TACE activation by MAPK-mediated regulation of cell surface dimerization and TIMP3 association

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

Natural Killer Cells Reprogram Myeloid-Derived Suppressor Cells to Induce TNF-α Release via NKG2D-Ligand Interaction after Cryo-Thermal Therapy

In our previous studies, a novel cryothermal therapy (CTT) was developed to induce systemic long-term anti-tumor immunity. Natural killer (NK) cells were found to play an important role in CTT-induced long-term immune-mediated tumor control at the late stage after CTT, but the underlying mechanism is unclear. Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that have potent immunosuppressive effects on T cells and weaken the long-term benefits of immunotherapy. Consequently, overcoming MDSC immunosuppression is essential for maintaining the long-term efficacy of immunotherapy. In this study, we revealed that NK cells considerably diminish MDSC accumulation at the late stage after CTT, boost T cell production, increase T cell activation, and promote MDSC maturation, culminating in Th1-dominant CD4+ T cell differentiation and enhancing NK and CD8+ T cell cytotoxicity. Additionally, NK cells activate ERK signaling in MDSCs through NKG2D-ligand interaction to increase the activity of tumor necrosis factor (TNF)-α converting enzyme (TACE)-cleaved membrane TNF-α. Furthermore, Increased TACE activity releases more soluble TNF-α from MDSCs to promote MDSC maturation. In our studies, we propose a novel mechanism by which NK cells can overcome MDSC-induced immunosuppression and maintain CTT-induced persistent anti-tumor immunity, providing a prospective therapeutic option to improve the performance of cancer immunotherapy.

The protease ADAM17 at the crossroads of disease: revisiting its significance in inflammation, cancer, and beyond

The protease A Disintegrin And Metalloproteinase 17 (ADAM17) plays a central role in the pathophysiology of several diseases. ADAM17 is involved in the cleavage and shedding of at least 80 known membrane-tethered proteins, which subsequently modulate several intracellular signaling pathways, and therefore alter cell behavior. Dysregulated expression and/or activation of ADAM17 has been linked to a wide range of autoimmune and inflammatory diseases, cancer, and cardiovascular disease. In this review, we provide an overview of the current state of knowledge from preclinical models and clinical data on the diverse pathophysiological roles of ADAM17, and discuss the mechanisms underlying ADAM17-mediated protein shedding and the potential therapeutic implications of targeting ADAM17 in these diseases.

ADAM10-a "multitasker" in sepsis: focus on its posttranslational target

BACKGROUND

Sepsis has a complex pathogenesis in which the uncontrolled systemic inflammatory response triggered by infection leads to vascular barrier disruption, microcirculation dysfunction and multiple organ dysfunction syndrome. Numerous recent studies reveal that a disintegrin and metalloproteinase 10 (ADAM10) acts as a "molecular scissor" playing a pivotal role in the inflammatory response during sepsis by regulating proteolysis by cleaving various membrane protein substrates, including proinflammatory cytokines, cadherins and Notch, which are involved in intercellular communication. ADAM10 can also act as the cellular receptor for Staphylococcus aureus α-toxin, leading to lethal sepsis. However, its substrate-specific modulation and precise targets in sepsis have not yet to be elucidated.

METHODS

We performed a computer-based online search using PubMed and Google Scholar for published articles concerning ADAM10 and sepsis.

CONCLUSIONS

In this review, we focus on the functions of ADAM10 in sepsis-related complex endothelium-immune cell interactions and microcirculation dysfunction through the diversity of its substrates and its enzymatic activity. In addition, we highlight the posttranslational mechanisms of ADAM10 at specific subcellular sites, or in multimolecular complexes, which will provide the insight to intervene in the pathophysiological process of sepsis caused by ADAM10 dysregulation.

Periostin derived from cancer-associated fibroblasts promotes esophageal squamous cell carcinoma progression via ADAM17 activation

Periostin (POSTN) is a matricellular protein that was originally identified in osteoblasts. Past studies have shown that POSTN is also preferentially expressed in cancer-associated fibroblasts (CAFs) in various types of cancer. We previously demonstrated that the increased expression of POSTN in stromal tissues is associated with an unfavorable clinical outcome in esophageal squamous cell carcinoma (ESCC) patients. In this study, we aimed to elucidate the role of POSNT in ESCC progression and its underlying molecular mechanism. We found that POSTN is predominantly produced by CAFs in ESCC tissues, and that CAFs-cultured media significantly promoted the migration, invasion, proliferation, and colony formation of ESCC cell lines in a POSTN-dependent manner. In ESCC cells, POSTN increased the phosphorylation of ERK1/2 and stimulated the expression and activity of a disintegrin and metalloproteinase 17 (ADAM17), which is critically involved in tumorigenesis and tumor progression. The effects of POSTN on ESCC cells were suppressed by interfering with the binding of POSTN to integrin αvβ3 or αvβ5 using neutralizing antibody against POSTN. Taken together, our data show that CAFs-derived POSTN stimulates ADAM17 activity through activation of the integrin αvβ3 or αvβ5-ERK1/2 pathway and thereby contributes to the progression of ESCC.

Cardiomyocyte cohesion is increased after ADAM17 inhibition

A Disintegrin And Metalloprotease (ADAM) family proteins are involved in several cardiac diseases, and some ADAMs have been associated with cardiomyopathies. ADAM17 is known to cleave desmoglein 2 (DSG2), one of the proteins involved in the pathogenesis of arrhythmogenic cardiomyopathy (AC). Desmosomal stability is impaired in AC, an inheritable genetic disease, the underlying causes of which can be mutations in genes coding for proteins of the desmosome, such as DSG2, desmoplakin (DP), plakoglobin (PG), plakophilin 2 or desmocollin 2. Stabilizing desmosomal contacts can therefore be a treatment option. In the heart of the murine Jup -/- AC model, (Jup being the gene coding for PG) mice, elevated levels of p38MAPK, an activator of ADAM17, were found. However, ADAM17 levels were unaltered in Jup -/- mice hearts. Nonetheless, inhibition of ADAM17 led to enhanced cardiomyocyte cohesion in both Jup +/+ and Jup -/- mice, and in HL-1 cardiomyocytes. Further, enhanced cohesion in HL-1 cardiomyocytes after acute inhibition of ADAM17 was paralleled by enhanced localization of DSG2 and DP at the membrane, whereas no changes in desmosomal assembly or the desmosomal complex were observed. In conclusion, acute inhibition of ADAM17 might lead to reduced cleavage of DSG2, thereby stabilizing the desmosomal adhesion, evidenced by increased DSG2 and DP localization at cell borders and eventually cardiomyocyte cohesion. We believe that similar mechanisms exist in AC.

