EGFR stimulation enables IL-6 trans-signalling via iRhom2-dependent ADAM17 activation in mammary epithelial cells.

The cytokine interleukin-6 (IL-6) has considerable pro-inflammatory properties and is a driver of many physiological and pathophysiological processes. Cellular responses to IL-6 are mediated by membrane-bound or soluble forms of the IL-6 receptor (IL-6R) complexed with the signal-transducing subunit gp130. While expression of the membrane-bound IL-6R is restricted to selected cell types, soluble IL-6R (sIL-6R) enables gp130 engagement on all cells, a process termed IL-6 trans-signalling and considered to be pro-inflammatory. sIL-6R is predominantly generated through proteolytic processing by the metalloproteinase ADAM17. ADAM17 also liberates ligands of the epidermal growth factor receptor (EGFR), which is a prerequisite for EGFR activation and results in stimulation of proliferative signals. Hyperactivation of EGFR mostly due to activating mutations drives cancer development. Here, we reveal an important link between overshooting EGFR signalling and the IL-6 trans-signalling pathway. In epithelial cells, EGFR activity induces not only IL-6 expression but also the proteolytic release of sIL-6R from the cell membrane by increasing ADAM17 surface activity. We find that this derives from the transcriptional upregulation of iRhom2, a crucial regulator of ADAM17 trafficking and activation, upon EGFR engagement, which results in increased surface localization of ADAM17. Also, phosphorylation of the EGFR-downstream mediator ERK mediates ADAM17 activity via interaction with iRhom2. In sum, our study reveals an unforeseen interplay between EGFR activation and IL-6 trans-signalling, which has been shown to be fundamental in inflammation and cancer.

Cell-Autonomous Constitutive gp130 Signaling in T Cells Amplifies TH17 Cell Responses and Causes Severe Lung Inflammation.

IL-6 plays a fundamental role in T cell differentiation and is strictly controlled by surface expression and shedding of IL-6R. IL-6 also acts on other cells that might affect T cell maturation. To study the impact of cell-autonomous and uncontrolled IL-6 signaling in T cells, we generated mice with a constitutively active IL-6R gp130 chain (Lgp130) expressed either in all T cells (Lgp130 × CD4Cre mice) or inducible in CD4+ T cells (Lgp130 × CD4CreERT2 mice). Lgp130 × CD4Cre mice accumulated activated T cells, including TH17 cells, in the lung, resulting in severe inflammation. Tamoxifen treatment of Lgp130 × CD4CreERT2 mice caused Lgp130 expression in 40-50% of CD4+ T cells, but mice developed lung disease only after several months. Lgp130+ CD4+ T cells were also enriched for TH17 cells; however, there was concomitant expansion of Lgp130- regulatory T cells, which likely restricted pathologic Lgp130+ T cells. In vitro, constitutive gp130 signaling in T cells enhanced but was not sufficient for TH17 cell differentiation. Augmented TH17 cell development of Lgp130+ T cells was also observed in Lgp130 × CD4CreERT2 mice infected with Staphylococcus aureus, but gp130 activation did not interfere with formation of TH1 cells against Listeria monocytogenes. Lgp130+ CD4+ T cells acquired a memory T cell phenotype and persisted in high numbers as a polyclonal T cell population in lymphoid and peripheral tissues, but we did not observe T cell lymphoma formation. In conclusion, cell-autonomous gp130 signaling alters T cell differentiation. Although gp130 signaling is not sufficient for TH17 cell differentiation, it still promotes accumulation of activated T cells in the lung that cause tissue inflammation.

The Alzheimer's disease-linked protease BACE1 modulates neuronal IL-6 signaling through shedding of the receptor gp130.

