TNF, acting through p55 tumor necrosis factor receptor 1 (TNFR1), contributes to the pathogenesis of many inflammatory diseases. TNFR-associated periodic syndrome (TRAPS, OMIM 142680) is an autosomal ...dominant autoinflammatory disorder characterized by prolonged attacks of fevers, peritonitis, and soft tissue inflammation. TRAPS is caused by missense mutations in the extracellular domain of TNFR1 that affect receptor folding and trafficking. These mutations lead to loss of normal function rather than gain of function, and thus the pathogenesis of TRAPS is an enigma. Here we show that mutant TNFR1 accumulates intracellularly in peripheral blood mononuclear cells of TRAPS patients and in multiple cell types from two independent lines of knockin mice harboring TRAPS-associated TNFR1 mutations. Mutant TNFR1 did not function as a surface receptor for TNF but rather enhanced activation of MAPKs and secretion of proinflammatory cytokines upon stimulation with LPS. Enhanced inflammation depended on autocrine TNF secretion and WT TNFR1 in mouse and human myeloid cells but not in fibroblasts. Heterozygous TNFR1-mutant mice were hypersensitive to LPS-induced septic shock, whereas homozygous TNFR1-mutant mice resembled TNFR1-deficient mice and were resistant to septic shock. Thus WT and mutant TNFR1 act in concert from distinct cellular locations to potentiate inflammation in TRAPS. These findings establish a mechanism of pathogenesis in autosomal dominant diseases where full expression of the disease phenotype depends on functional cooperation between WT and mutant proteins and also may explain partial responses of TRAPS patients to TNF blockade.
Tumor necrosis factor (TNF) receptor–associated periodic syndrome (TRAPS) is an autosomal dominant systemic autoinflammatory disease associated with heterozygous mutations in TNF receptor 1 (TNFR1). ...Here we examined the structural and functional alterations caused by 9 distinct TRAPS-associated TNFR1 mutations in transfected cells and a mouse “knock-in” model of TRAPS. We found that these TNFR1 mutants did not generate soluble versions of the receptor, either through membrane cleavage or in exosomes. Mutant receptors did not bind TNF and failed to function as dominant-negative inhibitors of TNFR1-induced apoptosis. Instead, TRAPS mutant TNFR1 formed abnormal disulfide-linked oligomers that failed to interact with wild-type TNFR1 molecules through the preligand assembly domain (PLAD) that normally governs receptor self-association. TRAPS mutant TNFR1 molecules were retained intracellularly and colocalized with endoplasmic reticulum (ER) markers. The capacity of mutant receptors to spontaneously induce both apoptosis and nuclear factor κB (NF-κB) activity was reduced. In contrast, the R92Q variant of TNFR1 behaved like the wild-type receptor in all of these assays. The inflammatory phenotype of TRAPS may be due to consequences of mutant TNFR1 protein misfolding and ER retention.
The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies comprise multidomain proteins with diverse roles in cell activation, proliferation and cell death. These proteins play pivotal ...roles in the initiation, maintenance and termination of immune responses and have vital roles outside the immune system. The discovery and analysis of diseases associated with mutations in these families has revealed crucial mechanistic details of their normal functions. This review focuses on mutations causing four different diseases, which represent distinct pathological mechanisms that can exist within these superfamilies: autoimmune lymphoproliferative syndrome (ALPS; FAS mutations), common variable immunodeficiency (CVID; TACI mutations), tumor necrosis factor receptor associated periodic syndrome (TRAPS; TNFR1 mutations) and hypohidrotic ectodermal dysplasia (HED; EDA1/EDAR mutations). In particular, we highlight how mutations have revealed information about normal receptor–ligand function and how such studies might direct new therapeutic approaches.
Psoriasis is a human skin condition characterized by epidermal hyperproliferation and infiltration of multiple leukocyte populations. In characterizing a novel insulin growth factor (IGF)-like (IGFL) ...gene in mice (mIGFL), we found transcripts of this gene to be most highly expressed in skin with enhanced expression in models of skin wounding and psoriatic-like inflammation. A possible functional ortholog in humans, IGFL1, was uniquely and significantly induced in psoriatic skin samples. In vitro IGFL1 expression was up-regulated in cultured primary keratinocytes stimulated with tumor necrosis factor α but not by other psoriasis-associated cytokines. Finally, using a secreted and transmembrane protein library, we discovered high affinity interactions between human IGFL1 and mIGFL and the TMEM149 ectodomain. TMEM149 (renamed here as IGFLR1) is an uncharacterized gene with structural similarity to the tumor necrosis factor receptor family. Our studies demonstrate that IGFLR1 is expressed primarily on the surface of mouse T cells. The connection between mIGFL and IGFLR1 receptor suggests mIGFL may influence T cell biology within inflammatory skin conditions.
