Regulated shedding of transmembrane chemokines by the disintegrin and metalloproteinase 10 facilitates detachment of adherent leukocytes

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

ADAM10 and Neprilysin level decreases in immune cells of mice bearing metastatic breast carcinoma: Possible role in cancer inflammatory response

OBJECTIVE AND DESIGN

ADAM10 and Neprilysin, proteases, play critical role in inflammatory disease, however their role in cancer immune response is not clear. We here evaluated changes in immune response using an experimental model for breast cancer.

MATERIAL AND METHOD

Highly metastatic breast cancer cells (4T1-derived) were injected orthotopically (mammary-pad of Balb-c mice) to induce tumors. Changes in enzyme level and activity as well as alterations in inflammatory cytokine release in the presence or absence of ADAM10 and NEP activity was determined using specific inhibitors and recombinant proteins. Cytokine response was evaluated using mix leucocyte cultures obtained from control and tumor-bearing mice. ANOVA with Dunnett's posttest was used for statistical analysis.

RESULTS

ADAM10 and NEP expression was decreased markedly in lymph nodes and spleens of tumor-bearing mice. ADAM10 activity was reduced together with apparent alterations of ADAM10 processing. ADAM10 and NEP activity decreased TNF-α, IL-6 and IFN-ɣ secretion. Suppression of these inflammatory cytokines were more prominent in cultures obtained from control mice demonstrating counteracting factors that are exist in tumor-bearing mice.

CONCLUSION

Loss of ADAM10 and NEP activity in immune cells during breast cancer metastasis might be one of the main factors involved in induction of chronic inflammation by tumors.

The cellular microenvironment regulates CX3CR1 expression on CD8+ T cells and the maintenance of CX3CR1+ CD8+ T cells

Expression levels of the chemokine receptor CX3CR1 serve as high-resolution marker delineating functionally distinct antigen-experienced T-cell states. The factors that influence CX3CR1 expression in T cells are, however, incompletely understood. Here, we show that in vitro priming of naïve CD8+ T cells failed to robustly induce CX3CR1, which highlights the shortcomings of in vitro priming settings in recapitulating in vivo T-cell differentiation. Nevertheless, in vivo generated memory CD8+ T cells maintained CX3CR1 expression during culture. This allowed us to investigate whether T-cell receptor ligation, cell death, and CX3CL1 binding influence CX3CR1 expression. T-cell receptor stimulation led to downregulation of CX3CR1. Without stimulation, CX3CR1+ CD8+ T cells had a selective survival disadvantage, which was enhanced by factors released from necrotic but not apoptotic cells. Exposure to CX3CL1 did not rescue their survival and resulted in a dose-dependent loss of CX3CR1 surface expression. At physiological concentrations of CX3CL1, CX3CR1 surface expression was only minimally reduced, which did not hamper the interpretability of T-cell differentiation states delineated by CX3CR1. Our data further support the broad utility of CX3CR1 surface levels as T-cell differentiation marker and identify factors that influence CX3CR1 expression and the maintenance of CX3CR1 expressing CD8+ T cells.

Age-dependent changes on fractalkine forms and their contribution to neurodegenerative diseases

The chemokine fractalkine (FKN, CX3CL1), a member of the CX3C subfamily, contributes to neuron-glia interaction and the regulation of microglial cell activation. Fractalkine is expressed by neurons as a membrane-bound protein (mCX3CL1) that can be cleaved by extracellular proteases generating several sCX3CL1 forms. sCX3CL1, containing the chemokine domain, and mCX3CL1 have high affinity by their unique receptor (CX3CR1) which, physiologically, is only found in microglia, a resident immune cell of the CNS. The activation of CX3CR1contributes to survival and maturation of the neural network during development, glutamatergic synaptic transmission, synaptic plasticity, cognition, neuropathic pain, and inflammatory regulation in the adult brain. Indeed, the various CX3CL1 forms appear in some cases to serve an anti-inflammatory role of microglia, whereas in others, they have a pro-inflammatory role, aggravating neurological disorders. In the last decade, evidence points to the fact that sCX3CL1 and mCX3CL1 exhibit selective and differential effects on their targets. Thus, the balance in their level and activity will impact on neuron-microglia interaction. This review is focused on the description of factors determining the emergence of distinct fractalkine forms, their age-dependent changes, and how they contribute to neuroinflammation and neurodegenerative diseases. Changes in the balance among various fractalkine forms may be one of the mechanisms on which converge aging, chronic CNS inflammation, and neurodegeneration.

Role of the CXCR6/CXCL16 axis in autoimmune diseases

The C-X-C motif ligand 16, or CXCL16, is a chemokine that belongs to the ELR - CXC subfamily. Its function is to bind to the chemokine receptor CXCR6, which is a G protein-coupled receptor with 7 transmembrane domains. The CXCR6/CXCL16 axis has been linked to the development of numerous autoimmune diseases and is connected to clinical parameters that reflect disease severity, activity, and prognosis in conditions such as multiple sclerosis, autoimmune hepatitis, rheumatoid arthritis, Crohn's disease, and psoriasis. CXCL16 is expressed in various immune cells, such as dendritic cells, monocytes, macrophages, and B cells. During autoimmune diseases, CXCL16 can facilitate the adhesion of immune cells like monocytes, T cells, NKT cells, and others to endothelial cells and dendritic cells. Additionally, sCXCL16 can regulate the migration of CXCR6-expressing leukocytes, which includes CD8⁺ T cells, CD4⁺ T cells, NK cells, constant natural killer T cells, plasma cells, and monocytes. Further investigation is required to comprehend the intricate interactions between chemokines and the pathogenesis of autoimmune diseases. It remains to be seen whether the CXCR6/CXCL16 axis represents a new target for the treatment of these conditions.

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

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

ADAM10 and ADAM17, Major Regulators of Chronic Kidney Disease Induced Atherosclerosis?

Chronic kidney disease (CKD) is a major health problem, affecting millions of people worldwide, in particular hypertensive and diabetic patients. CKD patients suffer from significantly increased cardiovascular disease (CVD) morbidity and mortality, mainly due to accelerated atherosclerosis development. Indeed, CKD not only affects the kidneys, in which injury and maladaptive repair processes lead to local inflammation and fibrosis, but also causes systemic inflammation and altered mineral bone metabolism leading to vascular dysfunction, calcification, and thus, accelerated atherosclerosis. Although CKD and CVD individually have been extensively studied, relatively little research has studied the link between both diseases. This narrative review focuses on the role of a disintegrin and metalloproteases (ADAM) 10 and ADAM17 in CKD and CVD and will for the first time shed light on their role in CKD-induced CVD. By cleaving cell surface molecules, these enzymes regulate not only cellular sensitivity to their micro-environment (in case of receptor cleavage), but also release soluble ectodomains that can exert agonistic or antagonistic functions, both locally and systemically. Although the cell-specific roles of ADAM10 and ADAM17 in CVD, and to a lesser extent in CKD, have been explored, their impact on CKD-induced CVD is likely, yet remains to be elucidated.