BACKGROUND: The protease BACE1 is a major drug target for Alzheimer's disease, but chronic BACE1 inhibition is associated with non-progressive cognitive worsening that may be caused by modulation of unknown physiological BACE1 substrates. METHODS: To identify in vivo-relevant BACE1 substrates, we applied pharmacoproteomics to non-human-primate cerebrospinal fluid (CSF) after acute treatment with BACE inhibitors. RESULTS: Besides SEZ6, the strongest, dose-dependent reduction was observed for the pro-inflammatory cytokine receptor gp130/IL6ST, which we establish as an in vivo BACE1 substrate. Gp130 was also reduced in human CSF from a clinical trial with a BACE inhibitor and in plasma of BACE1-deficient mice. Mechanistically, we demonstrate that BACE1 directly cleaves gp130, thereby attenuating membrane-bound gp130 and increasing soluble gp130 abundance and controlling gp130 function in neuronal IL-6 signaling and neuronal survival upon growth-factor withdrawal. CONCLUSION: BACE1 is a new modulator of gp130 function. The BACE1-cleaved, soluble gp130 may serve as a pharmacodynamic BACE1 activity marker to reduce the occurrence of side effects of chronic BACE1 inhibition in humans.

The metalloprotease ADAM10 generates soluble interleukin-2 receptor alpha (sCD25) in vivo.

The cytokine interleukin-2 (IL-2) plays a critical role in controlling the immune homeostasis by regulating the proliferation and differentiation of immune cells, especially T cells. IL-2 signaling is mediated via the IL-2 receptor (IL-2R) complex, which consists of the IL-2Rα (CD25), the IL-2Rß, and the IL-2Rγ. While the latter are required for signal transduction, IL-2Rα controls the ligand-binding affinity of the receptor complex. A soluble form of the IL-2Rα (sIL-2Rα) is found constitutively in human serum, though its levels are increased under various pathophysiological conditions. The sIL-2Rα originates partly from activated T cells through proteolytic cleavage, but neither the responsible proteases nor stimuli that lead to IL-2Rα cleavage are known. Here, we show that the metalloproteases ADAM10 and ADAM17 can cleave the IL-2Rα and generate a soluble ectodomain, which functions as a decoy receptor that inhibits IL-2 signaling in T cells. We demonstrate that ADAM10 is mainly responsible for constitutive shedding of the IL-2Rα, while ADAM17 is involved in IL-2Rα cleavage upon T cell activation. In vivo, we found that mice with a CD4-specific deletion of ADAM10, but not ADAM17, show reduced steady-state sIL-2Rα serum levels. We propose that the identification of proteases involved in sIL-2Rα generation will allow for manipulation of IL-2Rα cleavage, especially as constitutive and induced cleavage of IL-2Rα are executed by different proteases, and thus offer a novel opportunity to alter IL-2 function.

ADAM17 orchestrates Interleukin-6, TNFα and EGF-R signaling in inflammation and cancer.

It was realized in the 1990s that some membrane proteins such as TNFα, both TNF receptors, ligands of the EGF-R and the Interleukin-6 receptor are proteolytically cleaved and are shed from the cell membrane as soluble proteins. The major responsible protease is a metalloprotease named ADAM17. So far, close to 100 substrates, including cytokines, cytokine receptors, chemokines and adhesion molecules of ADAM17 are known. Therefore, ADAM17 orchestrates many different signaling pathways and is a central signaling hub in inflammation and carcinogenesis. ADAM17 plays an important role in the biology of Interleukin-6 (IL-6) since the generation of the soluble Interleukin-6 receptor (sIL-6R) is needed for trans-signaling, which has been identified as the pro-inflammatory activity of this cytokine. In contrast, Interleukin-6 signaling via the membrane-bound Interleukin-6 receptor is mostly regenerative and protective. Probably due to its broad substrate spectrum, ADAM17 is essential for life and most of the few human individuals identified with ADAM17 gene defects died at young age. Although the potential of ADAM17 as a therapeutic target has been recognized, specific blockade of ADAM17 is not trivial since the metalloprotease domain of ADAM17 shares high structural homology with other proteases, in particular matrix metalloproteases. Here, the critical functions of ADAM17 in IL-6, TNFα and EGF-R pathways and strategies of therapeutic interventions are discussed.

Inhibition of ADAM17 impairs endothelial cell necroptosis and blocks metastasis.

