Regulation of mature ADAM17 by redox agents for L-selectin shedding

Role of non-coding RNAs and exosomal non-coding RNAs in vasculitis: A narrative review

A category of very uncommon systemic inflammatory blood vessel illnesses known as vasculitides. The pathogenesis and etiology of vasculitis are still poorly known. Despite all of the progress made in understanding the genetics and causes behind vasculitis, there is still more to learn. Epigenetic dysregulation is a significant contributor to immune-mediated illnesses, and epigenetic aberrancies in vasculitis are becoming more widely acknowledged. Less than 2 % of the genome contains protein-encoding DNA. Studies have shown that a variety of RNAs originating from the non-coding genome exist. Long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) have attracted the most attention in recent years as they are becoming more and more important regulators of different biological processes, such as diseases of the veins. Extracellular vehicles (EVs) such as exosomes, are membrane-bound vesicular structures that break free either during programmed cell death, such as apoptosis, pyroptosis, and necroptosis or during cell activation. Exosomes may be involved in harmful ways in inflammation, procoagulation, autoimmune reactions, endothelial dysfunction/damage, intimal hyperplasia and angiogenesis, all of which may be significant in vasculitis. Herein, we summarized various non-coding RNAs that are involved in vasculitides pathogenesis. Moreover, we highlighted the role of exosomes in vasculitides.

Endothelial Dysfunction in Patients Undergoing Cardiac Surgery: A Narrative Review and Clinical Implications

Cardiac surgery is one of the highest-risk procedures, usually involving cardiopulmonary bypass and commonly inducing endothelial injury that contributes to the development of perioperative and postoperative organ dysfunction. Substantial scientific efforts are being made to unravel the complex interaction of biomolecules involved in endothelial dysfunction to find new therapeutic targets and biomarkers and to develop therapeutic strategies to protect and restore the endothelium. This review highlights the current state-of-the-art knowledge on the structure and function of the endothelial glycocalyx and mechanisms of endothelial glycocalyx shedding in cardiac surgery. Particular emphasis is placed on potential strategies to protect and restore the endothelial glycocalyx in cardiac surgery. In addition, we have summarized and elaborated the latest evidence on conventional and potential biomarkers of endothelial dysfunction to provide a comprehensive synthesis of crucial mechanisms of endothelial dysfunction in patients undergoing cardiac surgery, and to highlight their clinical implications.

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.

Ectodomain shedding of proteins important for SARS-CoV-2 pathogenesis in plasma of tobacco cigarette smokers compared to electronic cigarette vapers: a cross-sectional study

The impact of tobacco cigarette (TCIG) smoking and electronic cigarette (ECIG) vaping on the risk of development of severe COVID-19 is controversial. The present study investigated levels of proteins important for SARS-CoV-2 pathogenesis present in plasma because of ectodomain shedding in smokers, ECIG vapers, and non-smokers (NSs). Protein levels of soluble angiotensin-converting enzyme 2 (ACE2), angiotensin (Ang) II (the ligand of ACE2), Ang 1-7 (the main peptide generated from Ang II by ACE2 activity), furin (a protease that increases the affinity of the SARS-CoV-2 spike protein for ACE2), and products of ADAM17 shedding activity that predict morbidity in COVID-19 (IL-6/IL-6R alpha (IL-6/IL-6Rα) complex, soluble CD163 (sCD163), L-selectin) were determined in plasma from 45 NSs, 30 ECIG vapers, and 29 TCIG smokers using ELISA. Baseline characteristics of study participants did not differ among groups. TCIG smokers had increased sCD163, L-selectin compared to NSs and ECIG vapers (p < 0.001 for all comparisons). ECIG vapers had higher plasma furin compared to both NSs (p < 0.001) and TCIG smokers (p < 0.05). ECIG vaping and TCIG smoking did not impact plasma ACE2, Ang 1-7, Ang II, and IL-6 levels compared to NSs (p > 0.1 for all comparisons). Further studies are needed to determine if increased furin activity and ADAM17 shedding activity that is associated with increased plasma levels of sCD163 and L-selectin in healthy young TCIG smokers may contribute to the future development of severe COVID-19 and cardiovascular complications of post-acute COVID-19 syndrome.

Pseudomonas aeruginosa Alters Critical Lung Epithelial Cell Functions through Activation of ADAM17

Severe epithelial dysfunction is one major hallmark throughout the pathophysiological progress of bacterial pneumonia. Junctional and cellular adhesion molecules (e.g., JAMA-A, ICAM-1), cytokines (e.g., TNFα), and growth factors (e.g., TGFα), controlling proper lung barrier function and leukocyte recruitment, are proteolytically cleaved and released into the extracellular space through a disintegrin and metalloproteinase (ADAM) 17. In cell-based assays, we could show that the protein expression, maturation, and activation of ADAM17 is upregulated upon infection of lung epithelial cells with Pseudomonas aeruginosa and Exotoxin A (ExoA), without any impact of infection by Streptococcus pneumoniae. The characterization of released extracellular vesicles/exosomes and the comparison to heat-inactivated bacteria revealed that this increase occurred in a cell-associated and toxin-dependent manner. Pharmacological targeting and gene silencing of ADAM17 showed that its activation during infection with Pseudomonas aeruginosa was critical for the cleavage of junctional adhesion molecule A (JAM-A) and epithelial cell survival, both modulating barrier integrity, epithelial regeneration, leukocyte adhesion and transepithelial migration. Thus, site-specific targeting of ADAM17 or blockage of the activating toxins may constitute a novel anti-infective therapeutic option in Pseudomonas aeruginosa lung infection preventing severe epithelial and organ dysfunctions and stimulating future translational studies.

Preferential Antibody and Drug Conjugate Targeting of the ADAM10 Metalloprotease in Tumours

ADAM10 is a transmembrane metalloprotease that sheds a variety of cell surface proteins, including receptors and ligands that regulate a range of developmental processes which re-emerge during tumour development. While ADAM10 is ubiquitously expressed, its activity is normally tightly regulated, but becomes deregulated in tumours. We previously reported the generation of a monoclonal antibody, 8C7, which preferentially recognises an active form of ADAM10 in human and mouse tumours. We now report our investigation of the mechanism of this specificity, and the preferential targeting of 8C7 to human tumour cell xenografts in mice. We also report the development of novel 8C7 antibody–drug conjugates that preferentially kill cells displaying the 8C7 epitope, and that can inhibit tumour growth in mice. This study provides the first demonstration that antibody–drug conjugates targeting an active conformer of ADAM10, a widely expressed transmembrane metalloprotease, enable tumour-selective targeting and inhibition.

