A novel, secreted form of human ADAM 12 (meltrin alpha) provokes myogenesis in vivo

ADAM 12 protease induces adipogenesis in transgenic mice

ADAM 12 (meltrin-alpha) is a member of the ADAM (a disintegrin and metalloprotease) family. ADAM 12 functions as an active metalloprotease, supports cell adhesion, and has been implicated in myoblast differentiation and fusion. Human ADAM 12 exists in two forms: the prototype membrane-anchored protein, ADAM 12-L, and a shorter secreted form, ADAM 12-S. Here we report the occurrence of adipocytes in the skeletal muscle of transgenic mice in which overexpression of either form is driven by the muscle creatine kinase promoter. Cells expressing a marker of early adipogenesis were apparent in the perivascular space in muscle tissue of 1- to 2-week-old transgenic mice whereas mature lipid-laden adipocytes were seen at 3 to 4 weeks. Moreover, female transgenics expressing ADAM 12-S exhibited increases in body weight, total body fat mass, abdominal fat mass, and herniation, but were normoglycemic and did not exhibit increased serum insulin, cholesterol, or triglycerides. Male transgenics were slightly overweight and also developed herniation but did not become obese. Transgenic mice expressing a truncated form of ADAM 12-S lacking the prodomain and the metalloprotease domain did not develop this adipogenic phenotype, suggesting a requirement for ADAM 12 protease activity. This is the first in vivo demonstration that an ADAM protease is involved in adipogenesis.

Mechanisms of syncytial fusion: a review

Syncytial fusion of trophoblast is a key process in placental morphogenesis and physiology. Disturbed syncytial fusion may lead to a number of pregnancy-associated pathologies. The mechanisms regulating syncytial fusion are only partly understood. This review tries to summarize the available knowledge on trophoblast fusion, originating from different scientific disciplines. Among the themes addressed in this paper are: morphogenesis and functions of syncytiotrophoblast; early apoptotic events and changes in plasmalemmal phospholipid orientation; proteins involved in membrane fusion: ADAMs and retrovirally-derived proteins and short-lived proteolipid intermediates in membrane fusion. Deeper understanding of syncytiotrophoblast fusion in future studies is only to be anticipated from collaborative studies focusing in parallel on physicochemical events in the participating plasmalemmas, early apoptotic/differentiation events preceding the fusion and role of the fusogenic membrane proteins.

Altered expression of ADAMs (A Disintegrin And Metalloproteinase) in fibrillating human atria

BACKGROUND

ADAMs (A Disintegrin And Metalloproteinase) are ectoproteases that have recently been reported to be expressed in cardiac tissue. Although they are known to regulate cell-cell and cell-matrix interactions, their pathophysiological role in various cardiac diseases is unclear. The purpose of the present study was to determine whether structural remodeling of the atria during atrial fibrillation (AF) is associated with altered ADAM expression.

METHODS AND RESULTS

Atrial tissue samples of 30 patients undergoing open-heart surgery were examined. Fifteen patients had persistent AF (> or =6 months), and the remaining 15 patients had no history of AF. ADAM9, ADAM10, and ADAM15 expression was analyzed quantitatively at the mRNA and protein levels. ADAM expression was localized by immunohistochemistry. ADAM expression was correlated with amounts of integrins beta1 and beta3. The amount of ADAM10 protein more than doubled during AF (82+/-15 versus 36+/-8 U; P<0.01). Amounts of ADAM15 protein (102+/-12 versus 40+/-6 U; P<0.01) and mRNA (24.0+/-5.6 versus 10.5+/-2.5 U; P<0.05) increased significantly during AF compared with sinus rhythm. ADAM9 protein was not detected in any sample. ADAM/integrin ratios showed an increase of 4- to 6-fold (P<0.05) in patients with AF who had significantly dilated atria (4.94+/-0.6 versus 4.3+/-0.7 cm; P<0.05). ADAM/integrin ratios correlated with atrial diameter.

CONCLUSIONS

AF is associated with an increase in the expression of ADAM10 and ADAM15. Enhanced ADAM-dependent disintegrin and metalloproteinase activity may be a molecular mechanism that contributes to the dilation of fibrillating human atria.

Skeletal muscle cell hypertrophy induced by inhibitors of metalloproteases; myostatin as a potential mediator

Cell growth and differentiation are controlled in many tissues by paracrine factors, which often require proteolytic processing for activation. Metalloproteases of the metzincin family, such as matrix metalloproteases and ADAMs, recently have been shown to be involved in the shedding of growth factors, cytokines, and receptors. In the present study, we show that hydroxamate-based inhibitors of metalloproteases (HIMPs), such as TAPI and BB-3103, increase the fusion of C(2)C(12) myoblasts and provoke myotube hypertrophy. HIMPs did not seem to effect hypertrophy via proteins that have previously been shown to regulate muscle growth in vitro, such as insulin-like growth factor-I, calcineurin, and tumor necrosis factor-alpha. Instead, the proteolytic maturation of myostatin (growth differentiation factor-8) seemed to be reduced in C(2)C(12) cells treated with HIMPs, as suggested by the presence of nonprocessed myostatin precursor only in hypertrophic myotubes. Myostatin is a known negative regulator of skeletal muscle growth, belonging to the transforming growth factor-beta/bone morphogenetic protein superfamily. These results indicate that metalloproteases are involved in the regulation of skeletal muscle growth and differentiation, that the proteolytic maturation of myostatin in C(2)C(12) cells may be directly or indirectly linked to the activity of some unidentified HIMP-sensitive metalloproteases, and that the lack of myostatin processing on HIMP treatment may be a mediator of myotube hypertrophy in this in vitro model.

