A family of cellular proteins related to snake venom disintegrins

ADAM9 promotes type I interferon-mediated innate immunity during encephalomyocarditis virus infection

Viral myocarditis, an inflammatory disease of the heart, causes significant morbidity and mortality. Type I interferon (IFN)-mediated antiviral responses protect against myocarditis, but the mechanisms are poorly understood. We previously identified A Disintegrin And Metalloproteinase domain 9 (ADAM9) as an important factor in viral pathogenesis. ADAM9 is implicated in a range of human diseases, including inflammatory diseases; however, its role in viral infection is unknown. Here, we demonstrate that mice lacking ADAM9 are more susceptible to encephalomyocarditis virus (EMCV)-induced death and fail to mount a characteristic type I IFN response. This defect in type I IFN induction is specific to positive-sense, single-stranded RNA (+ ssRNA) viruses and involves melanoma differentiation-associated protein 5 (MDA5)-a key receptor for +ssRNA viruses. Mechanistically, ADAM9 binds to MDA5 and promotes its oligomerization and thereby downstream mitochondrial antiviral-signaling protein (MAVS) activation in response to EMCV RNA stimulation. Our findings identify a role for ADAM9 in the innate antiviral response, specifically MDA5-mediated IFN production, which protects against virus-induced cardiac damage, and provide a potential therapeutic target for treatment of viral myocarditis.

A Disintegrin and Metalloproteinase 9 Domain (ADAM9) Is a Major Susceptibility Factor in the Early Stages of Encephalomyocarditis Virus Infection

Encephalomyocarditis virus (EMCV) is a picornavirus that produces lytic infections in murine and human cells. Employing a genome-wide CRISPR-Cas9 knockout screen to find host factors required for EMCV infection, we identified a role for ADAM9 in EMCV infection. CRISPR-mediated deletion of ADAM9 in multiple human cell lines rendered the cells highly resistant to EMCV infection and cell death. Primary fibroblasts from ADAM9 KO mice were also strongly resistant to EMCV infection and cell death. In contrast, ADAM9 KO and WT cells were equally susceptible to infection with other viruses, including the picornavirus Coxsackie virus B. ADAM9 KO cells failed to produce viral progeny when incubated with EMCV. However, bypassing EMCV entry into cells through delivery of viral RNA directly to the cytosol yielded infectious EMCV virions from ADAM9 KO cells, suggesting that ADAM9 is not required for EMCV replication post-entry. These findings establish that ADAM9 is required for the early stage of EMCV infection, likely for virus entry or viral genome delivery to the cytosol.IMPORTANCE Viral myocarditis is a leading cause of death in the United States, contributing to numerous unexplained deaths in people ≤35 years old. Enteroviruses contribute to many cases of human myocarditis. Encephalomyocarditis virus (EMCV) infection causes viral myocarditis in rodent models, but its receptor requirements have not been fully identified. CRISPR-Cas9 screens can identify host dependency factors essential for EMCV infection and enhance our understanding of key events that follow viral infection, potentially leading to new strategies for preventing viral myocarditis. Using a CRISPR-Cas9 screen, we identified a disintegrin and metalloproteinase 9 domain (ADAM9) as a major factor required for the early stages of EMCV infection in both human and murine infection.

Critical role of exosomes in sperm-egg fusion and virus-induced cell-cell fusion

In mammals, two integral membrane proteins, sperm IZUMO1 and egg CD9, regulate sperm-egg fusion, and their roles are critical, but yet unclear. Recent studies, however, indicate interesting connections between the sperm-egg fusion and virus-induced cell-cell fusion. First, CD9-containing exosome-like vesicles, which are released from wild-type eggs, can induce the fusion between sperm and CD9-deficient egg, even though CD9-deficient eggs are highly refractory to the fusion with sperm. This finding provides strong evidence for the involvement of CD9-containing, fusion-facilitating vesicles in the sperm-egg fusion. Secondly, there are similarities between the generation of retroviruses in the host cells and the formation of small cellular vesicles, termed exosomes, in mammalian cells. The exosomes are involved in intercellular communication through transfer of proteins and ribonucleic acids (RNAs) including mRNAs and microRNAs. These collective studies provide an insight into the molecular mechanism of membrane fusion events.

Phylogenetic and molecular evolution of the ADAM (A Disintegrin And Metalloprotease) gene family from Xenopus tropicalis, to Mus musculus, Rattus norvegicus, and Homo sapiens

ADAM (a disintegrin and metalloprotease) genes have been identified in various tissues and species, and recently associated with several important human diseases such as tumor and asthma. Although various biological processes have been known for the ADAM family in different species including fertilization, neurogenesis, infection and inflammation, little is known about its detailed phylogenetic and molecular evolutionary history. In this study, the ADAMs of Xenopus (Silurana) tropicalis, Mus musculus, Rattus norvegicus, and Homo sapiens were collected and analyzed by using the Bayesian analysis and gene synteny analysis to establish a comprehensive phylogenetic relationship and evolutionary drive of this gene family. It was found that there were more ADAMs in the two rodents than in the amphibian, suggesting an expansion of the ADAM gene family during the early evolution of mammals. All ADAMs from this expansion were retained in both the rodents, but other duplication events occurred subsequently in the two rodents, respectively, leading to the classification of rodent ADAMs as classes I, II and III. Moreover, these duplicated ADAM genes in the rodents were found to be driven by positive selection, which might be the major force to retain them in the genome. Importantly, it was also found that orthologs of ADAM3 and 5 have been lost in humans. These results not only provide valuable information of the evolution of ADAM genes, but may also help in understanding the role of ADAM genes in the pathobiology of relevant diseases.

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.

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.

Role of the endothelium during tumor cell metastasis: is the endothelium a barrier or a promoter for cell invasion and metastasis?

The malignancy of cancer disease depends on the ability of the primary tumor to metastasize to distant organs. The process of the metastasis formation has largely been analyzed, but still main pathways regarding the extravasation step at the end of the metastasis formation process are controversially discussed. An agreement has been reached about the importance of the endothelium to promote metastasis formation either by enhancing the growth of the primary tumor or by homing (targeting) the tumor cells to blood or lymph vessels. The mechanical properties of the invading tumor cells become the focus of several studies, but the endothelial cell mechanical properties are still elusive. This paper describes the different roles of the endothelium in the process of metastasis formation and focuses on a novel role of the endothelium in promoting tumor cell invasion. It discusses how novel biophysical tools and in vivo animal models help to determine the role of the endothelium in the process of tumor cell invasion. Evidence is provided that cell mechanical properties, for example, contractile force generation of tumor cells, are involved in the process of tumor cell invasion.

