Is nuclear respiratory factor 2 a master transcriptional coordinator for all ten nuclear-encoded cytochrome c oxidase subunits in neurons?

Cytochrome c oxidase (COX), the terminal enzyme of the mitochondrial electron transport chain, is a multi-subunit, bigenomically encoded inner mitochondrial membrane protein. Of the thirteen subunits, three are encoded in the mitochondrial genome and ten others are encoded in the nuclear genome. Transcriptional coordination of nuclear-encoded COX subunit genes is likely accomplished by transcription factors responding to upstream signals. Previous studies have found that nuclear-encoded COX subunit genes are under the control of specific transcription factors, such as nuclear respiratory factor 2 (NRF-2). However, it is not known if a single transcription factor binds to all ten of COX subunit promoters. In the current study, we identified in silico putative NRF-2 binding sites on all ten nuclear-encoded COX gene promoters in the rat genome. Chromatin immunoprecipitation assay showed that NRF-2 bound in vivo to six of the ten nuclear-encoded COX subunit promoters. Electrophoretic mobility supershift assays demonstrated binding of NRF-2 to the other four subunits, and promoter mutation study confirmed the functionality of these NRF-2 binding sites. Finally, transfection of dominant-negative constructs of NRF-2 proteins caused a significant reduction of COX expression. We conclude that NRF-2 is an important mediator of coordinated regulation of all ten nuclear-encoded COX subunit genes in neurons.