Apoptosis and syncytial fusion in human placental trophoblast and skeletal muscle

Skeletal muscle fibers and placental villous trophoblast are the main representatives of syncytia in the human. Both syncytia are derived from fusion of mononucleated stem cells, show a high degree of differentiation, and have lost their generative potency. Consequently, for their growth both depend on fusion of additional stem cells. There is evidence that syncytial fusion is directly or indirectly related to apoptotic events: As early as in the differentiated stages of the mononucleated stem cells, initiation stages of the apoptosis cascade have been observed. After syncytial fusion progression of the cascade is retarded or blocked by a variety of mechanisms. In this review we emphasize the links between apoptosis cascade, differentiation pathways and syncytial fusion. It needs to be elucidated whether these processes simply take place in parallel, both temporally and spatially, or whether there are causal connections between apoptosis cascade and syncytial fusion. Based on recent data obtained for placental villous trophoblast, it is tempting to speculate that early molecular mechanisms of the apoptosis cascade are involved in differentiation and syncytial fusion. Data obtained in skeletal muscles support this assumption and reveal a considerable degree of homology in genesis, maintenance and turnover of both tissues.

Activation of ADAM 12 protease by copper

Conversion of latent proteases to the active form occurs by various mechanisms characteristic for different protease families. Here we report that the disintegrin metalloprotease ADAM 12-S is activated by Cu(II). Copper activation is distinct from the cysteine switch component of latency: elimination of the ADAM 12 cysteine switch by a point mutation in the propeptide had no effect on copper activation, whereas mutation of an unpaired cysteine residue in the catalytic domain resulted in a mutant form of ADAM 12-S that was insensitive to copper. This suggests a multi-step activation mechanism for ADAM 12 involving both furin cleavage and copper binding.

Mutational analysis of the proteolytic domain of pregnancy-associated plasma protein-A (PAPP-A): classification as a metzincin

The bioavailability of insulin-like growth factor (IGF)-I and -II is controlled by six IGF-binding proteins (IGFBPs 1-6). Bound IGF is not active, but proteolytic cleavage of the binding protein causes release of IGF. Pregnancy-associated plasma protein-A (PAPP-A) has recently been found to cleave IGFBP-4 in an IGF-dependent manner. To experimentally support the hypothesis that PAPP-A belongs to the metzincin superfamily of metalloproteinases, all containing the elongated zinc-binding motif HEXXHXXGXXH (His-482-His-492 in PAPP-A), we expressed mutants of PAPP-A in mammalian cells. Substitution of Glu-483 with Ala causes a complete loss of activity, defining this motif as part of the active site of PAPP-A. Interestingly, a mutant with Glu-483 replaced by Gln shows residual activity. Known metzincin structures contain a so-called Met-turn, whose strictly conserved Met residue is thought to interact directly with residues of the active site. By further mutagenesis we provide experimental evidence that Met-556 of PAPP-A, 63 residues from the zinc-binding motif, is located in a Met-turn of PAPP-A. Our hypothesis is also supported by secondary-structure prediction, and the ability of a 55-residue deletion mutant (d[S498-Y552]) to express and retain antigenecity. However, because PAPP-A differs in the features defining the individual established metzincin families, we suggest that PAPP-A belongs to a separate family. We also found that PAPP-A can undergo autocleavage, and that autocleaved PAPP-A is inactive. A lack of unifying elements in the sequences around the found cleavage sites of PAPP-A and a variant suggests steric regulation of substrate specificity.

Metalloprotease-disintegrin ADAM 12 interacts with alpha-actinin-1

ADAM 12, a member of the ADAM family of proteins (containing A Disintegrin And Metalloprotease domain), has been implicated in differentiation and fusion of myoblasts. While the extracellular domain of ADAM 12 contains an active metalloprotease and a region involved in cell adhesion, the function of the cytoplasmic tail of ADAM 12 has been less clear. Here we show that the cytoplasmic domain of ADAM 12 interacts in vitro and in vivo with alpha-actinin-1, an actin-binding and cross-linking protein. Green fluorescent protein fused to ADAM 12 cytoplasmic domain co-localizes with alpha-actinin-1-containing actin stress fibres in C2C12 cells. The interaction between ADAM 12 and alpha-actinin-1 is direct and involves the 58-amino acid C-terminal fragment of ADAM 12 and the 27 kDa N-terminal domain of alpha-actinin-1. Consistently, expression of the 27 kDa fragment of alpha-actinin-1 in C2C12 cells using a mitochondrial targeting system results in recruitment of the co-expressed ADAM 12 cytoplasmic domain to the mitochondrial surface. Moreover, alpha-actinin-1 co-purifies with a transmembrane, His6-tagged form of ADAM 12 expressed in C2C12 myoblasts, indicating that the transmembrane ADAM 12 forms a complex with alpha-actinin-1 in vivo. These results indicate that the actin cytoskeleton may play a critical role in ADAM 12-mediated cell-cell adhesion or cell signalling during myoblast differentiation and fusion.

Direct interaction between the cytoplasmic tail of ADAM 12 and the Src homology 3 domain of p85alpha activates phosphatidylinositol 3-kinase in C2C12 cells

ADAM 12, a member of the ADAM family of transmembrane metalloprotease-disintegrins, has been implicated previously in the differentiation of skeletal myoblasts. In the present study, we show that the cytoplasmic tail of mouse ADAM 12 interacts in vitro and in vivo with the Src homology 3 domain of the p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase. By site-directed mutagenesis, we have identified three p85alpha-binding sites in ADAM 12 involving PXXP motifs located at amino acids 825-828, 833-836, and 884-887. Using green fluorescent protein (GFP)-pleckstrin homology (PH) domain fusion protein as a probe for PI 3-kinase lipid products, we have further demonstrated that expression of ADAM 12 in C2C12 cells resulted in translocation of GFP-PH to the plasma membrane. This suggests that transmembrane ADAM 12, by providing docking sites for the Src homology 3 domain of p85alpha, activates PI 3-kinase by mediating its recruitment to the membrane. Because PI 3-kinase is critical for terminal differentiation of myoblasts, and because expression of ADAM 12 is up-regulated at the onset of the differentiation process, ADAM 12-mediated activation may constitute one of the regulatory mechanisms for PI 3-kinase during myoblast differentiation.

