Pathological mutations reveal the key role of the cytosolic iRhom2 N-terminus for phosphorylation-independent 14-3-3 interaction and ADAM17 binding, stability, and activity.

The protease ADAM17 plays an important role in inflammation and cancer and is regulated by iRhom2. Mutations in the cytosolic N-terminus of human iRhom2 cause tylosis with oesophageal cancer (TOC). In mice, partial deletion of the N-terminus results in a curly hair phenotype (cub). These pathological consequences are consistent with our findings that iRhom2 is highly expressed in keratinocytes and in oesophageal cancer. Cub and TOC are associated with hyperactivation of ADAM17-dependent EGFR signalling. However, the underlying molecular mechanisms are not understood. We have identified a non-canonical, phosphorylation-independent 14-3-3 interaction site that encompasses all known TOC mutations. Disruption of this site dysregulates ADAM17 activity. The larger cub deletion also includes the TOC site and thus also dysregulated ADAM17 activity. The cub deletion, but not the TOC mutation, also causes severe reductions in stimulated shedding, binding, and stability of ADAM17, demonstrating the presence of additional regulatory sites in the N-terminus of iRhom2. Overall, this study contrasts the TOC and cub mutations, illustrates their different molecular consequences, and reveals important key functions of the iRhom2 N-terminus in regulating ADAM17.

Molecular characterization of the craniosynostosis-associated interleukin-11 receptor variants p.T306_S308dup and p.E364_V368del.

Interleukin-11 (IL-11) is a member of the IL-6 family of cytokines and is an important factor for bone homeostasis. IL-11 binds to and signals via the membrane-bound IL-11 receptor (IL-11R, classic signaling) or soluble forms of the IL-11R (sIL-11R, trans-signaling). Mutations in the IL11RA gene, which encodes the IL-11R, are associated with craniosynostosis, a human condition in which one or several of the sutures close prematurely, resulting in malformation of the skull. The biological mechanisms of how mutations within the IL-11R are linked to craniosynostosis are mostly unexplored. In this study, we analyze two variants of the IL-11R described in craniosynostosis patients: p.T306_S308dup, which results in a duplication of three amino-acid residues within the membrane-proximal fibronectin type III domain, and p.E364_V368del, which results in a deletion of five amino-acid residues in the so-called stalk region adjacent to the plasma membrane. The stalk region connects the three extracellular domains to the transmembrane and intracellular region of the IL-11R and contains cleavage sites for different proteases that generate sIL-11R variants. Using a combination of bioinformatics and different biochemical, molecular, and cell biology methods, we show that the IL-11R-T306_S308dup variant does not mature correctly, is intracellularly retained, and does not reach the cell surface. In contrast, the IL-11R-E364_V368del variant is fully biologically active and processed normally by proteases, thus allowing classic and trans-signaling of IL-11. Our results provide evidence that mutations within the IL11RA gene may not be causative for craniosynostosis and suggest that other regulatory mechanism(s) are involved but remain to be identified.

Mechanical activation of lung epithelial cells through the ion channel Piezo1 activates the metalloproteinases ADAM10 and ADAM17 and promotes growth factor and adhesion molecule release.

In the lung, pulmonary epithelial cells undergo mechanical stretching during ventilation. The associated cellular mechanoresponse is still poorly understood at the molecular level. Here, we demonstrate that activation of the mechanosensitive cation channel Piezo1 in a human epithelial cell line (H441) and in primary human lung epithelial cells induces the proteolytic activity of the metalloproteinases ADAM10 and ADAM17 at the plasma membrane. These ADAMs are known to convert cell surface expressed proteins into soluble and thereby play major roles in proliferation, barrier regulation and inflammation. We observed that chemical activation of Piezo1 promotes cleavage of substrates that are specific for either ADAM10 or ADAM17. Activation of Piezo1 also induced the synthesis and ADAM10/17-dependent release of the growth factor amphiregulin (AREG). In addition, junctional adhesion molecule A (JAM-A) was shed in an ADAM10/17-dependent manner resulting in a reduction of cell contacts. Stretching experiments combined with Piezo1 knockdown further demonstrated that mechanical activation promotes shedding via Piezo1. Most importantly, high pressure ventilation of murine lungs increased AREG and JAM-A release into the alveolar space, which was reduced by a Piezo1 inhibitor. Our study provides a novel link between stretch-induced Piezo1 activation and the activation of ADAM10 and ADAM17 in lung epithelium. This may help to understand acute respiratory distress syndrome (ARDS) which is induced by ventilation stress and goes along with perturbed epithelial permeability and release of growth factors.

