α6β1 integrin expression in hepatocarcinoma cells: Regulation and role in cell adhesion and migration

Liver carcinogenesis is associated with striking changes in the integrin repertoire of hepatocytes, including the overexpression of the laminin and collagen receptors α1β1 and the de novo induction of the laminin receptor α6β1. Our aim was to analyze the role of pro-inflammatory cytokines, interferons and fibrogenic cytokines TGF-β and FGF2 in the regulation of the expression of β1 integrins by neoplastic hepatocytes. The 2 human hepatocellular cell lines HepG2 and Hep3B were used as models. Integrin expression was assessed by qualitative methods (immunocytochemistry, Western blotting) and semi-quantitative techniques (FACS, cellular ELISA), before and after stimulation by TNFα, ILI-β, TGF-β, FGF2, interferon γ and interferon α-2b. HepG2 and Hep3B constitutively expressed α1, α2, α6 and α1 chains. A 24 to 48-hr stimulation with pro-inflammatory cytokines, TGF-β and FGF2 induced a significant increase in the concentrations of all integrin chains. The maximum induction was registered for β1 chain, which presented increases amounting up to 3, 4 and 7 times the control values in the presence of, respectively, TNF α/ILI-β, TGF-β and FGF2. Interferons had no direct effect on integrin expression and partially antagonized the effects of TNF α and TGF-β. The increased concentrations of integrin chains were associated with an increased membrane expression of the corresponding dimers and with an increased adhesion of stimulated hepatocytes to laminin, which was antagonized by neutralizing anti-β1 and anti-α6 antibodies. Finally, anti- α6 antibody inhibited the migration of HepG2 and Hep3B cells in reconstituted basement membrane. Our results suggest that the stimulation of α6β1 integrin expression in hepatocarcinoma cells is essential for cell adhesion and migration.