Metargidin, a membrane-anchored metalloprotease-disintegrin protein with an RGD integrin binding sequence

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.

ADAM15 correlates with prognosis, immune infiltration and apoptosis in hepatocellular carcinoma

ADAM15 is highly expressed in malignant tumors and is correlated with tumor progression. However, the role of ADAM15 in hepatocellular carcinoma (HCC) remains unclear. In the study, our results indicated that ADAM15 was highly expressed in HCC tissues and cells compared with corresponding tissues and liver cells. Overexpression of ADAM15 was linked to poor prognosis, and was an independent risk factor for HCC prognosis. Besides, analysis of immune infiltration indicated that ADAM15 expression was related to tumor infiltrating lymphocytes based on the TIMER, TISIDB and GEPIA databases. Many immune checkpoint gene expression was associated with ADAM15 expression. Functional enrichment analyses indicated that apoptosis, cell adhesion was enriched. ADAM15 knockdown promoted apoptosis and suppressed proliferation, migration and invasion of liver cancer cells. The findings of western blot showed that ADAM15 knockdown reduced the expression of Bcl-2, Vimentin, N-Cadherin and Snail, and elevated the expression of Bax, E-cadherin and ZO-1. However, overexpression of ADAM15 had the opposite results. Collectively, our findings demonstrated that ADAM15 was connected with poor prognosis of HCC patients, and could be considered as a potential biomarker for the diagnosis and treatment of HCC.

Differential roles of protease isoforms in the tumor microenvironment

Alternative splicing of precursor mRNA is a key mediator of gene expression regulation leading to greater diversity of the proteome in complex organisms. Systematic sequencing of the human genome and transcriptome has led to our understanding of how alternative splicing of critical genes leads to multiple pathological conditions such as cancer. For many years, proteases were known only for their roles as proteolytic enzymes, acting to regulate/process proteins associated with diverse cellular functions. However, the differential expression and altered function of various protease isoforms, such as (i) anti-apoptotic activities, (ii) mediating intercellular adhesion, and (iii) modifying the extracellular matrix, are evidence of their specific contribution towards shaping the tumor microenvironment. Revealing the alternative splicing of protease genes and characterization of their protein products/isoforms with distinct and opposing functions creates a platform to understand how protease isoforms contribute to specific cancer hallmarks. Here, in this review, we address cancer-specific isoforms produced by the alternative splicing of proteases and their distinctive roles in the tumor microenvironment.

ADAMTS and ADAM metalloproteinases in osteoarthritis - looking beyond the 'usual suspects'

INTRODUCTION

Matrix metalloproteinases (MMPs) and 'aggrecanase' a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) are well established to play key roles in osteoarthritis (OA) through degradation of extracellular matrix (ECM) type II collagen and aggrecan, and are thus potential targets for development of OA therapies.

OBJECTIVE

This paper aims to provide a comprehensive review of the expression and potential roles of other, lesser-known ADAMTSs and related adamalysins (or a disintegrin and metalloproteinases (ADAMs)) in cartilage, with a view to identifying potentially protective or homeostatic metalloproteinases in the joint and informing consequent selective inhibitor design.

DESIGN

A comprehensive literature search was performed using PubMed terms 'osteoarthritis' and 'ADAMTS' or 'ADAM'.

RESULTS

Several ADAMTSs and ADAMs were identified as having reportedly increased expression in OA. These include enzymes likely to play roles in cartilage matrix anabolism (e.g., the procollagen N-proteinases ADAMTS-2, ADAMTS-3 and ADAMTS-14), chondrocyte differentiation and proliferation (e.g., ADAM9, ADAM10, ADAM12), as well as enzymes contributing to cartilage catabolism (e.g., Cartilage oligomeric protein (COMP)-degrading ADAMTS-7 and ADAMTS-12).

CONCLUSIONS

In addition to the well-characterised MMPs, ADAMTS-4 and ADAMTS-5, many other ADAMTSs and ADAMs are expressed in cartilage and several show significantly altered expression in OA. Studies aimed at elucidating the pathophysiological roles of these enzymes in cartilage will contribute to our understanding of OA pathogenesis and enable design of targeted inhibitors that effectively target metalloproteinase-mediated cartilage degradation while sparing cartilage repair pathways.

miR-720 is a downstream target of an ADAM8-induced ERK signaling cascade that promotes the migratory and invasive phenotype of triple-negative breast cancer cells

BACKGROUND

ADAM8 (a disintegrin and metalloproteinase 8) protein promotes the invasive and metastatic phenotype of triple-negative breast cancer (TNBC) cells. High ADAM8 expression in breast cancer patients is an independent predictor of poor prognosis. Here, we investigated whether ADAM8 regulates specific miRNAs, their roles in aggressive phenotype, and potential use as biomarkers of disease.

METHODS

Microarray analysis was performed on RNA from MDA-MB-231 cells after transient ADAM8 knockdown using TaqMan miRNA cards. Changes in miRNA levels were confirmed using two ADAM8 siRNAs in TNBC cell lines. Kinase inhibitors, β1-integrin antagonist antibody, and different forms of ADAM8 were employed to elucidate the signaling pathway required for miR-720 expression. miR-720 levels were modulated using a specific antagomiR or a mimic, and effects on aggressive phenotype of TNBC cells were determined using Boyden chamber and 3D-Matrigel outgrowth assays. Plasma was isolated from mice before and after implantation of MDA-MB-231 cells and analyzed for miR-720 levels. Serum samples of TNBC patients were evaluated for their ADAM8 and miR-720 levels.

RESULTS

We identified 68 miRNAs differentially regulated upon ADAM8 knockdown, including decreased levels of secreted miR-720. Ectopic overexpression of wild-type ADAM8 or forms that lack metalloproteinase activity similarly induced miR-720 levels. The disintegrin and cysteine-rich domains of ADAM8 were shown to induce miR-720 via activation of a β1-integrin to ERK signaling cascade. Knockdown of miR-720 led to a significant decrease in migratory and invasive abilities of TNBC cells. Conversely, miR-720 overexpression rescued these properties. A profound increase in plasma levels of miR-720 was detected 7 days after TNBC cell inoculation into mouse mammary fat pads when tumors were barely palpable. Concordantly, miR-720 levels were found to be significantly higher in serum samples of TNBC patients with high ADAM8 expression.

CONCLUSIONS

We have shown for the first time that miR-720 is induced by ADAM8 signaling via ERK and plays an essential role in promoting the aggressive phenotype of TNBCs. miR-720 is elevated in serum of patients with ADAM8-high TNBC and, in a group with other miRNAs downstream of ADAM8, holds promise as a biomarker for early detection of or treatment response of ADAM8-positive TNBCs.

ADAM15 targets MMP9 activity to promote lung cancer cell invasion

ADAM15 is a membrane-associated proteinase belonging to a disintegrin and metalloproteinase (ADAM) family. Recent studies suggested that ADAM15 is overexpressed in several types of cancer and is involved in metastatic tumor progression. However, the function of ADAM15 in non-small cell lung cancer (NSCLC) is currently unknown. In the present study, we found that high expression of ADAM15 was associated with decreased overall survival (OS) and disease-free survival (DFS) in NSCLC patients. Furthermore, shRNA-mediated knockdown of ADAM15 attenuated cell migration and invasion. Mechanistic study demonstrated that ADAM15 upregulated MMP9 expression in lung cancer cells via activation of the MEK-ERK pathway. Moreover, ADAM15 proteolytically cleaved and activated pro-MMP9 in vitro and interacted with MMP9 in vivo. Overexpression of ADAM15 in A549 cells promoted cell invasion, while knocking down MMP9 attenuated cell invasive ability. Therefore, our data not only support a pro-metastatic role of ADAM15 in lung cancer progression, but also reveal a novel mechanism of ADAM15 in promoting cancer cell invasion through directly targeting MMP9 activation.