Metastasis is the major cause of death in cancer patients. Circulating tumor cells need to migrate through the endothelial layer of blood vessels to escape the hostile circulation and establish metastases at distant organ sites. Here, we identified the membrane-bound metalloprotease ADAM17 on endothelial cells as a key driver of metastasis. We show that TNFR1-dependent tumor cell-induced endothelial cell death, tumor cell extravasation, and subsequent metastatic seeding is dependent on the activity of endothelial ADAM17. Moreover, we reveal that ADAM17-mediated TNFR1 ectodomain shedding and subsequent processing by the γ-secretase complex is required for the induction of TNF-induced necroptosis. Consequently, genetic ablation of ADAM17 in endothelial cells as well as short-term pharmacological inhibition of ADAM17 prevents long-term metastases formation in the lung. Thus, our data identified ADAM17 as a novel essential regulator of necroptosis and as a new promising target for antimetastatic and advanced-stage cancer therapies.

Cell-autonomous hepatocyte-specific GP130 signaling is sufficient to trigger a robust innate immune response in mice.

BACKGROUND & AIMS: Interleukin (IL)-6 cytokine family members contribute to inflammatory and regenerative processes. Engagement of the signaling receptor subunit gp130 is common to almost all members of the family. In the liver, all major cell types respond to IL-6-type cytokines, making it difficult to delineate cell type-specific effects. We therefore generated mouse models for liver cell type-specific analysis of IL-6 signaling. METHODS: We produced mice with a Cre-inducible expression cassette encoding a designed pre-dimerized constitutive active gp130 variant. We bred these mice to different Cre-drivers to induce transgenic gp130 signaling in distinct liver cell types: hepatic stellate cells, cholangiocytes/liver progenitor cells or hepatocytes. We phenotyped these mice using multi-omics approaches, immunophenotyping and a bacterial infection model. RESULTS: Hepatocyte-specific gp130 activation led to the upregulation of innate immune system components, including acute-phase proteins. Consequently, we observed peripheral mobilization and recruitment of myeloid cells to the liver. Hepatic myeloid cells, including liver-resident Kupffer cells were instructed to adopt a bactericidal phenotype which ultimately conferred enhanced resistance to bacterial infection in these mice. We demonstrate that persistent hepatocyte-specific gp130 activation resulted in amyloid A amyloidosis in aged mice. In contrast, we did not observe overt effects of hepatic stellate cell- or cholangiocyte/liver progenitor cell-specific transgenic gp130 signaling. CONCLUSIONS: Hepatocyte-specific gp130 activation alone is sufficient to trigger a robust innate immune response in the absence of NF-κB activation. We therefore conclude that gp130 engagement, e.g. by IL-6 trans-signaling, represents a safe-guard mechanism in innate immunity. LAY SUMMARY: Members of the interleukin-6 cytokine family signal via the receptor subunit gp130 and are involved in multiple processes in the liver. However, as several liver cell types respond to interleukin-6 family cytokines, it is difficult to delineate cell type-specific effects. Using a novel mouse model, we provide evidence that hepatocyte-specific gp130 activation is sufficient to trigger a robust systemic innate immune response.

ADAM-Mediated Signalling Pathways in Gastrointestinal Cancer Formation.

Tumour growth is not solely driven by tumour cell-intrinsic mechanisms, but also depends on paracrine signals provided by the tumour micro-environment. These signals comprise cytokines and growth factors that are synthesized as trans-membrane proteins and need to be liberated by limited proteolysis also termed ectodomain shedding. Members of the family of A disintegrin and metalloproteases (ADAM) are major mediators of ectodomain shedding and therefore initiators of paracrine signal transduction. In this review, we summarize the current knowledge on how ADAM proteases on tumour cells but also on cells of the tumour micro-environment contribute to the formation of gastrointestinal tumours, and discuss how these processes can be exploited pharmacologically.

Increased CXCL4 expression in hematopoietic cells links inflammation and progression of bone marrow fibrosis in MPN.

