Common and Differential Transcriptional Actions of Nuclear Receptors Liver X Receptors α and β in Macrophages.

The liver X receptors α and β (LXRα and LXRβ) are oxysterol-activated transcription factors that coordinately regulate gene expression that is important for cholesterol and fatty acid metabolism. In addition to their roles in lipid metabolism, LXRs participate in the transcriptional regulation of macrophage activation and are considered potent regulators of inflammation. LXRs are highly similar, and despite notable exceptions, most of their reported functions are substantially overlapping. However, their individual genomic distribution and transcriptional capacities have not been characterized. Here, we report a macrophage cellular model expressing equivalent levels of tagged LXRs. Analysis of data from chromatin immunoprecipitation coupled with deep sequencing revealed that LXRα and LXRβ occupy both overlapping and exclusive genomic regulatory sites of target genes and also control the transcription of a receptor-exclusive set of genes. Analysis of genomic H3K27 acetylation and mRNA transcriptional changes in response to synthetic agonist or antagonist treatments revealed a putative mode of pharmacologically independent regulation of transcription. Integration of microarray and sequencing data enabled the description of three possible mechanisms of LXR transcriptional activation. Together, these results contribute to our understanding of the common and differential genomic actions of LXRs and their impact on biological processes in macrophages.