The salivary gland transcriptome of the neotropical malaria vector Anopheles darlingi reveals accelerated evolution of genes relevant to hematophagy

BACKGROUND

Mosquito saliva, consisting of a mixture of dozens of proteins affecting vertebrate hemostasis and having sugar digestive and antimicrobial properties, helps both blood and sugar meal feeding. Culicine and anopheline mosquitoes diverged ~150 MYA, and within the anophelines, the New World species diverged from those of the Old World ~95 MYA. While the sialotranscriptome (from the Greek sialo, saliva) of several species of the Cellia subgenus of Anopheles has been described thoroughly, no detailed analysis of any New World anopheline has been done to date. Here we present and analyze data from a comprehensive salivary gland (SG) transcriptome of the neotropical malaria vector Anopheles darlingi (subgenus Nyssorhynchus).

RESULTS

A total of 2,371 clones randomly selected from an adult female An. darlingi SG cDNA library were sequenced and used to assemble a database that yielded 966 clusters of related sequences, 739 of which were singletons. Primer extension experiments were performed in selected clones to further extend sequence coverage, allowing for the identification of 183 protein sequences, 114 of which code for putative secreted proteins.

CONCLUSION

Comparative analysis of sialotranscriptomes of An. darlingi and An. gambiae reveals significant divergence of salivary proteins. On average, salivary proteins are only 53% identical, while housekeeping proteins are 86% identical between the two species. Furthermore, An. darlingi proteins were found that match culicine but not anopheline proteins, indicating loss or rapid evolution of these proteins in the old world Cellia subgenus. On the other hand, several well represented salivary protein families in old world anophelines are not expressed in An. darlingi.

Anti-platelet effect of cumanastatin 1, a disintegrin isolated from venom of South American Crotalus rattlesnake

Disintegrins have been previously described in the venom of several snake families inhibiting signal transduction, cell-cell interactions, and cell-matrix interactions and may have therapeutic potential in heart attacks, thrombotic diseases, and cancers. This investigation describes the first disintegrin isolated from South American Crotalus venom (Venezuelan rattlesnake Crotalus durissus cumanensis), which inhibits platelet adhesion to matrix proteins. C. d. cumanensis crude venom was first separated on a Sephadex G-100 column into 4 fractions (SI to SIV). Crude venom and SIII fraction significantly diminished platelet adhesion to fibrinogen (Fg) and to fibronectin (Fn). Anti-adhesive SIII fraction was further separated by DEAE-Sephacel followed by C-18 reverse phase high performance liquid chromatography (HPLC). The platelet anti-adhesive fraction obtained was designated as cumanastatin-1. This disintegrin has a mass of 7.442 kDa as determined by mass spectrometry (MALDI-TOF/TOF) and pI of 8.5. Cumanastatin-1 also inhibited ADP-induced platelet aggregation with an IC(50) of 158 nM. However, it did not significantly inhibit collagen and thrombin-induced platelet aggregation. Cumanastatin-1 considerably inhibited anti-alpha(IIb)beta(3) integrin binding to platelets in a dose-dependent manner; however, it did not present any effect on the alpha(5)beta(1) integrin or on P-selectin.

ADAM function in embryogenesis

Cleavage of proteins inserted into the plasma membrane (shedding) is an essential process controlling many biological functions including cell signaling, cell adhesion and migration as well as proliferation and differentiation. ADAM surface metalloproteases have been shown to play an essential role in these processes. Gene inactivation during embryonic development have provided evidence of the central role of ADAM proteins in nematodes, flies, frogs, birds and mammals. The relative contribution of four subfamilies of ADAM proteins to developmental processes is the focus of this review.

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/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.

ADAM19 expression in human nephrogenesis and renal disease: Associations with clinical and structural deterioration

ADAM19, an enzyme from the ADAM (a disintegrin and metalloproteinase) family, is involved in various cell-cell and cell-matrix interactions. It can cleave epidermal growth factor (EGF)-like growth factors, such as heparin-binding (HB)-EGF and neuregulin (NRG), from the cell membrane. ADAM-mediated EGF receptor activation is crucial in the development of renal pathology. Based on these data, we studied ADAM19 in human nephrogenesis and renal disease. We collected 20 fetal kidneys and 56 biopsies from patients with various renal diseases. The unaffected part of kidneys from eight patients with renal cell carcinoma served as control. RNA in situ hybridization revealed widespread ADAM19 mRNA expression in the nephrogenic zone of human fetal kidneys. Normal human kidneys showed constitutive ADAM19 expression in distal tubules and endothelial cells, whereas proximal tubules were negative. In renal disease, ADAM19 was de novo expressed in proximal tubules and glomerular mesangium and upregulated in distal tubules and endothelial cells. ADAM19 colocalized with tubular and interstitial NRG, however, not with HB-EGF. Independent of renal disorder, mesangial ADAM19 expression was associated with glomerular damage as assessed by mesangial matrix expansion, focal glomerulosclerosis, and glomerular macrophage influx (all P<0.001). ADAM19 in proximal tubules and in peritubular capillaries was associated with interstitial fibrosis (P<0.05). Finally, increasing tubular ADAM19 was associated with declining renal function (P<0.05). The abundant ADAM19 expression during nephrogenesis points to a role in growth promotion and regulation. The high ADAM19 expression in renal disease suggests involvement in profibrotic and proinflammatory processes leading to renal deterioration.

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.

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.

Distinct roles for ADAM10 and ADAM17 in ectodomain shedding of six EGFR ligands

All ligands of the epidermal growth factor receptor (EGFR), which has important roles in development and disease, are released from the membrane by proteases. In several instances, ectodomain release is critical for activation of EGFR ligands, highlighting the importance of identifying EGFR ligand sheddases. Here, we uncovered the sheddases for six EGFR ligands using mouse embryonic cells lacking candidate-releasing enzymes (a disintegrin and metalloprotease [ADAM] 9, 10, 12, 15, 17, and 19). ADAM10 emerged as the main sheddase of EGF and betacellulin, and ADAM17 as the major convertase of epiregulin, transforming growth factor α, amphiregulin, and heparin-binding EGF-like growth factor in these cells. Analysis of adam9/12/15/17^−/− knockout mice corroborated the essential role of adam17^−/− in activating the EGFR in vivo. This comprehensive evaluation of EGFR ligand shedding in a defined experimental system demonstrates that ADAMs have critical roles in releasing all EGFR ligands tested here. Identification of EGFR ligand sheddases is a crucial step toward understanding the mechanism underlying ectodomain release, and has implications for designing novel inhibitors of EGFR-dependent tumors.

AmpA, a modular protein containing disintegrin and ornatin domains, has multiple effects on cell adhesion and cell fate specification

Proteins containing disintegrin domains play a variety of roles in regulating processes involving adhesion, migration and cell type specification during development of many metazoan organisms. Most disintegrin domain containing proteins belong to the ADAM (a disintegrin and a metalloprotease) family of proteins that also contain a metalloprotease domain. Here we describe a small secreted protein from Dictyostelium that contains multiple repeated domains sharing homology with both the disintegrin motif and with a second class of fibrinogen receptor antagonists, the ornatins. This protein, called AmpA for its role in modulating adhesion, differs from the ADAM family proteins in that it lacks a metalloprotease domain. Nonetheless, it appears to be involved in the same complex spectrum of developmental functions as the metazoan ADAM family proteins. Here we review the structure and evolution of this protein and its function in cell adhesion and cell type specification. We discuss possible mechanisms by which it might function and review the emerging evidence for a close coupling between cell adhesion and cell type specification.