The Biochemistry and Physiology of A Disintegrin and Metalloproteinases (ADAMs and ADAM-TSs) in Human Pathologies

Metalloproteinases are a group of proteinases that plays a substantial role in extracellular matrix remodeling and its molecular signaling. Among these metalloproteinases, ADAMs (a disintegrin and metalloproteinases) and ADAM-TSs (ADAMs with thrombospondin domains) have emerged as highly efficient contributors mediating proteolytic processing of various signaling molecules. ADAMs are transmembrane metalloenzymes that facilitate the extracellular domain shedding of membrane-anchored proteins, cytokines, growth factors, ligands, and their receptors and therefore modulate their biological functions. ADAM-TSs are secretory, and soluble extracellular proteinases that mediate the cleavage of non-fibrillar extracellular matrix proteins. ADAMs and ADAM-TSs possess pro-domain, metalloproteinase, disintegrin, and cysteine-rich domains in common, but ADAM-TSs have characteristic thrombospondin motifs instead of the transmembrane domain. Most ADAMs and ADAM-TSs are activated by cleavage of pro-domain via pro-protein convertases at their N-terminus, hence directing them to various signaling pathways. In this article, we are discussing not only the structure and regulation of ADAMs and ADAM-TSs, but also the importance of these metalloproteinases in various human pathophysiological conditions like cardiovascular diseases, colorectal cancer, autoinflammatory diseases (sepsis/rheumatoid arthritis), Alzheimer's disease, proliferative retinopathies, and infectious diseases. Therefore, based on the emerging role of ADAMs and ADAM-TSs in various human pathologies, as summarized in this review, these metalloproteases can be considered as critical therapeutic targets and diagnostic biomarkers.

Immune-vascular mural cell interactions: consequences for immune cell trafficking, cerebral blood flow, and the blood-brain barrier

Brain barriers are crucial sites for cerebral energy supply, waste removal, immune cell migration, and solute exchange, all of which maintain an appropriate environment for neuronal activity. At the capillary level, where the largest area of brain-vascular interface occurs, pericytes adjust cerebral blood flow (CBF) by regulating capillary diameter and maintain the blood-brain barrier (BBB) by suppressing endothelial cell (EC) transcytosis and inducing tight junction expression between ECs. Pericytes also limit the infiltration of circulating leukocytes into the brain where resident microglia confine brain injury and provide the first line of defence against invading pathogens. Brain "waste" is cleared across the BBB into the blood, phagocytosed by microglia and astrocytes, or removed by the flow of cerebrospinal fluid (CSF) through perivascular routes-a process driven by respiratory motion and the pulsation of the heart, arteriolar smooth muscle, and possibly pericytes. "Dirty" CSF exits the brain and is probably drained around olfactory nerve rootlets and via the dural meningeal lymphatic vessels and possibly the skull bone marrow. The brain is widely regarded as an immune-privileged organ because it is accessible to few antigen-primed leukocytes. Leukocytes enter the brain via the meninges, the BBB, and the blood-CSF barrier. Advances in genetic and imaging tools have revealed that neurological diseases significantly alter immune-brain barrier interactions in at least three ways: (1) the brain's immune-privileged status is compromised when pericytes are lost or lymphatic vessels are dysregulated; (2) immune cells release vasoactive molecules to regulate CBF, modulate arteriole stiffness, and can plug and eliminate capillaries which impairs CBF and possibly waste clearance; and (3) immune-vascular interactions can make the BBB leaky via multiple mechanisms, thus aggravating the influx of undesirable substances and cells. Here, we review developments in these three areas and briefly discuss potential therapeutic avenues for restoring brain barrier functions.

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

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

Scavenger receptors in host defense: from functional aspects to mode of action

Scavenger receptors belong to a superfamily of proteins that are structurally heterogeneous and encompass the miscellaneous group of transmembrane proteins and soluble secretory extracellular domain. They are functionally diverse as they are involved in various disorders and biological pathways and their major function in innate immunity and homeostasis. Numerous scavenger receptors have been discovered so far and are apportioned in various classes (A-L). Scavenger receptors are documented as pattern recognition receptors and known to act in coordination with other co-receptors such as Toll-like receptors in generating the immune responses against a repertoire of ligands such as microbial pathogens, non-self, intracellular and modified self-molecules through various diverse mechanisms like adhesion, endocytosis and phagocytosis etc. Unlike, most of the scavenger receptors discussed below have both membrane and soluble forms that participate in scavenging; the role of a potential scavenging receptor Angiotensin-Converting Enzyme-2 has also been discussed whereby only its soluble form might participate in preventing the pathogen entry and replication, unlike its membrane-bound form. This review majorly gives an insight on the functional aspect of scavenger receptors in host defence and describes their mode of action extensively in various immune pathways involved with each receptor type. Video abstract.

SFRP1 modulates astrocyte-to-microglia crosstalk in acute and chronic neuroinflammation

Neuroinflammation is a common feature of many neurodegenerative diseases. It fosters a dysfunctional neuron-microglia-astrocyte crosstalk that, in turn, maintains microglial cells in a perniciously reactive state that often enhances neuronal damage. The molecular components that mediate this critical communication are not fully explored. Here, we show that secreted frizzled-related protein 1 (SFRP1), a multifunctional regulator of cell-to-cell communication, is part of the cellular crosstalk underlying neuroinflammation. In mouse models of acute and chronic neuroinflammation, SFRP1, largely astrocyte-derived, promotes and sustains microglial activation, and thus a chronic inflammatory state. SFRP1 promotes the upregulation of components of the hypoxia-induced factor-dependent inflammatory pathway and, to a lower extent, of those downstream of the nuclear factor-kappa B. We thus propose that SFRP1 acts as an astrocyte-to-microglia amplifier of neuroinflammation, representing a potential valuable therapeutic target for counteracting the harmful effect of chronic inflammation in several neurodegenerative diseases.

Key metalloproteinase-mediated pathways in the kidney

Matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs) belong to the metzincin family of zinc-containing multidomain molecules, and can act as soluble or membrane-bound proteases. These enzymes inactivate or activate other soluble or membrane-expressed mediator molecules, which enables them to control developmental processes, tissue remodelling, inflammatory responses and proliferative signalling pathways. The dysregulation of MMPs and ADAMs has long been recognized in acute kidney injury and in chronic kidney disease, and genetic targeting of selected MMPs and ADAMs in different mouse models of kidney disease showed that they can have detrimental and protective roles. In particular, MMP-2, MMP-7, MMP-9, ADAM10 and ADAM17 have been shown to have a mainly profibrotic effect and might therefore represent therapeutic targets. Each of these proteases has been associated with a different profibrotic pathway that involves tissue remodelling, Wnt-β-catenin signalling, stem cell factor-c-kit signalling, IL-6 trans-signalling or epidermal growth factor receptor (EGFR) signalling. Broad-spectrum metalloproteinase inhibitors have been used to treat fibrotic kidney diseases experimentally but more targeted approaches have since been developed, including inhibitory antibodies, to avoid the toxic side effects initially observed with broad-spectrum inhibitors. These advances not only provide a solid foundation for additional preclinical studies but also encourage further translation into clinical research.

Regulated Intramembrane Proteolysis of ACE2: A Potential Mechanism Contributing to COVID-19 Pathogenesis?

