Pro-metastatic signaling by c-Met through RAC-1 and reactive oxygen species (ROS)

Overexpression of the c-Met/hepatocyte growth factor receptor( HGF-R) proto-oncogene and abnormal generation of intracellular oxygen species ( reactive oxygen species ( ROS)) have been linked, by independent lines of evidence, to cell transformation and to malignant growth. By comparing two subpopulations of the B16 mouse melanoma ( B16-F0 and B16-F10) endowed with different lung metastasis capacities ( low and high, respectively) we found that both the expression/phosphorylation of c-Met and the steady-state levels of ROS positively correlated with metastatic growth. shRNA-mediated downregulation of c-Met in F10 cells led to a parallel decrease in the generation of oxygen species and in metastatic capacity, suggesting that oxidants may mediate the pro-metastatic activity of the HGF receptor. c-Met activation by a ligand elicits the formation of oxidant species through the oxidase-coupled small GTPase Rac-1, a relevant downstream target of the HGF-R. Moreover, cell treatment with the catalytic ROS scavengers EUK-134 and EUK-189 attenuates Met signaling to ERKs and inhibits the anchorage-independent growth of F10 cells, consistent with a critical role for oxygen species in HGF signaling and in aggressive cell behavior. Finally, genetic manipulation of the Rac-ROS cascade at different levels demonstrated its crucial role in the pro-metastatic activity of c- Met in vivo. Thus, we have outlined a novel cascade triggered by c- Met and mediated by ROS, linked to metastasis and potentially targetable by new antimetastatic, redox-based therapies.