FIG. 1.

UV irradiation inhibits retinoid signaling through RAR. (A) UV irradiation inhibits ligand-induced RARE activation. HeLa cells were transiently cotransfected with DR5TK-luc reporters and the β-Gal expression plasmid. After 24 h, the cells were serum starved overnight and then treated (+) or not treated (−) with UV radiation. Cells were treated or not treated with 1 μM RA and subjected to luciferase assays. Luciferase activity was normalized to other wells by β-Gal values and expressed as the means and standard deviations from three identical wells. (B) UV radiation inhibits ligand-induced RAR target gene expression. Calu-6 cells were treated (+) or not treated (−) with UV radiation and then treated or not treated with 1 μM RA. Total RNA was isolated and analyzed for RARβ and GAPDH transcripts by semiquantitative RT-PCR. (C) UV inhibits transcriptional activation of RAR but not RXR. HeLa cells were transiently cotransfected with G5E1b-luc reporter construct, β-Gal plasmid, and GAL-RARα or GAL-RXRα. Cells were treated (+) or not treated (−) with UV, treated or not treated with 1 μM 9-cis RA (a ligand for both RAR and RXR), and subjected to luciferase assays as described above. The experiment was performed three times, and the results of one experiment are illustrated. Results are means ± standard deviations from three identical wells for GAL-RAR and nine identical wells for GAL-RXR.