ADAM15 gene structure and differential alternative exon use in human tissues

Identification of potential molecular mimicry in pathogen-host interactions

Pathogens have evolved sophisticated strategies to manipulate host signaling pathways, including the phenomenon of molecular mimicry, where pathogen-derived biomolecules imitate host biomolecules. In this study, we resurrected, updated, and optimized a sequence-based bioinformatics pipeline to identify potential molecular mimicry candidates between humans and 32 pathogenic species whose proteomes' 3D structure predictions were available at the start of this study. We observed considerable variation in the number of mimicry candidates across pathogenic species, with pathogenic bacteria exhibiting fewer candidates compared to fungi and protozoans. Further analysis revealed that the candidate mimicry regions were enriched in solvent-accessible regions, highlighting their potential functional relevance. We identified a total of 1,878 mimicked regions in 1,439 human proteins, and clustering analysis indicated diverse target proteins across pathogen species. The human proteins containing mimicked regions revealed significant associations between these proteins and various biological processes, with an emphasis on host extracellular matrix organization and cytoskeletal processes. However, immune-related proteins were underrepresented as targets of mimicry. Our findings provide insights into the broad range of host-pathogen interactions mediated by molecular mimicry and highlight potential targets for further investigation. This comprehensive analysis contributes to our understanding of the complex mechanisms employed by pathogens to subvert host defenses and we provide a resource to assist researchers in the development of novel therapeutic strategies.

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

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

IsoTV: processing and visualizing functional features of translated transcript isoforms

SUMMARY

Despite the continuous discovery of new transcript isoforms, fueled by the recent increase in accessibility and accuracy of long-read RNA sequencing data, functional differences between isoforms originating from the same gene often remain obscure. To address this issue and enable researchers to assess potential functional consequences of transcript isoform variation on the proteome, we developed IsoTV. IsoTV is a versatile pipeline to process, predict and visualize the functional features of translated transcript isoforms. Attributes such as gene and isoform expression, transcript composition and functional features are summarized in an easy-to-interpret visualization. IsoTV is able to analyze a variety of data types from all eukaryotic organisms, including short- and long-read RNA-seq data. Using Oxford Nanopore long read data, we demonstrate that IsoTV facilitates the understanding of potential protein isoform function in different cancer cell types.

AVAILABILITY AND IMPLEMENTATION

IsoTV is available at https://github.molgen.mpg.de/MayerGroup/IsoTV, with the corresponding documentation at https://isotv.readthedocs.io/.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Differential roles of protease isoforms in the tumor microenvironment

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

ADAM15 mediates upregulation of Claudin-1 expression in breast cancer cells

A Disintegrin and Metalloproteinase-15 (ADAM15) is a transmembrane protein involved in protein ectodomain shedding, cell adhesion and signalling. We previously cloned and characterised alternatively spliced variants of ADAM15 that differ in their intracellular domains and demonstrated correlation of the expression of specific variants with breast cancer prognosis. In this study we have created isogenic cell panels (MDA-MB-231 and MCF-7) expressing five ADAM15 variants including wild-type and catalytically inactive forms. The expression of ADAM15 isoforms in MDA-MB-231 cells led to cell clustering to varying degree, without changes in EMT markers vimentin, slug and E-cadherin. Analysis of tight junction molecules revealed ADAM15 isoform specific, catalytic function dependent upregulation of Claudin-1. The expression of ADAM15A, and to a lesser degree of C and E isoforms led to an increase in Claudin-1 expression in MDA-MB-231 cells, while ADAM15B had no effect. In MCF-7 cells, ADAM15E was the principal variant inducing Claudin-1 expression. Sh-RNA mediated down-regulation of ADAM15 in ADAM15 over-expressing cells reduced Claudin-1 levels. Additionally, downregulation of endogenous ADAM15 expression in T47D cells by shRNA reduced endogenous Claudin-1 expression confirming a role for ADAM15 in regulating Claudin-1 expression. The PI3K/Akt/mTOR pathway was involved in regulating Claudin-1 expression downstream of ADAM15. Immunofluorescence analysis of MDA-MB-231 ADAM15A expressing cells showed Claudin-1 at cell-cell junctions, in the cytoplasm and nuclei. ADAM15 co-localised with Claudin-1 and ZO1 at cell-cell junctions. Immunoprecipitation analysis demonstrated complex formation between ADAM15 and ZO1/ZO2. These findings highlight the importance of ADAM15 Intra Cellular Domain-mediated interactions in regulating substrate selection and breast cancer cell phenotype.

