NRF-2 transcription factor is required for human TOMM20 gene expression

TOMM20 is a subunit of the outer mitochondrial membrane translocase that plays a major role as a receptor of precursor proteins with N-terminal cleavable presequences targeted to the mitochondria. Nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2) play an important role in governing nucleo-mitochondrial interactions implicated in mitochondrial biogenesis. It was recently reported that NRF-2 is critical for maintaining normal transcriptional levels of the TOMM20 gene, but the promoter of this gene is uncharacterized. We report the presence of a NRF-2 and two NRF-1 binding motifs in the 5'-flanking region of the human TOMM20 gene and provide insight into their roles for promoter activity by using chromatin immunoprecipitation experiments and reporter assays in HeLa S3 and A204 cells. We show that only NRF-2 and the proximal NRF-1 motifs are involved in the expression of the gene. The NRF-2 binding site is required to activate transcription. The proximal NRF-1 site cooperates with NRF-2 in regulating the expression of the gene. The distal NRF-1 binding site is not functional.