Interleukin (IL)-12 and IL-12 gene transfer up-regulate Fas expression in human osteosarcoma and breast cancer cells

Expression of Fas (CD95, APO-1), a cell surface receptor capable of inducin g ligand-mediated apoptosis, is involved in tissue homeostasis and eliminat ion of targeted cells by natural killer and T cells. Corruption of this pat hway, such as reduced Fas expression, can allow tumor cells to escape elimi nation and promote metastatic potential. In this study, the status of Fas e xpression has been examined in the parental SAGS human osteosarcoma cells t hat do not metastasize and in selected variants that cause lung metastases in 16 weeks (LM2) or 8 weeks (LM6) after i.v. injection into nude mice. Fas expression correlated with the metastatic potentials of the three cell lin es. Northern and fluorescence-activated cell-sorting analyses indicated tha t LM6 cells expressed Fas at a lower level than seen in the parental cells. Infection of the LM6 cells with an adenoviral vector containing the murine interleukin (IL)-12 gene (Ad.mIL-12) or treatment with recombinant murine IL-12 resulted in a dose-dependent up-regulation of Fas, The up-regulation of Fas by IL-12 was also demonstrated in human etoposide-resistant MDA-MB-2 31 breast cancer cells. [H-3]Thymidine growth inhibition studies indicated that the cell surface Fas induced after IL-12 exposure was functional and a ble to mediate cell death on cross-linking with anti-Fas, We also demonstra te that this effect is independent of IFN-gamma, Whereas these cell lines a re sensitive to IFN-gamma, incubation with IFN-gamma does not increase susc eptibility to Fas-mediated cell death, nor do these cells produce IFN-gamma with or without IL-12 treatment, We hypothesize that expression of Fas may play a role in the elimination of metastatic tumor cells in the lung, an o rgan in which Fas ligand is expressed. The antitumor activity of IL-12 may be secondary in part to its ability to up-regulate Fas expression on tumor cells, which subsequently increases immune-mediated destruction of osteosar coma cells.