Quorum-Sensing Signaling Molecule 2-Aminoacetophenone Mediates the Persistence of Pseudomonas aeruginosa in Macrophages by Interference with Autophagy through Epigenetic Regulation of Lipid Biosynthesis

Macrophages are crucial components of the host's defense against pathogens. Recent studies indicate that macrophage functions are influenced by lipid metabolism. However, knowledge of how bacterial pathogens exploit macrophage lipid metabolism for their benefit remains rudimentary. We have shown that the Pseudomonas aeruginosa MvfR-regulated quorum-sensing (QS) signaling molecule 2-aminoacetophenone (2-AA) mediates epigenetic and metabolic changes associated with this pathogen's persistence in vivo. We provide evidence that 2-AA counteracts the ability of macrophages to clear the intracellular P. aeruginosa, leading to persistence. The intracellular action of 2-AA in macrophages is linked to reduced autophagic functions and the impaired expression of a central lipogenic gene, stearoyl-CoA desaturase 1 (Scd1), which catalyzes the biosynthesis of monounsaturated fatty acids. 2-AA also reduces the expression of the autophagic genes Unc-51-like autophagy activating kinase 1 (ULK1) and Beclin1 and the levels of the autophagosomal membrane protein microtubule-associated protein 1, light chain 3 isoform B (LC3B) and p62. Reduced autophagy is accompanied by the reduced expression of the lipogenic gene Scd1, preventing bacterial clearance. Adding the SCD1 substrates palmitoyl-CoA and stearoyl-CoA increases P. aeruginosa clearance by macrophages. The impact of 2-AA on lipogenic gene expression and autophagic machinery is histone deacetylase 1 (HDAC1) mediated, implicating the HDAC1 epigenetic marks at the promoter sites of Scd1 and Beclin1 genes. This work provides novel insights into the complex metabolic alterations and epigenetic regulation promoted by QS and uncovers additional 2-AA actions supporting P. aeruginosa sustainment in macrophages. These findings may aid in designing host-directed therapeutics and protective interventions against P. aeruginosa persistence. IMPORTANCE This work sheds new light on how P. aeruginosa limits bacterial clearance in macrophages through 2-aminoacetophenone (2-AA), a secreted signaling molecule by this pathogen that is regulated by the quorum-sensing transcription factor MvfR. The action of 2-AA on the lipid biosynthesis gene Scd1 and the autophagic genes ULK1 and Beclin1 appears to secure the reduced intracellular clearance of P. aeruginosa by macrophages. In support of the 2-AA effect on lipid biosynthesis, the ability of macrophages to reduce the intracellular P. aeruginosa burden is reinstated following the supplementation of palmitoyl-CoA and stearoyl-CoA. The 2-AA-mediated reduction of Scd1 and Beclin1 expression is linked to chromatin modifications, implicating the enzyme histone deacetylase 1 (HDAC1), thus opening new avenues for future strategies against this pathogen's persistence. Overall, the knowledge obtained from this work provides for developing new therapeutics against P. aeruginosa.

A review of AI and Data Science support for cancer management

INTRODUCTION

Thanks to improvement of care, cancer has become a chronic condition. But due to the toxicity of treatment, the importance of supporting the quality of life (QoL) of cancer patients increases. Monitoring and managing QoL relies on data collected by the patient in his/her home environment, its integration, and its analysis, which supports personalization of cancer management recommendations. We review the state-of-the-art of computerized systems that employ AI and Data Science methods to monitor the health status and provide support to cancer patients managed at home.

OBJECTIVE

Our main objective is to analyze the literature to identify open research challenges that a novel decision support system for cancer patients and clinicians will need to address, point to potential solutions, and provide a list of established best-practices to adopt.

METHODS

We designed a review study, in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, analyzing studies retrieved from PubMed related to monitoring cancer patients in their home environments via sensors and self-reporting: what data is collected, what are the techniques used to collect data, semantically integrate it, infer the patient's state from it and deliver coaching/behavior change interventions.

RESULTS

Starting from an initial corpus of 819 unique articles, a total of 180 papers were considered in the full-text analysis and 109 were finally included in the review. Our findings are organized and presented in four main sub-topics consisting of data collection, data integration, predictive modeling and patient coaching.

CONCLUSION

Development of modern decision support systems for cancer needs to utilize best practices like the use of validated electronic questionnaires for quality-of-life assessment, adoption of appropriate information modeling standards supplemented by terminologies/ontologies, adherence to FAIR data principles, external validation, stratification of patients in subgroups for better predictive modeling, and adoption of formal behavior change theories. Open research challenges include supporting emotional and social dimensions of well-being, including PROs in predictive modeling, and providing better customization of behavioral interventions for the specific population of cancer patients.

Design and Development of a Mobile System for Supporting Emergency Triage

Objectives: Our objective was to design and develop a mobile clinical decision support system for emergency triage of different acute pain presentations. The system should interact with existing hospital information systems, run on mobile computing devices (handheld computers) and be suitable for operation in weak-connectivity conditions (with unstable connections between mobile clients and a server).

Methods: The MET (Mobile Emergency Triage) system was designed following an extended client-server architecture. The client component, responsible for triage decision support, is built as a knowledge-based system, with domain ontology separated from generic problem solving methods and used for the automatic creation of a user interface.

