Abstract
The organic anion transporting polypeptide 4c1 (Oatp4c1) was previously identified as a novel uptake transporter predominantly expressed at the basolateral membrane in the rat kidney proximal tubules. Its functional role was suggested to be a vectorial transport partner of an apically-expressed efflux transporter for the efficient translocation of physiological substrates into urine, some of which were suggested to be uremic toxins. However, our in vitro studies with MDCKII cells showed that upon transfection rat Oatp4c1 polarizes to the apical membrane. In this report, we validated the trafficking and function of Oatp4c1 in polarized cell systems as well as its subcellular localization in rat kidney. Using several complementary biochemical, molecular and proteomic methods as well as antibodies amenable to immunohistochemistry, immunofluorescence, and immunobloting we investigated the expression pattern of Oatp4c1 in polarized cell systems and in the rat kidney. Collectively, these data demonstrate that rat Oatp4c1 traffics to the apical cell surface of polarized epithelium and localizes primarily in the proximal straight tubules, the S3 fraction of the nephron. Drug uptake studies in Oatp4c1-overexpressing cells demonstrated that Oatp4c1-mediated estrone-3-sulfate (E3S) uptake was pH-dependent and ATP-independent. These data definitively demonstrate the subcellular localization and histological location of Oatp4c1 and provide additional functional evidence that reconciles expression-function reports found in the literature.
Highlights
The kidney is responsible for homeostasis of endogenous and exogenous substances through tubular secretion and reabsorption, which in part is mediated by various membrane transporters, including the solute carrier family (SLC) and ATP-binding cassette (ABC) superfamily
organic anion transporting polypeptide 4c1 (Oatp4c1) was observed on the cell membrane (Fig. 1B, inset) in the MDCKII-Oatp4c1 cells, and no staining was observed in the negative control or in the MDCKII-pcDNA cells
We undertook a comprehensive approach to determine the subcellular localization of Oatp4c1 in polarized epithelium
Summary
The kidney is responsible for homeostasis of endogenous and exogenous substances through tubular secretion and reabsorption, which in part is mediated by various membrane transporters, including the solute carrier family (SLC) and ATP-binding cassette (ABC) superfamily. Several studies have demonstrated that overlapping substrate specificity among uptake and efflux transporters is likely to accelerate the translocation of endogenous and exogenous substances across epithelial or endothelial barriers [1,2]. OATP4C1 is the only OATP detected in renal proximal tubules [6]. The physiological role of OATP4C1, reportedly a basolateral uptake transporter, has been postulated to be coupling with P-glycoprotein, an apical efflux transporter, to facilitate the renal clearance of common substrates such as digoxin [5] and uremic toxins [10]. In studies with transgenic rats harboring human SLCO4C1, the decrease of uremic toxin (guanidino succinate, asymmetric dimethylarginine, and trans-aconitate) concentrations in plasma suggests that OATP4C1 may facilitate the excretion of uremic toxins in renal failure models and, by extension, in patients with chronic kidney disease. Direct evidence that these toxins are OATP4C1 substrates is lacking
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
