Alzheimer's amyloid precursor protein alpha-secretase is inhibited by hydroxamic acid-based zinc metalloprotease inhibitors: similarities to the angiotensin converting enzyme secretase

Neuroprotection and neurorescue against Abeta toxicity and PKC-dependent release of nonamyloidogenic soluble precursor protein by green tea polyphenol (-)-epigallocatechin-3-gallate

Green tea extract and its main polyphenol constituent (-)-epigallocatechin-3-gallate (EGCG) possess potent neuroprotective activity in cell culture and mice model of Parkinson's disease. The central hypothesis guiding this study is that EGCG may play an important role in amyloid precursor protein (APP) secretion and protection against toxicity induced by beta-amyloid (Abeta). The present study shows that EGCG enhances (approximately 6-fold) the release of the non-amyloidogenic soluble form of the amyloid precursor protein (sAPPalpha) into the conditioned media of human SH-SY5Y neuroblastoma and rat pheochromocytoma PC12 cells. sAPPalpha release was blocked by the hydroxamic acid-based metalloprotease inhibitor Ro31-9790, which indicated mediation via alpha-secretase activity. Inhibition of protein kinase C (PKC) with the inhibitor GF109203X, or by down-regulation of PKC, blocked the EGCG-induced sAPPalpha secretion, suggesting the involvement of PKC. Indeed, EGCG induced the phosphorylation of PKC, thus identifying a novel PKC-dependent mechanism of EGCG action by activation of the non-amyloidogenic pathway. EGCG is not only able to protect, but it can rescue PC12 cells against the beta-amyloid (Abeta) toxicity in a dose-dependent manner. In addition, administration of EGCG (2 mg/kg) to mice for 7 or 14 days significantly decreased membrane-bound holoprotein APP levels, with a concomitant increase in sAPPalpha levels in the hippocampus. Consistently, EGCG markedly increased PKCalpha and PKC in the membrane and the cytosolic fractions of mice hippocampus. Thus, EGCG has protective effects against Abeta-induced neurotoxicity and regulates secretory processing of non-amyloidogenic APP via PKC pathway.

Effect of tumor necrosis factor-alpha converting enzyme (TACE) and metalloprotease inhibitor on amyloid precursor protein metabolism in human neurons

Tumor necrosis factor-alpha (TNF-alpha) is implicated in inflammatory processes and much effort is being directed at inhibiting the release of TNF-alpha for treatment of inflammatory conditions. In this context, the drug CP-661,631 has been developed to inhibit the TNF-alpha converting enzyme (TACE). However, TACE is also implicated in amyloid precursor protein secretion. Amyloid precursor protein (APP) undergoes constitutive and regulated secretion by alpha-secretase endoproteolytic cleavage within the amyloid beta peptide (Abeta) domain. Alternative cleavage at the N- and C-terminus of the Abeta domain by beta- and gamma-secretases results in the production of Abeta. In many cellular and in vivo animal models, increased secretion of APP results in a concomitant decrease in the production of Abeta suggesting that the two pathways are intricately linked. However, in human primary neuron cultures, increased APP secretion is not associated with a decrease in total Abeta production. To determine if the use of CP-661,631 may enhance amyloidogenic processing in human brain, we have assessed the effect of CP-661,631 on APP metabolism in primary cultures of human neurons. Our results show that CP-661,631 effectively prevents regulated APP secretion but does not increase total Abeta levels in human primary neuron cultures.

Metalloproteases and guidance of retinal axons in the developing visual system

Axonal growth cones read cues in their environment that guide them to their target. Metalloproteases have been implicated in vitro in modulating the interaction of these cues with receptors in the growth cone. To determine whether metalloprotease function is important in the guidance of vertebrate axons in vivo, we applied hydroxamate-based metalloprotease inhibitors to Xenopus retinal ganglion cell (RGC) axons as they extended through the optic tract. In the presence of two different inhibitors, 0.5-20 microm N-[(2R)-2(hydroxamideocarbonylmethyl)-4-methylpantanoyl]-l-tryptophan methylamide and batimastat, RGC axons made similar dose-dependent guidance errors. Most axons failed to make the expected caudal turn in the diencephalon and continued straight, growing aberrantly toward and across the dorsal midline. As a result, few RGC axons innervated their midbrain target, the optic tectum. Similarly, if the inhibitors were applied after the axons made the turn, many failed to grow into the optic tectum and instead turned to grow along its anterior border. Interestingly, in many instances pathfinding defects were observed in the absence of problems with axon extension, although outgrowth was impaired at the higher doses of the inhibitors. These data provide compelling in vivo evidence that metalloproteases are important for both axon guidance and extension in the developing visual system.

Involvement of MAP kinase in the regulation of amyloid precursor protein processing by novel cholinesterase inhibitors derived from rasagiline

Two novel neuroprotective cholinesterase (ChE) inhibitors, TV3326, (N-propargyl-(3R) aminoindan-5-yl)-ethyl methyl carbamate, and TV3279, (N-propargyl-(3S) aminoindan-5-yl)-ethyl methyl carbamate, were derived from rasagiline for the treatment of Alzheimer's disease (AD). TV3326 also inhibits monoamine oxidase (MAO)-A and -B, whereas its S-isomer, TV3279, lacks MAO inhibitory activity. The action of these drugs in the regulation of amyloid precursor protein (APP) processing, using rat PC12 and human SH-SY5Y neuroblastoma cells, was examined. Both isomers stimulated the release of the non-amyloidogenic a-secretase form of soluble APP (sAPPalpha) from these cell lines. The increases in sAPPalpha, induced by TV3326 and TV3279, were dose-dependent (0.1-100 mM) and blocked by the hydroxamic acid-based metalloprotease inhibitor, Ro31-9790, suggesting mediation via a-secretase activity. Using several signal transduction inhibitors, we identified the involvement of protein kinase C (PKC), mitogen-activated protein (MAP) kinase, and tyrosine kinase-dependent pathways in the enhancement of sAPPalpha release by TV3326 and TV3279. In addition, both drugs directly induced the phosphorylation of p44 and p42 MAP kinase, which was abolished by the specific inhibitors of MAP kinase activation, PD98059 and U0126. These data suggest a novel pharmacological mechanism whereby these ChE inhibitors regulate the secretory processes of APP via activation of the MAP kinase pathway.

