Antiporter that mediates the import of reduced folates or a subset of cyclic dinucleotides, driven by the export of organic anions (    ). Mechanistically, acts as a secondary active transporter, which exports intracellular organic anions down their concentration gradients to facilitate the uptake of its substrates ( ). Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate ( ). Also able to mediate the import of antifolate drug methotrexate ( , ). Also acts as an importer of immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytosol, and its linkage isomer 3'-3'-cGAMP, thus playing a role in triggering larger immune responses (, ). 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity .
Subcellular locations: Cell membrane, Apical cell membrane, Basolateral cell membrane
Placenta, liver, and to a much smaller extent, in lung.