Overexpression of oxidized protein hydrolase protects COS-7 cells from oxidative stress-induced inhibition of cell growth and survival

HNF4A Regulated APEH Deficiency Promotes UPR Activation in Diabetic Kidney Disease

Diabetic kidney disease (DKD) constitutes a severe microvascular complication of diabetes and ranks among the leading causes of end-stage renal disease (ESRD). Endoplasmic reticulum stress (ERS) significantly contributes to the initiation and progression of DKD, as persistent ERS leads to excessive activation of the unfolded protein response (UPR), triggering cellular apoptosis. Protein carbonylation, a prominent oxidative modification caused by reactive oxygen species (ROS), is recognized as a critical initiator of ERS. Acyl peptide enzyme hydrolase (APEH) demonstrates cytoprotective properties by degrading carbonylated proteins and alleviating their abnormal aggregation. Nonetheless, the precise roles and mechanisms of APEH in DKD remain inadequately elucidated. This study employs 24-week db/db mice and a renal tubular epithelial cell model stimulated by high glucose and high fat conditions. By combining comprehensive multidatabase bioinformatics analysis, morphological characterization, and molecular biology techniques, we aim to elucidate the functional role and underlying regulatory mechanisms of APEH in DKD. Our findings indicate that DKD is associated with significantly reduced expression of both APEH and hepatocyte nuclear factor 4 alpha (HNF4A), leading to elevated protein carbonylation and subsequent activation of the UPR pathway, ultimately causing increased apoptosis in renal tubular epithelial cells. Further investigation through dual-luciferase reporter assays and ChIP-qPCR analysis confirmed that HNF4A directly regulates APEH expression by binding to its promoter region. Reduced APEH expression impairs the protective effects mediated by HNF4A, resulting in elevated protein carbonylation, enhanced UPR activation, and increased apoptosis, thereby exacerbating renal tubular epithelial cell injury in DKD. Collectively, these findings underscore the critical role of the HNF4A/APEH axis in regulating protein carbonylation and UPR signaling during DKD progression, highlighting a potential novel therapeutic target for DKD treatment.

A snapshot of the Physcomitrella N-terminome reveals N-terminal methylation of organellar proteins

KEY MESSAGE

Analysis of the N-terminome of Physcomitrella reveals N-terminal monomethylation of nuclear-encoded, mitochondria-localized proteins. Post- or co-translational N-terminal modifications of proteins influence their half-life as well as mediating protein sorting to organelles via cleavable N-terminal sequences that are recognized by the respective translocation machinery. Here, we provide an overview on the current modification state of the N-termini of over 4500 proteins from the model moss Physcomitrella (Physcomitrium patens) using a compilation of 24 N-terminomics datasets. Our data reveal distinct proteoforms and modification states and confirm predicted targeting peptide cleavage sites of 1,144 proteins localized to plastids and the thylakoid lumen, to mitochondria, and to the secretory pathway. In addition, we uncover extended N-terminal methylation of mitochondrial proteins. Moreover, we identified PpNTM1 (P. patens alpha N-terminal protein methyltransferase 1) as a candidate for protein methylation in plastids, mitochondria, and the cytosol. These data can now be used to optimize computational targeting predictors, for customized protein fusions and their targeted localization in biotechnology, and offer novel insights into potential dual targeting of proteins.

A deeply conserved protease, acylamino acid-releasing enzyme (AARE), acts in ageing in Physcomitrella and Arabidopsis

Reactive oxygen species (ROS) are constant by-products of aerobic life. In excess, ROS lead to cytotoxic protein aggregates, which are a hallmark of ageing in animals and linked to age-related pathologies in humans. Acylamino acid-releasing enzymes (AARE) are bifunctional serine proteases, acting on oxidized proteins. AARE are found in all domains of life, albeit under different names, such as acylpeptide hydrolase (APEH/ACPH), acylaminoacyl peptidase (AAP), or oxidized protein hydrolase (OPH). In humans, AARE malfunction is associated with age-related pathologies, while their function in plants is less clear. Here, we provide a detailed analysis of AARE genes in the plant lineage and an in-depth analysis of AARE localization and function in the moss Physcomitrella and the angiosperm Arabidopsis. AARE loss-of-function mutants have not been described for any organism so far. We generated and analysed such mutants and describe a connection between AARE function, aggregation of oxidized proteins and plant ageing, including accelerated developmental progression and reduced life span. Our findings complement similar findings in animals and humans, and suggest a unified concept of ageing may exist in different life forms.

