The retinoid X receptor (RXR)
is a type of
nuclear receptor
In the field of molecular biology, nuclear receptors are a class of proteins responsible for sensing steroids, thyroid hormones, vitamins, and certain other molecules. These intracellular receptors work with other proteins to regulate the ex ...
that is activated by
9-cis retinoic acid, which is discussed controversially to be of endogenous relevance,
and 9-''cis''-13,14-dihydroretinoic acid, which may be an endogenous mammalian RXR-selective agonist.
is the only specific activator of the RXRs which does not activate the
Retinoic Acid Receptors.
There are three retinoic X receptors (RXR):
RXR-alpha,
RXR-beta, and
RXR-gamma, encoded by the , , genes, respectively.
RXR
heterodimerizes with multiple nuclear receptors including
CAR
A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billio ...
,
FXR,
LXR,
PPAR,
PXR
In the field of molecular biology, the pregnane X receptor (PXR), also known as the steroid and xenobiotic sensing nuclear receptor (SXR) or nuclear receptor subfamily 1, group I, member 2 (NR1I2) is a protein that in humans is encoded by the ' ...
,
RAR,
TR,
ER and
VDR. RXRs are permissive co-receptors as only one of six alleles is needed for normal development and health. Given this, it is difficult to extrapolate whether the RXR pathway has its own endogenous activity driven by 9-cis retinoic acid species or whether it merely participates in other pathways, predominantly the retinoic nuclear receptor pathway. Genomic knockout of the RXRs results in obesity resistance while
bexarotene treatment causes severe
hypothyroidism
Hypothyroidism is an endocrine disease in which the thyroid gland does not produce enough thyroid hormones. It can cause a number of symptoms, such as cold intolerance, poor ability to tolerate cold, fatigue, extreme fatigue, muscle aches, co ...
,
suggesting that the RXR pathway functions at least to regulate the
Thyroid Receptor pathway.
As with other
type II nuclear receptors, the RXR heterodimer in the absence of ligand is bound to hormone response elements complexed with
corepressor protein. Binding of agonist
ligand
In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s to RXR results in dissociation of corepressor and recruitment of
coactivator protein, which, in turn, promotes
transcription of the downstream target
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
into
mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
and eventually
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
.
See also
*
Retinoic acid receptor
*
Retinoid X receptor alpha
*
Retinoid X receptor beta
*
Retinoid X receptor gamma
References
External links
*
Intracellular receptors
Transcription factors
{{receptor-stub