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Anthony J Turner

Publications and source records attributed to Anthony J Turner.

13 recordsLinked to original sources
PubMed2003

The ectodomain shedding of angiotensin-converting enzyme is independent of its localisation in lipid rafts.

Angiotensin-converting enzyme (ACE), a type I integral membrane protein that plays a major role in vasoactive peptide metabolism, is shed from the plasma membrane by proteolytic cleavage within the juxtamembrane stalk. To investigate whether this shedding is regulated by lateral segregation in cholesterol-rich lipid rafts, Chinese hamster ovary cells and human neuroblastoma SH-SY5Y cells were transfected with either wild-type ACE (WT-ACE) or a construct with a glycosylphosphatidylinositol (GPI) anchor attachment signal replacing the transmembrane and cytosolic domains (GPI-ACE). In both cell types, GPI-ACE, but not WT-ACE, was sequestered in caveolin or flotillin-enriched lipid rafts and was released from the cell surface by treatment with phosphatidylinositol-specific phospholipase C. When cells were treated with activators of the protein kinase C signalling cascade (phorbol myristate acetate or carbachol) the shedding of GPI-ACE was stimulated to a similar extent to that of WT-ACE. The release of WT-ACE and GPI-ACE from the cells was inhibited in an identical manner by a range of hydroxamate-based zinc metalloprotease inhibitors. Disruption of lipid rafts by filipin treatment did not alter the shedding of GPI-ACE, and phorbol ester treatment did not alter the distribution of WT-ACE or GPI-ACE between raft and non-raft membrane compartments. These data clearly show that the protein kinase C-stimulated shedding of ACE does not require the transmembrane or cytosolic regions of the protein, and that sequestration in lipid rafts does not regulate the shedding of the protein.

Animals↗
PubMed2003

An ACE structure.

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Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

Muscarine enhances soluble amyloid precursor protein secretion in human neuroblastoma SH-SY5Y by a pathway dependent on protein kinase C(alpha), src-tyrosine kinase and extracellular signal-regulated kinase but not phospholipase C.

The signalling pathways by which muscarine and epidermal growth factor (EGF) regulate the secretion of the alpha-secretase cleavage product (sAPPalpha) of the amyloid precursor protein (APP) were examined in the human neuroblastoma SH-SY5Y. Using specific inhibitors it was found that over 80% of sAPPalpha secretion, enhanced by muscarine, occurred via the extracellular signal-regulated kinase (ERK1/2) member of the mitogen-activated protein kinase (MAPK) family and was dependent on protein kinase Calpha (PKCalpha) and a member of the Src family of non-receptor tyrosine kinases (Src-TK). In contrast the stimulation of sAPPalpha secretion by EGF was not affected by inhibitors of PKC nor Src-TK but was dependent on ERK1/2. In addition muscarine-enhanced sAPPalpha secretion and ERK1/2 activation were inhibited 60 and 80%, respectively, by micromolar concentrations of the phosphatidylinositol 3 kinase (PI-3K) inhibitor wortmannin. In comparison wortmannin decreased EGF stimulation of sAPPalpha secretion and ERK 1/2 activation by approximately 40%. Unexpectedly, U73122, an inhibitor of phosphoinositide-specific phospholipase C, did not inhibit muscarine enhancement of sAPPalpha secretion. These data are discussed in relation to a pathway for the enhancement of sAPPalpha secretion by muscarine which involves the activation of a Src-TK by G-protein beta/gamma-subunits leading to activation of PKCalpha, and ERK1/2 by a mechanism not involving phospholipase C.

Alzheimer Disease↗
PubMed2002

Structure-activity relationship of hydroxamate-based inhibitors on the secretases that cleave the amyloid precursor protein, angiotensin converting enzyme, CD23, and pro-tumor necrosis factor-alpha.