A carbapenem antibiotic inhibiting a mammalian serine protease: structure of the acylaminoacyl peptidase-meropenem complex

The structure of porcine AAP (pAAP) in a covalently bound complex with meropenem was determined by cryo-EM to 2.1 Å resolution, showing the mammalian serine-protease inhibited by a carbapenem antibiotic. AAP is a modulator of the ubiquitin-proteasome degradation system and the site of a drug-drug interaction between the widely used antipsychotic, valproate and carbapenems. The active form of pAAP - a toroidal tetramer - binds four meropenem molecules covalently linked to the catalytic Ser587 of the serine-protease triad, in an acyl-enzyme state. AAP is hindered from fully processing the antibiotic by the displacement and protonation of His707 of the catalytic triad. We show that AAP is made susceptible to the association by its unusually sheltered active pockets and flexible catalytic triads, while the carbapenems possess sufficiently small substituents on their β-lactam rings to fit into the shallow substrate-specificity pocket of the enzyme.

Cryo-EM structure of acylpeptide hydrolase reveals substrate selection by multimerization and a multi-state serine-protease triad

The first structure of tetrameric mammalian acylaminoacyl peptidase, an enzyme that functions as an upstream regulator of the proteasome through the removal of terminal N-acetylated residues from its protein substrates, was determined by cryo-EM and further elucidated by MD simulations. Self-association results in a toroid-shaped quaternary structure, guided by an amyloidogenic β-edge and unique inserts. With a Pro introduced into its central β-sheet, sufficient conformational freedom is awarded to the segment containing the catalytic Ser587 that the serine protease catalytic triad alternates between active and latent states. Active site flexibility suggests that the dual function of catalysis and substrate selection are fulfilled by a novel mechanism: substrate entrance is regulated by flexible loops creating a double-gated channel system, while binding of the substrate to the active site is required for stabilization of the catalytic apparatus – as a second filter before hydrolysis. The structure not only underlines that within the family of S9 proteases homo-multimerization acts as a crucial tool for substrate selection, but it will also allow drug design targeting of the ubiquitin-proteasome system.

The structure of tetrameric mammalian acylaminoacyl peptidase – a key upstream regulator of the proteasome – was determined by cryo-EM (and elucidated by MD), showing a “shutters-and-channels” substrate selection apparatus created by oligomerization.

Oxidized Substrates of APEH as a Tool to Study the Endoprotease Activity of the Enzyme

APEH is a ubiquitous and cytosolic serine protease belonging to the prolyl oligopeptidase (POP) family, playing a critical role in the processes of degradation of proteins through both exo- and endopeptidase events. Endopeptidase activity has been associated with protein oxidation; however, the actual mechanisms have yet to be elucidated. We show that a synthetic fragment of GDF11 spanning the region 48–64 acquires sensitivity to the endopeptidase activity of APEH only when the methionines are transformed into the corresponding sulphoxide derivatives. The data suggest that the presence of sulphoxide-modified methionines is an important prerequisite for the substrates to be processed by APEH and that the residue is crucial for switching the enzyme activity from exo- to endoprotease. The cleavage occurs on residues placed on the C-terminal side of Met(O), with an efficiency depending on the methionine adjacent residues, which thereby may play a crucial role in driving and modulating APEH endoprotease activity.