Since being identified as a key receptor for SARS-CoV-2, Angiotensin converting enzyme 2 (ACE2) has been studied as one of the potential targets for the development of preventative and/or treatment options. Tissue expression of ACE2 and the amino acids interacting with the spike protein of SARS-CoV-2 have been mapped. Furthermore, the recombinant soluble extracellular domain of ACE2 is already in phase 2 trials as a treatment for SARS-CoV-2 infection. Most studies have continued to focus on the ACE2 extracellular domain, which is known to play key roles in the renin angiotensin system and in amino acid uptake. However, few also found ACE2 to have an immune-modulatory function and its intracellular tail may be one of the signaling molecules in regulating cellular activation. The implication of its immune-modulatory role in preventing the cytokine-storm, observed in severe COVID-19 disease outcomes requires further investigation. This review focuses on the regulated proteolytic cleavage of ACE2 upon binding to inducer(s), such as the spike protein of SARS-CoV, the potential of cleaved ACE2 intracellular subdomain in regulating cellular function, and the ACE2's immune-modulatory function. This knowledge is critical for targeting ACE2 levels for developing prophylactic treatment or preventative measures in SARS-CoV infections.

ADAM10-Mediated Ectodomain Shedding Is an Essential Driver of Podocyte Damage

BACKGROUND

Podocytes embrace the glomerular capillaries with foot processes, which are interconnected by a specialized adherens junction to ultimately form the filtration barrier. Altered adhesion and loss are common features of podocyte injury, which could be mediated by shedding of cell-adhesion molecules through the regulated activity of cell surface-expressed proteases. A Disintegrin and Metalloproteinase 10 (ADAM10) is such a protease known to mediate ectodomain shedding of adhesion molecules, among others. Here we evaluate the involvement of ADAM10 in the process of antibody-induced podocyte injury.

METHODS

Membrane proteomics, immunoblotting, high-resolution microscopy, and immunogold electron microscopy were used to analyze human and murine podocyte ADAM10 expression in health and kidney injury. The functionality of ADAM10 ectodomain shedding for podocyte development and injury was analyzed, in vitro and in vivo, in the anti-podocyte nephritis (APN) model in podocyte-specific, ADAM10-deficient mice.

RESULTS

ADAM10 is selectively localized at foot processes of murine podocytes and its expression is dispensable for podocyte development. Podocyte ADAM10 expression is induced in the setting of antibody-mediated injury in humans and mice. Podocyte ADAM10 deficiency attenuates the clinical course of APN and preserves the morphologic integrity of podocytes, despite subepithelial immune-deposit formation. Functionally, ADAM10-related ectodomain shedding results in cleavage of the cell-adhesion proteins N- and P-cadherin, thus decreasing their injury-related surface levels. This favors podocyte loss and the activation of downstream signaling events through the Wnt signaling pathway in an ADAM10-dependent manner.

CONCLUSIONS

ADAM10-mediated ectodomain shedding of injury-related cadherins drives podocyte injury.

Shedding light on the role of CX3CR1 in the pathogenesis of schizophrenia

Schizophrenia has a complex and heterogeneous molecular and clinical picture. Over the years of research on this disease, many factors have been suggested to contribute to its pathogenesis. Recently, the inflammatory processes have gained particular interest in the context of schizophrenia due to the increasing evidence from epidemiological, clinical and experimental studies. Within the immunological component, special attention has been brought to chemokines and their receptors. Among them, CX3C chemokine receptor 1 (CX3CR1), which belongs to the family of seven-transmembrane G protein-coupled receptors, and its cognate ligand (CX3CL1) constitute a unique system in the central nervous system. In the view of regulation of the brain homeostasis through immune response, as well as control of microglia reactivity, the CX3CL1–CX3CR1 system may represent an attractive target for further research and schizophrenia treatment. In the review, we described the general characteristics of the CX3CL1–CX3CR1 axis and the involvement of this signaling pathway in the physiological processes whose disruptions are reported to participate in mechanisms underlying schizophrenia. Furthermore, based on the available clinical and experimental data, we presented a guide to understanding the implication of the CX3CL1–CX3CR1 dysfunctions in the course of schizophrenia.

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.

Modulation of microglia activation and Alzheimer's disease: CX3 chemokine ligand 1/CX3CR and P2X7R signaling

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive deficits. Two hallmarks of AD that cause chronic inflammation and lead to neuronal dysfunction and damage are tau tangles and amyloid plaques. Microglial cells, the primary immune cells of the central nervous system, maintain a homeostatic active/inactive state via a bidirectional, dynamic communication with neurons. Several studies have revealed that dysregulated microglial activation leads to AD pathology. Therefore, we reviewed the relationship between AD and two important signaling complexes, CX3 chemokine ligand 1 (CX3CL1)/CX3CR1 and ATP/P2X₇R, that play critical roles in the regulation of microglial activation. CX3CL1/CX3CR1 is one important signaling which controls the microglia function. Altering this pathway can have opposite effects on amyloid and tau pathology in AD. Another important molecule is P2X₇R which involves in the activation of microglia. Over activation of P2X₇R is evident in AD pathogenesis. In this review, we discuss influence of the two signaling pathways at different stages of AD pathology as well as the drug candidates that can modulate CX3CL1/CX3CR1 and ATP/P2X₇R.

Aberrant Methylation of Tumour Suppressor Gene ADAM12 in Chronic Lympocytic Leukemia Patients: Application of Methylation Specific-PCR Technique

Objective:

Chronic Lymphocytic Leukemia (CLL) is a common leukemia among Caucasians but rare in Asians population. We postulated that aberrant methylation either hypermethylation or partial methylation might be one of the silencing mechanisms that inactivates the tumour suppressor genes in CLL. This study aimed to compare the methylation status of tumour suppressor gene, ADAM12, among CLL patients and normal individuals. We also evaluated the association between methylation of ADAM12 and clinical and demographic characteristics of the participants.

Methods:

A total of 25 CLL patients and 25 normal individuals were recruited in this study. The methylation status of ADAM12 was determined using Methylation-Specific PCR (MSP); whereas, DNA sequencing method was applied for validation of the MSP results.

Results:

Among CLL patients, 12 (48%) were partially methylated and 13 (52%) were unmethylated. Meanwhile, 5 (20%) and 20 (80.6%) of healthy individuals were partially methylated and unmethylated, respectively. There was a statistically significant association between the status of methylation at ADAM12 and the presence of CLL (p=0.037).

Conclusion:

The aberrant methylation of ADAM12 found in this study using MSP assay may provide new exposure to CLL that may improve the gaps involved in genetic epigenetic study in CLL.

The metalloproteinase ADAM10 requires its activity to sustain surface expression

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

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.

Proteolytic chemokine cleavage as a regulator of lymphocytic infiltration in solid tumors

In the past decade, immune-based therapies such as monoclonal antibodies against tumor epitopes or immune checkpoint inhibitors have become an integral part of contemporary cancer treatment in many entities. However, a fundamental prerequisite for the success of such therapies is a sufficient trafficking of tumor-infiltrating lymphocytes into the tumor microenvironment. This infiltration is facilitated by chemokines, a group of about 50 small proteins capable of chemotactically guiding leukocytes. Proteolytic inactivation of chemokines leading to an impaired infiltration of immune effector cells appears to be an efficient immune escape mechanism of solid cancers.

