Protein Tyrosine Kinase Inhibitors Block Tumor Necrosis Factor-Induced Activation of Nuclear Factor-κB, Degradation of IκBα, Nuclear Translocation of p65, and Subsequent Gene Expression

Several inflammatory effects of tumor necrosis factor (TNF) are known to be mediated through activation of a nuclear transcription factor NF-κB, but how TNF activates NF-κB is incompletely understood. In the present report, we examined the role of protein tyrosine kinases (PTK) in TNF-mediated NF-κB activation by using genistein and erbstatin, two potent inhibitors of PTK. The treatment of human myeloid U-937 cells with either inhibitor completely suppressed the TNF-induced NF-κB activation in a dose- and time-dependent manner. Suppression correlated with PTK activity, since among the structural analogues of genistein, only an active inhibitor of PTK, quercetin blocked TNF-induced NF-κB activation and not daidzein, an inactive inhibitor. Inhibition of NF-κB activation was not limited to myeloid cells, as it was observed with T cells and epithelial cells. Both the PTK inhibitors blocked the degradation of IκBα, the inhibitory subunit of NF-κB, and the consequent translocation of the p65 subunit without any significant effect on p50 or on c-Rel. The PTK inhibitors did not interfere with NF-κB binding to DNA. The NF-κB-dependent CAT reporter gene expression in transient transfection assays was also suppressed by the PTK inhibitors. Both PTK inhibitors abolished TNF-induced activation of N-terminal c-Jun kinase and mitogen-activated protein kinase kinase. Overall, our results suggest that a genistein- and erbstatin-sensitive PTK is involved in the pathway leading to NF-κB activation and gene expression by TNF and thus could be used as a target for development of antiinflammatory drugs.