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) that leads to progressive bone marrow (BM) fibrosis. Although the cellular mutations involved in the pathogenesis of PMF have been extensively investigated, the sequential events that drive stromal activation and fibrosis by hematopoietic-stromal cross-talk remain elusive. Using an unbiased approach and validation in patients with MPN, we determined that the differential spatial expression of the chemokine CXCL4/platelet factor-4 marks the progression of fibrosis. We show that the absence of hematopoietic CXCL4 ameliorates the MPN phenotype, reduces stromal cell activation and BM fibrosis, and decreases the activation of profibrotic pathways in megakaryocytes, inflammation in fibrosis-driving cells, and JAK/STAT activation in both megakaryocytes and stromal cells in 3 murine PMF models. Our data indicate that higher CXCL4 expression in MPN has profibrotic effects and is a mediator of the characteristic inflammation. Therefore, targeting CXCL4 might be a promising strategy to reduce inflammation in PMF.

A variant in IL6ST with a selective IL-11 signaling defect in human and mouse.

The GP130 cytokine receptor subunit encoded by IL6ST is the shared receptor for ten cytokines of the IL-6 family. We describe a homozygous non-synonymous variant in IL6ST (p.R281Q) in a patient with craniosynostosis and retained deciduous teeth. We characterize the impact of the variant on cytokine signaling in vitro using transfected cell lines as well as primary patient-derived cells and support these findings using a mouse model with the corresponding genome-edited variant Il6st p.R279Q. We show that human GP130 p.R281Q is associated with selective loss of IL-11 signaling without affecting IL-6, IL-27, OSM, LIF, CT1, CLC, and CNTF signaling. In mice Il6st p.R279Q lowers litter size and causes facial synostosis and teeth abnormalities. The effect on IL-11 signaling caused by the GP130 variant shows incomplete penetrance but phenocopies aspects of IL11RA deficiency in humans and mice. Our data show that a genetic variant in a pleiotropic cytokine receptor can have remarkably selective defects.

Gut microbiota shape 'inflamm-ageing' cytokines and account for age-dependent decline in DNA damage repair.

OBJECTIVE: Failing to properly repair damaged DNA drives the ageing process. Furthermore, age-related inflammation contributes to the manifestation of ageing. Recently, we demonstrated that the efficiency of repair of diethylnitrosamine (DEN)-induced double-strand breaks (DSBs) rapidly declines with age. We therefore hypothesised that with age, the decline in DNA damage repair stems from age-related inflammation. DESIGN: We used DEN-induced DNA damage in mouse livers and compared the efficiency of their resolution in different ages and following various permutations aimed at manipulating the liver age-related inflammation. RESULTS: We found that age-related deregulation of innate immunity was linked to altered gut microbiota. Consequently, antibiotic treatment, MyD88 ablation or germ-free mice had reduced cytokine expression and improved DSBs rejoining in 6-month-old mice. In contrast, feeding young mice with a high-fat diet enhanced inflammation and facilitated the decline in DSBs repair. This latter effect was reversed by antibiotic treatment. Kupffer cell replenishment or their inactivation with gadolinium chloride reduced proinflammatory cytokine expression and reversed the decline in DSBs repair. The addition of proinflammatory cytokines ablated DSBs rejoining mediated by macrophage-derived heparin-binding epidermal growth factor-like growth factor. CONCLUSIONS: Taken together, our results reveal a previously unrecognised link between commensal bacteria-induced inflammation that results in age-dependent decline in DNA damage repair. Importantly, the present study support the notion of a cell non-autonomous mechanism for age-related decline in DNA damage repair that is based on the presence of 'inflamm-ageing' cytokines in the tissue microenvironment, rather than an intrinsic cellular deficiency in the DNA repair machinery.

ADAM17 Activity and IL-6 Trans-Signaling in Inflammation and Cancer.

