Regulation of BCO1 expression and activity by dexamethasone.

<p><b>A</b>. BCO1 mRNA was determined by RT-PCR. Two x 10⁶ cells were plated in 10-cm dishes. After 24 h, cells were treated with DEX (10⁻⁷ M) or FSK (10⁻⁵ M) for 24 h. Cells were harvested, total RNA extracted, and RT-PCR performed. GAPDH served as a loading control. <b>B</b>. Quantification of BCO1 was examined by real time PCR. Relative fold changes are presented as 2^-ΔΔCt. Results are presented as means ± S.D. of five independent experiments, each performed in triplicate. * <i>P</i><0.05; ** <i>P<0</i>.<i>01</i>. <b>C</b>. BCO1 protein from each treatment was analyzed by western blot using rabbit anti-BCO1 antibody with β-actin serving as a loading control (<i>top panel</i>). The <i>bottom panel</i> indicates the adjusted BCO1 levels (mean ± S.D., n = 3). <b>D</b>. A549 cells were treated with β-carotene (10⁻⁶ M) in the absence or presence of DEX (10⁻⁷ M) for 24 h. Carotenoids and retinoids were extracted from culture media as described in “Materials and Methods”. Retinoic acid isomers were analyzed by HPLC as described above. * <i>P</i><<i>0.05</i>; ** <i>P</i><<i>0.01</i> compared to respective controls.