The activation of nuclear factor kappa B (NF-kappa B) has been implicated in the regulation of transcription of a variety of genes and has been shown to be essential for the expression of genes controlled by the long terminal repeat of human immunodeficiency virus (HIV LTR). We show here that intracellular thiol levels play a key role in regulating this process. That is, stimulation with tumor necrosis factor alpha and/or phorbol 12-myristate 13-acetate activates NF-kappa B and markedly decreases intracellular thiols; N-acetyl-L-cysteine, an efficient thiol source, prevents this thiol decrease and blocks the activation of NF-kappa B; and the lack of activated NF-kappa B prevents the activation of the HIV LTR and the transcription of genes under its control. These findings reveal a previously unrecognized genetic regulatory mechanism in which cytokine-induced shifts in intracellular thiol levels are crucial in the control of NF-kappa B activity and thereby influence the spectrum of genes expressed by cytokine-stimulated cells VSports手机版. .