All ligands of the epidermal growth factor receptor (EGF-R) are transmembrane proteins, which need to be proteolytically cleaved in order to be systemically active. The major protease responsible for this cleavage is the membrane metalloprotease ADAM17, which also has been implicated in cleavage of TNFα and interleukin-6 (IL-6) receptor. It has been recently shown that in the absence of ADAM17, the main protease for EGF-R ligand processing, colon cancer formation is largely abrogated. Intriguingly, colon cancer formation depends on EGF-R activity on myeloid cells rather than on intestinal epithelial cells. A major activity of EGF-R on myeloid cells is the stimulation of IL-6 synthesis. Subsequently, IL-6 together with the ADAM17 shed soluble IL-6 receptor acts on intestinal epithelial cells via IL-6 trans-signaling to induce colon cancer formation, which can be blocked by the inhibitor of IL-6 trans-signaling, sgp130Fc. Blockade of IL-6 trans-signaling therefore offers a new therapeutic window downstream of the EGF-R for the treatment of colon cancer and possibly of other EGF-R related neoplastic diseases.

Structural and Functional Analyses of the Shedding Protease ADAM17 in HoxB8-Immortalized Macrophages and Dendritic-like Cells.

A disintegrin and metalloproteinase (ADAM) 17 has been implicated in many shedding processes. Major substrates of ADAM17 are TNF-α, IL-6R, and ligands of the epidermal growth factor receptor. The essential role of the protease is emphasized by the fact that ADAM17 deficiency is lethal in mice. To study ADAM17 function in vivo, we generated viable hypomorphic ADAM17 mice called ADAM17ex/ex mice. Recent studies indicated regulation of proteolytic ADAM17 activity by cellular processes such as cytoplasmic phosphorylation and removal of the prodomain by furin cleavage. Maturation and thus activation of ADAM17 is not fully understood. So far, studies of ADAM17 maturation have been mainly limited to mouse embryonic fibroblasts or transfected cell lines relying on nonphysiologic stimuli such as phorbol esters, thus making interpretation of the results difficult in a physiologic context. In this article, we present a robust cell system to study ADAM17 maturation and function in primary cells of the immune system. To this end, HoxB8 conditionally immortalized macrophage precursor cell lines were derived from bone marrow of wild-type and hypomorphic ADAM17ex/ex mice, which are devoid of measurable ADAM17 activity. ADAM17 mutants were stably expressed in macrophage precursor cells, differentiated to macrophages under different growth factor conditions (M-CSF versus GM-CSF), and analyzed for cellular localization, proteolytic activity, and podosome disassembly. Our study reveals maturation and activity of ADAM17 in a more physiological-immune cell system. We show that this cell system can be further exploited for genetic modifications of ADAM17 and for studying its function in immune cells.

ADAM17 is required for EGF-R-induced intestinal tumors via IL-6 trans-signaling.

Colorectal cancer is treated with antibodies blocking epidermal growth factor receptor (EGF-R), but therapeutic success is limited. EGF-R is stimulated by soluble ligands, which are derived from transmembrane precursors by ADAM17-mediated proteolytic cleavage. In mouse intestinal cancer models in the absence of ADAM17, tumorigenesis was almost completely inhibited, and the few remaining tumors were of low-grade dysplasia. RNA sequencing analysis demonstrated down-regulation of STAT3 and Wnt pathway components. Because EGF-R on myeloid cells, but not on intestinal epithelial cells, is required for intestinal cancer and because IL-6 is induced via EGF-R stimulation, we analyzed the role of IL-6 signaling. Tumor formation was equally impaired in IL-6-/- mice and sgp130Fc transgenic mice, in which only trans-signaling via soluble IL-6R is abrogated. ADAM17 is needed for EGF-R-mediated induction of IL-6 synthesis, which via IL-6 trans-signaling induces ß-catenin-dependent tumorigenesis. Our data reveal the possibility of a novel strategy for treatment of colorectal cancer that could circumvent intrinsic and acquired resistance to EGF-R blockade.

Cancer-associated mutations in the canonical cleavage site do not influence CD99 shedding by the metalloprotease meprin ß but alter cell migration in vitro.

