Optineurin functions for optimal immunity

Optineurin (OPTN) was identified 20 years ago in a yeast-two-hybrid screen with a viral protein known to inhibit the cytolytic effects of tumor necrosis factor. Since then, OPTN has been identified as a ubiquitin-binding protein involved in many signaling pathways and cellular processes, and mutations in the OPTN gene have been associated with glaucoma, Paget's disease of bone and neurodegenerative pathologies. Its role in autophagy, however, has attracted most attention in recent years and may explain (some of) the mechanisms behind the disease-associated mutations of OPTN. In this brief review, we focus on the role of OPTN in inflammation and immunity and describe how this may translate to its involvement in human disease

Dynamics and Topology of Flexible Chains: Knots in Steady Shear Flows

We use numerical simulations of a bead-spring model chain to investigate the evolution of the conformation of long and flexible elastic fibers in a steady shear flow. In particular, for rather open initial configurations, and by varying a dimensionless elastic parameter, we identify two distinct conformational modes with different final size, shape, and orientation. Through further analysis we identify slipknots in the chain. Finally, we provide examples of initial configurations of an "open" trefoil knot that the flow unknots and then knots again, sometimes repeating several times. These changes in topology should be reflected in changes in bulk rheological and/or transport properties.Comment: 22 pages, 12 figure

Lateral migration of flexible fibers in Poiseuille flow between two parallel planar solid walls

Dynamics of non-Brownian flexible fibers in Poiseuille flow between two parallel planar solid walls is evaluated from the Stokes equations, solved numerically by an accurate multipole code HYDROMULTIPOLE. Fibers migrate towards a critical distance from the wall zc, which depends significantly on the fiber length N and bending stiffness A. Therefore, the calculated values of zc can be used to sort fibers. Three modes of the dynamics are found, depending on a shear-to-bending parameter Gamma. In the first mode, stiff fibers deform only a little and accumulate close to the wall, as the result of a balance between the tendency to drift away from the channel and the repulsive hydrodynamic interaction with the wall. This mechanism is confirmed by simulations in the unbounded Poiseuille flow. In the second mode, flexible fibers deform significantly and accumulate far from the wall. In both modes, the tumbling pattern is repeatable. In the third mode, the fibers are even more curved, and their tumbling is irregular.Comment: 11 pages, 13 figure

A20 protects cells from TNF-induced apoptosis through linear ubiquitin-dependent and -independent mechanisms

The cytokine TNF promotes inflammation either directly by activating the MAPK and NF-kappa B signaling pathways, or indirectly by triggering cell death. A20 is a potent anti-inflammatory molecule, and mutations in the gene encoding A20 are associated with a wide panel of inflammatory pathologies, both in human and in the mouse. Binding of TNF to TNFR1 triggers the NF-kappa B-dependent expression of A20 as part of a negative feedback mechanism preventing sustained NF-kappa B activation. Apart from acting as an NF-kappa B inhibitor, A20 is also well-known for its ability to counteract the cytotoxic potential of TNF. However, the mechanism by which A20 mediates this function and the exact cell death modality that it represses have remained incompletely understood. In the present study, we provide in vitro and in vivo evidences that deletion of A20 induces RIPK1 kinase-dependent and -independent apoptosis upon single TNF stimulation. We show that constitutively expressed A20 is recruited to TNFR1 signaling complex (Complex I) via its seventh zinc finger (ZF7) domain, in a cIAP1/2-dependent manner, within minutes after TNF sensing. We demonstrate that Complex I-recruited A20 protects cells from apoptosis by stabilizing the linear (M1) ubiquitin network associated to Complex I, a process independent of its E3 ubiquitin ligase and deubiquitylase (DUB) activities and which is counteracted by the DUB CYLD, both in vitro and in vivo. In absence of linear ubiquitylation, A20 is still recruited to Complex I via its ZF4 and ZF7 domains, but this time protects the cells from death by deploying its DUB activity. Together, our results therefore demonstrate two distinct molecular mechanisms by which constitutively expressed A20 protect cells from TNF-induced apoptosis

Physical and functional interaction between A20 and ATG16L1-WD40 domain in the control of intestinal homeostasis

