Experimental and clinicopathologic studies on the function of the HGF receptor in human colon cancer metastasis

The organ-specific metastasis characterizes several human cancers, includin g colon carcinoma, a disease that frequently involves metastases in the liv er. The data on the molecular mechanisms of liver metastasis would therefor e be highly useful for prognostic purposes. Although the upregulation/ampli fication of the hepatocyte growth factor (HGF) receptor, c-met, has been fr equently observed in colon cancer metastasis, the actual functional signifi cance of the feature in the liver metastatization is not yet known. We have used three human colon carcinoma cell lines (HT29, HT25 and WiDr), charact erized by different liver metastatic potentials in SCID mice, to analyze th e expression of c-met and the biological effects of HGF. We found that HGF induces scattering in in vitro liver-metastatic cell lines (HT25 and WiDr) only at doses which are non-mitogenic (1-20 ng/ml). Analysis of the c-met e xpression revealed that the metastatic cell lines express authentic c-met g ene and protein material, unlike the non-metastatic HT29 cell line, which e xpresses only the c-terminal cytoplasmic domain of the c-met beta -chain. I nterestingly, c-met was found to be localized in the substrate-attached per ipheral membrane and partially colocalized with phosphotyrosine-proteins in the metastatic cells only when kept on fibronectin. On the other hand, we have analyzed 86 primary human colon cancers in Dukes' B (invasive but non- metastatic) and C (invasive and lymph node metastatic) stages. Western blot ting of the proteins isolated from the tumor tissues and immunohistochemica l control study on the paraffin samples of a third of these cases (25/86) a ll indicated a significant upregulation of the c-met protein in the Dukes' C tumor glands compared to the Dukes' B stages (P <0.001 and P <0.05, respe ctively). Since the two stages differ in the involvement of the regional ly mph nodes but not in the invasion depth, the clinicopathological data and o ur experimental findings further support the notion that the c-met expressi on in human colon cancer can be considered as a marker of the metastatic po tential due to its involvement in the generation of the motility signal.