Tumor necrosis factor-alpha converting enzyme is processed by proprotein-convertases to its mature form which is degraded upon phorbol ester stimulation

Tumor necrosis factor-alpha converting enzyme (TACE or ADAM17) is a member of the ADAM (a disintegrin and metalloproteinase) family of type I membrane proteins and mediates the ectodomain shedding of various membrane-anchored signaling and adhesion proteins. TACE is synthesized as an inactive zymogen, which is subsequently proteolytically processed to the catalytically active form. We have identified the proprotein-convertases PC7 and furin to be involved in maturation of TACE. This maturation is negatively influenced by the phorbol ester phorbol-12-myristate-13-acetate (PMA), which decreases the cellular amount of the mature form of TACE in PMA-treated HEK293 and SH-SY5Y cells. Furthermore, we found that stimulation of protein kinase C or protein kinase A signaling pathways did not influence long-term degradation of mature TACE. Interestingly, PMA treatment of furin-deficient LoVo cells did not affect the degradation of mature TACE. By examination of furin reconstituted LoVo cells we were able to exclude the possibility that PMA modulates furin activity. Moreover, the PMA dependent decrease of the mature enzyme form is specific for TACE, as the amount of mature ADAM10 was unaffected in PMA-treated HEK293 and SH-SY5Y cells. Our results indicate that the activation of TACE by the proprotein-convertases PC7 and furin is very similar to the maturation of ADAM10 although there is a significant difference in the cellular stability of the mature enzyme forms after phorbol ester treatment.

A recombinant chimeric epidermal growth factor-like module with high binding affinity for integrins

Integrins are cell surface receptors involved in numerous pathological processes such as metastasis invasion and abnormal angiogenesis. To target these receptors, the epidermal growth factor (EGF)-like domain of human complement protease C1r was used as a natural scaffold to design chimeric modules containing the RGD motif. Here we report a high yield bacterial expression system and its application to the production of two such modules, EGF-RGD and V2, the latter variant mimicking the RGD-containing domain of disintegrins. These modules were characterized chemically, and their biological activity was investigated by cellular assays using various Chinese hamster ovary cell lines expressing beta1 and beta3 integrins and by surface plasmon resonance spectroscopy. Remarkably, the modifications leading to the V2 variant had differential effects on the interaction with beta3 and beta1 integrins. The disintegrin-like V2 module exhibited enhanced binding affinities compared with EGF-RGD, with KD values of 7.2 nm for alpha5beta1 (a 4-fold decrease) and 3.5 nm for alphavbeta3 (a 1.5-fold decrease), comparable with the values determined for natural integrin ligands. Analysis by NMR spectroscopy also revealed a differential dynamic behavior of the RGD motif in the EGF-RGD and V2 variants, providing insights into the structural basis of their relative binding efficiency. These novel RGD-containing EGF modules open the way to the design of improved variants with selective affinity for particular integrins and their use as carriers for other biologically active modules.

Application of Recombinant Rhodostomin in Studying Cell Adhesion

Rhodostomin from venom of Agkistrodon rhodostoma (also called Calloselasma rhodostoma) contains 68 amino acid residues including 6 pairs of disulfide bonds and an arginine-glycine-aspartic acid (RGD) sequence at positions 49-51. It has been known as one of the strongest antagonists to platelet aggregation among the family termed disintegrin. In this review paper, in addition to introducing the characteristics of disintegrin and its related molecules, the advantages of using recombinant DNA technology to produce rhodostomin are described. The recombinant rhodostomin has been demonstrated to facilitate cell adhesion via interaction between the RGD motif of rhodostomin and integrins on the cell surface. This property allowed us to use the recombinant rhodostomin as an extracellular matrix to study cell adhesion and to distinguish attachment efficiency between two melanoma cell lines B16-F1 and B16-F10, the former is a low metastasis cell while the latter is a high metastasis cell. Furthermore, by using the recombinant rhodostomin as a substrate, osteoprogenitor-like cells are able to be selected and enriched within 3 days from rat bone marrow which contains a heterogeneous cell population. Finally, we show that the recombinant rhodostomin can be immobilized on beads and which serve as an affinity column to dissect cell-surface protein(s) binding to the RGD motif of rhodostomin.

Functional classification of ADAMs based on a conserved motif for binding to integrin alpha 9beta 1: implications for sperm-egg binding and other cell interactions

ADAMs (a disintegrin and metalloproteases) are members of the metzincin superfamily of metalloproteases. Among integrins binding to disintegrin domains of ADAMs are alpha(9)beta(1) and alpha(v)beta(3), and they bind in an RGD-independent and an RGD-dependent manner, respectively. Human ADAM15 is the only ADAM with the RGD motif in the disintegrin domain. Thus, both integrin alpha(9)beta(1) and alpha(v)beta(3) recognize the ADAM15 disintegrin domain. We determined how these integrins recognize the ADAM15 disintegrin domain by mutational analysis. We found that the Arg(481) and the Asp-Leu-Pro-Glu-Phe residues (residues 488-492) were critical for alpha(9)beta(1) binding, but the RGD motif (residues 484-486) was not. In contrast, the RGD motif was critical for alpha(v)beta(3) binding, but the other residues flanking the RGD motif were not. As the RX(6)DLPEF alpha(9)beta(1) recognition motif (residues 481-492) is conserved among ADAMs, except for ADAM10 and 17, we hypothesized that alpha(9)beta(1) may recognize disintegrin domains in all ADAMs except ADAM10 and 17. Indeed we found that alpha(9)beta(1) bound avidly to the disintegrin domains of ADAM1, 2, 3, and 9 but not to the disintegrin domains of ADAM10 and 17. As several ADAMs have been implicated in sperm-oocyte interaction, we tested whether the functional classification of ADAMs, based on specificity for integrin alpha(9)beta(1), applies to sperm-egg binding. We found that the ADAM2 and 15 disintegrin domains bound to oocytes, but the ADAM17 disintegrin domain did not. Furthermore, the ADAM2 and 15 disintegrin domains effectively blocked binding of sperm to oocytes, but the ADAM17 disintegrin domain did not. These results suggest that oocytes and alpha(9)beta(1) have similar binding specificities for ADAMs and that alpha(9)beta(1), or a receptor with similar specificity, may be involved in sperm-egg interaction during fertilization. As alpha(9)beta(1) is a receptor for many ADAM disintegrins and alpha(9)beta(1) and ADAMs are widely expressed, alpha(9)beta(1)-ADAM interaction may be of a broad biological importance.

Downregulated expression of ADAM9 in anterior polar cataracts

PURPOSE

To determine whether ADAM (a disintegrin and metalloproteinase) is regulated in lens epithelial cells (LECs) of patients with anterior polar cataracts and by transforming growth factor (TGF)-beta 1 in cultured LECs.

