Shared Ligands Between Organic Anion Transporters (OAT1 and OAT6) and Odorant Receptors

The multispecific organic anion drug transporters OAT6 (SLC22A20) and OAT1 (SLC22A6) are expressed in nasal epithelial cells and both can bind odorants. Sequence analysis of OAT6 revealed an evolutionarily conserved 79-amino acid (AA) fragment present not only in OAT6 but also in other SLC22 transporters, such as the organic anion transporter (OAT), organic carnitine transporter (OCTN), and organic cation transporter (OCT) subfamilies. A similar fragment is also conserved in some odorant receptors (ORs) in both humans and rodents. This fragment is located in regions believed to be important for ligand/substrate preference and recognition in both classes of proteins, raising the possibility that it may be part of a potential common ligand/substrate recognition site in certain ORs and SLC22 transporters. In silico screening of an odorant database containing known OR ligands with a pharmacophore hypothesis (generated from a set of odorants known to bind OAT6 and/or OAT1), followed by in vitro uptake assays in transfected cells, identified OR ligands capable of inhibiting OAT6- and/or OAT1-mediated transport, albeit with different affinities. The conservation of the AA fragments between these two different classes of proteins, together with their coexpression in olfactory as well as other tissues, suggests the possibility that ORs and SLC22 transporters function in concert, and raises the question as to whether these transporters function in remote sensing and signaling and/or as transceptors.