Receptor-specific signaling for both the alternative and the canonical NF-κB activation pathways by NF-κB-inducing kinase

The NF-κB-inducing kinase (NIK) induces proteolytic processing of NF-κB2/p100 and, hence, the generation of NF-κB dimers such as p52:RelB but was suggested not to signal for the processing of IκB. Here, we show that although the induction of IκB degradation in lymphocytes by TNF is independent of NIK, its induction by CD70, CD40 ligand, and BLyS/BAFF, which all also induce NF-κB2/p100 processing, does depend on NIK function. Both CD70 and TNF induce recruitment of the IKK kinase complex to their receptors. In the case of CD70, but not TNF, this process is associated with NIK recruitment and is followed by prolonged receptor association of just IKK1 and NIK. Recruitment of the IKK complex to CD27, but not that of NIK, depends on NIK kinase function. Our findings indicate that NIK participates in a unique set of proximal signaling events initiated by specific inducers, which activate both canonical and noncanonical NF-κB dimers.