Allenby G, Bocquel M T, Saunders M, Kazmer S, Speck J, Rosenberger M, Lovey A, Kastner P, Grippo J F, Chambon P
Department of Toxicology and Pathology, Hoffmann-La Roche, Nutley, NJ 07110.
Proc Natl Acad Sci U S A. 1993 Jan 1;90(1):30-4. doi: 10.1073/pnas.90.1.30.
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.
利用瞬时转染的COS-1细胞的核溶质制剂，对内源性类视黄醇和视黄酸（RA）的立体异构体与类视黄醇核受体、RA受体（RARs）和类视黄醇X受体（RXRs）的结合进行了表征。在测试的几种RA立体异构体中，包括7-顺式、9-顺式、11-顺式、13-顺式和全反式RA，只有9-顺式RA能有效竞争9-顺式-[3H]RA与RXRs的结合。此外，内源性类视黄醇反式双脱氢RA（t-ddRA）不与RXRs相互作用，而9-顺式形式的ddRA能有效竞争。RXRs（α、β和γ）与9-顺式RA结合的解离常数（Kd）分别为15.7、18.3和14.1 nM。与RXRs对9-顺式RA的选择性不同，RARs对全反式RA和9-顺式RA都具有高亲和力，两种配体的Kd值均在0.2-0.7 nM范围内。与RARs不同，细胞RA结合蛋白CRABPI或CRABPII结合全反式RA，但不结合9-顺式RA。与结合数据一致，9-顺式RA和9-顺式-ddRA以3-20 nM的EC50值转录激活GAL4-RXR和GAL4-RAR嵌合受体，而全反式RA和全反式-ddRA仅有效激活GAL4-RAR嵌合受体。因此，内源性类视黄醇的9-顺式形式可通过与RARs和RXRs相互作用，促成类视黄醇的多效性作用。
