Platelet-derived growth factor receptor tyrosine kinase inhibitor AG1295 attenuates rat hepatic stellate cell growth

Abstract

Enhanced activity of receptor tyrosine kinases such as the platelet-derived growth factor-receptorβ (PDGF-Rβ) has been implicated as a contributing factor in the development of hepatic fibrosis. In this study we have used tyrosine kinase inhibitors of the tyrphostin class (AG1295) to specifically block autophosphorylation of PDGF-Rβ and proliferation of rat hepatic stellate cells. We also examined the effect of AG1295 on the PDGF-BB-induced activation of the 44 kd and 42 kd mitogen-activated protein (MAP) kinase isoforms (p44mapk/p42mapk). Rat hepatic stellate cells were treated with AG1295 (10 μmol/L) for 24 hours and stimulated with PDGF-BB for 5 minutes. AG1295 specifically inhibited autophosphorylation of PDGF-Rβ and caused a 20% decrease in PDGF-BB-stimulated bromodeoxyuridine incorporation by rat hepatic stellate cells. Treatment of rat hepatic stellate cells with AG1295 resulted in an inhibition of the PDGF-BB-induced activation of MAP kinase isoforms. Quantification of the immunoprecipitated tyrosine-phosphorylated phosphatidylinositol 3-kinase, phospholipase C-γ, and p21ras guanosine triphosphatase–activating protein by Western blotting revealed that AG1295 treatment effectively inhibits tyrosine phosphorylation of these kinases in hepatic stellate cells. Our findings demonstrate that AG1295 is a selective inhibitor of the tyrosine phosphorylation of PDGF-Rβ and its downstream signaling pathway, and this compound could offer a strategy for the treatment of fibrotic liver diseases. (J Lab Clin Med 2000;135:406-12)