Importance of Efferocytosis in COVID-19 Mortality

COVID-19 is a generally benign coronavirus disease that can spread rapidly, except for those with a group of risk factors. Since the pathogenesis responsible for the severity of the disease has not been clearly revealed, effective treatment alternatives has not been developed. The hallmark of the SARS-CoV-2-infected cells is apoptosis. Apoptotic cells are cleared through a sterile process defined as efferocytosis by professional and nonprofessional phagocytic cells. The disease would be rapidly brought under control in the organism that can achieve effective efferocytosis, which is also a kind of innate immune response. In the risk group, the efferocytic process is defective. With the addition of the apoptotic cell load associated with SARS-COV-2 infection, failure to achieve efferocytosis of dying cells can initiate secondary necrosis, which is a highly destructive process. Uncontrolled inflammation and coagulation abnormalities caused by secondary necrosis reason in various organ failures, lung in particular, which are responsible for the poor prognosis. Following the short and simplified information, this opinion paper aims to present possible treatment options that can control the severity of COVID-19 by detailing the mechanisms that can cause defective efferocytosis.

Mitochondria Lead the Way: Mitochondrial Dynamics and Function in Cellular Movements in Development and Disease

The dynamics, distribution and activity of subcellular organelles are integral to regulating cell shape changes during various physiological processes such as epithelial cell formation, cell migration and morphogenesis. Mitochondria are famously known as the powerhouse of the cell and play an important role in buffering calcium, releasing reactive oxygen species and key metabolites for various activities in a eukaryotic cell. Mitochondrial dynamics and morphology changes regulate these functions and their regulation is, in turn, crucial for various morphogenetic processes. In this review, we evaluate recent literature which highlights the role of mitochondrial morphology and activity during cell shape changes in epithelial cell formation, cell division, cell migration and tissue morphogenesis during organism development and in disease. In general, we find that mitochondrial shape is regulated for their distribution or translocation to the sites of active cell shape dynamics or morphogenesis. Often, key metabolites released locally and molecules buffered by mitochondria play crucial roles in regulating signaling pathways that motivate changes in cell shape, mitochondrial shape and mitochondrial activity. We conclude that mechanistic analysis of interactions between mitochondrial morphology, activity, signaling pathways and cell shape changes across the various cell and animal-based model systems holds the key to deciphering the common principles for this interaction.

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.

Pathophysiological roles of cell surface and extracellular protein disulfide isomerase and their molecular mechanisms

Protein disulfide isomerase (PDI) is the prototypic member of the thiol isomerase family that catalyses disulfide bond rearrangement. Initially identified in the endoplasmic reticulum as folding catalysts, PDI and other members in its family have also been widely reported to reside on the cell surface and in the extracellular matrix. Although how PDI is exported and retained on the cell surface remains a subject of debate, this unique pool of PDI is developing into an important mechanism underlying the redox regulation of protein sulfhydryls that are critical for the cellular activities under various disease conditions. This review aims to provide an overview of the pathophysiological roles of surface and extracellular PDI and their underlying molecular mechanisms. Understanding the involvement of extracellular PDI in these diseases will advance our knowledge in the molecular aetiology to facilitate the development of novel pharmacological strategies by specifically targeting PDI in extracellular compartments.

Implications of ADAM17 activation for hyperglycaemia, obesity and type 2 diabetes

In this review, we focus specifically on the role that the metalloproteinase, A Disintegrin and Metalloproteinase 17 [ADAM17] plays in the development and progression of the metabolic syndrome. There is a well-recognised link between the ADAM17 substrate tumour necrosis factor α (TNF-α) and obesity, inflammation and diabetes. In addition, knocking out ADAM17 in mice leads to an extremely lean phenotype. Importantly, ADAM17-deficient mice exhibit one of the most pronounced examples of hypermetabolism in rodents to date. It is vital to further understand the mechanistic role that ADAM17 plays in the metabolic syndrome. Such studies will demonstrate that ADAM17 is a valuable therapeutic target to treat obesity and diabetes.

Functionally confirmed compound heterozygous ADAM17 missense loss-of-function variants cause neonatal inflammatory skin and bowel disease 1

A disintegrin and metalloprotease 17 (ADAM17) is the major sheddase that processes more than 80 substrates, including tumour necrosis factor-α (TNFα). The homozygous genetic deficiency of ADAM17 causing a complete loss of ADAM17 expression was reported to be linked to neonatal inflammatory skin and bowel disease 1 (NISBD1). Here we report for the first time, a family with NISBD1 caused by functionally confirmed compound heterozygous missense variants of ADAM17, namely c.1699T>C (p.Cys567Arg) and c.1799G>A (p.Cys600Tyr). Both variants were detected in two siblings with clinical features of NISBD1, such as erythroderma with exudate in whole body, recurrent skin infection and sepsis and prolonged diarrhoea. In a cell-based assay using Adam10/17 double-knockout mouse embryonic fibroblasts (Adam10/17^−/− mEFs) exogenously expressing each of these mutants, phorbol 12-myristate 13-acetate-stimulated shedding was strongly reduced compared with wild-type ADAM17. Thus, in vitro functional assays demonstrated that both missense variants cause the loss-of-function of ADAM17, resulting in the development of NISBD1. Our study further expands the spectrum of genetic pathology underlying ADAM17 in NISBD1 and establishes functional assay systems for its missense variants.

Contribution of ADAM17 and related ADAMs in cardiovascular diseases

A disintegrin and metalloproteases (ADAMs) are key mediators of cell signaling by ectodomain shedding of various growth factors, cytokines, receptors and adhesion molecules at the cellular membrane. ADAMs regulate cell proliferation, cell growth, inflammation, and other regular cellular processes. ADAM17, the most extensively studied ADAM family member, is also known as tumor necrosis factor (TNF)-α converting enzyme (TACE). ADAMs-mediated shedding of cytokines such as TNF-α orchestrates immune system or inflammatory cascades and ADAMs-mediated shedding of growth factors causes cell growth or proliferation by transactivation of the growth factor receptors including epidermal growth factor receptor. Therefore, increased ADAMs-mediated shedding can induce inflammation, tissue remodeling and dysfunction associated with various cardiovascular diseases such as hypertension and atherosclerosis, and ADAMs can be a potential therapeutic target in these diseases. In this review, we focus on the role of ADAMs in cardiovascular pathophysiology and cardiovascular diseases. The main aim of this review is to stimulate new interest in this area by highlighting remarkable evidence.