The CXCR3 and CX3CR1 chemokine receptor ligands CXCL9-11 and CX3CL1, respectively, are mainly responsible for the tumor-suppressive lymphocytic infiltration into the tumor micromilieu. Their structure explains the biochemical basis of their proteolytic cleavage, while in vivo data from mouse models and patient samples shed light on the corresponding processes in cancer. The emerging roles of proteases, e.g., matrix metalloproteinases, cathepsins, and dipeptidyl peptidase 4, in chemokine inactivation define new resistance mechanisms against immunotherapies and identify attractive new targets to enhance immune intervention in cancer.

Regulation of CX3CL1 Expression in Human First-Trimester Decidual Cells: Implications for Preeclampsia

C-X3-C motif ligand 1 (CX3CL1) mediates migration, survival, and adhesion of natural killer (NK) cells, monocytes, and T-cells to endothelial/epithelial cells. Aberrant numbers and/or activation of these decidual immune cells elicit preeclampsia development. Decidual macrophages and NK cells are critical for implantation, while macrophage-derived tumor necrosis factor-α (TNF-α), interleukin-1 β (IL-1β), and NK cell-derived interferon-γ (IFN-γ) are associated with preeclampsia development. Thus, serum and decidual levels of CX3CL1 from first-trimester pregnancy and preeclampsia-complicated term pregnancy were examined by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry, respectively. The effects of incubating primary human first-trimester decidual cells (FTDCs) with estradiol + medroxyprogesterone acetate + either IL-1β or TNF-α and/or IFN-γ on CX3CL1 expression were also assessed by quantitative reverse transcription-polymerase chain reaction and ELISA. The inhibition of each signaling pathway with each kinase and nuclear factor κB (NFκB) inhibitors was evaluated by ELISA. Chemotaxis of CD56brightCD16- NK cells by various concentrations of CX3CL1 was evaluated. C-X3-C motif ligand 1 is expressed by both cytotrophoblasts and decidual cells in first-trimester decidua. C-X3-C motif ligand 1 expression is increased in term decidua but unchanged in first-trimester and term serum of patients with preeclampsia. Interferon-gamma and either IL-1β or TNF-α synergistically upregulated CX3CL1 expression in FTDCs. Coincubation with IL-1β or TNF-α or IFN-γ, mitogen-activated protein kinase kinase 1 and 2 (MEK1/2), c-JUN N-terminal kinase (JNK), and NFκB inhibitors suppressed CX3CL1 production. C-X3-C motif ligand 1 elicited concentration-dependent enhancement of CD56brightCD16- NK cell migration. In conclusion, the current study suggests that decidual cell-secreted CX3CL1 is involved in the later development of preeclampsia, whereas circulating CX3CL1 levels do not predict preeclampsia. Mitogen-activated protein kinase kinase 1 and 2, JNK, and NFκB signaling mediate IL-1β-, TNF-α-, and IFN-γ-induced CX3CL1 production by FTDCs.

Microglia-neuron interactions in the models of neuropathic pain

Chronic pain is a debilitating condition that often emerges as a clinical symptom of inflammatory diseases. It has therefore been widely accepted that the immune system critically contributes to the pathology of chronic pain. Microglia, a type of immune cell in the central nervous system, has attracted researchers' attention because in rodent models of neuropathic pain that develop strong mechanical and thermal hypersensitivity, histologically activated microglia are seen in the dorsal horn of spinal cord. Several kinds of cytokines are generated by damaged peripheral neurons and contribute to microglial activation at the distal site of the injury where damaged neurons send their projections. Microglia are known as key players in the surveillance of the local environment in the central nervous system and have a significant role of circuit remodeling by physical contact to synapses. Key molecules for the pathology of neuropathic pain exist in the activated microglia, but the factors driving pain-inducible microglial activation remain unclear. Therefore, to find the key molecules inducing activation of spinal microglia and to figure out the precise mechanism of how microglia modulate neuronal circuits in the spinal cord to form chronic pain state is a critical step for developing effective treatment of neuropathic pain.

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.

Enhanced expression of TACE contributes to elevated levels of sVCAM-1 in endometriosis

STUDY QUESTION

Are increased sVCAM-1 and sICAM-1 levels associated with tumor necrosis factor-alpha-converting enzyme (TACE) activity in endometriosis?

SUMMARY ANSWER

Here we provide the first functional evidence that induced TACE activity in human endometriotic epithelial cells is at least in part responsible for the enhanced release of sVCAM-1 from these cells.

WHAT IS KNOWN ALREADY

We and others have shown that serum-soluble (s)VCAM-1 levels are significantly higher in women with endometriosis, compared to disease-free controls. Experimental evidence exists suggesting a role of sICAM-1 and sVCAM-1 in the pathogenesis of endometriosis. TACE was identified as the protease responsible for phorbol 12-myristate 13-acetate (PMA)-induced VCAM-1 release in murine endothelial cells. Additionally, it has recently been shown that TACE is upregulated in the endometrial luminal epithelium of the mid-secretory phase in infertile women.

STUDY DESIGN, SIZE, DURATION

This study was conducted at the Tertiary Endometriosis Referral Center of the Medical University of Vienna. Samples from a total number of 97 women were collected between July 2013 and September 2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After complete surgical exploration of the abdominopelvic cavity, 49 women with histologically proven endometriosis and 48 endometriosis-free control women were enrolled. Each participating woman contributed only one sample of eutopic endometrium and normal peritoneum, and some of the women with endometriosis contributed samples of diverse types of endometriotic lesions (in total 52 ectopic samples). Among the 49 women with endometriosis, 36 matched samples of endometriotic lesions and corresponding eutopic endometrium were collected. In order to detect sVCAM-1 and TACE protein by ELISA, peritoneal fluid (PF) samples were collected from 44 cases and 32 controls during surgery. Expression of TACE mRNA was analyzed by qRT-PCR in 111 endometrium tissue samples (28 eutopic control samples, 33 eutopic samples from women with endometriosis, 50 ectopic samples from lesions) and 37 healthy peritoneum samples. Immunohistochemistry was performed in 123 tissue samples (39 eutopic control samples, 42 eutopic samples from women with endometriosis, 42 ectopic samples from lesions) and the relation between tissue TACE protein levels and sVCAM-1 secretion was examined. PMA-induced sVCAM-1 release, and TACE- and VCAM-1-transcripts or proteins were measured in an immortalized endometriotic epithelial cell line (11Z) pre-incubated either with TACE inhibitors or following TACE siRNA knockdown.

