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 mesenchymal‐derived factor that acts via a dual system receptor, consisting of the MET receptor and proteoglycans present on adjacent epithelial cells. Surprisingly, HGS/SF stimulated the migration of rat mammary (Rama) 27 fibroblasts, although it failed to stimulate their proliferation. HGF/SF stimulated a transient activation of mitogen‐activated protein kinases p44 and p42 (p42/44MAPK), with a maximum level of dual phosphorylation of p42/44MAPK occurring 10–15 min after the addition of the growth factor, which was followed by a rapid decrease to near basal levels after 20 min. Interestingly, a second phase of p42/44MAPK dual phosphorylation was observed at later times (3 h to 10 h). PD098059, a specific inhibitor of MEK‐1, prevented the dual phosphorylation of p42/44MAPK and also the phosphorylation of p90RSK (ribosomal subunit S6 kinase), which mirrored the kinetics of p42/44MAPK phosphorylation. Moreover, PD098059 prevented the HGF/SF‐induced migration of Rama 27 cells. HGF/SF also induced an early increase in the phosphorylation of protein kinase B/Akt. Akt phosphorylation was elevated 15 min after the addition of HGF/SF and then declined to basal levels by 30 min. Wortmannin, an inhibitor of phosphatidylinositol 3‐kinase (PtdIns3K), prevented the increase in Akt phosphorylation and abolished HGF/SF‐induced migration of fibroblasts. PD098059 also inhibited the stimulation of Akt phosphorylation by HGF/SF and wortmannin similarly inhibited the stimulation of p42/44MAPK dual phosphorylation. These results suggest that HGF/SF‐induced motility depends on both the transient dual phosphorylation of p42/44MAPK and the activation of PtdIns3K in Rama 27 fibroblasts and that these pathways are mutually dependent.