Roles of PI3-kinase and map-kinase pathways for the effects of IGF-1 on DNA synthesis and HGF production

Hepatic stellate cells (HSC) are located adjacent to hepatocytes and produc e hepatocyte growth factor (HGF) in the normal liver. In addition to the en docrine actions of hepatic insulinlike growth factor 1 (IGF-I), it also sti mulates the proliferation of HSC locally in the liver. We have now studied the effects of IGF-I on DNA synthesis and HGF production in HSC. Further mo re on we used selective blockers to investigate crucial signalling pathways for the effects of IGF-1 in cultured rat HSC. We found that addition of IGF-I (100 ng/ml) for 48 hours to 4-day-old prima ry cultures of rat BSC increased the concentrations of immunoreactive HGF i n the medium, as well as DNA synthesis measured as thymidine incorporation. These parameters were also enhanced by IGF-2 and des(1-3)IGF-l, which has reduced binding to IGF-binding proteins. IGF-1 also increased the abundance of HGF mRNA. Both LY294002, a phosphatidylinositol 3-kinase (PI3-K) inhibi tor, and rapamycin, a blocker of p70(S6K), a molecule downstream from PI3-K , completely reversed the IGF-l-induced stimulation of DNA synthesis. MAPK inhibition by PD98059 also had a suppressory effect. Both LY294002 and PD98 059 maximally lowered the IGF-l-induced increase of HGF in the medium by ab out 40%, but LY294002 was 10 times more potent than PD98059. In conclusion, IGFs stimulate both DNA synthesis and production of HGF by HSC in vitro. B oth PI3-K; and MAPK seem to be important for IGF-l-stimulated DNA synthesis and HGF production.