β1-adrenergic receptor N-terminal cleavage by ADAM17; the mechanism for redox-dependent downregulation of cardiomyocyte β1-adrenergic receptors

β₁-adrenergic receptors (β₁ARs) are the principle mediators of catecholamine action in cardiomyocytes. We previously showed that the β₁AR extracellular N-terminus is a target for post-translational modifications that impact on signaling responses. Specifically, we showed that the β₁AR N-terminus carries O-glycan modifications at Ser³⁷/Ser⁴¹, that O-glycosylation prevents β₁AR N-terminal cleavage, and that N-terminal truncation influences β₁AR signaling to downstream effectors. However, the site(s) and mechanism for β₁AR N-terminal cleavage in cells was not identified. This study shows that β₁ARs are expressed in cardiomyocytes and other cells types as both full-length and N-terminally truncated species and that the truncated β₁AR species is formed as a result of an O-glycan regulated N-terminal cleavage by ADAM17 at R³¹↓L³². We identify Ser⁴¹ as the major O-glycosylation site on the β₁AR N-terminus and show that an O-glycan modification at Ser⁴¹ prevents ADAM17-dependent cleavage of the β₁-AR N-terminus at S⁴¹↓L⁴², a second N-terminal cleavage site adjacent to this O-glycan modification (and it attenuates β₁-AR N-terminal cleavage at R³¹↓L³²). We previously reported that oxidative stress leads to a decrease in β₁AR expression and catecholamine responsiveness in cardiomyocytes. This study shows that redox-inactivation of cardiomyocyte β₁ARs is via a mechanism involving N-terminal truncation at R³¹↓L³² by ADAM17. In keeping with the previous observation that N-terminally truncated β₁ARs constitutively activate an AKT pathway that affords protection against doxorubicin-dependent apoptosis, overexpression of a cleavage resistant β₁AR mutant exacerbates doxorubicin-dependent apoptosis. These studies identify the β₁AR N-terminus as a structural determinant of β₁AR responses that can be targeted for therapeutic advantage.

Thiol switches in membrane proteins - Extracellular redox regulation in cell biology

Redox-mediated signal transduction depends on the enzymatic production of second messengers such as hydrogen peroxide, nitric oxide and hydrogen sulfite, as well as specific, reversible redox modifications of cysteine-residues in proteins. So-called thiol switches induce for instance conformational changes in specific proteins that regulate cellular pathways e.g., cell metabolism, proliferation, migration, gene expression and inflammation. Reduction, oxidation and disulfide isomerization are controlled by oxidoreductases of the thioredoxin family, including thioredoxins, glutaredoxins, peroxiredoxins and protein dsisulfide isomerases. These proteins are located in different cellular compartments, interact with substrates and catalyze specific reactions. Interestingly, some of these proteins are released by cells. Their extracellular functions and generally extracellular redox control have been widely underestimated. Here, we give an insight into extracellular redox signaling, extracellular thiol switches and their regulation by secreted oxidoreductases and thiol-isomerases, a topic whose importance has been scarcely studied so far, likely due to methodological limitations. We focus on the secreted redox proteins and characterized thiol switches in the ectodomains of membrane proteins, such as integrins and the metalloprotease ADAM17, which are among the best-characterized proteins and discuss their underlying mechanisms and biological implications.

Syndecan-4 as a Marker of Endothelial Dysfunction in Patients with Resistant Hypertension

(1) Background: Arterial hypertension (HTN) is one of the most relevant cardiovascular risk factors. Nowadays multiple pharmaceutical treatment options exist with novel interventional methods (e.g., baroreflex activation therapy (BAT)) as a last resort to treat patients with resistant HTN. Although pathophysiology behind resistant HTN is still not fully understood. There is evidence that selected biomarkers may be involved in the pathophysiology of HTN. (2) Methods: We investigated serum SDC4-levels in patients suffering from resistant HTN before and 6 months after BAT implantation. We collected 19 blood samples from patients with resistant HTN and blood pressure above target and measured serum SDC4-levels. (3) Results: Our results showed high serum SDC4-levels in patients with resistant HTN as compared to a healthy population. Patients with both, resistant HTN and diabetes mellitus type II, demonstrated higher serum SDC4-levels. β-blockers had lowering effects on serum SDC4-levels, whereas calcium channel blockers were associated with higher levels of serum SDC4. BAT implantation did not lead to a significant difference in serum SDC4-levels after 6 months of therapy. (4) Conclusion: Based on our results we propose SDC4 is elevated in patients suffering from resistant HTN. Thus, SDC4 might be a potential marker for endothelial dysfunction in patients with resistant hypertension.

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.

Sirtuin 1 and endothelial glycocalyx

Sirtuin1 deficiency or reduced activity comprises one of the hallmarks of diseases as diverse as chronic cardiovascular, renal, and metabolic, some malignancies, and infections, as well as aging-associated diseases. In a mouse model of endothelium-limited defect in sirtuin 1 deacetylase activity, we found a dramatic reduction in the volume of endothelial glycocalyx. This was associated with the surge in the levels of one of key scaffolding heparan sulfate proteoglycans of endothelial glycocalyx, syndecan-4, and specifically, its extracellular domain (ectodomain). We found that the defect in endothelial sirtuin 1 deacetylase activity is associated with (a) elevated basal and stimulated levels of superoxide generation (via the FoxO1 over-acetylation mechanism) and (b) increased nuclear translocation of NF-kB (via p65 over-acetylation mechanism). These findings laid the foundation for the proposed novel function of sirtuin 1, namely, the maintenance of endothelial glycocalyx, particularly manifest in conditions associated with sirtuin 1 depletion. In the forthcoming review, we summarize the emerging conceptual framework of the enhanced glycocalyx degradation in the states of defective endothelial sirtuin 1 function, thus explaining a broad footprint of the syndrome of endothelial dysfunction, from impaired flow-induced nitric oxide production, deterrent leukocytes infiltration, increased endothelial permeability, coagulation, and pro-inflammatory changes to development of microvascular rarefaction and progression of an underlying disease.

Redox-Mediated Post-Translational Modifications of Proteolytic Enzymes and Their Role in Protease Functioning

Proteolytic enzymes play a crucial role in metabolic processes, providing the cell with amino acids through the hydrolysis of multiple endogenous and exogenous proteins. In addition to this function, proteases are involved in numerous protein cascades to maintain cellular and extracellular homeostasis. The redox regulation of proteolysis provides a flexible dose-dependent mechanism for proteolytic activity control. The excessive reactive oxygen species (ROS) and reactive nitrogen species (RNS) in living organisms indicate pathological conditions, so redox-sensitive proteases can swiftly induce pro-survival responses or regulated cell death (RCD). At the same time, severe protein oxidation can lead to the dysregulation of proteolysis, which induces either protein aggregation or superfluous protein hydrolysis. Therefore, oxidative stress contributes to the onset of age-related dysfunction. In the present review, we consider the post-translational modifications (PTMs) of proteolytic enzymes and their impact on homeostasis.

