Enhanced IκB kinase activity is responsible for the augmented activity of NF-κB in human head and neck carcinoma cells

The nuclear transcription factor κB (NF-κB) plays an important role in the development and progression of cancers. However, the mechanism by which cancer cells in the head and neck region acquire high NF-κB activity has not yet been clarified. In this study, we examined the NF-κB binding activity and the expression of the signal-transduction-related proteins of NF-κB in head and neck carcinoma cell lines. These cancer cells showed significantly higher NF-κB binding activity than normal oral epithelial and salivary gland cells. We also demonstrated the increased phosphorylation and degradation of IκB-α protein in cancer cells. Thus, enhanced NF-κB activity in cancer cells is attributable to the rapid phosphorylation and degradation of IκB-α protein. To further elucidate the mechanism involved in this phenomenon, we analyzed both the expression levels of upstream kinases (IκB kinase- (IKK-) α, IKK-β, IKK-γ, and NF-κB-inducing kinase (NIK)) and the IKK activity in cells. Although there was no significant difference in the expression levels of NIK, IKK-β, or IKK-γ in cancer cell lines compared to those in normal cells, increased expression of IKK-α protein was observed in cancer cells. In addition, IKK activity was significantly augmented in cancer cells as compared to normal cells. Thus, our results suggest that enhanced NF-κB activity in head and neck cancer cells may be due to the augmentation of IKK activity.