Neuronal IL-17 controls Caenorhabditis elegans developmental diapause through CEP-1/p53.

During metazoan development, how cell division and metabolic programs are coordinated with nutrient availability remains unclear. Here, we show that nutrient availability signaled by the neuronal cytokine, ILC-17.1, switches Caenorhabditis elegans development between reproductive growth and dormancy by controlling the activity of the tumor suppressor p53 ortholog, CEP-1. Specifically, upon food availability, ILC-17.1 signaling by amphid neurons promotes glucose utilization and suppresses CEP-1/p53 to allow growth. In the absence of ILC-17.1, CEP-1/p53 is activated, up-regulates cell-cycle inhibitors, decreases phosphofructokinase and cytochrome C expression, and causes larvae to arrest as stress-resistant, quiescent dauers. We propose a model whereby ILC-17.1 signaling links nutrient availability and energy metabolism to cell cycle progression through CEP-1/p53. These studies describe ancestral functions of IL-17 s and the p53 family of proteins and are relevant to our understanding of neuroimmune mechanisms in cancer. They also reveal a DNA damage-independent function of CEP-1/p53 in invertebrate development and support the existence of a previously undescribed C. elegans dauer pathway.

FGFR2 mutations promote endometrial cancer progression through dual engagement of EGFR and Notch signalling pathways.

BACKGROUND: Mutations in the receptor tyrosine kinase gene fibroblast growth factor receptor 2 (FGFR2) occur at a high frequency in endometrial cancer (EC) and have been linked to advanced and recurrent disease. However, little is known about how these mutations drive carcinogenesis. METHODS: Differential transcriptomic analysis and two-step quantitative real-time PCR (qRT-PCR) assays were applied to identify genes differentially expressed in two cohorts of EC patients carrying mutations in the FGFR2 gene as well as in EC cells harbouring mutations in the FGFR2. Candidate genes and target signalling pathways were investigated by qRT-PCR assays, immunohistochemistry and bioinformatics analysis. The functional roles of differently regulated genes were analysed using in vitro and in vivo experiments, including 3D-orthotypic co-culture systems, cell proliferation and migration protocols, as well as colony and focus formation assays together with murine xenograft tumour models. The molecular mechanisms were examined using CRISPR/Cas9-based loss-of-function and pharmacological approaches as well as luciferase reporter techniques, cell-based ectodomain shedding assays and bioinformatics analysis. RESULTS: We show that common FGFR2 mutations significantly enhance the sensitivity to FGF7-mediated activation of a disintegrin and metalloprotease (ADAM)17 and subsequent transactivation of the epidermal growth factor receptor (EGFR). We further show that FGFR2 mutants trigger the activation of ADAM10-mediated Notch signalling in an ADAM17-dependent manner, highlighting for the first time an intimate cooperation between EGFR and Notch pathways in EC. Differential transcriptomic analysis in EC cells in a cohort of patients carrying mutations in the FGFR2 gene identified a strong association between FGFR2 mutations and increased expression of members of the Notch pathway and ErbB receptor family. Notably, FGFR2 mutants are not constitutively active but require FGF7 stimulation to reprogram Notch and EGFR pathway components, resulting in ADAM17-dependent oncogenic growth. CONCLUSIONS: These findings highlight a pivotal role of ADAM17 in the pathogenesis of EC and provide a compelling rationale for targeting ADAM17 protease activity in FGFR2-driven cancers.

DNA demethylation fine-tunes IL-2 production during thymic regulatory T cell differentiation.

Regulatory T (T reg) cells developing in the thymus are essential to maintain tolerance and prevent fatal autoimmunity in mice and humans. Expression of the T reg lineage-defining transcription factor FoxP3 is critically dependent upon T cell receptor (TCR) and interleukin-2 (IL-2) signaling. Here, we report that ten-eleven translocation (Tet) enzymes, which are DNA demethylases, are required early during double-positive (DP) thymic T cell differentiation and prior to the upregulation of FoxP3 in CD4 single-positive (SP) thymocytes, to promote Treg differentiation. We show that Tet3 selectively controls the development of CD25- FoxP3lo CD4SP Treg cell precursors in the thymus and is critical for TCR-dependent IL-2 production, which drive chromatin remodeling at the FoxP3 locus as well as other Treg-effector gene loci in an autocrine/paracrine manner. Together, our results demonstrate a novel role for DNA demethylation in regulating the TCR response and promoting Treg cell differentiation. These findings highlight a novel epigenetic pathway to promote the generation of endogenous Treg cells for mitigation of autoimmune responses.

