Involvement of FXR phosphorylation in the potentiatng effect of SC on the transactivation of BSEP. (A) FXR phosphorylation mutants reduced or eliminated the potentiation induced by SC. Huh7 cells were transfected with a mixture containing 50 ng BSEP(2.6)-Luc, 5 ng FXR or a mutant, 5 ng of the null-Renilla luciferase plasmid along with 125 ng CYP1A2. The transfected cells were treated with CDCA (10 µM) or CDCA plus SC (10 µM) for 24 h. Luciferase activities were determined. *Significant difference between CDCA and SC/CDCA co-treatment. (B) GF109203X Huh7 cells (in which the potentiating effect of SC on transactivation of BSEP was abolished) were transfected with a mixture containing 50 ng BSEP(2.6)-Luc, 5 ng FXR, 5 ng null-Renilla luciferase plasmid and 125 ng CYP1A2. The transfected cells were treated with CDCA (10 µM), SC (10 µM), GF109203X (1 µM) or in various combinations for 24 h. Luciferase activities were determined. Columns with different letters are statistically, significantly different.