DREF [DRE (DNA replication-related element) binding factor] is an 80 kDa polypeptide homodimer which plays an important role in regulating cell proliferation-related genes. Both DNA binding and dimer formation activities are associated with residues 16–115 of the N-terminal region. However, the mechanisms by which DREF dimerization and DNA binding are regulated remain unknown. Here, we report that the DNA binding activity of DREF is regulated by a redox mechanism, and that the cysteine residues are involved in this regulation. Electrophoretic mobility shift analysis using Drosophila Kc cell extracts or recombinant DREF proteins indicated that the DNA binding domain is sufficient for redox regulation. Site-directed mutagenesis and transient transfection assays showed that Cys59 and/or Cys62 are critical both for DNA binding and for redox regulation, whereas Cys91 is dispensable. In addition, experiments using Kc cells indicated that the DNA binding activity and function of DREF are affected by the intracellular redox state. These findings give insight into the exact nature of DREF function in the regulation of target genes by the intracellular redox state.
Abbreviations used: AP-1, activator protein-1; CR1, conserved region 1; DRE, DNA replication-related element; DREF, DRE binding factor; DTT, dithiothreitol; EMSA, electrophoretic mobility shift assay; GST, glutathione S-transferase; hDREF, human DREF; NEM, N-ethylmaleimide; MTT, 3-(4,5-diphenylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NF-κB, nuclear factor-κB; PCNA, proliferating cell nuclear antigen; ROS, reactive oxygen species; TBP, TATA box binding protein; TRF, TBP-related factor.