Activation of proteinase-activated receptor 1 stimulates epithelial chloride secretion through a unique MAP kinase- and cyclo-oxygenase-dependent pathway

Proteinase-activated receptor 1 (PAR-1) is activated by thrombin and induces chloride secretion by intestinal epithelial cells. To elucidate further the mechanisms whereby PAR-1 stimulates secretion, monolayers of SCBN intestinal epithelial cells were studied in modified Ussing chambers. Short circuit current responses were determined after basolateral application of thrombin and the PAR-1-activating peptide, Ala-parafluoro-Phe-Arg-cyclohexyl-Ala-Citrulline-Tyr (Cit-NH2) in the presence or absence of a variety of signal transduction and cyclo-oxygenase (COX) pathway inhibitors. Increased kinase activity was monitored by immunoprecipitation and Western blot analysis of target phosphoproteins. The PAR-1-induced chloride secretory response was significantly attenuated by inhibitors of the EGF receptor tyrosine kinase, Src-kinase, MEK1/2, as well as by inhibitors of cytosolic phospholipase (cPL) A2, COX-1 and COX-2. PAR-1-induced activation of cPLA2, as shown by Western blot of phosphoserine residues, was blocked in cells treated with the MEK inhibitor U0126, indicating that the MEK-ERK1/2 MAP kinase pathway mediated PAR-1-induced cPLA2 phosphorylation. Our data show that PAR-1-induced chloride secretion in SCBN cells involves Src, EGF receptor trans-activation, activation of a MAPK pathway, phosphorylation of cPLA2, COX activity, but not PGF2alpha or PGE2. These findings may be of clinical importance in inflammatory diseases of the intestine where secretory dysfunction is evident and thrombin levels are elevated.

Non-steroidal anti-inflammatory drugs stimulate secretion of non-amyloidogenic precursor protein

Chronic inflammatory processes are associated with the pathophysiology of Alzheimer's disease (AD), and it has been proposed that treatment with non-steroidal anti-inflammatory drugs (NSAIDs) reduces the risk for AD. Here we report that various NSAIDs, such as the cyclooxygenase inhibitors, nimesulide, ibuprofen and indomethacin, as well as thalidomide (Thal) and its non-teratogenic analogue, supidimide, significantly stimulated the secretion of the non-amyloidogenic alpha-secretase form of the soluble amyloid precursor protein (sAPP alpha) into the conditioned media of SH-SY5Y neuroblastoma and PC12 cells. These NSAIDs markedly reduced the levels of the cellular APP holoprotein, further accelerating non-amyloidogenic processes. sAPP alpha release, induced by nimesulide and Thal, was modulated by inhibitors of protein kinase C and Erk mitogen-activated protein (MAP) kinase. Furthermore, in results complementary to the inhibitor studies, we show for the first time that NSAIDs can activate the Erk MAP kinase signaling cascade, thus identifying a novel pharmacology mechanism of NSAIDs. Our findings suggest that NSAIDs and Thal might prove useful to favor non-amyloidogenic APP processing by enhancing alpha-secretase activity, thereby reducing the formation of amyloidogenic derivatives, and therefore are of potential therapeutic value in AD.

Generation of C-terminally truncated amyloid-beta peptides is dependent on gamma-secretase activity

Aberrant production of amyloid-beta peptides by processing of the beta-amyloid precursor protein leads to the formation of characteristic extracellular protein deposits which are thought to be the cause of Alzheimer's disease. Therefore, inhibiting the key enzymes responsible for amyloid-beta peptide generation, beta- and gamma-secretase may offer an opportunity to intervene with the progression of the disease. In human brain and cell culture systems a heterogeneous population of amyloid-beta peptides with various truncations is detected and at present, it is unclear how they are produced. We have used a combination of surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) and a specific inhibitor of gamma-secretase to investigate whether the production of all amyloid-beta peptide species requires the action of gamma-secretase. Using this approach, we demonstrate that the production of all truncated amyloid-beta peptides except those released by the action of the nonamyloidogenic alpha-secretase enzyme or potentially beta-site betaAPP cleaving enzyme 2 depends on gamma-secretase activity. This indicates that none of these peptides are generated by a separate enzyme entity and a specific inhibitor of the gamma-secretase enzyme should havethe potential to block the generation of all amyloidogenicpeptides. Furthermore in the presence of gamma-secretase inhibitors, the observation of increased cleavage of the membrane-bound betaAPP C-terminal fragment C99 by alpha-secretase suggests that during its trafficking C99 encounters compartments in which alpha-secretase activity resides.

A novel mechanism for the regulation of amyloid precursor protein metabolism

Modifier of cell adhesion protein (MOCA; previously called presenilin [PS] binding protein) is a DOCK180-related molecule, which interacts with PS1 and PS2, is localized to brain areas involved in Alzheimer's disease (AD) pathology, and is lost from the soluble fraction of sporadic Alzheimer's disease (AD) brains. Because PS1 has been associated with gamma-secretase activity, MOCA may be involved in the regulation of beta-amyloid precursor protein (APP) processing. Here we show that the expression of MOCA decreases both APP and amyloid beta-peptide secretion and lowers the rate of cell-substratum adhesion. In contrast, MOCA does not lower the secretion of amyloid precursor-like protein (APLP) or several additional type 1 membrane proteins. The phenotypic changes caused by MOCA are due to an acceleration in the rate of intracellular APP degradation. The effect of MOCA expression on the secretion of APP and cellular adhesion is reversed by proteasome inhibitors, suggesting that MOCA directs nascent APP to proteasomes for destruction. It is concluded that MOCA plays a major role in APP metabolism and that the effect of MOCA on APP secretion and cell adhesion is a downstream consequence of MOCA-directed APP catabolism. This is a new mechanism by which the expression of APP is regulated.

