Ligand-activated liver X receptors (LXRα, NR1H3 and LXRβ NR1H2) induce expression of a cluster of apolipoprotein genes APOE, APOC1, APOC2 and APOC4 in both human and mouse macrophages (Mak PA et al. 2002). Induction was attenuated or abolished in macrophages derived from LXR α/β-/- mice. Studies with reporter genes suggest that the LXR response element (LXRE) in the distal multienhancer regions ME.1 and ME.2 are necessary for the expression of this gene cluster (Mak PA et al. 2002). These secreted apolipoproteins regulate lipid transport and catabolism. In particular, APOC1
has been suggested to serve as an inhibitor of cholesteryl ester transfer protein (CETP) activity to impact cholesterol distribution among lipoprotein particles (Gautier T et al. 2000).