Glycocalyx Degradation in Ischemia-Reperfusion Injury

The glycocalyx is a layer coating the luminal surface of vascular endothelial cells. It is vital for endothelial function as it participates in microvascular reactivity, endothelium interaction with blood constituents, and vascular permeability. Structural and functional damage to glycocalyx occurs in various disease states. A prominent clinical situation characterized by glycocalyx derangement is ischemia-reperfusion (I/R) of the whole body as well as during selective I/R to organs such as the kidney, heart, lung, or liver. Degradation of the glycocalyx is now considered a cornerstone in I/R-related endothelial dysfunction, which further impairs local microcirculation with a feed-forward loop of organ damage, due to vasoconstriction, leukocyte adherence, and activation of the immune response. Glycocalyx damage during I/R is evidenced by rising plasma levels of its principal constituents, heparan sulfate and syndecan-1. By contrast, the concentrations of these compounds in the circulation decrease after successful protective interventions in I/R, suggesting their use as surrogate biomarkers of endothelial integrity. In light of the importance of the glycocalyx in preserving endothelial cell integrity and its involvement in pathologic conditions, several promising therapeutic strategies to restore the damaged glycocalyx and to attenuate its deleterious consequences have been suggested. This review focuses on alterations of glycocalyx during I/R injury in general (to vital organs in particular), and on maneuvers aimed at glycocalyx recovery during I/R injury.

Pluripotent stem cell-derived NK cells with high-affinity noncleavable CD16a mediate improved antitumor activity

Antibody-dependent cellular cytotoxicity (ADCC) is a key effector mechanism of natural killer (NK) cells that is mediated by therapeutic monoclonal antibodies (mAbs). This process is facilitated by the Fc receptor CD16a on human NK cells. CD16a appears to be the only activating receptor on NK cells that is cleaved by the metalloprotease a disintegrin and metalloproteinase-17 upon stimulation. We previously demonstrated that a point mutation of CD16a prevents this activation-induced surface cleavage. This noncleavable CD16a variant is now further modified to include the high-affinity noncleavable variant of CD16a (hnCD16) and was engineered into human induced pluripotent stem cells (iPSCs) to create a renewable source for human induced pluripotent stem cell-derived NK (hnCD16-iNK) cells. Compared with unmodified iNK cells and peripheral blood-derived NK (PB-NK) cells, hnCD16-iNK cells proved to be highly resistant to activation-induced cleavage of CD16a. We found that hnCD16-iNK cells were functionally mature and exhibited enhanced ADCC against multiple tumor targets. In vivo xenograft studies using a human B-cell lymphoma demonstrated that treatment with hnCD16-iNK cells and anti-CD20 mAb led to significantly improved regression of B-cell lymphoma compared with treatment utilizing anti-CD20 mAb with PB-NK cells or unmodified iNK cells. hnCD16-iNK cells, combined with anti-HER2 mAb, also mediated improved survival in an ovarian cancer xenograft model. Together, these findings show that hnCD16-iNK cells combined with mAbs are highly effective against hematologic malignancies and solid tumors that are typically resistant to NK cell-mediated killing, demonstrating the feasibility of producing a standardized off-the-shelf engineered NK cell therapy with improved ADCC properties to treat malignancies that are otherwise refractory.

Potential implications of hydrogen peroxide in the pathogenesis and therapeutic strategies of gliomas

Glioma is the most common type of primary brain tumor, and it has a high mortality rate. Currently, there are only a few therapeutic approaches for gliomas, and their effects are unsatisfactory. Therefore, uncovering the pathogenesis and exploring more therapeutic strategies for the treatment of gliomas are urgently needed to overcome the ongoing challenges. Cellular redox imbalance has been shown to be associated with the initiation and progression of gliomas. Among reactive oxygen species (ROS), hydrogen peroxide (H₂O₂) is considered the most suitable for redox signaling and is a potential candidate as a key molecule that determines the fate of cancer cells. In this review, we discuss the potential cellular and molecular roles of H₂O₂ in gliomagenesis and explore the potential implications of H₂O₂ in radiotherapy and chemotherapy and in the ongoing challenges of current glioma treatment. Moreover, we evaluate H₂O₂ as a potential redox sensor and potential driver molecule of nanocatalytic therapeutic strategies for glioma treatment.

ADAM proteases: Emerging role and targeting of the non-catalytic domains

ADAM proteases are multi domain transmembrane metalloproteases that cleave a range of cell surface proteins and activate signaling pathways implicated in tumor progression, including those mediated by Notch, EFGR, and the Eph receptors. Consequently, they have emerged as key therapeutic targets in the efforts to inhibit tumor initiation and progression. To that end, two main approaches have been taken to develop ADAM antagonists: (i) small molecule inhibitors, and (ii) monoclonal antibodies. In this mini-review we describe the distinct features of ADAM proteases, particularly of ADAM10 and ADAM17, their domain organization, conformational rearrangements, regulation, as well as their emerging importance as therapeutic targets in cancer. Further, we highlight an anti-ADAM10 monoclonal antibody that we have recently developed, which has shown significant promise in inhibiting Notch signaling and deterring growth of solid tumors in pre-clinical settings.

ADAM Metalloproteinases as Potential Drug Targets

The ADAMs, together with ADAMTSs and snake venom metalloproteases (SVMPs), are members of the Adamalysin family. Differences in structural organization, functions and localization are known and their domains, catalytic or non-catalytic, show key roles in the substrate recognition and protease activity. Some ADAMs, as membrane-bound enzymes, show sheddase activity. Sheddases are key to modulation of functional proteins such as the tumor necrosis factor, growth factors, cytokines and their receptors, adhesion proteins, signaling molecules and stress molecules involved in immunity. These activities take part in the regulation of several physiological and pathological processes including inflammation, tumor growth, metastatic progression and infectious diseases. On these bases, some ADAMs are currently investigated as drug targets to develop new alternative therapies in many fields of medicine. This review will be focused on these aspects.

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.

Matrix metalloproteinases and ADAMs in stroke

Stroke is a leading cause of death and disability worldwide. However, after years of in-depth research, the pathophysiology of stroke is still not fully understood. Increasing evidence shows that matrix metalloproteinases (MMPs) and "a disintegrin and metalloproteinase" (ADAMs) participate in the neuro-inflammatory cascade that is triggered during stroke but also in recovery phases of the disease. This review covers the involvement of these proteins in brain injury following cerebral ischemia which has been widely studied in recent years, with efforts to modulate this group of proteins in neuroprotective therapies, together with their implication in neurorepair mechanisms. Moreover, the review also discusses the role of these proteins in specific forms of neurovascular disease, such as small vessel diseases and intracerebral hemorrhage. Finally, the potential use of MMPs and ADAMs as guiding biomarkers of brain injury and repair for decision-making in cases of stroke is also discussed.

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.

