How does S‐palmitoylation affect the Organic Anion Transporting Polypeptide 1B1 (OATP1B1)?

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BackgroundOrganic Anion Transporting Polypeptide 1B1 (OATP1B1) is an important transporter localized to the basolateral membrane of human hepatocytes that mediates the uptake of numerous therapeutics like statins, antibiotics, and anti‐cancer agents. Previous studies from our lab suggest that OATP1B1 is localized in membrane microdomains, also known as lipid rafts, which contain various components like saturated lipids, cholesterol, and lipidated proteins. Lipidated proteins are frequently the result of S‐palmitoylation, a reversible post translational modification that adds palmitic acid (C16:0) to cysteine residues. Currently, not much is known about the potential impact of S‐palmitoylation on OATP1B1 function and localization. Aim: We hypothesize that OATP1B1 is S‐palmitoylated and that this affects its function and localization.MethodsWe measured uptake of the model substrate estradiol‐17β‐glucuronide in cells expressing OATP1B1. S‐palmitoylation was detected using an acyl‐biotin exchange (ABE) assay in combination with western blotting. To prevent S‐palmitoylation, cells were preincubated with 2‐bromopalmitate (2BP). Expression of OATP1B1 at the plasma membrane was assessed using surface biotinylation.ResultsThe ABE assay demonstrated that OATP1B1 is S‐palmitoylated and that pretreatment of the cells for 18 hours with 2BP reduces S‐palmitoylation. Inhibition of S‐palmitoylation with 2BP for 18 hours also resulted in decreased OATP1B1‐mediated transport of estradiol‐17β‐glucuronide as well as in a reduction of surface expression of OATP1B1.Summary and ConclusionsOur results demonstrate that OATP1B1 is S‐palmitoylated. Inhibition of S‐palmitoylation reduces the function and the surface expression of OATP1B1. Thus, these findings suggest that S‐palmitoylation is a post‐translational modification involved in the regulation of this important hepatic drug uptake transporter.