Phosphatidylinositol-3 kinase and extracellular signal-regulated kinase mediate the chemotactic and mitogenic effects of insulin-lice growth factor-Iin human hepatic stellate cells

Background/Aim: Several studies have shown that proliferation of hepatic st ellate cells is stimulated by insulin-like growth factor-I. The aim of this study was to investigate the effect of insulin-like growth factor-I on hum an hepatic stellate cells chemotaxis and the intracellular pathways involve d in both mitogenic and chemotactic effects. Methods/Results: Insulin-like growth factor-I, at the concentration of 100 ng/ml, was able to induce a 2- to 3-fold increase in human hepatic stellate cells migration in a modified Boyden chamber system. This effect was assoc iated with a marked activation of phosphatidylinositol 3-kinase by insulin- like growth factor-I, as evaluated by measurement of phosphatidylinositol 3 -kinase activity in phosphotyrosine immunoprecipitates. In order to establi sh a functional link between these observations,,ve then performed experime nts employing two selective phosphatidylinositol 3-kinase inhibitors, namel y wortmannin and LY294002. These compounds blocked activation of phosphatid ylinositol 3-kinase and inhibited insulin like growth factor-I-induced hepa tic stellate cells migration. Since phosphatidylinositol 3-kinase activatio n has been shown to be necessary for platelet-derived growth factor-induced mitogenesis in hepatic stellate cells, we verified the effects of phosphat idylinositol 3-kinase inhibition on insulin-like growth factor-I-induced DN A synthesis. Incubation with either wortmannin or LY294002, dose-dependentl y reduced the mitogenic potential of insulin-like growth factor-I. Since ph osphatidylinositol 3-kinase is involved, at least in part, in the activatio n of the Ras/extracellular signal-regulated kinase pathway in hepatic stell ate cells, the role of extracellular signal-regulated kinase activation in mediating the biological effects of insulin-like growth factor-I was explor ed. Insulin-like growth factor-I induced mitogenesis and chemotaxis were ma rkedly reduced by pre-incubation of hepatic stellate cells with PD-98059, a selective inhibitor of MEK. Conclusions: Activation of phosphatidylinositol 3-kinase and extracellular signal-regulated kinase is required for both insulin-like growth factor-I-d ependent hepatic stellate cells proliferation and chemotaxis. Insulin-like growth factor-I, together with other soluble mediators, may contribute to t he hepatic mound-healing response by modulating hepatic stellate cells migr ation and proliferation.