An ADAM-10 dependent EPCR shedding links meningococcal interaction with endothelial cells to purpura fulminans

Purpura fulminans is a deadly complication of Neisseria meningitidis infections due to extensive thrombosis of microvessels. Although a Disseminated Intra-vascular Coagulation syndrome (DIC) is frequently observed during Gram negative sepsis, it is rarely associated with extensive thrombosis like those observed during meningococcemia, suggesting that the meningococcus induces a specific dysregulation of coagulation. Another specific feature of N. meningitidis pathogenesis is its ability to colonize microvessels endothelial cells via type IV pili. Importantly, endothelial cells are key in controlling the coagulation cascade through the activation of the potent anticoagulant Protein C (PC) thanks to two endothelial cell receptors among which the Endothelial Protein C Receptor (EPCR). Considering that congenital or acquired deficiencies of PC are associated with purpura fulminans, we hypothesized that a defect in the activation of PC following meningococcal adhesion to microvessels is responsible for the thrombotic events observed during meningococcemia. Here we showed that the adhesion of N. meningitidis on endothelial cells results in a rapid and intense decrease of EPCR expression by inducing its cleavage in a process know as shedding. Using siRNA experiments and CRISPR/Cas9 genome edition we identified ADAM10 (A Disintegrin And Metalloproteinase-10) as the protease responsible for this shedding. Surprisingly, ADAM17, the only EPCR sheddase described so far, was not involved in this process. Finally, we showed that this ADAM10-mediated shedding of EPCR induced by the meningococcal interaction with endothelial cells was responsible for an impaired activation of Protein C. This work unveils for the first time a direct link between meningococcal adhesion to endothelial cells and a severe dysregulation of coagulation, and potentially identifies new therapeutic targets for meningococcal purpura fulminans.

Neisseria meningitidis (meningococcus) is responsible for a severe syndrome called purpura fulminans in which the coagulation system is totally dysregulated, leading to an extensive occlusion of blood microvessels. The pathogenesis of this syndrome is still not understood. Here we show that the meningococcus, when adhering on the apical surface of endothelial cells, induces the activation of membranous protease named ADAM-10, which in turn hydrolyses a cellular receptor called EPCR. The latter is key for the activation of a circulating potent anticoagulant, the Protein C (PC). PC activation is then impaired following meningococcal adhesion on endothelial cells. This work unveils for the first time a specific dysregulation of coagulation induced by the meningococcus and potentially identifies new therapeutic targets for meningococcal purpura fulminans.

ADAMs family and relatives in cardiovascular physiology and pathology

A disintegrin and metalloproteinases (ADAMs) are a family of membrane-bound proteases. ADAM-TSs (ADAMs with thrombospondin domains) are a close relative of ADAMs that are present in soluble form in the extracellular space. Dysregulated production or function of these enzymes has been associated with pathologies such as cancer, asthma, Alzheimer's and cardiovascular diseases. ADAMs contribute to angiogenesis, hypertrophy and apoptosis in a stimulus- and cell type-dependent manner. Among the ADAMs identified so far (34 in mouse, 21 in human), ADAMs 8, 9, 10, 12, 17 and 19 have been shown to be involved in cardiovascular development or cardiomyopathies; and among the 19 ADAM-TSs, ADAM-TS1, 5, 7 and 9 are important in development of the cardiovascular system, while ADAM-TS13 can contribute to vascular disorders. Meanwhile, there remain a number of ADAMs and ADAM-TSs whose function in the cardiovascular system has not been yet explored. The current knowledge about the role of ADAMs and ADAM-TSs in the cardiovascular pathologies is still quite limited. The most detailed studies have been performed in other cell types (e.g. cancer cells) and organs (nervous system) which can provide valuable insight into the potential functions of ADAMs and ADAM-TSs, their mechanism of action and therapeutic potentials in cardiomyopathies. Here, we review what is currently known about the structure and function of ADAMs and ADAM-TSs, and their roles in development, physiology and pathology of the cardiovascular system.

