Tryptophan and iodothyronine transport interactions in HepG2 human hepatoma cells

This study identifies interactions between transport of the aromatic amino acid l-tryptophan (Trp) and thyroid hormones (TH) in HepG2 human hepatoma cells. The major portion of Trp uptake in HepG2 cells occurs via the NEM-sensitive amino acid transport System L2 (consistent with hepatic LAT3 expression), with a smaller aromatic-AA selective System T (MCT10) component. LAT3 and MCT10 mRNA were both detected in HepG2 cells. Uptake of TH does not involve System L2, but a significant portion of T-3 uptake is mediated by System T, alongside a taurocholate-sensitive organic anion transporter. T-4 uptake into HepG2 cells appears to be mediated principally by organic anion/monocarboxylate transporters, with smaller contributions by System T and receptor-mediated endocytosis. TH-Trp transport interactions in liver cells centre on System T which, due to a perivenous localisation alongside deiodinase 1, may impact on hepatic T-3 generation and release.