Purification, cDNA cloning and characterization of the vascular apoptosis-inducing protein, HV1, from Trimeresurus flavoviridis

Hemorrhagic snake venom induces apoptosis in vascular endothelial cells (VEC). In previous reports, we described the purification and cDNA cloning from Crotalus atrox of a vascular apoptosis-inducing protein (VAP1) that specifically induces apoptosis in vascular endothelial cells. We report here the purification and cDNA cloning of another vascular apoptosis-inducing protein, HV1, from crude venom of Trimeresurus flavoviridis. The protein, namely HV1, was purified as an inducer of apoptosis in cultured vascular endothelial cells. HV1 was a homodimeric protein with a molecular mass of 110 kDa. HV1 cDNA encoded a protein with 612 amino-acid residues. The amino-acid sequence predicted from the cDNA was highly homologous to VAP1. The amino-acid sequence of HV1 indicated that HV1 belongs to the metalloprotease/disintegrin family, and that it is a multidomain polypeptide with a proprotein domain, a metalloprotease domain, a disintegrin-like domain and a cysteine-rich domain. In the disintegrin-like domain, the sequence DECD, replaces the RGD sequence that has frequently been found in such domains. This replacement also occurs in VAP1. Our results indicate HV1 as the first identified homolog of VAP1.

Identification, characterization, and intracellular processing of ADAM-TS12, a novel human disintegrin with a complex structural organization involving multiple thrombospondin-1 repeats

We have identified and cloned a human fetal lung cDNA encoding a new protein of the ADAM-TS family (a disintegrin and metalloproteinase domain, with thrombospondin type-1 modules) that has been called ADAM-TS12. This protein exhibits a domain organization similar to the remaining family members including a propeptide and metalloproteinase-like, disintegrin-like, and cysteine-rich domains. However, the number and organization of the TS repeats is unique with respect to other human ADAM-TSs. A total of eight TS-1 repeats arranged in three groups are present in this novel ADAM-TS. Analysis of intracellular processing of ADAM-TS12 revealed that it is synthesized as a precursor molecule that is first activated by cleavage of the prodomain in a furin-mediated process and subsequently processed into two fragments of different size: a 120-kDa N-terminal proteolytically active fragment containing the metalloproteinase and disintegrin domains, and a 83-kDa C-terminal fragment containing most of the TS-1 repeats. Somatic cell hybrid and radiation hybrid mapping experiments showed that the human ADAM-TS12 gene maps to 5q35, a location that differs from all ADAM genes mapped to date. Northern blot analysis of RNAs from human adult and fetal tissues demonstrated that ADAM-TS12 transcripts are only detected at significant levels in fetal lung but not in any other analyzed tissues. In addition, ADAM-TS12 transcripts were detected in gastric carcinomas and in tumor cell lines from diverse sources, being induced by transforming growth factor-beta in KMST human fibroblasts. These data suggest that ADAM-TS12 may play roles in pulmonary cells during fetal development or in tumor processes through its proteolytic activity or as a molecule potentially involved in regulation of cell adhesion.

Vesicular release of ebola virus matrix protein VP40

We have analysed the expression and cellular localisation of the matrix protein VP40 from Ebola virus. Full-length VP40 and an N-terminal truncated construct missing the first 31 residues [VP40(31-326)] both locate to the plasma membrane of 293T cells when expressed transiently, while a C-terminal truncation of residues 213 to 326 [VP40(31-212)] shows only expression in the cytoplasm, when analysed by indirect immunofluorescence and plasma membrane preparations. In addition, we find that full-length VP40 [VP40(1-326)] and VP40(31-326) are both released into the cell culture supernatant and float up in sucrose gradients. The efficiency of their release, however, is dependent on the presence of the N-terminal 31 residues. VP40 that is released into the supernatant is resistant to trypsin digestion, a finding that is consistent with the formation of viruslike particles detected by electron microscopy. Together, these results provide strong evidence that Ebola virus VP40 is sufficient for virus assembly and budding from the plasma membrane.

TACE and other ADAM proteases as targets for drug discovery

Tumor necrosis factor (TNF)-converting enzyme (TACE) and other ADAM proteases (those that contain a disintegrin and a metalloprotease domain) have emerged as potential therapeutic targets in the areas of arthritis, cancer, diabetes and HIV cachexia. TACE is the first ADAM protease to process the known physiological substrate and inflammatory cytokine, membrane-bound precursor-TNF-alpha, to its mature soluble form. Subsequently, TACE was shown to be required for several different processing events such as tumor growth factor-alpha (TGF-alpha) precursor and amyloid precursor protein (APP) cleavage. With the recent discoveries of the proteolytic specificities of other ADAM family members, the information surrounding these metalloproteases is expanding at an exponential rate. This review focuses on TACE and other family members with known proteolytic function as well as the inhibitors of this class of enzyme.

