EXPRESSION OF FAS AND ANTI-FAS-MEDIATED APOPTOSIS IN HUMAN HEPATOCELLULAR-CARCINOMA CELL-LINES

Background/Aims: Fas transduces apoptotic signals upon cross-linking w ith the Fas ligand, which is experimentally replaced by anti-Fas antib odies. Because little is known about Fas expression and function in he patocellular carcinoma, these issues are addressed in the current arti cle. Methods: We examined Fas expressions at protein and mRNA levels, and susceptibility to anti-Fas-mediated apoptosis, on six hepatocellul ar carcinoma cell lines. Results: Two cell lines constitutively expres sed high levels of Fas both on their cell surface and in their cytopla sm, whereas the other four cell lines expressed Fas mainly in their cy toplasm. Fas mRNA of normal size was detected in all cell lines in rev erse transcriptase-polymerase chain reaction analyses. Although a Fas mRNA variant, suggesting a soluble Fas molecule, was detected in the t wo cell lines expressing high levels of Fas, its amount was very small compared to that of normal-sized Fas transcript. Anti-Fas dose-depend ently induced apoptosis exclusively in the two cell lines which consti tutively express high levels of cell surface as. However, after preinc ubation with interferon-gamma, one cell line with low surface Fas expr ession became anti-Fas sensitive equivalent to the two cell lines expr essing surface Fas at high levels. Studies of two clonally related cel l lines showed that dedifferentiated clones had lower Fas expression a nd resistance to anti-Fas, suggesting deterioration of Fas system afte r clonal cell dedifferentiation. Conclusions: These findings suggest s ensitivity to anti-Fas is virtually relevant to cell surface Fas, but not to cytoplasmic Fas expression. However, its expression level does not correlate to sensitivity to anti-Fas.