SETTING

Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, Seoul, Korea.

METHODS

Lens epithelial cells attached to the anterior capsules of human cataractous lenses with nuclear and anterior subcapsular cataracts and noncataractous lenses were analyzed by reverse transcribed-polymerase chain reaction for the expression of ADAMs. The effect of TGF-beta 1 on ADAM gene expression was also tested in mouse lens epithelial explants and cultured LEC lines (alpha TN-4 and HLE B-3).

RESULTS

Significantly reduced expression of mRNA for ADAM9 was observed in LECs from patients with anterior polar cataracts. The expression of mRNA for ADAM9 was downregulated by TGF-beta 1 in cultured human LECs. Treatment of cultured mouse LECs with TGF-beta 1 led to a reduction in ADAM1 mRNA.

CONCLUSIONS

ADAMs are expressed and regulated in LECs. The downregulated expression of ADAM9 may serve as a marker for anterior polar cataracts in addition to previously known proteins, fibronectin, alpha-SMA, and beta ig-h3. The functions of this protein in lens pathology require further investigation.

Snake venoms

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins act on components of the haemostatic system in humans. The paper focuses on those venom constituents that affect the blood coagulation pathway, endothelial cells and platelets. Several highly purified venom enzymes have been used clinically as anticoagulants, and other venom proteins are being used in preclinical research to investigate their possible therapeutic potential. Haemostatically active components are distributed widely in the venom of many different snake species. In no case are all the components described below found in any single venom. Venom components can be grouped into several categories depending on their haemostatic effect. The following haemostatically active components are discussed in this chapter: enzymes that cause fibrinogen coagulation: enzymes that degrade fibrin(ogen); plasminogen activator; prothrombin activators; factor V activator; factor X activator; anticoagulant activities: enzymes with haemorrhagic activity; platelet aggregation inducers: and platelet aggregation inhibitors.

RGD-independent binding of integrin alpha9beta1 to the ADAM-12 and -15 disintegrin domains mediates cell-cell interaction

ADAMs (a disintegrin and metalloproteases) mediate several important processes (e.g. tumor necrosis factor-alpha release, fertilization, and myoblast fusion). The ADAM disintegrin domains generally lack RGD motifs, and their receptors are virtually unknown. Here we show that integrin alpha(9)beta(1) specifically interacts with the recombinant ADAMs-12 and -15 disintegrin domains in an RGD-independent manner. We also show that interaction between ADAM-12 or -15 and alpha(9)beta(1) supports cell-cell interaction. Interestingly, the cation requirement and integrin activation status required for alpha(9)beta(1)/ADAM-mediated cell adhesion and cell-cell interaction is similar to those required for known integrin-extracellular matrix interaction. These results are quite different from recent reports that ADAM-2/alpha(6)beta(1) interaction during sperm/egg fusion requires an integrin activation status distinct from that for extracellular matrix interaction. These results suggest that alpha(9)beta(1) may be a major receptor for ADAMs that lack RGD motifs, and that, considering a wide distribution of ADAMs and alpha(9)beta(1), this interaction may be of potential biological and pathological significance.

Cloning and characterization of ADAM28: evidence for autocatalytic pro-domain removal and for cell surface localization of mature ADAM28

The metalloprotease disintegrins are a family of membrane-anchored glycoproteins with diverse functions in fertilization, myoblast fusion, neurogenesis and protein ectodomain shedding. Here we report a cDNA sequence, encoding a metalloprotease disintegrin, termed ADAM28 ('a disintegrin and metalloprotease 28'), which was cloned from mouse lung. From protein sequence comparisons, ADAM28 is more closely related to snake venom metalloproteases (SVMPs) than to other ADAMs, and hence may cleave similar substrates to SVMPs, perhaps including components of the extracellular matrix. Northern blot analysis of selected mouse tissues revealed that ADAM28 is expressed highly and in alternatively spliced forms in the epididymis, suggesting a possible role in sperm maturation, and at lower levels in lung. The intracellular maturation of ADAM28 expressed in COS-7 cells resembles that of other ADAMs, in that ADAM28 is made as a precursor and processed to a mature form in a late Golgi compartment of the secretory pathway. Most or all of the mature, and thus presumably catalytically active, form of ADAM28 in COS-7 cells is accessible to cell surface trypsinization, suggesting that ADAM28 functions mainly on the cell surface. A mutation converting the catalytic-site glutamate residue into alanine abolishes pro-domain removal, even though this mutant form of ADAM28 can be transported to the cell surface in a manner similar to the wild-type protein. This suggests that pro-domain removal and maturation of ADAM28 may be, at least in part, autocatalytic. This is in contrast with several other ADAMs, for which furin-like proprotein convertases are involved in pro-domain removal, and in which a glutamate-to-alanine mutation in the catalytic site does not alter pro-domain removal.

Meltrin gamma(ADAM-9) mediates cellular adhesion through alpha(6)beta(1)integrin, leading to a marked induction of fibroblast cell motility

The ADAMs (A Disintegrin and Metalloprotease Domains) are a family of membrane-anchored proteins that play a role in fertilisation, myoblast fusion and ectodomain shedding of cell surface proteins. Meltrin gamma (ADAM-9) is a widely expressed member of this family and is involved in the shedding of heparin binding epidermal growth factor. Here we report that meltrin gamma can function as a cell adhesion molecule via its disintegrin domain. Using solid-phase binding assays and antibody inhibition experiments, we demonstrate that a murine meltrin gamma-Fc (Mel gamma -Fc) fusion protein binds to the integrin alpha(6)beta(1) on the surface of fibroblast cell lines, HT1080 and Wehi 164 in a specific manner. Since alpha(6)beta(1) is important for the motility of several cell types on laminin, cell migration studies using time-lapse video microscopy were performed. Cells adhering to Mel gamma-Fc displayed a rounded morphology and a marked increase (eight- to tenfold) in their motility compared to that on laminin. Furthermore, the p160 ROCK kinase inhibitor Y-27632 specifically reduced the migration of cells on meltrin gamma but had no effect on migration of cells on laminin, whilst the general tyrosine phoshorylation inhibitor, genistein, inhibited cell migration on both substrates. These results together suggest that meltrin gamma may play a role in regulating the motility of cells by binding to alpha(6)beta(1) integrin and this may be important during a variety of biological and pathological processes.

Identification of ADAM 31: a protein expressed in Leydig cells and specialized epithelia

A family of proteins containing a disintegrin and metalloproteinase domain (ADAMs) has been identified recently. Here, we report the identification of a novel member of the ADAM protein family from mouse. This protein is designated ADAM 31. The complementary DNA sequence of ADAM 31 predicts a transmembrane protein with metalloproteinase, disintegrin, cysteine-rich, and cytoplasmic domains. Messenger RNA encoding ADAM 31 was most abundant in testes, but was also detected in many other tissues. More significantly, the antibodies raised against ADAM 31 reveal that the protein has a unique and restricted expression pattern. ADAM 31 is expressed in Leydig cells of the testes, but unlike many other ADAMs, it is not found on developing sperm. Furthermore, ADAM 31 is highly expressed on four types of specialized epithelia: the cauda epididymidis, the vas deferens, the convoluted tubules of the kidney, and the parietal cells of the stomach.