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.

A structural model of the iRhom-ADAM17 sheddase complex reveals functional insights into its trafficking and activity.

Several membrane-anchored signal mediators such as cytokines (e.g. TNFα) and growth factors are proteolytically shed from the cell surface by the metalloproteinase ADAM17, which, thus, has an essential role in inflammatory and developmental processes. The membrane proteins iRhom1 and iRhom2 are instrumental for the transport of ADAM17 to the cell surface and its regulation. However, the structure-function determinants of the iRhom-ADAM17 complex are poorly understood. We used AI-based modelling to gain insights into the structure-function relationship of this complex. We identified different regions in the iRhom homology domain (IRHD) that are differentially responsible for iRhom functions. We have supported the validity of the predicted structure-function determinants with several in vitro, ex vivo and in vivo approaches and demonstrated the regulatory role of the IRHD for iRhom-ADAM17 complex cohesion and forward trafficking. Overall, we provide mechanistic insights into the iRhom-ADAM17-mediated shedding event, which is at the centre of several important cytokine and growth factor pathways.

The collectrin-like part of the SARS-CoV-1 and -2 receptor ACE2 is shed by the metalloproteinases ADAM10 and ADAM17.

The transmembrane protease angiotensin converting enzyme 2 (ACE2) is a protective regulator within the renin angiotensin system and additionally represents the cellular receptor for SARS-CoV. The release of soluble ACE2 (sACE2) from the cell surface is hence believed to be a crucial part of its (patho)physiological functions, as both, ACE2 protease activity and SARS-CoV binding ability, are transferred from the cell membrane to body fluids. Yet, the molecular sources of sACE2 are still not completely investigated. In this study, we show different sources and prerequisites for the release of sACE2 from the cell membrane. By using inhibitors as well as CRISPR/Cas9-derived cells, we demonstrated that, in addition to the metalloprotease ADAM17, also ADAM10 is an important novel shedding protease of ACE2. Moreover, we observed that ACE2 can also be released in extracellular vesicles. The degree of either ADAM10- or ADAM17-mediated ACE2 shedding is dependent on stimulatory conditions and on the expression level of the pro-inflammatory ADAM17 regulator iRhom2. Finally, by using structural analysis and in vitro verification, we determined for the first time that the susceptibility to ADAM10- and ADAM17-mediated shedding is mediated by the collectrin-like part of ACE2. Overall, our findings give novel insights into sACE2 release by several independent molecular mechanisms.

ADAM17 Is an Essential Factor for the Infection of Bovine Cells with Pestiviruses.

The entry of BVDV into bovine cells was studied using CRIB cells (cells resistant to infection with bovine viral diarrhea virus [BVDV]) that have evolved from MDBK cells by a spontaneous loss of susceptibility to BVDV. Recently, larger genetic deletions were reported but no correlation of the affected genes and the resistance to BVDV infection could be established. The metalloprotease ADAM17 was reported as an essential attachment factor for the related classical swine fever virus (CSFV). To assess whether ADAM17 might be involved in the resistance of CRIB-1 cells to pestiviruses, we analyzed its expression in CRIB-1 and MDBK cells. While ADAM17 protein was detectable in MBDK cells, it was absent from CRIB-1 cells. No functional full-length ADAM17 mRNA could be detected in CRIB cells and genetic analysis revealed the presence of two defective alleles. Transcomplementation of functional ADAM17 derived from MDBK cells in CRIB-1 cells resulted in a nearly complete reversion of their resistance to pestiviral infection. Our results demonstrate that ADAM17 is a key cellular factor for the pestivirus resistance of CRIB-1 cells and establishes its essential role for a broader range of pestiviruses.

Inflammatory activation of surface molecule shedding by upregulation of the pseudoprotease iRhom2 in colon epithelial cells.

