Proteins were extracted with a radio-immunoprecipitation assay (RIPA) buffer containing phenylmethane sulfonyl fluoride (Sigma, St. Louis, MO, USA) and a protease inhibitor cocktail (Sigma). Herein, protein concentration was determined using the bicinchoninic acid assay (BCA, Thermo). Then, proteins were separated by 10% SDS-PAGE and then transferred to polyvinylidene difluoride (PVDF) membranes. Subsequently, the membranes were incubated with primary antibodies at 4 °C overnight. The primary antibodies used were as follows: anti-OATP1B1(1:1000 dilutions; Santa Cruz Biotechnology, Santa Cruz, USA), anti-LXRα (1:500 dilutions; Santa Cruz Biotechnology, Santa Cruz, USA), and anti-β-actin (1:2000 dilutions; ZSGB-BIO, Beijing, China). Then, the membranes were incubated with appropriate horseradish peroxidase (HRP)-conjugated secondary antibody at room temperature for 1 h and visualized using electrochemiluminescence (ECL) HRP substrate. Meanwhile, signals of antibody binding were detected by Gensye automatic gel imaging analysis system. Relative protein levels were standardized with the β-actin protein level and protein band intensities were analyzed by ImageJ (National Institutes of Health, Bethesda, MD).