A Bioengineering Strategy to Control ADAM10 Activity in Living Cells

A Disintegrin and Metalloprotease 10, also known as ADAM10, is a cell surface protease ubiquitously expressed in mammalian cells where it cuts several membrane proteins implicated in multiple physiological processes. The dysregulation of ADAM10 expression and function has been implicated in pathological conditions, including Alzheimer's disease (AD). Although it has been suggested that ADAM10 is expressed as a zymogen and the removal of the prodomain results in its activation, other potential mechanisms for the ADAM10 proteolytic function and activation remain unclear. Another suggested mechanism is post-translational modification of the cytoplasmic domain, which regulates ADAM10-dependent protein ectodomain shedding. Therefore, the precise and temporal activation of ADAM10 is highly desirable to reveal the fine details of ADAM10-mediated cleavage mechanisms and protease-dependent therapeutic applications. Here, we present a strategy to control prodomain and cytosolic tail cleavage to regulate ADAM10 shedding activity without the intervention of small endogenous molecule signaling pathways. We generated a series of engineered ADAM10 analogs containing Tobacco Etch Virus protease (TEV) cleavage site (TEVcs), rendering ADAM10 cleavable by TEV. This strategy revealed that, in the absence of other stimuli, the TEV-mediated removal of the prodomain could not activate ADAM10. However, the TEV-mediated cleavage of the cytosolic domain significantly increased ADAM10 activity. Then, we generated ADAM10 with a minimal constitutively catalytic activity that increased significantly in the presence of TEV or after activating a chemically activatable TEV. Our results revealed a bioengineering strategy for controlling the ADAM10 activity in living cells, paving the way to obtain spatiotemporal control of ADAM10. Finally, we proved that our approach of controlling ADAM10 promoted α-secretase activity and the non-amyloidogenic cleavage of amyloid-β precursor protein (APP), thereby increasing the production of the neuroprotective soluble ectodomain (sAPPα). Our bioengineering strategy has the potential to be exploited as a next-generation gene therapy for AD.

ADAM17 cleaves the insulin receptor ectodomain on endothelial cells and causes vascular insulin resistance

Inflammation and vascular insulin resistance are hallmarks of type 2 diabetes (T2D). However, several potential mechanisms causing abnormal endothelial insulin signaling in T2D need further investigation. Evidence indicates that the activity of ADAM17 (a disintegrin and metalloproteinase-17) and the presence of insulin receptor (IR) in plasma are increased in subjects with T2D. Accordingly, we hypothesized that in T2D, increased ADAM17 activity sheds the IR ectodomain from endothelial cells and impairs insulin-induced vasodilation. We used small visceral arteries isolated from a cross-sectional study of subjects with and without T2D undergoing bariatric surgery, human cultured endothelial cells, and recombinant proteins to test our hypothesis. Here, we demonstrate that arteries from subjects with T2D had increased ADAM17 expression, reduced presence of tissue inhibitor of metalloproteinase-3 (TIMP3), decreased extracellular IRα, and impaired insulin-induced vasodilation versus those from subjects without T2D. In vitro, active ADAM17 cleaved the ectodomain of the IRβ subunit. Endothelial cells with ADAM17 overexpression or exposed to the protein kinase-C activator, PMA, had increased ADAM17 activity, decreased IRα presence on the cell surface, and increased IR shedding. Moreover, pharmacological inhibition of ADAM17 with TAPI-0 rescued PMA-induced IR shedding and insulin-signaling impairments in endothelial cells and insulin-stimulated vasodilation in human arteries. In aggregate, our findings suggest that ADAM17-mediated shedding of IR from the endothelial surface impairs insulin-mediated vasodilation. Thus, we propose that inhibition of ADAM17 sheddase activity should be considered a strategy to restore vascular insulin sensitivity in T2D.NEW & NOTEWORTHY To our knowledge, this is the first study to investigate the involvement of ADAM17 in causing impaired insulin-induced vasodilation in T2D. We provide evidence that ADAM17 activity is increased in the vasculature of patients with T2D and support the notion that ADAM17-mediated shedding of endothelial IRα ectodomains is a novel mechanism causing vascular insulin resistance. Our results highlight that targeting ADAM17 activity may be a potential therapeutic strategy to correct vascular insulin resistance in T2D.

Matrix Metalloproteinases: From Molecular Mechanisms to Physiology, Pathophysiology, and Pharmacology

The first matrix metalloproteinase (MMP) was discovered in 1962 from the tail of a tadpole by its ability to degrade collagen. As their name suggests, matrix metalloproteinases are proteases capable of remodeling the extracellular matrix. More recently, MMPs have been demonstrated to play numerous additional biologic roles in cell signaling, immune regulation, and transcriptional control, all of which are unrelated to the degradation of the extracellular matrix. In this review, we will present milestones and major discoveries of MMP research, including various clinical trials for the use of MMP inhibitors. We will discuss the reasons behind the failures of most MMP inhibitors for the treatment of cancer and inflammatory diseases. There are still misconceptions about the pathophysiological roles of MMPs and the best strategies to inhibit their detrimental functions. This review aims to discuss MMPs in preclinical models and human pathologies. We will discuss new biochemical tools to track their proteolytic activity in vivo and ex vivo, in addition to future pharmacological alternatives to inhibit their detrimental functions in diseases. SIGNIFICANCE STATEMENT: Matrix metalloproteinases (MMPs) have been implicated in most inflammatory, autoimmune, cancers, and pathogen-mediated diseases. Initially overlooked, MMP contributions can be both beneficial and detrimental in disease progression and resolution. Thousands of MMP substrates have been suggested, and a few hundred have been validated. After more than 60 years of MMP research, there remain intriguing enigmas to solve regarding their biological functions in diseases.

Attenuation of Excess TNF-α Release in Crohn’s Disease by Silencing of iRHOMs 1/2 and the Restoration of TGF-β Mediated Immunosuppression Through Modulation of TACE Trafficking

TNFα converting enzyme (TACE) is a transmembrane metalloprotease that sheds an assortment of signaling receptors, cytokines, growth factors, and pro-inflammatory mediators. In Crohn’s disease (CD), TACE activity is upregulated, resulting in a marked increase of TNFα secretion and inflammation. Although treatment of CD with TNFα monoclonal antibodies is beneficial, many patients are at risk for acquiring opportunistic infections, and the treatment efficacy of TNFα monoclonal antibodies typically decreases over time. This study investigated an alternative approach for mitigating TNFα release by knocking down TACE membrane translocation in macrophages via inhibitory rhomboid proteins 1 and 2 (iRHOMs 1/2) siRNA treatment. First we measured TGFβRII shedding in ex vivo plasma samples collected from CD patients and healthy control subjects (N=40 per group). Then, we measured TGFβRII shedding and the expression and production of TGFβ ligand, TNFα, IL-6, IL-1β, IL-10, and total versus membranous TACE in vitro with THP-1 derived macrophage infected with Mycobacterium avium subspecies paratuberculosis (MAP), a highly studied CD-related pathogen. We determined that TGFβRII shedding was significantly higher in CD patients compared to healthy controls [515.52 ± 54.23 pg/mL vs 310.81 ± 43.16 pg/mL, respectively], and MAP-infected CD plasma samples had significantly more TGFβRII shedding (601.83 ± 49.56 pg/mL) than MAP-negative CD samples (430.37 ± 45.73 pg/mL). Moreover, we also determined that TACE production; TGFβ ligand expression and production; and TGFβRII shedding were also higher in MAP-infected THP-1 macrophages. Nevertheless, once we transfected the MAP infected macrophages with iRHOM siRNA, TACE production and membrane localization were significantly decreased, resulting in a significant decrease in TGFβRII shedding; an increase in Smad3 phosphorylation; a decrease in the expression and production of pro-inflammatory cytokines; and a decrease in the expression and production of stricture-associated factor, plasminogen activator inhibitor-1 (PAI-1). Our data clearly demonstrates that the regression of TACE trafficking, via iRHOM 1/2 silencing, significantly reduces the release of TNFα and restores the immunosuppressive capabilities of TGFβ signaling, which ultimately reverses inflammatory tissue damage. Accordingly, this study may provide a framework for the creation of newer, safer therapeutic options designed to treat inflammatory autoimmune diseases such as CD and rheumatoid arthritis.