Transendothelial cell migration (TEM) is crucial for inflammation and metastasis. The adhesion molecule CD99 was shown to be important for correct immune cell extravasation and is highly expressed on certain cancer cells. Recently, we demonstrated that ectodomain shedding of CD99 by the metalloprotease meprin ß promotes TEM in vitro. In this study, we employed an acute inflammation model (air pouch/carrageenan) and found significantly less infiltrated cells in meprin ß knock-out animals validating the previously observed pro-inflammatory activity. To further analyze the impact of meprin ß on CD99 shedding with regard to cell adhesion and proliferation we characterized two lung cancer associated CD99 variants (D92H, D92Y), carrying point mutations at the main cleavage site. Interestingly, ectodomain shedding of these variants by meprin ß was still detectable. However the cleavage site shifted to adjacent positions. Nevertheless, expression of CD99 variants D92H and D92Y revealed partial misfolding and proteasomal degradation. A previously observed influence of CD99 on Src activation and increased proliferation could not be confirmed in this study, independent of wild-type CD99 or the variants D92H and D92Y. However, we identified meprin ß as a potent inducer of Src phosphorylation. Importantly, we found significantly increased cell migration when expressing the cancer-associated CD99 variant D92H compared to the wild-type protein.

Enzymatic characterization of novel arylsulfatase A variants using human arylsulfatase A-deficient immortalized mesenchymal stromal cells.

Metachromatic leukodystrophy (MLD) is an autosomal-recessive lysosomal storage disease caused by mutations in the ARSA gene leading to arylsulfatase A (ARSA) deficiency and causing sulfatide accumulation. Main symptoms of the disease are progressive demyelination, neurological dysfunction, and reduced life expectancy. To date, more than 200 different ARSA variants have been reported in MLD patients. Here, we report the biochemical characterization of seven novel pathogenic variants (c.98T > C, c.195delC, c.229G > C, c.545C > G, c.674A > G, c.852T > A, and c.1274A > G), which were found when sequencing a cohort of 31 German MLD families. For that purpose, the ARSA cDNAs carrying the respective mutations inserted by site-directed mutagenesis were cloned into a MigR1 (MSCV, IRES, GFP, retrovirus-1) vector. The constructs were overexpressed using retroviral gene transfer in immortalized, human multipotent mesenchymal stromal cells prepared from a patient deficient in ARSA activity (late infantile MLD). In this novel ARSA-/- cell system, the seven ARSA mutants showed ARSA activity of less than 10% when compared with wild type, which is evidence for the pathogenicity of all seven variants. In conclusion, the system of ARSA-/- -immortalized MSC turned out to be a helpful novel tool for the biochemical characterization of ARSA variants.

Meprin Metalloproteases Generate Biologically Active Soluble Interleukin-6 Receptor to Induce Trans-Signaling.

Soluble Interleukin-6 receptor (sIL-6R) mediated trans-signaling is an important pro-inflammatory stimulus associated with pathological conditions, such as arthritis, neurodegeneration and inflammatory bowel disease. The sIL-6R is generated proteolytically from its membrane bound form and A Disintegrin And Metalloprotease (ADAM) 10 and 17 were shown to perform ectodomain shedding of the receptor in vitro and in vivo. However, under certain conditions not all sIL-6R could be assigned to ADAM10/17 activity. Here, we demonstrate that the IL-6R is a shedding substrate of soluble meprin α and membrane bound meprin ß, resulting in bioactive sIL-6R that is capable of inducing IL-6 trans-signaling. We determined cleavage within the N-terminal part of the IL-6R stalk region, distinct from the cleavage site reported for ADAM10/17. Interestingly, meprin ß can be shed from the cell surface by ADAM10/17 and the observation that soluble meprin ß is not capable of shedding the IL-6R suggests a regulatory mechanism towards trans-signaling. Additionally, we observed a significant negative correlation of meprin ß expression and IL-6R levels on human granulocytes, providing evidence for in vivo function of this proteolytic interaction.

Circulating Soluble IL-6R but Not ADAM17 Activation Drives Mononuclear Cell Migration in Tissue Inflammation.