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.

A secreted form of human ADAM9 has an alpha-secretase activity for APP

ADAM9 (MDC9, meltrin gamma) is a member of the ADAM family of metalloproteases, which play important roles in cell-cell fusion, intracellular signaling, and other cellular functions. Here we cloned a novel form of human ADAM9, designated hADAM9s (s for short), which lacks the carboxyl-terminus. Human ADAM9s was found to be secreted from transfected COS cells. RT-PCR analysis demonstrated that the mRNA for hADAM9s is expressed in human brain, liver, heart, kidney, lung, and trachea. When hADAM9s was co-expressed in COS cells with APP and treated with phorbol ester, the APP was digested exclusively at the alpha-secretory site. These results suggest that hADAM9s has an alpha-secretase-like activity for APP. Non-amyloidgenic cleavage of APP may occur at the plasma membrane. Our new results support a new therapeutic strategy to decrease in the Abeta content by directly activating ADAM9 in the extracellular space.

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.

Is "somatic" angiotensin I-converting enzyme a mechanosensor?

"Somatic" angiotensin I-converting enzyme (ACE) appears to be one of the evolutionary advances that made a closed circulation possible, and may have contributed to the Cambrian "explosion" of species approximately 540 million years ago. It also appears to be at the origin of a large number of common human diseases. A model is proposed in which the duplicated form of ACE ("somatic" ACE) functions as a mechanotransducer, defending downstream vessels and tissues from an increase in pressure. In the model, ACE senses shear stress (blood velocity) in regions of turbulent blood flow. An increase in shear stress strips an autoinhibitor tripeptide, FQP, from the N-terminal active site, thereby activating it. The C-terminal domain is constitutively activated by chloride. This model explains the clinical superiority of hydrophobic ACE inhibitors relative to hydrophilic ones.

Ectodomain shedding of cystinyl aminopeptidase from human placental membranes

Cystinyl aminopeptidase (CAP; EC 3.4.11.3) is an integral protein of the placental membrane that is also found in a soluble form in maternal serum during pregnancy. CAP was found to be shed from human placental membranes in a temperature- and time-dependent process. The released form of CAP was hydrophilic as assessed by phase separation in Triton X-114 and high-speed centrifugation. This ectodomain shedding of CAP was inhibited by the hydroxamic acid-based compounds marimastat and BB3103. The inhibition profile for the shedding of CAP was distinct to that for the release of angiotensin converting enzyme, implicating the involvement of distinct zinc metallosecretases in the shedding of these two proteins. These results have implications for our understanding of the mechanism underlying the reduction in serum levels of CAP observed in certain pregnancy-related disorders, such as pre-eclampsia.

Constitutive shedding of the amyloid precursor protein ectodomain is up-regulated by tumour necrosis factor-alpha converting enzyme

The amyloid precursor protein (APP) of Alzheimer's disease is a transmembrane protein that is cleaved within its extracellular domain, liberating a soluble N-terminal fragment (sAPP alpha). Putative mediators of this process include three members of the ADAM (a disintegrin and metalloprotease) family, ADAM9, ADAM10 and ADAM17/TACE (tumour necrosis factor-alpha converting enzyme). Tumour necrosis factor-alpha protease inhibitor (TAPI-1), an inhibitor of ADAMs, reduced constitutive and muscarinic receptor-stimulated sAPP alpha release in HEK-293 cells stably expressing M3 muscarinic receptors. However, the former was less sensitive to TAPI-1 (IC(50)=8.09 microM) than the latter (IC(50)=3.61 microM), suggesting that these processes may be mediated by different metalloproteases. Constitutive sAPP alpha release was increased several-fold in cells transiently transfected with TACE, and this increase was proportional to TACE expression. In contrast, muscarinic-receptor-activated sAPP alpha release was not altered in TACE transfectants. TACE-dependent constitutive release of co-transfected APP(695) was inhibited by TAPI-1 with an IC(50) of 0.92 microm, a value significantly lower than the IC(50)s for inhibition of either constitutive or receptor-regulated sAPP alpha shedding mediated by endogenous secretases. The results indicate that TACE is capable of catalysing constitutive alpha-secretory cleavage of APP, but it is likely that additional members of the ADAM family mediate endogenous constitutive and receptor-coupled release of sAPP alpha in HEK-293 cells.

A portrait of Alzheimer secretases--new features and familiar faces

The amyloid beta-peptide (Abeta) is a principal component of the cerebral plaques found in the brains of patients with Alzeheimer's disease (AD). This insoluble 40- to 42-amino acid peptide is formed by the cleavage of the Abeta precursor protein (APP). The three proteases that cleave APP, alpha-, beta-, and gamma-secretases, have been implicated in the etiology of AD. beta-Secretase is a membrane-anchored protein with clear homology to soluble aspartyl proteases, and alpha-secretase displays characteristics of certain membrane-tethered metalloproteases. gamma-Secretase is apparently an oligomeric complex that includes the presenilins, which may be the catalytic component of this protease. Identification of the alpha-, beta-, and gamma-secretases provides potential targets for designing new drugs to treat AD.