Preferred SH3 domain partners of ADAM metalloproteases include shared and ADAM-specific SH3 interactions

A disintegrin and metalloproteinases (ADAMs) constitute a protein family essential for extracellular signaling and regulation of cell adhesion. Catalytic activity of ADAMs and their predicted potential for Src-homology 3 (SH3) domain binding show a strong correlation. Here we present a comprehensive characterization of SH3 binding capacity and preferences of the catalytically active ADAMs 8, 9, 10, 12, 15, 17, and 19. Our results revealed several novel interactions, and also confirmed many previously reported ones. Many of the identified SH3 interaction partners were shared by several ADAMs, whereas some were ADAM-specific. Most of the ADAM-interacting SH3 proteins were adapter proteins or kinases, typically associated with sorting and endocytosis. Novel SH3 interactions revealed in this study include TOCA1 and CIP4 as preferred partners of ADAM8, and RIMBP1 as a partner of ADAM19. Our results suggest that common as well as distinct mechanisms are involved in regulation and execution of ADAM signaling, and provide a useful framework for addressing the pathways that connect ADAMs to normal and aberrant cell behavior.

Identification of latent biomarkers in hepatocellular carcinoma by ultra-deep whole-transcriptome sequencing

There is an urgent need to identify biomarkers for hepatocellular carcinoma due to limited treatment options and the poor prognosis of this common lethal disease. Whole-transcriptome shotgun sequencing (RNA-Seq) provides new possibilities for biomarker identification. We sequenced ∼250 million pair-end reads from a pair of adjacent normal and tumor liver samples. With the aid of bioinformatics tools, we determined the transcriptome landscape and sought novel biomarkers by further empirical validations in 55 pairs of adjacent normal and tumor liver samples with various viral statuses such as HBV(+), HCV(+) and HBV(-)HCV(-). We identified a novel gene with coding regions, termed DUNQU1, which has a tissue-specific expression pattern in tumor liver samples of HCV(+) and HBV(-)HCV(-) hepatocellular carcinomas. Overexpression of DUNQU1 in Huh7 cell lines enhances the ability to form colonies in soft agar. Also, we identified three novel differentially-expressed protein-coding genes (ALG1L, SERPINA11 and TMEM82) that lack documented expression profiles in liver cancer and showed that the level of SREPINA11 is correlated with pathology stages. Moreover, we showed that the alternative splicing event of FGFR2 is associated with virus infection, tumor size, cirrhosis and tumor recurrence. The findings indicate that these new markers of hepatocellular carcinoma may be of value in improving prognosis and could have potential as new targets for developing new treatment options.

Alternative mRNA splicing generates two distinct ADAM12 prodomain variants

Human ADAM12, transcript variant 1 (later on referred to as Var-1b), present in publicly available databases contains the sequence 5′-GTAATTCTG-3′ at the nucleotide positions 340–348 of the coding region, at the 3′ end of exon 4. The translation product of this variant, ADAM12-Lb, includes the three amino acid motif ¹¹⁴VIL¹¹⁶ in the prodomain. This motif is not conserved in ADAM12 from different species and is not present in other human ADAMs. Currently, it is not clear whether a shorter variant, Var-1a, encoding the protein version without the ¹¹⁴VIL¹¹⁶ motif, ADAM12-La, is expressed in human. In this work, we have established that human mammary epithelial cells and breast cancer cells express both Var-1a and Var-1b transcripts. Importantly, the proteolytic processing and intracellular trafficking of the corresponding ADAM12-La and ADAM12-Lb proteins are different. While ADAM12-La is cleaved and trafficked to the cell surface in a manner similar to ADAM12 in other species, ADAM12-Lb is retained in the ER and is not proteolytically processed. Furthermore, the relative abundance of ADAM12-La and ADAM12-Lb proteins detected in several breast cancer cell lines varies significantly. We conclude that the canonical form of transmembrane ADAM12 is represented by Var-1a/ADAM12-La, rather than Var-1b/ADAM12-Lb currently featured in major sequence databases.

