Selective Inhibition of IκBα Phosphorylation and HIV-1 LTR-Directed Gene Expression by Novel Antioxidant Compounds

Abstract

Oxidative stress activates the NF-κB/Rel transcription factors which are involved in the activation of numerous immunoregulatory genes and the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). In the present study, we examined the effects of established and novel compounds including antioxidants, ribonucleotide reductase inhibitors, and iron chelators on NF-κB activation and HIV LTR-mediated gene expression induced by TNF-α.N-Acetylcysteine (NAC), pyrrolidinedithiocarbamate (PDTC), and Trimidox (TD) at various concentrations inhibited TNF-α-induced NF-κB binding in Jurkat cells. Pretreatment of cells with these compounds prior to stimulation prevented IκBα degradation. Phosphorylation of IκBα, a prerequisite for its signal-induced degradation, was abrogated in these cells, indicating that oxidative stress is an essential step in the NF-κB activation pathway. On the other hand, iron chelators desferrioxamine, pyridoxal isonicotinoyl hydrazone (PIH), and salicylaldehyde isonicotinoyl hydrazone (SIH) showed no inhibition of TNF-α-induced NF-κB DNA-binding activity. Synergistic induction of HIV-1 LTR-mediated gene expression by TNF-α and the HIV-1 transactivator Tat in Jurkat cells was significantly suppressed in the presence of NAC and TD, but not PDTC. The inhibition of NAC and TD on LTR-directed gene expression was diminished when NF-κB-binding sites in the LTR were deleted, indicating that these compounds affected the NF-κB component of the synergism. Iron chelators PIH and SIH also showed some inhibitory effect on LTR-mediated gene activation, presumably through an NF-κB-independent mechanism. These experiments demonstrate that TD, at concentration 50 times lower than the effective concentration of NAC, potently inhibits NF-κB activity and suppresses HIV LTR expression.