Meltrin beta mini, a new ADAM19 isoform lacking metalloprotease and disintegrin domains, induces morphological changes in neuronal cells

Secretome analysis to elucidate metalloprotease-dependent ectodomain shedding of glycoproteins during neuronal differentiation

Many membrane proteins are subjected to limited proteolyses at their juxtamembrane regions, processes referred to as ectodomain shedding. Shedding ectodomains of membrane-bound ligands results in activation of downstream signaling pathways, whereas shedding those of cell adhesion molecules causes loss of cell-cell contacts. Secreted proteomics (secretomics) using high-resolution mass spectrometry would be strong tools for both comprehensive identification and quantitative measurement of membrane proteins that undergo ectodomain shedding. In this study, to elucidate the ectodomain shedding events that occur during neuronal differentiation, we establish a strategy for quantitative secretomics of glycoproteins released from differentiating neuroblastoma cells into culture medium with or without GM6001, a broad-spectrum metalloprotease inhibitor. Considering that most of transmembrane and secreted proteins are N-glycosylated, we include a process of N-glycosylated peptides enrichment as well as isotope tagging in our secretomics workflow. Our results show that differentiating N1E-115 neurons secrete numerous glycosylated polypeptides in metalloprotease-dependent manners. They are derived from cell adhesion molecules such as NCAM1, CADM1, L1CAM, various transporters and receptor proteins. These results show the landscape of ectodomain shedding and other secretory events in differentiating neurons and/or during axon elongation, which should help elucidate the mechanism of neurogenesis and the pathogenesis of neurological disorders.

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.

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.

ADAM function in embryogenesis

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

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.

Estrogen effects on cognition and hippocampal transcription in middle-aged mice

Young and middle-aged female mice were ovariectomized and given cyclic injections of either estradiol or vehicle treatments. During the fifth week after surgery the Morris water maze was used to assess cognitive function. Age and treatment effects emerged over the course of spatial training such that middle-aged vehicle treated mice exhibited deficits in acquiring a spatial search strategy compared to younger vehicle treated mice and middle-age estradiol treated mice. Following behavioral characterization, mice were maintained on their injection schedule until week seven and hippocampi were collected 24h after the last injection. Hippocampal RNA was extracted and genes responsive to age and estrogen were identified using cDNA microarrays. Estradiol treatment in middle-aged mice altered the expression of genes related to transcriptional regulation, biosynthesis, growth, neuroprotection, and elements of cell signaling pathways. Expression profiles for representative genes were confirmed in a separate set of animals using oligonucleotide arrays and RT-PCR. Our results indicate that estrogen treatment in middle-aged animals may promote hippocampal health during the aging process.

Emerging roles of ADAM and ADAMTS metalloproteinases in cancer

A disintegrin and metalloproteinases (ADAMs) are a recently discovered family of proteins that share the metalloproteinase domain with matrix metalloproteinases (MMPs). Among this family, structural features distinguish the membrane-anchored ADAMs and the secreted ADAMs with thrombospondin motifs referred to as ADAMTSs. By acting on a large panel of membrane-associated and extracellular substrates, they control several cell functions such as adhesion, fusion, migration and proliferation. The current review addresses the contribution of these proteinases in the positive and negative regulation of cancer progression as mainly mediated by the regulation of growth factor activities and integrin functions.

ADAM proteins in the brain

ADAM proteins are a family of metalloproteinases with a disintegrin domain. They have proteolytic as well as adhesive functions and can be involved in cell fusion events. Some ADAM proteins are expressed in a highly tissue restricted fashion, whereas others are expressed quite ubiquitously. In the brain, ADAM proteins have a role in neural development, axon guidance and inflammatory responses. Although there may be some functional overlap, homozygous deletion of some ADAM genes in mice can have fatal consequences. The expression and possible role of ADAM proteins in the brain will be discussed.

ADAM33 expression in asthmatic airways and human embryonic lungs

RATIONALE

Polymorphic variation in ADAM33 (A Disintegrin And Metalloprotease) is strongly associated with asthma and bronchial hyperresponsiveness in different populations.

OBJECTIVE AND METHODS

To study the role of ADAM33 in asthma, we investigated its expression in normal, asthmatic, and embryonic airways using reverse transcriptase-quantitative polymerase chain reaction and immunochemistry.

RESULTS

Several ADAM33 mRNA splice variants were detected in bronchial biopsies and embryonic lung; however, the beta-isoform and variants encoding the metalloprotease domain were rare transcripts. Western blotting of bronchial biopsies confirmed the presence of multiple isoforms of ADAM33, which had molecular weights of 22, 37, 55, and 65 kD. Immunohistochemistry and laser confocal microscopy of adult bronchial biopsies showed that alpha-smooth muscle actin and ADAM33 immunoreactivity were mostly colocalized to smooth muscle and isolated cells in the submucosa. There was no significant difference in ADAM33 mRNA amplicons or protein in subjects with asthma compared with control subjects. In developing lung, ADAM33 was found around bronchial tubes; however, immunoreactivity was more widely distributed than alpha-smooth muscle actin within undifferentiated mesenchyme; on Western blots, an additional 25-kD ADAM33 variant was detected.