Prevention of inflammatory bowel disease (IBD) relies on tight control of inflammatory, cell death and autophagic mechanisms, but how these pathways are integrated at the molecular level is still unclear. Here we show that the anti-inflammatory protein A20 and the critical autophagic mediator Atg16l1 physically interact and synergize to regulate the stability of the intestinal epithelial barrier. A proteomic screen using the WD40 domain of ATG16L1 (WDD) identified A20 as a WDD-interacting protein. Loss of A20 and Atg16l1 in mouse intestinal epithelium induces spontaneous IBD-like pathology, as characterized by severe inflammation and increased intestinal epithelial cell death in both small and large intestine. Mechanistically, absence of A20 promotes Atg16l1 accumulation, while elimination of Atg16l1 or expression of WDD-deficient Atg16l1 stabilizes A20. Collectively our data show that A20 and Atg16l1 cooperatively control intestinal homeostasis by acting at the intersection of inflammatory, autophagy and cell death pathways

Two distinct ubiquitin-binding motifs in A20 mediate its anti-inflammatory and cell-protective activities

Protein ubiquitination regulates protein stability and modulates the composition of signaling complexes. A20 is a negative regulator of inflammatory signaling, but the molecular mechanisms involved are ill understood. Here, we generated Tnfaip3 gene-targeted A20 mutant mice bearing inactivating mutations in the zinc finger 7 (ZnF7) and ZnF4 ubiquitin-binding domains, revealing that binding to polyubiquitin is essential for A20 to suppress inflammatory disease. We demonstrate that a functional ZnF7 domain was required for recruiting A20 to the tumor necrosis factor receptor 1 (TNFR1) signaling complex and to suppress inflammatory signaling and cell death. The combined inactivation of ZnF4 and ZnF7 phenocopied the postnatal lethality and severe multiorgan inflammation of A20-deficient mice. Conditional tissue-specific expression of mutant A20 further revealed the key role of ubiquitin-binding in myeloid and intestinal epithelial cells. Collectively, these results demonstrate that the anti-inflammatory and cytoprotective functions of A20 are largely dependent on its ubiquitin-binding properties. van Loo and colleagues provide insights into the action of the anti-inflammatory protein A20. The ZnF7 and ZnF4 ubiquitin-binding domains of A20 are both required to suppress inflammatory signaling and cell death; however, these zinc fingers operate via distinct mechanisms

A20 deficiency in myeloid cells protects mice from diet-induced obesity and insulin resistance due to increased fatty acid metabolism

Obesity-induced inflammation is a major driving force in the development of insulin resistance, type 2 diabetes (T2D), and related metabolic disorders. During obesity, macrophages accumulate in the visceral adipose tissue, creating a low-grade inflammatory environment. Nuclear factor kappa B (NF-kappa B) signaling is a central coordinator of inflammatory responses and is tightly regulated by the anti-inflammatory protein A20. Here, we find that myeloid-specific A20-deficient mice are protected from diet-induced obesity and insulin resistance despite an inflammatory environment in their metabolic tissues. Macrophages lacking A20 show impaired mitochondrial respiratory function and metabolize more palmitate both in vitro and in vivo. We hypothesize that A20-deficient macrophages rely more on palmitate oxidation and metabolize the fat present in the diet, resulting in a lean phenotype and protection from metabolic disease. These findings reveal a role for A20 in regulating macrophage immunometabolism

Ileal immune tonus is a prognosis marker of proximal colon cancer in mice and patients

Ileal epithelial cell apoptosis and the local microbiota modulate the effects of oxaliplatin against proximal colon cancer by modulating tumor immunosurveillance. Here, we identified an ileal immune profile associated with the prognosis of colon cancer and responses to chemotherapy. The whole immune ileal transcriptome was upregulated in poor-prognosis patients with proximal colon cancer, while the colonic immunity of healthy and neoplastic areas was downregulated (except for the Th17 fingerprint) in such patients. Similar observations were made across experimental models of implanted and spontaneous murine colon cancer, showing a relationship between carcinogenesis and ileal inflammation. Conversely, oxaliplatin-based chemotherapy could restore a favorable, attenuated ileal immune fingerprint in responders. These results suggest that chemotherapy inversely shapes the immune profile of the ileum-tumor axis, influencing clinical outcome