Effects of the NIK aly Mutation on NF-κB Activation by the Epstein-Barr Virus Latent Infection Membrane Protein, Lymphotoxin β Receptor, and CD40*

Homozygosity for the aly point mutation in NF-κB-inducing kinase (NIK) results in alymphoplasia in mice, a phenotype similar to that of homozygosity for deletion of the lymphotoxin β receptor (LTβR). We now find that NF-κB activation by Epstein-Barr virus latent membrane protein 1 (LMP1) or by an LMP1 transmembrane domain chimera with the LTβR signaling domain in human embryonic kidney 293 cells is selectively inhibited by a wild type dominant negative NIK comprised of amino acids 624–947 (DN-NIK) and not by aly DN-NIK. In contrast, LMP1/CD40 is inhibited by both wild type (wt) and alyDN-NIK. LMP1, an LMP1 transmembrane domain chimera with the LTβR signaling domain, and LMP1/CD40 activate NF-κB in wt oraly murine embryo fibroblasts. Although wt andaly NIK do not differ in their in vitro binding to tumor necrosis factor receptor-associated factor 1, 2, 3, or 6 or in their in vivo association with tumor necrosis factor receptor-associated factor 2 and differ marginally in their very poor binding to IκB kinase β (IKKβ), only wt NIK is able to bind to IKKα. These data are compatible with a model in which activation of NF-κB by LMP1 and LTβR is mediated by an interaction of NIK or a NIK-like kinase with IKKα that is abrogated by the alymutation. On the other hand, CD40 mediates NF-κB activation through a kinase that interacts with a different component of the IKK complex.