Interleukin-1 receptor antagonist induction as an additional mechanism for liver receptor homolog-1 to negatively regulate the hepatic acute phase response

Abstract

The liver receptor homolog-1 (LRH-1) is an orphan nuclear receptor believed to play a key role in bile acid metabolism, cholesterol homeostasis, and intestinal cell crypt renewal. LRH-1 has recently been reported to negatively regulate the hepatic acute phase response by antagonizing, at least in part, the CCAAT/enhancer-binding protein signaling pathway. Here we have shown, using adenovirus-mediated LRH-1 overexpression and gene-silencing experiments, that the interleukin-1 receptor antagonist (IL-1RA) gene is a novel LRH-1 target gene in hepatic cells. Promoter mapping and chromatin immunoprecipitation experiments revealed that LRH-1 regulates IL-1RA gene expression under inflammatory conditions at the transcriptional level via the binding to an LRH-1 response element. Interestingly, IL-1RA induction by an intraperitoneal injection of lipopolysaccharide is significantly lower in LRH-1 heterozygous compared with wild-type mice, demonstrating the contribution of LRH-1 in IL-1RA gene regulation. Finally, RNA interference experiments indicate that LRH-1 blocks the hepatic acute phase response by, at least in part, inducing IL-1RA expression. Taken together, these results lead to the identification of IL-1RA as a novel LRH-1 target gene and demonstrate the existence of multiple mechanisms contributing to the overall anti-inflammatory properties of LRH-1 in hepatic cells. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.