Progressive cerebral accumulation of amyloid beta-protein (Abeta) is an early and invariant feature of Alzheimer's disease. Little is known about how Abeta, after being secreted, is degraded and cleared from the extracellular space of the brain. Defective Abeta degradation could be a risk factor for the development of Alzheimer's disease in some subjects. We reported previously that microglial cells release substantial amounts of an Abeta-degrading protease that, after purification, is indistinguishable from insulin-degrading enzyme (IDE). Here we searched for and characterized a role for IDE in Abeta degradation by neurons, the principal cell type that produces Abeta. Whole cultures of differentiated pheochromocytoma (PC12) cells and primary rat cortical neurons actively degraded endogenously secreted Abeta via IDE. However, unlike that in microglia, IDE in differentiated neurons was not released but localized to the cell surface, as demonstrated by biotinylation. Undifferentiated PC12 cells released IDE into their medium, whereas after differentiation, IDE was cell associated but still degraded Abeta in the medium. Overexpression of IDE in mammalian cells markedly reduced the steady-state levels of extracellular Abeta(40) and Abeta(42), and the catalytic site mutation (E111Q) abolished this effect. We observed a novel membrane-associated form of IDE that is approximately 5 kDa larger than the known cytosolic form in a variety of cells, including differentiated PC12 cells. Our results support a principal role for membrane-associated and secreted IDE isoforms in the degradation and clearance of naturally secreted Abeta by neurons and microglia.

Congenital heart disease is the most common form of human birth defects, yet much remains to be learned about its underlying causes. Here we report that mice lacking functional ADAM19 (mnemonic for a disintegrin and metalloprotease 19) exhibit severe defects in cardiac morphogenesis, including a ventricular septal defect (VSD), abnormal formation of the aortic and pulmonic valves, leading to valvular stenosis, and abnormalities of the cardiac vasculature. During mouse development, ADAM19 is highly expressed in the conotruncus and the endocardial cushion, structures that give rise to the affected heart valves and the membranous ventricular septum. ADAM19 is also highly expressed in osteoblast-like cells in the bone, yet it does not appear to be essential for bone growth and skeletal development. Most adam19 ؊/؊ animals die perinatally, likely as a result of their cardiac defects. These findings raise the possibility that mutations in ADAM19 may contribute to human congenital heart valve and septal defects.ADAMs (mnemonic for a disintegrin and metalloprotease) are membrane-anchored glycoproteins with key roles in fertilization, neurogenesis, angiogenesis, Alzheimer's disease, and the release of proteins such as epidermal growth factor (EGF) receptor ligands and tumor necrosis factor family members from the plasma membrane (3,4,17,37,39,41). ADAM19 (also referred to as meltrin ␤) was initially identified in muscle cells and was later found to be expressed in several other tissues, most prominently in heart, lung, and bone (18, 27, 52), during dendritic cell differentiation (13) and Notch-induced T-cell maturation (9). The catalytic activity of ADAM19 towards candidate substrates has been explored by overexpression in cells and by purifying recombinantly expressed soluble forms of the entire ectodomain or the pro-and metalloprotease domains (7,42,49,53). Overexpressed ADAM19 enhances ectodomain shedding of two of several splice variants of neuregulin I-␤ (42), a ligand for the ErbB family of receptor tyrosine kinases (11). Furthermore, overexpression of ADAM19 increases ectodomain release of tumor necrosis factor-related activation-induced cytokine (TRANCE, also referred to as osteoprotegerin-ligand [OPGL]) (7), a protein with important roles in osteoclast differentiation, dendritic cell survival, and mammary gland development (12,25,28).In light of the high expression of ADAM19 in heart and bone and its ability to cleave TRANCE as well as splice variants of neuregulin I-␤, we were interested in evaluating the function of ADAM19 in mice, with an emphasis on its role in heart and bone development. Here we present an analysis of mice lacking functional ADAM19 (adam19 Ϫ/Ϫ mice). MATERIALS AND METHODS Generation of adam19؊/؊ mice. adam19 ϩ/Ϫ mice were generated by the SloanKettering Institute transgenic facility by following standard procedures using stem cells with a secretory gene trap insertion in ADAM19 (30). All mice evaluated in this study were of mixed genetic background (129Sv/C57BL6), and morphological and hist...

