Enhanced activity of receptor tyrosine kinases such as the platelet-derived
growth factor-receptor beta (PDGF-R beta) has been implicated as a contrib
uting factor in the development of hepatic fibrosis. In this study we have
used tyrosine kinase inhibitors of the tyrphostin class (AG1295) to specifi
cally block autophosphorylation of PDGF-R beta and proliferation of rat hep
atic stellate cells. We also examined the effect of AG1295 on the PDGF-BB-i
nduced activation of the 44 kd and 42 kd mitogen-activated protein (MAP) ki
nase isoforms (p44(mapk)/p42(mapk)). Rat hepatic stellate cells were treate
d with AG1295 (10 mu mol/L) for 24 hours and stimulated with PDGF-BB for 5
minutes. AG1295 specifically inhibited autophosphorylation of PDGF-R beta a
nd caused a 20% decrease in PDGF-BB-stimulated bromodeoxyuridine incorporat
ion 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-phos
phorylated phosphatidylinositol 3-kinase, phospholipase C-gamma, and p21(ra
s) guanosine triphosphatase-activating protein by Western blotting revealed
that AG1295 treatment effectively inhibits tyrosine phosphorylation of the
se kinases in hepatic stellate cells. Our findings demonstrate that AG1295
is a selective inhibitor of the tyrosine phosphorylation of PDGF-R beta and
its downstream signaling pathway, and this compound could offer a strategy
for the treatment of fibrotic liver diseases.