ADAM15 protein amplifies focal adhesion kinase phosphorylation under genotoxic stress conditions

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

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

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

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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Secreted and membrane-bound isoforms of protease ADAM9 have opposing effects on breast cancer cell migration

Tumor cell migration is mediated by cell-autonomous signaling mechanisms as well as paracrine and autocrine factors secreted by activated stromal cells in the tumor microenvironment. Like other members of the ADAM (a disintegrin and metalloproteinase) family, the integrin-binding metalloproteinase ADAM9 modulates cell-cell and cell-matrix interactions as well as ectodomain shedding of cell surface receptors and ligands, thereby modifying intracellular and extracellular signaling. ADAM9 transcripts are alternatively spliced to express a transmembrane protein (ADAM9-L) and a secreted variant (ADAM9-S). In this study, we show that ADAM9-S promotes breast cancer cell migration in a manner requiring its metalloproteinase activity, whereas ADAM9-L suppresses cell migration independent of its metalloproteinase activity. Suppression of migration by ADAM9-L requires a functional disintegrin domain and integrin binding. Expression analysis revealed that both ADAM9 isoforms are expressed in breast cancer cell lines and tissues. Therefore, relative levels of membrane-tethered and secreted variants of ADAM9 are a key determinant in manifestation of aggressive migratory phenotypes associated with breast cancer progression.

Conservation and divergence of ADAM family proteins in the Xenopus genome

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Gene hunting of the Genetic Analysis Workshop 16 rheumatoid arthritis data using rough set theory

We propose to use the rough set theory to identify genes affecting rheumatoid arthritis risk from the data collected by the North American Rheumatoid Arthritis Consortium. For each gene, we employ generalized dynamic reducts in the rough set theory to select a subset of single-nucleotide polymorphisms (SNPs) to represent the genetic information from this gene. We then group the study subjects into different clusters based on their genotype similarity at the selected markers. Statistical association between disease status and cluster membership is then studied to identify genes associated with rheumatoid arthritis. Based on our proposed approach, we are able to identify a number of statistically significant genes associated with rheumatoid arthritis. Aside from genes on chromosome 6, our identified genes include known disease-associated genes such as PTPN22 and TRAF1. In addition, our list contains other biologically plausible genes, such as ADAM15 and AGPAT2. Our findings suggest that ADAM15 and AGPAT2 may contribute to a genetic predisposition through abnormal angiogenesis and adipose tissue.

The ADAM metalloproteinases

The ADAMs (a disintegrin and metalloproteinase) are a fascinating family of transmembrane and secreted proteins with important roles in regulating cell phenotype via their effects on cell adhesion, migration, proteolysis and signalling. Though all ADAMs contain metalloproteinase domains, in humans only 13 of the 21 genes in the family encode functional proteases, indicating that at least for the other eight members, protein–protein interactions are critical aspects of their biological functions. The functional ADAM metalloproteinases are involved in “ectodomain shedding” of diverse growth factors, cytokines, receptors and adhesion molecules. The archetypal activity is shown by ADAM-17 (tumour necrosis factor-α convertase, TACE), which is the principal protease involved in the activation of pro-TNF-α, but whose sheddase functions cover a broad range of cell surface molecules. In particular, ADAM-17 is required for generation of the active forms of Epidermal Growth Factor Receptor (EGFR) ligands, and its function is essential for the development of epithelial tissues. Several other ADAMs have important sheddase functions in particular tissue contexts. Another major family member, ADAM-10, is a principal player in signalling via the Notch and Eph/ephrin pathways. For a growing number of substrates, foremost among them being Notch, cleavage by ADAM sheddases is essential for their subsequent “regulated intramembrane proteolysis” (RIP), which generates cleaved intracellular domains that translocate to the nucleus and regulate gene transcription. Several ADAMs play roles in spermatogenesis and sperm function, potentially by effecting maturation of sperm and their adhesion and migration in the uterus. Other non-catalytic ADAMs function in the CNS via effects on guidance mechanisms. The ADAM family are thus fundamental to many control processes in development and homeostasis, and unsurprisingly they are also linked to pathological states when their functions are dysregulated, including cancer, cardiovascular disease, asthma, Alzheimer’s disease. This review will provide an overview of current knowledge of the human ADAMs, discussing their structure, function, regulation and disease involvement.

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

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