Mitochondrial transcription factor A induction by redox activation of nuclear respiratory factor 1.
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 as a side-product, we tested the idea that reactive oxygen species regulate Tfam expression through phosphorylation of nuclear respiratory factor (NRF-1) and binding to the Tfam promoter. In mitochondria-rich rat hepatoma cells that overexpress 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 and chromatin immunoprecipitation. 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 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 phosphatidylinositol 3,4,5-triphosphate kinase/Akt signaling in controlling Tfam induction by an anti-oxidant pro-survival network.
Piantadosi
Claude A
CA
Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710, USA. piant001@mc.duke.edu
Suliman
Hagir B
HB
D024506:5' Flanking Region; D000818:Animals; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D004272:DNA, Mitochondrial / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D020868:Gene Silencing; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D051266:Nuclear Respiratory Factor 1 / Q000235:genetics / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
D004272:DNA, Mitochondrial; D051266:Nuclear Respiratory Factor 1; D016877:Oxidants; C489030:Tfam protein, rat; D014157:Transcription Factors; D051057:Proto-Oncogene Proteins c-akt