Antitumor and anti-angiogenic activity of the recombinant human disintegrin domain of A disintegrin and metalloproteinase 15

A disintegrin and metalloproteinases (ADAMs), a family of transmembrane glycoproteins, are expressed in numerous tissues and organs, and have been implicated in a variety of physiological and pathological processes. ADAM15 is unique among the ADAMs in having an Arg-Gly-Asp motif in its disintegrin domain. In the present study, the antitumor and anti-angiogenic effects of the recombinant human disintegrin domain (rhdd) ADAM15, expressed by Escherichia coli, were evaluated. rhddADAM15 inhibited the proliferation and migration of several tumor cells, with a half maximal inhibitory concentration of 1.0-6.0 µM. In addition, rhddADAM15 inhibited the proliferation of Bel-7402 cells via the mitogen-activated protein kinase pathway and reduced the activation of Src. rhddADAM15 (1-10 µM) inhibited the proliferation, migration and tube formation of vascular endothelial EA.hy926 cells. G0/G1 arrest (10.96 ± 1.40%) and apoptotic cells (55.85 ± 1.06%) were observed in the EA.hy926 cells treated with 4 µM and 6 µM rhddADAM15, respectively. In vivo, rhddADAM15 significantly inhibited angiogenesis in zebrafish. rhddADAM15 at concentrations of 20 nmol/fish or 5 nmol/fish inhibited the angiogenesis of subintestinal and intersegmental vessels in the zebrafish by 72 ± 1.26 and 48 ± 2.92%, respectively. In conclusion, the results of the present study identified rhddADAM15 as a potent inhibitor of tumor formation and angiogenesis, rendering it a promising tool for use in anticancer treatment.

ADAM15 participates in fertilization through a physical interaction with acrogranin

Mammalian fertilization is completed by direct interaction between sperm and egg. This process is primarily mediated by both adhesion and membrane-fusion proteins found on the gamete surface. ADAM1, 2, and 3 are members of the ADAMs protein family, and have been involved in sperm–egg binding. In this study, we demonstrate the proteolytic processing of ADAM15 during epididymal maturation of guinea pig spermatozoa to produce a mature form a size of 45 kDa. We find that the size of the mature ADAM15, 45 kDa, in cauda epididymal spermatozoa indicates that the pro-domain and metalloprotease domain are absent. In addition, using indirect immunofluorescence, ADAM15 was found throughout the acrosome, at the equatorial region and along the flagellum of guinea pig spermatozoa. After acrosome reaction, ADAM15 is lost from the acrosomal region and retained in the equatorial region and flagellum. In this study, we also report the first evidence of a complex between ADAM15 and acrogranin. By immunoprecipitation, we detected a protein band of 65 kDa which co-immunoprecipated together ADAM15. Analysis of the N-terminal sequence of this 65 kDa protein has revealed its identity as acrogranin. In addition, using cell-surface labeling, ADAM15 was found to be present on the cell surface. Assays of heterologous fertilization showed that the antibody against acrogranin inhibited the sperm–egg adhesion. Interestingly, ADAM15 and acrogranin were also found associated in two breast cancer cell lines. In conclusion, our results demonstrated that ADAM15 and acrogranin are present on and associated with the surface of guinea pig spermatozoa; besides both proteins may play a role during sperm–egg binding.

MicroRNA-147b regulates vascular endothelial barrier function by targeting ADAM15 expression

A disintegrin and metalloproteinase15 (ADAM15) has been shown to be upregulated and mediate endothelial hyperpermeability during inflammation and sepsis. This molecule contains multiple functional domains with the ability to modulate diverse cellular processes including cell adhesion, extracellular matrix degradation, and ectodomain shedding of transmembrane proteins. These characteristics make ADAM15 an attractive therapeutic target in various diseases. The lack of pharmacological inhibitors specific to ADAM15 prompted our efforts to identify biological or molecular tools to alter its expression for further studying its function and therapeutic implications. The goal of this study was to determine if ADAM15-targeting microRNAs altered ADAM15-induced endothelial barrier dysfunction during septic challenge by bacterial lipopolysaccharide (LPS). An in silico analysis followed by luciferase reporter assay in human vascular endothelial cells identified miR-147b with the ability to target the 3′ UTR of ADAM15. Transfection with a miR-147b mimic led to decreased total, as well as cell surface expression of ADAM15 in endothelial cells, while miR-147b antagomir produced an opposite effect. Functionally, LPS-induced endothelial barrier dysfunction, evidenced by a reduction in transendothelial electric resistance and increase in albumin flux across endothelial monolayers, was attenuated in cells treated with miR-147b mimics. In contrast, miR-147b antagomir exerted a permeability-increasing effect in vascular endothelial cells similar to that caused by LPS. Taken together, these data suggest the potential role of miR147b in regulating endothelial barrier function by targeting ADAM15 expression.

ADAM15 deficiency attenuates pulmonary hyperpermeability and acute lung injury in lipopolysaccharide-treated mice

ADAM15 is a disintegrin and metalloprotease recently implicated in cancer and chronic immune disorders. We have recently characterized ADAM15 as a mediator of endothelial barrier dysfunction. Whether this molecule contributes to acute inflammation has not been evaluated. The purpose of this study was to investigate the role of ADAM15 in mediating pulmonary microvascular leakage during acute inflammatory injury. Immunofluorescent staining and Western blotting revealed that the endothelium was the main source of ADAM15 in lung tissue. In a mouse model of acute lung injury induced by lipopolysaccharide (LPS), upregulation of ADAM15 was observed in association with pulmonary edema and neutrophil infiltration. The LPS-induced inflammatory injury, as demonstrated by bronchoalveolar lavage neutrophil count, lung wet-to-dry weight ratio, and myeloperoxidase activity, was significantly attenuated in Adam15(-/-) mice. Studies with primary cell culture demonstrated abundant ADAM15 expression in endothelial cells (ECs) of mouse lung but not in neutrophils. Deficiency of ADAM15 in ECs had no obvious effect on basal permeability but significantly attenuated hyperpermeability response to LPS as evidenced by albumin flux assay and measurements of transendothelial electrical resistance, respectively. ADAM15 deficiency also reduced neutrophil chemotactic transmigration across endothelial barriers in the presence or absence of formyl-methionyl-leucyl-phenylalanine (fMLP). Rescue expression of ADAM15 in Adam15(-/-) ECs restored neutrophil transendothelial migration. These data indicate that ADAM15 upregulation contributes to inflammatory lung injury by promoting endothelial hyperpermeability and neutrophil transmigration.

A disintegrin and metalloproteinase 15 contributes to atherosclerosis by mediating endothelial barrier dysfunction via Src family kinase activity

OBJECTIVE

Endothelium dysfunction is an initiating factor in atherosclerosis. A disintegrin and metalloproteinase 15 (ADAM 15) is a multidomain metalloprotease recently identified as a regulator of endothelial permeability. However, whether and how ADAM15 contributes to atherosclerosis remains unknown.

METHODS AND RESULTS

Genetic ablation of ADAM15 in apolipoprotein E-deficient mice led to a significant reduction in aortic atherosclerotic lesion size (by 52%), plaque macrophage infiltration (by 69%), and smooth muscle cell deposition (by 82%). In vitro studies implicated endothelial-derived ADAM15 in barrier dysfunction and monocyte transmigration across mouse aortic and human umbilical vein endothelial cell monolayers. This role of ADAM15 depended on intact functioning of the cytoplasmic domain, as evidenced in experiments with site-directed mutagenesis targeting the metalloprotease active site (E349A), the disintegrin domain (Arginine-Glycine-Aspartic acid→Threonine-Aspartic acid-Aspartic acid), or the cytoplasmic tail. Further investigations revealed that ADAM15-induced barrier dysfunction was concomitant with dissociation of endothelial adherens junctions (vascular endothelial [VE]-cadherin/γ-catenin), an effect that was sensitive to Src family kinase inhibition. Through small interfering RNA-mediated knockdown of distinct Src family kinase members, c-Src and c-Yes were identified as important mediators of these junctional effects of ADAM15.

CONCLUSIONS

These results suggest that endothelial cell-derived ADAM15, signaling through c-Src and c-Yes, contributes to atherosclerotic lesion development by disrupting adherens junction integrity and promoting monocyte transmigration.

