Hepatocyte growth factor/scatter factor stimulates migration of rat mammary fibroblasts through both mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt pathways

Hepatocyte growth factor/scatter factor (HGF/SF) is considered to be a mese nchymal-derived factor that acts via a dual system receptor, consisting of the MET receptor and proteoglycans present on adjacent epithelial cells. Su rprisingly, HGS/SF stimulated the migration of rat mammary (Rama) 27 fibrob lasts, although it failed to stimulate their proliferation. HGF/SF stimulat ed a transient activation of mitogen-activated protein kinases p44 and p42 (p42/44(MAPK)), with a maximum level of dual phosphorylation of p42/44(MAPK ) occurring 10-15 min after the addition of the growth factor, which was fo llowed by a rapid decrease to near basal levels after 20 min. Interestingly , a second phase of p42/44(MAPK) dual phosphorylation was observed at later times (3 h to 10 h). PD098059, a specific inhibitor of MEK-1, prevented th e dual phosphorylation of p42/44(MAPK) and also the phosphorylation of p90( RSK) (ribosomal subunit S6 kinase), which mirrored the kinetics of p42/44(M APK) phosphorylation. Moreover, PD098059 prevented the HGF/SF-induced migra tion of Rama 27 cells. HGF/SF also induced an early increase in the phospho rylation of protein kinase B/Akt. Akt phosphorylation was elevated 15 min a fter the addition of HGF/SF and then declined to basal levels by 30 min. Wo rtmannin, an inhibitor of phosphatidylinositol 3-kinase (PtdIns3K), prevent ed the increase in Akt phosphorylation and abolished HGF/SF-induced migrati on of fibroblasts. PD098059 also inhibited the stimulation of Akt phosphory lation by HGF/SF and wortmannin similarly inhibited the stimulation of p42/ 44(MAPK) dual phosphorylation. These results suggest that HGF/SF-induced mo tility depends on both the transient dual phosphorylation of p42/44(MAPK) a nd the activation of PtdIns3K in Rama 27 fibroblasts and that these pathway s are mutually dependent.