Presence of a genisteinâresponsive inhibitory mechanism on interleukinâ1αâinduced NFâκB activation

Interleukin 1 (IL‐1) is known to activate the signal transduction machinery, including the transcription factor, nuclear factor kappa B (NF‐IoB). The activation mechanism of NF‐IoB has been studied intensively, while the negative regulatory mechanisms of NF‐IoB remain to be clarified. In the present study, we found that genistein, a tyrosine kinase inhibitor, augmented IL‐1I±â€dependent NF‐IoB activation, suggesting the presence of a tyrosine kinase mediating a suppression signal on NF‐IoB. As determined by luciferase reporter gene assay using IoB‐responsive element, genistein enhanced IL‐1I±â€induced NF‐IoB activation. Although genistein failed to increase luciferase activity at 1 and 3 h after IL‐1I± 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‐IoB, using electrophoretic mobility shift assay. In the case of the control experiment, the binding of NF‐ IoB to the IoB‐responsive element peaked at 30 min after IL‐1I± 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‐1I±â€dependent degradation of IIoBI±. Taken together, our results indicate that genistein augments IIoB degradation, resulting in continuous NF‐IoB activation. This suggests the possibility that tyrosine kinase negatively regulates NF‐IoB.