Many studies have suggested a role for the hepatocyte growth factor (HGF)/c-Met pathway in tumorigenesis. Some actions of HGF are believed to be mediated by cyclooxygenase-2 (COX-2), resulting in the production of prostaglandin E2 (PGE2). We examined four c-Met-positive non-small-cell lung cancer (NSCLC) cell lines for effects of HGF on COX-2. HGF increased COX-2 protein expression 3-fold over basal levels. Induction of COX-2 occurred through both the extracellular signal-regulated kinase 1/2 and p38 pathways. HGF treatment caused activation of the activator protein-1, CCAAT/enhancer-binding protein, and cAMP response element-binding protein transcription factors, and COX-2 induction was blocked by actinomycin D. The half-life of COX-2 mRNA was also increased by HGF. HGF stimulation resulted in a 4-fold increase in PGE2 secretion, and treatment of NSCLC cells with exogenous PGE2 significantly increased cell proliferation. The addition of PGE2 to NSCLC cells also led to rapid phosphorylation of c-Met in the absence of HGF, which was blocked by epidermal growth factor receptor (EGFR) inhibition. EGFR ligands were released in response to PGE 2. This suggests that secretion of PGE2 induced by HGF/c-Met pathway activation can further activate the c-Met pathway via EGFR in a reinforcing loop that is independent of HGF. HGF and PGE2 each significantly stimulated invasion in NSCLC cells. Cells transiently transfected with c-Met antisense plasmid showed a significant decrease in HGF- or PGE 2-induced invasion. PGE2-induced invasion was EGFR-dependent, confirming a link between PGE2, EGFR, and c-Met. Targeting of both the HGF/c-Met and PGE2 pathways with a neutralizing antibody to HGF and celecoxib resulted in enhanced anti-invasion effects in response to HGF.