Multiple proteins are proteolytically shed from the membrane, including the amyloid precursor protein (APP) involved in Alzheimer's disease, the blood pressure regulating angiotensin converting enzyme (ACE), the low affinity IgE receptor CD23, and the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). The inhibitory effect of a range of hydroxamic acid-based compounds on the secretases involved in cleaving and releasing these four proteins has been examined to build up a structure-activity relationship. Compounds have been identified that can discriminate between TNF-alpha convertase and the other three secretases (compound 15), between the shedding of CD23 and the shedding of APP and ACE (compound 21), and between the secretases and matrix metalloproteinase-1 (compound 22). The structure-activity relationship for the APP alpha-secretase and the ACE secretase were remarkably similar, and both secretases were activated in whole cell systems by the serine proteinase inhibitor 3,4-dichloroisocoumarin. The basal and carbachol-stimulated shedding of APP and ACE from human SH-SY5Y neuroblastoma cells could not be differentiated by any of the hydroxamate compounds, implying that the same or very similar activities are involved in the constitutive and regulated shedding of these two proteins. By utilizing a key discriminatory compound (compound 15) that potently inhibits TNF-alpha convertase but not alpha-secretase, we show that TNF-alpha convertase is not involved in the regulated shedding of APP from human neuronal cells. The compounds reported here will be useful in future studies aimed at identifying and validating candidate secretases.

Amyloid Precursor Protein Secretases↗
PubMed2002

Kinetic analysis of PPi-dependent phosphofructokinase from Porphyromonas gingivalis.

We have previously cloned the gene encoding a pyrophosphate-dependent phosphofructokinase (PFK), designated PgPFK, from Porphyromonas gingivalis, an oral anaerobic bacterium implicated in advanced periodontal disease. In this study, recombinant PgPFK was purified to homogeneity, and biochemically characterized. The apparent K(m) value for fructose 6-phosphate was 2.2 mM, which was approximately 20 times higher than that for fructose 1,6-bisphosphate. The value was significantly greater than any other described PFKs, except for Amycolatopsis methanolica PFK which is proposed to function as a fructose 1,6 bisphosphatase (FBPase). The PgPFK appears to serves as FBPase in this organism. We postulate that this may lead to the gluconeogenic pathways to synthesize the lipopolysaccharides and/or glycoconjugates essential for cell viability.

Escherichia coli↗
PubMed2002

The angiotensin-converting enzyme gene family: genomics and pharmacology.

Modulation of the renin-angiotensin system (RAS), and particularly inhibition of angiotensin-converting enzyme (ACE), a zinc metallopeptidase, has long been a prime strategy in the treatment of hypertension. However, other angiotensin metabolites are gaining in importance as our understanding of the RAS increases. Recently, genomic approaches have identified the first human homologue of ACE, termed ACEH (or ACE2). ACEH differs in specificity and physiological roles from ACE, which opens a potential new area for discovery biology. The gene that encodes collectrin, a homologue of ACEH, is upregulated in response to renal injury. Collectrin lacks a catalytic domain, which indicates that there is more to ACE-like function than simple peptide hydrolysis.

Animals↗
PubMed2002

Characterization of PgPepO, a bacterial homologue of endothelin-converting enzyme-1.

PgPepO is a homologue of endothelin-converting enzyme-1 (ECE-1), with which it shares 31% identity. PgPepO was isolated from the periodontal pathogen Porphyromonas gingivalis. Recent studies have suggested a link between periodontal and cardiovascular disease, and several groups have suggested that bacterial and viral infections may contribute to the latter. P. gingivalis possesses the ability to invade, and multiply within, aortic endothelial cells and has been localized to atherosclerotic plaques. PgPepO was expressed and purified to homogeneity and we have begun detailed functional analysis, in terms of substrate preference and inhibitor specificity, in order to provide active-site comparisons with other members of the neprilysin (NEP)/ECE family. PgPepO possesses similar substrate specificity to ECE-1 and has been shown to cleave big endothelin-1 (big ET-1), big ET-2 and big ET-3, converting the substrates into their respective mature endothelin peptides. Substance P, angiotensin I, angiotensin II and neurotensin are all cleaved at multiple sites by PgPepO and the kinetics of these reactions have been compared. The potent vasoconstrictor urotensin II is not hydrolysed by PgPepO. Cleavage of bradykinin by PgPepO occurs at the Pro(7)-Phe(8) bond and is inhibited by the NEP and ECE-1 inhibitor phosphoramidon in a pH-dependent fashion (IC(50) =10 microM at pH 7.0) but not by thiorphan, an NEP-specific inhibitor. PgPepO activity is completely inhibited by EDTA. Characterization of this enzyme is important in elucidating possible links between periodontal pathogens and cardiovascular disorders such as atherosclerosis, and provides an opportunity to gain structural information on a bacterial protein with striking similarity to human ECE-1.

