Presence of a genistein-responsive inhibitory mechanism on interleukin-1alpha-induced NF-kappaB activation

Interleukin 1 (IL-1) is known to activate the signal transduction machinery, including the transcription factor, nuclear factor kappa B (NF-kappaB). The activation mechanism of NF-kappaB has been studied intensively, while the negative regulatory mechanisms of NF-kappaB remain to be clarified. In the present study, we found that genistein, a tyrosine kinase inhibitor, augmented IL-1alpha-dependent NF-kappaB activation, suggesting the presence of a tyrosine kinase mediating a suppression signal on NF-kappaB. As determined by luciferase reporter gene assay using kappaB-responsive element, genistein enhanced IL-1alpha-induced NF-kappaB activation. Although genistein failed to increase luciferase activity at 1 and 3 h after IL-1alpha stimulation, it induced prolonged activation beginning at 6 h after the initial stimulation. We next examined whether genistein augmented the DNA-binding activity of NF-kappaB, using electrophoretic mobility shift assay. In the case of the control experiment, the binding of NF- kappaB to the kappaB-responsive element peaked at 30 min after IL-1alpha stimulation, and decreased thereafter. In contrast, treatment with genistein maintained the maximum binding activity for at least 2 h after stimulation. Moreover, genistein enhanced the IL-1alpha-dependent degradation of IkappaBalpha. Taken together, our results indicate that genistein augments IkappaB degradation, resulting in continuous NF-kappaB activation. This suggests the possibility that tyrosine kinase negatively regulates NF-kappaB.