Background/Purpose: The NF-kB essential modulator (NEMO) is a scaffolding protein with a broad immune cell and tissue expression profile. Hypomorphic mutations in IKBKG encoding NEMO typically present with immune deficiency. However, we previously showed that the absence of the NEMO C-terminus zinc finger domain (NEMO-ΔCT), encoded by exon 10, leads to impaired negative regulation of the canonical IKK kinase and additional inflammatory disease phenotypes. Other functional NEMO domains are likely important for the regulation of NF-κB activation and type I IFN induction.

Methods: Patients and healthy controls enrolled in an IRB-approved natural history protocol provided blood and skin samples that were used for genetic and functional analyses. These studies included WGS/WES, minigene cDNA analysis, primary cell line gene reconstitution and knockdown experiments, signal transduction by microscopy, Western blot (WB), and intracellular flow cytometry, transcriptome, cytokine release, co-immunoprecipitation and WB, and in vitro viral infection models.

Results: Here we describe the diagnosis, disease features and molecular mechanism underlying enhanced NF-κB and Interferon induction due to expression of the alternative NEMO isoform lacking the domain encoded by exon 5 (NEMO-Δex5). We demonstrate that the NEMO Deleted exon 5 Autoinflammatory Syndrome (NDAS) is distinct from the immunodeficiency syndrome resulting from loss-of-function IKBKG mutations clinically. Dermal fibroblasts from NDAS patients uniquely activate NF-κB in response to TNF, but not TLR3 or RLR stimulation, and type I IFN and antiviral responses are blunted in vitro. By contrast, T cells, monocytes and macrophages expressing NEMO-Δex5 express a strong Type I Interferon and NF-κB transcriptional signature that correlates highly with alternative isoform expression. We utilized these cell specific differences to dissect the roles of TNF and the atypical IKK kinases, TBK1 and IKKε, in altered NEMO-Δex5 signaling and antiviral cell function. NEMO-Δex5 expression in both immune cells and TNF-stimulated dermal fibroblasts specifically protected IKKε from stimulation-induced protein destabilization, promoting type I IFN induction and enhanced antiviral responses in vitro.

Conclusion: NEMO-NDAS represents a distinct disease phenotype with unique cellular gene expression and functional profiles. Ongoing work is directed at understanding the regulation and function of NEMO-Δex5 in host defense and in both monogenic and complex genetic rheumatic diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterization-and-molecular-mechanism-underlying-nemo-deleted-exon-5-autoinflammatory-syndrome-ndas/