Figure 1.

(a) 25OHC (10 μM) specifically activates SF-1. Transfected cells were incubated with the indicated compounds, and the fold-activation was determined. 25OHC (10 μM) markedly activated SF-1, whereas pregnenolone (30 μM) was a weak activator. (b) Activation of SF-1 by oxysterols and pregnenolones. 25OHC, 26OHC, and 27OHC activated SF-1 10-, 7-, and 5-fold, respectively at 10 μM. Other oxysterols were weaker activators (2–3-fold) at the same concentration. Pregnenolone and 21-hydroxypregnenolone activated SF-1 3–4-fold at 30 μM. (c) Dose response profile of SF-1 activation. Shown are the complete dose response curves of SF-1 with the indicated compounds. The EC₅₀ values calculated from these curves for each compound are: 25OHC, 5 μM; 26OHC, 5 μM; 27OHC, 5 μM; and 21-hydroxypregnenolone, 11 μM. (d) Structure Activity Relationship. Based on their activities, hydroxyl groups at positions 25, 26, or 27 of the cholesterol molecule appear critical for up-regulating SF-1 function suggesting a specific structure activity relationship.