Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver (original) (raw)
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Localization and function of the organic anion–transporting polypeptide Oatp2 in rat liver
Gastroenterology, 1999
Background & Aims: Multispecific organic anion-transporting polypeptides (Oatps) are involved in the transcellular movement of amphipathic compounds in many tissues including the liver, kidney, and blood-brain barrier. Recently, a high-affinity digoxin transporter (Oatp2) was cloned from rat brain and shown to be also expressed in the liver. Methods: We investigated the cellular and subcellular distribution of Oatp2 in rat liver by in situ hybridization technology and immunofluorescence microscopy and compared its substrate specificity with that of Oatp1 in complementary RNA-injected Xenopus laevis oocytes. Results: The results show a selective basolateral (sinusoidal) expression of Oatp2 in midzonal to perivenous hepatocytes, but not in periportal or the innermost layer of perivenous hepatocytes. Common substrates of both Oatp1 and Oatp2 include bile salts, steroid conjugates, thyroid hormones (T3, T4), ouabain, and the endothelin receptor antagonist BQ-123 (Michaelis constants: Oatp1, D600 mol/L; Oatp2, D30 mol/L). Other organic anions including sulfolithotaurocholate, bilirubin monoglucuronide, and sulfobromophthalein were transported only by Oatp1. Conclusions: These results provide definite evidence for the partially overlapping and partially selective substrate specificities of Oatp1 and Oatp2. The unique acinar distribution of Oatp2 might indicate that it represents a high-affinity ''backup'' system for complete hepatocellular removal of certain cholephilic substances from portal blood plasma.
Journal of Pharmacology and Experimental Therapeutics, 2005
The organic anion transporting polypeptides OATPs are key membrane transporters for which crystal structures are not currently available. They transport a diverse array of xenobiotics and are expressed at the interface of hepatocytes, renal tubular cells, enterocytes and the choroid plexus. To aid the understanding of the key molecular features for substratetransporter interactions, pharmacophore models were produced for the two OATPs that have been most extensively studied, namely rat Oatp1a1 and human OATP1B1. Literature data from CHO, HeLa, Hek-293 cells and X. laevis oocytes were used to construct pharmacophores for each individual transporter which were later merged to show similarities across cell lines for the same transporter. Additionally, meta-pharmacophores were generated from the combined datasets of each cell system used with the same transporter. The pharmacophores for each transporter consisted of hydrogen bond acceptor and hydrophobic features. There was good agreement between the merged and meta-pharmacophores containing 2 hydrogen bond acceptors and 2 or 3 hydrophobic features for Oatp1a1 and OATP1B1. External test sets were used to validate the individual pharmacophores. The metapharmacophores were also used to make predictions for molecules not included in the models and provided new molecular insight into the key features for these OATP transporters. This approach can be extended to other transporters for which limited data are available. Downloaded from JPET #82370 23 Kanai N, Lu R, Bao Y, Wolkoff AW, Vore M and Schuster VL (1996) Estradiol 17 beta-Dglucuronide is a high-affinity substrate for oatp organic anion transporter. Am J Physiol 270:F326-331. Kim RB (2003) Organic anion-transporting polypeptide (OATP) transporter family and drug disposition. Eur J Clin Invest 33:1-5. Konig J, Cui Y, Nies AT and Keppler D (2000) A novel human organic anion transporting polypeptide localized to the basolateral hepatocyte membrane. Am J Physiol Gastrointest Liver Physiol 278:G156-164. Kontaxi M, Echkardt U, Hagenbuch B, Stieger B, Meier PJ and Petzinger E (1996) Uptake of the mycotoxin ochratoxin A in liver cells occurs via the cloned organic anion transporting polypeptide. J Pharmacol Exp Ther 279:1507-1513. Kouzuki H, Suzuki H, Ito K, Ohashi R and Sugiyama Y (1999) Contribution of organic anion transporting polypeptide to uptake of its possible substrates into rat hepatocytes. J Pharmacol Exp Ther 288:627-634. Kullack-Ublick G-A, Hagenbuch B, Stieger B, Wolkoff AW and Meier PJ (1994) Functional characterization of the basolateral rat liver organic anion transporting polypeptide. Hepatology 20:411-416. Li L, Lee TK, Meier PJ and Ballatori N (1998) Identification of glutathione as a driving force and leukotriene C4 as a substrate for oatp1, the hepatic sinusoidal organic solute transporter. J Biol Chem 273:16184-16191.
