c-met expression in pancreatic cancer and effects of hepatocyte growth factor on pancreatic cancer cell growth.

Hepatocyte growth factor (HGF) is a widely expressed growth factor secreted by cells of mesenchymal origin, which has been shown to be involved in growth processes of multiple cell types. The HGF receptor, the product of the c-met protooncogene, is expressed mainly by epithelial cells. Increased expression of the HGF receptor has been observed in various tumors. To investigate the expression of the HGF receptor in the pancreas, we analyzed rat and human normal tissue and pancreatic carcinoma by Western blot analysis. We observed weak expression of c-met reactivity in normal pancreas but markedly enhanced expression in both rat and human pancreatic cancer. To test the possibility that HGF could act as a growth factor on pancreatic carcinoma, the effects of HGF on DNA synthesis in a rat and two human pancreatic carcinoma cell lines were analyzed. HGF induced dose-dependent [3H]thymidine incorporation, reaching 320, 210, and 180% above unstimulated controls in AR4-2J, PancTu-1, and 818/4 cells, respectively. The activation of signal transduction pathways by HGF was further analyzed in AR4-2J cells. After stimulation, a rapid and intense increase in receptor tyrosine phosphorylation was detected. Furthermore, HGF induced a time- and dose-dependent induction of c-fos expression. The addition of tyrphostin, a specific tyrosine kinase inhibitor, prevented c-fos induction and inhibited HGF-induced [3H]thymidine incorporation. In summary, our results demonstrate strongly increased HGF receptor expression in pancreatic carcinoma and support the assumption that HGF could act as a growth promoting factor on this cancer via stimulation of tyrosine kinases.