Mitochondrial transcription factor-A induction by redox activation of nuclear respiratory factor-1.
Piantadosi CA, Suliman HB
Journal of Biological Chemistry (2006)
Category: mitochondria-gene expression ¤ Added: Jan 05, 2006 ¤ Rating: ◊◊
The nuclear expression of mitochondrial transcription factor A (Tfam), which is required for mitochondrial DNA (mtDNA) transcription and replication, must be linked to cellular energy needs. Because respiration generates reactive oxygen species (ROS) as a side-product, we tested the idea that ROS regulate Tfam expression through phosphorylation of nuclear respiratory factor-1 (NRF-1) and binding to the Tfam promoter. In mitochondria-rich rat hepatoma cells that over-express NRF-1, basal and oxidant-induced increases were found in Tfam expression and mtDNA content. Specific binding of NRF-1 to Tfam promoter was demonstrated by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). NRF-1-Tfam binding was augmented under pro-oxidant conditions. NRF-1 gene silencing produced 1:1 knockdown of Tfam expression and decreased mtDNA content. To evaluate oxidation-reduction (redox) regulation of NRF-1 in Tfam expression, blockade of upstream phosphatidylinositol 3-kinase (PI3-K) was used to demonstrate loss of oxidant-stimulation of NRF-1 phosphorylation and Tfam expression. The oxidant response was also abrogated by specific inhibition of Akt/protein kinase B. Examination of the NRF-1 amino acid sequence revealed an Akt-phosphorylation consensus at which site-directed mutagenesis abolished NRF-1 phosphorylation by Akt. Finally, Akt phosphorylation and NRF-1 translocation predictably lacked oxidant regulation in a cancer line having no PTEN tumor suppressor (HCC1937 cells). This study discloses novel redox-regulation of NRF-1 phosphorylation and nuclear translocation by PI3-K/Akt signaling in controlling Tfam induction by an anti-oxidant pro-survival network.
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