ADAM15 protein amplifies focal adhesion kinase phosphorylation under genotoxic stress conditions

ADAM15, a disintegrin and metalloproteinase, is capable of counteracting genotoxic stress-induced apoptosis by the suppression of caspase-3 activation. A cell line expressing the membrane-bound ADAM15 without its cytoplasmic tail, however, lost this anti-apoptotic property, suggesting a crucial role of the intracellular domain as a scaffold for recruitment of survival signal-transducing kinases. Accordingly, an enhanced phosphorylation of FAK at Tyr-397, Tyr-576, and Tyr-861 was detected upon genotoxic stress by camptothecin in ADAM15-transfected T/C28a4 cells, but not in transfectants expressing an ADAM15 mutant without the cytoplasmic tail. Accordingly, a specific binding of the cytoplasmic ADAM15 domain to the C terminus of FAK could be shown by mammalian two-hybrid, pulldown, and far Western studies. In cells expressing full-length ADAM15, a concomitant activation of Src at Tyr-416 was detected upon camptothecin exposure. Cells transfected with a chimeric construct consisting of the extracellular IL-2 receptor α-chain and the cytoplasmic ADAM15 domain were IL-2-stimulated to prove that the ADAM15 tail can transduce a percepted extracellular signal to enhance FAK and Src phosphorylation. Our studies further demonstrate Src binding to FAK but not a direct Src interaction with ADAM15, suggesting FAK as a critical intracellular adaptor for ADAM15-dependent enhancement of FAK/Src activation. Moreover, the apoptosis induction elicited by specific inhibitors (PP2, FAK 14 inhibitor) of FAK/Src signaling was significantly reduced by ADAM15 expression. The newly uncovered counter-regulatory response to genotoxic stress in a chondrocytic survival pathway is potentially also relevant to apoptosis resistance in neoplastic growth.

ADAM15 to α5β1 integrin switch in colon carcinoma cells: a late event in cancer progression associated with tumor dedifferentiation and poor prognosis

ADAM15, a member of the A Disintegrin And Metalloproteinase (ADAM) family, is a membrane protein containing an adhesion domain that binds to α5β1 integrin through a unique RGD domain. ADAM15, expressed by human normal colonocytes, is involved in epithelial wound healing and tissue remodeling in inflammatory bowel disease. The aims of our study were (i) to analyze ADAM15 expression in a series of colon carcinomas and paired normal mucosa and (ii) to integrate the spatial relationship of ADAM15 with its binding partners α5β1 integrin, a mesenchymal marker, as well as with other adhesion molecules, α3β1 integrin and E-cadherin. A series of 94 colon carcinomas of the non other specified category were graded according to the World Health Organization classification. Immunohistochemistry was performed on frozen tissue sections using antibodies directed to ADAM15, α5β1 and α3β1 integrins, and E-cadherin. ADAM15 was quantified at the mRNA level. Finally, promoter methylation of ADAM15 was examined as well as the microsatellite instability status (MSS/MSI). Thirty-six percent of colorectal carcinomas displayed a reduced expression of ADAM15 in cancer cells, confirmed at the mRNA level in most cases, without promoter methylation. ADAM15 down-regulation was associated with histologically poorly differentiated carcinomas. In addition, it was associated with the acquisition of α5β1 by cancer cells and down-regulation of α3β1 integrin and E-cadherin. Finally this profile that includes characteristic of epithelial to mesenchymal transition is a late progression event of colon cancer with a poor prognosis.

Myocardial infarction induces early increased remote ADAM8 expression of rat hearts after cardiac arrest

BACKGROUND

A disintegrin and metalloproteinase-8 (ADAM8) is a potential surrogate of inflammation which has recently been associated with myocardial infarction. We evaluated in a rat cardiac transplantation model whether ischemia-reperfusion injury alone (IRI) or with early regional myocardial infarction (MI) would suffice to induce inflammatory myocardial remodeling and ADAM8 expression.

MATERIAL AND METHODS

Isogenic heterotopic cardiac transplantation after cardiac arrest was performed to 48 Fischer 344 rats to induce ischemia-reperfusion injury (IRI), of which 27 rats also underwent ligation of the left anterior coronary artery (LAD) of the heart to yield MI. Histology was performed at 0.5, 24 and 48 h after transplantation. ADAM8 was evaluated by qRT-PCR after graft harvesting.

RESULTS

After 0.5 and 48 h respectively, edematous intramyocardial artery nuclei and periadventitial inflammation were more prominent in MI after transplantation, as compared with IRI alone and Controls (57.0 vs 40.0 and 5.0; 1.9 vs 1.1 and 0.9, point score units, p < 0.05, respectively). The expression of ADAM-8 was increased in MI as compared with Controls (1.9 vs 1.0, 1.9 fold increase) at 48 h. In grafts with MI, ADAM8 was localized using immunohistochemistry to the vicinity of the area corresponding to the developing infarction as well as in intramyocardial arteries remote to the infarction area.

CONCLUSIONS

Remote histopathological changes of ischemic cardiac grafts are associated with increased expression of ADAM8 thus emphasizing a global myocardial impact of MI.

Halting angiogenesis by non-viral somatic gene therapy alleviates psoriasis and murine psoriasiform skin lesions

Dysregulated angiogenesis is a hallmark of chronic inflammatory diseases, including psoriasis, a common skin disorder that affects approximately 2% of the population. Studying both human psoriasis in 2 complementary xenotransplantation models and psoriasis-like skin lesions in transgenic mice with epidermal expression of human TGF-β1, we have demonstrated that antiangiogenic non-viral somatic gene therapy reduces the cutaneous microvasculature and alleviates chronic inflammatory skin disorders. Transient muscular expression of the recombinant disintegrin domain (RDD) of metargidin (also known as ADAM-15) by in vivo electroporation reduced cutaneous angiogenesis and vascularization in all 3 models. As demonstrated using red fluorescent protein-coupled RDD, the treatment resulted in muscular expression of the gene product and its deposition within the cutaneous hyperangiogenic connective tissue. High-resolution ultrasound revealed reduced cutaneous blood flow in vivo after electroporation with RDD but not with control plasmids. In addition, angiogenesis- and inflammation-related molecular markers, keratinocyte proliferation, epidermal thickness, and clinical disease scores were downregulated in all models. Thus, non-viral antiangiogenic gene therapy can alleviate psoriasis and may do so in other angiogenesis-related inflammatory skin disorders.

ADAM-15 disintegrin-like domain structure and function

The ADAM (a disintegrin-like and metalloproteinase) proteins are a family of transmembrane cell-surface proteins with important functions in adhesion and proteolytic processing in all animals. Human ADAM-15 is the only member of the ADAM family with the integrin binding motif Arg-Gly-Asp (RGD) in its disintegrin-like domain. This motif is also found in most snake venom disintegrins and other disintegrin-like proteins. This unique RGD motif within ADAM-15 serves as an integrin ligand binding site, through which it plays a pivotal role in interacting with integrin receptors, a large family of heterodimeric transmembrane glycoproteins. This manuscript will present a review of the RGD-containing disintegrin-like domain structures and the structural features responsible for their activity as antagonists of integrin function in relation to the canonical RGD template.

Conservation and divergence of ADAM family proteins in the Xenopus genome

BACKGROUND

Members of the disintegrin metalloproteinase (ADAM) family play important roles in cellular and developmental processes through their functions as proteases and/or binding partners for other proteins. The amphibian Xenopus has long been used as a model for early vertebrate development, but genome-wide analyses for large gene families were not possible until the recent completion of the X. tropicalis genome sequence and the availability of large scale expression sequence tag (EST) databases. In this study we carried out a systematic analysis of the X. tropicalis genome and uncovered several interesting features of ADAM genes in this species.

RESULTS

Based on the X. tropicalis genome sequence and EST databases, we identified Xenopus orthologues of mammalian ADAMs and obtained full-length cDNA clones for these genes. The deduced protein sequences, synteny and exon-intron boundaries are conserved between most human and X. tropicalis orthologues. The alternative splicing patterns of certain Xenopus ADAM genes, such as adams 22 and 28, are similar to those of their mammalian orthologues. However, we were unable to identify an orthologue for ADAM7 or 8. The Xenopus orthologue of ADAM15, an active metalloproteinase in mammals, does not contain the conserved zinc-binding motif and is hence considered proteolytically inactive. We also found evidence for gain of ADAM genes in Xenopus as compared to other species. There is a homologue of ADAM10 in Xenopus that is missing in most mammals. Furthermore, a single scaffold of X. tropicalis genome contains four genes encoding ADAM28 homologues, suggesting genome duplication in this region.

