Differential involvement of the CD95 (Fas/APO-1) receptor/ligand system onapoptosis induced by the wild-type p53 gene transfer in human cancer cells

The CD95 (Fas/APO-1) system regulates a number of physiological and patholo gical processes of cell death. The ligand for CD95 induces apoptosis in sen sitive target cells by interacting with a transmembrane cell surface CD95 r eceptor. We previously reported that the recombinant adenovirus-mediated tr ansfer of the wildtype p53 gene caused apoptotic cell death in a variety of human cancer cells. To better understand the mechanism responsible for thi s cell death signaling, we have investigated the potential involvement of t he CD95 receptor/ligand system in p53-mediated apoptosis. The transient exp ression of the wild-type p53 gene upregulated the CD95 ligand mRNA as well as protein expression in H1299 human lung cancer cells deficient for p53 an d in DLD-1 and SW620 human colon cancer cells with mutated p53, all of whic h constitutively expressed CD95 receptor as shown by a flow cytometric anal ysis, and induced rapid apoptotic cell death as early as 24 h after gene tr ansfer. However, the sensitivity to the cytolytic effect of agonistic anti- CD95 antibody (CH11) varied among these cell lines: CN11 induced apoptosis in H1299 cells, but not in DLD-1 and SW620 cells despite their abundant CD9 5 receptor expression, suggesting that the CD95 receptors on DLD-1 and SW62 0 cells might be inactivated. In addition, an antagonistic anti-CD95 ligand antibody (4H9) that interfered with the CD95-receptor-ligand interaction p artially reduced the apoptosis induced by the wild-type p53 gene transfer i n H1299 cells, whereas apoptosis of DLD-1 and SW620 cells occurred in the p resence of 4H9. Taken together, these findings led us to conclude that the CD95 receptor/ligand system is differentially involved in p53-mediated apop tosis, suggesting that the restoration of the wild-type p53 function may me diate apoptosis through CD95 receptor/ligand interactions as well as an alt ernative pathway.