Differences in H3K4me3 and chromatin accessibility contribute to altered T-cell receptor signaling in neonatal naïve CD4 T cells.

Neonatal CD4+ T cells have reduced or delayed T-cell receptor (TCR) signaling responses compared with adult cells, but the mechanisms underlying this are poorly understood. This study tested the hypothesis that human neonatal naïve CD4+ TCR signaling and activation deficits are related to differences in H3K4me3 patterning and chromatin accessibility. Following initiation of TCR signaling using anti-CD3/anti-CD28 beads, adult naïve CD4+ T cells demonstrated increased CD69, phospho-CD3ε and interleukin (IL)-2, tumor necrosis factor-α (TNF-α), interferon-γ and IL-17A compared with neonatal cells. By contrast, following TCR-independent activation using phorbol myristate acetate (PMA)/ionomycin, neonatal cells demonstrated increased expression of CD69, IL-2 and TNF-α and equivalent phospho-ERK compared with adult cells. H3K4me3 chromatin immunoprecipitation-sequencing (ChIP-seq) and assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) were performed on separate cohorts of naïve CD4+ T cells from term neonates and adults, and RNA-seq data from neonatal and adult naïve CD4+ T cells were obtained from the Blueprint Consortium. Adult cells demonstrated overall increased chromatin accessibility and a higher proportion of H3K4me3 sites associated with open chromatin and active gene transcription compared with neonatal cells. Adult cells demonstrated increased mRNA expression of the TCR-associated genes FYN, ITK, CD4, LCK and LAT, which was associated with increased H3K4me3 at the FYN and ITK gene loci and increased chromatin accessibility at the CD4, LCK and LAT loci. These findings indicate that neonatal TCR-dependent defects in activation are epigenetically regulated and provide a potentially targetable mechanism to enhance neonatal CD4+ T-cell responses.

CD4 expression in effector T cells depends on DNA demethylation over a developmentally established stimulus-responsive element.

The epigenetic patterns that are established during early thymic development might determine mature T cell physiology and function, but the molecular basis and topography of the genetic elements involved are not fully known. Here we show, using the Cd4 locus as a paradigm for early developmental programming, that DNA demethylation during thymic development licenses a novel stimulus-responsive element that is critical for the maintenance of Cd4 gene expression in effector T cells. We document the importance of maintaining high CD4 expression during parasitic infection and show that by driving transcription, this stimulus-responsive element allows for the maintenance of histone H3K4me3 levels during T cell replication, which is critical for preventing de novo DNA methylation at the Cd4 promoter. A failure to undergo epigenetic programming during development leads to gene silencing during effector T cell replication. Our study thus provides evidence of early developmental events shaping the functional fitness of mature effector T cells.

The Role of iRhom2 in Metabolic and Cardiovascular-Related Disorders.

Chronic obesity is associated with metabolic imbalance leading to diabetes, dyslipidemia, and cardiovascular diseases (CVDs), in which inflammation is caused by exposure to inflammatory stimuli, such as accumulating sphingolipid ceramides or intracellular stress. This inflammatory response is likely to be prolonged by the effects of dietary and blood cholesterol, thereby leading to chronic low-grade inflammation and endothelial dysfunction. Elevated levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF) are predictive of CVDs and have been widely studied for potential therapeutic strategies. The release of TNF is controlled by a disintegrin and metalloprotease (ADAM) 17 and both are positively associated with CVDs. ADAM17 also cleaves most of the ligands of the epidermal growth factor receptor (EGFR) which have been associated with hypertension, atherogenesis, vascular dysfunction, and cardiac remodeling. The inactive rhomboid protein 2 (iRhom2) regulates the ADAM17-dependent shedding of TNF in immune cells. In addition, iRhom2 also regulates the ADAM17-mediated cleavage of EGFR ligands such as amphiregulin and heparin-binding EGF-like growth factor. Targeting iRhom2 has recently become a possible alternative therapeutic strategy in chronic inflammatory diseases such as lupus nephritis and rheumatoid arthritis. However, what role this intriguing interacting partner of ADAM17 plays in the vasculature and how it functions in the pathologies of obesity and associated CVDs, are exciting questions that are only beginning to be elucidated. In this review, we discuss the role of iRhom2 in cardiovascular-related pathologies such as atherogenesis and obesity by providing an evaluation of known iRhom2-dependent cellular and inflammatory pathways.