CONCLUSIONS

Our genome-wide analysis of ADAM genes in X. tropicalis revealed both conservation and evolutionary divergence of these genes in this amphibian species. On the one hand, all ADAMs implicated in normal development and health in other species are conserved in X. tropicalis. On the other hand, some ADAM genes and ADAM protease activities are absent, while other novel ADAM proteins in this species are predicted by this study. The conservation and unique divergence of ADAM genes in Xenopus probably reflect the particular selective pressures these amphibian species faced during evolution.

Expression of ADAM-15 in rat myocardial infarction

A disintegrin and metalloprotease-15 (ADAM-15) is a potential novel regulator of inflammatory response and tissue remodelling, which is thought to have the ability to attenuate the cardiac function resulting from myocardial infarction (MI). Therefore, the aim of our study was to investigate the expression of ADAM-15 in rat MI. Wistar rats were subjected to MI by ligation of the left anterior descending coronary artery. Euthanasia was performed at 1, 3, 7 and 14 days following MI. The mRNA and protein expression levels of ADAM-15 were detected respectively by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. The localization of ADAM-15 protein was observed by immunohistochemistry. Compared with sham-MI, the expression of ADAM-15 in MI increased at day 1, reached to maximum at day 3, decreased at day 7 and day 14 gradually. In addition, we also found that the localization of ADAM-15 was mainly at cardiac myocytes in the border area of MI and some macrophages in the border and infarcted areas. This study revealed a significant difference of ADAM-15 expression in rat MI and indicated that ADAM-15 maybe one of the important factors involved in inflammatory response and cardiac remodelling of rat MI.

Gene expression analysis of drug-resistant MCF-7 cells: implications for relation to extracellular matrix proteins

PURPOSE

Since multidrug resistance is a multifactorial phenomenon, a large-scale expression analysis of drug-resistant cells by using high-density oligonucleotide microarrays may provide information about new candidate genes contributing to resistance. Extracellular matrix (ECM) is responsible for many aspects of proliferation and invasive/metastatic behavior of tumor cells. This study demonstrates alterations in gene expression levels of several ECM components, matrix metalloproteinases (MMPs), adamalysins (ADAMs and ADAMTSs) and tissue inhibitors of metalloproteinases (TIMPs) in paclitaxel, docetaxel, vincristine and doxorubicin-resistant MCF-7 cells.

METHODS

Resistant MCF-7 cells were developed by stepwise selection of cells in increasing concentrations of drugs. Affymetrix GeneChip Human Genome U133 Plus 2.0 Array was used for hybridizations. Statistical significance was determined by independent sample t test. The genes having altered expression levels in drug-resistant sublines were selected and filtered by volcano plots.

RESULTS

Genes up/downregulated more than twofolds were selected and listed. Expression of 25 genes encoding ECM proteins (including collagen, finronectin and syndecan) and integrin receptor subunits were found to be upregulated in drug-resistant cells. In addition, expression levels of, 13 genes encoding MMPs, ADAMs, ADAMTSs and TIMPs (including MMP1, MMP9, ADAM9 and TIMP3) were found to be altered in drug-resistant sublines when compared with sensitive MCF-7.

CONCLUSIONS

Based on the expression analysis profiles, this report provides a preliminary insight into the relationship between drug resistance and ECM components, which are related to invasion and metastasis. Correlation of each specific ECM component with drug resistance requires further analysis.

Inhibition of platelets and tumor cell adhesion by the disintegrin domain of human ADAM9 to collagen I under dynamic flow conditions

This work aimed to investigate the role of the disintegrin domain of the human ADAM9 (ADAM9D) on the adhesion of breast tumor cells and platelets to collagen I, in a dynamic flow assay to simulate in vivo shear conditions. Recombinant ADAM9D was able to support tumor cell adhesion through binding to the beta1 integrin subunit and also to inhibit the invasion through matrigel in vitro. In a dynamic flow assay ADAM9D inhibited about 75% and 65% of MDA-MB-231 tumor cells and platelet adhesion to collagen I, respectively. In addition, it was demonstrated that alphaVbeta3 integrin is new interacting partner for ADAM9D. In conclusion, these results suggest a role for the disintegrin domain of ADAM9 in the metastatic process. Also, ADAM9D may be a tool for investigating the role of ADAMs in metastasis and cancer progression and for the design of selective inhibitors against the adhesion and extravasation of cancer cells.

Characterization of the catalytic activity of the membrane-anchored metalloproteinase ADAM15 in cell-based assays

ADAM15 (a disintegrin and metalloproteinase 15) is a membrane-anchored metalloproteinase, which is overexpressed in several human cancers and has been implicated in pathological neovascularization and prostate cancer metastasis. Yet, little is known about the catalytic properties of ADAM15. Here, we purified soluble recombinant ADAM15 to test for its ability to cleave a library of peptide substrates. However, we found no processing of any of the peptide substrates tested here, and therefore turned to cell-based assays to characterize the catalytic properties of ADAM15. Overexpression of full-length membrane-anchored ADAM15 or the catalytically inactive ADAM15E-->A together with various membrane proteins resulted in increased release of the extracellular domain of the fibroblast growth factor receptor 2iiib (FGFR2iiib) by ADAM15, but not ADAM15E-->A. This provided a robust assay for a characterization of the catalytic properties of ADAM15 in intact cells. We found that increased expression of ADAM15 resulted in increased FGFR2iiib shedding, but that ADAM15 was not stimulated by phorbol esters or calcium ionophores, two commonly used activators of ectodomain shedding. Moreover, ADAM15-dependent processing of FGFR2iiib was inhibited by the hydroxamate-based metalloproteinase inhibitors marimastat, TAPI-2 and GM6001, and by 50 nM TIMP-3 (tissue inhibitor of metalloproteinases 3), but not by 100 nM TIMP-1, and only weakly by 100 nM TIMP-2. These results define key catalytic properties of ADAM15 in cells and its response to stimulators and inhibitors of ectodomain shedding. A cell-based assay for the catalytic activity of ADAM15 could aid in identifying compounds, which could be used to block the function of ADAM15 in pathological neovascularization and cancer.

ADAM10, the rate-limiting protease of regulated intramembrane proteolysis of Notch and other proteins, is processed by ADAMS-9, ADAMS-15, and the gamma-secretase

ADAM10 is involved in the proteolytic processing and shedding of proteins such as the amyloid precursor protein (APP), cadherins, and the Notch receptors, thereby initiating the regulated intramembrane proteolysis (RIP) of these proteins. Here, we demonstrate that the sheddase ADAM10 is also subject to RIP. We identify ADAM9 and -15 as the proteases responsible for releasing the ADAM10 ectodomain, and Presenilin/gamma-Secretase as the protease responsible for the release of the ADAM10 intracellular domain (ICD). This domain then translocates to the nucleus and localizes to nuclear speckles, thought to be involved in gene regulation. Thus, ADAM10 performs a dual role in cells, as a metalloprotease when it is membrane-bound, and as a potential signaling protein once cleaved by ADAM9/15 and the gamma-Secretase.

Enhancement of recombinant human ADAM15 disintegrin domain expression level by releasing the rare codons and amino acids restriction

This study was aimed at increasing the production of the recombinant human ADAM15 disintegrin domain (RADD) in Escherichia coli by releasing the rare codons and restricting amino acid residues. Three different strategies for increasing RADD production were examined: to select the suitable host strain, to optimize the rare codons, and to delete the amino acids residues. The total fusion protein glutathione-S-transferase (GST)-RADD concentration of 298 mg/l and 326 mg/l were achieved by selecting E. coli Rosetta (DE3) as the host strain and by changing GGA to GGC at the GST-RADD cassette, respectively. The RADD concentration was increased by 35.7% by eliminating the "Pro-Glu-Phe" residues at the GST-RADD junction. By combinational utilizing the preferred codon introduction and amino acid sequence optimization in E. coli Rosetta (DE3), the highest RADD concentration of 68 mg/l was achieved. The proposed strategy may provide an alternative approach for other enhanced recombinant protein production by E. coli.