Achieving Functionality Through Modular Build-up: Structure and Size Selection of Serine Oligopeptidases

Enzymes of the prolyl oligopeptidase family (S9 family) recognize their substrates not only by the specificity motif to be cleaved but also by size - they hydrolyze oligopeptides smaller than 30 amino acids. They belong to the serine-protease family, but differ from classical serine-proteases in size (80 kDa), structure (two domains) and regulation system (size selection of substrates). This group of enzymes is an important target for drug design as they are linked to amnesia, schizophrenia, type 2 diabetes, trypanosomiasis, periodontitis and cell growth. By comparing the structure of various members of the family we show that the most important features contributing to selectivity and efficiency are: (i) whether the interactions weaving the two domains together play a role in stabilizing the catalytic triad and thus their absence may provide for its deactivation: these oligopeptidases can screen their substrates by opening up, and (ii) whether the interaction-prone β-edge of the hydrolase domain is accessible and thus can guide a multimerization process that creates shielded entrance or intricate inner channels for the size-based selection of substrates. These cornerstones can be used to estimate the multimeric state and selection strategy of yet undetermined structures.

Acylpeptide hydrolase is a novel regulator of KRAS plasma membrane localization and function

The primary site for KRAS signaling is the inner leaflet of the plasma membrane (PM). We previously reported that oxanthroquinone G01 (G01) inhibited KRAS PM localization and blocked KRAS signaling. In this study, we identified acylpeptide hydrolase (APEH) as a molecular target of G01. APEH formed a stable complex with biotinylated G01, and the enzymatic activity of APEH was inhibited by G01. APEH knockdown caused profound mislocalization of KRAS and reduced clustering of KRAS that remained PM localized. APEH knockdown also disrupted the PM localization of phosphatidylserine (PtdSer), a lipid critical for KRAS PM binding and clustering. The mislocalization of KRAS was fully rescued by ectopic expression of APEH in knockdown cells. APEH knockdown disrupted the endocytic recycling of epidermal growth factor receptor and transferrin receptor, suggesting that abrogation of recycling endosome function was mechanistically linked to the loss of KRAS and PtdSer from the PM. APEH knockdown abrogated RAS-RAF-MAPK signaling in cells expressing the constitutively active (oncogenic) mutant of KRAS (KRASG12V), and selectively inhibited the proliferation of KRAS-transformed pancreatic cancer cells. Taken together, these results identify APEH as a novel drug target for a potential anti-KRAS therapeutic.

Catalytically distinct states captured in a crystal lattice: the substrate-bound and scavenger states of acylaminoacyl peptidase and their implications for functionality

Acylaminoacyl peptidase (AAP) is an oligopeptidase that only cleaves short peptides or protein segments. In the case of AAP from Aeropyrum pernix (ApAAP), previous studies have led to a model in which the clamshell-like opening and closing of the enzyme provides the means of substrate-size selection. The closed form of the enzyme is catalytically active, while opening deactivates the catalytic triad. The crystallographic results presented here show that the open form of ApAAP is indeed functionally disabled. The obtained crystal structures also reveal that the closed form is penetrable to small ligands: inhibitor added to the pre-formed crystal was able to reach the active site of the rigidified protein, which is only possible through the narrow channel of the propeller domain. Molecular-dynamics simulations investigating the structure of the complexes formed with longer peptide substrates showed that their binding within the large crevice of the closed form of ApAAP leaves the enzyme structure unperturbed; however, their accessing the binding site seems more probable when assisted by opening of the enzyme. Thus, the open form of ApAAP corresponds to a scavenger of possible substrates, the actual cleavage of which only takes place if the enzyme is able to re-close.

Screening of β-hairpin peptide-engrafted 1,2,3-triazoles to identify APEH enzyme inhibitors

Peptide-engrafted triazoles, obtained via click chemistry, drive the inhibition activity toward Acyl Peptide Hydrolase (APEH), a modulator of the proteasome activity.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of acylpeptide hydrolase from Deinococcus radiodurans

