Direct evidence that hepatocyte growth factor-induced invasion of hepatocellular carcinoma cells is mediated by urokinase

Background/Aims: We have shown that hepatocyte growth factor secreted by hu man hepatic myofibroblasts increased the in vitro invasion of the hepatocar cinoma cell line HepG2 through Matrigel. Our aim in this study was to evalu ate the role of urokinase in this process. Methods: Expression of urokinase in HepG2 cells was measured by Northern bl ot and zymography, and plasminogen activation was shown by a chromogenic su bstrate assay, Cell invasion was assayed on Matrigel-coated filters. Urokin ase and urokinase receptor transcripts in hepatocarcinoma were detected by reverse transcription-polymerase chain reaction. Activated hepatocyte growt h factor was detected by Western blot with a hepatocyte growth factor-beta chain-specific antibody. Results: HepG2 cells expressed urokinase mRNA and secreted active urokinase . Urokinase expression was enhanced by hepatocyte growth factor at the prot ein and mRNA level. Notably, cell-surface-associated urokinase was increase d 22-fold by hepatocyte growth factor. Hepatocyte growth factor also increa sed urokinase receptor mRNA expression. B428, a urokinase inhibitor, decrea sed by up to 70% HepG2 invasion induced by myofibroblasts and by 90% that i nduced by recombinant hepatocyte growth factor. This was not due to a decre ase in the generation of activated hepatocyte growth factor by myofibroblas ts. Finally, all 17 hepatocarcinoma samples tested expressed urokinase and urokinase receptor transcripts. Conclusion: Hepatocyte growth factor-dependent, myofibroblasts-induced inva sion of HepG2 cells is secondary to the induction of urokinase expression o n tumor cells.