L-selectin: A Major Regulator of Leukocyte Adhesion, Migration and Signaling

L-selectin (CD62L) is a type-I transmembrane glycoprotein and cell adhesion molecule that is expressed on most circulating leukocytes. Since its identification in 1983, L-selectin has been extensively characterized as a tethering/rolling receptor. There is now mounting evidence in the literature to suggest that L-selectin plays a role in regulating monocyte protrusion during transendothelial migration (TEM). The N-terminal calcium-dependent (C-type) lectin domain of L-selectin interacts with numerous glycans, including sialyl Lewis X (sLe^x) for tethering/rolling and proteoglycans for TEM. Although the signals downstream of L-selectin-dependent adhesion are poorly understood, they will invariably involve the short 17 amino acid cytoplasmic tail. In this review we will detail the expression of L-selectin in different immune cell subsets, and its influence on cell behavior. We will list some of the diverse glycans known to support L-selectin-dependent adhesion, within luminal and abluminal regions of the vessel wall. We will describe how each domain within L-selectin contributes to adhesion, migration and signal transduction. A significant focus on the L-selectin cytoplasmic tail and its proposed contribution to signaling via the ezrin-radixin-moesin (ERM) family of proteins will be outlined. Finally, we will discuss how ectodomain shedding of L-selectin during monocyte TEM is essential for the establishment of front-back cell polarity, bestowing emigrated cells the capacity to chemotax toward sites of damage.

L-selectin expression is regulated by CXCL8-induced reactive oxygen species produced during human neutrophil rolling

Neutrophils destroy invading microorganisms by phagocytosis by bringing them into contact with bactericidal substances, among which ROS are the most important. However, ROS also function as important physiological regulators of cellular signaling pathways. Here, we addressed the involvement of oxygen derivatives in the regulation of human neutrophil rolling, an essential component of the inflammatory response. Flow experiments using dihydroethidium-preloaded human neutrophils showed that these cells initiate an early production of intracellular ROS during the rolling phase of the adhesion cascade, a phenomenon that required cell rolling, and the interaction of the chemokine receptor CXCR2 with their ligand CXCL8. Flow cytometry experiments demonstrated that L-selectin shedding in neutrophils is triggered by ROS through an autocrine-paracrine mechanism. Preincubation of neutrophils with the NADPH oxidase complex inhibitor diphenyleniodonium chloride significantly increased the number of rolling neutrophils on endothelial cells. Interestingly, the same effect was observed when CXCL8 signaling was interfered using either a blocking monoclonal antibody or an inhibitor of its receptor. These findings indicate that, in response to CXCL8, neutrophils initiate ROS production during the rolling phase of the inflammatory response. This very early ROS production might participate in the modulation of the inflammatory response by inducing L-selectin shedding in neutrophils.

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

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

Fibrogenic Secretome of Sirtuin 1-Deficient Endothelial Cells: Wnt, Notch and Glycocalyx Rheostat

Sirtuins (SIRT) are ubiquitous histone and protein deacetylases and a member of this family, SIRT1, is the best-studied one. Its functions in endothelial cells encompass branching angiogenesis, activation of endothelial nitric oxide synthase, regulation of proapoptotic and proinflammatory pathways, among others. Defective SIRT1 activity has been described in various cardiovascular, renal diseases and in aging-associated conditions. Therefore, understanding of SIRT1-deficient, endothelial dysfunctional phenotype has much to offer clinically. Here, we summarize recent studies by several investigative teams of the characteristics of models of global endothelial SIRT1 deficiency, the causes of facilitative development of fibrosis in these conditions, dissect the protein composition of the aberrant secretome of SIRT1-deficient endothelial cells and present several components of this aberrant secretome that are involved in fibrogenesis via activation of fibroblasts to myofibroblasts. These include ligands of Wnt and Notch pathways, as well as proteolytic fragments of glycocalyx core protein, syndecan-4. The latter finding is crucial for understanding the degradation of glycocalyx that accompanies SIRT1 deficiency. This spectrum of abnormalities associated with SIRT1 deficiency in endothelial cells is essential for understanding the origins and features of endothelial dysfunction in a host of cardiovascular and renal diseases.

Dysregulation of the ADAM17/Notch signalling pathways in endometriosis: from oxidative stress to fibrosis

STUDY QUESTION

Is oxidative stress associated with the A disintegrin and metalloproteases (ADAM) metallopeptidase domain 17 (ADAM17)/Notch signalling pathway and fibrosis in the development of endometriosis?

SUMMARY ANSWER

Oxidative stress is correlated with hyperactivation of the ADAM17/Notch signalling pathway and a consequent increase in fibrosis in patients with endometriosis.

WHAT IS KNOWN ALREADY

It is nowadays accepted that oxidative stress plays an important role in the onset and progression of endometriosis. Oxidative stress is able to induce the synthesis of some members of the 'ADAM' family, such as ADAM17. ADAM17/Notch signalling is dysregulated in other profibrotic and inflammatory diseases.

STUDY DESIGN, SIZE, DURATION

This was a prospective laboratory study conducted in a tertiary-care university hospital between January 2011 and April 2013. We investigated non-pregnant, younger than 42-year-old patients (n = 202) during surgery for a benign gynaecological condition.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After complete surgical exploration of the abdominopelvic cavity, 121 women with histologically proven endometriosis and 81 endometriosis-free control women were enrolled. Peritoneal fluid (PF) samples were obtained from all the study participants during surgery in order to detect advanced oxidation protein products (AOPPs) and metalloproteinase activity of ADAM17. Stromal cells from endometrial specimens (n = 8) were obtained from endometrium of control patients (Cs), and from eutopic (Es) and ectopic (Ps) endometrium of patients with deep infiltrating endometriosis (DIE) (n = 8). ADAM17, Notch and the fibrosis markers α-smooth muscle actin (α-SMA) and type-I collagen were assessed using immunoblotting in all the endometrial samples obtained. Additionally, fibrosis was assessed after using Notch cleavage inhibitors (DAPT and FLI-06). Notch and fibrosis were also evaluated after stimulation of stromal endometrial cells with ADAM17 purified protein, increasing concentrations of H2O2 and primary cell culture supernatants.

MAIN RESULTS AND THE ROLE OF CHANCE

Patients with DIE presented higher PF AOPP and ADAM17 protein levels than controls (P < 0.01 and P < 0.05, respectively). In addition, these two markers were positively correlated (r = 0.614; P < 0.001). At the cellular level, ADAM17 activity was increased in Es and Ps compared to Cs (P < 0.001 and P < 0.01, respectively). Furthermore, Ps presented hyperactivation of Notch signalling (P < 0.05) and augmentation of fibrosis markers (P = 0.009 for α-SMA and P = 0.015 for type-I collagen) compared to controls. The use of DAPT and FLI-06 reduced both fibrosis markers in Ps but not in Cs. Stimulation with ADAM17, H2O2 and Ps supernatant culture significantly increased Notch and fibrosis in both Ps and Cs.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

The control group consisted of women who underwent surgery for benign gynaecological conditions, which could lead to biases because some of these conditions may cause alterations in oxidative stress and the ADAM17/Notch pathways. The small sample size of endometrial biopsies used for each group of patients (n = 8) is a limitation of the study, and results should be interpreted with caution.

