AF1q enhancement of γ irradiation-induced apoptosis by up-regulation of BAD expression via NF-κB in human squamous carcinoma A431 cells

BAD (BCL-2 antagonist of cell death) is a proapoptotic BCL-2 family protein that plays a critical role in the regulation of apoptotic response. This study presents direct evidence that AF1q increased the radiation-induced apoptosis through up-regulation of BAD in human squamous carcinoma A431 cells and the key transcription factor involved is NF-κB. The minimal promoter sequence of BAD was identified; the activity was increased in AF1q stable transfectants and decreased upon AF1q siRNA transfection. The NF-κB consensus binding sequence is detected on BAD promoter. Inactivation of NF-κB by NF-κB inhibitor Bay 11-7082 or NF-κB p65 siRNA suppressed the expression and promoter activity of BAD; the suppression is more obvious in AF1q stable transfectants which also have an elevated NF-κB level. Mutation of putative NF-κB motif decreased the BAD promoter activity. The binding of NF-κB to the BAD promoter was confirmed by chromatinimmunoprecipitation. These findings indicate that AF1q upregulation of BAD is through its effect on NF-κB and this may hint of its oncogenic mechanism in cancer.