Roles of the juxtamembrane and extracellular domains of angiotensin-converting enzyme in ectodomain shedding

Angiotensin-converting enzyme (ACE) is one of a growing number of integral membrane proteins that is shed from the cell surface through proteolytic cleavage by a secretase. To investigate the requirements for ectodomain shedding, we replaced the glycosylphosphatidylinositol addition sequence in membrane dipeptidase (MDP) - a membrane protein that is not shed - with the juxtamembrane stalk, transmembrane (TM) and cytosolic domains of ACE. The resulting construct, MDP-STM(ACE), was targeted to the cell surface in a glycosylated and enzymically active form, and was shed into the medium. The site of cleavage in MDP-STM(ACE) was identified by MS as the Arg(374)-Ser(375) bond, corresponding to the Arg(1203)-Ser(1204) secretase cleavage site in somatic ACE. The release of MDP-STM(ACE) and ACE from the cells was inhibited in an identical manner by batimastat and two other hydroxamic acid-based zinc metallosecretase inhibitors. In contrast, a construct lacking the juxtamembrane stalk, MDP-TM(ACE), although expressed at the cell surface in an enzymically active form, was not shed, implying that the juxtamembrane stalk is the critical determinant of shedding. However, an additional construct, ACEDeltaC, in which the N-terminal domain of somatic ACE was fused to the stalk, TM and cytosolic domains, was also not shed, despite the presence of a cleavable stalk, implying that in contrast with the C-terminal domain, the N-terminal domain lacks a signal required for shedding. These data are discussed in the context of two classes of secretases that differ in their requirements for recognition of substrate proteins.

Regulation of Membrane Metalloproteolytic Cleavage of L-selectin (CD62L) by the Epidermal Growth Factor Domain

The adhesion molecule L-selectin is cleaved rapidly from the surface of activated leukocytes by tumor necrosis factor-alpha converting enzyme, a cell surface metalloprotease, and also undergoes slower constitutive shedding in unactivated cells. The structural features that render it susceptible to shedding are poorly understood. We therefore analyzed the shedding of a series of mutant and chimeric L-selectin molecules. Although murine L-selectin is cleaved at a specific location in the juxtamembrane region 11 amino acids distal to the cell membrane, this cleavage has little sequence specificity. However, proline substitution at the P2' or P3' position or deletion of the epidermal growth factor (EGF) domain completely blocks the rapid phorbol ester-induced cleavage, but does not affect the slower basal proteolytic shedding. Insertion of the 15-residue membrane-proximal region (MPR) of L-selectin into the heterologous protein B7.2 results in a molecule that undergoes constitutive proteolytic turnover. In contrast, insertion of both the EGF domain and the MPR confers susceptibility to both slow constitutive shedding and the rapid proteolytic cleavage induced by phorbol 12-myristate 13-acetate. These results demonstrate that constitutive and induced L-selectin cleavage are separable processes and that the rapid phorbol ester-induced shedding requires the presence of the EGF domain, a sequence that is remote from the cleavage site.

Constitutive shedding of the amyloid precursor protein ectodomain is up-regulated by tumour necrosis factor-alpha converting enzyme

The amyloid precursor protein (APP) of Alzheimer's disease is a transmembrane protein that is cleaved within its extracellular domain, liberating a soluble N-terminal fragment (sAPP alpha). Putative mediators of this process include three members of the ADAM (a disintegrin and metalloprotease) family, ADAM9, ADAM10 and ADAM17/TACE (tumour necrosis factor-alpha converting enzyme). Tumour necrosis factor-alpha protease inhibitor (TAPI-1), an inhibitor of ADAMs, reduced constitutive and muscarinic receptor-stimulated sAPP alpha release in HEK-293 cells stably expressing M3 muscarinic receptors. However, the former was less sensitive to TAPI-1 (IC(50)=8.09 microM) than the latter (IC(50)=3.61 microM), suggesting that these processes may be mediated by different metalloproteases. Constitutive sAPP alpha release was increased several-fold in cells transiently transfected with TACE, and this increase was proportional to TACE expression. In contrast, muscarinic-receptor-activated sAPP alpha release was not altered in TACE transfectants. TACE-dependent constitutive release of co-transfected APP(695) was inhibited by TAPI-1 with an IC(50) of 0.92 microm, a value significantly lower than the IC(50)s for inhibition of either constitutive or receptor-regulated sAPP alpha shedding mediated by endogenous secretases. The results indicate that TACE is capable of catalysing constitutive alpha-secretory cleavage of APP, but it is likely that additional members of the ADAM family mediate endogenous constitutive and receptor-coupled release of sAPP alpha in HEK-293 cells.

Cortical alterations of angiotensin converting enzyme, angiotensin II and AT1 receptor in Alzheimer's dementia

We investigated the immunohistochemical alterations of angiotensin converting enzyme (ACE), angiotensin II and AT1 receptor in the parietal cortex in Alzheimer's dementia (AD) to reveal the contributive role of the brain renin-angiotensin system in the disease process. In controls, ACE, angiotensin II and AT1 immunoreactivities were localized to pyramidal neurons of the cortex. The staining intensity was distinctly increased in AD for all three antigens, involving predominantly cortical layer V, which may reflect the enhanced brain renin-angiotensin system activity in the disease process. In addition, a prominent perivascular ACE and angiotensin II immunoreactivity surrounding some cortical vessels in aged controls and AD patients points to an underlying microvascular pathology in the process of neurodegeneration.