Evaluating the Causal Effects of TIMP-3 on Ischaemic Stroke and Intracerebral Haemorrhage: A Mendelian Randomization Study

Aim: Since tissue inhibitors of matrix metalloproteinase 3 (TIMP-3) was reported to be a potential risk factor of atherosclerosis, aneurysm, hypertension, and post-ischaemic neuronal injury, it may also be a candidate risk factor of stress. Therefore, this study was designed to explore the causal role of TIMP-3 in the risk of ischaemic stroke (IS) and intracerebral haemorrhage (ICH), which are the two main causes of stress via this Mendelian Randomisation (MR) study. Methods: The summarised data of TIMP-3 level in circulation was acquired from the Cooperative Health Research in the Region of Augsburg public database and the outcome of IS and ICH was obtained from genome-wide association studies conducted by MEGASTROKE and the International Stroke Genetics Consortium, respectively. Five statistical methods including inverse-variance weighting, weighted-median analysis, MR-Egger regression, MR Pleiotropy RESidual Sum and Outlier test, and MR-Robust Adjusted Profile Score were applied to evaluate the causal role of TIMP-3 in the occurrence of IS and ICH. Inverse-variance weighting was applied for assessing causality. Furthermore, heterogeneity and pleiotropic tests were utilised to confirm the reliability of this study. Results: We found that TIMP-3 could be a positively causal relationship with the incidence of IS (OR = 1.026, 95% CI: 1.007-1.046, p = 0.0067), especially for the occurrence of small vessel stroke (SVS; OR = 1.045, 95% CI: 1.016-1.076, p = 0.0024). However, the causal effects of TIMP-3 on another IS subtype cardioembolic stroke (CES; OR = 1.049, 95% CI: 1.006-1.094, p = 0.024), large artery stroke (LAS; OR = 1.0027, 95% CI: 0.9755-1.0306, p = 0.849) and ICH (OR = 0.9900, 95% CI: 0.9403-1.0423, p = 0.701), as well as ICH subtypes were not observed after Bonferroni corrections (p = 0.00714). Conclusion: Our results revealed that high levels of circulating TIMP-3 causally increased the risk of developing IS and SVS, but not CES, LAS, ICH, and all ICH subtypes. Further investigation is required to elucidate the underlying mechanism.

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.

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.

ADAM17, A Key Player of Cardiac Inflammation and Fibrosis in Heart Failure Development During Chronic Catecholamine Stress

Heart failure development is characterized by persistent inflammation and progressive fibrosis owing to chronic catecholamine stress. In a chronic stress state, elevated catecholamines result in the overstimulation of beta-adrenergic receptors (βARs), specifically β2-AR coupling with Gαi protein. Gαi signaling increases the activation of receptor-stimulated p38 mitogen-activated-protein-kinases (p38 MAPKs) and extracellular signal-regulated kinases (ERKs). Phosphorylation by these kinases is a common way to positively regulate the catalytic activity of A Disintegrin and Metalloprotease 17 (ADAM17), a metalloprotease that has grown much attention in recent years and has emerged as a chief regulatory hub in inflammation, fibrosis, and immunity due to its vital proteolytic activity. ADAM17 cleaves and activates proinflammatory cytokines and fibrotic factors that enhance cardiac dysfunction via inflammation and fibrosis. However, there is limited information on the cardiovascular aspect of ADAM17, especially in heart failure. Hence, this concise review provides a comprehensive insight into the structure of ADAM17, how it is activated and regulated during chronic catecholamine stress in heart failure development. This review highlights the inflammatory and fibrotic roles of ADAM17’s substrates; Tumor Necrosis Factor α (TNFα), soluble interleukin-6 receptor (sIL-6R), and amphiregulin (AREG). Finally, how ADAM17-induced chronic inflammation and progressive fibrosis aggravate cardiac dysfunction is discussed.

ADAM17 Mediates Hypoxia-Induced Keratinocyte Migration via the p38/MAPK Pathway

Although hypoxia has been shown to promote keratinocyte migration and reepithelialization, the underlying molecular mechanisms remain largely unknown. ADAM17, a member of the metalloproteinase superfamily, has been implicated in a variety of cellular behaviors such as proliferation, adhesion, and migration. ADAM17 is known to promote cancer cell migration under hypoxia, and whether or how ADAM17 plays a role in hypoxia-induced keratinocyte migration has not been identified. Here, we found that ADAM17 expression and activity were significantly promoted in keratinocytes under hypoxic condition, inhibition of ADAM17 by TAPI-2, or silencing of ADAM17 using small interfering RNA which suppressed the hypoxia-induced migration of keratinocytes significantly, indicating a pivotal role for ADAM17 in keratinocyte migration. Further, we showed that p38/MAPK was activated by hypoxia. SB203580, an inhibitor of p38/MAPK, significantly attenuated the upregulation of ADAM17 as well as the migration of keratinocytes induced by hypoxia. Activation of p38/MAPK by MKK6 (Glu) overexpression, however, had adverse effects. Taken together, our study demonstrated that hypoxia-induced keratinocyte migration requires the p38/MAPK-ADAM17 signal axis, which sheds new light on the regulatory mechanisms of keratinocyte migration. Our study might also help in developing therapeutic strategies to facilitate wound healing in vivo, where cells are migrated in a hypoxic microenvironment.

Molecular switch in human diseases-disintegrin and metalloproteinases, ADAM17

The ADAMs (a disintegrin and metalloproteinase) are a family of cell surface proteins with crucial roles in the regulation of cell adhesion, cell proliferation to migration, proteolysis and cell signaling transduction pathways. Among these enzymes, the ADAM17 shows significant effects in the “ectodomain shedding” of its substrates such as cytokines (e.g., tumor necrosis factor α, TNFα), growth factors (e.g., epidermal growth factor, EGF), adhesion proteins (e.g., L-selectin), and their receptors (e.g., IL-6R and TNFα). Several studies focus on the underlying molecular mechanisms of ADAM17 in diseased conditions. Here, we took several different approaches to elucidate the function of ADAM17, the participation of ADAM17 in several human diseases, and the potential as targeted therapy reagents. As more and more studies verify the miRNA-mediated expression variation of ADAM17, the specific regulation network of miRNAs and ADAM17 was exploited in this review as well.