A Pathophysiological Perspective on COVID-19's Lethal Complication: From Viremia to Hypersensitivity Pneumonitis-like Immune Dysregulation.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the coronavirus responsible for our recent coronavirus disease 2019 pandemic, is driving a lung immunopathology that strongly resembles a severe form of hypersensitivity pneumonitis (HP). A review of recent Severe acute respiratory syndrome-related coronavirus (SARS-CoV) and SARS-CoV-2 medical reports, as well as described characteristics of HP, lead us to postulate a theory for SARS-CoV-2 severe disease. We propose that the novel SARS-CoV-2 can act as a trigger and substrate of an HP-like severe immune reaction especially in genetically vulnerable individuals in addition to those with immune senescence and dysregulation. Accordingly, the purpose of our letter is to shift the emphasis of concern surrounding immune activity from viral infection to an HP-like severe immune reaction. We review similarities in disease presentation between infection and allergy, relevant immunopathology, and outline phases of SARS-CoV-2 disease with perspectives on therapy and critical care. Altogether, the favored course is to begin treatments that address the disease at the earliest phase before immune dysregulation leading to uncontrolled pulmonary inflammation.

Loss of iRhom2 accelerates fat gain and insulin resistance in diet-induced obesity despite reduced adipose tissue inflammation.

BACKGROUND: Low-grade inflammation and metabolic dysregulation are common comorbidities of obesity, both of which are associated with alterations in iRhom2-regulated pro-inflammatory cytokine and epidermal growth factor receptor (EGFR) ligand signaling. OBJECTIVE: Our objective was to determine the role of iRhom2 in the regulation of low-grade inflammation and metabolic dysregulation in a murine model of diet-induced obesity. METHODS: Wild type (WT) and iRhom2-deficient mice were fed normal chow (NC) or a high-fat diet (HFD) starting at 5 weeks of age for up to 33 weeks. Body composition, glucose and insulin tolerance, feeding behavior, and indirect calorimetry were measured at defined time points. Adipose tissue cytokine expression and inflammatory lesions known as crown-like structures (CLS) were analyzed at the end-point of the study. RESULTS: iRhom2-deficient mice show accelerated fat gain on a HFD, accompanied by insulin resistance. Indirect calorimetry did not demonstrate changes in energy expenditure or food intake, but locomotor activity was significantly reduced in HFD iRhom2-deficient mice. Interestingly, CLS, macrophage infiltration, and tumor necrosis factor (TNF) production were decreased in adipose tissue from HFD iRhom2-deficient mice, but circulating cytokines were unchanged. In inguinal and perigonadal fat, the EGFR ligand amphiregulin was markedly induced in HFD controls but completely prevented in iRhom2-deficient mice, suggesting a potentially dominant role of EGFR-dependent mechanisms over TNF in the modulation of insulin sensitivity. CONCLUSIONS: This study elucidates a novel role for iRhom2 as an immuno-metabolic regulator that affects adipose tissue inflammation independent of insulin resistance.

The Threshold Effect: Lipopolysaccharide-Induced Inflammatory Responses in Primary Macrophages Are Differentially Regulated in an iRhom2-Dependent Manner.