Cloning and characterization of ADAM28: evidence for autocatalytic pro-domain removal and for cell surface localization of mature ADAM28

The metalloprotease disintegrins are a family of membrane-anchored glycoproteins with diverse functions in fertilization, myoblast fusion, neurogenesis and protein ectodomain shedding. Here we report a cDNA sequence, encoding a metalloprotease disintegrin, termed ADAM28 ('a disintegrin and metalloprotease 28'), which was cloned from mouse lung. From protein sequence comparisons, ADAM28 is more closely related to snake venom metalloproteases (SVMPs) than to other ADAMs, and hence may cleave similar substrates to SVMPs, perhaps including components of the extracellular matrix. Northern blot analysis of selected mouse tissues revealed that ADAM28 is expressed highly and in alternatively spliced forms in the epididymis, suggesting a possible role in sperm maturation, and at lower levels in lung. The intracellular maturation of ADAM28 expressed in COS-7 cells resembles that of other ADAMs, in that ADAM28 is made as a precursor and processed to a mature form in a late Golgi compartment of the secretory pathway. Most or all of the mature, and thus presumably catalytically active, form of ADAM28 in COS-7 cells is accessible to cell surface trypsinization, suggesting that ADAM28 functions mainly on the cell surface. A mutation converting the catalytic-site glutamate residue into alanine abolishes pro-domain removal, even though this mutant form of ADAM28 can be transported to the cell surface in a manner similar to the wild-type protein. This suggests that pro-domain removal and maturation of ADAM28 may be, at least in part, autocatalytic. This is in contrast with several other ADAMs, for which furin-like proprotein convertases are involved in pro-domain removal, and in which a glutamate-to-alanine mutation in the catalytic site does not alter pro-domain removal.

Binding of ADAM12, a marker of skeletal muscle regeneration, to the muscle-specific actin-binding protein, alpha -actinin-2, is required for myoblast fusion

ADAM12 belongs to the transmembrane metalloprotease ADAM ("a disintegrin and metalloprotease") family. ADAM12 has been implicated in muscle cell differentiation and fusion, but its precise function remains unknown. Here, we show that ADAM12 is dramatically up-regulated in regenerated, newly formed fibers in vivo. In C2C12 cells, ADAM12 is expressed at low levels in undifferentiated myoblasts and is transiently up-regulated at the onset of differentiation when myoblasts fuse into multinucleated myotubes, whereas other ADAMs, such as ADAMs 9, 10, 15, 17, and 19, are expressed at all stages of differentiation. Using the yeast two-hybrid screen, we found that the muscle-specific alpha-actinin-2 strongly binds to the cytoplasmic tail of ADAM12. In vitro binding assays with GST fusion proteins confirmed the specific interaction. The major binding site for alpha-actinin-2 was mapped to a short sequence in the membrane-proximal region of ADAM12 cytoplasmic tail; a second binding site was identified in the membrane-distal region. Co-immunoprecipitation experiments confirm the in vivo association of ADAM12 cytoplasmic domain with alpha-actinin-2. Overexpression of the entire cytosolic ADAM12 tail acted in a dominant negative fashion by inhibiting fusion of C2C12 cells, whereas expression of a cytosolic ADAM12 lacking the major alpha-actinin-2 binding site had no effect on cell fusion. Our results suggest that interaction of ADAM12 with alpha-actinin-2 is important for ADAM12 function.

Identification, cellular distribution and potential function of the metalloprotease-disintegrin MDC9 in the kidney

The complex interactions of glomerular and tubular epithelial cells with the basal laminae play a critical role in renal function. Disruption of these interactions has been widely implicated in glomerular diseases and acute renal failure. MDC are a large family of membrane-bound proteins containing metalloprotease, disintegrin (integrin interaction sites), and cysteine-rich domains. Little information is available concerning the presence of MDC in the kidney or their role in renal pathophysiology. Using degenerate PCR primers for the conserved metalloprotease and disintegrin domains of this protein family, cDNA templates from tubules, whole glomeruli, and glomerular epithelial cells (GEC) yielded a single, 195-bp product, which on sequence analysis corresponded to a region in the disintegrin domain of MDC9. Northern analysis of poly(A)+ RNA from tubules, whole glomeruli, and GEC revealed a 3.9-kb transcript, identical to that of mouse MDC9. Using antibodies generated against a 21-amino acid peptide present in the metalloprotease domain of MDC9, Western analysis of concanavalin A-enriched glomerular microsomal extracts demonstrated both processed (76 kD) and unprocessed (116 kD) forms of MDC9, which upon reduction changed to the corresponding 84- and 124-kD forms. Histochemical studies revealed a basolateral localization of intrinsic MDC9 protein in renal cortical tubule cells and glomerular visceral epithelial cells, which colocalized with the beta1 integrin chain. Expression of green fluorescence protein MDC9 chimeric constructs in GEC or polarized Madin-Darby canine kidney epithelial cells revealed a similar punctate basolateral surface localization. Transient overexpression of the soluble disintegrin domain-green fluorescence protein chimera in GEC led to dramatic changes in cellular morphology with rounding and detachment from cell monolayers. These studies document the presence of MDC9 in renal epithelial cells and suggest an important role for MDC9 in renal epithelial cellular interactions with the basal lamina and adjoining cells.

Metalloprotease-disintegrins: modular proteins capable of promoting cell-cell interactions and triggering signals by protein-ectodomain shedding

Metalloprotease-disintegrins (ADAMs) have captured our attention as key players in fertilization and in the processing of the ectodomains of proteins such as tumor necrosis factor (α) (TNF(α)), and because of their roles in Notch-mediated signaling, neurogenesis and muscle fusion. ADAMs are integral membrane glycoproteins that contain a disintegrin domain, which is related to snake-venom integrin ligands, and a metalloprotease domain (which can contain or lack a catalytic site). Here, we review and critically discuss current topics in the ADAMs field, including the central role of fertilin in fertilization, the role of the TNF(α) convertase in protein ectodomain processing, the role of Kuzbanian in Notch signaling, and links between ADAMs and processing of the amyloid-precursor protein.