WIDER IMPLICATIONS OF THE FINDINGS

We propose a novel pathway in endometriosis pathogenesis that correlates oxidative stress, hyperactivation of ADAM17/Notch signalling and a consequent increase in fibrosis. This study suggests that Notch signalling plays a key role in the fibrotic processes that take place in ectopic lesions of patients with DIE, as already observed in other pro-fibrotic diseases.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by grants from University Paris Descartes, INSERM and Fundación Alfonso Martín Escudero. The authors have no competing interests to declare.

Perioperative implication of the endothelial glycocalyx

The endothelial glycocalyx (EG) is a gel-like layer lining the luminal surface of healthy vascular endothelium. Recently, the EG has gained extensive interest as a crucial regulator of endothelial funtction, including vascular permeability, mechanotransduction, and the interaction between endothelial and circulating blood cells. The EG is degraded by various enzymes and reactive oxygen species upon pro-inflammatory stimulus. Ischemia-reperfusion injury, oxidative stress, hypervolemia, and systemic inflammatory response are responsible for perioperative EG degradation. Perioperative damage of the EG has also been demonstrated, especially in cardiac surgery. However, the protection of the EG and its association with perioperative morbidity needs to be elucidated in future studies. In this review, the present knowledge about EG and its perioperative implication is discussed from an anesthesiologist's perspective.

Metalloprotease ADAM17 regulates porcine epidemic diarrhea virus infection by modifying aminopeptidase N

Porcine epidemic diarrhea virus (PEDV) is a causative agent of porcine epidemic diarrhea (PED). PED, characterized by acute diarrhea, vomiting, dehydration, has caused serious economic losses in pig industry worldwide. Here, we demonstrate that activation of a disintergrin and metalloprotease 17 (ADAM17) induced the decrease of PEDV infection in HEK293 and IPEC-J2 cells and the downregulation of cell surface aminopeptidase N (APN) expression, an important entry factor for PEDV infection. Furthermore, overexpression of ADAM17 suppressed PEDV infection in HEK293 and IPEC-J2 cells, whereas ablation of ADAM17 expression using ADAM17 specific siRNA resulted in a corresponding increase of PEDV infection and an upregulation of cell surface APN expression. Taken together, these data demonstrate that modulation of APN expression by metalloprotease ADAM17 regulates PEDV infection. Hence, the reduction in APN expression represents another component of the anti-PEDV infection response initiated by ADAM17.

A head-to-tail view of L-selectin and its impact on neutrophil behaviour

L-selectin is a type I transmembrane cell adhesion molecule expressed on most circulating leukocytes, including neutrophils. Engagement of L-selectin with endothelial-derived ligands initiates neutrophil tethering and rolling behaviour along luminal walls of post-capillary venules, constituting the first step of the multi-step adhesion cascade. There is a large body of evidence to suggest that signalling downstream of L-selectin can influence neutrophil behaviour: adhesion, migration and priming. This review will cover aspects of L-selectin form and function and introduce the “triad of L-selectin regulation”, highlighting the inextricable links between adhesion, signalling and ectodomain shedding and also highlighting the cytosolic proteins that interconnect them. Recent advances in how L-selectin impacts priming, transendothelial migration (TEM) and cell polarity will also be discussed.

Redundancy of protein disulfide isomerases in the catalysis of the inactivating disulfide switch in A Disintegrin and Metalloprotease 17

A Disintegrin and Metalloprotease 17 (ADAM17) can cause the fast release of growth factors and inflammatory mediators from the cell surface. Its activity has to be turned on which occurs by various stimuli. The active form can be inactivated by a structural change in its ectodomain, related to the pattern of the formed disulphide bridges. The switch-off is executed by protein disulfide isomerases (PDIs) that catalyze an isomerization of two disulfide bridges and thereby cause a disulfide switch. We demonstrate that the integrity of the CGHC-motif within the active site of PDIs is indispensable. In particular, no major variation is apparent in the activities of the two catalytic domains of PDIA6. The affinities between PDIA1, PDIA3, PDIA6 and the targeted domain of ADAM17 are all in the nanomolar range and display no significant differences. The redundancy between PDIs and their disulfide switch activity in ectodomains of transmembrane proteins found in vitro appears to be a basic characteristic. However, different PDIs might be required in vivo for disulfide switches in different tissues and under different cellular and physiological situations.

The EGFR-ADAM17 Axis in Chronic Obstructive Pulmonary Disease and Cystic Fibrosis Lung Pathology

Chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) share molecular mechanisms that cause the pathological symptoms they have in common. Here, we review evidence suggesting that hyperactivity of the EGFR/ADAM17 axis plays a role in the development of chronic lung disease in both CF and COPD. The ubiquitous transmembrane protease A disintegrin and metalloprotease 17 (ADAM17) forms a functional unit with the EGF receptor (EGFR), in a feedback loop interaction labeled the ADAM17/EGFR axis. In airway epithelial cells, ADAM17 sheds multiple soluble signaling proteins by proteolysis, including EGFR ligands such as amphiregulin (AREG), and proinflammatory mediators such as the interleukin 6 coreceptor (IL-6R). This activity can be enhanced by injury, toxins, and receptor-mediated external triggers. In addition to intracellular kinases, the extracellular glutathione-dependent redox potential controls ADAM17 shedding. Thus, the epithelial ADAM17/EGFR axis serves as a receptor of incoming luminal stress signals, relaying these to neighboring and underlying cells, which plays an important role in the resolution of lung injury and inflammation. We review evidence that congenital CFTR deficiency in CF and reduced CFTR activity in chronic COPD may cause enhanced ADAM17/EGFR signaling through a defect in glutathione secretion. In future studies, these complex interactions and the options for pharmaceutical interventions will be further investigated.

Endothelial dysfunction is a superinducer of syndecan-4: fibrogenic role of its ectodomain