A well-controlled innate immune response is characterized by a rapid yet self-limiting inflammatory response. Although much is known about the range of inflammatory stimuli capable of triggering an innate immune response, the mechanisms which govern the degree of inflammation induced by inflammatory insults and the mechanisms in place to reset or maintain homeostasis are poorly understood. Tumor necrosis factor (TNF) is a potent early response pro-inflammatory cytokine produced by immune cells following a broad range of insults spanning autoimmunity and metabolic diseases to pathogenic infections. Previous studies have shown that a disintegrin and metalloproteinase (ADAM) 17 controls the release of soluble TNF and epidermal growth factor receptor signaling. Utilizing a genetic model of ADAM17 deficiency through the deletion of its regulator, the inactive rhomboid 2 (iRhom2), we show that loss of ADAM17 activity in innate immune cells leads to decreased expression of various cytokines in response to low levels of pathogen-associated molecular pattern (PAMP) stimulation but not at high-dose stimulation. In addition, TNF receptor (TNFR) 1/2-deficient bone marrow-derived macrophages yielded significantly reduced TNF expression following low levels of PAMP stimulation, suggesting that signaling through the TNFRs in immune cells drives a feed-forward regulatory mechanism wherein low levels of TNF allow sustained enhancement of TNF expression in an iRhom2/ADAM17-dependent manner. Thus, we demonstrate that inflammatory expression of TNF and IL1ß is differentially regulated following high or low doses of PAMP stimulation, invoking the activation of a previously unknown regulatory mechanism of inflammation.

Novel functions of inactive rhomboid proteins in immunity and disease.

iRhoms are related to a family of intramembrane serine proteinases called rhomboids but lack proteolytic activity. In mammals, there are two iRhoms, iRhom1 and iRhom2, which have similar domain structures and overlapping specificities as well as distinctive functions. These catalytically inactive rhomboids are essential regulators for the maturation and trafficking of the disintegrin metalloprotease ADAM17 from the endoplasmic reticulum to the cell surface, and are required for the cleavage and release of a variety of membrane-associated proteins, including the IL-6 receptor, l-selectin, TNF, and EGFR ligands. iRhom2-dependent regulation of ADAM17 function has been recently implicated in the development and progression of several autoimmune diseases including rheumatoid arthritis, lupus nephritis, as well as hemophilic arthropathy. In this review, we discuss our current understanding of iRhom biology, their implications in autoimmune pathologies, and their potential as therapeutic targets.

Loss of RHBDF2 results in an early-onset spontaneous murine colitis.

Inflammatory bowel disease (IBD) is a heterogeneous group of inflammation-mediated pathologies that include Crohn's disease and ulcerative colitis and primarily affects the colon and small intestine. Previous studies have shown that a disintegrin and metalloprotease (ADAM) 17, a membrane-bound sheddase, capable of cleaving the proinflammatory cytokine TNF and epidermal growth factor receptor ligands, plays a critical role in maintaining gut homeostasis and modulating intestinal inflammation during IBD. Rhomboid 5 homolog 2 (RHBDF2), a catalytically inactive member of the rhomboid family of intramembrane serine proteases, was recently identified as a crucial regulator of ADAM17. Here, we assessed the role of RHBDF2 in the development of colitis in the context of IL10 deficiency. Il10-/- /Rhbdf2-/- mice developed spontaneous colitis and experienced severe weight loss starting at 8 wk of age, without the need for exogenous triggers. Severity of disease pathology in Il10-/- /Rhbdf2-/- mice correlated with a dysbiotic gut microbiota and elevated Th1-associated immune responses with increased interferon gamma and IL2 production. In addition, Il10-/- /Rhbdf2-/- mice failed to maintain their epithelial cell homeostasis, although the intestinal epithelial barrier of Rhbdf2-/- mice is intact and loss of Rhbdf2 did not significantly exacerbate sensitivity to dextran sulfate sodium-induced colitis, suggesting differences in the underlying disease pathway of intestinal inflammation in this model. Taken together, our results demonstrate a critical regulatory role for RHBDF2 in the maintenance of the unique homeostasis between intestinal microbiota and host immune responses in the gut that is dysregulated during the pathogenesis of IBD.

Stage-specific epigenetic regulation of CD4 expression by coordinated enhancer elements during T cell development.

