Transport of (sulfated) iodothyronines across the plasma membrane is required for their intracellular metabolism. Rat Na+/taurocholate cotransporting polypeptide (Ntcp; Slc10a1) has been identified as an important transporter protein. We demonstrate that among the 7 members of the solute carrier family SLC10, only human SLC10A1 mediates sodium-dependent transport of the iodothyronine T4 and iodothyronine sulfates T3S and T4S. In contrast to SLC10A2-7, cells co-expressing SLC10A1 and the deiodinase D1 demonstrate a dramatic increase in T3S and T4S metabolism. The SLC10A1 substrates taurocholate, DHEAS and E3S inhibit T3S and T4S transport. Furthermore, co-transfection of SLC10A1 with CRYM, a well-known intracellular iodothyronine-binding protein, results in an enhanced intracellular accumulation of T3S and T4S, indicating that CRYM binds iodothyronine sulfates. The present findings indicate that the liver-specific transporter SLC10A1 transports (sulfated) iodothyronines, thereby increasing their intracellular availability. Therefore, SLC10A1 may fulfill a critical step in providing liver D1 with iodothyronine sulfates for rapid degradation.

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Molecular and Cellular Endocrinology
Erasmus MC: University Medical Center Rotterdam