Figure 4.

Effect of RB on P1-Luc activity in the presence of nuclear receptor RXRα and LXRβ agonists (a) BeWo cells were transfected with P1-Luc construct alone or co-transfected with RB-expressing vector, and incubated with LXR agonist T091713 or RXRα agonist 9-Cis-retinoic acid. Luciferase activity was measured 72 h after transfection. RB itself stimulated fivefold, and in presence of agonists stimulation reached 10-fold over basal levels. The location of nuclear receptor binding sites is indicated below. (b) P1-Luc promoter activity in BeWo cells in the presence of various cofactors. Vectors expressing nuclear receptor co-activators NCOA2 or CBP were co-transfected with or without RB-expressing vector, as indicated, and luciferase levels from the P1 promoter were then measured as in (a). Stimulation by RB was maximal when both CBP and NCOA2 were coexpressed and agonists for RXRα and LXRβ were also added. (c) Activity of wild-type and Mut2 P173-Luc promoter in BeWo cells in the presence of RB alone and RB with agonists. Mut2 construct (below the panel) is a version of P173-Luc with mutations in the RXRα-binding site.⁷ The Mut2 construct failed to show stimulation by RB with or without agonists.