Mitochondrial DNA damage and a hypoxic response are induced by CoCI2 in rat neuronal PC12 cells

Generation of reactive oxygen species (ROS) and activation of a transcripti onal program that mimics the hypoxic response have been documented in cultu red cells in the presence of cobalt chloride. We found that in the presence of hypoxia-mimicking concentrations of CoCl2,, mitochondrial but not nucle ar DNA damage is induced in rat neuronal, PC12 cells, To our knowledge, thi s is the first documentation of induction of mitochondrial DNA (mtDNA) dama ge under these conditions. Likewise, we provide the first evidence for elev ation of MYH, the mam malian homolog of the Escherichia coli MutY DNA glyco sylase, in mammalian cells. Recently, the human MYH was implicated in repai r of oxidative DNA damage and shown to carry a mitochondrial localization s equence. Here, an induction of mtDNA damage and a time-dependent increase i n the MYH level were detected with exposure of cells to 100 mu M CoCl2,, In addition, the levels of proteins involved in cellular responses to hypoxia , ROS and nuclear DNA damage; hypoxia-inducible factor 1 alpha (HIF-1 alpha ), p53, p21 and PCNA were also modulated temporally. Earlier studies sugges ted that the mtDNA is a primary target for oxidative damage. Our findings e xtend these observations and suggest that activation of DNA repair processe s is associated with the presence of mtDNA damage.