ObjectiveTo investigate the molecular mechanisms of the anti-apoptotic action of hepatocyte growth factor (HGF), a novel angiogenic growth factor that may have a pivotal role in the regulation of endothelial cells, on human aortic endothelial cells.MethodsAn index of cell number and death was determined using a water-soluble tetrazolium salt dye assay, DNA fragmentation enzyme-linked immunosorbent assay, and non-confocal fluorescence microscopy of nuclear staining with Hoechst 33258 and propidium iodide. Extracellular-signal-regulated protein kinase (ERK) and the p38 mitogen-activated protein kinase (p38MAPK) were analysed by Western blotting using a phospho-specific antibody.ResultsTreatment of quiescent endothelial cells with HGF resulted in significant dose-dependent increases in cell numbers and decreases in lactate dehydrogenase (LDH) release. Moreover, HGF significantly attenuated endothelial cell death induced by culture in serum-free conditions. We therefore focused on the signal transduction system, and in particular on ERK and p38MAPK. ERK was markedly phosphorylated by HGF. The contribution of ERK to cell growth was supported by the observation that addition of PD98059, a specific inhibitor of MAPK kinase, significantly attenuated the increase in endothelial cell numbers induced by HGF, in a dose-dependent manner. Similarly, PD98059 also attenuated the decrease in LDH release and DNA fragmentation by HGF under serum-free conditions. Interestingly, ERK was re-phosphorylated at 12 h after stimulation. Re-phosphorylation of ERK was the result of induction of endogenous HGF by exogenously added HGF, as addition of neutralizing anti-HGF antibody to the conditioned medium attenuated re-phosphorylation of ERK at 12 h. In contrast, although p38MAPK was also phosphorylated by HGF, SB203580, a specific inhibitor of p38MAPK, failed to change the endothelial cell growth induced by HGF.ConclusionWe have demonstrated that the anti-apoptotic action of HGF against endothelial cell death was mainly through phosphorylation of ERK on human endothelial cells.