A point mutation in the juxtamembrane stalk of human angiotensin I-converting enzyme invokes the action of a distinct secretase

Angiotensin I-converting enzyme (ACE) is one of a number of integral membrane proteins that is proteolytically shed from the cell surface by a zinc metallosecretase. Mutagenesis of Asn(631) to Gln in the juxtamembrane stalk region of ACE resulted in more efficient secretion of the mutant protein (ACE(NQ)) as determined by pulse-chase analysis. In contrast to the wild-type ACE, the cleavage of ACE(NQ) was not blocked by the metallosecretase inhibitor batimastat but by the serine protease inhibitor, 1,3-dichloroisocoumarin. Incubation of the cells at 15 degrees C revealed that ACE(NQ) was cleaved in the endoplasmic reticulum, and mass spectrometric analysis of the secreted form of the protein indicated that it had been cleaved at the Asn(635)-Ser(636) bond, three residues N-terminal to the normal secretase cleavage site at Arg(638)-Ser(639). These data clearly show that a point mutation in the juxtamembrane region of an integral membrane protein can invoke the action of a mechanistically and spatially distinct secretase. In light of this observation, previous data on the effect of mutations in the juxtamembrane stalk of shed proteins being accommodated by a single secretase having a relaxed specificity need to be re-evaluated.

Presenilins as therapeutic targets for the treatment of Alzheimer's disease

Studies demonstrating that accumulation and aggregation of the amyloid beta protein (Abeta) within the brain is likely to cause Alzheimer's disease (AD) have provided the rationale for therapeutic strategies aimed at influencing Abeta production, aggregation and clearance. gamma-secretase catalyzes the final cleavage that releases the Abeta from its precursor; therefore, it is a potential therapeutic target for the treatment of AD. Recent data show that the polytopic membrane proteins presenilin 1 and presenilin 2 are either catalytic components or essential co-factors of a membrane-bound proteolytic complex that possesses gamma-secretase activity. Although recent findings demonstrating that gamma-secretase inhibitors bind directly to presenilins (PSs) further support a catalytic role for PSs in gamma-secretase cleavage, additional studies are still needed to clarify the role of PSs in gamma-secretase cleavage and the use of targeting PSs to reduce Abeta production.

The amyloid-beta peptide and its role in Alzheimer's disease

Amyloid formation plays a central role in the cause and progression of Alzheimer's disease. The major component of this amyloid is the amyloid-beta (A beta) peptide, which is currently the subject of intense study. This review discusses some recent studies in the area of A beta synthesis, purification and structural analysis. Also discussed are proposed mechanisms for A beta-induced neurotoxicity and some recent advances in the development of A beta-related therapeutic strategies.

Activation of MAPKs by angiotensin II in vascular smooth muscle cells. Metalloprotease-dependent EGF receptor activation is required for activation of ERK and p38 MAPK but not for JNK

In cultured vascular smooth muscle cells (VSMC), the vasculotrophic factor, angiotensin II (AngII) activates three major MAPKs via the G(q)-coupled AT1 receptor. Extracellular signal-regulated kinase (ERK) activation by AngII requires Ca(2+)-dependent "transactivation" of the EGF receptor that may involve a metalloprotease to stimulate processing of an EGF receptor ligand from its precursor. Whether EGF receptor transactivation also contributes to activation of other members of MAPKs such as p38MAPK and c-Jun N-terminal kinase (JNK) by AngII remains unclear. In the present study, we have examined the effects of a synthetic metalloprotease inhibitor BB2116, and the EGF receptor kinase inhibitor AG1478 on AngII-induced activation of MAPKs in cultured VSMC. BB2116 markedly inhibited ERK activation induced by AngII or the Ca(2+) ionophore without affecting the activation by EGF or PDGF. BB2116 as well as HB-EGF neutralizing antibody inhibited the EGF receptor transactivation by AngII, suggesting a critical role of HB-EGF in the metalloprotease-dependent EGF receptor transactivation. In addition to the ERK activation, activation of p38MAPK and JNK by AngII was inhibited by an AT1 receptor antagonist, RNH6270. and EGF markedly activate p38MAPK, whereas but not EGF markedly activates JNK, indicating the possible contribution of the EGF receptor transactivation to the p38MAPK activation. The findings that both BB2116 and AG1478 specifically inhibited activation of p38MAPK but not JNK by AngII support this hypothesis. From these data, we conclude that ERK and p38MAPK activation by AngII requires the metalloprotease-dependent EGF receptor transactivation, whereas the JNK activation is regulated without involvement of EGF receptor transactivation.

The role of proteolysis in Alzheimer's disease

Alzheimer's disease is characterised by the progressive deposition of the 4 kDa beta-amyloid peptide (A beta) in extracellular senile plaques in the brain. A beta is derived by proteolytic cleavage of the amyloid precursor protein (APP) by various proteinases termed secretases. alpha-Secretase is inhibited by hydroxamate-based zinc metalloproteinase inhibitors such as batimastat with I50 values in the low micromolar range, and displays many properties in common with the secretase that releases angiotensin converting enzyme. A cell impermeant biotinylated derivative of one such inhibitor completely blocked the release of APP from the surface of neuronal cells, indicating that alpha-secretase cleaves APP at the cell-surface. A range of hydroxamate-based compounds have been used to distinguish between alpha-secretase and tumour necrosis factor-alpha convertase, a member of the ADAMs (a disintegrin and metalloproteinase-like) family of zinc metalloproteinases. Recent data suggests that the presenilins may be aspartyl proteinases with the specificity of gamma-secretase. Although APP and the presenilins are present in detergent-insoluble, cholesterol- and glycosphingolipid-rich lipid rafts, they do not behave as typical lipid raft proteins, and thus it is unclear whether these membrane domains are the sites for proteolytic processing of APP.

In search of an enzyme: the beta-secretase of Alzheimer's disease is an aspartic proteinase

The deposition of beta-amyloid (Abeta) in the brain is a neuropathological feature of Alzheimer's disease. Abeta is cleaved from its precursor protein (APP) by processing at its N and C termini by enzymes known as beta- and gamma-secretases,respectively. The identity of these enzymes has been elusive but the search for the N-terminal secretase might have ended recently with the almost simultaneous publication by five major laboratories claiming a transmembrane aspartic proteinase to be the long sought after beta-secretase. Even at this early stage of its characterization, this aspartic proteinase fulfils many of the key criteria necessary for beta-secretase. The race is now on to develop inhibitors that could prove effective in halting the progression of Alzheimer's disease.