The inheritance of gene expression patterns is dependent on epigenetic regulation, but the establishment and maintenance of epigenetic landscapes during T cell differentiation are incompletely understood. Here we show that two stage-specific Cd4 cis-elements, the previously characterized enhancer E4p and a novel enhancer E4m, coordinately promote Cd4 transcription in mature thymic MHC-II-specific T cells, in part through the canonical Wnt pathway. Specifically, E4p licenses E4m to orchestrate DNA demethylation by TET1 and TET3, which in turn poises the Cd4 locus for transcription in peripheral T cells. Cd4 locus demethylation is important for subsequent Cd4 transcription in activated peripheral T cells wherein these cis-elements become dispensable. By contrast, in developing thymocytes the loss of TET1/3 does not affect Cd4 transcription, highlighting an uncoupled event between transcription and epigenetic modifications. Together our findings reveal an important function for thymic cis-elements in governing gene expression in the periphery via a heritable epigenetic mechanism.

iRhom2 promotes lupus nephritis through TNF-α and EGFR signaling.

Lupus nephritis (LN) often results in progressive renal dysfunction. The inactive rhomboid 2 (iRhom2) is a newly identified key regulator of A disintegrin and metalloprotease 17 (ADAM17), whose substrates, such as TNF-α and heparin-binding EGF (HB-EGF), have been implicated in the pathogenesis of chronic kidney diseases. Here, we demonstrate that deficiency of iRhom2 protects the lupus-prone Fcgr2b-/- mice from developing severe kidney damage without altering anti-double-stranded DNA (anti-dsDNA) Ab production by simultaneously blocking HB-EGF/EGFR and TNF-α signaling in the kidney tissues. Unbiased transcriptome profiling of kidneys and kidney macrophages revealed that TNF-α and HB-EGF/EGFR signaling pathways are highly upregulated in Fcgr2b-/- mice, alterations that were diminished in the absence of iRhom2. Pharmacological blockade of either TNF-α or EGFR signaling protected Fcgr2b-/- mice from severe renal damage. Finally, kidneys from LN patients showed increased iRhom2 and HB-EGF expression, with interstitial HB-EGF expression significantly associated with chronicity indices. Our data suggest that activation of iRhom2/ADAM17-dependent TNF-α and EGFR signaling plays a crucial role in mediating irreversible kidney damage in LN, thereby uncovering a target for selective and simultaneous dual inhibition of 2 major pathological pathways in the effector arm of the disease.

Heritable Gene Regulation in the CD4:CD8 T Cell Lineage Choice.

The adaptive immune system is dependent on functionally distinct lineages of T cell antigen receptor αß-expressing T cells that differentiate from a common progenitor in the thymus. CD4+CD8+ progenitor thymocytes undergo selection following interaction with MHC class I and class II molecules bearing peptide self-antigens, giving rise to CD8+ cytotoxic and CD4+ helper or regulatory T cell lineages, respectively. The strict correspondence of CD4 and CD8 expression with distinct cellular phenotypes has made their genes useful surrogates for investigating molecular mechanisms of lineage commitment. Studies of Cd4 and Cd8 transcriptional regulation have uncovered cis-regulatory elements that are critical for mediating epigenetic modifications at distinct stages of development to establish heritable transcriptional programs. In this review, we examine the epigenetic mechanisms involved in Cd4 and Cd8 gene regulation during T cell lineage specification and highlight the features that make this an attractive system for uncovering molecular mechanisms of heritability.

iRhom2 regulates CSF1R cell surface expression and non-steady state myelopoiesis in mice.

CSF1R (colony stimulating factor 1 receptor) is the main receptor for CSF1 and has crucial roles in regulating myelopoeisis. CSF1R can be proteolytically released from the cell surface by ADAM17 (A disintegrin and metalloprotease 17). Here, we identified CSF1R as a major substrate of ADAM17 in an unbiased degradomics screen. We explored the impact of CSF1R shedding by ADAM17 and its upstream regulator, inactive rhomboid protein 2 (iRhom2, gene name Rhbdf2), on homeostatic development of mouse myeloid cells. In iRhom2-/- mice, we found constitutive accumulation of membrane-bound CSF1R on myeloid cells at steady state, although cell numbers of these populations were not altered. However, in the context of mixed bone marrow (BM) chimera, under competitive pressure, iRhom2-/- BM progenitor-derived monocytes, tissue macrophages and lung DCs showed a repopulation advantage over those derived from wild-type (WT) BM progenitors, suggesting enhanced CSF1R signaling in the absence of iRhom2. In vitro experiments indicate that iRhom2-/- Lin- SCA-1+ c-Kit+ (LSKs) cells, but not granulocyte-macrophage progenitors (GMPs), had faster growth rates than WT cells in response to CSF1. Our results shed light on an important role of iRhom2/ADAM17 pathway in regulation of CSF1R shedding and repopulation of monocytes, macrophages and DCs.

