Stable expression and functional characterization of a Na+-taurocholate cotransporting green fluorescent protein in human hepatoblastoma HepG2 cells

Sodium-dependent uptake of bile acids from blood is a liver-specific functi on which is mediated by the Na+-taurocholate cotransporting polypeptide (Nt cp). We report the stable expression of a Na+-taurocholate cotransporting g reen fluorescent fusion protein in the human hepatoblastoma cell line HepG2 , normally lacking Ntcp expression. Ntcp-EGFP associated green fluorescence colocalized with Ntcp immunofluorescence in the plasma membrane. In transf ected HepG2 cells, the fusion protein mediated the sodium-dependent uptake of the bile acid taurocholate (K-m: 24.6 mu mol/l) and of the anionic stero ids estrone-3-sulfate and dehydroepiandrosterone sulfate. We conclude that the Ntcp-EGFP fusion protein follows the sorting route of Ntcp, is function ally identical to Ntcp and could be used to monitor protein trafficking in living HepG2 cells.