Functional Characterization Reveals the Significance of Rare Coding Variations in Human Organic Anion Transporting Polypeptide 2B1 (21).

The organic anion transporting polypeptide 2B1 (OATP2B1), which is encoded by the 21 gene, plays important roles in the absorption and disposition of its substrate drugs. Nonsynonymous variations of 21 change its amino acid sequence and may alter its function. However, so far, very few genetic variants of 21 have been functionally characterized. In the present study, first of all, 14 nonsynonymous single nucleotide variants (SNVs) of 21 have been identified from the dbSNP database. Then, human embryonic kidney (HEK293) cells were employed as the expression system and functional studies were carried out for these 14 SNVs using substrates 4',5'-dibromofluorescein (DBF), estrone-3-sulfate (E3S), atorvastatin, and rosuvastatin. Our results showed that four nonsynonymous rare variants, namely, 21 c.332G > A (p.R111Q), c.1184C > A (p.P395H), c.1624G > A (p.V542M), and c.1998C > A (p.F666L), have great effect on the function of OATP2B1. Surface biotinylation and immunoblot analysis indicated that the variant c.1184C > A (p.P395H) almost completely disrupted OATP2B1's expression on the plasma membrane. According to the three-dimensional structural model of OATP2B1 we developed, these four mutated residues are not located at the substrate binding region of OATP2B1. Their significant effect on the function of OATP2B1 could probably be attributed to jeopardizing OATP2B1's surface expression as exemplified by c.1184C > A (p.P395H), altering the transporter's overall structure and affecting its interactions with other proteins or the lipid bilayer. Taken together, our results demonstrated that rare coding variants could have a great impact on the function and expression of OATP2B1.