Retinoic acid and synthetic analogs differentially activate retinoic acid receptor dependent transcription

We have developed an assay where the potency of retinoids in retinoic acid receptor (RAR) mediated transcriptional activation can be rapidly evaluated. In this assay hRAR-alpha, hRAR-beta and hRAR-gamma were expressed in CV-1 cells together with a reporter gene containing a retinoic acid responsive element (TRE3-tk-CAT). Concentrations required to obtain half-maximum induction (ED50) of CAT-activity were determined for several retinoids, e.g., all-trans-retinoic acid (RA), 13-cis-retinoic acid (13-cis-RA), arotinoid acid (TTNPB) and m-carboxy-arotinoid acid (m-carboxy-TTNPB, an inactive arotinoid analog). The ED50 values for RA decreased in the order of RAR-alpha (24 nM) greater than RAR-beta (4.0 nM) greater than RAR-gamma (1.3 nM), while the ED50 values for TTNPB and 13-cis-RA decreased in the order of RAR-alpha (6.5 nM, 190 nM) greater than RAR-gamma (2.3 nM, 140 nM) greater than RAR-beta (0.6 nM, 43 nM), respectively. No significant inductions were obtained when cells were treated with m-carboxy-TTNPB, even at 10 microM concentrations. The fold induction of CAT-activity for all compounds tested decreased in the order of RAR-alpha greater than RAR-beta greater than RAR-gamma.