The use of seldi proteinchip arrays to monitor production of Alzheimer's betaamyloid in transfected cells

beta-Amyloid (Abeta), a 39-43 residue peptide, is the principal component of senile plaques found in the brains of patients with Alzheimer's disease (AD). There are two main lines of evidence that its deposition is the cause of neurodegeneration. First, mutations found in three genes in familial Alzheimer's cases give rise to increased production of the longest, most toxic, form, Abeta 1-42. Second. aggregated Abeta is toxic to neuronal cells in culture. Inhibitors of the proteases involved in its release from the amyloid precursor protein are, therefore, of major therapeutic interest. The best candidates for the releasing proteases are both aspartyl proteases, which are integrated into the membranes of the endoplasmic reticulum and Golgi network. A sensitive assay using Ciphergen's Seldi system has been developed to measure all the variants of Abeta in culture supernatants, which will be of great value in screening inhibitors of these proteases. With this assay, it has been shown that increasing intracellular cholesterol increases the activities of both beta-secretase, and gamma-secretase 42. Moreover, changing the intracellular targeting of amyloid precursor glycoprotein (APP) yields increased alpha-secretase cleavage, and increases in the amounts of oxidized/nitrated forms of Abeta.

Treatment with BB-94, a broad spectrum inhibitor of zinc-dependent metalloproteinases, causes deviation of the cytokine profile towards type-2 in experimental pulmonary tuberculosis in Balb/c mice

BB-94 (batimastat) is a broad- spectrum hydroxamic acid-based zinc metalloproteinase inhibitor that inhibits both the matrix metalloproteinases (MMP) and members of the ADAM family of enzymes such as Tumour Necrosis Factor-alpha Cleaving Enzyme (TACE). These enzymes are involved in the regulation of inflammatory processes in tuberculosis. Balb/c mice infected with M. tuberculosis via the intratracheal route were treated with BB-94 for 1 month, starting on the day of infection. Immunohistochemistry, semiquantitative RT-PCR and ELISA assays for cytokines revealed a deficit in IL-1 and IL-2 expression and a premature bias towards IL-4 expression, accompanied by a delay in granuloma formation and more rapid progression of disease in BB-94-treated animals. This situation corrected itself after the drug was withdrawn at 28 days. In contrast, when BB-94 was administered only after 1 month there were no significant changes apart from the presence of amyloid, and a paradoxically increased expression of IL-1alpha. These results cast light on mechanisms of immunity in tuberculosis and also indicate that in patients treated with similar broad-spectrum MMP inhibitors there may be a risk of inappropriate deviation of some immune responses towards a Type-2 cytokine profile.

Insulin regulates soluble amyloid precursor protein release via phosphatidyl inositol 3 kinase-dependent pathway

Several lines of biochemical evidence correlate the presence of energy metabolic defects with the functional alterations associated with brain aging and with the pathogenesis of neurodegenerative disorders such as Alzheimer's disease. Within this context we tested the ability of insulin to regulate the amyloid precursor protein (APP) processing in SH-SY5Y neuroblastoma cells. Our findings show that insulin promotes APP metabolism by a glucose-independent mechanism. We demonstrate a novel intracellular pathway that increases the rate of secretion of soluble APP through the activity of phosphatidyl-inositol 3 kinase (PI3-K). This pathway, downstream of insulin receptor tyrosine kinase activity, does not involve either the activation of protein kinase C or the mitogen-activated protein kinase (MAP-K) pathway. Because of the physiological role of PI3-K in the translocation of glucose transporter-containing vesicles, we speculate that PI3-K involvement in APP metabolism may act at the level of vesicular trafficking.

Matrix metalloproteinases contribute to brain damage in experimental pneumococcal meningitis

The present study was performed to evaluate the role of matrix metalloproteinases (MMP) in the pathogenesis of the inflammatory reaction and the development of neuronal injury in a rat model of bacterial meningitis. mRNA encoding specific MMPs (MMP-3, MMP-7, MMP-8, and MMP-9) and the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) were significantly (P < 0.04) upregulated, compared to the beta-actin housekeeping gene, in cortical homogenates at 20 h after infection. In parallel, concentrations of MMP-9 and TNF-alpha in cerebrospinal fluid (CSF) were significantly increased in rats with bacterial meningitis compared to uninfected animals (P = 0.002) and showed a close correlation (r = 0.76; P < 0. 001). Treatment with a hydroxamic acid-type MMP inhibitor (GM6001; 65 mg/kg intraperitoneally every 12 h) beginning at the time of infection significantly lowered the MMP-9 (P < 0.02) and TNF-alpha (P < 0.02) levels in CSF. Histopathology at 25.5 +/- 5.7 h after infection showed neuronal injury (median [range], 3.5% [0 to 17.5%] of the cortex), which was significantly (P < 0.01) reduced to 0% (0 to 10.8%) by GM6001. This is the first report to demonstrate that MMPs contribute to the development of neuronal injury in bacterial meningitis and that inhibition of MMPs may be an effective approach to prevent brain damage as a consequence of the disease.

Identification of a novel aspartic protease (Asp 2) as beta-secretase

The Alzheimer's disease beta-amyloid peptide (Abeta) is produced by excision from the type 1 integral membrane glycoprotein amyloid precursor protein (APP) by the sequential actions of beta- and then gamma-secretases. Here we report that Asp 2, a novel transmembrane aspartic protease, has the key activities expected of beta-secretase. Transient expression of Asp 2 in cells expressing APP causes an increase in the secretion of the N-terminal fragment of APP and an increase in the cell-associated C-terminal beta-secretase APP fragment. Mutation of either of the putative catalytic aspartyl residues in Asp 2 abrogates the production of the fragments characteristic of cleavage at the beta-secretase site. The enzyme is present in normal and Alzheimer's disease (AD) brain and is also found in cell lines known to produce Abeta. Asp 2 localizes to the Golgi/endoplasmic reticulum in transfected cells and shows clear colocalization with APP in cells stably expressing the 751-amino-acid isoform of APP.