Therapeutic potential of novel modulators of neovascularization

Neovacularization is an important biological process whereby new blood vessels develop in both health and disease. During development, blood vessels are formed from mesodermal cells in a process called vasculogenesis. The vascular network then expands by the sprouting of new vessel networks from pre-established vessels in a process known as angiogenesis. However, in adult life, undesirable neovascularization is associated with tumor development and a growing list of 'angiogenesis-dependent' diseases, including cardiovascular complications. Furthermore, diseases characterized by ischemia-induced tissue damage cause a neovascularization response to facilitate tissue repair. Recent research has identified novel molecular and cellular mediators of neovascularization that, in adult life, recapitulate angiogenic processes observed during embryonic development. The discovery of vascular progenitor cells and new molecules that display selective functions in modulating endothelial cell fate, migration and patterning, vessel morphogenesis and the amplification of angiogenic signaling by regulating the master signal VEGF, opens the door to new clinical strategies that target angiogenesis-dependent diseases or that can promote therapeutic neovascularization.

An Adam15 amplification loop promotes vascular endothelial growth factor-induced ocular neovascularization

Proteins with a disintegrin and a metalloproteinase domain (ADAMs) are a family of membrane-bound proteinases that bind integrins through their disintegrin domain. In this study, we have found modest expression of ADAM15 in pericytes in normal retina and strong up-regulation of ADAM15 in retinal vascular endothelial cells in ischemic retina. Increased expression of vascular endothelial growth factor (VEGF) in the retina in the absence of ischemia also increased ADAM15 levels, and knockdown of Vegf mRNA in ischemic retina reduced Adam15 mRNA. Mice deficient in ADAM15 showed a significant reduction in ischemia-induced retinal neovascularization, choroidal neovascularization at rupture sites in Bruch's membrane, and VEGF-induced subretinal neovascularization. ADAM15-deficient mice also showed reduced levels of VEGF(164), VEGF receptor 1, and VEGF receptor 2 in ischemic retina. These data suggest that ADAM15 and VEGF participate in an amplification loop; VEGF increases expression of ADAM15, which in turn increases expression of VEGF and its receptors. Perturbation of the loop by elimination of ADAM15 suppresses ocular neovascularization in 3 different model systems, and thus ADAM15 provides a new therapeutic target for diseases complicated by neovascularization.

ADAM15 suppresses cell motility by driving integrin alpha5beta1 cell surface expression via Erk inactivation

Human ADAM15 is unique among the A disintegrin and metalloprotease domain (ADAM) family because of the integrin binding motif Arg-Gly-Asp (RGD) within its disintegrin domain. Integrin alpha5beta1 has been reported to bind to ADAM15 in an RGD-dependent manner, but the biological significance of the interaction between ADAM15 and alpha5beta1 is unknown. To characterize the effects of ADAM15 on alpha5beta1-mediated cell adhesion and migration and elucidate the potential mechanism, CHO cells which express endogenous integrin alpha5beta1 were transfected with human ADAM15 cDNA. ADAM15 overexpression led to enhanced cell adhesion and decreased migration on fibronectin, which were suppressed by down-regulation of integrin alpha5. Overexpression of ADAM15 not only increased the cell surface expression of integrin alpha5 but also resulted in a more clustered staining of alpha5 on cell surface, while the beta1 subunit remained unchanged. Unexpectedly, results from immunoprecipitation and immunofluorescence indicated that ADAM15 and alpha5beta1 integrin did not interact directly in CHO cells. We found that ADAM15 expression decreased the phosphorylation of Erk1/2. Consistently, down-regulation of Erk1/2 phosphorylation by MEK inhibitor PD98059 or siRNA against Erk1/2 enhanced the expression of alpha5 on cell surface. By using a B16F10 pulmonary metastasis model, we revealed that overexpression of ADAM15 significantly reduced the number of metastatic nodules on the lung. Taken together, this study reveals for the first time that ADAM15 could drive alpha5 integrin expression on cell surface via down-regulation of phosphorylated Erk1/2. This presents a novel mechanism by which ADAM15 regulates cell-matrix adhesion and migration.

Distinct functions of natural ADAM-15 cytoplasmic domain variants in human mammary carcinoma

Adamalysins [a disintegrin and metalloproteinase (ADAM)] are a family of cell surface transmembrane proteins that have broad biological functions encompassing proteolysis, adhesion, and cell signal regulation. We previously showed that the cytoplasmic domain of ADAM-15 interacts with Src family protein tyrosine kinases and the adaptor protein growth factor receptor binding protein 2 (Grb2). In the present study, we have cloned and characterized four alternatively spliced forms of ADAM-15, which differ only in their cytoplasmic domains. We show that the four ADAM-15 variants were differentially expressed in human mammary carcinoma tissues compared with normal breast. The expression of the individual isoforms did not correlate with age, menopausal status, tumor size or grade, nodal status, Nottingham Prognostic Index, or steroid hormone receptor status. However, higher levels of two isoforms (ADAM-15A and ADAM-5B) were associated with poorer relapse-free survival in node-negative patients, whereas elevated ADAM-15C correlated with better relapse-free survival in node-positive, but not in node-negative, patients. The expression of ADAM-15A and ADAM-15B variants in MDA-MB-435 cells had differential effects on cell morphology, with adhesion, migration, and invasion enhanced by expression of ADAM-15A, whereas ADAM-15B led to reduced adhesion. Using glutathione S-transferase pull-down assays, we showed that the cytoplasmic domains of ADAM-15A, ADAM-15B, and ADAM-15C show equivalent abilities to interact with extracellular signal-regulated kinase and the adaptor molecules Grb2 and Tks5/Fish, but associate in an isoform-specific fashion with Nck and the Src and Brk tyrosine kinases. These data indicate that selective expression of ADAM-15 variants in breast cancers could play an important role in determining tumor aggressiveness by interplay with intracellular signaling pathways.

ADAM15 gene structure and differential alternative exon use in human tissues

Background

ADAM15 is a metalloprotease-disintegrin implicated in ectodomain shedding and cell adhesion. Aberrant ADAM15 expression has been associated with human cancer and other disorders. We have previously shown that the alternative splicing of ADAM15 transcripts is mis-regulated in cancer cells. To gain a better understanding of ADAM15 regulation, its genomic organization and regulatory elements as well as the alternative exon use in human tissues were characterized.

Results

Human ADAM15, flanked by the FLJ32785/DCST1 and ephrin-A4 genes, spans 11.4 kb from the translation initiation codon to the polyadenylation signal, being the shortest multiple-exon ADAM gene. The gene contains 23 exons varying from 63 to 316 bp and 22 introns from 79 to 1283 bp. The gene appeared to have several transcription start sites and their location suggested the promoter location within a CpG island proximal to the translation start. Reporter expression experiments confirmed the location of functional GC-rich, TATAless and CAATless promoter, with the most critical transcription-supporting elements located -266 to -23 bp relative to the translation start. Normal human tissues showed different complex patterns of at least 13 different ADAM15 splice variants arising from the alternative use of the cytosolic-encoding exons 19, 20a/b, and 21a/b. The deduced ADAM15 protein isoforms have different combinations of cytosolic regulatory protein interaction motifs.

Conclusion

Characterization of human ADAM15 gene and identification of elements involved in the regulation of transcription and alternative splicing provide important clues for elucidation of physiological and pathological roles of ADAM15. The present results also show that the alternative exon use is a physiological post-transcriptional mechanism regulating ADAM15 expression in human tissues.

Inhibition of Airway Smooth Muscle Adhesion and Migration by the Disintegrin Domain of ADAM-15

Disintegrin and metalloprotease proteins (ADAMs) are membrane-anchored glycoproteins involved in cell adhesion, cell fusion, protein ecto-domain shedding, and intracellular signaling. We examined whether the disintegrin domain of ADAM-15 (named ddADAM-15) containing an Asp-Gly-Asp (RGD) integrin-binding motif could interfere with airway smooth muscle cell (ASMC) adhesion and migration. Recombinant ddADAM-15 adhered to human ASMCs with saturation kinetics, and was beta(1)-integrin dependent. ddADAM-15 inhibited the binding of fibrinogen but not of fibronectin to ASMCs. ddADAM-15 also inhibited platelet-derived growth factor (PDGF)-induced ASMC migration, and this was reversed by an anti-beta(1)-integrin antibody. PDGF induced the activation of phosphoinositol-3-kinase (PI3K) and p38 mitogen-activated protein kinase (MAPK), and selective inhibitors of these kinases inhibited PDGF-induced ASMC migration. ddADAM-15 did not inhibit PDGF-induced activation of PI3K or p38, thereby excluding these kinase pathways as a mechanism by which ddADAM-15 inhibits ASMC migration. ADAM-15 mRNA and protein were expressed under basal conditions, and both gene and protein expression were inhibited by PDGF. In summary, ddADAM-15 inhibits ASMC adhesion and migration through the beta(1)-integrin, without modulating signaling pathways involved in ASMC migratory responses.

