Apoptosis induced by the nuclear death domain protein p84N5 is associated with caspase-6 and NF-kappa B activation

Although the mechanisms involved in responses to extracellular or mitochond rial apoptotic signals have received considerable attention, the mechanisms utilized within the nucleus to transduce apoptotic signals are not well un derstood. We have characterized apoptosis induced by the nuclear death doma in-containing protein p84N5, Adenovirus-mediated N5 gene transfer or transf ection of p84N5 expression vectors induces apoptosis in tumor cell lines wi th nearly 10096 efficiency as indicated by cellular morphology, DNA fragmen tation, and annexin V staining, Using peptide substrates and Western blotti ng, we have determined that NB-induced apoptosis is initially accompanied b y activation of caspase-6. Activation of caspases-3 and -9 does not peak un til 3 days after the peak of caspase-8 activity. Expression of p84N5 also l eads to activation of NF-KB as indicated by nuclear translocation of p65Rel A and transcriptional activation of a NF-kappa B-dependent reporter promote r. Changes in the relative expression level of Bcl-2 family proteins, inclu ding Bak and Bcl-Xs, are also observed during p84N5-induced apoptosis, Fina lly, we demonstrate that p84N5-induced apoptosis does not require p53 and i s not inhibited by p53 coexpression. We propose that p84N5 is involved in a n apoptotic pathway distinct from those triggered by death domain-containin g receptors or by p53.