The metalloproteinase ADAM17 contributes to inflammatory and proliferative responses by shedding of cell-surface molecules. By this ADAM17 is implicated in inflammation, regeneration, and permeability regulation of epithelial cells in the colon. ADAM17 maturation and surface expression requires the adapter proteins iRhom1 or iRhom2. Here we report that expression of iRhom2 but not iRhom1 is upregulated in intestinal tissue of mice with acute colitis. Our analysis of public databases indicates elevated iRhom2 expression in mucosal tissue and epithelial cells from patients with inflammatory bowel disease (IBD). Consistently, expression of iRhom2 but not iRhom1 is upregulated in colon or intestinal epithelial cell lines after co-stimulation with tumor necrosis factor (TNF) and interferon gamma (IFNgamma). This upregulation can be reduced by inhibition of Janus kinases or transcription factors NF-kappaB or AP-1. Upregulation of iRhom2 can be mimicked by iRhom2 overexpression and is associated with enhanced maturation and surface expression of ADAM17 which then results in increased cleavage of transforming growth factor (TGF) alpha and junctional adhesion molecule (JAM)-A. Finally, the induction of these responses is suppressed by inhibition of iRhom2 transcription. Thus, inflammatory induction of iRhom2 may contribute to upregulated ADAM17-dependent mediator and adhesion molecule release in IBD. The development of iRhom2-dependent inhibitors may allow selective targeting of inflammatory ADAM17 activities.

The iRhom homology domain is indispensable for ADAM17-mediated TNFα and EGF receptor ligand release.

Membrane-tethered signalling proteins such as TNFα and many EGF receptor ligands undergo shedding by the metalloproteinase ADAM17 to get released. The pseudoproteases iRhom1 and iRhom2 are important for the transport, maturation and activity of ADAM17. Yet, the structural and functional requirements to promote the transport of the iRhom-ADAM17 complex have not yet been thoroughly investigated. Utilising in silico and in vitro methods, we here map the conserved iRhom homology domain (IRHD) and provide first insights into its structure and function. By focusing on iRhom2, we identified different structural and functional factors within the IRHD. We found that the structural integrity of the IRHD is a key factor for ADAM17 binding. In addition, we identified a highly conserved motif within an unstructured region of the IRHD, that, when mutated, restricts the transport of the iRhom-ADAM17 complex through the secretory pathway in in vitro, ex vivo and in vivo systems and also increases the half-life of iRhom2 and ADAM17. Furthermore, the disruption of this IRHD motif was also reflected by changes in the yet undescribed interaction profile of iRhom2 with proteins involved in intracellular vesicle transport. Overall, we provide the first insights into the forward trafficking of iRhoms which is critical for TNFα and EGF receptor signalling.

Interleukin-6 controls recycling and degradation, but not internalization of its receptors.

Interleukin-6 (IL-6) is a cytokine implicated in proinflammatory as well as regenerative processes and acts via receptor complexes consisting of the ubiquitously expressed, signal-transducing receptor gp130 and the IL-6 receptor (IL-6R). The IL-6R is expressed only on hepatocytes and subsets of leukocytes, where it mediates specificity of the receptor complex to IL-6 as the subunit gp130 is shared with all other members of the IL-6 cytokine family such as IL-11 or IL-27. The amount of IL-6R at the cell surface thus determines the responsiveness of the cell to the cytokine and might therefore be decisive in the development of inflammatory disorders. However, how the expression levels of IL-6R and gp130 at the cell surface are controlled is largely unknown. Here, we show that IL-6R and gp130 are constitutively internalized independent of IL-6. This process depends on dynamin and clathrin and is temporally controlled by motifs within the intracellular region of gp130 and IL-6R. IL-6 binding and internalization of the receptors is a prerequisite for activation of the Jak/STAT signaling cascade. Targeting of gp130, but not of the IL-6R, to the lysosome for degradation depends on stimulation with IL-6. Furthermore, we show that after internalization and activation of signaling, both the IL-6R and gp130 are recycled back to the cell surface, a process that is enhanced by IL-6. These data reveal an important function of IL-6 beyond the pure activation of signaling.

Interleukin-11 (IL-11) receptor cleavage by the rhomboid protease RHBDL2 induces IL-11 trans-signaling.

