p53 activates the CD95 (APO-1/Fas) gene in response to DNA damage by anticancer drugs

Chemotherapeutic drugs cause DNA damage and kill cancer cells mainly by apo ptosis. p53 mediates apoptosis after DNA damage. To explore the pathway of p53-dependent cell death, we investigated if p53-dependent apoptosis after DNA damage is mediated by the CD95 (APO-1/Fas) receptor/ligand system. We i nvestigated hepatoma, gastric cancer, colon cancer, and breast cancer cell lines upon treatment with different anticancer agents known to act via p53 accumulation. Cisplatin, mitomycin, methotrexate, mitoxantrone, doxorubicin , and bleomycin at concentrations present in the sera of patients during th erapy led to an upregulation of both CD95 receptor and CD95 ligand. Inducti on of the CD95 ligand occurred in p53 wildtype (wt), p53 mutant (mt), and p 53 deficient (p53(-/-)) cell lines and at wt and mt conformation of tempera ture-sensitive p53 mutants. In contrast, upregulation of the CD95 receptor was observed only in cells with wt p53, not in cells with mt or without any p53. Restitution of inducible wt p53 function restored the ability o p53(- /-) Hep3B cells to upregulate the CD95 receptor in response to anticancer d rugs. This rendered the cells sensitive to CD95-mediated apoptosis. In an a ttempt to understand how CD95 expression is regulated by p53, we identified a p53-responsive element within the first intron of the CD95 gene, as well as three putative elements within the promoter. The intronic element confe rred transcriptional activation by p53 and cooperated with p53-responsive e lements in the promoter of the CD95 gene, wt p53 bound to and transactivate d the CD95 gene, whereas mt p53 failed to induce apoptosis via activation o f the CD95 gene. These observations provide a mechanistic explanation for t he ability of p53 to contribute to tumor progression and to resistance of c ancer cells to chemotherapy.