Processing of tumor necrosis factor by the membrane-bound TNF-alpha-converting enzyme, but not its truncated soluble form

Tumour necrosis factor (TNF)-alpha-converting enzyme (TACE) is a membrane protein belonging to the ADAM (a disintegrin and metalloproteinase) family that cleaves various membrane proteins, including the proform of TNF-alpha. In this study, we constructed expression vectors for the membrane-bound full-length TACE (mTACE) and its truncated soluble form (sTACE). When a human TNF-alpha expression vector was introduced into human 293 cells, processing of TNF-alpha to its mature form was enhanced by coexpressing mTACE, and this processing was inhibited by a metalloproteinase inhibitor. On the other hand, coexpression of sTACE had no effect on the processing of TNF-alpha, although the culture medium of sTACE-transfected cells could cleave a peptide containing the TNF-alpha cleavage site. Fas ligand (FasL)-transfected 293 cells released a considerable amount of soluble FasL, and coexpression of neither mTACE nor sTACE enhanced this shedding. Immunoprecipitation and Western blotting analysis with cells that were cotransfected with TACE and TNF-alpha indicated that both mTACE and sTACE could interact with the proform of TNF-alpha. In the same assay, neither mTACE nor sTACE interacted with FasL. The catalytic domain-lacking TACE mutant, which could also interact TNF-alpha, showed a dominant negative effect on not only TNF-alpha secretion but also FasL secretion. These results suggest that binding of the membrane-anchored but not the soluble form of TACE to TNF-alpha results in efficient ectodomain shedding, and that FasL secretase is a metalloproteinase similar, but not identical, to TACE.

EGF regulates a complex pattern of gene expression and represses smooth muscle differentiation during the neurotypic conversion of the neural-crest-derived TC-1S cell line

EGF, known to sustain CNS neuronal progenitors, also promotes a neurotypic response in the thymic neural-crest-derived TC-1S cell line. We report here the use of TC-1S cells as a model to identify the genetic programs regulated during the neurotypic response induced by EGF and to isolate 23 EGF-responsive genes. Among them 5 represent novel cDNAs, while 18 are known genes, whose regulation by EGF is associated with the mitogenic or differentiating effects of the growth factor. The repression of smooth muscle alpha-actin and SM22alpha genes by EGF and their increase by TGFbeta suggest that the TC-1S line includes neural crest multipotent cells whose smooth muscle differentiation is repressed upon EGF treatment and stimulated by TGFbeta. Therefore, we identified a complex pattern of EGF-target genes and propose EGF as a novel signal able to recruit postmigratory neural-crest-derived cells along proliferation and cell lineage choice pathways.

Analysis for transcript expression of meltrin alpha in normal, regenerating, and denervated rat muscle

Meltrin alpha (a disintegrin and metalloprotease (ADAM) 12) is a recently discovered molecule of the metalloprotease-disintegrin family which has been shown to participate in myotube formation in vitro and in myogenesis in vivo. In this study we investigated meltrin alpha in regenerating rat muscle, which is a condition where satellite cells (SC) contribute to myofiber growth by fusing with one another and with myotubes or muscle fibers. We studied meltrin alpha mRNA expression by RT-PCR and in situ-hybridization in normal adult muscle, in soleus muscle regenerating for 2, 5, or 10 days, and in muscle which had been denervated 1 week, 4 weeks, or 6 months previously. SC do not fuse after denervation. They detach from the principal muscle fiber. Immunohistochemistry using an antibody against M-cadherin was performed in parallel in order to identify SC. Messenger RNA as revealed by RT-PCR was absent in normal adult muscle, but present in regenerating and also in denervated muscle. Meltrin alpha transcript detected by in situ-hybridization was present in regenerating muscle only, not in normal or denervated muscle. It was localized to SC. Taken together, meltrin alpha is absent in normal muscle, and localized to SC in fusing conditions. After denervation, the transcript is upregulated. However, it is so lowly abundant that it fails to be detected by in situ-hybridization. This expression profile suggests a role for meltrin alpha in the fusion of SC with myotubes or muscle fibers, but not in SC adhesion to the adjacent myofiber in normal adult muscle.

ADAM 12-S cleaves IGFBP-3 and IGFBP-5 and is inhibited by TIMP-3

ADAMs are a family of multidomain proteins having proteolytic and cell adhesion activities. We have previously shown that ADAM 12-S, the secreted soluble form of human ADAM 12, is a catalytically active protease. We now describe the purification of full-length recombinant ADAM 12-S and demonstrate that it cleaves insulin-like growth factor binding protein-3 (IGFBP-3). This result supports a role for ADAM 12-S in the degradation of IGFBP-3 in the blood of pregnant women. Furthermore, we tested for proteolysis of other members of the IGF binding protein family and found that ADAM 12-S cleaves IGFBP-5 in addition to IGFBP-3, but does not cleave IGFBP-1, -2, -4, or -6. ADAM 12-S may therefore be the IGFBP-5 protease that is secreted by osteoblasts and other cells. Cleavage of both IGFBP-3 and -5 by ADAM 12-S was inhibited by TIMP-3, raising the possibility that TIMP-3 is a physiological inhibitor of ADAM 12-S.

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.

Differentiation of myoblasts in serum-free media: effects of modified media are cell line-specific

Myoblast cell lines are grown and differentiated readily in cell culture. Two cell lines typically used for investigating the growth and differentiation of muscle are the mouse cell line C2C12 and the rat cell line L6. The differentiation of these cells in vitro requires a switch from a serum-rich medium to a less rich medium after the cells have reached confluence. Since the components present in serum are not well characterized, the use of a better defined medium for these studies was investigated. C2C12 and L6 myoblasts were differentiated in both serum-containing and serum-free media. The differentiation state of these cultures was then tested both microscopically and biochemically. Cultures were checked for myotube formation, the activity of creatine phosphokinase and the presence of sarcomeric actin. In C2C12 cells, the extent of differentiation was greater in the serum-free than in the serum-containing system. In both media types, the C2C12 cells produced sarcomeric actin, showing the presence of sarcomere structure in the myotubes. In L6 cells, however, myotubes were readily formed in medium containing 2% horse serum, but not in the serum-free system. In addition, the ability of C2C12 cells to differentiate on substrates coated with extracellular matrix proteins was shown to be media-dependent. The presence of extracellular matrix proteins did not enable L6 cells to form myotubes when cultured in serum-free media. Primary cultures of chick myoblasts were able to differentiate in both media tested, with Dulbecco's modified Eagle medium containing horse serum being a more efficient medium for cell fusion. This study shows a divergence in muscle cell line responses in three cell lines, two of which are typically used as 'model systems' for understanding muscle growth and development.

