PHOSPHATIDYLINOSITOL 3-KINASE IS REQUIRED FOR PLATELET-DERIVED GROWTH-FACTORS ACTIONS ON HEPATIC STELLATE CELLS

Background & Aims: Platelet-derived growth factor (PDGF) is the most p otent mitogen for hepatic stellate cells (HSCs) in vitro. The aim of t his study was to investigate the role of phosphatidylinositol 3-kinase (PI 3-K) activation in mediating the biological effects of PDGF on cu ltured HSCs and its involvement in vivo. Methods: HSCs were isolated f rom normal human livers. PI 3-K was assayed on phosphotyrosine or PDGF -receptor immunoprecipitates by in vitro kinase assay. Results: Incuba tion of HSCs with PDGF caused a time-dependent increase in PI 3-K acti vity. Immunoprecipitation of PDGF-alpha and -beta receptors showed tha t 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 (homodim er)-BB also stimulated HSC chemotaxis, which was inhibited by pretreat ment with wortmannin. To explore the potential role of PI 3-K in vivo, liver homogenates from rats treated with CCl4 and from control rats w ere immunoprecipitated with anti-PDGF-beta-receptor antibodies. Liver injury was associated with increased PDGF-Preceptor autophosphorylatio n, and greater PI 3-K activity associated with the receptor itself. Co nclusions: This study shows that in cultured HSCs, PI 3-K activation i s necessary for both mitogenesis and chemotaxis induced by PDGF and th at this pathway is up-regulated during liver injury in vivo.