N-Arg dibasic convertase is a me tidase from rat brain cortex and testis that cleaves peptide substrates on the N terminu ofArg residues in dibasic s s.By using both an oinu ide and antibodies to screen a rat testis cDNA library, a fill-length cDNA (4,5). On the basis of its similarity to subtilisin and to furin (6), a human homolog of the Kex2 protein, a family of prohormone convertases (PCs) has been identified by PCR techniques. Their involvement in processing of a number of propeptides and proproteins was inferred mainly from cotransfection experiments (7-9), and for PC1, by the use of antisense mRNA (10).Characterization of putative processing endoproteases by classical biochemical techniques has led to the identification of a number of activities, selective for basic residues in precursors, that belong to the four classes of proteases (metallo-, serine, aspartyl, and thiol enzymes; for review, see ref. 11). This suggested that more than one processing endoprotease family could exist (12). To our knowledge, none of these basic-residue-specific enzymes has been cloned.Recently, a metalloendopeptidase was completely purified from rat testis and shown to cleave a number of peptide substrates on the N terminus of Arg residues in dibasic moieties (13). This enzyme was also present in rat brain cortex and its functional properties appeared undistinguishable from those of the somatostatin-28 convertase activity previously identified in this tissue (14,15). By using microsequencing of tryptic fragments of the purified enzyme to design an oligonucleotide probe and polyclonal antibodies raised against the purified protein (13) (20)].The in vitro highly restricted specificity ofNRD convertase for Arg residues in dibasic processing signals and its belonging to the M16 family, which contains other enzymes involved in maturation, suggest that this enzyme is the prototype of a distinct family of processing endoproteases. MATERIALS AND METHODSIsolatin and Cherizatin of cDNA Cones E d NRD Convertae. Four tryptic fragments were sequenced after digestion of previously purified NRD convertase following native PAGE. One fragment, GMQLIYLPPSPLLAE, was used to design the following degenerate inosine-containing oligonucleotide: 5'-GGIGGIAG(A/G)TAIATIA(G/A)(T/ C)TGCATICC-3'. Two additional peptides were obtained by endolysine C treatment (13) autoradiography of the filters, positive phage plaques were isolated and rescreened to obtain single purified phage isolates. A similar aliquot ofthe library was plated onto NZ-amine medium plates for screening using polyclonal antibodies raised Abbreviations: NRD convertase, N-arginine dibasic convertase; IDE, insulin degrading enzyme; MPP, mitochondrial matrixprocessing peptidase.

ADAMs are membrane-anchored glycoproteins with functions in fertilization, heart development, neurogenesis, and protein ectodomain shedding. Here we report an evaluation of the catalytic activity of recombinantly expressed soluble forms of ADAM19, a protein that is essential for cardiovascular morphogenesis. Proteolytic activity of soluble forms of ADAM19 was first demonstrated by their autocatalytic removal of a purification tag (Myc-His) and their ability to cleave myelin basic protein and the insulin B chain. The metalloprotease activity of ADAM19 is sensitive to the hydroxamic acid-type metalloprotease inhibitor BB94 (batimastat) but not to tissue inhibitors of metalloproteases (TIMPs) 1-3. Moreover, ADAM19 cleaves peptides corresponding to the known cleavage sites of tumor necrosis factor-alpha (TNF-alpha), TNF-related activation-induced cytokine (TRANCE, also referred to as osteoprotegerin ligand), and kit ligand-1 (KL-1) in vitro. Although ADAM19 is not required for shedding of TNFalpha and TRANCE in mouse embryonic fibroblasts, its overexpression in COS-7 cells results in strongly increased TRANCE shedding. This suggests a potential role for ADAM19 in shedding TRANCE in cells where both molecules are highly expressed, such as in osteoblasts. Interestingly, our results also indicate that ADAM19 can function as a negative regulator of KL-1 shedding in both COS-7 cells and mouse embryonic fibroblasts, instead of acting directly on KL-1. The identification of potential in vitro substrates offers the basis for further functional studies of ADAM19 in cells and in mice.

All ligands of the epidermal growth factor receptor (EGFR) are made as membrane anchored precursors that can be proteolytically processed and released from the plasma membrane. This process, which is referred to as protein ectodomain shedding, is emerging as a key regulator of the function of EGFR ligands. In light of the important roles of EGFR signaling in development and disease, it will be important to understand more about the regulation of proteolytic processing of EGFR ligands. This chapter describes a sensitive and semiquantitative method to measure ectodomain shedding of EGFR ligands that was designed to facilitate studies of this process in cells.