The Synergy of ADAM17-Induced Myocardial Inflammation and Metabolic Lipids Dysregulation During Acute Stress: New Pathophysiologic Insights Into Takotsubo Cardiomyopathy

Due to its reversible nature, Takotsubo cardiomyopathy (TTC) is considered an intriguing and fascinating cardiovascular disease characterized by a transient wall motion abnormality of the left ventricle, affecting more than one coronary artery territory, often in a circumferential apical distribution. Takotsubo cardiomyopathy was discovered by a Japanese cardiovascular expert and classified as acquired primary cardiomyopathy by the American Heart Association (AHA) in 1990 and 2006, respectively. Regardless of the extensive research efforts, its pathophysiology is still unclear; therefore, there are no well-established guidelines specifically for treating and managing TTC patients. Increasing evidence suggests that sympatho-adrenergic stimulation is strongly associated with the pathogenesis of this disease. Under acute stressful conditions, the hyperstimulation of beta-adrenergic receptors (β-ARs) resulting from excessive release of catecholamines induces intracellular kinases capable of phosphorylating and activating “A Disintegrin and Metalloprotease 17” (ADAM17), a type-I transmembrane protease that plays a central role in acute myocardial inflammation and metabolic lipids dysregulation which are the main hallmarks of TTC. However, our understanding of this is limited; hence this concise review provides a comprehensive insight into the key role of ADAM17 in acute myocardial inflammation and metabolic lipids dysregulation during acute stress. Also, how the synergy of ADAM17-induced acute inflammation and lipids dysregulation causes TTC is explained. Finally, potential therapeutic targets for TTC are also discussed.

ADAM10 Site-Dependent Biology: Keeping Control of a Pervasive Protease

Enzymes, once considered static molecular machines acting in defined spatial patterns and sites of action, move to different intra- and extracellular locations, changing their function. This topological regulation revealed a close cross-talk between proteases and signaling events involving post-translational modifications, membrane tyrosine kinase receptors and G-protein coupled receptors, motor proteins shuttling cargos in intracellular vesicles, and small-molecule messengers. Here, we highlight recent advances in our knowledge of regulation and function of A Disintegrin And Metalloproteinase (ADAM) endopeptidases at specific subcellular sites, or in multimolecular complexes, with a special focus on ADAM10, and tumor necrosis factor-α convertase (TACE/ADAM17), since these two enzymes belong to the same family, share selected substrates and bioactivity. We will discuss some examples of ADAM10 activity modulated by changing partners and subcellular compartmentalization, with the underlying hypothesis that restraining protease activity by spatial segregation is a complex and powerful regulatory tool.

Targeted truncation of the ADAM17 cytoplasmic domain in mice results in protein destabilization and a hypomorphic phenotype

A disintegrin and metalloprotease 17 (ADAM17) is a cell-surface metalloprotease that serves as the principle sheddase for tumor necrosis factor α (TNFα), interleukin-6 receptor (IL-6R), and several ligands of the epidermal growth factor receptor (EGFR), regulating these crucial signaling pathways. ADAM17 activation requires its transmembrane domain, but not its cytoplasmic domain, and little is known about the role of this domain in vivo. To investigate, we used CRISPR-Cas9 to mutate the endogenous Adam17 locus in mice to produce a mutant ADAM17 lacking its cytoplasmic domain (Adam17Δcyto). Homozygous Adam17Δcyto animals were born at a Mendelian ratio and survived into adulthood with slightly wavy hair and curled whiskers, consistent with defects in ADAM17/EGFR signaling. At birth, Adam17Δcyto mice resembled Adam17−/− mice in that they had open eyes and enlarged semilunar heart valves, but they did not have bone growth plate defects. The deletion of the cytoplasmic domain resulted in strongly decreased ADAM17 protein levels in all tissues and cells examined, providing a likely cause for the hypomorphic phenotype. In functional assays, Adam17Δcyto mouse embryonic fibroblasts and bone-marrow-derived macrophages had strongly reduced ADAM17 activity, consistent with the reduced protein levels. Nevertheless, ADAM17Δcyto could be stimulated by PMA, a well-characterized posttranslational activator of ADAM17, corroborating that the cytoplasmic domain of endogenous ADAM17 is not required for its rapid response to PMA. Taken together, these results provide the first evidence that the cytoplasmic domain of ADAM17 plays a pivotal role in vivo in regulating ADAM17 levels and function.

Strategies to Target ADAM17 in Disease: From its Discovery to the iRhom Revolution

For decades, disintegrin and metalloproteinase 17 (ADAM17) has been the object of deep investigation. Since its discovery as the tumor necrosis factor convertase, it has been considered a major drug target, especially in the context of inflammatory diseases and cancer. Nevertheless, the development of drugs targeting ADAM17 has been harder than expected. This has generally been due to its multifunctionality, with over 80 different transmembrane proteins other than tumor necrosis factor α (TNF) being released by ADAM17, and its structural similarity to other metalloproteinases. This review provides an overview of the different roles of ADAM17 in disease and the effects of its ablation in a number of in vivo models of pathological conditions. Furthermore, here, we comprehensively encompass the approaches that have been developed to accomplish ADAM17 selective inhibition, from the newest non-zinc-binding ADAM17 synthetic inhibitors to the exploitation of iRhom2 to specifically target ADAM17 in immune cells.

ADAM17 Deficiency Protects against Pulmonary Emphysema

Pulmonary emphysema is the major debilitating component of chronic obstructive pulmonary disease (COPD), which is a leading cause of morbidity and mortality worldwide. The ADAM17 (A disintegrin and metalloproteinase 17) protease mediates inflammation via ectodomain shedding of numerous proinflammatory cytokines, cytokine receptors, and adhesion molecules; however, its role in the pathogenesis of emphysema and COPD is poorly understood. This study aims to define the role of the protease ADAM17 in the pathogenesis of pulmonary emphysema. ADAM17 protein expression and activation was investigated in lung biopsies from patients with emphysema, as well as lungs of the emphysematous gp130F/F mouse model and an acute (4 d) cigarette smoke (CS)-induced lung pathology model. The Adam17ex/ex mice, which display significantly reduced global ADAM17 expression, were coupled with emphysema-prone gp130F/F mice to produce gp130F/F:Adam17ex/ex. Both Adam17ex/ex and wild-type mice were subjected to acute CS exposure. Histological, immunohistochemical, immunofluorescence, and molecular analyses as well as lung function tests were performed to assess pulmonary emphysema, inflammation, and alveolar cell apoptosis. ADAM17 was hyperphosphorylated in the lungs of patients with emphysema and also in emphysematous gp130F/F and CS-exposed mice. ADAM17 deficiency ameliorated the development of pulmonary emphysema in gp130F/F mice by suppressing elevated alveolar cell apoptosis. In addition, genetic blockade of ADAM17 protected mice from CS-induced pulmonary inflammation and alveolar cell apoptosis. Our study places the protease ADAM17 as a central molecular switch implicated in the development of pulmonary emphysema, which paves the way for using ADAM17 inhibitors as potential therapeutic agents to treat COPD and emphysema.