ADAM-15: a metalloprotease that mediates inflammation

Cell-cell and cell-matrix interactions are of utmost importance in the pathogenesis of inflammatory diseases. For example, cell-cell and cell-matrix interactions are crucial for leukocyte homing and recruitment to inflammatory sites. The discovery of the disintegrin and metalloprotease (ADAM) proteins, which have both adhesive and proteolytic activities, raised the question of their involvement in inflammatory processes. More interestingly, the presence of the RGD integrin-binding sequence in the disintegrin domain of ADAM-15 (MDC-15; metargidin) highlighted ADAM-15 as a protein particularly involved in cell-cell interactions. These findings therefore prompted authors to investigate the roles of ADAM-15 in inflammatory diseases. Because of the early description of ADAM-15 expression in endothelial cells, work first focused on the roles of ADAM-15 in vascular diseases, and ADAM-15 was found to be associated with atherosclerosis. Other studies also pointed at ADAM-15 as a mediator of rheumatoid arthritis and intestinal inflammation as well as inherent angiogenesis. The roles of ADAM-15 in these diseases appear to involve mechanisms as different as cell-cell interactions, cell-extracellular matrix (ECM) interactions, and shedding activity. Here we review and discuss these recent discoveries pointing to ADAM-15 as a mediator of mechanisms underlying inflammation and as a possible therapeutic target for prevention of inflammatory diseases.

ADAM-15/metargidin mediates homotypic aggregation of human T lymphocytes and heterotypic interactions of T lymphocytes with intestinal epithelial cells

Intestinal epithelial cells (IEC) play an immunoregulatory role in the intestine. This role involves cell-cell interactions with intraepithelial lymphocytes that may also play a role in some enteropathies. The discovery of the RGD motif-containing Protein ADAM-15 (a disintegrin and metalloprotease-15) raises the question of its involvement in these cell-cell interactions. Cell adhesion assays were performed using the Jurkat E6.1 T cell line as a model of T lymphocytes and Caco2-BBE monolayers as a model of intestinal epithelia. Our results show that an anti-ADAM-15 ectodomain antibody inhibited the attachment of Jurkat cells on Caco2-BBE monolayers. Overexpression of ADAM-15 in Caco2-BBE cells enhanced Jurkat cell binding, and overexpression of ADAM-15 in Jurkat cells enhanced their aggregation. Mutagenesis experiments showed that both the mutation of ADAM-15 RGD domain or the deletion of its cytoplasmic tail decreased these cell-cell interactions. Moreover, wound-healing experiments showed that epithelial ADAM-15-mediated Jurkat cell adhesion to Caco2-BBE cells enhances the mechanisms of wound repair. We also found that ADAM-15-mediated aggregation of Jurkat cells increases the expression of tumor necrosis factor-alpha mRNA. These results demonstrate the following: 1) ADAM-15 is involved in heterotypic adhesion of intraepithelial lymphocytes to IEC as well as in homotypic aggregation of T cells; 2) both the RGD motif and the cytoplasmic tail of ADAM-15 are involved for these cell-cell interactions; and 3) ADAM-15-mediated cell-cell interactions are involved in mechanisms of epithelial restitution and production of pro-inflammatory mediators. Altogether these findings point to ADAM-15 as a possible therapeutic target for prevention of inappropriate T cell activation involved in some pathologies.

Novel function of human ADAM15 disintegrin-like domain and its derivatives in platelet aggregation

INTRODUCTION

A Disintegrin and Metalloproteinase (ADAM) proteins are a family of multifunctional proteins containing disintegrin and metalloproteinase domains that perform both adhesive and proteolytic functions in cell-cell and cell-matrix interactions. ADAM15 is unique among these proteins in having an Arg-Gly-Asp (RGD) motif in its disintegrin-like domain. This motif is known to interact with the integrin alphaIIbbeta3 on platelets.

MATERIALS AND METHODS

We cloned and expressed the human ADAM15 disintegrin-like domain and its derivatives in Pichia pastoris, and purified them by chromatographic fractionation. We then characterized the integrin binding specificities and their antiplatelet activities of the proteins. Antiplatelet function was assessed by inhibition of platelet adhesion and aggregation.

RESULTS

The yeast-expressed ADAM15 disintegrin-like domains were able to inhibit the binding of alphaIIbbeta3 as well as alphavbeta3 to its biological ligands in a dose-dependent manner. Remarkably, mutation of the three residues proximal to the RGD tripeptide sequence, RPTRGD sequence to NWKRGD, increased its affinity for alphaIIbbeta3. The NWK mutant had a much greater inhibitory action on human platelet aggregation than the original ADAM15 disintegrin-like domain.

CONCLUSIONS

The structural context of the RGD tripeptide sequence in the disintegrin domain determines the specificity and affinity of the protein for its binding partners. The human ADAM15 disintegrin-like domain may provide useful information for developing an antithrombotic agent.

ADAM15 upregulation and interaction with multiple binding partners in inflammatory bowel disease

A disintegrin and metalloproteinase (ADAM)15 is upregulated in some tissues undergoing remodeling. This glycoprotein is characterized by adhesive function through its interaction with members of the integrin family and protease properties. The goal of this work was to describe the tissue distribution of ADAM15 and its spatial relationship with its known binding partners in inflammatory bowel disease. ADAM15 expression was examined using frozen tissues from eight patients with ulcerative colitis or Crohn's disease and four normal colons by immunohistochemistry, immunoblotting and quantitative reverse transcription-polymerase chain reaction. In addition expression of alpha5beta1- and alphavbeta3-integrins, VE-cadherin, alpha-smooth muscle actin (alpha-SMA) and collagen IV was examined using immunohistochemistry and confocal microscopy. In the normal colon, ADAM15 was expressed by all epithelial cells throughout the crypt and by pericryptic myofibroblasts coexpressing alpha-SMA and collagen IV. ADAM15 was also expressed by endothelial cells and vascular myocytes in all layers of the intestinal wall as well as by nonvascular myocytes of the muscularis mucosae and muscularis propria. In inflammatory bowel diseases, ADAM15 was strongly upregulated at the mRNA level and expressed only as an active form as shown by immunoblotting analysis. Parallel to its upregulation, ADAM15 expression was found both at the plasma membrane and in the cytoplasm of epithelial cells in acute attacks of the disease. In the crypt abcesses, ADAM15-positive epithelial cells were in close contact with alpha5beta1-integrin-positive leukocytes localized between these cells and in the crypt lumen. In the regenerative areas, ADAM15-positive epithelial cells were in close contact with alpha5beta1- and alphavbeta3-positive pericryptic myofibroblasts. In endothelial cells, VE-cadherin was decreased. In contrast, ADAM15 was strongly expressed by endothelial cells and was in close contact with alpha5beta1-positive leukocytes. There is a differential expression of ADAM15 in epithelial cells during inflammatory bowel disease compared with the normal colon. In addition, the spatial relationships with its binding partners suggest a role for ADAM15 in the differentiation of regenerative colonic mucosa as well as in leukocyte transmigration across epithelial and endothelial barriers.

