Solute Carrier Organic Anion Transporter Family, Member 2B1 (SLCO2B1)

The predicted 709-amino acid SLC21A9 protein contains 8 membrane-spanning regions. SLC21A9 shares 42.8% amino acid sequence identity with a rat prostaglandin transporter across 678 residues. RT-PCR followed by ELISA detected SLC21A9 expression in all human tissues examined, with the highest expression in liver, lower expression in lung, ovary, brain, heart, kidney, pancreas, spleen, and testis, and lowest expression in skeletal muscle. OATPB mRNA levels were measured in isolated trophoblasts under culture conditions that promoted syncytia formation. Real-time quantitative PCR estimated an 8-fold increase in OATPB expression on differentiation to syncytia. Pregnenolone sulfate partially inhibited OATPB-mediated transport of estrone-3-sulfate in an oocyte expression system.