2011 Volume 28 Issue 3 Pages 128-138
We have previously reported that maoto inhibits a serum-induced motility of human breast cancer MDA-MB-231 cells. However, the molecular mechanism by which maoto realizes this inhibition was not elucidated. In this study, we focused on the effects of maoto on hepatocyte growth factor (HGF)-c-Met signaling, because HGF is one of the growth factors in serum and stimulates cell migration through tyrosine phosphorylation of c-Met. A Transwell migration assay demonstrated that maoto extract prevented the HGF-induced motility, and a major component of maoto, Ephedrae herba extract, had the same effect. However, both extracts of maoto that did not contain Ephedrae herba (maotokyomao) and a reference prescription, shikunshito, had no such effect. To confirm the effects of maoto and Ephedrae herba on HGF-c-Met signaling,we examined the effects of these medicines on HGF-induced phosphorylation of c-Met. Both extracts of maoto and Ephedrae herba inhibited c-Met phosphorylation, but neither maotokyomao extract nor shikunshito extract had such effects. Moreover, Ephedrae herba extract directly inhibited the tyrosine-kinase activity of c-Met and suppressed the HGF-induced phosphorylations of Akt, which is a signal molecule downstream of c-Met. We further investigated whether maoto and Ephedrae herba inhibit the expression of c-Met. The c-Met protein and gene expression were reduced after 24 h of the treatment with maoto extract or Ephedrae herba extract. These inhibitory effects of maoto were lost by removal of Ephedrae herba from the prescription, suggesting that the effects were attributable to Ephedrae herba. Taken together, these results suggested that Ephedrae herba, a major component of maoto, inhibits the HGF-induced motility of MDA-MB-231 cells by the suppression of HGF-c-Met-Akt signaling through the inhibition of both c-Met tyrosine phosphorylation and c-Met expression.
