Phosphatidylinositol 3-kinase is required for platelet-derived growth factor's actions on hepatic stellate cells

Background and Aims: Platelet-derived growth factor (PDGF) is the most potent mitogen for hepatic stellate cells (HSCs) in vitro. The aim of this study was to investigate the role of phosphatidylinositol 3-kinase (PI 3-K) activation in mediating the biological effects of PDGF on cultured HSCs and its involvement in vivo. Methods: HSCs were isolated from normal human livers. PI 3-K was assayed on phosphotyrosine or PDGF-receptor immunoprecipitates by in vitro kinase assay. Results: Incubation of HSCs with PDGF caused a time-dependent increase in PI 3-K activity. Immunoprecipitation of PDGF-α and -β receptors showed that both subunits associate with active PI 3-K in PDGF-stimulated HSCs. Wortmannin, a specific PI 3-K inhibitor, dose-dependently blocked PI 3-K activity induced by PDGF and inhibited DNA synthesis. PDGF (homodimer)-BB also stimulated HSC chemotaxis, which was inhibited by pretreatment with wortmannin. To explore the potential role of PI 3-K in vivo, liver homogenates from rats treated with CCl₄ and from control rats were immunoprecipitated with anti-PDGF-β-receptor antibodies. Liver injury was associated with increased PDGF-β-receptor autophosphorylation, and greater PI 3-K activity associated with the receptor itself. Conclusions: This study shows that in cultured HSCs, PI 3-K activation is necessary for both mitogenesis and chemotaxis induced by PDGF and that this pathway is up-regulated during liver injury in vivo.