2 DIFFERENT CELLULAR REDOX SYSTEMS REGULATE THE DNA-BINDING ACTIVITY OF THE P50 SUBUNIT OF NF-KAPPA-B IN-VITRO

The NF-KB/Rel/Dorsal (NRD) transcription factor family binds target DN A sequences through their conserved N-terminal basic region that conta ins a single cysteine residue flanked by basic residues. This cysteine residue plays a critical role in the regulation of the DNA-binding ac tivity of NRD members, since chemical modifications of this residue mo dulate the DNA-binding activity of NRD members. Here we show that cell ular factors regulate the DNA-binding activity of NRD members in vitro by reduction-oxidation (redox) mechanisms. Two cellular redox systems , thioredoxin/thioredoxin reductase and apurinic/apyrimidinic endonucl ease (also called Redox factor-1), independently, as well as, synergis tically stimulate the DNA-binding activity of bacterially synthesized (recombinant) p50, one of the subunits of NF-KB that is a major NRD fa ctor inducible in various types of cells. Since the mutation of the co nserved residue (Cys(61)) in the N-terminal basic region of p50 impair s the stimulation of p50 DNA-binding activity by these redox factors, the regulation of p50 DNA-binding activity by these redox factors is m ediated through this cysteine residue. It is, therefore, possible that these two cellular redox systems could play independent, as well as s ynergistic roles in the regulation of NF-KB functions in vivo through the redox control of their DNA-binding activity.