Regulation of DNA methylation dictates Cd4 expression during the development of helper and cytotoxic T cell lineages.

During development, progenitor cells with binary potential give rise to daughter cells that have distinct functions. Heritable epigenetic mechanisms then lock in gene-expression programs that define lineage identity. Regulation of the gene encoding the T cell-specific coreceptor CD4 in helper and cytotoxic T cells exemplifies this process, with enhancer- and silencer-regulated establishment of epigenetic memory for stable gene expression and repression, respectively. Using a genetic screen, we identified the DNA-methylation machinery as essential for maintaining silencing of Cd4 in the cytotoxic lineage. Furthermore, we found a requirement for the proximal enhancer in mediating the removal of DNA-methylation marks from Cd4, which allowed stable expression of Cd4 in helper T cells. Our findings suggest that stage-specific methylation and demethylation events in Cd4 regulate its heritable expression in response to the distinct signals that dictate lineage 'choice' during T cell development.

iRhoms 1 and 2 are essential upstream regulators of ADAM17-dependent EGFR signaling.

The metalloproteinase ADAM17 (a disintegrin and metalloprotease 17) controls EGF receptor (EGFR) signaling by liberating EGFR ligands from their membrane anchor. Consequently, a patient lacking ADAM17 has skin and intestinal barrier defects that are likely caused by lack of EGFR signaling, and Adam17(-/-) mice die perinatally with open eyes, like Egfr(-/-) mice. A hallmark feature of ADAM17-dependent EGFR ligand shedding is that it can be rapidly and posttranslationally activated in a manner that requires its transmembrane domain but not its cytoplasmic domain. This suggests that ADAM17 is regulated by other integral membrane proteins, although much remains to be learned about the underlying mechanism. Recently, inactive Rhomboid 2 (iRhom2), which has seven transmembrane domains, emerged as a molecule that controls the maturation and function of ADAM17 in myeloid cells. However, iRhom2(-/-) mice appear normal, raising questions about how ADAM17 is regulated in other tissues. Here we report that iRhom1/2(-/-) double knockout mice resemble Adam17(-/-) and Egfr(-/-) mice in that they die perinatally with open eyes, misshapen heart valves, and growth plate defects. Mechanistically, we show lack of mature ADAM17 and strongly reduced EGFR phosphorylation in iRhom1/2(-/-) tissues. Finally, we demonstrate that iRhom1 is not essential for mouse development but regulates ADAM17 maturation in the brain, except in microglia, where ADAM17 is controlled by iRhom2. These results provide genetic, cell biological, and biochemical evidence that a principal function of iRhoms1/2 during mouse development is to regulate ADAM17-dependent EGFR signaling, suggesting that iRhoms1/2 could emerge as novel targets for treatment of ADAM17/EGFR-dependent pathologies.

iRhom2 controls the substrate selectivity of stimulated ADAM17-dependent ectodomain shedding.

