In addition, the 5’ UTR of the OATP1B1 DNA containing the LXRα response element was cloned into the pGL3 vector to assess the effect of DXM on LXRα-mediated OATP1B1 promoter activation. The activity of the firefly luciferase was monitored after incubation by 400 nM DXM or LXRα agonist GW3965 as a positive control. As shown in Figure 6, the reporter activity was increased by 74% in the GW3965 group (****P< 0.0001) and decreased by 33% in the DXM group (***P< 0.001) as compared with 0.1% DMSO negative control. Meanwhile, compared with the GW3965 group, the DXM+GW3965 group also reduced the reporter activity by about 27% (****P < 0.0001). Thus, these results suggested that the repressive effect of DXM on the OATP1B1 expression was the result of the inhibition of OATP1B1 promoter activation via LXRα.