Hepatology, 2001
The organic anion transporting polypeptides, Oatp1 (Slc21a1) and Oatp2 (Slc21a5), mediate hepatic uptake of cardiac glycosides. Previously, we demonstrated that chemicals that increase cytochrome P450s differentially affect hepatic uptake of cardiac glycosides. We postulated that increased uptake of cardiac glycosides observed after pretreatment of animals with phenobarbital (PB) and pregnenolone-16␣-carbonitrile (PCN) occurs via increased hepatic expression of Oatp1 and/or Oatp2. Male Sprague-Dawley rats were injected with PB, PCN, 3-methylcholanthrene (3-MC), or vehicle for 4 days. Branched-DNA (bDNA) signal amplification and Western blot analyses were used to assess hepatic Oatp1 and Oatp2 mRNA and protein, respectively. The expression of Oatp1 was not increased by any chemical treatment. Increases in Oatp2 expression were observed from livers of rats treated with PB and PCN, in which PCN caused a robust elevation of Oatp2 mRNA and protein. Oatp2 expression was suppressed in response to 3-MC. To determine the temporal effects of PCN treatment on the expression of Oatp2, rats were administered PCN, livers were extracted at various times, and Oatp2 expression was analyzed. Maximal expression of Oatp2 mRNA was observed at 24 hours and remained elevated, whereas the amount of Oatp2 protein increased throughout the 96-hour interval. The finding that Oatp2 expression increases in response to PB and PCN is consistent with our previous findings that PB and PCN enhance hepatic uptake of cardiac glycosides. These results suggest that Oatp2, but not Oatp1, is inducible by PB and PCN, which imparts the increased capacity of the liver to extract cardiac glycosides from the plasma. (HEPATOLOGY 2001;33:1469-1478.)
Functional characterization of the mouse organic-anion-transporting polypeptide 2
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2002
We have isolated and functionally characterized an additional murine member of the organic-anion-transporting polypeptide (Oatp) family of membrane transport proteins from mouse liver. The 3.6 kb cDNA insert contains an open reading frame of 2010 bp coding for a 670 amino acid protein. Based on its amino acid identity of 88% to the rat Oatp2, it is considered the mouse Oatp2 orthologue. Functional expression in Xenopus laevis oocytes demonstrated that mouse Oatp2 transports several general Oatp substrates such as estrone-3-sulfate, dehydroepiandrosterone sulfate (DHEAS), ouabain and BQ-123 but hardly any taurocholate nor rocuronium or deltorphin II. The highaffinity rat Oatp2 substrate digoxin is transported with a rather low affinity with an apparent K m value of 5.7 AM. Bromosulfophthalein (BSP), a substrate not transported by the rat Oatp2, is transported very well by mouse Oatp2. Northern blot analysis demonstrated a predominant expression in the liver with additional signals in kidney and brain. Using fluorescence in situ hybridization, the Oatp2 gene (gene symbol Slc21a5) was mapped to chromosome 6G1-G3.
Localization and Genomic Organization of a New Hepatocellular Organic Anion Transporting Polypeptide
Journal of Biological Chemistry, 2000
Based on sequence homology to the human organic anion transporting polypeptide 2 (OATP2; SLC21A6), we cloned a new member of the SLC21A superfamily of solute carriers, termed OATP8 (SLC21A8). The protein of 702 amino acids showed an amino acid identity of 80% with human OATP2. Based on Northern blotting, the expression of OATP8 was restricted to human liver. Cosmid clones containing the genes encoding human OATP1 (SLC21A3), OATP2 (SLC21A6), and OATP8 (SLC21A8) served to establish their genomic organization. All three genes contained 14 exons with 13 identical splice sites when transferred to the amino acid sequence. An antibody raised against the carboxyl terminus localized OATP8 to the basolateral membrane of human hepatocytes and the recombinant glycoprotein, expressed in MDCKII cells, to the lateral membrane. Transport properties of OATP8 were studied in stably transfected MDCKII and HEK293 cells. Organic anions transported by human OATP8 included sulfobromophthalein, with a K m of 3.3 M, and 17-glucuronosyl estradiol, with a K m of 5.4 M. Several bile salts were not substrates. Thus, human OATP8 is a new uptake transporter in the basolateral hepatocyte membrane with an overlapping but distinct substrate specificity as compared with OATP2, which is localized to the same membrane domain. . The abbreviations used are: SLC, solute carrier superfamily; BSP, sulfobromophthalein; E 2 17G, 17-glucuronosyl estradiol; OATP, organic anion transporting polypeptide; PBS, phosphate-buffered saline; bp, base pair(s); Tricine, N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine.
HORMONAL REGULATION OF HEPATIC ORGANIC ANION TRANSPORTING POLYPEPTIDES
Molecular Pharmacology, 2005
This work was supported by grants DK46923 (to M.V.), training grant ES07266 (to M.W. and R.W.-K.),and HD20632 (to F.J.S.) from the United States Public Health Service. Article, publication date, and citation information can be found at http:// molpharm.aspetjournals.org. ABBREVIATIONS: Oatp/OATP organic anion transporting polypeptide Ntcp Na + -taurocholate cotransporting polypeptide PRL prolactin GH growth hormone PRLR L long form of the prolactin receptor GHR growth hormone receptor Stat5 signal transducer and activator of transcription FXR/BAR bile acid receptor PCR polymerase chain reaction FBS fetal bovine serum PBS phosphate-buffered saline MOPS 4-morpholinepropanesulfonic acid o ovine r rat.
