Session Type: ACR Concurrent Abstract Session
Session Time: 4:30PM-6:00PM
Background/Purpose: Autoinflammatory diseases are caused by mutations in genes regulating innate immune responses. More than 20 genes have been associated with various monogenic autoinflammatory disorders.
Methods: We performed whole-exome and candidate gene sequencing in the patients and their unaffected family members. We used an NF-κB luciferase assay and overexpression experiments in 293 cells to confirm the causality of mutations. Patient samples were analyzed using immunoprecipitation, immunoblotting, gene expression and cytokine profiling.
Results: We studied 3 unrelated families, one of Pakistani and two of Turkish ancestry, with neonatal-onset systemic inflammation, neutrophilic dermatitis/rash, and lipodystrophy. We identified three novel homozygous mutations in the FAM105Bgene, which encodes OTULIN, the only deubiquitinase that specifically hydrolyzes Met-1 linked ubiquitin chains. The p.Leu272Pro and p.Tyr244Cys mutations are located near the linear ubiquitination binding region, and they reduce OTULIN protein stability, while the p.Gly174Aspfs*2 mutation truncates the protein. The three mutations do not disrupt OTULIN interaction with LUBAC. Over-expressed mutant OTULIN plasmid p. Leu272Pro and p.Gly174Aspfs*2 failed to restrain NF-κB activity compared to WT OTULIN. Patient-derived PBMCs and fibroblasts sustained higher levels of phosphorylated IKKα/IKKβ and IκBα, and showed increased phosphorylation of P38 and JNK MAP-kinases compared to healthy controls. These results demonstrate enhanced signaling of the NF-κB and MAPK pathways in OTULIN deficient patients. Transfected OTULIN mutant plasmids showed decreased enzyme activity and a substantial defect in deubiquitination of target molecules NEMO, RIPK1, TNFR1 and ASC. This defect could be partially rescued by cotransfecting the mutation proteins with wild type OTULIN. Stimulated patients’ fibroblasts and PBMCs showed a higher linear-ubiquitinaton level of NEMO, RIPK1, TNFR1, and ASC. These results indicate that inefficient deubiquitination of OTULIN target proteins might explain increased NF-κB activity in mutant cells. OTULIN-deficient patients’ cells showed a strong inflammatory signature. We observed an excessive production of IL-1β, IL-6, IL-12, IL-18, and IFN-γ in stimulated patient whole blood and patients’ serum. Purified patient’s monocytes had significantly higher secretion of IL-1β, IL-6, IL-16, IL-18, and TNF in response to LPS, TNF, or IL-1β stimulation relative to controls. Intracellular staining for TNF and IL-6 from Patient 1 and 3 was higher at basal levels in monocytes, dendritic cells and T cells than in controls.
Conclusion: A new disorder caused by loss-of-function mutations in OTULIN expands the spectrum of autoinflammatory diseases caused by defects in deubiquitination and proteasomal degradation.
To cite this abstract in AMA style:Zhou Q, Yu X, Demirkaya E, Deuitch N, Stone DL, Tsai WL, Wang H, Park YH, Ombrello AK, Romeo T, Remmers EF, Chae J, Gadina MG, Welch SB, Ozen S, Topaloglu R, Abinun M, Kastner DL, Aksentijevich I. Biallelic Hypomorphic Mutations in a Linear Deubiquitinase Define Otulipenia, an Early-Onset Systemic Autoinflammatory Disease [abstract]. Arthritis Rheumatol. 2016; 68 (suppl 10). https://acrabstracts.org/abstract/biallelic-hypomorphic-mutations-in-a-linear-deubiquitinase-define-otulipenia-an-early-onset-systemic-autoinflammatory-disease/. Accessed May 22, 2019.
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