Syndecan-4 (Synd4) is a member of the membrane-spanning, glycocalyx-forming proteoglycan family. It has been suggested that Synd4 participates in renal fibrosis. We compared wild-type and fibrosis-prone endothelial sirtuin 1-deficient (Sirt1^endo-/-) mice, the latter being a model of global endothelial dysfunction. We performed mass spectrometry analysis, which revealed that Synd4 was highly enriched in the secretome of renal microvascular endothelial cells obtained from Sirt1^endo-/- mice upon stimulation with transforming growth factor-β₁; notably, all detectable peptides were confined to the ectodomain of Synd4. Elevated Synd4 was due to enhanced NF-κB signaling in Sirt1^endo-/- mice, while its shedding occurred as a result of oxidative stress in Sirt1 deficiency. Synd4 expression was significantly enhanced after unilateral ureteral obstruction compared with contralateral kidneys. Furthermore, hyperplasia of renal myofibroblasts accompanied by microvascular rarefaction and overexpression of Synd4 were detected in Sirt1^endo-/- mice. The ectodomain of Synd4 acted as a chemoattractant for monocytes with higher levels of macrophages and higher expression levels of Synd4 in the extracellular matrix of Sirt1^endo-/- mice. In vitro, ectodomain application resulted in generation of myofibroblasts from cultured renal fibroblasts, while in vivo, subcapsular injection of ectodomain increased interstitial fibrosis. Moreover, the endothelial glycocalyx was reduced in Sirt1^endo-/- mice, highlighting the induction of Synd4 occurring in parallel with the depletion of its intact form and accumulation of its ectodomain in Sirt1^endo-/- mice. On the basis of our experimental results, we propose that it is the Synd4 ectodomain per se that is partially responsible for fibrosis in unilateral ureteral obstruction, especially when it is combined with endothelial dysfunction. NEW & NOTEWORTHY Our findings suggest that endothelial dysfunction induces the expression of syndecan-4 via activation of the NF-κB pathway. Furthermore, we show that syndecan-4 is shed to a greater amount because of increased oxidative stress in dysfunctional endothelial cells and that the release of the syndecan-4 ectodomain leads to tubulointerstitial fibrosis.

GRP78 protects a disintegrin and metalloprotease 17 against protein-disulfide isomerase A6 catalyzed inactivation

The shedding of ectodomains is a crucial mechanism in many physiological and pathological events. A disintegrin and metalloprotease-17 (ADAM17) is a key sheddase involved in essential processes, such as development, regeneration, and immune defense. ADAM17 exists in two conformations which differ in their disulfide connection in the membrane-proximal domain (MPD). Protein-disulfide isomerases (PDIs) on the cell surface convert the open MPD into a rigid closed form, which corresponds to inactive ADAM17. ADAM17 is expressed in its open activatable form in the endoplasmic reticulum (ER) and consequently must be protected against ER-resident PDI activity. Here, we show that the chaperone 78-kDa glucose-regulated protein (GRP78) protects the MPD against PDI-dependent disulfide-bond isomerization by binding to this domain and, thereby, preventing ADAM17 inhibition.

Redox Regulation of Inflammatory Processes Is Enzymatically Controlled

Redox regulation depends on the enzymatically controlled production and decay of redox active molecules. NADPH oxidases, superoxide dismutases, nitric oxide synthases, and others produce the redox active molecules superoxide, hydrogen peroxide, nitric oxide, and hydrogen sulfide. These react with target proteins inducing spatiotemporal modifications of cysteine residues within different signaling cascades. Thioredoxin family proteins are key regulators of the redox state of proteins. They regulate the formation and removal of oxidative modifications by specific thiol reduction and oxidation. All of these redox enzymes affect inflammatory processes and the innate and adaptive immune response. Interestingly, this regulation involves different mechanisms in different biological compartments and specialized cell types. The localization and activity of distinct proteins including, for instance, the transcription factor NFκB and the immune mediator HMGB1 are redox-regulated. The transmembrane protein ADAM17 releases proinflammatory mediators, such as TNFα, and is itself regulated by a thiol switch. Moreover, extracellular redox enzymes were shown to modulate the activity and migration behavior of various types of immune cells by acting as cytokines and/or chemokines. Within this review article, we will address the concept of redox signaling and the functions of both redox enzymes and redox active molecules in innate and adaptive immune responses.

Protective role of cellular prion protein against TNFα-mediated inflammation through TACE α-secretase

Although cellular prion protein PrP^C is well known for its implication in Transmissible Spongiform Encephalopathies, its functions remain elusive. Combining in vitro and in vivo approaches, we here show that PrP^C displays the intrinsic capacity to protect neuronal cells from a pro-inflammatory TNFα noxious insult. Mechanistically, PrP^C coupling to the NADPH oxidase-TACE α-secretase signaling pathway promotes TACE-mediated cleavage of transmembrane TNFα receptors (TNFRs) and the release of soluble TNFR, which limits the sensitivity of recipient cells to TNFα. We further show that PrP^C expression is necessary for TACE α-secretase to stay at the plasma membrane in an active state for TNFR shedding. Such PrP^C control of TACE localization depends on PrP^C modulation of β1 integrin signaling and downstream activation of ROCK-I and PDK1 kinases. Loss of PrP^C provokes TACE internalization, which in turn cancels TACE-mediated cleavage of TNFR and renders PrP^C-depleted neuronal cells as well as PrP^C knockout mice highly vulnerable to pro-inflammatory TNFα insult. Our work provides the prime evidence that in an inflammatory context PrP^C adjusts the response of neuronal cells targeted by TNFα through TACE α-secretase. Our data also support the view that abnormal TACE trafficking and activity in prion diseases originate from a-loss-of-PrP^C cytoprotective function.

Molecular insights into the multilayered regulation of ADAM17: The role of the extracellular region

In contrast to many other signalling mechanisms shedding of membrane-anchored proteins is an irreversible process. A Disintegrin And Metalloproteinase (ADAM) 17 is one of the major sheddases involved in a variety of physiological and pathophysiological processes including regeneration, differentiation, and cancer progression. Due to its central role in signalling the shedding activity of ADAM17 is tightly regulated, especially on the cell surface, where shedding events take place. The activity of ADAM17 can be subdivided into a catalytic activity and the actual shedding activity. Whereas the catalytic activity is constitutively present, the shedding activity has to be induced and is tightly controlled to prevent pathological situations induced by the release of its substrates. The regulation of the shedding activity of ADAM17 is multilayered and different regions of the protease are involved. Intriguingly, its extracellular domains play crucial roles in different regulatory mechanisms. We will discuss the role of these domains in the control of ADAM17 activity. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Ectodomain Shedding by ADAM17: Its Role in Neutrophil Recruitment and the Impairment of This Process during Sepsis

Neutrophils are specialized at killing bacteria and are recruited from the blood in a rapid and robust manner during infection. A cascade of adhesion events direct their attachment to the vascular endothelium and migration into the underlying tissue. A disintegrin and metalloproteinase 17 (ADAM17) functions in the cell membrane of neutrophils and endothelial cells by cleaving its substrates, typically in a cis manner, at an extracellular site proximal to the cell membrane. This process is referred to as ectodomain shedding and it results in the downregulation of various adhesion molecules and receptors, and the release of immune regulating factors. ADAM17 sheddase activity is induced upon cell activation and rapidly modulates intravascular adhesion events in response to diverse environmental stimuli. During sepsis, an excessive systemic inflammatory response against infection, neutrophil migration becomes severely impaired. This involves ADAM17 as indicated by increased levels of its cleaved substrates in the blood of septic patients, and that ADAM17 inactivation improves neutrophil recruitment and bacterial clearance in animal models of sepsis. Excessive ADAM17 sheddase activity during sepsis thus appears to undermine in a direct and indirect manner the necessary balance between intravascular adhesion and de-adhesion events that regulate neutrophil migration into sites of infection. This review provides an overview of ADAM17 function and regulation and its potential contribution to neutrophil dysfunction during sepsis.

