Functional activation of the egr-1 (early growth response-1) gene by hydrogen peroxide.

The redox-based regulation of gene expression is one of the fundamental mechanisms of cellular functions, and hydrogen peroxide seems to act as an intracellular second messenger of signal transduction of cytokines. Hydrogen peroxide at non-toxic doses induced the accumulation of mRNA for the early growth response-1 (egr-1) gene in mouse osteoblastic cells. The Egr-1 protein is a transcription factor that binds the GCGGGGGCG sequence and contains a zinc-finger structure that is essential for DNA binding. Egr-1 protein is sensitive to oxidative stress and loses specific DNA-binding activity when exposed to high levels of oxidative stress. Incubating cells with hydrogen peroxide at about 50 microM, however, increased the accumulation of Egr-1 protein, and the Egr-1 product seemed to be functional, judging by its binding activity to the GCGGGGGCG sequence and its ability to activate the chloramphenicol acetyltransferase reporter gene under the control of the human thymidine kinase enhancer containing the Egr-1 binding sequence. It was reported that the activity of Egr-1 protein as a transcription factor was negatively regulated by active oxygens. However, with appropriate concentrations of active oxygen, its capacity to bind a specific DNA sequence and to enhance the transcriptional activity of target genes is thought to be elevated.