Repa J J, Hanson K K, Clagett-Dame M
Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin-Madison 53706.
Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7293-7. doi: 10.1073/pnas.90.15.7293.
Competition of all-trans-retinol and all-trans-retinaldehyde with 3H-labeled all-trans-retinoic acid (RA) for binding to retinoic acid receptors (RARs) was examined in human neuroblastoma cell nuclear extracts. All-trans-retinol was 35-fold less potent than all-trans-RA, whereas all-trans-retinaldehyde was 500-fold less active in binding to the nuclear receptors. To confirm that all-trans-retinol binds to RARs, experiments were carried out with RARs alpha, beta, and gamma expressed as bacterial fusion proteins. All-trans-retinol was only 4- to 7-fold less potent than all-trans-RA in binding to all three RAR subtypes. The all-trans-retinol binding observed was not the result of metabolism of retinol to RA or some other active compound during the binding experiment. Retinyl acetate was virtually inactive in competition binding experiments, while very slight activity was observed with 13-cis-RA and all-trans-retinaldehyde. Significant competition occurred with 4-hydroxy-RA and 4-keto-RA, which were 15- to 40-fold less potent than all-trans-RA. The 9-cis isomer of RA was equipotent with all-trans-retinol in these studies. These results suggest that all-trans-retinol cannot be excluded as a physiologically significant ligand for RAR-mediated gene expression.
在人神经母细胞瘤细胞核提取物中检测了全反式视黄醇和全反式视黄醛与3H标记的全反式视黄酸（RA）竞争结合视黄酸受体（RARs）的情况。全反式视黄醇的效力比全反式视黄酸低35倍，而全反式视黄醛与核受体结合的活性低500倍。为了证实全反式视黄醇与RARs结合，对以细菌融合蛋白形式表达的RARα、β和γ进行了实验。全反式视黄醇与所有三种RAR亚型结合时的效力仅比全反式视黄酸低4至7倍。观察到的全反式视黄醇结合并非结合实验期间视黄醇代谢为视黄酸或其他活性化合物的结果。醋酸视黄酯在竞争结合实验中几乎没有活性，而13-顺式视黄酸和全反式视黄醛的活性非常微弱。4-羟基视黄酸和4-酮基视黄酸发生了显著竞争，它们的效力比全反式视黄酸低15至40倍。在这些研究中，视黄酸的9-顺式异构体与全反式视黄醇效力相当。这些结果表明，不能排除全反式视黄醇作为RAR介导的基因表达的生理上重要的配体。
