The mechanisms by which growth factors trigger signal transduction pathways 
leading to protection against apoptosis are of great interest. In this study, we 
investigated the effect of hepatocyte growth factor (HGF/SF) and epidermal 
growth factor (EGF) on adriamycin (ADR)-induced apoptosis. Treatment of human 
epithelial MKN74 cells with ADR, a DNA topoisomerase IIalpha inhibitor, caused 
apoptosis. However, cells pretreated with HGF/SF, but not those pretreated with 
EGF, were resistant to this apoptosis. The protective effect of HGF/SF against 
the ADR-induced apoptosis was abolished in the presence of either LY294002, an 
inhibitor of phosphatidylinositol-3'-OH kinase (PI3-K) or 
1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate, an 
inhibitor of Akt, thus implicating the activation of PI3-K-Akt signaling in the 
antiapoptotic action of HGF/SF. Immunoblotting analysis revealed that HGF/SF 
stimulated the sustained phosphorylation of Akt for several hours but that EGF 
stimulated the phosphorylation only transiently. Furthermore, ADR-induced 
activation of caspase-9, a downstream molecule of Akt, was inhibited for at 
least 24 h after HGF/SF stimulation, but it was not affected by EGF stimulation. 
Cell-surface biotin-labeling analysis showed that the HGF/SF receptor remained 
on the cell surface until at least 30 min after HGF/SF addition but that the EGF 
receptor level on the cell surface was attenuated at an earlier time after EGF 
addition. These results indicate that HGF/SF, but not EGF, transmitted 
protective signals against ADR-induced apoptosis by causing sustained activation 
of the PI3-K-Akt signaling pathway. Furthermore, the difference in antiapoptotic 
capacity between HGF/SF and EGF is explained, at least in part, by the delayed 
down-regulation of the HGF/SF receptor.