Loss of palmitoylation impacts the interaction between the organic anion transporting polypeptide (OATP) 1B1 and OATP1B3.

Abstract

The organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are hepatic transporters that mediate the uptake of numerous therapeutics like antibiotics and statins. Various post-translational modifications, eg, phosphorylation and glycosylation, have been shown to impact OATP1B1 and OATP1B3 function and localization. S-palmitoylation (also known as S-acylation or palmitoylation) is a reversible post-translational modification that adds palmitic acid (C16:0) to cysteine residues and can influence a protein's function, localization, and protein-protein interactions. In this study, we investigated and characterized palmitoylation in OATP1B1 and OATP1B3. Using site-directed mutagenesis and acyl-resin-assisted capture assays, residue Cys24 was identified as the palmitoylation site for both these proteins. Uptake function and surface biotinylation experiments demonstrated that palmitoylation does not affect the individual function and surface expression of OATP1B1 and OATP1B3. Coexpression studies revealed a decrease in OATP1B1-OATP1B3 interactions when nonpalmitoylated OATP1B1 or nonpalmitoylated OATP1B3 are coexpressed with their wild-type counterparts, suggesting that S-palmitoylation regulates protein-protein interactions between OATP1B1 and OATP1B3. SIGNIFICANCE STATEMENT: This study identified and characterized palmitoylation of the organic anion transporting polypeptide (OATP) 1B1 and OATP1B3. Both OATP1B1 and OATP1B3 can be palmitoylated on the conserved Cys24 residue. Palmitoylation of these 2 transporters does not impact their individual function or surface expression. However, the interaction between these 2 proteins is affected when their palmitoylation state is altered.