Interleukin-11 (IL-11) is a pleiotropic cytokine with both pro- and anti-inflammatory properties. It activates its target cells via binding to the membrane-bound IL-11 receptor (IL-11R), which then recruits a homodimer of the ubiquitously expressed, signal-transducing receptor gp130. Besides this classic signaling pathway, IL-11 can also bind to soluble forms of the IL-11R (sIL-11R), and IL-11/sIL-11R complexes activate cells via the induction of gp130 homodimerization (trans-signaling). We have previously reported that the metalloprotease ADAM10 cleaves the membrane-bound IL-11R and thereby generates sIL-11R. In this study, we identify the rhomboid intramembrane protease RHBDL2 as a so far unrecognized alternative sheddase that can efficiently trigger IL-11R secretion. We determine the cleavage site used by RHBDL2, which is located in the extracellular part of the receptor in close proximity to the plasma membrane, between Ala-370 and Ser-371. Furthermore, we identify critical amino acid residues within the transmembrane helix that are required for IL-11R proteolysis. We also show that ectopically expressed RHBDL2 is able to cleave the IL-11R within the early secretory pathway and not only at the plasma membrane, indicating that its subcellular localization plays a central role in controlling its activity. Moreover, RHBDL2-derived sIL-11R is biologically active and able to perform IL-11 trans-signaling. Finally, we show that the human mutation IL-11R-A370V does not impede IL-11 classic signaling, but prevents RHBDL2-mediated IL-11R cleavage.

The metalloproteinase ADAM10 requires its activity to sustain surface expression.

The metalloproteinase ADAM10 critically contributes to development, inflammation, and cancer and can be controlled by endogenous or synthetic inhibitors. Here, we demonstrate for the first time that loss of proteolytic activity of ADAM10 by either inhibition or loss of function mutations induces removal of the protease from the cell surface and the whole cell. This process is temperature dependent, restricted to mature ADAM10, and associated with an increased internalization, lysosomal degradation, and release of mature ADAM10 in extracellular vesicles. Recovery from this depletion requires de novo synthesis. Functionally, this is reflected by loss and recovery of ADAM10 substrate shedding. Finally, ADAM10 inhibition in mice reduces systemic ADAM10 levels in different tissues. Thus, ADAM10 activity is critically required for its surface expression in vitro and in vivo. These findings are crucial for development of therapeutic ADAM10 inhibition strategies and may showcase a novel, physiologically relevant mechanism of protease removal due to activity loss.

Expression levels of the metalloproteinase ADAM8 critically regulate proliferation, migration and malignant signalling events in hepatoma cells.

Hepatocellular carcinoma (HCC) is one of the most common metastatic tumours. Tumour growth and metastasis depend on the induction of cell proliferation and migration by various mediators. Here, we report that the A Disintegrin and Metalloproteinase (ADAM) 8 is highly expressed in murine HCC tissues as well as in murine and human hepatoma cell lines Hepa1-6 and HepG2, respectively. To establish a dose-dependent role of different ADAM8 expression levels for HCC progression, ADAM8 expression was either reduced via shRNA- or siRNA-mediated knockdown or increased by using a retroviral overexpression vector. These two complementary approaches revealed that ADAM8 expression levels correlated positively with proliferation, clonogenicity, migration and matrix invasion and negatively with apoptosis of hepatoma cells. Furthermore, the analysis of pro-migratory and proliferative signalling pathways revealed that ADAM8 expression level was positively associated with expression of ß1 integrin as well as with the activation of focal adhesion kinase (FAK), mitogen-activated protein kinase (MAPK), Src kinase and Rho A GTPase. Finally, up-regulation of promigatory signalling and cell migration was also seen with a proteolytically inactive ADAM8 mutant. These findings reveal that ADAM8 is critically up-regulated in hepatoma cells contributes to cell proliferation and survival and furthermore induces pro-migratory signalling pathways independently of its proteolytic activity. By this, ADAM8 can promote cell functions most relevant for HCC growth and metastasis.

Cathepsin S provokes interleukin-6 (IL-6) trans-signaling through cleavage of the IL-6 receptor in vitro.

The cytokine interleukin-6 (IL-6) fulfills its pleiotropic functions via different modes of signaling. Regenerative and anti-inflammatory activities are mediated via classic signaling, in which IL-6 binds to the membrane-bound IL-6 receptor (IL-6R). For IL-6 trans-signaling, which accounts for the pro-inflammatory properties of the cytokine, IL-6 activates its target cells via soluble forms of the IL-6R (sIL-6R). We have previously shown that the majority of sIL-6R in human serum originates from proteolytic cleavage and mapped the cleavage site of the IL-6R. The cleavage occurs between Pro-355 and Val-356, which is the same cleavage site that the metalloprotease ADAM17 uses in vitro. However, sIL-6R serum levels are unchanged in hypomorphic ADAM17ex/ex mice, making the involvement of ADAM17 questionable. In order to identify other proteases that could be relevant for sIL-6R generation in vivo, we perform a screening approach based on the known cleavage site. We identify several candidate proteases and characterize the cysteine protease cathepsin S (CTSS) in detail. We show that CTSS is able to cleave the IL-6R in vitro and that the released sIL-6R is biologically active and can induce IL-6 trans-signaling. However, CTSS does not use the Pro-355/Val-356 cleavage site, and sIL-6R serum levels are not altered in Ctss-/- mice. In conclusion, we identify a novel protease of the IL-6R that can induce IL-6 trans-signaling, but does not contribute to steady-state sIL-6R serum levels.