MAIN RESULTS AND THE ROLE OF CHANCE

Here, we demonstrate that TACE protein is overexpressed in epithelium of tissue samples of both eutopic endometrium and ectopic lesions of women with endometriosis compared to disease-free controls (P < 0.001 both) and that the overexpression of the protein in the lesions is due to activation of TACE gene transcription (P < 0.001). Moreover, epithelial TACE protein was significantly higher in ectopic samples than in corresponding eutopic tissue of women with the disease (P < 0.001). High endometrial tissue TACE protein expression correlated with higher serum sVCAM-1 levels (P < 0.05) but not with sICAM-1 levels. Inhibition of TACE either by TACE inhibitors or by TACE siRNA knockdown resulted in decreased PMA-induced shedding of sVCAM-1 in vitro (P < 0.005 or P < 0.01, respectively), but the TACE inhibitors did not affect transcription of TACE or VCAM-1. Additionally, we observed an upregulation of TACE in proliferative endometrial epithelium of infertile (P < 0.005), compared to fertile women. TACE was increased in infertile women with endometriosis (P = 0.051) but not in infertile women without endometriosis.

LIMITATIONS, REASONS FOR CAUTION

Albeit well characterized, our control population included women with other gynecologic diseases, which may have impacted the levels of sVCAM-1 and tissue TACE expression levels, e.g. benign ovarian cysts or uterine fibroids. Thus, the results of our analysis have to be interpreted carefully and in the context of the current experimental settings.

WIDER IMPLICATIONS OF THE FINDINGS

The dysregulation of TACE substrate shedding represents a promising yet relatively unexplored area of endometriosis progression and could serve as a basis for the development of new treatments of the disease.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by the Ingrid Flick Foundation. The authors have no competing interests to declare.

More Than Just a Removal Service: Scavenger Receptors in Leukocyte Trafficking

Scavenger receptors are a highly diverse superfamily of proteins which are grouped by their inherent ability to bind and internalize a wide array of structurally diverse ligands which can be either endogenous or exogenous in nature. Consequently, scavenger receptors are known to play important roles in host homeostasis, with common endogenous ligands including apoptotic cells, and modified low density lipoproteins (LDLs); additionally, scavenger receptors are key regulators of inflammatory diseases, such as atherosclerosis. Also, as a consequence of their affinity for a wide range of microbial products, their role in innate immunity is also being increasingly studied. However, in this review, a secondary function of a number of endothelial-expressed scavenger receptors is discussed. There is increasing evidence that some endothelial-expressed scavenger receptors are able to directly bind leukocyte-expressed ligands and subsequently act as adhesion molecules in the trafficking of leukocytes in lymphatic and vascular tissues. Here, we cover the current literature on this alternative role for endothelial-expressed scavenger receptors and also speculate on their therapeutic potential.

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.

Human Umbilical Cord Blood Serum-derived α-Secretase: Functional Testing in Alzheimer's Disease Mouse Models

Alzheimer’s disease (AD) is an age-related disorder that affects cognition. Our previous studies showed that the neuroprotective fragment of amyloid procurer protein (APP) metabolite, soluble APPα (sAPPα), interferes with β-site APP-cleaving enzyme 1 (BACE1, β-secretase) cleavage and reduces amyloid-β (Aβ) generation. In an attempt to identify approaches to restore sAPPα levels, we found that human cord blood serum (CBS) significantly promotes sAPPα production compared with adult blood serum (ABS) and aged blood serum (AgBS) in Chinese hamster ovary cells stably expressing wild-type human APP. Interestingly, CBS selectively mediated the α-secretase cleavage of human neuron-specific recombinant APP₆₉₅ in a cell-free system independent of tumor necrosis factor-α converting enzyme (TACE; a disintegrin and metalloproteinase domain-containing protein 17 [ADAM17]) and ADAM. Subsequently, using 3-step chromatographic separation techniques (i.e., diethylaminoethanol, size-exclusion, and ion-exchange chromatography), we purified and ultimately identified a CBS-specific fraction with enhanced α-secretase catalytic activity (termed αCBSF) and found that αCBSF has more than 3,000-fold increased α-secretase catalytic activity compared with the original pooled CBS. Furthermore, intracerebroventricular injection of αCBSF markedly increased cerebral sAPPα levels together with significant decreases in cerebral Aβ production and abnormal tau (Thr²³¹) phosphorylation compared with the AgBS fraction with enhanced α-secretase activity (AgBSF) treatment in triple transgenic Alzheimer’s disease (3xTg-AD) mice. Moreover, AgBSF administered intraperitoneally to transgenic mice with five familial Alzheimer’s disease mutations (5XFAD) via an osmotic mini pump for 6 weeks (wk) ameliorated β-amyloid plaques and reversed cognitive impairment measures. Together, our results propose the necessity for further study aimed at identification and characterization of α-secretase in CBS for novel and effective AD therapy.

Allergenic proteases cleave the chemokine CX3CL1 directly from the surface of airway epithelium and augment the effect of rhinovirus

CX3CL1 has been implicated in allergen-induced airway CD4⁺ T-lymphocyte recruitment in asthma. As epidemiological evidence supports a viral infection-allergen synergy in asthma exacerbations, we postulated that rhinovirus (RV) infection in the presence of allergen augments epithelial CX3CL1 release. Fully differentiated primary bronchial epithelial cultures were pretreated apically with house dust mite (HDM) extract and infected with rhinovirus-16 (RV16). CX3CL1 was measured by enzyme-linked immunosorbent assay and western blotting, and shedding mechanisms assessed using inhibitors, protease-activated receptor-2 (PAR-2) agonist, and recombinant CX3CL1-expressing HEK293T cells. Basolateral CX3CL1 release was unaffected by HDM but stimulated by RV16; inhibition by fluticasone or GM6001 implicated nuclear factor-κB and ADAM (A Disintegrin and Metalloproteinase) sheddases. Conversely, apical CX3CL1 shedding was stimulated by HDM and augmented by RV16. Although fluticasone or GM6001 reduced RV16+HDM-induced apical CX3CL1 release, heat inactivation or cysteine protease inhibition completely blocked CX3CL1 shedding. The HDM effect was via enzymatic cleavage of CX3CL1, not PAR-2 activation, yielding a product mitogenic for smooth muscle cells. Extracts of Alternaria fungus caused similar CX3CL1 shedding. We have identified a novel mechanism whereby allergenic proteases cleave CX3CL1 from the apical epithelial surface to yield a biologically active product. RV16 infection augmented HDM-induced CX3CL1 shedding-this may contribute to synergy between allergen exposure and RV infection in triggering asthma exacerbations and airway remodeling.

Platelets from flowing blood attach to the inflammatory chemokine CXCL16 expressed in the endothelium of the human vessel wall

Endothelial chemokine CXC motif ligand 16 (CXCL16) expression is associated with atherosclerosis, while platelets, particularly those attaching to atherosclerotic plaque, contribute to all stages of athero-sclerotic disease. This investigation was designed to examine the role of CXCL16 in capturing platelets from flowing blood. CXCL16 was expressed in human atherosclerotic plaques, and lesion severity in human carotid endarterectomy specimens was positively correlated with CXCL16 levels. CXCL16 expression in plaques was co-localised with platelets deposited to the endothelium. Immobilised CXCL16 promoted CXCR6-dependent platelet adhesion to the human vessel wall, endothelial cells and von Willebrand factor during physiologic flow. At low shear, immobilised CXCL16 captured platelets from flowing blood. It also induced irreversible platelet aggregation and a rise in intra-platelet calcium levels. These results demonstrate that endothelial CXCL16’s action on platelets is not only limited to platelet activation, but that immobilised CXCL16 also acts as a potent novel platelet adhesion ligand, inducing platelet adhesion to the human vessel wall.

