Does mitochondrial DNA damage play a role in cell death?
Ionizing radiation and some anticancer drugs induce damage both in genomic and in mitochondrial DNA (mtDNA). Although the role of nuclear DNA damage in initiation of cell death has been discussed extensively, the involvement of mtDNA is this process is controversial. Damage to mtDNA, if not repaired, could lead to disruption of the electron transport chain and the production of reactive oxygen species (ROS). For some years, it has been known that mitochondrial and nuclear DNA can be affected differently by DNA damaging drugs. Detailed investigation of DNA integrity in mitochondria suggested that DNA fragmentation during apoptosis is usually specifically nuclear (Murgia et al., 1992). Furthermore, when human leukaemia cell lines were exposed to conditions which resulted in necrosis, mtDNA was damaged at approximately the same rate as nuclear DNA, but in apoptosis mtDNA was not degraded (Tepper and Studzinski, 1993). At this time, it was believed that DNA degradation occurred early after
