Induction of uPA in BAECs by RAR-activating retinoids. Cellular PA levels were determined using a chromogenic substrate, S2403, after treatment of BAECs for 12 hours in MEM-BSA either with (A) various concentrations of atRA (panel a), 9cRA (panel b), Ch55 (panel c), Am580 (panel d), CD2019 (panel e), CD666 (panel f), Ro47-5944 (panel g), and Ro25-7386 (panel h) or with a combination of various concentrations of atRA and 0.1 μmol/L Ro47-5944 (panel i) or (B) with 10⁻⁸ mol/L atRA (sample 2), Ch55 (sample 3), and Am580 (sample 4) in the absence or presence of 10⁻⁵ mol/L Ro41-5253 (▨) or LE135 (▩). The specificity and characterization of each compound are described under Materials and Methods. Data are expressed as urokinase (UK) units (U) per milligram of protein in the sample. Each point represents the average ± SD (n = 3).