NF-kappa B p65 transactivation domain is involved in the NF-kappa B-inducing kinase pathway.

NF-kappa B-inducing kinase (NIK) is involved in the signal transduction pathway leading to the NF-kappa B activation. In this report, we demonstrate that the NIK-mediated NF-kappa B activation involves the transactivation (TA) domain of p65 subunit of NF-kappa B and the nuclear translocation of IKK alpha. By using luciferase assay, we found that both IKK alpha and IKK beta could activate NF-kappa B in synergy with NIK. Interestingly, although IKK beta stimulated the NIK-mediated I kappa B degradation, IKK alpha stimulated the action of NF-kappa B without enhancing the I kappa B degradation. By using heterologous transactivation system with Gal4 DNA-binding domain in fusion with various portions of p65 TA domain, we found that the transactivation domain 1 (TA1) of p65 serves as the direct target for the NIK-IKK alpha cascade and that the serine residue at 536 within p65 TA1 is indispensable for this action. Furthermore, we found that this action of NIK depends on the energy-dependent action of Ras-related protein (Ran) since the dominant negative mutant of Ran (RanQ69L) inhibited the transcriptional activity of p65 by preventing the nuclear import of IKK alpha.