Apoptotic behaviour of hepatic and extra-hepatic tumor cell lines differs after Fas stimulation

Fas-induced apoptosis is one form of programmed cell death responsible for hepatocyte demise. However, the role of this cell surface receptor in the death of tumoral hepatic cells is still being debated. It has been shown that some hepatoma cell lines may escape apoptosis because of abnormal Fas localization correlated with non-functionality of the Fas protein or dysfunctionality in the Fas pathway cascade. The aim of this study was to investigate the behaviour of four hepatoma cell lines, HepG2, Hep3B, SKHep1 and Chang-Liver and two extrahepatic cell lines, MCF7, a mammary tumoral cell line and OVCAR-3, an ovarian tumoral cell line, when they were treated with an agonistic anti-Fas antibody alone, with interferon gamma (IFNgamma), an up-regulator of Fas protein expression, alone or with a combination of both agents. We first performed immunofluorescence and flow cytometry to confirm that Fas was present on the cell surface of each cell line in the normal state. Apoptosis was then investigated after induction with the various treatments, by DAPI staining, agarose gel DNA electrophoresis and PARP cleavage. Caspase 8 and 3 expression, as well as two anti-apoptotic proteins Bcl-2 and HSP70, and one proapoptotic protein Bax were also investigated by immunoblot allowing identification of several apoptotic pathways based on the behaviour of the different studied proteins. HepG2 and OVCAR-3 cells were sensitive to the anti-Fas antibody alone. Hep3B was resistant to Fas-induced apoptosis but sensitive to IFNgamma-induced apoptosis. MCF7 was resistant to anti-Fas antibody and IFNgamma Chang-Liver and SKHep1 were sensitive to IFNgamma and anti-Fas antibody but at different degrees. Chang-Liver used the Fas and IFNgamma pathways, while SKHep1 involved mostly the Fas pathway. These results show that each tumor cell line is characterized by different apoptotic behaviour in relation to Fas and/or IFNgamma-induced apoptosis. In addition, despite the high level of Bcl-2 and HSP70 proteins in the tumoral cells investigated here, they were not fully protected against apoptosis, except for MCF7. This emphasizes the necessity to analyse the different proteins responsible for apoptosis to adapt anti-tumoral therapeutics.