PHYSICAL AND FUNCTIONAL SENSITIVITY OF ZINC-FINGER TRANSCRIPTION FACTORS TO REDOX CHANGE

Redox regulation of DNA-binding proteins through the reversible oxidat ion of key cysteine sulfhydryl groups has been demonstrated to occur i n vitro for a range of transcription factors. The direct redox regulat ion of DNA binding has not been described in vivo, possibly because mo st protein thiol groups are strongly buffered against oxidation by the highly reduced intracellular environment mediated by glutathione, thi oredoxin, and associated pathways. For this reason, only accessible pr otein thiol groups with high thiol-disulfide oxidation potentials are likely to be responsive to intracellular redox changes. In this articl e, we demonstrate that zinc finger DNA-binding proteins, in particular members of the Sp-1 family, appear to contain such redox-sensitive -S H groups. These proteins displayed a higher sensitivity to redox regul ation than other redox-responsive factors both in vitro and in vivo. T his effect was reflected in the hyperoxidative repression of transcrip tion from promoters with essential Sp-1 binding sites, including the s imian virus 40 early region, glycolytic enzyme, and dihydrofolate redu ctase genes. Promoter analyses implicated the Sp-1 sites in this repre ssion. Non-Sp-1 dependent redox-regulated genes including metallothion ein and heme oxygenase were induced by the same hyperoxic stress. The studies demonstrate that cellular redox changes can directly regulate gene expression in vivo by determining the level of occupancy of strat egically positioned GC-binding sites.