Liver X Receptor  (肝x受体)

Liver X receptors (LXRs) are ligand-activated transcription factors of the nuclear receptor superfamily. LXRs have two subtypes: LXRα (nuclear receptor subfamily 1, group H, member 3, NR1H3) and LXRβ (nuclear receptor subfamily 1, group H, member 2, NR1H2). LXRα and LXRβ share extensive sequence homology [(77% identity in both the DNA binding domain (DBD) and ligand binding domain (LBD)] and appear to respond to the same endogenous ligands. They are expressed in an overlapping but nonidentical pattern. LXRα is the dominant subtype expressed in the liver and is also highly expressed in tissues that play roles in cholesterol metabolism including intestine, adipose, kidney and adrenals. On the other hand LXRβ is widely expressed. Cholesterol derivatives including oxidized forms of cholesterol (oxysterols), cholesterol precursors (e.g., desmosterol) and plant sterols (e.g., stigmosterol) are endogenous LXR agonists. LXRs bind to DNA as heterodimers with a second subgroup of the nuclear receptor superfamily, the retinoid X receptors (RXRs). The LXR/RXR heterodimer can be activated by ligands for either LXR or RXR and sequentially bind to LXR response elements in the promoters of their target genes and activate target gene expression. Importantly, they play pivotal roles in the transcriptional control of lipid metabolism.