Biochem/physiol Actions

Retinoid X receptor (RXR) serves as a promiscuous heterodimerization partner for many nuclear receptors through the identity box, a 40-amino acid subregion within the ligand binding domain. RXR partners include thyroid hormone receptors (TRs), retinoic acid receptors (RARs), peroxisome proliferator-activated receptor (PPAR), several constitutive active orphan nuclear receptors (e.g. nuclear growth factor I-B, NGFI-B), oxysterol receptors (LXR,FXR), and constitutive androstane receptors (CAR). RXRs also form homodimers to mediate the effects of 9-cis-retinoic acid (9-cRA). Depending on these protein-protein interactions, RXR-containing complexes have distinct ligand-dependent and constitutive functions (1). RXRβ was originally identified as a protein able to bind to the regulatory region II of the murine major histocompatibility complex (MHC) class I promoter and referred to as H2RIIBP. The human RXRβ gene has been mapped to the short arm or centromeric region of chromosome 6 (6pter-q13) which also contains the MHC I locus (3). Two major RXRβ isoforms in the mouse, designated RXRβ1 and RXRβ2 (GenBank accession numbers D21830 and D21831), differ in the N-terminal (A) domain with RXRβ1 containing an extra 72 amino acids. These isoform mRNAs are transcribed from two CpG island promoters and the different N-terminal exons are spliced to exons common to both isoforms from the remainder of the gene. Although the two mouse RXR isoforms have been characterised in some detail, less information is available about their human counterparts. Since the expression of different RXR isoforms appears to be well conserved between species, each receptor isoform may hold a specific role in retinoid signalling. However, many RXR expression studies have not recognised the importance of establishing which RXR isoforms are expressed in a particular system. RXRβ is predominantly involved in retinoid responses in the N-type SH SY 5Y and the S-type SH S EP neuroblastoma cells, both derivatives of a mixed phenotype neuroblastoma cell line.

Physical form

Clear and colorless frozen liquid solution

Preparation Note

Use a manual defrost freezer and avoid repeated freeze-thaw cycles. While working, please keep sample on ice.