Regulation of gene expression by reactive oxygen

Reactive oxygen intermediates are produced in all aerobic organisms during respiration and exist in the cell in a balance with biochemical antioxidant s. Excess reactive oxygen resulting from exposure to environmental oxidants , toxicants, and heavy metals perturbs cellular redox balance and disrupts normal biological functions. The resulting imbalance may be detrimental to the organism and contribute to the pathogenesis of disease and aging. To co unteract the oxidant effects and to restore a state of redox balance, cells must reset critical homeostatic parameters. Changes associated with oxidat ive damage and with restoration of cellular homeostasis often lead to activ ation or silencing of genes encoding regulatory transcription factors, anti oxidant defense enzymes, and structural proteins. in this review, we examin e the sources and generation of free radicals and oxidative stress in biolo gical systems and the mechanisms used by reactive oxygen to modulate signal transduction cascades and redirect gene expression.