Neutrophil and mononuclear cell infiltration during inflammatory processes is highly regulated. The first cells at the site of infection or inflammation are neutrophils, followed by mononuclear cells. IL-6 plays an important role during inflammatory states. It has been shown in several models that the soluble form of IL-6R (sIL-6R) is involved in the recruitment of mononuclear cells by a mechanism called IL-6 trans-signaling. It had been speculated that sIL-6R was generated at the site of inflammation by shedding from neutrophils via activation of the metalloprotease ADAM17. Attempts to genetically delete the floxed ADAM17 gene selectively in myeloid cells infiltrating an air pouch cavity upon injection of carrageenan failed because in transgenic mice, LysMcre did not lead to appreciable loss of the ADAM17 protein in these cells. We therefore used ADAM17 hypomorphic mice, which only express ∼5% of ADAM17 wild-type levels in all tissues and show virtually no shedding of all tested ADAM17 substrates, to clarify the role of ADAM17 during local inflammation in the murine air pouch model. In the present study, we demonstrate that although IL-6 and the trans-signaling mechanism is mandatory for cellular infiltration in this model, it is not ADAM17-mediated shedding of IL-6R within the pouch that orchestrates this inflammatory process. Instead, we demonstrate that sIL-6R is infiltrating from the circulation in an ADAM17-independent process. Our data suggest that this infiltrating sIL-6R, which is needed for IL-6 trans-signaling, is involved in the controlled resolution of an acute inflammatory episode.

Proteolytic Cleavage Governs Interleukin-11 Trans-signaling.

Interleukin (IL)-11 has been shown to be a crucial factor for intestinal tumorigenesis, lung carcinomas, and asthma. IL-11 is thought to exclusively mediate its biological functions through cell-type-specific expression of the membrane-bound IL-11 receptor (IL-11R). Here, we show that the metalloprotease ADAM10, but not ADAM17, can release the IL-11R ectodomain. Chimeric proteins of the IL-11R and the IL-6 receptor (IL-6R) revealed that a small juxtamembrane portion is responsible for this substrate specificity of ADAM17. Furthermore, we show that the serine proteases neutrophil elastase and proteinase 3 can also cleave the IL-11R. The resulting soluble IL-11R (sIL-11R) is biologically active and binds IL-11 to activate cells. This IL-11 trans-signaling pathway can be inhibited specifically by the anti-inflammatory therapeutic compound sgp130Fc. In conclusion, proteolysis of the IL-11R represents a molecular switch that controls the IL-11 trans-signaling pathway and widens the number of cells that can be activated by IL-11.

ADAM17 controls IL-6 signaling by cleavage of the murine IL-6Rα from the cell surface of leukocytes during inflammatory responses.

The cytokine IL-6 is part of a regulatory signaling network that controls immune responses. IL-6 binds either to the membrane-bound IL-6 receptor-α (classic signaling) or to the soluble IL-6 receptor-α (trans-signaling) to initiate signal transduction via gp130 activation. Because classic and trans-signaling of IL-6 fulfill different tasks during immune responses, controlled shedding of the membrane-bound IL-6 receptor-α from the surface of immune cells can be considered a central regulator of IL-6 function. The results from cell culture-based experiments have implicated both a disintegrin and metalloprotease 10 and a disintegrin and metalloprotease 17 in IL-6 receptor-α shedding. However, the nature of the protease mediating IL-6 receptor-α release in vivo is not yet known. We used hypomorphic a disintegrin and metalloprotease 17 mice and conditional a disintegrin and metalloprotease 10 knock-out mice to identify the natural protease of the murine IL-6 receptor-α. Circulating homeostatic soluble IL-6 receptor-α levels are not dependent on a disintegrin and metalloprotease 10 or 17 activity. However, during Listeria monocytogenes infection, IL-6 receptor-α cleavage by the α-secretase a disintegrin and metalloprotease 17 is rapidly induced from the surface of different leukocyte populations. In contrast, CD4-Cre-driven a disintegrin and metalloprotease 10 deletion in T cells did not influence IL-6 receptor-α shedding from these cells after L. monocytogenes infection. A disintegrin and metalloprotease 17 was also required for IL-6 receptor-α ectodomain cleavage and release during endotoxemia. These results demonstrate a novel physiologic role for a disintegrin and metalloprotease 17 in regulating murine IL-6 signals during inflammatory processes.