Regulated intramembrane proteolysis: emergent role in cell signalling pathways

Receptor signalling events including those initiated following activation of cytokine and growth factor receptors and the well-characterised death receptors (tumour necrosis factor receptor, type 1, FasR and TRAIL-R1/2) are initiated at the cell surface through the recruitment and formation of intracellular multiprotein signalling complexes that activate divergent signalling pathways. Over the past decade, research studies reveal that many of these receptor-initiated signalling events involve the sequential proteolysis of specific receptors by membrane-bound proteases and the γ-secretase protease complexes. Proteolysis enables the liberation of soluble receptor ectodomains and the generation of intracellular receptor cytoplasmic domain fragments. The combined and sequential enzymatic activity has been defined as regulated intramembrane proteolysis and is now a fundamental signal transduction process involved in the termination or propagation of receptor signalling events. In this review, we discuss emerging evidence for a role of the γ-secretase protease complexes and regulated intramembrane proteolysis in cell- and immune-signalling pathways.

Chemokines in neuron-glial cell interaction and pathogenesis of neuropathic pain

Neuropathic pain resulting from damage or dysfunction of the nervous system is a highly debilitating chronic pain state and is often resistant to currently available treatments. It has become clear that neuroinflammation, mainly mediated by proinflammatory cytokines and chemokines, plays an important role in the establishment and maintenance of neuropathic pain. Chemokines were originally identified as regulators of peripheral immune cell trafficking and were also expressed in neurons and glial cells in the central nervous system. In recent years, accumulating studies have revealed the expression, distribution and function of chemokines in the spinal cord under chronic pain conditions. In this review, we provide evidence showing that several chemokines are upregulated after peripheral nerve injury and contribute to the pathogenesis of neuropathic pain via different forms of neuron-glia interaction in the spinal cord. First, chemokine CX3CL1 is expressed in primary afferents and spinal neurons and induces microglial activation via its microglial receptor CX3CR1 (neuron-to-microglia signaling). Second, CCL2 and CXCL1 are expressed in spinal astrocytes and act on CCR2 and CXCR2 in spinal neurons to increase excitatory synaptic transmission (astrocyte-to-neuron signaling). Third, we recently identified that CXCL13 is highly upregulated in spinal neurons after spinal nerve ligation and induces spinal astrocyte activation via receptor CXCR5 (neuron-to-astrocyte signaling). Strategies that target chemokine-mediated neuron-glia interactions may lead to novel therapies for the treatment of neuropathic pain.

Scissor sisters: regulation of ADAM10 by the TspanC8 tetraspanins

A disintegrin and metalloprotease 10 (ADAM10) is a ubiquitously expressed transmembrane protein which is essential for embryonic development through activation of Notch proteins. ADAM10 regulates over 40 other transmembrane proteins and acts as a ‘molecular scissor’ by removing their extracellular regions. ADAM10 is also a receptor for α-toxin, a major virulence factor of Staphylococcus aureus. Owing to the importance of its substrates, ADAM10 is a potential therapeutic target for cancer, neurodegenerative diseases such as Alzheimer's and prion diseases, bacterial infection and inflammatory diseases such as heart attack, stroke and asthma. However, targetting ADAM10 is likely to result in toxic side effects. The tetraspanins are a superfamily of 33 four-transmembrane proteins in mammals which interact with and regulate specific partner proteins within membrane nanodomains. Tetraspanins appear to have a cone-shaped structure with a cholesterol-binding cavity, which may enable tetraspanins to undergo cholesterol-regulated conformational change. An emerging paradigm for tetraspanin function is the regulation of ADAM10 by the TspanC8 subgroup of tetraspanins, namely Tspan5, 10, 14, 15, 17 and 33. This review will describe how TspanC8s are required for ADAM10 trafficking from the endoplasmic reticulum and its enzymatic maturation. Moreover, different TspanC8s localise ADAM10 to different subcellular localisations and may cause ADAM10 to adopt distinct conformations and cleavage of distinct substrates. We propose that ADAM10 should now be regarded as six different scissor proteins depending on the interacting TspanC8. Therapeutic targetting of specific TspanC8/ADAM10 complexes could allow ADAM10 targetting in a cell type- or substrate-specific manner, to treat certain diseases while minimising toxicity.

ADAM10-Interacting Tetraspanins Tspan5 and Tspan17 Regulate VE-Cadherin Expression and Promote T Lymphocyte Transmigration

The recruitment of blood leukocytes across the endothelium to sites of tissue infection is central to inflammation, but also promotes chronic inflammatory diseases. A disintegrin and metalloproteinase 10 (ADAM10) is a ubiquitous transmembrane molecular scissor that is implicated in leukocyte transmigration by proteolytically cleaving its endothelial substrates. These include VE-cadherin, a homotypic adhesion molecule that regulates endothelial barrier function, and transmembrane chemokines CX3CL1 and CXCL16, which have receptors on leukocytes. However, a definitive role for endothelial ADAM10 in transmigration of freshly isolated primary leukocytes under flow has not been demonstrated, and the relative importance of distinct ADAM10 substrates is unknown. Emerging evidence suggests that ADAM10 can be regarded as six different molecular scissors with different substrate specificities, depending on which of six TspanC8 tetraspanins it is associated with, but TspanC8s remain unstudied in leukocyte transmigration. In the current study, ADAM10 knockdown on primary HUVECs was found to impair transmigration of freshly isolated human peripheral blood T lymphocytes, but not neutrophils or B lymphocytes, in an in vitro flow assay. This impairment was due to delayed transmigration rather than a complete block, and was overcome in the presence of neutrophils. Transmigration of purified lymphocytes was dependent on ADAM10 regulation of VE-cadherin, but not CX3CL1 and CXCL16. Tspan5 and Tspan17, the two most closely related TspanC8s by sequence, were the only TspanC8s that regulated VE-cadherin expression and were required for lymphocyte transmigration. Therefore endothelial Tspan5- and Tspan17-ADAM10 complexes may regulate inflammation by maintaining normal VE-cadherin expression and promoting T lymphocyte transmigration.

The metalloproteinase ADAM8 promotes leukocyte recruitment in vitro and in acute lung inflammation

Alveolar leukocyte recruitment is a hallmark of acute lung inflammation and involves transmigration of leukocytes through endothelial and epithelial layers. The disintegrin and metalloproteinase (ADAM) 8 is expressed on human isolated leukocytic cells and can be further upregulated on cultured endothelial and epithelial cells by proinflammatory cytokines. By shRNA-mediated knockdown we show that leukocytic ADAM8 is required on monocytic THP-1 cells for chemokine-induced chemotaxis as well as transendothelial and transepithelial migration. Furthermore, ADAM8 promotes α_L-integrin upregulation and THP-1 cell adhesion to endothelial cells. On endothelial cells ADAM8 enhances transendothelial migration and increases cytokine-induced permeability. On epithelial cells the protease facilitates migration in a wound closure assay but does not affect transepithelial leukocyte migration. Blood leukocytes and bone marrow-derived macrophages (BMDM) from ADAM8-deficient mice show suppressed chemotactic response. Intranasal application of LPS to mice is accompanied with ADAM8 upregulation in the lung. In this model of acute lung inflammation ADAM8-deficient mice are protected against leukocyte infiltration. Finally, transfer experiments of BMDM in mice indicate that ADAM8 exerts a promigratory function predominantly on leukocytes. Our study provides in vitro and in vivo evidence that ADAM8 on leukocytes holds a proinflammatory function in acute lung inflammation by promoting alveolar leukocyte recruitment.