The expression of the ADAMs proteases in prostate cancer cell lines and their regulation by dihydrotestosterone

The ADAMs are a multi-functional gene family, some of which have been shown to play a role in diverse biological processes such as fertilization, myogenesis, neurogenesis and the activation of growth factors/immune regulators such as TNF-alpha. So-named because they possess both A Disintegrin And Metalloprotease domain, the ADAMs have potential implications for the metastasis of human tumour cells via cell adhesion and protease activities. However, no studies have yet comprehensively examined the expression or regulation of ADAMs in solid tumours. Therefore, the aim of this study was to examine the expression of the ADAMs in human prostate cancer cell lines and to examine their possible regulation by androgen, a primary hormonal regulator of prostate cancer cell proliferation and metastasis. Applying RT-PCR, ADAM-9, -10, -11, -15 and -17 mRNA expression was found in the androgen-dependent prostate cancer cell lines, LNCaP and ALVA-41 and the androgen-independent cell lines, DU-145 and PC-3. Northern blotting of LNCaP cell total RNA revealed transcripts for ADAM-9 (3.8 kb), ADAM-10 (4.4, 3.2 and 0.54 kb), ADAM-15 (3 kb) and ADAM-17 (4 and 2.6 kb). ADAM-11 transcript was not detected by Northern blotting possibly due to low levels of ADAM-11 mRNA expression. This is the first report of ADAM expression in prostate cancer cell lines. Since androgens are implicated in prostate cancer cell growth and maintenance, the regulation of ADAMs by dihydrotestosterone (DHT) was investigated in the androgen-dependent cell line LNCaP. It was shown by quantitative RT-PCR using continuous fluorescence monitoring that ADAM-10 mRNA expression was regulated in a bell shaped, dose-dependent manner by DHT. Maximum stimulation was observed at 1.0 nM DHT (5-fold significant increase). For ADAM-9 mRNA, a significant upregulation was found at 1.0 and 10 nM (1.5-1.7-fold increase). In contrast, ADAM-17 mRNA, was significantly inhibited at 0.1 and 1.0 nM (1.7-fold decrease). This is the first report, to our knowledge, illustrating hormonal regulation of ADAM mRNA. The novel data described here also provide a strong stimulus to the development of specific quantitative and functional assays for particular ADAMs. These assays, which are not yet available, are required to enable subsequent investigation, both in vitro and in vivo, of the specific roles of each ADAM in prostate cancer cell proliferation, cell motility and invasion.

Trafficking of human ADAM 12-L: retention in the trans-Golgi network

We have investigated the trafficking of the membrane-anchored form of human ADAM 12 (ADAM 12-L) fused to a green fluorescence protein tag. Subcellular localization of the protein in transiently transfected cells was determined by fluorescence microscopy and trypsin sensitivity. Full-length ADAM 12-L was retained in a perinuclear compartment, which was shown to be the trans-Golgi network. In contrast, ADAM 12-L lacking the cytoplasmic domain reached the cell surface. Based on analysis of deletions and mutations of the cytoplasmic tail of ADAM 12-L, the retention signal is comprised of both the cytoplasmic and transmembrane domains, but not the Src homology 3 domain (SH3) binding sites. These results raise the possibility that a trafficking checkpoint in the trans-Golgi network is one of the cellular mechanisms for regulation of ADAM 12-L function, by allowing a rapid release of ADAM 12-L to the cell surface under specific stimuli.

TNF-Induced shedding of TNF receptors in human polymorphonuclear leukocytes: role of the 55-kDa TNF receptor and involvement of a membrane-bound and non-matrix metalloproteinase

A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Proteolytic cleavage of the extracellular region of both receptors (shedding) and, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the proposed mechanisms. We have characterized the TNF-induced shedding of TNF receptors in neutrophils and determined the nature of the involved proteinase. Neutrophils exposed to TNF release both TNF receptors. A release of TNF receptors comparable to that observed with TNF was induced with TNF-R55-specific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF-R75-specific reagents. A hydroxamic acid compound (KB8301) almost completely inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75. KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inhibited TNF and FMLP-induced PMN activation. Diisopropylfluorophosphate partially inhibited shedding of TNF-R75, suggesting the contribution of a serine proteinase to the release of this receptor. Shedding activity was not affected by matrix metalloproteinases inhibitors nor was it released in the supernatants of FMLP-stimulated neutrophils. These results suggest that TNF induces release of its receptors, that such a release is mediated via TNF-R55, and that a membrane-bound and non-matrix metalloproteinase is involved in the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed.

ADAM 12, a disintegrin metalloprotease, interacts with insulin-like growth factor-binding protein-3

Insulin-like growth factor-binding protein (IGFBP)-3 binds the insulin-like growth factors with high affinity and modulates their actions. Proteolytic cleavage of IGFBP-3 may regulate insulin-like growth factor bioavailability. IGFBP-3 is extensively degraded in serum during pregnancy; however, as yet the pregnancy-specific protease, or proteases, have not been identified. We utilized a yeast two-hybrid assay and a human placental cDNA library to investigate IGFBP-3-interacting proteins. A disintegrin and metalloprotease-12 (ADAM 12), a member of a family of metalloprotease disintegrins that is highly expressed in placental tissue, was identified as interacting with IGFBP-3. This interaction involved the cysteine-rich domain of ADAM 12. Unlike other members of this family of disintegrin metalloproteases that are membrane proteins, ADAM 12 exists as an alternatively spliced soluble secreted protein. To verify the interaction between ADAM 12 and IGFBP-3, an expression construct containing an ADAM 12-S cDNA was transfected into COS-1 cells. Co-precipitation was observed when conditioned medium was analyzed by immunoprecipitation with an antibody against either ADAM 12 or IGFBP-3 followed by Western blotting with anti-IGFBP-3 or anti-ADAM 12. Although minimal proteolysis of IGFBP-3 was observed in conditioned medium from control cells, this was increased approximately 4-fold in conditioned medium from ADAM 12-S-transfected cells. Recombinant ADAM 12-S partially purified from conditioned medium on a heparin-Sepharose column also proteolyzed IGFBP-3. The degradation pattern was similar to that seen with pregnancy serum, and the presence of ADAM 12-S in serum during pregnancy was confirmed. The data suggest that ADAM 12-S has IGFBP-3 protease activity, and it may contribute to the IGFBP-3 protease activity present in pregnancy serum.

