Up-regulation of nuclear PP1 alpha and PP1 delta in hepatoma cells

Activities of nuclear type 1 protein phosphatase (PP1) were significantly e levated in human HepG2 and rat AH13 hepatoma cells compared with primary cu ltured hepatocytes. We examined and compared the nuclear PP1 activities dur ing the cell cycle between synchronized HepG2 cells and HGF-stimulated hepa tocytes. Nuclear PP1 activity was significantly and more elevated at the G( 1)/S transition in hepatoma cells compared with hepatocytes, although the a mounts of PP 1 isoforms remained constant. On the contrary, it was found th at the basal levels of nuclear PP1 activity were significantly higher in he patoma cells and that the amounts of PP1 alpha and PP1 delta were dramatica lly increased in the nuclear fraction of hepatoma cells.