Activation of HGF/c-Met pathway contributes to the reactive oxygen species generation and motility of small cell lung cancer cells

Small cell lung cancer ( SCLC) is a difficult disease to treat and sometimes has overexpression or mutation of c- Met receptor tyrosine kinase. The effects of c- Met/ hepatocyte growth factor ( c- Met/ HGF, ligand for c- Met) on activation of reactive oxygen species ( ROS) was determined. HGF stimulation of c- Met-overexpressing H69 SCLC cells ( 40 ng/ ml, 15 min) resulted in an increase of ROS, measured with fluorescent probe 2'-7'- dichlorofluorescein diacetate ( DCFH-DA) or dihydroethidine ( DHE) but not in c-Met- null H446 cells. ROS was increased in juxtamembrane ( JM)- mutated variants ( R988C and T1010I) of c- Met compared with wild- type c- Met- expressing cells. ROS was significantly inhibited by preincubation of SCLC cells with pyrrolidine dithiocarbamate ( PDTC, 100 mu M) and/ or SU11274 ( small molecule c- Met tyrosine kinase inhibitor, 2 mu M) for 3 h. PDTC and SU11274 also abrogated the HGF proliferative signal and cell motility in a cooperative fashion. H2O2 treatment of SCLC cells ( over 15 min) led to phosphorylation of c- Met receptor tyrosine kinase and further upregulated downstream phosphorylation of phospho- AKT, ERK1/ 2, and paxillin in a dose- dependent manner ( 125 mu M to 500 mu M). c- Met is an important target in lung cancer, and the pathways responsible for ROS generation together may provide novel therapeutic intervention.