Transport of estrone sulfate by the novel organic anion transporter Oat6 (Slc22a20)

Abstract

Recently, a novel Slc22 gene family member expressed in murine olfactory mucosa was identified and based on sequence homology proposed to be an organic anion transporter [Oat6 (Slc22a20); J. C. Monte, M. A. Nagle, S. A. Eraly, and S. K. Nigam. Biochem Biophys Res Commun 323: 429-436, 2004]. However, no functional data for Oat6 was reported. In the present study, we demonstrate that murine Oat6 mediates the inhibitable transport of estrone sulfate using both Xenopus oocyte expression assay and Chinese hamster ovary (CHO) cells stably transfected with mOat6 (CHO-mOat6). Uptake was virtually eliminated by probenecid and the anionic herbicide 2,4-dichlorophenoxyacetate. The organic anions ochratoxin A, salicylate, penicillin G, p-aminohippurate, and urate inhibited mOat6-mediated accumulation to varying degrees. Transport of estrone sulfate by mOat6 was demonstrated to be saturable, and K(m) estimates of 109.8 +/- 22.6 microM in oocytes and 44.8 +/- 7.3 microM in CHO-mOat6 cells were obtained. Inhibitory constants for 2,4-dichlorophenoxyacetate (15.7 +/- 2.0 microM), salicylate (49.0 +/- 4.4 microM), probenecid (8.3 +/- 2.5 microM), and penicillin G (1,450 +/- 480 microM) were also determined. Accumulation of estrone sulfate mediated by mOat6 was significantly trans-stimulated by glutarate, indicating that mOat6 functions as an organic anion/dicarboxylate exchanger. These data demonstrate for the first time that the novel murine gene Oat6 (Slc22a20) encodes a functional organic anion transporter and mOat6 is indeed the newest member of the OAT gene family.

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

“…That is, saturable transport of estrone sulfate was observed, and was potently inhibited by several compounds; salicylic acid, probenecid, 2,4-dichlorophenoxyacetate and ochratoxin A. In addition, benzylpenicillin, uric acid and p-aminohippurate were less potent inhibitors [78]. Similar to Oat1 and Oat3, organic anion transport by Oat6 was trans-stimulated by glutarate, indicating that Oat6 is also an exchanger fueled by TCA cycle intermediates [78].…”

“…In addition, benzylpenicillin, uric acid and p-aminohippurate were less potent inhibitors [78]. Similar to Oat1 and Oat3, organic anion transport by Oat6 was trans-stimulated by glutarate, indicating that Oat6 is also an exchanger fueled by TCA cycle intermediates [78]. Localization within the nasal mucosa, coupled with interaction with odorant-like molecules, e.g.…”

Olfactory mucosa-expressed organic anion transporter, Oat6, manifests high affinity interactions with odorant organic anions

“…To characterize the transport function of Oat6 in comparison to that of Oat1, we initially measured uptake of the known Oat6 substrate, [ 3 H]-ES [14], and of the known Oat1 substrate, [ 3 H]-PAH [1], in Oat1-and Oat6-expressing oocytes respectively (Figure 3a). In these experiments, transporter-mediated uptake of [ 3 H]-labeled tracer considerably exceeded (typically 10-fold or more) the background uptake in uninjected oocytes.…”

Alteration in Renal Organic Anion Transporter 1 After Ischemia/Reperfusion in Cadaveric Renal Allografts

“…Recently, a family of organic anion transporters (OAT1-6) has been cloned. Our understanding of their molecular and functional characteristics has increased (Lopez-Nieto et al 1997;Sekine et al 1997Sekine et al ,1998Sekine et al ,2006Hosoyamada et al1999;Kusuhara et al 1999;Cha et al 2000;You 2002;Monte et al 2004;Youngblood and Sweet 2004;Anzai et al 2005Anzai et al ,2006Schnabolk et al 2006). hOAT1 is a prototypical organic anion transporter with the highest affinity for PAH among the OAT isoforms; transport affinity (Km) of hOAT1 for PAH is 5-9.3 mM, whereas Km of hOAT3 for PAH is 87 mM and OAT2 is present predominantly in the liver.…”