The therapeutic potential of targeting chemokine signalling in the treatment of chronic pain

Chronic pain is a distressing condition, which is experienced even when the painful stimulus, whether surgery or disease related, has subsided. Current treatments for chronic pain show limited efficacy and come with a host of undesirable side-effects, and thus there is a need for new, more effective therapies to be developed. The mechanisms underlying chronic pain are not fully understood at present, although pre-clinical models have facilitated the progress of this understanding considerably in the last decade. The mechanisms underlying chronic pain were initially thought to be neurocentric. However, we now appreciate that non-neuronal cells play a significant role in nociceptive signalling through their communication with neurons. One of the major signalling pathways, which mediates neuron/non-neuronal communication, is chemokine signalling. In this review, we discuss selected chemokines that have been reported to play a pivotal role in the mechanisms underlying chronic pain in a variety of pre-clinical models. Approaches that target each of the chemokines discussed in this review come with their advantages and disadvantages; however, the inhibition of chemokine actions is emerging as an innovative therapeutic strategy, which is now reaching the clinic, with the chemokine Fractalkine and its CX3 CR1 receptor leading the way. This article is part of the special article series "Pain".

Characterization of the catalytic properties of the membrane-anchored metalloproteinase ADAM9 in cell-based assays

ADAM9 (A Disintegrin And Metalloprotease 9) is a membrane-anchored metalloproteinase that has been implicated in pathological retinal neovascularization and in tumor progression. ADAM9 has constitutive catalytic activity in both biochemical and cell-based assays and can cleave several membrane proteins, including epidermal growth factor and Ephrin receptor B4; yet little is currently known about the catalytic properties of ADAM9 and its post-translational regulation and inhibitor profile in cell-based assays. To address this question, we monitored processing of the membrane-anchored Ephrin receptor B4 (EphB4) by co-expressing ADAM9, with the catalytically inactive ADAM9 E > A mutant serving as a negative control. We found that ADAM9-dependent shedding of EphB4 was not stimulated by three commonly employed activators of ADAM-dependent ectodomain shedding: phorbol esters, pervanadate or calcium ionophores. With respect to the inhibitor profile, we found that ADAM9 was inhibited by the hydroxamate-based metalloprotease inhibitors marimastat, TAPI-2, BB94, GM6001 and GW280264X, and by 10 nM of the tissue inhibitor of metalloproteinases (TIMP)-3, but not by up to 20 nM of TIMP-1 or -2. Additionally, we screened a non-hydroxamate small-molecule library for novel ADAM9 inhibitors and identified four compounds that selectively inhibited ADAM9-dependent proteolysis over ADAM10- or ADAM17-dependent processing. Taken together, the present study provides new information about the molecular fingerprint of ADAM9 in cell-based assays by showing that it is not stimulated by strong activators of ectodomain shedding and by defining a characteristic inhibitor profile. The identification of novel non-hydroxamate inhibitors of ADAM9 could provide the basis for designing more selective compounds that block the contribution of ADAM9 to pathological neovascularization and cancer.

Fine Tuning Cell Migration by a Disintegrin and Metalloproteinases

Cell migration is an instrumental process involved in organ development, tissue homeostasis, and various physiological processes and also in numerous pathologies. Both basic cell migration and migration towards chemotactic stimulus consist of changes in cell polarity and cytoskeletal rearrangement, cell detachment from, invasion through, and reattachment to their neighboring cells, and numerous interactions with the extracellular matrix. The different steps of immune cell, tissue cell, or cancer cell migration are tightly coordinated in time and place by growth factors, cytokines/chemokines, adhesion molecules, and receptors for these ligands. This review describes how a disintegrin and metalloproteinases interfere with several steps of cell migration, either by proteolytic cleavage of such molecules or by functions independent of proteolytic activity.

Allelic Variation in CXCL16 Determines CD3+ T Lymphocyte Susceptibility to Equine Arteritis Virus Infection and Establishment of Long-Term Carrier State in the Stallion

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis (EVA), a respiratory, systemic, and reproductive disease of horses and other equid species. Following natural infection, 10-70% of the infected stallions can become persistently infected and continue to shed EAV in their semen for periods ranging from several months to life. Recently, we reported that some stallions possess a subpopulation(s) of CD3+ T lymphocytes that are susceptible to in vitro EAV infection and that this phenotypic trait is associated with long-term carrier status following exposure to the virus. In contrast, stallions not possessing the CD3+ T lymphocyte susceptible phenotype are at less risk of becoming long-term virus carriers. A genome wide association study (GWAS) using the Illumina Equine SNP50 chip revealed that the ability of EAV to infect CD3+ T lymphocytes and establish long-term carrier status in stallions correlated with a region within equine chromosome 11. Here we identified the gene and mutations responsible for these phenotypes. Specifically, the work implicated three allelic variants of the equine orthologue of CXCL16 (EqCXCL16) that differ by four non-synonymous nucleotide substitutions (XM_00154756; c.715 A → T, c.801 G → C, c.804 T → A/G, c.810 G → A) within exon 1. This resulted in four amino acid changes with EqCXCL16S (XP_001504806.1) having Phe, His, Ile and Lys as compared to EqCXL16R having Tyr, Asp, Phe, and Glu at 40, 49, 50, and 52, respectively. Two alleles (EqCXCL16Sa, EqCXCL16Sb) encoded identical protein products that correlated strongly with long-term EAV persistence in stallions (P<0.000001) and are required for in vitro CD3+ T lymphocyte susceptibility to EAV infection. The third (EqCXCL16R) was associated with in vitro CD3+ T lymphocyte resistance to EAV infection and a significantly lower probability for establishment of the long-term carrier state (viral persistence) in the male reproductive tract. EqCXCL16Sa and EqCXCL16Sb exert a dominant mode of inheritance. Most importantly, the protein isoform EqCXCL16S but not EqCXCL16R can function as an EAV cellular receptor. Although both molecules have equal chemoattractant potential, EqCXCL16S has significantly higher scavenger receptor and adhesion properties compared to EqCXCL16R.