TNF receptor-associated periodic syndrome (TRAPS) is a dominantly inherited disease caused by missense mutations in the TNF receptor 1 (TNFR1) gene. Patients suffer from periodic bouts of severe ...abdominal pain, localised inflammation, migratory rashes, and fever. More than 40 individual mutations have been identified, all of which occur in the extracellular domain of TNFR1. In the present review we discuss new findings describing aberrant trafficking and function of TNFR1 harbouring TRAPS mutations, challenging the hypothesis that TRAPS pathology is driven by defective receptor shedding, and we suggest that TNFR1 might acquire novel functions in the endoplasmic reticulum, distinct from its role as a cell surface receptor. We also describe the clinical manifestations of TRAPS, current treatment regimens, and the widening array of patient mutations.
To discuss recent developments in the molecular basis of several hereditary recurrent fever syndromes, specifically the cryopyrin-associated periodic syndromes, familial Mediterranean fever and the ...tumor necrosis factor receptor associated periodic syndrome.
Mutations of CIAS1, the gene encoding cryopyrin/NALP3, lead to a spectrum of disease states termed the cryopyrinopathies. Recently, cryopyrin-deficient mice have been used to show that the protein is a key regulator of interleukin-1beta production that functions by recognizing stimuli such as bacterial RNA and infectious agents. Tumor necrosis factor receptor-associated periodic syndrome was initially thought to be caused by deficient metalloprotease-induced tumor necrosis factor receptor shedding, however new findings suggest that mutations in this receptor may result in inappropriate protein folding, leading to a host of other functional abnormalities that may cause inflammatory disease. Finally, data are emerging that address the possible function of the C-terminal B30.2 domain of pyrin, the familial Mediterranean fever protein. This motif has recently been shown to interact with and inhibit caspase-1, and the modeled structure of this complex highlights how mutations may affect the binding interface.
Recent reports have advanced our understanding of the structural and functional biology underlying the hereditary recurrent fevers, and are beginning to suggest possible mechanisms by which specific mutations cause disease.
Mice expressing transgenic T cell receptors (TCR) are used to explore important questions in immunity. However, transgene expression may have unexpected effects. We previously reported a B cell ...immunodeficiency, comprising decreased B cell numbers and diminished antibody responses, in mice that express a transgenic TCR specific for nicotinic acetylcholine receptor; the mice were generated using cassette vectors designed specifically for transgenic TCR expression see Kouskoff et al. J. Immunol. Methods 1995. 180: 273–280. We now show data suggesting that this defect is due to the expression and accumulation of TCR α and β chains inside B cells and induction of an endoplasmic reticulum stress response, causing apoptosis at the pre B‐I and later B cell stage. Thus, inappropriate transgene expression can profoundly affect B cells, leading to a previously undescribed mechanism of immunodeficiency.
Definition of the immune process that causes demyelination in multiple sclerosis is essential to determine the feasibility of Ag-directed immunotherapy. Using the nonhuman primate, Callithrix jacchus ...jacchus (common marmoset), we show that immunization with myelin basic protein and proteolipid protein determinants results in clinical disease with significant demyelination. Demyelination was associated with spreading to myelin oligodendrocyte glycoprotein (MOG) determinants that generated anti-MOG serum Abs and Ig deposition in central nervous system white matter lesions. These data associate intermolecular "determinant spreading" with clinical autoimmune disease in primates and raise important issues for the pathogenesis and treatment of multiple sclerosis.
Mature T cells initially respond to Ag by activation and expansion, but high and repeated doses of Ag cause programmed cell death and can suppress T cell-mediated diseases in rodents. We evaluated ...repeated systemic Ag administration in a marmoset model of experimental allergic encephalomyelitis that closely resembles the human disease multiple sclerosis. We found that treatment with MP4, a chimeric, recombinant polypeptide containing human myelin basic protein and human proteolipid protein epitopes, prevented clinical symptoms and did not exacerbate disease. CNS lesions were also reduced as assessed in vivo by magnetic resonance imaging. Thus, specific Ag-directed therapy can be effective and nontoxic in primates.
Cross‐linking of the B cell antigen receptor (BCR) induces resistance to Fas (APO‐1 / CD95)‐dependent apoptosis and thereby regulates one mechanism of B cell selection during antigen stimulation. To ...investigate the molecular mechanism by which BCR signaling regulates the Fas pathway, we examined the expression of constituents of the death‐inducing signaling complex (DISC), including Fas, FADD, caspase‐8 and cellular FLICE‐inhibitory protein (c‐FLIP). No significant changes in the cellular levels of Fas, FADD or caspase‐8 were observed after BCR cross‐linking. By contrast, the long isoform of c‐FLIP (c‐FLIPL) was significantly up‐regulated by BCR cross‐linking in primary B cells and in two B cell lines, A20 and WEHI‐279. Moreover, transfection of c‐FLIPL into A20 cells inhibited Fas‐dependent apoptosis and suppressed recruitment of caspase‐8 to the DISC. BCR cross‐linking or FLIP overexpression also protects B cells from TRAIL‐induced apoptosis. Thus, BCR signaling up‐regulates c‐FLIPL and suppresses the Fas‐ and TRAIL‐receptor apoptosis pathways which could be important for tolerance and selection of antigen‐specific B cells.
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