MDC-L, a novel metalloprotease disintegrin cysteine-rich protein family member expressed by human lymphocytes

The metalloprotease disintegrin cysteine-rich (MDC) proteins are a recently identified family of transmembrane proteins that function in proteolytic processing of cell surface molecules and in cell adhesion. Since lymphocytes must interact with a constantly changing environment, we hypothesized that lymphocytes would express unique MDC proteins. To identify MDC proteins expressed in human lymph node, a polymerase chain reaction-based strategy combined with degenerate oligonucleotide primers was employed. We report here the identification of MDC-L (ADAM 23), a novel member of the MDC protein family. The results obtained from cDNA cloning and Northern blot analysis of mRNA isolated from various lymphoid tissues indicate that a 2.8-kilobase mRNA encoding a transmembrane form, MDC-Lm, and a 2.2-kilobase mRNA encoding a secreted form, MDC-Ls, are expressed in a tissue-specific manner. MDC-L mRNA was shown to be predominantly expressed in secondary lymphoid tissues, such as lymph node, spleen, small intestine, stomach, colon, appendix, and trachea. Furthermore, immunohistochemical staining with an anti-MDC-L antibody demonstrated that cells with typical lymphocyte morphology are responsible for expression of the MDC-L antigen in these lymphoid tissues. MDC-Lm was found to be expressed on the surface of human peripheral blood lymphocytes and transformed B- and T-lymphocyte cell lines as an 87-kDa protein. Thus, we have identified a novel lymphocyte-expressed MDC protein family member.

Effects of jarastatin, a novel snake venom disintegrin, on neutrophil migration and actin cytoskeleton dynamics

A new disintegrin, an RGD-containing peptide of 6 kDa called jarastatin, was purified from Bothrops jararaca venom. It is a potent inhibitor of platelet aggregation induced by ADP, collagen, and thrombin. The effect of jarastatin on neutrophil migration in vivo and in vitro and on the actin cytoskeleton dynamics of these cells was investigated. Incubation in vitro with jarastatin significantly inhibited, in a concentration-dependent manner, the chemotaxis of human neutrophils toward fMLP, IL-8, and jarastatin itself. Despite this inhibitory effect, jarastatin induced neutrophil chemotaxis. A significant increase of F-actin content was observed in jarastatin-treated neutrophils. Furthermore, as demonstrated by confocal microscopy after FITC-phalloidin labeling, these cells accumulated F-actin at the plasmalemma, a distribution similar to that observed in fMLP-stimulated cells. Pretreatment of mice with jarastatin inhibited neutrophil migration into peritoneal cavities induced by carrageenan injection. The results suggest that binding of jarastatin to neutrophil integrins promotes cellular activation and triggers a dynamic alteration of the actin filament system and that this is one of the first event in integrin-mediated signaling.

Identification of four novel ADAMs with potential roles in spermatogenesis and fertilization

The ADAM (A Disintegrin And Metalloprotease) family is known to have important roles in various developmental systems, e.g., myogenesis and neurogenesis. In this study, we searched for ADAMs that may function in spermatogenesis or fertilization, and have cloned and sequenced four new mouse ADAM cDNAs: ADAM 24, ADAM 25, ADAM 26 and ADAM 27. The deduced amino acid sequences show that all four contain the complete domain organization common to ADAM family members. Messenger RNA for each of the four ADAMs was found only in the testis. The conserved zinc-dependent metalloprotease active site HEXGHXXGXXHD was found in the metalloprotease domain of three of the novel ADAMs, suggesting that they are testis-specific proteases, to which we give the alternative names: testase 1, ADAM 24; testase 2, ADAM 25; and testase 3, ADAM 26. Using RNA extracted from testes of pre-pubertal males of increasing age (8-40days), we found that adult levels of transcription, assessed in Northern blots, are reached by day 20 (ADAM 27), day 25 (ADAMs 24 and 25) and in the range day 25-50 (ADAM 26). These results suggest that each ADAM is transcribed in spermatogenic cells in a regulated pattern at a specific developmental stage.

Structure-function analysis of the ADAM family of disintegrin-like and metalloproteinase-containing proteins (review)

The ADAMs belong to a disintegrin-like and metalloproteinase-containing protein family that are zinc-dependent metalloproteinases. These proteins share all or some of the following domain structure: a signal peptide, a propeptide, a metalloproteinase, a disintegrin, a cysteine-rich, and an epidermal growth factor (EGF)-like domains, a transmembrane region, and a cytoplasmic tail. ADAMs are widely distributed in many organs, tissues, and cells, such as brain, testis, epididymis, ovary, breast, placenta, liver, heart, lung, bone, and muscle. These proteins are capable of four potential functions: proteolysis, adhesion, fusion, and intracellular signaling. Because the number of ADAM genes has grown rapidly and the biological functions of most members are unclear, this review analyzes the protein structures and functions, their activation and processing, their known and potential activities, and their evolutionary relationships. A sequence alignment of human ADAMs is compiled and their homology and physical data are calculated. The conceivable functions of ADAMs in reproduction, development, and diseases are also discussed.

Interaction of metargidin (ADAM-15) with alphavbeta3 and alpha5beta1 integrins on different haemopoietic cells

Metargidin (ADAM-15) is a type I transmembrane glycoprotein belonging to the ADAM (A Disintegrin and Metalloprotease Domain) family of proteins and is widely expressed in different tissues and cell types. Members of this family contain an amino-terminal metalloprotease domain followed by a disintegrin domain, a cysteine-rich region and a membrane proximal EGF-like domain. The disintegrin domain of metargidin contains an RGD tripeptide sequence, suggesting that it may potentially interact with the integrin family of proteins. Here we identify integrin ligands for metargidin on haemopoietic cells, by using a chimeric protein containing the extracellular domain of metargidin fused to the Fc portion of human IgG. Binding activity to a panel of human cell lines was analysed by solid-phase cell-adhesion assays. Metargidin bound to a monocytic cell line, U937, and a T cell line, MOLT-4, in a specific manner. Adhesion was divalent cation- and temperature- dependent and strongly enhanced by Mn2+, all features of integrin-mediated binding. Using a panel of anti-integrin antibodies we show that alphavbeta3 is a ligand for metargidin on U937 cells. In contrast, for MOLT-4 cells, the integrin alpha5beta1 contributes to cell binding. Adhesion was mediated by the disintegrin domain of metargidin as RGD-based peptides inhibited cell binding to both cell lines. The specificity of the interaction between both alphavbeta3 and alpha5beta1 and metargidin was further confirmed by solid-phase adhesion assays using purified recombinant integrins. These results together indicate that metargidin can function as a cell adhesion molecule via interactions with alphavbeta3 and alpha5beta1 integrins.