Chemokine Receptor Signaling and the Hallmarks of Cancer

The chemokines are a family of chemotactic cytokines that mediate their activity by acting on seven-transmembrane-spanning G protein-coupled receptors. Both the ability of the chemokines and their receptors to form homo- and heterodimers and the promiscuity of the chemokine-chemokine receptor interaction endow this protein family with enormous signaling plasticity and complexity that are not fully understood at present. Chemokines were initially identified as essential regulators of homeostatic and inflammatory trafficking of innate and adaptive leucocytes from lymphoid organs to tissues. Chemokines also mediate the host response to cancer. Nevertheless, chemokine function in this response is not limited to regulating leucocyte infiltration into the tumor microenvironment. It is now known that chemokines and their receptors influence most-if not all-hallmark processes of cancer; they act on both neoplastic and untransformed cells in the tumor microenvironment, including fibroblasts, endothelial cells (blood and lymphatic), bone marrow-derived stem cells, and, obviously, infiltrating leucocytes. This review begins with an overview of chemokine and chemokine receptor structure, to better define how chemokines affect the proliferation, survival, stemness, and metastatic potential of neoplastic cells. We also examine the main mechanisms by which chemokines regulate tumor angiogenesis and immune cell infiltration, emphasizing the pro- and antitumorigenic activity of this protein superfamily in these interrelated processes.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

Changes in expressions of ADAM9, 10, and 17 as well as α-secretase activity in renal cell carcinoma

BACKGROUND

ADAM9, 10, and 17 are a class of disintegrins and metallproteinases with α-secretase activity. There are conflicting results regarding the role(s) of ADAM9, 10, and 17 in carcinogenesis, and only a few studies have examined their levels and cellular localization in renal cell carcinoma (RCC). Studies examining changes in α-secretase activity in RCC compared to enzymatic activity of the uninvolved kidney are lacking.

METHOD

A cross-sectional study was conducted in 56 patients undergoing radical nephrectomy after the diagnosis of RCC. α-Secretase activity was determined using flourogenic substrate in freshly frozen tumor tissues as well as similarly treated tissues from the neighboring kidney. Immunohistochemical analyses of ADAM9, 10, and 17 were also performed.

RESULTS

α-Secretase activity decreased markedly in all types of RCC as compared to neighboring uninvolved kidney tissue having 5 to 10 times higher levels of α-secretase activity. Although type-dependent variations were observed, tumoral expressions of ADAMs, except for ADAM17, were lower in the tumors compared to that of neighboring tissues, but the changes in α-secretase activity were greater. In RCC tissue, ADAM9 expressions were localized in nuclear and cytoplasmic compartments, whereas ADAM10 and 17 were present predominately in the cytoplasm potentially explaining the markedly decreased enzyme activity. Membranous localization of ADAMs was noted in uninvolved kidney tissue.

CONCLUSIONS

The loss of α-secretase activity observed here in conjunction with previous findings argue against tumorigenic effects of ADAM9, 10, and 17 supporting that increased nuclear and cytoplasmic expression may be an attempt to compensate for loss of function.

A cytoplasmic C-terminal fragment of Syndecan-1 is generated by sequential proteolysis and antagonizes Syndecan-1 dependent lung tumor cell migration

Syndecan-1 is a surface expressed heparan sulphate proteoglycan, which is upregulated by several tumor types and involved in tumor cell migration and metastasis. Syndecan-1 is shed from the cell surface and the remaining transmembrane fragment undergoes intramembrane proteolysis by γ-secretase. We here show that this generates a cytoplasmic C-terminal fragment (cCTF). In epithelial lung tumor A549 cells the endogenously produced cCTF accumulated when its proteasomal degradation was blocked with bortezomib and this accumulation was prevented by γ-secretase inhibition. Overexpression of the cCTF suppressed migration and invasion of A549 cells. This inhibitory effect was only seen when endogenous syndecan-1 was present, but not in syndecan-1 deficient cells. Further, overexpression of syndecan-1 cCTF increased the basal activation of Src kinase, focal adhesion kinase (FAK) and Rho GTPase. This was associated with increased adhesion to fibronectin and collagen G and an increased recruitment of paxillin to focal adhesions. Moreover, lung tumor formation of A549 cells in mice was reduced by overexpression of syndecan-1 cCTF. Finally, delivery of a synthetic peptide corresponding to the syndecan-1 cCTF suppressed A549 cell migration and increased basal phosphorylation of Src and FAK. Our data indicate that the syndecan-1 cCTF antagonizes syndecan-1 dependent tumor cell migration in vitro and in vivo by dysregulating proadhesive signaling pathways and suggest that the cCTF can be used as an inhibitory peptide.

A novel role for β2-microglobulin: a precursor of antibacterial chemokine in respiratory epithelial cells

We analyzed a panel of cationic molecules secreted in the culture medium of human respiratory epithelial cells (REC) upon activation by IL-1β and different pathogen-associated molecular patterns. A 9 kDa fragment derived from β2-microglobulin (B2M) was identified and named shed 9 kDa B2M (sB2M-9). The primary structure of sB2M-9 was revealed to increase its pI value that potentially could play an important role in innate defense. sB2M-9 exhibits antibacterial activity against Gram positive Staphylococcus aureus (SA) but not against Gram negative Klebsiella pneumonia (KP). Upon its binding to SA, sB2M-9 induces clumps, a phenomenon not observed with B2M. Migration of THP-1 monocytes exposed to SA clumps was significantly greater than that to SA without clumps. sB2M-9 binds to SA, more likely as a chemokine, to facilitate THP-1 migration. As a whole, we demonstrated that REC release a novel chemokine with antibacterial activity that is shed from B2M to facilitate THP-1 migration.

Regulation of A disintegrin and metalloproteinase (ADAM) family sheddases ADAM10 and ADAM17: The emerging role of tetraspanins and rhomboids

A disintegrin and metalloprotease (ADAM) 10 and ADAM17 are ubiquitous transmembrane “molecular scissors” which proteolytically cleave, or shed, the extracellular regions of other transmembrane proteins. ADAM10 is essential for development because it cleaves Notch proteins to induce Notch signaling and regulate cell fate decisions. ADAM17 is regarded as a first line of defense against injury and infection, by releasing tumor necrosis factor α (TNFα) to promote inflammation and epidermal growth factor (EGF) receptor ligands to maintain epidermal barrier function. However, the regulation of ADAM10 and ADAM17 trafficking and activation are not fully understood. This review will describe how the TspanC8 subgroup of tetraspanins (Tspan5, 10, 14, 15, 17, and 33) and the iRhom subgroup of protease-inactive rhomboids (iRhom1 and 2) have emerged as important regulators of ADAM10 and ADAM17, respectively. In particular, they are required for the enzymatic maturation and trafficking to the cell surface of the ADAMs, and there is evidence that different TspanC8s and iRhoms target the ADAMs to distinct substrates. The TspanC8s and iRhoms have not been studied functionally on platelets. On these cells, ADAM10 is the principal sheddase for the platelet collagen receptor GPVI, and the regulatory TspanC8s are Tspan14, 15, and 33, as determined from proteomic data. Platelet ADAM17 is the sheddase for the von Willebrand factor (vWF) receptor GPIb, and iRhom2 is the only iRhom that is expressed. Induced shedding of either GPVI or GPIb has therapeutic potential, since inhibition of either receptor is regarded as a promising anti-thrombotic therapy. Targeting of Tspan14, 15, or 33 to activate platelet ADAM10, or iRhom2 to activate ADAM17, may enable such an approach to be realized, without the toxic side effects of activating the ADAMs on every cell in the body.