Acylpeptide hydrolase (APH; EC 3.4.19.1), which belongs to the S9 family of serine peptidases (MEROPS), catalyzes the removal of an N-acylated amino acid from a blocked peptide. The role of this enzyme in mammalian cells has been suggested to be in the clearance of oxidatively damaged proteins as well as in the degradation of the β-amyloid peptides implicated in Alzheimer's disease. Detailed structural information for the enzyme has been reported from two thermophilic archaea; both of the archaeal APHs share a similar monomeric structure. However, the mechanisms of substrate selectivity and active-site accessibility are totally different and are determined by inter-domain flexibility or the oligomeric structure. An APH homologue from a bacterium, Deinococcus radiodurans (APHdr), has been crystallized using microbatch-under-oil employing the random microseed matrix screening method. The protein crystallized in space group P21, with unit-cell parameters a = 77.6, b = 189.6, c = 120.4 Å, β = 108.4°. A Matthews coefficient of 2.89 Å(3) Da(-1) corresponds to four monomers, each with a molecular mass of ∼73 kDa, in the asymmetric unit. The APHdr structure will reveal the mechanisms of substrate selectivity and active-site accessibility in the bacterial enzyme. It will also be helpful in elucidating the functional role of this enzyme in D. radiodurans.

Cellular Trojan horse based polymer nanoreactors with light-sensitive activity

Stimulus-sensitive systems at the nanoscale represent ideal candidates for improving therapeutic and diagnostic approaches by producing rapid responses to the presence of specific molecules or conditions either by changing properties or by acting "on demand". Here we introduce an optimized light-sensitive nanoreactor based on encapsulation of a photosensitizer inside polymer vesicles to serve as an efficient source of reactive oxygen species (ROS) "on demand". Two types of amphiphilic block copolymers, poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyloxazoline), PMOXA-PDMS-PMOXA, and poly(N-vinylpyrrolidone)-block-poly(dimethylsiloxane)-block-poly(N-vinylpyrrolidone), PNVP-PDMS-PNVP, were used to encapsulate Rose Bengal-bovine serum albumin (RB-BSA) inside the cavity of vesicles. The difference of copolymers molecular properties (hydrophobic to hydrophilic ratio, different chemical nature of the hydrophilic block) influenced the encapsulation ability, and uptake by cells, allowing therefore a selection of the most efficient polymer system. Nanoreactors were optimized in terms of (i) size, (ii) stability, and (iii) encapsulation efficiency based on a combination of light scattering, TEM, and UV-vis spectroscopy. By illumination, encapsulated RB-BSA conjugates generated in situ ROS, which diffused through the polymer membrane to the environment of the vesicles, as proved by electron spin resonance spectroscopy (ESR). Optimum illumination conditions were obtained based on the effect of the illumination time on the amount of ROS produced in situ by the encapsulated RB-BSA conjugates. ROS diffusion monitored by ESR was dependent on the molecular weight of copolymer that influences the thickness of the polymer membrane. Upon uptake into HeLa cells our nontoxic nanoreactors acted as a Trojan horse: they produced illumination-controlled ROS in sufficient amounts to induce cell death under photodynamic therapy (PDT) conditions. Straightforward production, stability, and Trojan horse activity inside cells support our light-sensitive nanoreactors for medical applications which require ROS to be generated with precise time and space control.

Proteomic analysis of mesenchymal stem cells from normal and deep carious dental pulp

Dental pulp stem cells (DPSCs), precursor cells of odontoblasts, are ideal seed cells for tooth tissue engineering and regeneration. Our previous study has demonstrated that stem cells exist in dental pulp with deep caries and are called carious dental pulp stem cells (CDPSCs). The results indicated that CDPSCs had a higher proliferative and stronger osteogenic differentiation potential than DPSCs. However, the molecular mechanisms responsible for the biological differences between DPSCs and CDPSCs are poorly understood. The aim of this study was to define the molecular features of DPSCs and CDPSCs by comparing the proteomic profiles using two-dimensional fluorescence difference gel electrophoresis (2-D DIGE) in combination with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Our results revealed that there were 18 protein spots differentially expressed between DPSCs and CDPSCs in a narrow pH range of 4 to 7. These differently expressed proteins are mostly involved in the regulation of cell proliferation, differentiation, cell cytoskeleton and motility. In addition, our results suggested that CDPSCs had a higher expression of antioxidative proteins that might protect CDPSCs from oxidative stress. This study explores some potential proteins responsible for the biological differences between DPSCs and CDPSCs and expands our understanding on the molecular mechanisms of mineralization of DPSCs in the formation of the dentin-pulp complex.