A combinatorial approach to the identification of dipeptide aldehyde inhibitors of beta-amyloid production

In an effort to rapidly identify potent inhibitors of Abeta production and to probe the amino acid sequence specificity of the protease(s) responsible for the production of this peptide, a large number of dipeptide aldehydes were combinatorially synthesized and manually evaluated for their inhibitory properties. The starting point for this study was the dipeptide aldehyde carbobenzoxyl-valinyl-phenylalanal previously shown to inhibit the production of Abeta in CHO cells stably transfected with the cDNA encoding betaAPP695. Pools of related dipeptide aldehydes were combinatorially synthesized, and the most active pool was deconvoluted, resulting in the identification of the most active inhibitor of this pool. Systematic optimization of this inhibitor resulted in a series of dipeptide aldehydes with enhanced potencies relative to carbobenzoxyl-valinyl-phenylalanal. The most active dipeptide aldehydes were those that possessed hydrophobic amino acids at both the P1 and P2 positions. The most potent compound identified in this study was 3, 5-dimethoxycinnamamide-isoleucinyl-leucinal with an IC(50) of 9.6 microM, approximately 10-fold more active than carbobenzoxyl-valinyl-phenylalanal. In immunoprecipitation experiments using antibodies directed toward either Abeta1-40 or Abeta1-42, 3,5-dimethoxycinnamamide-isoleucinyl-leucinal, like carbobenzoxyl-valinyl-phenylalanal, preferentially inhibited the shorter 1-40 form of Abeta, whereas the longer 1-42 form was not as strongly inhibited. These results suggest that dipeptide aldehydes related to carbobenzoxyl-valinyl-phenylalanal inhibit Abeta through similar mechanisms and demonstrate the utility of a combinatorial synthesis approach to rapidly identify potent inhibitors of Abeta production.

Alzheimer's disease: correlation of the suppression of beta-amyloid peptide secretion from cultured cells with inhibition of the chymotrypsin-like activity of the proteasome

Peptide aldehyde inhibitors of the chymotrypsin-like activity of the proteasome (CLIP) such as N-acetyl-Leu-Leu-Nle-H (or ALLN) have been shown previously to inhibit the secretion of beta-amyloid peptide (A beta) from cells. To evaluate more fully the role of the proteasome in this process, we have tested the effects on A beta formation of a much wider range of peptide-based inhibitors of CLIP than published previously. The inhibitors tested included several peptide boronates, some of which proved to be the most potent peptide-based inhibitors of beta-amyloid production reported so far. We found that the ability of the peptide aldehyde and boronate inhibitors to suppress A beta formation from cells correlated extremely well with their potency as CLIP inhibitors. Thus, we conclude that the proteasome may be involved either directly or indirectly in A beta formation.

Activity of alpha-secretase as the common final effector of protein kinase C-dependent and -independent modulation of amyloid precursor protein metabolism

The metabolic fate of the amyloid precursor protein (APP) is one of the key factors in the pathogenesis of Alzheimer's disease (AD). A complex cellular mechanism regulates the rate at which the precursor is cleaved by alpha-secretase and released as soluble protein in the extracellular space. We show here that alpha-secretase constitutes the common final effector of several independent means of stimulation of soluble APP (sAPP) release. The release of sAPP by alpha-secretase resembles that of several other membrane-bound proteins with soluble counterparts, a process that is sensitive to matrix metalloprotease inhibitors. The hydroxamic acid-based compound KD-IX-73-4 inhibits phorbol ester-mediated sAPP release from COS cells with an IC50 of 8 microM, consistent with previous data for the same compound against leukocyte L-selectin shedding. Beyond direct protein kinase C (PKC) activation we show that KD-IX-73-4 inhibits also receptor-mediated sAPP release induced by carbachol in SH-SY5Y cells and by bradykinin in human skin fibroblasts, with the latter being a PKC-independent mechanism. Altogether these data suggest that all pharmacological means of stimulating sAPP release converge to a hydroxamic acid-based inhibitor-sensitive proteolytic enzyme. Moreover, because KD-IX-73-4 was effective in the inhibition of stimulated but not constitutive sAPP release, these data suggest the existence of different enzymes regulating the two metabolic pathways leading to sAPP secretion.

Endogenous bax translocation in SH-SY5Y human neuroblastoma cells and cerebellar granule neurons undergoing apoptosis

Changes at the mitochondria are an early, required step in apoptosis in various cell types. We used western blot analysis to demonstrate that the proapoptotic protein Bax translocated from the cytosolic to the mitochondrial fraction in SH-SY5Y human neuroblastoma cells undergoing staurosporine- or EGTA-mediated apoptosis. Levels of mitochondrial Bax increased 15 min after staurosporine treatment. In EGTA-treated cells, increased levels of mitochondrial Bax were seen at 4 h, consistent with a slower onset of apoptosis in EGTA versus staurosporine treatments. We also demonstrate the concomitant translocation of cytochrome c from the mitochondrial to the cytosolic fractions. We correlated these translocations with changes in caspase-3-like activity. An increase in caspase-3-like activity was evident 2 h after staurosporine treatment. Inhibition of the mitochondrial permeability transition had no effect on Bax translocation or caspase-3-like activity in staurosporine-treated SH-SY5Y cells. In primary cultures of cerebellar granule neurons undergoing low K(+)-mediated apoptosis, Bax translocation to the mitochondrial fraction was evident at 3 h. Cytochrome c release into the cytosol was not significant until 8 h after treatment. These data support a model of apoptosis in which Bax acts directly at the mitochondria to allow the release of cytochrome c.