CONCLUSIONS

Several ADAM33 protein isoforms occur in adult bronchial smooth muscle and in human embryonic bronchi and surrounding mesenchyme, strongly suggesting its importance in smooth muscle development and/or function, which could explain its genetic association with bronchial hyperresponsiveness. The occurrence of ADAM33 in embryonic mesenchymal cells suggests that it may be involved in airway wall "modeling" that contributes to the early life origins of asthma.

Essential roles of Meltrin beta (ADAM19) in heart development

Morphogenesis of the heart requires development of the endocardial cushion tissue that gives rise to the membranous septa and valves. Here we show that Meltrin beta/ADAM19, a novel metalloprotease-disintegrin, participates in the development of the endocardial cushion. Mice lacking Meltrin beta exhibit ventricular septal defect (VSD) and immature valves, and most of the animals die soon after birth. During development of the endocardial cushion, epithelial-mesenchymal transformation (EMT) of endocardial epithelial cells generates most of the cushion mesenchymes that constitute the main components of the septa and valves. Meltrin beta is expressed in both the epithelia and the mesenchymes of the endocardial cushion. In the absence of Meltrin beta, the cushion is small or thin in the septum-forming region and show poor remodeling of cardiac jelly components; both of these characteristics suggest impaired growth and differentiation of the endocardial cushion. When embryonic fibroblasts are cultured sparsely, Meltrin beta-lacking cells exhibit aberrant ectodomain shedding of type I Neuregulin, one of the ErbB ligands expressed in endocardial cells. These results suggest the necessity of proteolytic regulation of ErbB ligands by Meltrin beta for proper heart development.

Mouse ADAM33: two splice variants differ in protein maturation and localization

We compared the tissue mRNA prevalence and protein maturation of two splice variants of mouse ADAM33, a metalloprotease implicated in airway hyperresponsiveness. These variant cDNAs, designated 914 (alpha) and 906 (beta), encode membrane-bound forms that differ primarily in 26 residues (exon 17) between the cysteine-rich and epidermal growth factor-like domains. Proteins of approximately 120 and 103 kD, detectable by anti-ADAM33 antibodies, were expressed in 914-transfected HEK293 cells. The time-dependent appearance of the approximately 100-kD form and its inhibition by a peptidyl chloromethylketone, or the calcium ionophore, A23187, indicated that this was mature ADAM33, which was processed by a furin-like convertase. One form, approximately 110 kD, was detected in 906-transfected cell lysates. Trypsin and biotinylation treatment of transfected cells demonstrated that all of the mature approximately 100-kD, a minority of the approximately 120-kD pro-form, and none of the 906-expressed 110-kD form localized to the cell surface. The mature form was resistant to endoglycosidase H(f). The approximately 110-kD form was endoglycosidase H(f)-sensitive, indicating retention proximal to the trans-Golgi, consistent with a lack of maturation. Quantitation of transcripts demonstrated that those containing exon 17 predominate, whereas those lacking exon 17 are negligible in the mouse lung, although detectable at low levels in mouse testis, heart, and brain. Thus, potential dominant-negative effects exerted by the nonprocessed 906-encoded beta splice variant are unlikely to occur in mouse lung.

The splicing and fate of ADAM33 transcripts in primary human airways fibroblasts

The ADAM (A Disintegrin and Metalloprotease) family of Zn++-dependent metalloproteases are multidomain proteins involved in diverse cellular activities. Polymorphic variation in ADAM33 is strongly associated with asthma and bronchial hyperresponsiveness. Identification of those isoforms of ADAM33 that are expressed in airways is fundamental to dissecting the role of ADAM33 in asthma. Analysis of primary human airways fibroblasts has shown the presence of a number of alternatively spliced forms of ADAM33, including one encoding a putative secreted variant, and many transcripts lacking the metalloproteinase domain. The relative abundance of these transcripts has been quantified using reverse transcription real-time polymerase chain reaction, in both nuclear and cytoplasmic fractions of RNA. These results demonstrate that a number of splice variants of ADAM33 are transported into the cytoplasm. Ninety percent of ADAM33 mRNA is retained in the nucleus and the subtle differences in the composition of nuclear and cytoplasmic RNA suggest important events in the splicing and selection of ADAM33 transcripts. Western blot analysis confirmed that several protein isoforms of ADAM33 are expressed in primary airways fibroblasts. These findings demonstrate that ADAM33 exists in multiple isoforms, suggesting that it is a complex molecule that plays multiple roles within mesenchymal cells.