Protein ectodomain shedding by ADAM17 (a disintegrin and metalloprotease 17), a principal regulator of EGF-receptor signaling and TNFα release, is rapidly and posttranslationally activated by a variety of signaling pathways, and yet little is known about the underlying mechanism. Here, we report that inactive rhomboid protein 2 (iRhom2), recently identified as essential for the maturation of ADAM17 in hematopoietic cells, is crucial for the rapid activation of the shedding of some, but not all substrates of ADAM17. Mature ADAM17 is present in mouse embryonic fibroblasts (mEFs) lacking iRhom2, and yet ADAM17 is unable to support stimulated shedding of several of its substrates, including heparin-binding EGF and Kit ligand 2 in this context. Stimulated shedding of other ADAM17 substrates, such as TGFα, is not affected in iRhom2(-/-) mEFs but can be strongly reduced by treating iRhom2(-/-) mEFs with siRNA against iRhom1. Activation of heparin-binding EGF or Kit ligand 2 shedding by ADAM17 in iRhom2(-/-) mEFs can be rescued by wild-type iRhom2 but not by iRhom2 lacking its N-terminal cytoplasmic domain. The requirement for the cytoplasmic domain of iRhom2 for stimulated shedding by ADAM17 may help explain why the cytoplasmic domain of ADAM17 is not required for stimulated shedding. The functional relevance of iRhom2 in regulating shedding of EGF receptor (EGFR) ligands is established by a lack of lysophasphatidic acid/ADAM17/EGFR-dependent crosstalk with ERK1/2 in iRhom2(-/-) mEFs, and a significant reduction of FGF7/ADAM17/EGFR-stimulated migration of iRhom2(-/-) keratinocytes. Taken together, these findings uncover functions for iRhom2 in the regulation of EGFR signaling and in controlling the activation and substrate selectivity of ADAM17-dependent shedding events.

iRHOM2 is a critical pathogenic mediator of inflammatory arthritis.

iRHOM2, encoded by the gene Rhbdf2, regulates the maturation of the TNF-α convertase (TACE), which controls shedding of TNF-α and its biological activity in vivo. TACE is a potential target to treat TNF-α-dependent diseases, such as rheumatoid arthritis, but there are concerns about potential side effects, because TACE also protects the skin and intestinal barrier by activating EGFR signaling. Here we report that inactivation of Rhbdf2 allows tissue-specific regulation of TACE by selectively preventing its maturation in immune cells, without affecting its homeostatic functions in other tissues. The related iRHOM1, which is widely expressed, except in hematopoietic cells, supported TACE maturation and shedding of the EGFR ligand TGF-α in Rhbdf2-deficient cells. Remarkably, mice lacking Rhbdf2 were protected from K/BxN inflammatory arthritis to the same extent as mice lacking TACE in myeloid cells or Tnfa-deficient mice. In probing the underlying mechanism, we found that two main drivers of K/BxN arthritis, complement C5a and immune complexes, stimulated iRHOM2/TACE-dependent shedding of TNF-α in mouse and human cells. These data demonstrate that iRHOM2 and myeloid-expressed TACE play a critical role in inflammatory arthritis and indicate that iRHOM2 is a potential therapeutic target for selective inactivation of TACE in myeloid cells.

ADAM17 is regulated by a rapid and reversible mechanism that controls access to its catalytic site.

Protein ectodomain shedding is crucial for cell-cell interactions because it controls the bioavailability of soluble tumor necrosis factor-α (TNFα) and ligands of the epidermal growth factor (EGF) receptor, and the release of many other membrane proteins. Various stimuli can rapidly trigger ectodomain shedding, yet much remains to be learned about the identity of the enzymes that respond to these stimuli and the mechanisms underlying their activation. Here, we demonstrate that the membrane-anchored metalloproteinase ADAM17, but not ADAM10, is the sheddase that rapidly responds to the physiological signaling pathways stimulated by thrombin, EGF, lysophosphatidic acid and TNFα. Stimulation of ADAM17 is swift and quickly reversible, and does not depend on removal of its inhibitory pro-domain by pro-protein convertases, or on dissociation of an endogenous inhibitor, TIMP3. Moreover, activation of ADAM17 by physiological stimuli requires its transmembrane domain, but not its cytoplasmic domain, arguing against inside-out signaling via cytoplasmic phosphorylation as the underlying mechanism. Finally, experiments with the tight binding hydroxamate inhibitor DPC333, used here to probe the accessibility of the active site of ADAM17, demonstrate that this inhibitor can quickly bind to ADAM17 in stimulated, but not quiescent cells. These findings support the concept that activation of ADAM17 involves a rapid and reversible exposure of its catalytic site.