title: Predominant contribution of organic anion transporting polypeptide OATP-B (OATP2B1) to apical uptake of estrone-3-sulfate by human intestinal Caco-2 cells.
abstract: Human organic anion transporting polypeptide OATP-B (OATP2B1) is a pH-sensitive transporter expressed in the apical membranes of small intestinal epithelial cells. In this study, we have examined the contribution of OATP-B to the uptake of [3H]estrone-3-sulfate in Caco-2 cells in comparison with those of its homologs OATP-D (OATP3A1) and OATP-E (OATP4A1). Immunocytochemical study revealed that OATP-B is expressed in the apical membranes of Caco-2 cells. The uptake of [3H]estrone-3-sulfate by Caco-2 cells was Na+-independent and inhibited by several organic anions. It showed biphasic saturation kinetics with Km values of 1.81 microM and 1.40 mM. The uptake of [3H]estrone-3-sulfate by human embryonic kidney (HEK) 293 cells stably expressing OATP-B (HEK293/OATP-B) was also Na+-independent and inhibited by several organic anions. The Km value for estrone-3-sulfate uptake by OATP-B (1.56 microM) was close to that for the high-affinity component observed in Caco-2 cells. The mRNA expression level of OATP-B was higher than that of OATP-D or OATP-E in Caco-2 cells and in human jejunum biopsies from healthy volunteers. The values of [3H]estrone-3-sulfate uptake normalized to OATP-B mRNA expression were similar in Caco-2 cells and HEK293/OATP-B cells. The specific activity of OATP-B per mRNA expression was much higher than that of OATP-D and OATP-E. [3H]Estrone-3-sulfate uptake by membrane vesicles prepared from HEK293/OATP-B cells exhibited an overshoot phenomenon in the presence of an inwardly directed H+ gradient, suggesting that an H+ gradient is the driving force of estrone-3-sulfate transport by OATP-B. These results suggest that OATP-B is predominantly responsible for the apical uptake of estrone-3-sulfate in Caco-2 cells.
authors.affiliation: Division of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Japan.
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Sai
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Satsuki
authors.initials: S
authors.lastname: Ito
authors.forename: Keisuke
authors.initials: K
authors.lastname: Mitsuoka
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kato
authors.forename: Ikumi
authors.initials: I
authors.lastname: Tamai
authors.forename: Per
authors.initials: P
authors.lastname: Artursson
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
mesh_terms: D000328:Adult; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism; D004970:Estrone / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D006801:Humans; D007583:Jejunum / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D027361:Organic Anion Transporters; D012333:RNA, Messenger; C450859:SLCO2B1 protein, human; C479544:SLCO3A1 protein, human; C498174:SLCO4A1 protein, human; D004970:Estrone; C017296:estrone sulfate