Functional characterization of the basolateral rat liver organic anion transporting polypeptide
Hepatology, 1994
To characterize the transport functions of a recently cloned basolateral organic anion transporting polypeptide of rat hepatocytes we performed further kinetic transport and substrate cis-inhibition studies in organic anion-transporting polypeptide—cRNA injected Xenopus laevis oocytes. The studies demonstrate saturable Na+-independent sulfobromophthalein (Michaelis-Menten constant, 1.5 μmol/L) and taurocholate (Michaelis-Menten constant, 50 μmol/L) uptake by organic anion-transporting polypeptide. Sulfobromophthalein uptake was inhibited by the following organic anions: 0.01 mmol/L bilirubin (43%), 0.1 mmol/L indocyanine green (81%), 0.1 mmol/L 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS; 52%) and 1 mmol/L probenecid (74%). Competitive inhibition was shown for indocyanine green (inhibition constant about 1.3 μmol/L). Sulfobromophthalein and taurocholate uptakes were also inhibited by cholate, chenodeoxycholate, deoxycholate and ursodeoxycholate, as well as their glycine and taurine conjugates. Organic anion-transporting polypeptide also mediated uptake of glycocholate, tauroursodeoxycholate and taurochenodeoxycholate. No cis-inhibition of sulfobromophthalein uptake was seen in the presence of ATP, para-aminohippuric acid, bumetanide, digitoxin, reduced glutathione, leukotriene C4, nicotinic acid, ouabain, oxalate, rifampicin, succinate or sulfate. Furthermore, radioactively labeled paraaminohippuric acid, α-ketoglutarate and reduced glutathione were not taken up by organic aniontransporting polypeptide in cRNA-injected frog oocytes. These data confirm that organic aniontransporting polypeptide represents a novel hepatocellular organic anion uptake system that can mediate Na+-independent transport of monovalent (e.g., bile acids) and divalent (e.g., sulfobromophthalein and indocyanine green) cholephilic organic anions. A variety of substrates previously shown to inhibit uptake of sulfobromophthalein and bile acids in perfused rat livers, isolated hepatocytes and basolateral membrane vesicles had no cis-inhibitory effects on organic aniontransporting polypeptide—mediated organic anion transport in X. laevis oocytes. Thus additional Na+-independent organic anion carriers must be present in the basolateral membranes of rat hepatocytes. (Hepatology 1994;20:411-416.)
Identification of multispecific organic anion transporter 2 expressed predominantly in the liver
FEBS Letters, 1998
In the present study, we demonstrate that NLT (novel liver-specific transport protein) is a multispecific organic anion transporter of the liver. The amino acid sequence of NLT shows 42% identity to that of the renal multispecific organic anion transporter, OAT1. When expressed in Xenopus laevis oocytes, NLT mediated uptake of organic anions, such as salicylate, acetylsalicylate, PGE P , dicarboxylates and p-aminohippurate.
Effects of Herbal Extracts on the Function of Human Organic Anion-Transporting Polypeptide Oatp-B
Drug Metabolism and Disposition, 2006
Most known interactions between herbal extracts and drugs involve the inhibition of drug-metabolizing enzymes, but little is yet known about the possible role of transporters in these interactions. In this study, we have examined the effects of herbal extracts used in dietary supplements on the function of organic aniontransporting polypeptide B (OATP-B; OATP2B1), which is expressed on human intestinal epithelial cells and is considered to be involved in the intestinal absorption of various drugs. Specifically, the effects of 15 herbal extracts on uptake of estrone-3-sulfate, a typical OATP-B substrate, by human embryonic kidney 293 cells stably expressing OATP-B were evaluated. At concentration levels considered likely to be attainable in the human intestine, extracts of bilberry, echinacea, green tea, banaba, grape seed, ginkgo, and soybean potently inhibited estrone-3-sulfate uptake by 75.5, 55.5, 82.1, 61.1, 64.5, 85.4, and 66.8%, respectively (P < 0.01). The inhibitory effect of ginkgo leaf extract was concentration-dependent (IC 50 ؍ 11.2 ؎ 3.3 g/ml) and reversible. Moreover, flavonol glycosides and catechins significantly inhibited the function of OATP-B, suggesting that the inhibitory effects of the herbal extracts on OATP-B may be primarily attributable to flavonoids. The extracts of mulberry, black cohosh, and Siberian ginseng moderately (but significantly) inhibited estrone-3-sulfate uptake by 39.1, 47.2, and 49.2%, respectively (P < 0.05). Extracts of barley, Job's tears, rutin, rafuma, and passionflower were ineffective. These results suggest that coadministration of some dietary supplements may decrease the absorption of orally administered substrates of OATP-B. Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.