Differential Induction of the ADAM17 Regulators iRhom1 and 2 in Endothelial Cells.

Background: Endothelial function significantly depends on the proteolytic release of surface expressed signal molecules, their receptors and adhesion molecules via the metalloproteinase ADAM17. The pseudoproteases iRhom1 and 2 independently function as adapter proteins for ADAM17 and are essential for the maturation, trafficking, and activity regulation of ADAM17. Bioinformatic data confirmed that immune cells predominantly express iRhom2 while endothelial cells preferentially express iRhom1. Objective: Here, we investigate possible reasons for higher iRhom1 expression and potential inflammatory regulation of iRhom2 in endothelial cells and analyze the consequences for ADAM17 maturation and function. Methods: Primary endothelial cells were cultured in absence and presence of flow with and without inflammatory cytokines (TNFα and INFγ). Regulation of iRhoms was studied by qPCR, involved signaling pathways were studied with transcriptional inhibitors and consequences were analyzed by assessment of ADAM17 maturation, surface expression and cleavage of the ADAM17 substrate junctional adhesion molecule JAM-A. Results: Endothelial iRhom1 is profoundly upregulated by physiological shear stress. This is accompanied by a homeostatic phenotype driven by the transcription factor KLF2 which is, however, only partially responsible for regulation of iRhom1. By contrast, iRhom2 is most prominently upregulated by inflammatory cytokines. This correlates with an inflammatory phenotype driven by the transcription factors NFκB and AP-1 of which AP-1 is most relevant for iRhom2 regulation. Finally, shear stress exposure and inflammatory stimulation have independent and no synergistic effects on ADAM17 maturation, surface expression and JAM-A shedding. Conclusion: Conditions of shear stress and inflammation differentially upregulate iRhom1 and 2 in primary endothelial cells which then results in independent regulation of ADAM17.

The iRhom2/ADAM17 Axis Attenuates Bacterial Uptake by Phagocytes in a Cell Autonomous Manner.

Uptake of bacteria by phagocytes is a crucial step in innate immune defence. Members of the disintegrin and metalloproteinase (ADAM) family critically control the immune response by limited proteolysis of surface expressed mediator molecules. Here, we investigated the significance of ADAM17 and its regulatory adapter molecule iRhom2 for bacterial uptake by phagocytes. Inhibition of metalloproteinase activity led to increased phagocytosis of pHrodo labelled Gram-negative and -positive bacteria (E. coli and S. aureus, respectively) by human and murine monocytic cell lines or primary phagocytes. Bone marrow-derived macrophages showed enhanced uptake of heat-inactivated and living E. coli when they lacked either ADAM17 or iRhom2 but not upon ADAM10-deficiency. In monocytic THP-1 cells, corresponding short hairpin RNA (shRNA)-mediated knockdown confirmed that ADAM17, but not ADAM10, promoted phagocytosis of E. coli. The augmented bacterial uptake occurred in a cell autonomous manner and was accompanied by increased release of the chemokine CXCL8, less TNFα release and only minimal changes in the surface expression of the receptors TNFR1, TLR6 and CD36. Inhibition experiments indicated that the enhanced bacterial phagocytosis after ADAM17 knockdown was partially dependent on TNFα-activity but not on CXCL8. This novel role of ADAM17 in bacterial uptake needs to be considered in the development of ADAM17 inhibitors as therapeutics.

ADAM17-triggered TNF signalling protects the ageing Drosophila retina from lipid droplet-mediated degeneration.