RedOx status, proteasome and APEH: insights into anticancer mechanisms of t10,c12-conjugated linoleic acid isomer on A375 melanoma cells

This study describes the investigation of the efficiency of conjugated linoleic acid (CLA) isomers in reducing cancer cells viability exploring the role of the oxidative stress and acylpeptide hydrolase (APEH)/proteasome mediated pathways on pro-apoptotic activity of the isomer trans10,cis12 (t10,c12)-CLA. The basal activity/expression levels of APEH and proteasome (β-5 subunit) were preliminarily measured in eight cancer cell lines and the functional relationship between these enzymes was clearly demonstrated through their strong positive correlation. t10,c12-CLA efficiently inhibited the activity of APEH and proteasome isoforms in cell-free assays and the negative correlation between cell viability and caspase 3 activity confirmed the pro-apoptotic role of this isomer. Finally, modulatory effects of t10,c12-CLA on cellular redox status (intracellular glutathione, mRNA levels of antioxidant/detoxifying enzymes activated through NF-E2-related factor 2, Nrf2, pathway) and on APEH/β-5 activity/expression levels, were investigated in A375 melanoma cells. Dose- and time-dependent variations of the considered parameters were established and the resulting pro-apoptotic effects were shown to be associated with an alteration of the redox status and a down-regulation of APEH/proteasome pathway. Therefore, our results support the idea that these events are involved in ROS-dependent apoptosis of t10,c12-CLA-treated A375 cells. The combined inhibition, triggered by t10,c12-CLA, via the modulation of APEH/proteasome and Nrf2 pathway for treating melanoma, is suggested as a subject for further in vivo studies.

Direct oxidative modifications of signalling proteins in mammalian cells and their effects on apoptosis

The production of ROS is an inevitable consequence of metabolism. However, high levels of ROS within a cell can be lethal and so the cell has a number of defences against oxidative cell stress. Occasionally the cell's antioxidant mechanisms fail and oxidative stress occurs. High levels of ROS within a cell have a number of direct and indirect consequences on cell signalling pathways and may result in apoptosis or necrosis. Although some of the indirect effects of ROS are well known, limitations in technology mean that the direct effects of the cell's redox environment upon proteins are less understood. Recent work by a number of groups has demonstrated that ROS can directly modify signalling proteins through different modifications, for example by nitrosylation, carbonylation, di-sulphide bond formation and glutathionylation. These modifications modulate a protein's activity and several recent papers have demonstrated their importance in cell signalling events, especially those involved in cell death/survival. Redox modification of proteins allows for further regulation of cell signalling pathways in response to the cellular environment. Understanding them may be critical for us to modulate cell pathways for our own means, such as in cytotoxic drug treatments of cancer cells. Protein modifications mediated by oxidative stress can modulate apoptosis, either through specific protein modifications resulting in regulation of signalling pathways, or through a general increase in oxidised proteins resulting in reduced cellular function. This review discusses direct oxidative protein modifications and their effects on apoptosis.

Identification and characterisation of a novel acylpeptide hydrolase from Sulfolobus solfataricus: structural and functional insights

A novel acylpeptide hydrolase, named APEH-3_Ss, was isolated from the hypertermophilic archaeon Sulfolobus solfataricus. APEH is a member of the prolyl oligopeptidase family which catalyzes the removal of acetylated amino acid residues from the N terminus of oligopeptides. The purified enzyme shows a homotrimeric structure, unique among the associate partners of the APEH cluster and, in contrast to the archaeal APEHs which show both exo/endo peptidase activities, it appears to be a “true” aminopeptidase as exemplified by its mammalian counterparts, with which it shares a similar substrate specificity. Furthermore, a comparative study on the regulation of apeh gene expression, revealed a significant but divergent alteration in the expression pattern of apeh-3_Ss and apeh_Ss (the gene encoding the previously identified APEH_Ss from S. solfataricus), which is induced in response to various stressful growth conditions. Hence, both APEH enzymes can be defined as stress-regulated proteins which play a complementary role in enabling the survival of S. solfataricus cells under different conditions. These results provide new structural and functional insights into S. solfataricus APEH, offering a possible explanation for the multiplicity of this enzyme in Archaea.