The effect of the single substitution of arginine within the RGD tripeptide motif of a modified neurotoxin dendroaspin on its activity of platelet aggregation and cell adhesion

The Arg-Gly-Asp (RGD) tripeptide unit is a cell-cell and cell-extracellular matrix recognition sequence of some integrins that is found within several extracellular matrix glycoproteins and dendroaspin, a disintegrin-like venom protein isolated from the snake venom of the Dendroaspis jamsonii. In the present study, the RGD motif in dendroaspin was substituted by Lys-Gly-Asp (KGD), His-Gly-Asp (HGD), Gln-Gly-Asp (QGD) and Ala-Gly-Asp (AGD) denoted as KGD-den, HGD-den, QGD-den and AGD-den, respectively. Each of the mutants exhibited activity as inhibitor of ADP-induced platelet aggregation with IC50 values of 0.26, 2.5, 6, and 17 microM for KGD-den, HGD-den, QGD-den, and AGD-den, respectively, as compared with RGD-den (IC50 = 0.18 microM). Interestingly, HGD-den was approx. two-fold more potent and a more selective inhibitor than either the KGD-den or QGD-den counterpart at blocking A375-SM human melanoma cell adhesion to fibrinogen (beta3-mediated). KGD-den, HGD-den, and QGD-den were preferentially antagonists of A375-SM human melanoma cell adhesion to fibrinogen rather than to fibronectin (alpha5beta1-, beta3-mediated). Both HGD-den and KGD-den were equipotent as inhibitors of human erythroleukaemia (HEL) cell adhesion to fibrinogen (IC50 = 0.15 microM) and also preferential inhibitors of HEL cell adhesion to fibrinogen (beta3 and beta1-mediated) rather than to fibronectin. These findings show that the presence of the arginine within the RGD motif of dendroaspin is not obligatory and substitution of this residue can modulate inhibitory potency and integrin binding selectivity.

Proteomic identification of desmoglein 2 and activated leukocyte cell adhesion molecule as substrates of ADAM17 and ADAM10 by difference gel electrophoresis

In contrast with the early view of metalloproteases as simple extracellular matrix-degrading entities, recent findings show that they are highly specific modulators of different signaling pathways involved, positively or negatively, in tumor development. Thus, before considering a given metalloprotease a therapeutic target, it seems advisable to characterize its function by identifying its repertoire of substrates. Here, we present a proteomic approach to identify ADAM17 substrates by difference gel electrophoresis. We found that the shedding of the extracellular domain of the transferrin receptor and those of two cell-cell adhesion molecules, activated leukocyte cell adhesion molecule (ALCAM) and desmoglein 2 (Dsg-2), is increased in cells overexpressing ADAM17. Genetic evidence shows that while ADAM17 is responsible for the shedding of ALCAM, both ADAM17 and ADAM10 can act on Dsg-2. Activation of the epidermal growth factor receptor leads to the upregulation of the shedding of Dsg-2 and to the concomitant upregulation of ADAM17, but not ADAM10, supporting the ability of overexpressed ADAM17 to shed Dsg-2. These results unveil a role of ADAM10 and ADAM17 in the shedding of cell-cell adhesion molecules. Since loss of cell adhesion is an early event in tumor development, these results suggest that ADAM17 is a useful target in anticancer therapy.

The ADAMs family: coordinators of nervous system development, plasticity and repair

A disintegrin and metalloprotease (ADAM) transmembrane proteins have metalloprotease, integrin-binding, intracellular signaling and cell adhesion activities. In contrast to other metalloproteases, ADAMs are particularly important for cleavage-dependent activation of proteins such as Notch, amyloid precursor protein (APP) and transforming growth factor alpha (TGFalpha), and can bind integrins. Not surprisingly, ADAMs have been shown or suggested to play important roles in the development of the nervous system, where they regulate proliferation, migration, differentiation and survival of various cells, as well as axonal growth and myelination. On the eleventh anniversary of the naming of this family of proteins, the relatively unknown ADAMs are emerging as potential therapeutic targets for neural repair. For example, over-expression of ADAM10, one of the alpha-secretases for APP, can prevent amyloid formation and hippocampal defects in an Alzheimer mouse model. Another example of this potential neural repair role is the finding that ADAM21 is uniquely associated with neurogenesis and growing axons of the adult brain. This comprehensive review will discuss the growing literature about the roles of ADAMs in the developing and adult nervous system, and their potential roles in neurological disorders. Most excitingly, the expanding understanding of their normal roles suggests that they can be manipulated to promote neural repair in the degenerating and injured adult nervous system.

(Make) stick and cut loose--disintegrin metalloproteases in development and disease

"A disintegrin and metalloprotease" (ADAM) proteases form a still growing family of about 40 type 1 transmembrane proteins. They are defined by a common modular ectodomain architecture that combines cell deadhesion/adhesion and fusion motifs (disintegrin and cysteine-rich domains), with a Zn-protease domain capped by a large prodomain. Their ectodomain thus strikingly resembles snake venom disintegrin proteases, which by combined integrin blocking and extracellular proteolysis, can cause extensive tissue damage after snake bites. A surprisingly large proportion (13 ADAMs) is exclusively expressed in the male gonads, and only a minority can be found throughout all tissues. As predicted by their amino acid sequence, a major proportion of this family has not maintained a functional protease domain, most probably rendering them into pure adhesion and/or fusion proteins. For most ADAMs, the respective key function has remained elusive. Despite their overall conserved ectodomain structure, ADAMs appear to be subdivided into those with a predominant role in direct adhesion (e.g., ADAMs 1, 2, and 3) and those mainly acting as proteases (e.g., ADAMs 10 and 17). Only for a few of them are functions of more than one domain documented (e.g., ADAM9 in cell fusion and proteolysis). Several ADAMs exist in both membrane-resident and secreted isoforms; the functional significance of this dichotomy is in most cases still unclear. Knockout phenotypes have been informative only in a few cases (ADAMs 1, 2, 10, 12, 15, 17, and 19) and are mainly related to their protease function. A common denominator of ADAM-mediated proteolysis is the ectodomain shedding of a broad spectrum of substrates, including paracrine growth factors like epidermal growth factor receptor (EGFR) ligands, cell adhesion molecules like CD44 or cadherins, and the initiation of regulated intramembrane proteolysis (RIP), whereby the transmembrane fragment of the respective substrate is further cleaved by an intramembrane cleaving protease to release an intracellular domain acting as a nuclear transcription regulator. Most ADAMs feature a significant overlap of substrate specificities, explaining why an inactivation of individual ADAMs only rarely causes major phenotypes.

Aberrant alternative exon use and increased copy number of human metalloprotease-disintegrin ADAM15 gene in breast cancer cells

ADAM genes have been associated with cancer, with ADAM expression, genomic rearrangements, and, by implication of ADAM proteins in the altered behavior found in tumor cells. In the present study, increased copy number of the ADAM15 gene in human breast cancer cell lines was demonstrated by fluorescence in situ hybridization. This was not reflected in mRNA levels, however. Instead, the use of alternative ADAM15 exons appeared erratic, leading to aberrant combinations of ADAM15 mRNA isoforms in the cancer cells. Clustering analysis indicated that these isoform patterns were nonrandom, suggesting a failure in the regulation mechanism or mechanisms of the alternative exon usage. Altered regulation of alternative exon usage may provide a useful target for cancer diagnostics development. ADAM15 would be particularly appropriate for breast cancer diagnostics because the various combinations of its three alternatively used exons can be readily examined with a simple, straightforward PCR protocol.

Expression of ADAM15 in rheumatoid synovium: up-regulation by vascular endothelial growth factor and possible implications for angiogenesis

ADAMs (a disintegrin and metalloproteinases) comprise a new gene family of metalloproteinases, and may play roles in cell-cell interaction, cell migration, signal transduction, shedding of membrane-anchored proteins and degradation of extracellular matrix. We screened the mRNA expression of 10 different ADAMs with a putative metalloproteinase motif in synovial tissues from patients with rheumatoid arthritis (RA) or osteoarthritis (OA). Reverse transcription PCR and real-time quantitative PCR analyses indicated that among the ADAMs, ADAM15 mRNA was more frequently expressed in the RA samples and its expression level was significantly 3.8-fold higher in RA than in OA (p < 0.01). In situ hybridization, immunohistochemistry and immunoblotting demonstrated that ADAM15 is expressed in active and precursor forms in the synovial lining cells, endothelial cells of blood vessels and macrophage-like cells in the sublining layer of RA synovium. There was a direct correlation between ADAM15 mRNA expression levels and vascular density in the synovial tissues (r = 0.907, p < 0.001; n = 20). ADAM15 was constitutively expressed in RA synovial fibroblasts and human umbilical vein endothelial cells (HUVECs), and the expression level was increased in HUVECs by treatment with vascular endothelial growth factor (VEGF)165. On the other hand, ADAM15 expression in RA synovial fibroblasts was enhanced with VEGF165 only if vascular endothelial growth factor receptor (VEGFR)-2 expression was induced by treatment with tumor necrosis factor-alpha, and the expression was blocked with SU1498, a specific inhibitor of VEGFR-2. These data demonstrate that ADAM15 is overexpressed in RA synovium and its expression is up-regulated by the action of VEGF165 through VEGFR-2, and suggest the possibility that ADAM15 is involved in angiogenesis in RA synovium.