Snake venoms and the hemostatic system

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins interact with components of the human hemostatic system. This review is focused on those venom constituents which affect the blood coagulation pathway, endothelial cells, and platelets. Only highly purified and well characterized snake venom proteins will be discussed in this review. Hemostatically active components are distributed widely in the venom of many different snake species, particularly from pit viper, viper and elapid venoms. The venom components can be grouped into a number of different categories depending on their hemostatic action. The following groups are discussed in this review: (i) enzymes that clot fibrinogen; (ii) enzymes that degrade fibrin(ogen); (iii) plasminogen activators; (iv) prothrombin activators; (v) factor V activators; (vi) factor X activators; (vii) anticoagulant activities including inhibitors of prothrombinase complex formation, inhibitors of thrombin, phospholipases, and protein C activators; (viii) enzymes with hemorrhagic activity; (ix) enzymes that degrade plasma serine proteinase inhibitors; (x) platelet aggregation inducers including direct acting enzymes, direct acting non-enzymatic components, and agents that require a cofactor; (xi) platelet aggregation inhibitors including: alpha-fibrinogenases, 5'-nucleotidases, phospholipases, and disintegrins. Although many snake venoms contain a number of hemostatically active components, it is safe to say that no single venom contains all the hemostatically active components described here. Several venom enzymes have been used clinically as anticoagulants and other venom components are being used in pre-clinical research to examine their possible therapeutic potential. The disintegrins are an interesting group of peptides that contain a cell adhesion recognition motif, Arg-Gly-Asp (RGD), in the carboxy-terminal half of their amino acid sequence. These agents act as fibrinogen receptor (integrin GPIIb/IIIa) antagonists. Since this integrin is believed to serve as the final common pathway leading to the formation of platelet-platelet bridges and platelet aggregation, blockage of this integrin leads to inhibition of platelet aggregation regardless of the stimulating agent. Clinical trials suggest that platelet GPIIb/IIIa blockade is an effective therapy for the thrombotic events and restenosis frequently accompanying cardiovascular and cerebrovascular disease. Therefore, because of their clinical poten tial, a large number of disintegrins have been isolated and characterized.

Intracellular maturation of the mouse metalloprotease disintegrin MDC15

Metalloprotease disintegrins are a family of membrane-anchored glycoproteins that play a role in fertilization, myoblast fusion, neuronal development, and cleavage of the membrane-anchored cytokine tumor necrosis factor-alpha. Here, we report the cloning and cDNA sequencing of the mouse metalloprotease disintegrin MDC15 and an analysis of its processing in the secretory pathway. A notable difference between mMDC15 and its putative human orthologue (hMDC15, metargidin) is the presence of the peptide sequence TDDC instead of the RGDC found in the disintegrin domain of hMDC15. In a Western blot analysis the majority of mMDC15 was found to lack the pro-domain in all mouse tissues examined. Pulse-chase experiments in transiently transfected COS-7 cells suggest that mMDC15 is processed by a pro-protein convertase in a late Golgi compartment, since (i) addition of brefeldin A or monensin blocks pro-domain removal, (ii) all detectable processed mMDC15 is endoglycosidase H -resistant, and (iii) a recombinant soluble form of the trans-Golgi network pro-protein convertase furin can mimic mMDC15 processing in vitro. Cell-surface trypsinization revealed that more than half of mature mMDC15 is intracellular. Immunolocalization provided evidence for a strong perinuclear accumulation in a region resembling the trans-Golgi network and/or endosomal compartments. This study provides the first characterization of the intracellular processing of a metalloprotease disintegrin, and highlights the potential role of pro-protein convertases in removal of the inhibitory pro-domain. These results further suggest possible intracellular functions for mMDC15, such as in protein maturation, in addition to a potential role in cell-surface proteolysis or cell adhesion.

Voltage-dependent activation of frog eggs by a sperm surface disintegrin peptide

Fertilin, a sperm protein of the metalloprotease/disintegrin/cysteine-rich (MDC) family, plays a critical role in sperm-egg binding in mammals. Peptides corresponding to the disintegrin domain of fertilin and antibodies against fertilin have been shown to inhibit mammalian sperm-egg binding and fusion. A protein from the same family, xMDC16, was recently cloned from frog (Xenopus laevis) testis and was found to be involved in frog sperm-egg binding. Here we report that xMDC16 is localized predominantly on the posterior surface of egg jelly-activated sperm, and peptides from the disintegrin domain of this protein activate eggs when applied near the egg surface. Egg activation was dependent on (1) specific amino acid residues (KTX); (2) the presence of divalent cations, but not external Ca2+ alone; and (3) voltage across the egg plasma membrane. This is the first demonstration of egg activation in vertebrates by the surface application of a peptide derived from a sperm surface protein, supporting a model for egg activation that involves a signal transducing receptor for sperm in the egg's plasma membrane.

Full-spreading platelets induced by the recombinant rhodostomin are via binding to integrins and correlated with FAK phosphorylation

We have previously reported that non-activated platelets can be induced by morphological changes from the recombinant fusion protein of GST-rhodostomin [GST-RHO(RGD)], a member of disintegrin with an arginine-glycine-aspartic acid (RGD) motif. In this study, we further characterized the factors involved in platelet shape changes induced by rhodostomin. From less to full-spreading, four cell spreading indexes, p1, p2, s1 and s2, were designated to the platelet shape based on the scanning electron micrographs. Results of peptide competition and antibody blocking confirmed that interaction between the RGD of rhodostomin and the alpha(IIb)beta3 integrins of platelets was required for induction of a higher percentage of s2 cells. When platelets were pretreated with calphostin C, herbimycin A and cytochalasin B, respectively, the percentage of p1 and p2 cells on rhodostomin-coated plates was increased and, concomitantly, the percentage of s1 and s2 cells was decreased. Biochemical analyses indicated that the focal adhesion kinase (FAK or pp125FAK) in platelets that adhered to GST-RHO(RGD) was phosphorylated in contrast to little or no phosphorylation of FAK in cells adhered to fibrinogen or non-activated cells. Furthermore, the degree of FAK phosphorylation was consistently correlated with morphological changes in platelets treated with various drugs. Taking all the results together, we suggested that rhodostomin could directly bind to integrins of platelets and then trigger signal transduction leading to FAK phosphorylation and actin polymerization and finally resulting in platelet full-spreading.

The disintegrin domain of ADAM 8 enhances protection against rat experimental autoimmune encephalomyelitis, neuritis and uveitis by a polyvalent autoantigen vaccine

Targeting peptides have potential as components of recombinant vaccines. Here, we have analyzed a set of structurally diverse peptides fused to a polyepitope vaccine in prevention of rat generalized autoimmunity of the nervous system (GANS), a combined model of experimental autoimmune encephalomyelitis (EAE), neuritis (EAN) and uveoretinitis (EAU). The peptide sequences studied included the endothelial-monocyte-activating polypeptide II (EMAP II), the allograft inflammatory factor-1 (AIF-1), and the interferon-gamma-inducing factor (IGIF, IL-18). Further, a variety of adhesive peptides were tested, including the disintegrin domain of mouse ADAM 8. Interestingly, this disintegrin domain considerably increased the effect of the polyepitope vaccine. Of the other peptides, only IL-18 enhanced tolerance induction, but was less effective than the ADAM 8 disintegrin peptide. In conclusion, disintegrin domains will be valuable leads in the development of targeting peptides for immunointervention.