Angiotensin I↗
PubMed2002

Differential expression of neutral endopeptidase-24.11 (neprilysin) and endothelin-converting enzyme in human prostate cancer cell lines.

Neutral endopeptidase-24.11 (neprilysin; NEP/CD10) is a cell surface metallopeptidase expressed by prostatic epithelial cells that degrades various bioactive peptides including endothelin. Endothelin-converting enzyme (ECE), the key enzyme of endothelin biosynthesis, catalyses the final processing step in the pathway. Neuropeptide substrates of NEP, including endothelin, have been implicated in the growth of androgen-independent prostate cancer. We have surveyed the expression of NEP and ECE in a range of prostate cancer cell lines. Western analysis reveals that ECE-1 is expressed abundantly in all the malignant cell lines tested, except for LNCaP. In contrast, LNCaP cells express high levels of NEP, while NEP was not detected in PC-3, DU145 and other metastatic cell lines that were tested. Of the normal immortalized prostate epithelial cell lines, PNT1a shows equivalent amounts of NEP and ECE. PNT2-C2 shows poor NEP expression but an abundance of ECE. P4E6, by comparison, has low levels of both ECE and NEP. These differences in expression may render these cell lines useful in experimental models for future study. Benign prostatic hyperplasia primary epithelial cells express much higher levels of NEP than malignant primary epithelial cells, but neither show ECE expression. On the other hand, surrounding stromal cell populations have detectable ECE levels. An absence of ECE in malignant and benign prostatic hyperplasia cells of primary epithelial origin suggests an important role for stromal interaction and paracrine production of ECE within the host. The upregulation of ECE expression in metastatic cells in culture may be indicative of its role in metastatic progression. A differential profile of ECE and NEP could contribute to an abundance of mitogenic peptides aiding the progression of androgen-independent prostate cancer.

Aspartic Acid Endopeptidases↗
PubMed2002

Effects of periodontopathic bacteria on the expression of endothelin-1 in gingival epithelial cells in adult periodontitis.

Adult periodontitis, which is the major cause of adult tooth loss, is commonly characterized by chronic inflammatory disease caused by infection with periodontopathic bacteria such as Porphyromonas gingivalis. Our aims in the present study were to examine the expression of endothelin-1 (ET-1) in cultured HEp-2 epithelial cells after infection with P. gingivalis, and in gingival tissue from adult periodontitis patients. The cell lines were infected with the strains P. gingivalis 33277 and 381 for assessment of bacterial invasion using an antibiotic protection assay, and the expression of ET-1, inflammatory cytokines and cell adhesion molecules was examined by ELISA and reverse transcription-PCR. The expression of ET-1, as well as that of interleukin-1 beta, interleukin-8 and ICAM-1 (intercellular cell adhesion molecule 1), was induced significantly in a time-dependent manner, whereas the expression of MCP-1 (monocyte chemotactic protein-1), RANTES (regulated upon activation, normal T-cell expressed and secreted) and VCAM-1 (vascular cell adhesion molecule 1) was not. Furthermore, in gingival tissues from adult periodontitis patients, we also observed increased expression of ET-1 mRNA compared with tissue from normal healthy donors. These results suggest that infection by periodontopathic bacteria up-regulates the expression of ET-1, together with that of inflammatory cytokines and ICAM-1, in gingival epithelial cells, and that ET-1 expression may be closely involved in the regulation of cytokine responses and cell-cell adhesion in adult periodontitis lesions.

