Liver X receptor

LXRα (nuclear receptor subfamily 1, group H, member 3)
Identifiers
Symbol	NR1H3
Entrez	10062
HUGO	7966
OMIM	602423
RefSeq	NM_005693
UniProt	Q13133

LXRβ (nuclear receptor subfamily 1, group H, member 2)
Identifiers
Symbol	NR1H2
Alt. symbols	UNR
Entrez	7376
HUGO	7965
OMIM	600380
RefSeq	NM_007121
UniProt	P55055

The liver X receptor (LXR) is a member of the nuclear receptor family of transcription factors and is closely related to nuclear receptors such as the PPARs, FXR and RXR. Liver X receptors (LXRs) are important regulators of cholesterol, fatty acid, and glucose homeostasis. LXRs were earlier classified as orphan nuclear receptors, however, upon discovery of endogenous oxysterols as ligands, they were subsequently deorphanized.

Two isoforms of LXR have been identified and are referred to as LXRα and LXRβ. The liver X receptors are classified into subfamily 1 (thyroid hormone receptor-like) of the nuclear receptor superfamily, and are given the nuclear receptor nomenclature symbols NR1H3 (LXRα) and NR1H2 (LXRβ) respectively.

LXRα and LXRβ were discovered separately between 1994-1995. LXRα isoform was independently identified by two groups and initially named RLD-1 and LXR, whereas four groups identified the LXRβ isoform and called it UR, NER, OR-1, and RIP-15. The human LXRα gene is located on chromosome 11p11.2, while the LXRβ gene is located on chromosome 19q13.3.

While the expression of LXRα and LXRβ in various tissues somewhat overlap, the tissue distribution pattern of these two isoforms overall differ considerably. LXRα expression is restricted to liver, kidney, intestine, fat tissue, macrophages, lung, and spleen and is highest in liver, hence the name liver X receptor α (LXRα). LXRβ is expressed in almost all tissues and organs, hence the early name UR (ubiquitous receptor). The different pattern of expression suggests that LXRα and LXRβ have different roles in regulating physiological function.

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