Fas/Fas ligand interaction in human colorectal hepatic metastases - A mechanism of hepatocyte destruction to facilitate local tumor invasion

This study demonstrates a novel role for the Fas pathway in the promotion of local tumor growth by inducing apoptotic cell death in normal hepatocytes at the tumor margin in colorectal hepatic metastases. Our results show that >85% of lymphocytes infiltrating colorectal liver cancer express high levels of Fas-ligand (Fas-L) by flow cytometry. Using immunohistochemistry of turner tissue we showed strong Fas expression in noninvolved hepatocytes, whereas Fas-L expression was restricted to tumor cells and infiltrating lymphocytes at the tumor margin. Apoptosis was observed in 45 +/- 13% of the Fas(high) hepatocytes at the tumor margin whereas only 7 +/- 3% tumor cells were apoptotic (n = 10), In vitro, primary human hepatocytes expressed Fas receptor and crosslinking with anti-Fas antibody induced apoptosis in 44 +/- 5% of the cells compared with 4.6 +/- 1.0% in untreated controls (P = 0.004). Both tumor-infiltrating lymphocytes (TIL) and human metastatic colon cancer cells cells are able to induce Fas-mediated apoptosis of primary human hepatocytes in coculture cytotoxic assays. TIL induced apoptosis in 47 +/- 9% hepatocytes compared with control 4.3 +/- 1.0% (P = 0.009) and this effect was reduced by anti-human Fas-L mAb (18.7 +/- 1.3%, P = 0.009). SW620 cells induced apoptosis in 26 +/- 2% hepatocytes compared with control 5.6 +/- 1.7% (P = 0.004) and this was reduced to 11.2 +/- 1.8% (P = 0.004) in the presence of anti-human Fas-L mAb, These data suggest that the inflammatory response at the margin of colorectal liver metastases induces Fas expression in surrounding hepatocytes, allowing them to be killed by Fas-L-bearing TIL or turner cells and facilitating the invasion of the tumor Into surrounding liver tissue.