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.

The cysteine-rich domain of human ADAM 12 supports cell adhesion through syndecans and triggers signaling events that lead to beta1 integrin-dependent cell spreading

The ADAMs (a disintegrin and metalloprotease) family of proteins is involved in a variety of cellular interactions, including cell adhesion and ecto- domain shedding. Here we show that ADAM 12 binds to cell surface syndecans. Three forms of recombinant ADAM 12 were used in these experiments: the cys-teine-rich domain made in Escherichia coli (rADAM 12-cys), the disintegrin-like and cysteine-rich domain made in insect cells (rADAM 12-DC), and full-length human ADAM 12-S tagged with green fluorescent protein made in mammalian cells (rADAM 12-GFP). Mesenchymal cells specifically and in a dose-dependent manner attach to ADAM 12 via members of the syndecan family. After binding to syndecans, mesenchymal cells spread and form focal adhesions and actin stress fibers. Integrin beta1 was responsible for cell spreading because function-blocking monoclonal antibodies completely inhibited cell spreading, and chondroblasts lacking beta1 integrin attached but did not spread. These data suggest that mesenchymal cells use syndecans as the initial receptor for the ADAM 12 cysteine-rich domain-mediated cell adhesion, and then the beta1 integrin to induce cell spreading. Interestingly, carcinoma cells attached but did not spread on ADAM 12. However, spreading could be efficiently induced by the addition of either 1 mM Mn(2+) or the beta1 integrin-activating monoclonal antibody 12G10, suggesting that in these carcinoma cells, the ADAM 12-syndecan complex fails to modulate the function of beta1 integrin.

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.

ADAM 23/MDC3, a human disintegrin that promotes cell adhesion via interaction with the alphavbeta3 integrin through an RGD-independent mechanism

ADAM 23 (a disintegrin and metalloproteinase domain)/MDC3 (metalloprotease, disintegrin, and cysteine-rich domain) is a member of the disintegrin family of proteins expressed in fetal and adult brain. In this work we show that the disintegrin-like domain of ADAM 23 produced in Escherichia coli and immobilized on culture dishes promotes attachment of different human cells of neural origin, such as neuroblastoma cells (NB100 and SH-S(y)5(y)) or astrocytoma cells (U373 and U87 MG). Analysis of ADAM 23 binding to integrins revealed a specific interaction with alphavbeta3, mediated by a short amino acid sequence present in its putative disintegrin loop. This sequence lacks any RGD motif, which is a common structural determinant supporting alphavbeta3-mediated interactions of diverse proteins, including other disintegrins. alphavbeta3 also supported adhesion of HeLa cells transfected with a full-length cDNA for ADAM 23, extending the results obtained with the recombinant protein containing the disintegrin domain of ADAM 23. On the basis of these results, we propose that ADAM 23, through its disintegrin-like domain, may function as an adhesion molecule involved in alphavbeta3-mediated cell interactions occurring in normal and pathological processes, including progression of malignant tumors from neural origin.

The ADAM gene family: surface proteins with adhesion and protease activity

An ADAM is a transmembrane protein that contains a disintegrin and metalloprotease domain and, therefore, it potentially has both cell adhesion and protease activities. Currently, the ADAM gene family has 29 members, although the function of most ADAM gene products is unknown. We discuss the ADAM gene products with known functions that act in a highly diverse set of biological processes, including fertilization, neurogenesis, myogenesis, embryonic TGF-alpha release and the inflammatory response.

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.

Isolation of two novel metalloproteinase-disintegrin (ADAM) cDNAs that show testis-specific gene expression

Metalloproteinase-disintegrins (ADAMs) are type 1 transmembrane proteins that contain a unique domain structure including a zinc-binding metalloproteinase domain. We have isolated cDNAs encoding two novel members of this family, ADAM29 and ADAM30 which show testis-specific expression. Three forms of ADAM29 were found that encode proteins of 820, 786 and 767 amino acids. All of the amino acid differences are located in the cytoplasmic domain. Two forms of ADAM30 were isolated that encode proteins of 790 and 781 amino acids, with the difference in the coding region occurring in the cytoplasmic domain. ADAM29 and ADAM30 map to human chromosome 4q34 and 1p11-13, respectively. An ancestral analysis of all known mammalian ADAMs indicates that the zinc-binding motif in the catalytic domain arose once in a common ancestor and was subsequently lost by those members lacking this motif.

The identification of seven metalloproteinase-disintegrin (ADAM) genes from genomic libraries

Metalloproteinase-disintegrins (ADAMs) are membrane-spanning multi-domain proteins containing a zinc metalloproteinase domain and a disintegrin domain which may serve as an integrin ligand. Based on a conserved sequence within the disintegrin domain, GE(E/Q)CDCG, seven genes were isolated from a human genomic library. Two of these genes lack introns and show testis-specific expression (ADAM20 and ADAM21), while the other two genes contain introns (ADAM22 and ADAM23) and are expressed predominantly in the brain. In addition, three pseudogenes were isolated; one of which evolved from ADAM21. Human chromosomal mapping indicated that ADAM22 and ADAM23 mapped to chromosome 7q21 and 2q33, respectively, while the three pseudogenes 1-2, 3-3, and 1-32 mapped to chromosome 14q24.1, 8p23, and 14q24.1, respectively. An ancestral analysis of all known ADAMs indicates that the zinc-binding motif in the catalytic domain arose once in a common ancestor and was lost by those members lacking this motif.

