Mutations in the SLCO1B3 gene affecting the substrate specificity of the hepatocellular uptake transporter OATP1B3 (OATP8)

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Abstract
Hepatocellular uptake transporters are involved in the hepatobiliary elimination of endogenous and xenobiotic substances. Mutations in genes encoding these uptake transporters may be key determinants of interindividual variability in hepatobiliary elimination and drug disposition. Our aim was to investigate the functional consequences of mutations in the SLCO1B3 gene encoding the hepatic uptake transporter for organic anions OATP1B3, formerly termed OATP8. Mutations occurring in Caucasian Europeans and observed in databases were introduced into the SLCO1B3 cDNA and the consequences were analyzed in stably transfected canine MDCKII cells and human HEK293 cells. The functional consequences were examined for two frequent polymorphisms SLCO1B3-334T>G, encoding OATP1B3-S112A (allelic frequency of 74%) and SLCO1B3-699G>A, encoding OATP1B3-M233I (allelic frequency of 71%) and one rare polymorphism SLCO1B3-1564G>T, encoding OATP1B3-G522C (allelic frequency of 1.9%) and one artificial mutation SLCO1B3-1748G>A, encoding OATP1B3-G583E. OATP1B3-S112A, OATP1B3-M233I, and the OATP1B3 protein corresponding to the reference sequence (accession NM_019844), showed a comparable lateral localization in stably transfected MDCKII cells, whereas OATP1B3-G522C and OATP1B3-G583E proteins were retained intracellularly. Both latter amino acid substitutions abolished the transport of bile acids mediated by OATP1B3, whereas other substrates, like bromosulfophthalein, were transported by all polymorphic variants of the protein. The functional consequences of three polymorphisms and one artificial mutation include differences in the localization and in transport characteristics of several OATP1B3 proteins. This study demonstrates the importance of the analysis of genetic variations in genes encoding transport proteins for the understanding of individual variations in the hepatobiliary elimination of substances.