HUMAN COLON-CANCER CELLS EXPRESS THE FUNCTIONAL FAS LIGAND

Fas ligand (FasL) belongs to the TNF superfamily. It is induced in act ivated lymphocytes and eliminates Fas-positive lymphocytes, resulting in the down-regulation of immune responses. Fast has also been detecte d in tissues other than lymphoid cells. We investigated the expression and function of Fast on human colon cancer cells. Fast mRNA was detec ted by RT-PCR in all six colon cancer cell lines tested and was not fo und on fibroblasts. Fast protein was detected in DLD-1, LoVo, HCT-116 and RPMI 4788 cells by immunohistochemical staining. DLD-1, LoVo and W iDr were cytotoxic against mouse T lymphoma cells which were transfect ed with human Fas receptor cDNA. The cytotoxicity was significantly en hanced by phorbol 12-myristate 13-acetate (PMA) and ionomycin. Our dat a suggest that the Fast expressed in human colon cancer cells may be r egulated by endogeneous factors in the microenvironment of the host an d facilitates the escape from the host immune system.