Serum-free culture conditions for analysis of secretory proteinases during myogenic differentiation of mouse C2C12 myoblasts

We have been studying extracellular proteins such as proteinases and attachment factors under serum-free culture conditions. A number of studies on myogenesis using an in vitro culture system have reported that proteinases and ECM components play significant roles in muscle differentiation. However, most of the studies were performed in the presence of serum. Serum is abundant in the aforementioned proteins and its use in serum-free culture affects many cellular functions significantly. In this study, we tried to establish serum-free culture conditions for analyzing extracellular proteins involved in mouse myogenic differentiation. By evaluating media, supplements, and procedure of cell inoculation under serum-free conditions and by comparing the resultant conditions with conventional conditions on differentiated characteristics of the cells, it was revealed that serum-free Dulbecco's modified Eagle's medium/Ham's F-12 plus insulin more efficiently supported myogenesis morphologically and biochemically than conventional 2% horse serum-containing culture and that secretory proteinases obtained from our serum-free culture were different from those obtained utilizing conventional serum-free cultures in their activities and patterns. Since our serum-free medium consists of simple components, the medium is low cost and easy to prepare. Furthermore, the results suggest that our culture conditions are superior to conventional conditions biochemically and morphologically and will provide more precise and accurate information on extracellular proteins involved in myogenesis.

Characterization of the cDNA and gene for mouse tumour necrosis factor alpha converting enzyme (TACE/ADAM17) and its location to mouse chromosome 12 and human chromosome 2p25

Numerous proteins are cleaved or "shed" from their membrane-bound form. One such protein, tumour necrosis factor alpha (TNF-alpha), is synthesized as a type 2 transmembrane protein. Recently, a human protease responsible for this shedding, the TNF-alpha converting enzyme (TACE/ADAM17), was isolated. TACE/ADAM17 is a member of the adamalysin class of zinc-binding metalloproteases or ADAM (a disintegrin and metalloprotease). We report the isolation and characterization of the mouse TACE/ADAM17 cDNA and gene. Mouse TACE/ADAM17 has a 92% amino-acid identity with the human protein and was ubiquitously expressed. A recombinant form of the protease is found to cleave a peptide representing the cleavage site of precursor mouse TNF-alpha. An alternatively spliced form of mouse TACE/ADAM17 was found that would produce a soluble protein. The gene for TACE/ADAM17 is approximately 50 kb and contains 19 exons. Chromosomal mapping places TACE/ADAM17 on mouse chromosome 12 and human chromosome 2p25.

Characterization of the human laminin beta2 chain locus (LAMB2): linkage to a gene containing a nonprocessed, transcribed LAMB2-like pseudogene (LAMB2L) and to the gene encoding glutaminyl tRNA synthetase (QARS)

The laminin beta2 chain is an important constituent of certain kidney and muscle basement membranes. We have generated a detailed physical map of a 110-kb genomic DNA segment surrounding the human laminin beta2 chain gene (LAMB2) on chromosome 3p21.3-->p21.2, a region paralogous with the chromosome 7q22-->q31 region that contains the laminin beta1 chain gene locus (LAMB1). Several CpG islands and a novel polymorphic microsatellite marker (D3S4594) were identified. The 3' end of LAMB2 lies 16 kb from the 5' end of the glutaminyl tRNA synthetase gene (QARS). About 20 kb upstream of LAMB2 we found a gene encoding a transcribed, non-processed LAMB2-like pseudogene (LAMB2L). The sequence of 1.75 kb of genomic DNA at the 3' end of LAMB2L was similar to exons 8-12 of the laminin beta2 chain gene. The LAMB2L-LAMB2-QARS cluster lies telomeric to the gene encoding the laminin-binding protein dystroglycan (DAG1).

Localization of ADAM10 and Notch receptors in bone

In Drosophila melanogaster, the role of the metallodisintegrin, Kuzbanian (kuz), is thought to involve activation of the Drosophila Notch receptor that plays a role in cell-fate determination during neurogenesis and myoblast differentiation. To understand the possible function(s) of a-disintegrin and metalloproteinase (ADAM10), the mammalian ortholog of kuz, in the skeleton, we studied its expression as well as the messenger RNA (mRNA) encoding one candidate substrate, the mammalian Notch2 receptor in bone, bone cells, and cartilage. In sections of neonatal rat tibiae, ADAM10 is expressed in specific regions of articular cartilage and metaphyseal bone. Expression of ADAM10 in articular cartilage occurs predominantly in superficial chondrocytes and becomes more sporadic with increasing distance from the articular surface. In bone, ADAM10 is expressed by periosteal cells, osteoblasts, and osteocytes at locations of active bone formation. Osteoclasts did not express ADAM10. Notch2 mRNA expression was not detectable in superficial chondrocytes. However it colocalized at all sites of ADAM10 expression in bone cells. In vitro, both primary human osteoblasts and osteoblast cell lines expressed a single 4.5 kb and 7.5 kb transcript of ADAM10 and the Notch2 receptor homolog, respectively. Subcellular localization of the ADAM10 protein in MG-63 cells was determined using immunofluorescent techniques. These observations showed clearly that the ADAM10 protein was expressed in the trans-Golgi network and on the plasma membrane. Western blot analysis of fractionated cells showed that, in the plasma membrane fraction, the previously characterized 58 kDa and 56 kDa isoforms were present, whereas, in the trans-Golgi network, the ADAM10 protein was present in several additional bands, possibly indicative of further interdomain processing of the ADAM10 protein. The metallodisintegrins (ADAMs) have several putative functions, including modulation of cell adhesion, membrane-associated proteolysis, and cell-cell signaling. These observations suggest that, in bone but not cartilage, ADAM10 has catalytic activity within the transGolgi network and may play a role in the activation of Notch receptor homologs. This implicates ADAM10 in cell-fate determination of osteoblast progenitor cells, possibly during skeletal development and normal bone remodeling. Plasma-membrane-associated ADAM10 may confer alternative functions.

