Characterization of Plasma Membrane Localization and Phosphorylation Status of Organic Anion Transporting Polypeptide (OATP) 1B1 c.521 T>C Nonsynonymous Single-Nucleotide Polymorphism

Purpose Membrane transport protein organic anion transporting polypeptide (OATP) 1B1 mediates hepatic uptake of many drugs (e.g. statins). The OATP1B1 c.521 T > C (p. V174A) polymorphism has reduced transport activity. Conflicting in vitro results exist regarding whether V174A-OATP1B1 has reduced plasma membrane localization; no such data has been reported in physiologically relevant human liver tissue. Other potential changes, such as phosphorylation, of the V174A-OATP1B1 protein have not been explored. Current studies characterized the plasma membrane localization of V174A-OATP1B1 in genotyped human liver tissue and cell culture and compared the phosphorylation status of V174A- and wild-type (WT)-OATP1B1. Methods Localization of V174A- and WT-OATP1B1 were determined in OATP1B1 c.521 T > C genotyped human liver tissue ( n = 79) by immunohistochemistry and in transporter-overexpressing human embryonic kidney (HEK) 293 and HeLa cells by surface biotinylation and confocal microscopy. Phosphorylation and transport of OATP1B1 was determined using 32 P-orthophosphate labeling and [ 3 H]estradiol-17β-glucuronide accumulation, respectively. Results All three methods demonstrated predominant plasma membrane localization of both V174A- and WT-OATP1B1 in human liver tissue and in cell culture. Compared to WT-OATP1B1, the V174A-OATP1B1 has significantly increased phosphorylation and reduced transport. Conclusions We report novel findings of increased phosphorylation, but not impaired membrane localization, in association with the reduced transport function of the V174A-OATP1B1.