THE SENSITIVITY OF FANCONI-ANEMIA GROUP-C CELLS TO APOPTOSIS INDUCED BY MITOMYCIN-C IS DUE TO OXYGEN RADICAL GENERATION, NOT DNA CROSS-LINKING

Fanconi's anaemia (FA) is characterized by increased spontaneous and i nduced chromosome fragility. This has been widely regarded to be due t o a defect in DNA crosslink repair, because of the sensitivity of cell s to known DNA crosslinking agents such as mitomycin C (MMC) and diepo xybutane (DEB). Although Fanconi cells are also sensitive to molecular oxygen, and may be protected by antioxidants, this has generally been considered to be a secondary phenomenon. However, it has recently bee n demonstrated that the FAC protein, coded for by the Fanconi anaemia gene for complementation group C, is strictly cytoplasmic and does not enter the nucleus even after DNA damage, which seems inconsistent wit h a role in DNA repair. We have studied the effects of MMC and oxygen on apoptotic cell death in FA group C (FA-C) and normal lymphoblastoid cell lines. Hyperoxia alone failed to induce apoptosis in either FA-C or normal cells. At ambient oxygen, MMC is known to generate oxygen f ree radicals, whereas decreased oxygen tension facilitates the metabol ic activation of MMC for DNA crosslinking. We therefore studied the ef fects of MMC at 20% and 5% oxygen to favour oxygen radical generation or DNA crosslinking respectively. FA-C cells showed increased sensitiv ity compared to normal cells for the induction of apoptosis by MMC at 20% oxygen. When cells were treated with MMC at 5% oxygen we found no increased sensitivity of Fanconi cells to MMC when compared to normal cells. These results imply a role for oxygen free radicals, but not fo r DNA crosslinking, in the sensitivity of EA cells to MMC.