Divergent and common groups of proteins in glands of venomous snakes

Protein contents of venom-producing glands from the sea-snake Laticauda colubrina (LC) and terrestrial Vipera Russelli (VR) were studied using high-resolution two-dimensional gels: isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (IEF/SDS-PAGE) and nonequilibrium pH gradient electrophoresis (NEPHGE) followed by SDS-PAGE. Tentative identities of numerous proteins were established using their amino acid compositions and in certain cases the identities were verified by microsequencing of their N-terminals and internal fragments. As expected, we found several proteins known to be present in the venom of the respective snakes. These include numerous isoforms of phospholipase A2 (PLA2) in both snake glands, various neurotoxins in LC glands and factor IX/factor X-binding protein, hemorrhagic factor and coagulation factor X activating enzyme in Russell's viper glands (VR). Not unexpectedly, we also found a number of cell housekeeping proteins, cytoskeletal proteins, proteins that are necessary for folding, such as heat-shock proteins, protein disulfide-isomerase and peptidyl-prolyl cis/trans isomerases. Unexpectedly, however, the glands of Laticauda colubrina and Russell's viper include a large quantity of antihemorrhagic factor and inhibitor of PLA2, respectively, that have been previously described in snake plasma. The possible reason associated with the presence of these components in venom glands is discussed.

Cloning and initial characterization of mouse meltrin beta and analysis of the expression of four metalloprotease-disintegrins in bone cells

Here we report the cloning and initial biochemical characterization of the mouse metalloprotease/disintegrin/cysteine-rich (MDC) protein meltrin beta and the analysis of the mRNA expression of four MDC genes (meltrin alpha, meltrin beta, mdc9, and mdc15) in bone cells, including osteoclasts and osteoblasts. Like most other MDC proteins, the predicted meltrin beta protein consists of a signal sequence, prodomain, metalloprotease domain with a predicted catalytic site, disintegrin domain, cysteine-rich region, epidermal growth factor repeat, transmembrane domain, and cytoplasmic domain with putative signaling motifs, such as potential SH3 ligand domains. Northern blot analysis indicates that meltrin beta is widely expressed, with the highest expression in bone, heart, and lung. RNase protection studies revealed expression of all four MDC genes analyzed here in osteoblasts, whereas only mdc9 and mdc15 mRNAs were detectable in osteoclast-like cells generated in vitro. Treatment of primary osteoblasts with 10 nM calcitriol increased meltrin beta expression more than 3-fold, and both meltrin alpha and meltrin beta expression is apparently regulated in a differentiation-associated manner in a mouse osteoblastic cell line, MC3T3E1. Collectively, these results suggest that meltrin alpha and meltrin beta may play a role in osteoblast differentiation and/or function but are not likely to be involved in osteoclast fusion.

Evidence for distinct serine protease activities with a potential role in processing the sperm protein fertilin

The guinea pig sperm protein fertilin (previously termed PH-30) plays an important role in sperm-egg fusion, and was the first recognized membrane-anchored metalloprotease/disintegrin protein. Fertilin is a heterodimeric glycoprotein which undergoes at least two distinct proteolytic processing steps. Fertilin alpha is processed first, in the testis, whereas fertilin beta is processed separately during sperm maturation in the epididymis. The final processing of fertilin beta occurs immediately adjacent to its predicted integrin ligand domain, and exposes an epitope recognized by a fusion blocking monoclonal antibody. Here, we demonstrate that one or more serine protease activities associated with testicular sperm can process fertilin beta in vitro in a fashion that closely mimics the processing pattern observed in vivo during epididymal sperm maturation. In contrast, several proteases that were added to testicular sperm did not mimic the pattern observed in vivo. These findings raise the intriguing possibility that a fertilin beta converting protease(s) active in vivo may originate from sperm, instead of from the epididymal epithelium. Further, we show that fertilin alpha is most likely processed intracellularly in the secretory pathway based on three observations: (i) only processed fertilin alpha, but not the precursor pro-alpha can be cell-surface biotinylated; (ii) some processed fertilin alpha is sensitive to endoglycosidase H, suggesting cleavage occurs prior to the medial Golgi apparatus; (iii) a reanalysis of the N-terminus of processed fertilin alpha showed that the proteolytic cleavage site is next to four arginine residues, a consensus sequence for intracellular subtilysin type pro-protein convertases. The N-terminal sequence analysis further showed that processed fertilin alpha contains an intact membrane anchored disintegrin domain, and not a truncated disintegrin domain as reported previously (Blobel, C. P., Wolfsberg, T. G., Turck, C. W., Myles, D. G., Primakoff, P., and White, J. M., Nature 356, 248-252, 1992). Proteolytic processing is thought to play an important role in regulating the function of fertilin, and the present study represents a first step toward a better understanding of protease activities involved in the maturation of fertilin, and potentially other sperm surface proteins.

Analysis of a cDNA sequence encoding a novel member of the snake venom metalloproteinase, disintegrin-like, cysteine-rich (MDC) protein family from Agkistrodon contortrix laticinctus

In this paper, we present a cDNA sequence encoding a full-length precursor form of a new member (ACLD) of the metalloproteinase-disintegrin-like protein family from the venom glands of Agkistrodon contortrix laticinctus (broad-banded copperhead) snake. Comparison of the deduced amino acid sequence of ACLD with those of other members of the metalloproteinase-disintegrin protein family from both mammalian and snake venom origin suggests that some conserved residues may be involved in processing of the disintegrin domain.

Identification of metalloprotease/disintegrins in Xenopus laevis testis with a potential role in fertilization

Proteins containing a membrane-anchored metalloprotease domain, a disintegrin domain, and a cysteine-rich region (MDC proteins) are thought to play an important role in mammalian fertilization, as well as in somatic cell-cell interactions. We have identified PCR sequence tags encoding the disintegrin domain of five distinct MDC proteins from Xenopus laevis testis cDNA. Four of these sequence tags (xMDC9, xMDC11.1, xMDC11.2, and xMDC13) showed strong similarity to known mammalian MDC proteins, whereas the fifth (xMDC16) apparently represents a novel family member. Northern blot analysis revealed that the mRNA for xMDC16 was only expressed in testis, and not in heart, muscle, liver, ovaries, or eggs, whereas the mRNAs corresponding to the four other PCR products were expressed in testis and in some or all somatic tissues tested. The xMDC16 protein sequence, as predicted from the full-length cDNA, contains a metalloprotease domain with the active-site sequence HEXXH, a disintegrin domain, a cysteine-rich region, an EGF repeat, a transmembrane domain, and a short cytoplasmic tail. To study a potential role for these xMDC proteins in fertilization, peptides corresponding to the predicted integrin-binding domain of each protein were tested for their ability to inhibit X. laevis fertilization. Cyclic and linear xMDC16 peptides inhibited fertilization in a concentration-dependent manner, whereas xMDC16 peptides that were scrambled or had certain amino acid replacements in the predicted integrin-binding domain did not affect fertilization. Cyclic and linear xMDC9 peptides and linear xMDC13 peptides also inhibited fertilization similarly to xMDC16 peptides, whereas peptides corresponding to the predicted integrin-binding site of xMDC11.1 and xMDC11.2 did not. These results are discussed in the context of a model in which multiple MDC protein-receptor interactions are necessary for fertilization to occur.