Constitutive and regulated alpha-secretase cleavage of Alzheimer's amyloid precursor protein by a disintegrin metalloprotease

Amyloid beta peptide (Abeta), the principal proteinaceous component of amyloid plaques in brains of Alzheimer's disease patients, is derived by proteolytic cleavage of the amyloid precursor protein (APP). Proteolytic cleavage of APP by a putative alpha-secretase within the Abeta sequence precludes the formation of the amyloidogenic peptides and leads to the release of soluble APPsalpha into the medium. By overexpression of a disintegrin and metalloprotease (ADAM), classified as ADAM 10, in HEK 293 cells, basal and protein kinase C-stimulated alpha-secretase activity was increased severalfold. The proteolytically activated form of ADAM 10 was localized by cell surface biotinylation in the plasma membrane, but the majority of the proenzyme was found in the Golgi. These results support the view that APP is cleaved both at the cell surface and along the secretory pathway. Endogenous alpha-secretase activity was inhibited by a dominant negative form of ADAM 10 with a point mutation in the zinc binding site. Studies with purified ADAM 10 and Abeta fragments confirm the correct alpha-secretase cleavage site and demonstrate a dependence on the substrate's conformation. Our results provide evidence that ADAM 10 has alpha-secretase activity and many properties expected for the proteolytic processing of APP. Increases of its expression and activity might be beneficial for the treatment of Alzheimer's disease.

XCE, a new member of the endothelin-converting enzyme and neutral endopeptidase family, is preferentially expressed in the CNS

In the present study, we have isolated a cDNA encoding a novel member of the family of zinc metallopeptidases that includes neutral endopeptidase and endothelin-converting enzyme. The predicted amino-acid sequence of this enzyme, termed XCE, consists of 775 amino-acids with a single putative membrane-spanning region, an N-terminal cytoplasmic domain of 59 residues, and a large luminal domain that contains a characteristic zinc-binding motif. Western blot analysis of cells stably expressing this new metallopeptidase revealed a glycosylated protein of approximately 95 kDa. XCE mRNA was found to be predominantly expressed in the central nervous system, sympathetic ganglia and in uterine subepithelial cells. In the rat and human CNS, a very specific pattern of neuronal labelling (in presumptive cholinergic interneurons of basal ganglia, basal forebrain neurons, as well as brainstem and spinal cord motoneurons) was detected by in situ hybridization histochemistry. The enzyme substrate, as yet unidentified, might be found among the numerous neuropeptide transmitters which are colocalized with acetylcholine in these neurons.

Tissue inhibitor of metalloproteinases-3 inhibits shedding of L-selectin from leukocytes

Although the enzyme or enzymes mediating shedding of L-selectin have not yet been identified, this activity can be blocked by synthetic hydroxamic acid-based inhibitors of metalloproteinases such as Ro 31-9790. However, the endogenous matrix metalloproteinase inhibitor tissue inhibitor of metalloproteinases (TIMP)-1 does not block L-selectin shedding. Here, we report that TIMP-3, but not TIMP-2, inhibits L-selectin shedding from mouse and human lymphocytes, Jurkat T cells, and human monocytes. TIMP-3 has an IC50 of 0.3-0.4 microM on these cell types compared with 0.7-4.8 microM for Ro 31-9790. A metalloproteinase (tumor necrosis factor-alpha (TNF-alpha)-converting enzyme; ADAM17) has recently been identified which cleaves the pro-form of TNF-alpha to produce soluble cytokine. We compared inhibition of L-selectin shedding by TIMPs and Ro 31-9790 with inhibition of TNF-alpha shedding from human monocytes. TIMP-3 inhibited TNF-alpha shedding (IC50 of 0.1 microM), as did Ro 31-9790 (IC50 of 0.4 microM). TIMP-2 had a partial effect, and TIMP-1 did not inhibit. This study confirms that L-selectin sheddase is a metalloproteinase, but not a matrix metalloproteinase, and investigates the relationship between shedding of L-selectin and TNF-alpha.

A matrix metalloproteinase inhibitor which prevents fibroblast-mediated collagen lattice contraction

Matrix metalloproteinases (MMPs) and the specific tissue inhibitors of metalloproteinases (TIMPs) are involved in tissue turnover in normal and pathological processes including wound healing. Marimastat, a potent inhibitor of MMPs, was used to investigate the role of MMPs in an in vitro wound contraction model, the dermal equivalent, in which fibroblasts are grown in a collagen matrix. Marimastat inhibited fibroblast-mediated lattice contraction and this inhibition was reversible upon removal of the inhibitor, indicating that MMPs play an important role in fibroblast-mediated collagen lattice contraction, modelling what may happen when granulation tissue contracts in a healing wound.

The secretases that cleave angiotensin converting enzyme and the amyloid precursor protein are distinct from tumour necrosis factor-alpha convertase

Angiotensin converting enzyme (ACE) and the Alzheimer's amyloid precursor protein are cleaved from the membrane by zinc metalloproteinases termed ACE secretase and alpha-secretase, respectively. Tumour necrosis factor-alpha (TNF-alpha) convertase (ADAM 17) is a recently identified member of the adamalysin family of mammalian zinc metalloproteinases that is involved in the production of TNF-alpha and possibly in the cleavage of other membrane proteins. Using two different cell-free assays we were unable to detect significant cleavage and secretion of ACE by TNF-alpha convertase. In addition, there was a different effect of three hydroxamic acid-based inhibitors (batimastat, compound 1 and compound 4) towards TNF-alpha convertase as compared to ACE secretase and alpha-secretase. Thus TNF-alpha convertase would appear to be distinct from, but possibly related to, the secretases that cleave ACE and the amyloid precursor protein.