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Modification of OATP2B1-Mediated Transport by Steroid Hormones

Research Center of Pharmacology and Experimental Therapeutics, Department of Pharmacology (M.G., K.K., S.K., S.R., G.J., H.K.K.) and Department of Pharmacy (C.A.R.), Ernst Moritz Arndt University, Greifswald, Germany

The family of the organic anion transporting polypeptides forms an increasing group of uptake transport proteins with a wide substrate spectrum. Although the expression of some members of this group, such as organic anion transporting polypeptide (OATP)-A or C, is limited to special tissues (such as liver or brain), the organic anion transporting polypeptide 2B1 (OATPB/SLCO2B1) is expressed in many organs, including liver, placenta, mammary gland, brain, and intestine. However, little is known about its function in those tissues because only a limited number of compounds, such as dehydroepiandrosterone-sulfate (DHEAS) and estrone-3-sulfate (E3S), have been characterized as OATP2B1 substrates. To further elucidate the role of OATP2B1 on steroid transport, we examined the influence of steroid hormones on OATP2B1-mediated E3S and DHEAS uptake using OATP2B1-overexpressing Madin-Darby canine kidney II cells. We identified unconjugated androgens (e.g., testosterone) as potent inhibitors for OATP2B1. In contrast, gestagenes such as progesterone enhanced E3S uptake in a concentration-dependent manner to up to 300% of the control, accompanied by a significant decrease in the OATP2B1 K_m value for E3S (control, K_m = 14 µM; in the presence of 31.6 µM progesterone, K_m = 3.6 µM). Moreover, we demonstrated that testosterone and progesterone are not substrates of OATP2B1, indicating an allosteric mechanism for the observed effects. Furthermore, we showed that progesterone enhances the OATP2B1-dependent pregnenolone sulfate transport. Taken together, the results indicate functional modification of OATP2B1-mediated E3S and DHEAS as well as pregnenolone sulfate transport through steroid hormones such as progesterone. These effects can have physiological consequences for the organ-specific uptake of steroids.

Address correspondence to: Dr. Heyo K. Kroemer, Department of Pharmacology, Friedrich-Loeffler-Str. 23d, 17487 Greifswald, Germany. E-mail: kroemer{at}uni-greifswald.de

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