Heterodimerization of Organic Anion Transporting Polypeptide 1B3 can affect function and surface expression

Abstract

OATP1B3 is a drug transporter expressed at the basolateral membrane of human hepatocytes, along with other transporters, including OATP1B1, OCT1 and NTCP. It has a broad spectrum of substrates including endogenous compounds and numerous drugs. Thus, modulation of OATP1B3 function and expression has the potential to affect drug efficacy and disposition. Previous studies in our lab demonstrated that OATP1B3 can form homo‐ and heterodimers, both in cell models and in frozen human liver tissue. However, functional consequences of these interactions have not been investigated so far. In this study, we used transient transfection of HEK293 cells with FLAG‐tagged OATP1B3 in combination with a His‐tagged non‐functional OATP1B3 mutant, or with His‐tagged OATP1B1 or NTCP, surface biotinylation, and cell‐based uptake assays to characterize the functional consequences of the dimerization. Co‐transfection of mutant and wild‐type OATP1B3 resulted in a similar uptake of both estrone‐3‐sulfate and estradiol‐17β‐glucuronide after normalization for surface expression as co‐transfection of empty vector with wild‐type OATP1B3, suggesting that the homodimer of OATP1B3 works as two independent functional subunits. Uptake of the OATP1B3‐specific substrate CCK8 decreased significantly when OATP1B3 was co‐expressed with NTCP, while co‐expression with OATP1B1 had no effect. In contrast, uptake of low concentration estrone‐3‐sulfate by OATP1B1 and taurocholic acid by NTCP was not affected by co‐expression with OATP1B3. Expression of OATP1B3 on the surface of HEK293 cells was reduced when OATP1B3 was co‐expressed with NTCP suggesting that the functional decrease might be a result of disturbed protein production and/or translocation to the plasma membrane. These results indicate that co‐expression of NTCP with OATP1B3 can affect OATP1B3‐mediate drug transport and as a consequence can have an effect on drug therapy.Support or Funding InformationNIH grants GM103549 and GM077336