Ectodomain shedding of the cell adhesion molecule Nectin-4 in ovarian cancer is mediated by ADAM10 and ADAM17

We previously showed that the cell adhesion molecule Nectin-4 is overexpressed in ovarian cancer tumors, and its cleaved extracellular domain can be detected in the serum of ovarian cancer patients. The ADAM (adisintegrin and metalloproteinase) proteases are involved in ectodomain cleavage of transmembrane proteins, and ADAM17 is known to cleave Nectin-4 in breast cancer. However, the mechanism of Nectin-4 cleavage in ovarian cancer has not yet been determined. Analysis of ovarian cancer gene microarray data showed that higher expression of Nectin-4, ADAM10, and ADAM17 is associated with significantly decreased progression-free survival. We quantified Nectin-4 shedding from the surface of ovarian cancer cells after stimulation with lysophosphatidic acid. We report that ADAM17 and ADAM10 cleave Nectin-4 and release soluble Nectin-4 (sN4). Small molecule inhibitors and siRNA knockdown of both ADAM proteases confirmed these results. In matched samples from 11 high-grade serous ovarian cancer patients, we detected 2-20-fold more sN4 in ascites fluid than serum. Co-incubation of ovarian cancer cells with ascites fluid significantly increased sN4 shedding, which could be blocked using a dual inhibitor of ADAM10 and ADAM17. Furthermore, we detected RNA for Nectin-4, ADAM10, and ADAM17 in primary ovarian carcinoma tumors, secondary omental metastases, and ascites cells isolated from serous ovarian cancer patients. In a signaling pathway screen, lysophosphatidic acid increased phosphorylation of AKT, EGF receptor, ERK1/2, JNK1/2/3, and c-Jun. Understanding the function of Nectin-4 shedding in ovarian cancer progression is critical to facilitate its development as both a serum biomarker and a therapeutic target for ovarian cancer.

Roles of extracellular nucleotides and P2 receptors in ectodomain shedding

Ectodomain shedding of integral membrane receptors results in the release of soluble molecules and modification of the transmembrane portions to mediate or modulate extracellular and intracellular signalling. Ectodomain shedding is stimulated by a variety of mechanisms, including the activation of P2 receptors by extracellular nucleotides. This review describes in detail the roles of extracellular nucleotides and P2 receptors in the shedding of various cell surface molecules, including amyloid precursor protein, CD23, CD62L, and members of the epidermal growth factor, immunoglobulin and tumour necrosis factor families. This review discusses the mechanisms involved in P2 receptor-mediated shedding, demonstrating central roles for the P2 receptors, P2X7 and P2Y2, and the sheddases, ADAM10 and ADAM17, in this process in a number of cell types.

Control of ADAM17 activity by regulation of its cellular localisation

An important, irreversible step in many signalling pathways is the shedding of membrane-anchored proteins. A Disintegrin And Metalloproteinase (ADAM) 17 is one of the major sheddases involved in a variety of physiological and pathophysiological processes including regeneration, differentiation, and cancer progression. This central role in signalling implies that ADAM17 activity has to be tightly regulated, including at the level of localisation. Most mature ADAM17 is localised intracellularly, with only a small amount at the cell surface. We found that ADAM17 is constitutively internalised by clathrin-coated pits and that physiological stimulators such as GPCR ligands induce ADAM17-mediated shedding, but do not alter the cell-surface abundance of the protease. In contrast, the PKC-activating phorbol ester PMA, often used as a strong inducer of ADAM17, causes not only proteolysis by ADAM17 but also a rapid increase of the mature protease at the cell surface. This is followed by internalisation and subsequent degradation of the protease. Eventually, this leads to a substantial downregulation of mature ADAM17. Our results therefore imply that physiological activation of ADAM17 does not rely on its relocalisation, but that PMA-induced PKC activity drastically dysregulates the localisation of ADAM17.

An activated form of ADAM10 is tumor selective and regulates cancer stem-like cells and tumor growth

The transmembrane metalloprotease ADAM10 sheds a range of cell surface proteins, including ligands and receptors of the Notch, Eph, and erbB families, thereby activating signaling pathways critical for tumor initiation and maintenance. ADAM10 is thus a promising therapeutic target. Although widely expressed, its activity is normally tightly regulated. We now report prevalence of an active form of ADAM10 in tumors compared with normal tissues, in mouse models and humans, identified by our conformation-specific antibody mAb 8C7. Structure/function experiments indicate mAb 8C7 binds an active conformation dependent on disulfide isomerization and oxidative conditions, common in tumors. Moreover, this active ADAM10 form marks cancer stem-like cells with active Notch signaling, known to mediate chemoresistance. Importantly, specific targeting of active ADAM10 with 8C7 inhibits Notch activity and tumor growth in mouse models, particularly regrowth after chemotherapy. Our results indicate targeted inhibition of active ADAM10 as a potential therapy for ADAM10-dependent tumor development and drug resistance.

The Cytosolic NADPH Oxidase Subunit NoxO1 Promotes an Endothelial Stalk Cell Phenotype

OBJECTIVE

Reactive oxygen species generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidases contribute to angiogenesis and vascular repair. NADPH oxidase organizer 1 (NoxO1) is a cytosolic protein facilitating assembly of constitutively active NADPH oxidases. We speculate that NoxO1 also contributes to basal reactive oxygen species formation in the vascular system and thus modulates angiogenesis.

APPROACH AND RESULTS

A NoxO1 knockout mouse was generated, and angiogenesis was studied in cultured cells and in vivo. Angiogenesis of the developing retina and after femoral artery ligation was increased in NoxO1(-/-) when compared with wild-type animals. Spheroid outgrowth assays revealed greater angiogenic capacity of NoxO1(-/-) lung endothelial cells (LECs) and a more tip-cell-like phenotype than wild-type LECs. Usually signaling by the Notch pathway switches endothelial cells from a tip into a stalk cell phenotype. NoxO1(-/-) LECs exhibited attenuated Notch signaling as a consequence of an attenuated release of the Notch intracellular domain on ligand stimulation. This release is mediated by proteolytic cleavage involving the α-secretase ADAM17. For maximal activity, ADAM17 has to be oxidized, and overexpression of NoxO1 promoted this mode of activation. Moreover, the activity of ADAM17 was reduced in NoxO1(-/-) LECs when compared with wild-type LECs.

CONCLUSIONS

NoxO1 stimulates α-secretase activity probably through reactive oxygen species-mediated oxidation. Deletion of NoxO1 attenuates Notch signaling and thereby promotes a tip-cell phenotype that results in increased angiogenesis.