Suppression of α-catenin and adherens junctions enhances epithelial cell proliferation and motility via TACE-mediated TGF-α autocrine/paracrine signaling

Sustained cell migration is essential for wound healing and cancer metastasis. The epidermal growth factor receptor (EGFR) signaling cascade is known to drive cell migration and proliferation. While the signal transduction downstream of EGFR has been extensively investigated, our knowledge of the initiation and maintenance of EGFR signaling during cell migration remains limited. The metalloprotease TACE (tumor necrosis factor alpha converting enzyme) is responsible for producing active EGFR family ligands in the via ligand shedding. Sustained TACE activity may perpetuate EGFR signaling and reduce a cell’s reliance on exogenous growth factors. Using a cultured keratinocyte model system, we show that depletion of α-catenin perturbs adherens junctions, enhances cell proliferation and motility, and decreases dependence on exogenous growth factors. We show that the underlying mechanism for these observed phenotypical changes depends on enhanced autocrine/paracrine release of the EGFR ligand transforming growth factor alpha in a TACE-dependent manner. We demonstrate that proliferating keratinocyte epithelial cell clusters display waves of oscillatory extracellular signal–regulated kinase (ERK) activity, which can be eliminated by TACE knockout, suggesting that these waves of oscillatory ERK activity depend on autocrine/paracrine signals produced by TACE. These results provide new insights into the regulatory role of adherens junctions in initiating and maintaining autocrine/paracrine signaling with relevance to wound healing and cellular transformation.

TGF-β Induced CTGF Expression in Human Lung Epithelial Cells through ERK, ADAM17, RSK1, and C/EBPβ Pathways

Background: Lung epithelial cells play critical roles in idiopathic pulmonary fibrosis. Methods: In the present study, we investigated whether transforming growth factor-β (TGF-β)-induced expression of connective tissue growth factor (CTGF) was regulated by the extracellular signal-regulated kinase (ERK)/a disintegrin and metalloproteinase 17 (ADAM17)/ribosomal S6 kinases 1 (RSK1)/CCAAT/enhancer-binding protein β (C/EBPβ) signaling pathway in human lung epithelial cells (A549). Results: Our results revealed that TGF-β-induced CTGF expression was weakened by ADAM17 small interfering RNA (ADAM17 siRNA), TNF-α processing inhibitor-0 (TAPI-0, an ADAM17 inhibitor), U0126 (an ERK inhibitor), RSK1 siRNA, and C/EBPβ siRNA. TGF-β-induced ERK phosphorylation as well as ADAM17 phosphorylation was attenuated by U0126. The TGF-β-induced increase in RSK1 phosphorylation was inhibited by TAPI-0 and U0126. TGF-β-induced C/EBPβ phosphorylation was weakened by U0126, ADAM17 siRNA, and RSK1 siRNA. In addition, TGF-β increased the recruitment of C/EBPβ to the CTGF promoter. Furthermore, TGF-β enhanced fibronectin (FN), an epithelial–mesenchymal transition (EMT) marker, and CTGF mRNA levels and reduced E-cadherin mRNA levels. Moreover, TGF-β-stimulated FN protein expression was reduced by ADAM17 siRNA and CTGF siRNA. Conclusion: The results suggested that TGF-β induces CTGF expression through the ERK/ADAM17/RSK1/C/EBPβ signaling pathway. Moreover, ADAM17 and CTGF participate in TGF-β-induced FN expression in human lung epithelial cells.

The ADAM17 protease promotes tobacco smoke carcinogen-induced lung tumorigenesis

Lung cancer is the leading cause of cancer-related mortality, with most cases attributed to tobacco smoking, in which nicotine-derived nitrosamine ketone (NNK) is the most potent lung carcinogen. The ADAM17 protease is responsible for the ectodomain shedding of many pro-tumorigenic cytokines, growth factors and receptors, and therefore is an attractive target in cancer. However, the role of ADAM17 in promoting tobacco smoke carcinogen-induced lung carcinogenesis is unknown. The hypomorphic Adam17ex/ex mice-characterized by reduced global ADAM17 expression-were backcrossed onto the NNK-sensitive pseudo-A/J background. CRISPR-driven and inhibitor-based (GW280264X, and ADAM17 prodomain) ADAM17 targeting was employed in the human lung adenocarcinoma cell lines A549 and NCI-H23. Human lung cancer biopsies were also used for analyses. The Adam17ex/ex mice displayed marked protection against NNK-induced lung adenocarcinoma. Specifically, the number and size of lung lesions in NNK-treated pseudo-A/J Adam17ex/ex mice were significantly reduced compared with wild-type littermate controls. This was associated with lower proliferative index throughout the lung epithelium. ADAM17 targeting in A549 and NCI-H23 cells led to reduced proliferative and colony-forming capacities. Notably, among select ADAM17 substrates, ADAM17 deficiency abrogated shedding of the soluble IL-6 receptor (sIL-6R), which coincided with the blockade of sIL-6R-mediated trans-signaling via ERK MAPK cascade. Furthermore, NNK upregulated phosphorylation of p38 MAPK, whose pharmacological inhibition suppressed ADAM17 threonine phosphorylation. Importantly, ADAM17 threonine phosphorylation was significantly upregulated in human lung adenocarcinoma with smoking history compared with their cancer-free controls. Our study identifies the ADAM17/sIL-6R/ERK MAPK axis as a candidate therapeutic strategy against tobacco smoke-associated lung carcinogenesis.

iRhom2: An Emerging Adaptor Regulating Immunity and Disease

The rhomboid family are evolutionary conserved intramembrane proteases. Their inactive members, iRhom in Drosophila melanogaster and iRhom1 and iRhom2 in mammals, lack the catalytic center and are hence labelled “inactive” rhomboid family members. In mammals, both iRhoms are involved in maturation and trafficking of the ubiquitous transmembrane protease a disintegrin and metalloprotease (ADAM) 17, which through cleaving many biologically active molecules has a critical role in tumor necrosis factor alpha (TNFα), epidermal growth factor receptor (EGFR), interleukin-6 (IL-6) and Notch signaling. Accordingly, with iRhom2 having a profound influence on ADAM17 activation and substrate specificity it regulates these signaling pathways. Moreover, iRhom2 has a role in the innate immune response to both RNA and DNA viruses and in regulation of keratin subtype expression in wound healing and cancer. Here we review the role of iRhom2 in immunity and disease, both dependent and independent of its 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.

