Iron-mediated H2O2 production as a mechanism for cell type-specific inhibition of tumor necrosis factor α-induced but not interleukin-1β-induced IκB kinase complex/nuclear factor-κB activation

Abstract

Coordinated and specific regulation of tumor necrosis factor (TNF) and interleukin (IL)-1 signaling pathways and how and whether they are modified by different agents are key events for proper immune responses. The IκB kinase complex (IKK)/NF-κB and JNK/AP-1 pathways are central mediators of TNF and IL-1 during inflammatory responses. Here we show that L-mimosine, a toxic non-protein amino acid that has been shown to reduce serum TNFa levels and affect inflammatory responses, specifically inhibits TNF-induced IKK but not JNK in a cell type-specific manner. L-Mimosine did not affect IKK and NF-κB activation by IL-1β. L-Mimosine caused cell cycle arrest at G1-S phase, but inhibition of IKK was found to be independent of cell cycle arrest. Treatment of cells with L-mimosine resulted in production of H2O2. Addition of FeSO4 restored IKK activation by TNFa as did ectopic expression of catalase or pretreatment of cells with N-aceltyl-L-cysteine, indicating a role for intracellular H2O 2 as a mediator of inhibition. Cleavage and degradation of TNF pathway components TNFR1, RIP, and Hsp90 were observed in L-mimosine and H 2O2 treated cells indicating a putative mechanism for selective inhibition of TNF but not IL-1β-induced IKK activation.