IGF-1 induces growth, survival and morphological change of primary hepatocytes on a galactose-bared polymer through both MAPK and β-catenin pathways

Abstract

PVLA poly-(N-p-vinylbenzyl-O-β-D-galactopyranosyl-D-gluconamide) is a glycopolymer composed of hydrophilic carbohydrate side chain and hydrophobic styrene polymer. The hydrophilic carbohydrate residue of PVLA can be recognized as a ligand for hepatocytes asialoglycoprotein receptor (ASGP-R), which is abundant on the hepatocyte cell surface. Adhering to the PVLA coated dishes, hepatocytes try to form aggregates that have a long time survival and also cells in these aggregates exhibit better maintenance of specific hepatocyte functions. Stimulation of the cells with IGF-1 in this culture condition results in the formation of lower aggregates. In addition to the morphological influences of IGF-1 to these cells, we have also found that IGF-1 transmits growth stimulatory responses to hepatocytes on PVLA through both mitogen activated protein kinase (MAPK) pathway and β-catenin pathways. The phosphorylation of MAPK can take place within 5 min of stimulation with IGF-1 and within at least 10 ng/ml of IGF-1 concentration. Inhibition of MAPK activation by MEK-1 inhibitor PD98059 reduces IGF-1 induced MAPK phosphorylation, and also IGF-1 stimulated DNA synthesis. Similarly, the use of PI3-K inhibitor LY294002 also inhibits IGF-1 stimulated DNA synthesis. IGF-1 stimulation enhances the migration of β-catenin from the cytoskeleton and cell membrane to the cytoplasm which also is the reason behind formation of spheroids and lower aggregates. IGF-1 stimulation also shows increased translocalization of β-catenin to the nucleus that is essentially important to produce β-catenin responsive effects to the cells. These studies thus suggest that IGF-1 can stimulate the growth and survival of hepatocytes on PVLA through both MAPK and β-catenin signaling pathways, and that the activation of β-catenin signaling pathway produces the morphological changes of IGF-1 induced cells.