The Role of TGFβ Signaling in Microglia Maturation and Activation

The pleiotropic cytokine transforming growth factor-beta 1 (TGFβ1) plays pivotal roles in different cell types, including immune cells such as T cells, monocytes/macrophages, and microglia. Microglia are essential during physiological and pathological events. Maturation of postnatal microglia, as well as the regulation of the complex functional repertoire of microglia, needs to be carefully orchestrated. However, an understanding of how mammalian microglia maturation and disease-associated microglia activation is regulated remains fragmentary. Here, we summarize recent observations made by employing transgenic approaches to silence microglial TGFβ signaling in mice. These revealed that TGFβ1 and TGFβ signaling are indispensable for microglia maturation, adult microglia homeostasis, and the control of microglia activation in central nervous system pathologies.

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.

Biology of Tissue Inhibitor of Metalloproteinase 3 (TIMP3), and Its Therapeutic Implications in Cardiovascular Pathology

Tissue inhibitor of metalloproteinase 3 (TIMP3) is unique among the four TIMPs due to its extracellular matrix (ECM)-binding property and broad range of inhibitory substrates that includes matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAM with thrombospondin motifs (ADAMTSs). In addition to its metalloproteinase-inhibitory function, TIMP3 can interact with proteins in the extracellular space resulting in its multifarious functions. TIMP3 mRNA has a long 3' untranslated region (UTR) which is a target for numerous microRNAs. TIMP3 levels are reduced in various cardiovascular diseases, and studies have shown that TIMP3 replenishment ameliorates the disease, suggesting a therapeutic potential for TIMP3 in cardiovascular diseases. While significant efforts have been made in identifying the effector targets of TIMP3, the regulatory mechanism for the expression of this multi-functional TIMP has been less explored. Here, we provide an overview of TIMP3 gene structure, transcriptional and post-transcriptional regulators (transcription factors and microRNAs), protein structure and partners, its role in cardiovascular pathology and its application as therapy, while also drawing reference from TIMP3 function in other diseases.

Sphingomyelinases D From Loxosceles Spider Venoms and Cell Membranes: Action on Lipid Rafts and Activation of Endogenous Metalloproteinases

Loxosceles spider venom contains Sphingomyelinase D (SMase D), the key toxin causing pathology. SMase D hydrolyzes the main component of lipid rafts, sphingomyelin, which changes the membrane microenvironment resulting in the activation of endogenous metalloproteinase from the ADAMs family. Alterations in membrane microenvironment of lipid rafts contribute to the activation of several cell surface molecules. Serine proteinases convertases acting on the pro-domain of membrane metalloproteinases, such as ADAMs, increase the cleavage and the release of proteins ectodomains and receptors located at the cell surface areas containing lipid rafts. We, therefore, investigated the interaction of SMases D with these membrane microdomains (lipid rafts) in human keratinocytes, to better understand the molecular mechanism of SMases D action, and identify the ADAM(s) responsible for the cleavage of cell surface molecules. Using specific inhibitors, we observed that ADAMs 10 and 17 are activated in the cell membrane after SMase D action. Furthermore, proproteins convertases, such as furin, are involved in the SMase D induced ADAMs activation. One of the signaling pathways that may be involved in the activation of these proteases is the MAPK pathway, since phosphorylation of ERK1/2 was observed in cells treated with SMase D. Confocal analysis showed a strong colocalization between SMase D and GM1 ganglioside present in rafts. Analysis of structural components of rafts, such as caveolin-1 and flotillin-1, showed that the action of SMase D on cell membranes leads to a reduction in caveolin-1, which is possibly degraded by toxin-induced superoxide production in cells. The action of the toxin also results in flotilin-1 increased detection in the cell membrane. These results indicate that SMases D from Loxosceles venoms alter membrane rafts structure, leading to the activation of membrane bound proteases, which may explain why the lipase action of this toxin can result in proteolytic cleavage of cell surface proteins, ultimately leading to pathology.

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.

TGF-β Signaling

Transforming growth factor-β (TGF-β) represents an evolutionarily conserved family of secreted polypeptide factors that regulate many aspects of physiological embryogenesis and adult tissue homeostasis. The TGF-β family members are also involved in pathophysiological mechanisms that underlie many diseases. Although the family comprises many factors, which exhibit cell type-specific and developmental stage-dependent biological actions, they all signal via conserved signaling pathways. The signaling mechanisms of the TGF-β family are controlled at the extracellular level, where ligand secretion, deposition to the extracellular matrix and activation prior to signaling play important roles. At the plasma membrane level, TGF-βs associate with receptor kinases that mediate phosphorylation-dependent signaling to downstream mediators, mainly the SMAD proteins, and mediate oligomerization-dependent signaling to ubiquitin ligases and intracellular protein kinases. The interplay between SMADs and other signaling proteins mediate regulatory signals that control expression of target genes, RNA processing at multiple levels, mRNA translation and nuclear or cytoplasmic protein regulation. This article emphasizes signaling mechanisms and the importance of biochemical control in executing biological functions by the prototype member of the family, TGF-β.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Substrate-selective protein ectodomain shedding by ADAM17 and iRhom2 depends on their juxtamembrane and transmembrane domains

The metalloprotease ADAM17 (a disintegrin and metalloprotease 17) regulates EGF-receptor and TNFα signaling, thereby not only protecting the skin and intestinal barrier, but also contributing to autoimmunity. ADAM17 can be rapidly activated by many stimuli through its transmembrane domain (TMD), with the seven membrane-spanning inactive Rhomboids (iRhom) 1 and 2 implicated as candidate regulatory partners. However, several alternative models of ADAM17 regulation exist that do not involve the iRhoms, such as regulation through disulfide bond exchange or through interaction with charged phospholipids. Here, we report that a non-activatable mutant of ADAM17 with the TMD of betacellulin (BTC) can be rescued by restoring residues from the ADAM17 TMD, but only in Adam17^-/- cells, which contain iRhoms, not in iRhom1/2^-/- cells. We also provide the first evidence that the extracellular juxtamembrane domains (JMDs) of ADAM17 and iRhom2 regulate the stimulation and substrate selectivity of ADAM17. Interestingly, a point mutation in the ADAM17 JMD identified in a patient with Tetralogy of Fallot, a serious heart valve defect, affects the substrate selectivity of ADAM17 toward Heparin-binding epidermal growth factor like growth factor (HB-EGF), a crucial regulator of heart valve development in mice. These findings provide new insights into the regulation of ADAM17 through an essential interaction with the TMD1 and JMD1 of iRhom2.

