Human colon cancer cells express functional Fas ligand

Fas ligand (FasL) belongs to the TNF superfamily. The ligation of Fas (CD95) on target cells induces cell death by apoptosis. Fas and FasL are induced on lymphocytes by activation. FasL-bearing activated lymphocytes eliminate Fas-positive lymphocytes to downregulate immune responses. FasL is reported to be detected in some tissues besides lymphoid cells. We investigated the expression and function of FasL on human colon cancer cells. FasL mRNA was detected by RT-PCR in six colon cancer cell lines, but not in fibroblast. FasL protein was detected by flow cytometry on DLD-1, LoVo, COLO320DM and HCT116, and by immunohistochemistry on DLD-1, LoVo, HCT116 and RPMI-4788. DLD-1, LoVo and WiDr exerted cytotoxicity against human Fas cDNA transfected mouse T cell lymphoma (WR19L-12a). The cytotoxicity of DLD-1 against WR19L-12a was enhanced by PMA and ionomycin in a dose-dependent fashion. In addition, we found that primary colorectal tumors obtained from surgical specimens expressed FasL mRNA and FasL protein. Our findings suggest that FasL positive colon cancer cells may escape from immunological attack by the host by eliminating Fas-bearing activated lymphocytes.