Mutations in the zinc finger domain of IKKγ block the activation of NF-κB and the induction of IL-2 in stimulated T lymphocytes

Mutations in the zinc finger of IκB kinase gamma (IKKγ) are associated with hypohidrotic ectodermal dysplasia-immune deficiency (HED-ID) in which the major immune deficit is the inability to switch Ab heavy chain class. However, the pathophysiologic role of the mutations has not been fully delineated. Since help from activated Th cells is essential in Ab class switching, we sought to examine how these mutations affect T cell activation. Using a human T cell line that was null for IKKγ, we generated cells stably expressing two of the reported mutations, namely, D406V and C417R. Cells expressing either mutation failed to induce IL-2 following stimulation with PMA/ionomycin while the induction of IL-2 was restored in cells reconstituted with the wild type IKKγ. The lack of IL-2 upregulation correlated with the lack of NF-κB activation as evidenced by the inability to induce IκBα degradation, NF-κB binding to DNA and the expression of a reporter gene. However, both mutations did not prevent the incorporation of IKKγ into the IKK complex and, interestingly, the induced phosphorylation of IκBα at S32 and S36 and its subsequent ubiquitination were not affected. The suppression of IL-2 induction was solely due to the inhibition of NF-κB activation as the mutations did not impair the activation of AP-1 and NFAT. Our data indicated that the failure of T cells to undergo activation in response to TCR stimuli may play a role in the pathophysiology of HED-ID and also showed that IKKγ has a role in the post-ubiquitination processing of IκBα.