Macrophage MerTK Promotes Liver Fibrosis in Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is emerging as a leading cause of chronic liver disease. However, therapeutic options are limited by incomplete understanding of the mechanisms of NASH fibrosis, which is mediated by activation of hepatic stellate cells (HSCs). In humans, human genetic studies have shown that hypomorphic variations in MERTK, encoding the macrophage c-mer tyrosine kinase (MerTK) receptor, provide protection against liver fibrosis, but the mechanisms remain unknown. We now show that holo- or myeloid-specific Mertk targeting in NASH mice decreases liver fibrosis, congruent with the human genetic data. Furthermore, ADAM metallopeptidase domain 17 (ADAM17)-mediated MerTK cleavage in liver macrophages decreases during steatosis to NASH transition, and mice with a cleavage-resistant MerTK mutant have increased NASH fibrosis. Macrophage MerTK promotes an ERK-TGFβ1 pathway that activates HSCs and induces liver fibrosis. These data provide insights into the role of liver macrophages in NASH fibrosis and provide a plausible mechanism underlying MERTK as a genetic risk factor for NASH fibrosis.

Regulation of Fibrotic Processes in the Liver by ADAM Proteases

Fibrosis in the liver is mainly associated with the activation of hepatic stellate cells (HSCs). Both activation and clearance of HSCs can be mediated by ligand–receptor interactions. Members of the a disintegrin and metalloprotease (ADAM) family are involved in the proteolytic release of membrane-bound ligands and receptor ectodomains and the remodelling of the extracellular matrix. ADAM proteases are therefore major regulators of intercellular signalling pathways. In the present review we discuss how ADAM proteases modulate pro- and anti-fibrotic processes and how ADAM proteases might be harnessed therapeutically in the future.

ADAM17: An Emerging Therapeutic Target for Lung Cancer

Lung cancer is the leading cause of cancer-related mortality, which histologically is classified into small-cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). NSCLC accounts for approximately 85% of all lung cancer diagnoses, with the majority of patients presenting with lung adenocarcinoma (LAC). KRAS mutations are a major driver of LAC, and are closely related to cigarette smoking, unlike mutations in the epidermal growth factor receptor (EGFR) which arise in never-smokers. Although the past two decades have seen fundamental progress in the treatment and diagnosis of NSCLC, NSCLC still is predominantly diagnosed at an advanced stage when therapeutic interventions are mostly palliative. A disintegrin and metalloproteinase 17 (ADAM17), also known as tumour necrosis factor-α (TNFα)-converting enzyme (TACE), is responsible for the protease-driven shedding of more than 70 membrane-tethered cytokines, growth factors and cell surface receptors. Among these, the soluble interleukin-6 receptor (sIL-6R), which drives pro-inflammatory and pro-tumourigenic IL-6 trans-signaling, along with several EGFR family ligands, are the best characterised. This large repertoire of substrates processed by ADAM17 places it as a pivotal orchestrator of a myriad of physiological and pathological processes associated with the initiation and/or progression of cancer, such as cell proliferation, survival, regeneration, differentiation and inflammation. In this review, we discuss recent research implicating ADAM17 as a key player in the development of LAC, and highlight the potential of ADAM17 inhibition as a promising therapeutic strategy to tackle this deadly malignancy.

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.

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.

Activation of Toll-like Receptor 2 (TLR2) induces Interleukin-6 trans-signaling

Signaling of the pleiotropic cytokine Interleukin-6 (IL-6) via its soluble IL-6R (sIL-6R) has been termed trans-signaling and is thought to be responsible for the pro-inflammatory properties of IL-6. The sIL-6R can be generated by alternative mRNA splicing or proteolytic cleavage of the membrane-bound IL-6R. However, which stimuli induce sIL-6R release and which endogenous signaling pathways are required for this process is poorly understood. Here, we show that activation of Toll-like receptor 2 (TLR2) on primary human peripheral blood mononuclear cells (PBMCs) and on the monocytic cell line THP-1 induces expression and secretion of IL-6 and the generation of sIL-6R. We show by flow cytometry that monocytes are a PBMC subset that expresses TLR2 in conjunction with the IL-6R and are the major cellular source for both IL-6 and sIL-6R. Mechanistically, we find that the metalloproteases ADAM10 and ADAM17 are responsible for cleavage of the IL-6R and therefore sIL-6R generation. Finally, we identify the Extracellular-signal Regulated Kinase (ERK) cascade as a critical pathway that differentially regulates both IL-6 and sIL-6R generation in monocytes.

Potential role of a disintegrin and metalloproteinase-17 (ADAM17) in age-associated ventricular remodeling of rats

Excessive tumor necrosis factor-α (TNF-α) could enhance cell death and aggravate left ventricular remodeling and myocardial dysfunction. A disintegrin and metalloproteinase-17 (ADAM17), an important maturation regulator of TNF-α, might be involved in the aging-associated ventricular remodeling. The present study observed myocardial ADAM17 expression in young and aged rats and explored the association between cardiac structure/function and expression of ADAM17 in 6 month-old (n = 10, young group) and 24 month-old SD rats (n = 10, old group). The body, heart weight and heart weight/body weight ratio of rats in the old group were all significantly increased compared to that in the young group (P < 0.05). The left ventricular systolic end-diameter and end-diastolic diameters were significantly enlarged in the old group compared to the young group (P < 0.05), while the systolic function index including the left ventricular ejection fraction and left ventricular fractional shortening were similar between the two groups. The peak mitral flow velocity (E)/peak mitral annulus velocity (E') ratio was significantly higher in the old group than in the young group (P < 0.05). Histological examination showed more damage of cardiomyocytes, interstitial collagen deposition and inflammatory cell infiltration in the old group. Immunohistochemistry examination showed that myocardial TNF-α expression was mainly located in cardiomyocytes and was significantly higher in the old group than in the young group (P < 0.05). The protein expression of myocardial ADAM17 detected by western blot was significantly higher in the old group than in the young group (P < 0.05), while TIMP-3 expression was similar between the two groups. The present study suggested that ADAM17 and inflammation might play an important role in aging-related myocardial remodeling through regulating TNF-α.

Functional Characterization of Colon Cancer-Associated Mutations in ADAM17: Modifications in the Pro-Domain Interfere with Trafficking and Maturation

Colorectal cancer is one of the most commonly diagnosed malignancies in the Western world and is associated with elevated expression and activity of epidermal growth factor receptors (EGF-R). The metalloproteinase ADAM17 is involved in EGF-R activation by processing EGF-R ligands from membrane-bound pro-ligands. Underlining the link between colon cancer and ADAM17, genetic intestinal cancer models in ADAM17-deficient mice show a reduced tumor burden. In this study, we characterize point mutations within the ADAM17 gene found in the tissue of colon cancer patients. In order to shed light on the role of ADAM17 in cancer development, as well as into the mechanisms that regulate maturation and cellular trafficking of ADAM17, we here perform overexpression studies of four ADAM17 variants located in the pro-, membrane-proximal- and cytoplasmic-domain of the ADAM17 protein in ADAM10/17-deficient HEK cells. Interestingly, we found a cancer-associated point mutation within the pro-domain of ADAM17 (R177C) to be most impaired in its proteolytic activity and trafficking to the cell membrane. By comparing this variant to an ADAM17 construct lacking the entire pro-domain, we discovered similar functional limitations and propose a crucial role of the pro-domain for ADAM17 maturation, cellular trafficking and thus proteolytic activity.

