Stabilization of p53 is a novel mechanism for proapoptotic function of NF-κB

Both pro- and antiapoptotic activities of NF-κB transcription factor have been observed; however, less is known about the mechanism by which NF-κB induces apoptosis. To elucidate how NF-κB regulates proapoptotic signaling, we performed functional analyses using wild-type, ikk1^-/-, ikk2^-/-, rela^-/- murine fibroblasts, MDAPanc-28/Puro, MDAPanc-28/IκBαM, and HCT116/p53^+/+ and HCT116/p53^-/- cells with investigational anticancer agent doxycycline as a superoxide inducer for generating apoptotic stimulus. In this report, we show that doxycycline increased superoxide generation and subsequently activated NF-κB, which in turn up-regulated p53 expression and increased the stability and DNA binding activity of p53. Consequently, NF-κB-dependent p53 activity induced the expression of p53-regulated genes PUMA and p21 ^waf1 as well as apoptosis. Importantly, lack of RelA, IKK, and p53 as well as expression of a dominant negative IκBα (IκBαM) inhibited NF-κB-dependent p53 activation and apoptosis. The doxycycline-induced NF-κB activation was not inhibited in HCT116/p53 ^-/- cells. Our results demonstrate that NF-κB plays an essential role in activation of wild-type p53 tumor suppressor to initiate proapoptotic signaling in response to overgeneration of superoxide. Thus, these findings reveal a mechanism of NF-κB-regulated proapoptotic signaling.