Ceramide triggers p53-dependent apoptosis in genetically defined fibrosarcoma tumour cells

p53 mutations are among the most common genetic alterations in human cancer and are frequently described in intrinsic or acquired radio- and chemother apy resistance. Radiation-induced cell kill is not only mediated by DNA dam age but also by the activation of signal transduction cascades generated at the plasma membrane like the sphingomyelin pathway. We used genetically de fined wild-type p53 or p53-deficient mouse fibrosarcoma cells to investigat e the p53-dependence of tumour response upon activation of the sphingomyeli n pathway. Treatment of the tumour cells with neutral sphingomyelinase dras tically reduced the amount of wild-type p53 fibrosarcoma cell proliferation over 72 h in a clear dose-response (0.2-1.0 U ml(-1) nSMase). Sphingomyeli nase had no effect on cell proliferation in tumour cells lacking p53. Simil arly, cell proliferation was abolished by C2-ceramide (5-20 mu M) only in w ild-type p53 cells. FAGS-analysis revealed that C2-ceramide induced massive p53-dependent apoptosis (40-50% after 12-24 h) and cell cycle analysis sho wed a transient G1 arrest in p53-deficient tumour cells 12-24 h after C2-ce ramide exposure. These results suggest that ceramide-induced apoptosis in t umour cells can be dependent on the status of p53 and imply that p53 is als o important for stress-induced apoptotic signal transduction cascades gener ated at the plasma membrane.