Dominant negative OTULIN Related Autoinflammatory Syndrome

Abstract

Biallelic loss of function mutations in the linear chain specific deubiquitinase (DUB) OTULIN (OTU Deubiquitinase With Linear Linkage Specificity) result in OTULIN Related Autoinflammatory Syndrome (ORAS). To date all reported ORAS patients have had homozygous or compound heterozygous loss of function mutations, however we identified a patient with a monoallelic heterozygous mutation p.Cys129Ser. Consistent with the ORAS phenotype, we observed accumulation of linear ubiquitin chains, increased sensitivity to TNF induced cell death and dysregulation of inflammatory signalling in both patient cells and in vitro exogenous expression models. Levels of the mutant OTULIN protein were consistent with wild type OTULIN in patient cells and exogenous expression systems and maintained binding capacity to both LUBAC and linear ubiquitin chains. However, even in a heterozygous context this mutant DUB promoted the global accumulation of linear ubiquitin chains. Furthermore, it allowed accumulation of ubiquitin on the linear ubiquitin chain assembly complex (LUBAC). Altered ubiquitination of LUBAC leads to a dysregulation of NF-κB signalling and promotion of TNF induced cell death. By reporting the first dominant negative mutation driving ORAS this study expands our clinical understanding of Otulin mediated pathology.

OTULIN-related conditions: Report of a new case and review of the literature using GenIA

“…Finally, OTULIN DUB activity is dependent on Cys129, a key conserved catalytic triad residue. Mutations at this site have been linked to a dominant-negative form of ORAS; specifically, in vitro studies show that co-expression of C129S and WT OTULIN in HEK293 cells leads to LUBAC-dependent linear Ub chain accumulation and consequent inability to suppress NF-κB activity [ 40 ]. Cells from DN-ORAS patients also phenotypically resemble those from ORAS patients in terms of increased M1-Ub chain accumulation on substrates, downstream expression of inflammatory cytokine genes (i.e.…”

“…All of the ORAS-associated mutations tested in vitro except for Y244C (associated with ORAS and OHI) led to some evidence of increased NF- κ B activity at baseline ( Figure 5 ). In vitro over-expression of Y244C in HEK293 cells by several groups showed WT-like to mildly increased levels of NF- κ B activity, target-specific linear deubiquitination, and M1-Ub accumulation at baseline, though TNF stimulation uncovered severely defective NF- κ B suppression [ 32 , 39 , 40 ], also seen in patient leukocytes and fibroblasts [ 32 ]. This suggests that stimulation using pathway-appropriate cytokines may sometimes be required to uncover defects not seen at baseline.…”

OTULIN-related conditions: Report of a new case and review of the literature using GenIA

“…Patient cell data For 7 ORAS patients, 8 IMD107 patients, and 2 unaffected heterozygotes (F066, F067), more detailed cellular characterization at baseline or in response to speci c stimuli was available (Figure S4, Table S3). Finally, ORAS and DN-ORAS skin broblasts or hepatocytes (A027) showed increased apoptosis after stimulation by TNF + BV6, TNF + CHX, alpha-toxin, or S. aureus, but not TNF alone, while IMD107 skin broblasts showed increased levels of cell death only after stimulation with alpha-toxin or S. aureus [Rows 61-65] [39,40].…”

OTULIN deficiency: focus on innate immune system impairment

“…Autosomal recessive OTULIN mutations cause ORAS, manifesting early in life with autoinflammation without clear evidence of infections, due to the defective downregulation of NF-κB-dependent inflammatory signaling. Recently, a group of patients carrying heterozygous variants of OTULIN were identified (named immunodeficiency 107 by MedGen) ( 38 , 43 , 50 ). Clinical manifestations presented, to some extent, with phenotypic heterogeneity.…”