Acylpeptide hydrolase inhibition as targeted strategy to induce proteasomal down-regulation

Acylpeptide hydrolase (APEH), one of the four members of the prolyl oligopeptidase class, catalyses the removal of N-acylated amino acids from acetylated peptides and it has been postulated to play a key role in protein degradation machinery. Disruption of protein turnover has been established as an effective strategy to down-regulate the ubiquitin-proteasome system (UPS) and as a promising approach in anticancer therapy.

Here, we illustrate a new pathway modulating UPS and proteasome activity through inhibition of APEH. To find novel molecules able to down-regulate APEH activity, we screened a set of synthetic peptides, reproducing the reactive-site loop of a known archaeal inhibitor of APEH (SsCEI), and the conjugated linoleic acid (CLA) isomers. A 12-mer SsCEI peptide and the trans10-cis12 isomer of CLA, were identified as specific APEH inhibitors and their effects on cell-based assays were paralleled by a dose-dependent reduction of proteasome activity and the activation of the pro-apoptotic caspase cascade. Moreover, cell treatment with the individual compounds increased the cytoplasm levels of several classic hallmarks of proteasome inhibition, such as NFkappaB, p21, and misfolded or polyubiquitinylated proteins, and additive effects were observed in cells exposed to a combination of both inhibitors without any cytotoxicity. Remarkably, transfection of human bronchial epithelial cells with APEH siRNA, promoted a marked accumulation of a mutant of the cystic fibrosis transmembrane conductance regulator (CFTR), herein used as a model of misfolded protein typically degraded by UPS. Finally, molecular modeling studies, to gain insights into the APEH inhibition by the trans10-cis12 CLA isomer, were performed.

Our study supports a previously unrecognized role of APEH as a negative effector of proteasome activity by an unknown mechanism and opens new perspectives for the development of strategies aimed at modulation of cancer progression.

Heterologous ferredoxin reductase and flavodoxin protect Cos-7 cells from oxidative stress

BACKGROUND

Ferredoxin-NADP(H) reductase (FNR) from Pisum sativum and Flavodoxin (Fld) from Anabaena PCC 7119 have been reported to protect a variety of cells and organisms from oxidative insults. In this work, these two proteins were expressed in mitochondria of Cos-7 cells and tested for their efficacy to protect these cells from oxidative stress in vitro.

PRINCIPAL FINDINGS

Cos-7/pFNR and Cos-7/pFld cell lines expressing FNR and Fld, respectively, showed a significantly higher resistance to 24 h exposure to 300-600 µM hydrogen peroxide measured by LDH retention, MTT reduction, malondialdehyde (MDA) levels and lipid peroxide (LPO; FOX assay) levels. However, FNR and Fld did not exhibit any protection at shorter incubation times (2 h and 4 h) to 4 mM hydrogen peroxide or to a 48 h exposure to 300 µM methyl viologen. We found enhanced methyl viologen damage exerted by FNR that may be due to depletion of NADPH pools through NADPH-MV diaphorase activity as previously observed for other overexpressed enzymes.

SIGNIFICANCE

The results presented are a first report of antioxidant function of these heterologous enzymes of vegetal and cyanobacterial origin in mammalian cells.

Acyl peptide hydrolase degrades monomeric and oligomeric amyloid-beta peptide

Background

The abnormal accumulation of amyloid-beta peptide is believed to cause malfunctioning of neurons in the Alzheimer's disease brain. Amyloid-beta exists in different assembly forms in the aging mammalian brain including monomers, oligomers, and aggregates, and in senile plaques, fibrils. Recent findings suggest that soluble amyloid-beta oligomers may represent the primary pathological species in Alzheimer's disease and the most toxic form that impairs synaptic and thus neuronal function. We previously reported the isolation of a novel amyloid-beta-degrading enzyme, acyl peptide hydrolase, a serine protease that degrades amyloid-beta, and is different in structure and activity from other amyloid-beta-degrading enzymes.