Adult↗
PubMed2002

Beta-amyloid catabolism: roles for neprilysin (NEP) and other metallopeptidases?

The steady-state level of amyloid beta-peptide (Abeta) represents a balance between its biosynthesis from the amyloid precursor protein (APP) through the action of the beta- and gamma-secretases and its catabolism by a variety of proteolytic enzymes. Recent attention has focused on members of the neprilysin (NEP) family of zinc metalloproteinases in amyloid metabolism. NEP itself degrades both Abeta(1-40) and Abeta(1-42) in vitro and in vivo, and this metabolism is prevented by NEP inhibitors. Other NEP family members, for example endothelin-converting enzyme, may contribute to amyloid catabolism and may also play a role in neuroprotection. Another metalloproteinase, insulysin (insulin-degrading enzyme) has also been advocated as an amyloid-degrading enzyme and may contribute more generally to metabolism of amyloid-forming peptides. Other candidate enzymes proposed include angiotensin-converting enzyme, some matrix metalloproteinases, plasmin and, indirectly, thimet oligopeptidase (endopeptidase-24.15). This review critically evaluates the evidence relating to proteinases implicated in amyloid catabolism. Therapeutic strategies aimed at promoting A,beta degradation may provide a novel approach to the therapy of Alzheimer's disease.

Amino Acid Sequence↗
PubMed2002

ACEH/ACE2 is a novel mammalian metallocarboxypeptidase and a homologue of angiotensin-converting enzyme insensitive to ACE inhibitors.

A human zinc metalloprotease (termed ACEH or ACE2) with considerable homology to angiotensin-converting enzyme (ACE) (EC 3.4.15.1) has been identified and subsequently cloned and functionally expressed. The translated protein contains an N-terminal signal sequence, a single catalytic domain with zinc-binding motif (HEMGH), a transmembrane region, and a small C-terminal cytosolic domain. Unlike somatic ACE, ACEH functions as a carboxypeptidase when acting on angiotensin I and angiotensin II or other peptide substrates. ACEH may function in conjunction with ACE and neprilysin in novel pathways of angiotensin metabolism of physiological significance. In contrast with ACE, ACEH does not hydrolyse bradykinin and is not inhibited by typical ACE inhibitors. ACEH is unique among mammalian carboxypeptidases in containing an HEXXH zinc motif but, in this respect, resembles a bacterial enzyme, Thermus aquaticus (Taq) carboxypeptidase (EC 3.4.17.19). Collectrin, a developmentally regulated renal protein, is homologous with the C-terminal region of ACEH but has no similarity with ACE and no catalytic domain. Thus, the ACEH protein may have evolved as a chimera of a single ACE-like domain and a collectrin domain. The collectrin domain may regulate tissue response to injury whereas the catalytic domain is involved in peptide processing events.

Amino Acid Sequence↗
PubMed2002

Glycosyl-phosphatidylinositol (GPI)-anchored renal dipeptidase is released by a phospholipase C in vivo.

The release mechanism of the glycosyl-phosphatidylinositol (GPI)-anchored renal dipeptidase (EC 3.4.13.19) in vivo has been investigated. Triton X-114 phase separation indicated that the dipeptidase is exclusively present as a hydrophilic form in urine from porcine, rat, rabbit and human. Western blot analysis of human and porcine purified dipeptidase and the urine concentrates with anti-(cross-reacting determinant) serum demonstrated the presence of inositol 1,2-cyclic monophosphate indicating that the renal dipeptidase had been released from the membrane by the action of a phospholipase C. This is the first direct evidence for cleavage of a human GPI-anchored protein by a responsible phospholipase C in vivo.

Animals↗