Expression of c-jun and c-fos in apoptotic cells after DNA damage

Apoptosis was induced in HeLa cells by exposure to 50 muM N-merhyl-N'-nitro -N-nitrosoguanidine (MNNG) for various time intervals (up to 120 min). Apop totic death was confirmed by the microscopic observation of cell blebbing, cell granulation, and cell aggregation. Cells also showed loss of phospholi pid symmetry as judged by immunofluorescent microscopy with fluorescently l abeled phosphatidyl serine-specific annexin V. In addition, staining of cel ls with ethidium bromide showed the presence of genomic DNA apoptotic bodie s. The protein expression levels of c-jun and c-fos increased in DNA-damage d HeLa cells after MNNG treatment in a time-dependent fashion. Although the levels of c-fos increased rapidly during the first 30 min and remained hig h for 2 hr, the increase in c-jun expression was more gradual and slower (6 0-120 min) after MNNG treatment. These results are consistent with the conc lusion that c-fos is important in the initial stages (commitment phase) of apoptosis and c-jun is involved in the late stages (execution phase) of apo ptosis induced with alkylating agents.