Results

Here we report the further characterization of acyl peptide hydrolase activity using mass spectrometry. Acyl peptide hydrolase cleaves the amyloid-beta peptide at amino acids 13, 14 and 19. In addition, by real-time PCR we found elevated acyl peptide hydrolase expression in brain areas rich in amyloid plaques suggesting that this enzyme's levels are responsive to increases in amyloid-beta levels. Lastly, tissue culture experiments using transfected CHO cells expressing APP751 bearing the V717F mutation indicate that acyl peptide hydrolase preferentially degrades dimeric and trimeric forms of amyloid-beta.

Conclusion

These data suggest that acyl peptide hydrolase is involved in the degradation of oligomeric amyloid-beta, an activity that, if induced, might present a new tool for therapy aimed at reducing neurodegeneration in the Alzheimer's brain.

Acyl peptide hydrolase, a serine proteinase isolated from conditioned medium of neuroblastoma cells, degrades the amyloid-? peptide

Considerable evidence indicates that the amyloid-beta (Abeta) peptide, a proteolytic fragment of the amyloid precursor protein, is the pathogenic agent in Alzheimer's disease (AD). A number of proteases have been reported as capable of degrading Abeta, among them: neprilysin, insulin-degrading enzyme, endothelin-converting enzyme-1 and -2, angiotensin-converting enzyme and plasmin. These proteases, originating from a variety of cell types, degrade Abeta of various conformational states and in different cellular locations. We report here the isolation of a serine protease from serum-free conditioned medium of human neuroblastoma cells. Tandem mass spectrometry (MS/MS)-based sequencing of the isolated protein identified acyl peptide hydrolase (APH; EC3.4.19.1) as the active peptidase. APH is one of four members of the prolyl oligopeptidase family of serine proteases expressed in a variety of cells and tissues, including erythrocytes, liver and brain, but its precise biological activity is unknown. Here, we describe the identification of APH as an Abeta-degrading enzyme, and we show that the degradation of Abeta by APH isolated from transfected cells is inhibited by APH-specific inhibitors, as well as by synthetic Abeta peptide. In addition, we cloned APH from human brain and from neuroblastoma cells. Most importantly, our results indicate that APH expression in AD brain is lower than in age-matched controls.

Coordination of oxidized protein hydrolase and the proteasome in the clearance of cytotoxic denatured proteins

Intracellular accumulation of denatured proteins impairs cellular function. The proteasome is recognized as an enzyme responsible for the effective clearance of those cytotoxic denatured proteins. As another enzyme that participates in the destruction of damaged proteins, we have identified oxidized protein hydrolase (OPH) and found that OPH confers cellular resistance to various kinds of oxidative stress. In this study, we demonstrate the roles of the proteasome and OPH in the clearance of denatured proteins. The inhibition of proteasome activity results in the elevation of protein carbonyls in cells under oxidative stress. On the other hand, cells overexpressing OPH retain higher resistance to oxidative stress, even though the proteasome activity is inhibited. Furthermore, upon inhibition of the proteasome activity, OPH is recruited to a novel organelle termed the aggresome where misfolded or denatured proteins are processed. Thus, OPH and the proteasome coordinately contribute to the clearance of cytotoxic denatured proteins.

Defense of Living Body against Oxidative Damage

Living bodies may experience oxidative stress induced by reactive oxygen species and heavy metal ions, which may damage components in the body and cause aging and disorders. In addition to the known defense systems against oxidative damage, the author describes new defense systems. Lipid peroxidation in living bodies, which has hitherto been thought to increase oxidative damage, was found to attenuate oxidative stress-induced DNA damage. Red blood cells become senescent due to oxidative stress during circulation, where membrane band 3 becomes aggregated to anti-band 3 IgG and macrophages attached through poly-N-acetyllactosaminyl sugar chains, and the sugar chain attachment to macrophages is stimulated by oxidative stress in macrophages. Oxidized protein hydrolase that preferentially hydrolyzes proteins damaged by oxidative stress was newly discovered, which may play an important role in saving cells from oxidative damage.