ABSTRACT
Mitochondrial transcription factor A (mtTFA) is a member of the HMG (high mobility group)-box protein family. We previously showed that mtTFA preferentially binds to both cisplatin-damaged and oxidatively damaged DNA. In this study, we found that expression levels of both mtTFA and the mitochondrial antioxidant protein thioredoxin2 (TRX2) are upregulated in cisplatin-resistant cell lines. In addition, TRX2 directly interacts with mtTFA and enhances its damaged DNA binding activity. The interaction between mtTFA and TRX2 requires the HMG box 1 motif of mtTFA. Furthermore, when amino acid substitutions were introduced at either C49G or C246stop, TRX2 interacted with mtTFA. However, the interaction of TRX2 with mtTFA was enhanced when both mutations (C49G and C246stop) were introduced. Binding to cisplatin-damaged DNA was similar among mutant mtTFA proteins. By contrast, binding to oxidized DNA was significantly enhanced when double mutations were introduced. These results suggest that TRX2 not only functions as an antioxidant, but also supports mtTFA functions.
Subject(s)
Antioxidants/metabolism , DNA Damage/physiology , DNA-Binding Proteins/metabolism , DNA/metabolism , Mitochondrial Proteins/metabolism , Thioredoxins/metabolism , Transcription Factors/metabolism , Amino Acid Motifs , Blotting, Western , DNA-Binding Proteins/chemistry , Electrophoretic Mobility Shift Assay , HeLa Cells , Humans , Immunoprecipitation , Mitochondrial Proteins/chemistry , Transcription Factors/chemistryABSTRACT
The CCAAT-binding transcription factor (CTF)/nuclear factor I (NF-I) group of cellular DNA-binding proteins recognizes the sequence GCCAAT and is implicated in eukaryotic transcription, as well as DNA replication. Molecular analysis of human CTF/NF-I cDNA clones revealed multiple mRNA species that contain alternative coding regions, apparently as a result of differential splicing. Expression and functional analysis established that individual gene products can bind to GCCAAT recognition sites and serve as both promoter-selective transcriptional activators and initiation factors for DNA replication. The interaction between CTF2 and p53/p73 was shown to modulate their ability to regulate transcription of their respective target genes. In the present paper, we report that p53 down-regulates the activity of the high mobility group 1 (HMG1) gene promoter, whereas p73alpha up-regulates the activity of this promoter. Furthermore, CTF2 transactivates p53-induced p21 promoter activity, but inhibits p73alpha-induced p21 promoter activity. Using deletion mutants, we found that the DNA-binding domains of both p53 and p73alpha are required for physical interaction with CTF2 via the regions between amino acid residues 161 and 223, and 228 and 312 respectively. CTF2 enhances the DNA-binding activity of p53 and inhibits the DNA-binding activity of p73alpha. These results provide novel information on the functional interplay between CTF2 and p53/p73 as important determinants of their function in cell proliferation, apoptosis, DNA repair and cisplatin resistance.
