Tauroursodeoxycholic acid mobilizes α‐PKC after uptake in human HepG2 hepatoma cells

Background Tauroursodeoxycholic acid (TUDCA) may exert anticholestatic effects via Ca ++ ‐ and α‐protein kinase C (α‐PKC)‐dependent apical vesicular insertion of canalicular transporters in cholestatic hepatocytes ( Hepatology 2001; 33: 1206–16). Tauroursodeoxycholic acid is mainly taken up into liver cells by Na + ‐taurocholate cotransporting polypeptide (Ntcp). Tauroursodeoxycholic acid selectively translocates α‐PKC, a key mediator of regulated exocytosis, to hepatocellular membranes. It is unclear whether TUDCA exerts its effects on α‐PKC after carrier‐mediated uptake into liver cells or by interaction with extracellular/membraneous structures . Materials and methods Human hepatoblastoma HepG2 cells lacking Ntcp were stably transfected with pcDNA3·1/Ntcp or sham‐transfected with pcDNA3·1 [+]. Distribution of α‐PKC was studied using a Western blotting technique. Uptake of [ 3 H]taurocholic acid (TCA) was determined radiochemically. Results [ 3 H]taurocholic acid uptake was approximately 180‐fold higher in Ntcp‐transfected than in sham‐transfected cells. Phorbol 12‐myristate 13‐acetate (1 µmol L −1 ; positive control) increased membrane binding of α‐PKC by 34% in Ntcp‐transfected and by 37% in sham‐transfected cells. Tauroursodeoxycholic acid (10 µmol L −1 ) increased membrane‐associated α‐PKC by 19% in Ntcp‐transfected, but not in sham‐transfected cells (−13%). Taurocholic acid (10 µmol L −1 ) did not affect the distribution of α‐PKC. Conclusion Carrier‐mediated uptake is a prerequisite for TUDCA‐induced translocation of α‐PKC to hepatocellular membranes.