Adamalysins. A family of metzincins including TNF-alpha converting enzyme (TACE)

The adamalysins are a family of proteins in the metzincin superfamily of metalloproteases, which also includes the matrix metalloproteinases. There are two subfamilies of adamalysins: the snake venom metalloproteases (SVMPs) and the ADAMs (proteins containing a disintegrin and metalloprotease domain). At least 23 ADAMs have been identified to date. The ADAMs are expressed by a wide variety of cell types, and are involved in functions as diverse as sperm-egg binding, myotube formation, neurogenesis, and proteolytic processing of cell surface proteins. An overview of the ADAM family and their functions will be presented. TACE is a unique member of the ADAM family that cleaves membrane-bound TNF-alpha to generate soluble TNF-alpha. Mice lacking proteolytically active TACE have been generated and characterized. The TACE knock-out results in perinatal lethality. Cells from the TACE-deficient mice release 80-90% less soluble TNF-alpha than do wild-type cells. Irradiated mice that are reconstituted with TACE knock-out hematopoeitic stem cells have markedly reduced levels of serum TNF-alpha following LPS challenge, compared to irradiated mice reconstituted with wild-type cells, suggesting that TACE is the major TNF-alpha converting enzyme in vivo. TACE-deficient cells are compromised in the generation of other soluble proteins that are produced as the result of cleavage of a membrane precursor form, suggesting that TACE is involved in multiple shedding events.

Regulation of human ADAM 12 protease by the prodomain. Evidence for a functional cysteine switch

The ADAMs (a disintegrin and metalloprotease) are a family of multidomain proteins that are believed to play key roles in cell-cell and cell-matrix interactions. We have shown recently that human ADAM 12-S (meltrin alpha) is an active metalloprotease. It is synthesized as a zymogen, with the prodomain maintaining the protease in a latent form. We now provide evidence that the latency mechanism of ADAM 12 can be explained by the cysteine switch model, in which coordination of Zn2+ in the active site of the catalytic domain by a cysteine residue in the prodomain is critical for inhibition of the protease. Replacing Cys179 with other amino acids results in an ADAM 12 proform that is proteolytically active, but latency can be restored by placing cysteine at other positions in the propeptide. None of the amino acids adjacent to the crucial cysteine residue is essential for blocking activity of the protease domain. In addition to its latency function, the prodomain is required for exit of ADAM 12 protease from the endoplasmic reticulum. Tissue inhibitor of metalloprotease-1, -2, and -3 were not found to block proteolytic activity of ADAM 12, hence a physiological inhibitor of ADAM 12 protease in the extracellular environment remains to be identified.

Cysteine-rich domain of human ADAM 12 (meltrin alpha) supports tumor cell adhesion

The ADAMs (A disintegrin and metalloprotease) comprise a family of membrane-anchored cell surface proteins with a putative role in cell-cell and/or cell-matrix interactions. By immunostaining, ADAM 12 (meltrin alpha) was up-regulated in several human carcinomas and could be detected along the tumor cell membranes. Because of this intriguing staining pattern, we investigated whether human ADAM 12 supports tumor cell adhesion. Using an in vitro assay using recombinant polypeptides expressed in Escherichia coli, we examined the ability of individual domains of human ADAM 12 and ADAM 15 to support tumor cell adhesion. We found that the disintegrin-like domain of human ADAM 15 supported adhesion of alphavbeta3-expressing A375 melanoma cells. In the case of human ADAM 12, however, recombinant polypeptides of the cysteine-rich domain but not the disintegrin-like domain supported cell adhesion of a panel of carcinoma cell lines. On attachment to recombinant polypeptides from the cysteine-rich domain of human ADAM 12, most tumor cell lines, such as MDA-MB-231 breast carcinoma cells, were rounded and associated with numerous actin-containing filopodia and used a cell surface heparan sulfate proteoglycan to attach. Finally, we demonstrated that authentic full-length human ADAM 12 could bind to heparin Sepharose. Together these results suggest a novel role of the cysteine-rich domain of ADAM 12 -- that of supporting tumor cell adhesion.

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.

ADAMs: focus on the protease domain

ADAMs are proteins containing a disintegrin and metalloproteinase domain. Several important insights were provided in the past year regarding ADAM metalloproteinases. ADAM 10 was implicated in the Notch signaling pathway. ADAM 17 was shown to be the long sought after tumor necrosis factor-alpha convertase and the crystal structure of its metalloproteinase domain was determined.

Human ADAM 12 (meltrin alpha) is an active metalloprotease

The ADAMs (a disintegrin and metalloprotease) are a family of multidomain proteins with structural homology to snake venom metalloproteases. We recently described the cloning and sequencing of human ADAM 12 (meltrin alpha). In this report we provide evidence that the metalloprotease domain of ADAM 12 is catalytically active. We used the trapping mechanism of alpha2-macroglobulin to assay for protease activity of wild-type and mutant ADAM 12 proteins produced in a COS cell transfection system. We found that ADAM 12 is synthesized as a zymogen, with the prodomain maintaining the metalloprotease in a latent form, probably by means of a cysteine switch. The zymogen could be activated chemically by alkylation with N-ethylmaleimide. Cleavage of the prodomain at a site for a furin-like endopeptidase resulted in an ADAM 12 protein with proteolytic activity. The protease activity was sensitive to inhibition by 1,10-phenanthroline and could be eliminated by mutation of the critical glutamate residue at the active site. The demonstration that the ADAM 12 metalloprotease domain is functional may have important implications for future studies that explore the role of ADAM 12 protein in development and disease.