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.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

LRP1 Controls TNF Release via the TIMP-3/ADAM17 Axis in Endotoxin-Activated Macrophages

The metalloproteinase ADAM17 plays a pivotal role in initiating inflammation by releasing TNF from its precursor. Prolonged TNF release causes many chronic inflammatory diseases, indicating that tight regulation of ADAM17 activity is essential for resolution of inflammation. In this study, we report that the endogenous ADAM17 inhibitor TIMP-3 inhibits ADAM17 activity only when it is bound to the cell surface and that cell surface levels of TIMP-3 in endotoxin-activated human macrophages are dynamically controlled by the endocytic receptor LRP1. Pharmacological blockade of LRP1 inhibited endocytic clearance of TIMP-3, leading to an increase in cell surface levels of the inhibitor that blocked TNF release. Following LPS stimulation, TIMP-3 levels on the surface of macrophages increased 4-fold within 4 h and continued to accumulate at 6 h, before a return to baseline levels at 8 h. This dynamic regulation of cell surface TIMP-3 levels was independent of changes in TIMP-3 mRNA levels, but correlated with shedding of LRP1. These results shed light on the basic mechanisms that maintain a regulated inflammatory response and ensure its timely resolution.

Sphingosine 1-phosphate stimulates eyelid closure in the developing rat by stimulating EGFR signaling

In many mammals, the eyelids migrate over the eye and fuse during embryogenesis to protect the cornea from damage during birth and early life. Loss-of-function mutations affecting the epidermal growth factor receptor (EGFR) signaling pathway cause an eyes-open-at-birth (EOB) phenotype in rodents. We identified an insertional mutation in Spinster homolog 2 (Spns2) in a strain of transgenic rats exhibiting the EOB phenotype. Spns2, a sphingosine 1-phosphate (S1P) transporter that releases S1P from cells, was enriched at the tip of developing eyelids in wild-type rat embryos. Spns2 expression or treatment with S1P or any one of several EGFR ligands rescued the EOB Spns2 mutant phenotype in vivo and in tissue explants in vitro and rescued the formation of stress fibers in primary keratinocytes from mutants. S1P signaled through the receptors S1PR1, S1PR2, and S1PR3 to activate extracellular signal–regulated kinase (ERK) and EGFR-dependent mitogen-activated protein kinase kinase kinase 1 (MEKK1)–c-Jun signaling. S1P also induced the nuclear translocation of the transcription factor MAL in a manner dependent on EGFR signaling. MAL and c-Jun stimulated the expression of the microRNAs miR-21 and miR-222, both of which target the metalloprotease inhibitor TIMP3, thus promoting metalloprotease activity. The metalloproteases ADAM10 and ADAM17 stimulated EGFR signaling by cleaving a membrane-anchored form of EGF to release the ligand. Our results outline a network by which S1P transactivates EGFR signaling through a complex mechanism involving feedback between several intra- and extracellular molecules to promote eyelid fusion in the developing rat.

Protein biomarker for psoriasis: A systematic review on their role in the pathomechanism, diagnosis, potential targets and treatment of psoriasis

Psoriasis is defined as a long-lasting multifactorial inflammatory autoimmune skin condition precisely characterized by delimited, erythematic papules with adherent shiny scales. The conditions are led by hyperproliferative responses of epidermis due to hyperactivation and immature keratinocytes production. The psoriatic skin consists of the thickened epidermal layer, in concurrence with inflammatory exudates in the dermis mainly of dendritic cells, neutrophils, T cells, and macrophages, contributing to the distinct manifestation of psoriatic lesions. It consents to multifaceted and discrete pathology due to the genetic and immunological alteration resulting from abnormal expression of various regulatory and structural proteins. These proteins are associated with various cellular and sub-cellular activities. Therefore, the presence of protein in a pathological cellular environment in the psoriatic lesions as well as in serum could be a great avenue for the insight of pathomechanism, anticipation and diagnosis of psoriasis. Research of protein biomarker in psoriasis is yet a developing realm to be explored by both fundamental and clinical researchers. This review is an attempt to assimilate the current discoveries and revelations of different proteins as a biomarker and their importance in pathogenesis, diagnosis, treatment, and anticipation of both the inflammatory and other dermatological aspects of psoriasis.

Gamma-secretase-dependent signaling of receptor tyrosine kinases

Human genome harbors 55 receptor tyrosine kinases (RTK). At least half of the RTKs have been reported to be cleaved by gamma-secretase-mediated regulated intramembrane proteolysis. The two-step process involves releasing the RTK ectodomain to the extracellular space by proteolytic cleavage called shedding, followed by cleavage in the RTK transmembrane domain by the gamma-secretase complex resulting in release of a soluble RTK intracellular domain. This intracellular domain, including the tyrosine kinase domain, can in turn translocate to various cellular compartments, such as the nucleus or proteasome. The soluble intracellular domain may interact with transcriptional regulators and other proteins to induce specific effects on cell survival, proliferation, and differentiation, establishing an additional signaling mode for the cleavable RTKs. On the other hand, the same process can facilitate RTK turnover and proteasomal degradation. In this review we focus on the regulation of RTK shedding and gamma-secretase cleavage, as well as signaling promoted by the soluble RTK ICDs. In addition, therapeutic implications of increased knowledge on RTK cleavage on cancer drug development are discussed.

Levels of ADAM10 are reduced in Alzheimer's disease CSF

Background

The disintegrin metalloproteinase 10 (ADAM10) is the main α-secretase acting in the non-amyloidogenic processing of the amyloid precursor protein. This study assesses whether ADAM10 is present in cerebrospinal fluid (CSF), and whether it has potential as a biomarker for Alzheimer’s disease (AD).

Methods

ADAM10 was characterized in human CSF samples by immunoprecipitation and western blotting using antibodies specific for different domains of the protein and by ultracentrifugation in sucrose density gradients. Samples from AD patients (n = 20) and age-matched non-AD controls (n = 20) were characterized for classical CSF biomarkers, Aβ42, T-tau, or P-tau by ELISA, and assayed for soluble ADAM10 levels by western blotting.

Results

We found that ADAM10 is present in human CSF as several distinct species: an immature form retaining the prodomain (proADAM10; ~ 80 kDa), a mature unprocessed full-length form (ADAM10f; ~ 55 kDa), and a truncated large soluble form released from the membrane (sADAM10; ~ 50 kDa). Fractionation by ultracentrifugation on sucrose density gradients showed that the ADAM10f and sADAM10 species form large complexes. Immunoblotting revealed a significant decrease in ADAM10f and sADAM10 in AD CSF compared to control CSF, while proADAM10 levels remained unaltered.

Conclusions

Several forms of ADAM10 are present in CSF, mainly assembled as high-molecular weight complexes. The determination of the levels of mature forms of CSF-ADAM10 may be useful as a biomarker for AD.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1255-9) contains supplementary material, which is available to authorized users.