The disintegrin domain of ADAM9: a ligand for multiple beta1 renal integrins

Renal tubular epithelial cells in all nephron segments express a distinct member of the metalloprotease-disintegrin family, ADAM9 (a disintegrin and metalloprotease 9), in a punctate basolateral distribution co-localized to the beta1 integrin chain [Mahimkar, Baricos, Visaya, Pollock and Lovett (2000) J. Am. Soc. Nephrol. 11, 595-603]. Discrete segments of the nephron express several defined beta1 integrins, suggesting that ADAM9 interacts with multiple renal integrins and thereby regulates epithelial cell-matrix interactions. Intact ADAM9 and a series of deletion constructs sequentially lacking the metalloprotease domain and the disintegrin domain were assembled as chimaeras with a C-terminal GFP (green fluorescent protein) tag. Stable expression of the ADAM9/GFP protein on the surface of HEK-293 cells (human embryonic kidney 293 cells) significantly decreased adhesion to types I and IV collagen, vitronectin and laminin, but had little effect on adhesion to fibronectin. Expression of the disintegrin/cysteine-rich/GFP construct yielded a similar, but more marked pattern of decreased adhesion. Expression of the cysteine-rich/GFP construct had no effect on adhesion, indicating that the disintegrin domain was responsible for the competitive inhibition of cell-matrix binding. To define the specific renal tubular beta1 integrins interacting with the ADAM9 disintegrin domain, a recombinant GST (glutathione S-transferase)-disintegrin protein was used as a substrate in adhesion assays in the presence or absence of specific integrin-blocking antibodies. Inclusion of antibodies to alpha1, alpha3, alpha6, alphav and beta1 blocked adhesion of HEK-293 cells to GST-disintegrin protein. Immobilized GST-disintegrin domain perfused with renal cortical lysates specifically recovered the alpha3, alpha6, alphav and beta1 integrin chains by Western analysis. It is concluded that ADAM9 is a polyvalent ligand, through its disintegrin domain, for multiple renal integrins of the beta1 class.

Expression of ADAM15 in lung carcinomas

ADAM15, a member of the ADAM (a disintegrin and metalloprotease) family, is a membrane protein containing both protease and adhesion domains and may, thus, be involved in tumor invasion and metastasis. The aim of this study was to analyze the expression of ADAM15 and its potential ligand, integrin alpha(v)beta3 (CD51/CD61), in lung carcinoma cell lines and tissues. Most small cell lung carcinomas (SCLCs) and non-SCLC cell lines were ADAM15, alpha(v) and beta3 integrin mRNA positive. Half of the cell lines expressed ADAM15, and three expressed the alpha(v)beta3 heterodimer at the cell surface as shown using flow cytometry. Paraffin sections of pulmonary epithelial tumors, including SCLCs (n=26), squamous cell cancer (SCCs, n=27) and adenocarcinomas (ACs, n=17) were stained with antibodies to the ectosolic and cytosolic domain of ADAM15 and alpha(v)beta3 integrin complex. The results were scored (0-12, according to Remmele's score). Normal epithelial cells of the lung were negative or slightly positive for ADAM15 (score<2). The score was always significantly higher for tumor cells. ACs showed the strongest staining (tumor center; ADAM15ecto; mean+/-SEM; 5.47+/-1.04), whereas SCLCs only showed weak ADAM15 expression (2.67+/-0.42; SCCs: 3.62+/-0.62). Frequently, significantly stronger ADAM15 expression has been shown in tumor cells located at the front of invasion compared with those within solid formations. Overall analysis of all tumor specimens and each tumor type revealed no significant correlation between tumor stage or degree of differentiation and ADAM15 ectosolic or cytosolic domain expression in tumor cells. Both molecules are often co-localized in the same tumor cells in ADAM15- and alpha(v)beta3 integrin-positive carcinomas. In summary, lung carcinoma cell lines and tissues were frequently ADAM15 positive.

ADAMs: key components in EGFR signalling and development

ADAM (a disintegrin and metalloprotease) proteins are membrane-anchored metalloproteases that process and shed the ectodomains of membrane-anchored growth factors, cytokines and receptors. ADAMs also have essential roles in fertilization, angiogenesis, neurogenesis, heart development and cancer. Research on ADAMs and their role in protein ectodomain shedding is emerging as a fertile ground for gathering new insights into the functional regulation of membrane proteins.

ADAM15 decreases integrin αvβ3/vitronectin-mediated ovarian cancer cell adhesion and motility in an RGD-dependent fashion

We have recently described that integrin alphavbeta3 upon interaction with its major extracellular matrix ligand vitronectin induces adhesion, motility, and proliferation of human ovarian cancer cells. Due to the important function of alphavbeta3 in cancer cell biology, it has been the effort of many scientific approaches to specifically target alphavbeta3-mediated cell adhesion and tumorbiological effects arising thereof by synthetic integrin antagonists. More recently, proteins of the ADAM family have been recognized as naturally occurring integrin ligands. Among those, human ADAM15 which encompasses the integrin binding RGD motif was shown to interact with integrin alphavbeta3. Thus, we investigated in human ovarian OV-MZ-6 cancer cells, expressing both ADAM15 and alphavbeta3, whether ADAM15 might affect alphavbeta3-mediated tumorbiological effects. We stably (over)expressed ADAM15 or its extracellular domain in OV-MZ-6 cells as well as respective ADAM15 mutants containing the tripeptide SGA instead of RGD. Cells (over)expressing ADAM15-RGD exhibited a significantly reduced alphavbeta3-mediated adhesion to vitronectin. Also, a significant time-dependent decline in numbers of cells cultivated on vitronectin was noticed. This effect was found to be rather due to impaired alphavbeta3-mediated cell adhesion than decreased cell proliferation rates, since de novo DNA synthesis was not significantly altered by elevated ADAM15 expression. Moreover, a substantially decreased random cellular motility was noticed as a function of ADAM15 encompassing an intact RGD motif. In conclusion, our results point to a physiological role of ADAM15 as a natural binding partner of integrin alphavbeta3 thereby loosening tumor cell adhesion to the underlying matrix and regulating tumor cell migration and invasion.

ADAM-15 inhibits wound healing in human intestinal epithelial cell monolayers

The disintegrin metalloproteases (or ADAMs) are membrane-anchored glycoproteins that have been implicated in cell-cell or cell-matrix interactions and in proteolysis of molecules on the cell surface. The expression and/or the pathophysiological implications of ADAMs are not known in intestinal epithelial cells. Therefore, our aim was to investigate the expression and the role of ADAMs in intestinal epithelial cells. Expression of ADAMs was assessed by RT-PCR, Western blot analysis, and immunufluorescence experiments. Wound-healing experiments were performed by using the electric cell substrate impedence sensing technology. Our results showed that ADAMs-10, -12, and -15 mRNA are expressed in the colonic human cell lines Caco2-BBE and HT29-Cl.19A. An ADAM-15 complementary DNA cloned from Caco2-BBE poly(A)+ RNA, and encompassing the entire coding region, was found to be shorter and to present a different region encoding the cytoplasmic tail compared with ADAM-15 sequence deposited in the database. In Caco2-BBE cells and colonic epithelial cells, ADAM-15 protein was found in the apical, basolateral, and intracellular compartments. We also showed that the overexpression of ADAM-15 reduced cell migration in a wound-healing assay in Caco2-BBE monolayers. Our data show that 1) ADAM-15 is expressed in human intestinal epithelia, 2) a new variant of ADAM-15 is expressed in a human intestinal epithelial cell line, and 3) ADAM-15 is involved in intestinal epithelial cells wound-healing processes. Together, these results suggest that ADAM-15 may have important pathophysiological roles in intestinal cells.