Apolipoprotein M regulates the orphan nuclear receptor LRH-1 gene expression through binding to its promoter region in HepG2 cells

Abstract

Yi Pan,1,2,* Hou-gang Zhou,1,* Hui Zhou,3 Min Hu,1 Li-jun Tang2 1Clinical Laboratory, The Second Xiangya Hospital of Central South University, Changsha, Hunan, People’s Republic of China; 2Molecular Biology Research Center, School of Life Sciences, Central South University, Changsha, Hunan, People’s Republic of China; 3Tumor Hospital of Xiangya School of Medicine, Central South University, Changsha, Hunan, People’s Republic of China *These authors contributed equally to this work Abstract: Apolipoprotein M (ApoM) is predominantly located in the high-density lipoprotein in human plasma. It has been demonstrated that ApoM expression could be regulated by several crucial nuclear receptors that are involved in the bile acid metabolism. In the present study, by combining gene-silencing experiments, overexpression studies, and chromatin immunoprecipitation assays, we showed that ApoM positively regulated liver receptor homolog-1 (LRH-1) gene expression via direct binding to an LRH-1 promoter region (nucleotides -406/-197). In addition, we investigated the effects of farnesoid X receptor agonist GW4064 on hepatic ApoM expression in vitro. In HepG2 cell cultures, both mRNA and protein levels of ApoM and LRH-1 were decreased in a time-dependent manner in the presence of 1 µM GW4064, and the inhibition effect was gradually attenuated after 24 hours. In conclusion, our findings present supportive evidence that ApoM is a regulator of human LRH-1 transcription, and further reveal the importance of ApoM as a critical regulator of bile acids metabolism. Keywords: bile acids, chromatin immunoprecipitation assay, farnesoid X receptor, GW4064, high-density lipoprotein