OTULIN deficiency in ORAS causes cell type‐specific LUBAC degradation, dysregulated TNF signalling and cell death

Abstract

The deubiquitinase OTULIN removes methionine‐1 (M1)‐linked polyubiquitin signals conjugated by the linear ubiquitin chain assembly complex (LUBAC) and is critical for preventing TNF‐driven inflammation in OTULIN‐related autoinflammatory syndrome (ORAS). Five ORAS patients have been reported, but how dysregulated M1‐linked polyubiquitin signalling causes their symptoms is unclear. Here, we report a new case of ORAS in which an OTULIN‐Gly281Arg mutation leads to reduced activity and stability in vitro and in cells. In contrast to OTULIN‐deficient monocytes, in which TNF signalling and NF‐κB activation are increased, loss of OTULIN in patient‐derived fibroblasts leads to a reduction in LUBAC levels and an impaired response to TNF. Interestingly, both patient‐derived fibroblasts and OTULIN‐deficient monocytes are sensitised to certain types of TNF‐induced death, and apoptotic cells are evident in ORAS patient skin lesions. Remarkably, haematopoietic stem cell transplantation leads to complete resolution of inflammatory symptoms, including fevers, panniculitis and diarrhoea. Therefore, haematopoietic cells are necessary for clinical manifestation of ORAS. Together, our data suggest that ORAS pathogenesis involves hyper‐inflammatory immune cells and TNF‐induced death of both leukocytes and non‐haematopoietic cells.

OTULIN prevents liver inflammation and hepatocellular carcinoma by inhibiting FADD- and RIPK1 kinase-mediated hepatocyte apoptosis

“…We could demonstrate that specific deletion of OTULIN in hepatocytes resulted in reduced expression of HOIP and SHARPIN (Fig. 2A), as previously reported in other cell types (Heger et al, 2018; Damgaard et al, 2016, 2019), including MEFs (Suppl. Fig.…”

“…Since OTULIN was previously shown to be essential to prevent TNF-dependent systemic inflammation in humans and in mice (Zhou et al, 2016; Damgaard et al, 2016, 2019), we next addressed the specific role of TNF in triggering the spontaneous death of OTULIN-deficient hepatocytes leading to the development of spontaneous liver pathology in OTULIN LPC-KO mice. For this, we generated TNF deficient OTULIN LPC-KO mice.…”

“…Accordingly, mice harboring a point mutation abolishing the ability of OTULIN to bind ubiquitin (so-called ‘gumby’ mice) or knockin mice expressing a catalytically inactive variant of OTULIN die in utero due to excessive inflammatory cell death (Rivkin et al, 2013; Heger et al, 2018). However, mice with inducible OTULIN deficiency were shown to be viable and develop a severe inflammatory disease (Damgaard et al, 2016), resembling an autoinflammatory syndrome in humans carrying homozygous hypomorphic OTULIN mutations, called OTULIN-related autoinflammatory syndrome (ORAS, also known as Otulipenia) (Zhou et al, 2016; Damgaard et al, 2016, 2019; Nabavi et al, 2019). Although OTULIN was originally shown to negatively regulate LUBAC activity, its deficiency does not induce LUBAC hyperactivity, as expected, but rather suppresses its function.…”

“…In light of the reported function of OTULIN in regulating both TNF-induced NF-κB signaling and cell death (Keusekotten et al, 2013; Damgaard et al, 2016, 2019; Heger et al, 2018), we questioned the role of OTULIN in liver (patho)physiology. For this, we generated OTULIN conditional knockout mice that are specifically deficient for OTULIN in liver parenchymal cells.…”

Regulation of human development by ubiquitin chain editing of chromatin remodelers

“…In particular, cleavage of K48-linked ubiquitin chains protects substrates from proteasomal degradation and cleavage of K63-linked ubiquitin chains limits cellular signaling. While some OTU DUBs are well characterized and have been linked to monogenetic developmental or autoinflammatory diseases (9,1,13,14), the physiological functions and underlying mechanisms of the majority of OTU DUBs have remained largely elusive.…”