Iridoviridae are known to cause disease in sturgeons in North America. Here, histological and molecular methods were used to screen for this family of virus in sturgeons from various European farms with low-to-high morbidity. Some histological samples revealed basophilic cells in the gill and labial epithelia, strongly suggesting the accumulation of iridovirus particles. Newly developed generic PCR tests targeting the major capsid protein (MCP) gene of sturgeon iridoviruses identified in North America, namely the white sturgeon iridovirus and the Namao virus (NV), produced positive signals in most samples from four sturgeon species: Russian (Acipenser gueldenstaedtii), Siberian (A. baerii), Adriatic (A. naccarii) and beluga (Huso huso). The sequences of the PCR products were generally highly similar one another, with nucleotide identities greater than 98%. They were also related to (74-88%), although distinct from, American sturgeon iridoviruses. These European viruses were thus considered variants of a single new virus, provisionally named Acipenser iridovirus-European (AcIV-E). Moreover, three samples infected with AcIV-E showed genetic heterogeneity, with the co-existence of two sequences differing by five nucleotides. One of our European samples carried a virus distinct from AcIV-E, but closely related to NV identified in Canada (95%). This study demonstrates the presence of two distinct sturgeon iridoviruses in Europe: a new genotype AcIV-E and an NV-related virus.

Amyloid beta-protein (Abeta) has been implicated as an early and essential factor in the pathogenesis of Alzheimer's disease. Although its cellular production has been studied extensively, little is known about Abeta clearance. Recently, insulin-degrading enzyme (IDE), a 110-kDa metalloendopeptidase, was found to degrade both endogenously secreted and synthetic Abeta peptides. Surprisingly, IDE-mediated proteolysis of [(125)I]Abeta(1-40) in microglial cell-culture media was accompanied by the formation of (125)I-labelled peptides with higher apparent molecular masses, raising the possibility that the degradation products act as 'seeds' for Abeta oligomerization. To directly address the role of IDE in Abeta degradation and oligomerization, we investigated the action of purified recombinant wild-type and catalytically inactive IDEs. Our data demonstrate that (i) IDE alone is sufficient to cleave purified Abeta that is either unlabelled, iodinated or (35)S-labelled; (ii) the initial cleavage sites are His(14)-Gln(15), Phe(19)-Phe(20) and Phe(20)-Ala(21); and (iii) incubation of IDE with [(125)I]Abeta, but not with [(35)S]-Abeta, leads to the formation of slower migrating species on gels. Since iodination labels N-terminal fragments of Abeta, and (35)S labels C-terminal products, we analysed unlabelled synthetic fragments of Abeta and determined that only the N-terminal fragments migrate with anomalously high molecular mass. These results indicate that IDE alone is sufficient to degrade Abeta at specific sites, and that its degradation products do not promote oligomerization of the intact Abeta peptide.

N-arginine (R) dibasic (NRD) convertase (nardilysin; EC 3.4.24.61), a metalloendopeptidase of the M16 family, specifically cleaves peptide substrates at the N-terminus of arginines in dibasic motifs in vitro. In rat testis, the enzyme localizes within the cytoplasm of spermatids and associates with microtubules of the manchette and axoneme. NRD1 and NRD2 convertases, two NRD convertase isoforms, differ by the absence (isoform 1) or presence (isoform 2) of a 68-amino acid insertion close to the active site. In this study, we overexpressed both isoforms, either by vaccinia virus infection of BSC40 cells or transfection of COS-7 cells. The partially purified enzymes exhibit very similar biochemical and enzymic properties. Microsequencing revealed that NRD convertase is N-terminally processed. Results of immunocytofluorescence, immunoelectron microscopy and subcellular fractionation studies argue in favour of a primary cytosolic localization of both peptidases. Although the putative signal peptide did not direct NRD convertase into microsomes in an in vitro translation assay, biotinylation experiments clearly showed the presence of both isoforms at the cell surface. In conclusion, although most known processing events at pairs of basic residues are achieved by proprotein convertases within the secretory pathway, NRD convertase may fulfil a similar function in the cytoplasm and/or at the cell surface.