Oxidative stress and upregulation of mitochondrial biogenesis genes in mitochondrial DNA-depleted HeLa cells

The signaling mechanism through which deficitary mitochondrial function would activate nuclear genes required for mitochondrial biogenesis, has not been established. To explore the hypothesis that reactive oxygen species (ROS), a mitochondrial product, constitute part of the mitochondria-nuclei signaling pathway, we obtained HeLa cells depleted of mitochondrial DNA (p⁰ cells) through exposure to ethidium bromide. We found evidences of oxidative stress in p⁰ cells, employing a fluorescent probe and measuring NF-κB activation. Nuclear Respiratory Factor-1 (NRF-1) and Mitochondrial Transcription Factor A (Tfam) mRNA were measured by RT-PCR. For both transcription factors, p⁰ cells revealed significantly higher levels of mRNA. These results support several hypothesis: that endogenous ROS enhance the expression of nuclear mitochondrial biogenesis genes NRF-1 and Tfam; that DNA deprived mitochondria lead to cellular oxidative stress, probably because of incomplete biogenesis of the mitochondrial electron transport chain, and consequently, that ROS are part of a mitochondria-nuclei regulatory signaling pathway.