DRUG-INDUCED APOPTOSIS IN HEPATOMA-CELLS IS MEDIATED BY THE CD95 (APO-1 FAS) RECEPTOR/LIGAND SYSTEM AND INVOLVES ACTIVATION OF WILD-TYPE P53/

Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug -sensitive cells. We investigated the mechanism of bleomycin-induced c ytotoxicity in hepatoma cells. At concentrations present in the sera o f patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Hu h7) or in hepatoma cells which were p53(-/-) (Hep3B). In addition, sen sitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2, cells had the same effect. In contrast, bleomycin did not enhance susceptibi lity towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furth ermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95 L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere w ith CD95 receptor/ligand interaction. These data suggest that apoptosi s induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to o ther anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the expla nation of drug sensitivity and resistance.