Animals have evolved multiple mechanisms to protect themselves from the cumulative effects of age-related cellular damage. Here, we reveal an unexpected link between the TNF (tumour necrosis factor) inflammatory pathway, triggered by the metalloprotease ADAM17/TACE, and a lipid droplet (LD)-mediated mechanism of protecting retinal cells from age-related degeneration. Loss of ADAM17, TNF and the TNF receptor Grindelwald in pigmented glial cells of the Drosophila retina leads to age-related degeneration of both glia and neurons, preceded by an abnormal accumulation of glial LDs. We show that the glial LDs initially buffer the cells against damage caused by glial and neuronally generated reactive oxygen species (ROS), but that in later life the LDs dissipate, leading to the release of toxic peroxidated lipids. Finally, we demonstrate the existence of a conserved pathway in human iPS-derived microglia-like cells, which are central players in neurodegeneration. Overall, we have discovered a pathway mediated by TNF signalling acting not as a trigger of inflammation, but as a cytoprotective factor in the retina.

Distance dependent shedding of IL-6R.

Proteolytic processing of membrane proteins by A disintegrin and metalloprotease-17 (ADAM17) is a key regulatory step in many physiological and pathophysiological processes. This so-called shedding is essential for development, regeneration and immune defense. An uncontrolled ADAM17 activity promotes cancer development, chronic inflammation and autoimmune diseases. Consequently, the ADAM17 activity is tightly regulated. As a final trigger for the shedding event a phosphatidylserine (PS) flip to the outer leaflet of the cell membrane was recently described. PS interacts with the extracellular part of ADAM17, which results in the shedding event by shifting the catalytic domain towards the membrane close to the cleavage sites within ADAM17 substrates. Our data indicate that the intrinsic proteolytic activity of the catalytic domain is prerequisite for the shedding activity and constantly present. However, the accessibility for substrate cleavage sites is controlled on several levels. In this report, we demonstrate that the positioning of the catalytic domain towards the cleavage sites is a crucial part of the shedding process. This finding contributes to the understanding of the complex and multilayered regulation of ADAM17 at the cell surface.

Status update on iRhom and ADAM17: It's still complicated.

Several membrane-bound proteins with a single transmembrane domain are subjected to limited proteolysis at the cell surface. This cleavage leads to the release of their biologically active ectodomains, which can trigger different signalling pathways. In many cases, this ectodomain shedding is mediated by members of the family of a disintegrins and metalloproteinases (ADAMs). ADAM17 in particular is responsible for the cleavage of several proinflammatory mediators, growth factors, receptors and adhesion molecules. Due to its direct involvement in the release of these signalling molecules, ADAM17 can be positively and negatively involved in various physiological processes as well as in inflammatory, fibrotic and malignant pathologies. This central role of ADAM17 in a variety of processes requires strict multi-level regulation, including phosphorylation, various conformational changes and endogenous inhibitors. Recent research has shown that an early, crucial control mechanism is interaction with certain adapter proteins identified as iRhom1 and iRhom2, which are pseudoproteases of the rhomboid superfamily. Thus, iRhoms have also a decisive influence on physiological and pathophysiological signalling processes regulated by ADAM17. Their characteristic gene expression profiles, the specific consequences of gene knockouts and finally the occurrence of disease-associated mutations suggest that iRhom1 and iRhom2 undergo different gene regulation in order to fulfil their function in different cell types and are therefore only partially redundant. Therefore, there is not only interest in ADAM17, but also in iRhoms as therapeutic targets. However, to exploit the therapeutic potential, the regulation of ADAM17 activity and in particular its interaction with iRhoms must be well understood.

The metalloprotease ADAM17 in inflammation and cancer.

Proteolytic cleavage of transmembrane proteins is an important post-translational modification that regulates the biological function of numerous transmembrane proteins. Among the 560 proteases encoded in the human genome, the metalloprotease A Disintegrin and Metalloprotease 17 (ADAM17) has gained much attention in recent years and has emerged as a central regulatory hub in inflammation, immunity and cancer development. In order to do so, ADAM17 cleaves a variety of substrates, among them the interleukin-6 receptor (IL-6R), the pro-inflammatory cytokine tumor necrosis factor α (TNFα) and most ligands of the epidermal growth factor receptor (EGFR). This review article provides an overview of the functions of ADAM17 with a special focus on its cellular regulation. It highlights the importance of ADAM17 to understand the biology of IL-6 and TNFα and their role in inflammatory diseases. Finally, the role of ADAM17 in the formation and progression of different tumor entities is discussed.