RAR-related orphan receptor

The RAR-related orphan receptors (RORs) are members of the nuclear receptor family of intracellular transcription factors. There are three forms of ROR, ROR-α, -β, and -γ and each is encoded by a separate gene (,, and respectively). The RORs are somewhat unusual in that they appear to bind as monomers to hormone response elements as opposed to the majority of other nuclear receptors which bind as dimers.

Ligands
Melatonin has been reported to be the endogenous ligand for ROR-α while CGP 52608 has been identified as a ROR-α selective synthetic ligand. However X-ray crystallographic ( and ) and functional data both suggest that cholesterol or a cholesterol derivative may be the endogenous ligand.

In contrast, all-trans retinoic acid binds with high affinity to ROR-β and -γ but not ROR-α.

Function
The three forms of RORs fulfill a number of critical roles including:
 * ROR-α - development of the cerebellum and lymph nodes, lipid metabolism, immune response, maintenance of bone
 * ROR-β - precise role unknown but highly expressed in the brain and retina
 * ROR-γ - lymph node development and immune response, survival of T helper 17 cells