Common and differential transcriptional actions of LXRalpha and LXRbeta in murine macrophages

The LXR proteins, LXRa and LXRß, are transcription factors that belong to the nuclear receptor superfamily. LXRs are activated by oxysterols and control the transcription of genes involved in the regulation of cholesterol and fatty acid metabolism. They also mediate several aspects of macrophage biology, including inflammatory responses, cell survival in response to infection and phagocytosis of apoptotic cells. LXRs share a high degree of sequence homology and most of their functions are believed to be performed similarly by LXRa and LXRß. However, the individual, transcriptional roles of each LXR isoform have not been characterized in detail, in part due to the lack of specific experimental tools that can discriminate between LXRa and LXRß actions. To identify common and differential transcriptional functions of LXR nuclear receptors in macrophages, we developed a cellular model of stable expression of FLAG-tagged LXRa or LXRß in LXR-null immortalized murine bone marrow-derived macrophages (parental line published Elife. 2015 Jul 14;4:e08009. doi: 10.7554/eLife.08009). To take a deeper insight into the epigenomic features of LXR nuclear receptors, we performed chromatin immunoprecipitation coupled to next-generation sequencing (ChIP-seq) to identify genome-wide binding locations of LXRa and LXRß in the presence of a synthetic agonist (GW3965, 1uM). Additionally, we identified genome-wide DNA locations of acetylation mark on lysine 27 of histone H3 (H3K27ac), upon LXR agonist (GW3965, 1uM) and antagonist (GW2033, 1uM) treatment. Collectively, these studies will increase our understanding of common and differential genomic actions of LXRa and LXRß in cultured murine macrophages. Overall design: Examination of genome-wide locations of LXRa and LXRß in 3xFLAG-LXRa and 3xFLAG-LXRß expressing cells using FLAG antibody. Also examination of H3K27ac acetylation mark on the same cells in response to pharmacological treatment with agonist versus antagonist.