Retinoic acid receptors and retinoid X receptors: interactions with endogenous retinoic acids.
The binding of endogenous retinoids and stereoisomers of retinoic acid (RA) to the retinoid nuclear receptors, RA receptor (RARs) and retinoid X receptors (RXRs), was characterized using nucleosol preparations from transiently transfected COS-1 cells. Among several stereoisomers of RA tested, including 7-cis-, 9-cis-, 11-cis-, 13-cis-, and all-trans-RA, only 9-cis-RA effectively competes with 9-cis-[3H]RA binding to the RXRs. Additionally, the endogenous retinoid trans-didehydro-RA (t-ddRA) does not interact with RXRs, whereas the 9-cis form of ddRA competes effectively. RXRs (alpha, beta, and gamma) bind 9-cis-RA with dissociation constants (Kd) of 15.7, 18.3, and 14.1 nM, respectively. In contrast to the selectivity of RXRs for 9-cis-RA, RARs bind both t-RA and 9-cis-RA with high affinity, exhibiting Kd values in the 0.2-0.7 nM range for both ligands. Unlike RARs, the cellular RA binding proteins CRABPI or CRABPII bind t-RA but do not bind 9-cis-RA. Consistent with the binding data, 9-cis-RA and 9-cis-ddRA transcriptionally activate both GAL4-RXR and GAL4-RAR chimeric receptors with EC50 values of 3-20 nM for 9-cis-RA and 9-cis-ddRA, whereas t-RA and t-ddRA efficiently activate only GAL4-RAR chimeric receptors. Thus, 9-cis forms of endogenous retinoids can contribute to the pleiotropic effects of retinoids by interacting with both the RARs and RXRs.
Allenby
G
G
Department of Toxicology and Pathology, Hoffmann-La Roche, Nutley, NJ 07110.
Bocquel
M T
MT
Saunders
M
M
Kazmer
S
S
Speck
J
J
Rosenberger
M
M
Lovey
A
A
Kastner
P
P
Grippo
J F
JF
Chambon
P
P
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D051379:Mice; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D014162:Transfection; D014212:Tretinoin / Q000378:metabolism*
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D011956:Receptors, Cell Surface; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D014212:Tretinoin