nuclear export signals have been identified to facilitate receptor shuttling in and out of the nucleus, there is no information regarding LRH-1 intranuclear trafficking, a key process that directly modulates DNA binding and transcriptional output. This propels the need to develop effective and specific tools to modulate LRH-1 localization and activity. While the use of chemical approaches to probe NRs in metabolism has increased over the years, the use of chemoproteomics in this area remains limited. Proteomic analysis of nuclear receptors remains problematic as they are relatively low abundant and tightly bound to chromatin. As such, there is a need for tools to probe and capture endogenous LRH-1 and LRH-1 transcriptional complexes. I propose the following specific aims to develop and employ LRH-1 specific chemoproteomic tools to elucidate the role of acetylation and a novel coregulator lamina associated polypeptide 2 (LAP2) in regulating LRH-1 intranuclear trafficking and signaling.
In Aim 1, I will establish two LRH-1 specific probes to more efficiently modulate and/or capture LRH-1 and LRH-1 transcriptional complexes. These include a biotinylated LRH-1 response element oligo probe and SR1848, small molecule inhibitor of LRH-1 signaling.
In Aim 2, I will identify LRH-1 acetylated residues and validate LAP2 isoforms as novel LRH-1 coregulators that coordinate to fine tune LRH-1 intranuclear trafficking and subsequent signaling. Elucidation of this regulatory pathway will directly enhance understanding of LRH-1 signaling driving hepatic cancer and other metabolic diseases.
Liver receptor homolog-1 (LRH-1) is a phospholipid sensing nuclear receptor that regulates a range of diverse cellular processes including bile acid metabolism, cholesterol homeostasis, and steroidogenesis. Aberrant receptor function has been characterized to drive metabolic syndrome risk factors such as type 2 diabetes and non-alcoholic fatty liver disease, that affect nearly a third of the US population, as well as cancers including hepatocellular carcinoma that is becoming the leading cause of cancer related deaths. The development of LRH-1 specific chemoproteomic tools will enable modulation and capture of receptor activity to uncover how the novel LRH-1 coregulator, lamina associated polypetide 2 (LAP2), and LRH-1 acetylation regulate receptor intranuclear trafficking and signaling.
