OTULIN inhibits RIPK1-mediated keratinocyte necroptosis to prevent skin inflammation in mice.

Linear ubiquitination regulates inflammatory and cell death signalling. Deficiency of the linear ubiquitin chain-specific deubiquitinase, OTULIN, causes OTULIN-related autoinflammatory syndrome (ORAS), a systemic inflammatory pathology affecting multiple organs including the skin. Here we show that mice with epidermis-specific OTULIN deficiency (OTULINE-KO) develop inflammatory skin lesions that are driven by TNFR1 signalling in keratinocytes and require RIPK1 kinase activity. OTULINE-KO mice lacking RIPK3 or MLKL have only very mild skin inflammation, implicating necroptosis as an important etiological mediator. Moreover, combined loss of RIPK3 and FADD fully prevents skin lesion development, showing that apoptosis also contributes to skin inflammation in a redundant function with necroptosis. Finally, MyD88 deficiency suppresses skin lesion development in OTULINE-KO mice, suggesting that toll-like receptor and/or IL-1 signalling are involved in mediating skin inflammation. Thus, OTULIN maintains homeostasis and prevents inflammation in the skin by inhibiting TNFR1-mediated, RIPK1 kinase activity-dependent keratinocyte death and primarily necroptosis.

Autophosphorylation at serine 166 regulates RIP kinase 1-mediated cell death and inflammation.

Receptor interacting protein kinase 1 (RIPK1) regulates cell death and inflammatory responses downstream of TNFR1 and other receptors, and has been implicated in the pathogenesis of inflammatory and degenerative diseases. RIPK1 kinase activity induces apoptosis and necroptosis, however the mechanisms and phosphorylation events regulating RIPK1-dependent cell death signaling remain poorly understood. Here we show that RIPK1 autophosphorylation at serine 166 plays a critical role for the activation of RIPK1 kinase-dependent apoptosis and necroptosis. Moreover, we show that S166 phosphorylation is required for RIPK1 kinase-dependent pathogenesis of inflammatory pathologies in vivo in four relevant mouse models. Mechanistically, we provide evidence that trans autophosphorylation at S166 modulates RIPK1 kinase activation but is not by itself sufficient to induce cell death. These results show that S166 autophosphorylation licenses RIPK1 kinase activity to induce downstream cell death signaling and inflammation, suggesting that S166 phosphorylation can serve as a reliable biomarker for RIPK1 kinase-dependent pathologies.

RIPK1 and Caspase-8 Ensure Chromosome Stability Independently of Their Role in Cell Death and Inflammation.

Receptor-interacting protein kinase (RIPK) 1 functions as a key mediator of tissue homeostasis via formation of Caspase-8 activating ripoptosome complexes, positively and negatively regulating apoptosis, necroptosis, and inflammation. Here, we report an unanticipated cell-death- and inflammation-independent function of RIPK1 and Caspase-8, promoting faithful chromosome alignment in mitosis and thereby ensuring genome stability. We find that ripoptosome complexes progressively form as cells enter mitosis, peaking at metaphase and disassembling as cells exit mitosis. Genetic deletion and mitosis-specific inhibition of Ripk1 or Caspase-8 results in chromosome alignment defects independently of MLKL. We found that Polo-like kinase 1 (PLK1) is recruited into mitotic ripoptosomes, where PLK1's activity is controlled via RIPK1-dependent recruitment and Caspase-8-mediated cleavage. A fine balance of ripoptosome assembly is required as deregulated ripoptosome activity modulates PLK1-dependent phosphorylation of downstream effectors, such as BUBR1. Our data suggest that ripoptosome-mediated regulation of PLK1 contributes to faithful chromosome segregation during mitosis.

Replication analysis of 15 susceptibility loci for nonsyndromic cleft lip with or without cleft palate in an italian population.

BACKGROUND: Nonsyndromic cleft lip with or without cleft palate (nsCL/P) is one of the most common congenital malformations in humans. Its average global incidence is 1.7 per 1000 live births, with wide variation according to geographical location and ethnicity. Its etiology involves both genetic and environmental factors. The aim of the present study was to confirm genetic association of a selection of 15 candidate nsCL/P loci using an independent sample of the Italian population. METHODS: At least one single-nucleotide polymorphism (SNP) for each locus was genotyped in 380 nuclear trios. RESULTS: Transmission disequilibrium analysis revealed significant associations for three variants at two loci (8q24 and 1p22). Two SNPs at 8q24 showed the strongest level of association, the rs987525 (PTDT = 6.81 × 10(-6) ; homozygous relative risk = 3.60 [95% confidence interval, 2.12-6.13]), and the rs17241253 (PTDT = 1.03 × 10(-5) ; homozygous relative risk = 3.75 [95% confidence interval, 2.10-6.67]). Four additional loci (at 1q32, 3q12, 8q21, and 10q25) achieved nominally significant p-values. Two SNPs at 1p36 achieved p-values of < 0.1. The present data suggest that 6 of the 15 analyzed nsCL/P risk loci contribute significantly to nsCL/P risk in the Italian population. These include the 1p22 locus, which previous research has implicated predominantly in Asian populations. CONCLUSION: Different loci, including 8q24 and 1p22 have been found associated with nsCL/P in multiple populations. Further efforts are needed to identify causative variants and transfer knowledge to clinical application, such as personal genetic risk assessment.