Results: The MET system is well suited for operation in the Emergency Department of a hospital. The system’s external interactions are managed by the server, while the MET clients, running on handheld computers are used by clinicians for collecting clinical data and supporting triage at the bedside. The functionality of the MET client is distributed into specialized modules, responsible for triaging specific types of acute pain presentations. The modules are stored on the server, and on request they can be transferred and executed on the mobile clients. The modular design provides for easy extension of the system’s functionality. A clinical trial of the MET system validated the appropriateness of the system’s design, and proved the usefulness and acceptance of the system in clinical practice.

Conclusions: The MET system captures the necessary hospital data, allows for entry of patient information, and provides triage support. By operating on handheld computers, it fits into the regular emergency department workflow without introducing any hindrances or disruptions. It supports triage anytime and anywhere, directly at the point of care, and also can be used as an electronic patient chart, facilitating structured data collection.

[Miscommunication as a risk focus in patient safety : Work process analysis in prehospital emergency care]

BACKGROUND

In an analysis of a critical incident reporting system (CIRS) in out-of-hospital emergency medicine, it was demonstrated that in 30% of cases deficient communication led to a threat to patients; however, the analysis did not show what exactly the most dangerous work processes are. Current research shows the impact of poor communication on patient safety.

OBJECTIVES

An out-of-hospital workflow analysis collects data about key work processes and risk areas. The analysis points out confounding factors for a sufficient communication. Almost 70% of critical incidents are based on human factors. Factors, such as communication and teamwork have an impact but fatigue, noise levels and illness also have a major influence.

MATERIAL AND METHODS

(I) CIRS database analysis The workflow analysis was based on 247 CIRS cases. This was completed by participant observation and interviews with emergency doctors and paramedics. The 247 CIRS cases displayed 282 communication incidents, which are categorized into 6 subcategories of miscommunication. One CIRS case can be classified into different categories if more communication incidents were validated by the reviewers and four experienced emergency physicians sorted these cases into six subcategories. (II) Workflow analysis The workflow analysis was carried out between 2015 and 2016 in Jena and Berlin, Germany. The focal point of research was to find accumulation of communication risks in different parts of prehospital patient care. During 30 h driving with emergency ambulances, the author interviewed 12 members of the emergency medical service of which 5 were emergency physicians and 7 paramedics. A total of 11 internal medicine cases and one automobile accident were monitored. After patient care the author asked in a 15-min interview if miscommunication or communication incidents occurred.

RESULTS

(I) CIRS analysis Between 2005 and 2015, 845 reports were reported to the database. The experts identified 247 incident reports with communication failure. All communication aspects were analyzed and classified. We identified 282 communication incidents. (II) Workflow analysis The analysis showed three phases of prehospital patient care: 1. incoming emergency call and dispatch of ambulance service, 2. prehospital treatment, 3. transportation to a hospital. Overall, the number of incidences is increasing as a consequence of parallel workflows. Category 1 was particularly significant and predominantly, paramedics criticized that emergency physicians did not acknowledge their advice (n = 73 vs. n = 9). Category 3 with n = 63, category 4 with n = 20 and category 2 with n = 13 were the major reasons for incidents.

CONCLUSION

A better interface communication helps to coordinate patient transfer and is an option for optimizing resources. Frequent training in communication is an option to avoid incidents.

Learning the Preferences of Physicians for the Organization of Result Lists of Medical Evidence Articles

Background: Online medical knowledge repositories such as MEDLINE and The Cochrane Library are increasingly used by physicians to retrieve articles to aid with clinical decision making. The prevailing approach for organizing retrieved articles is in the form of a rank-ordered list, with the assumption that the higher an article is presented on a list, the more relevant it is.

Objectives: Despite this common list-based organization, it is seldom studied how physicians perceive the association between the relevance of articles and the order in which articles are presented. In this paper we describe a case study that captured physician preferences for 3-element lists of medical articles in order to learn how to organize medical knowledge for decision-making.

Methods: Comprehensive relevance evaluations were developed to represent 3-element lists of hypothetical articles that may be retrieved from an online medical knowledge source such as MEDLINE or The Cochrane Library. Comprehensive relevance evalua tions asses not only an article’s relevance for a query, but also whether it has been placed on the correct list position. In other words an article may be relevant and correctly placed on a result list (e.g. the most relevant article appears first in the result list), an article may be relevant for a query but placed on an incorrect list position (e.g. the most relevant article appears second in a result list), or an article may be irrelevant for a query yet still appear in the result list. The relevance evaluations were presented to six senior physi cians who were asked to express their preferences for an article’s relevance and its position on a list by pairwise comparisons representing different combinations of 3-element lists. The elicited preferences were assessed using a novel GRIP (Generalized Regression with Intensities of Preference) method and represented as an additive value function. Value functions were derived for individual physicians as well as the group of physicians.

Results: The results show that physicians assign significant value to the 1st position on a list and they expect that the most relevant article is presented first. Whilst physicians still prefer obtaining a correctly placed article on position 2, they are also quite satisfied with misplaced relevant article. Low consideration of the 3rd position was uniformly confirmed.

Conclusions: Our findings confirm the importance of placing the most relevant article on the 1st position on a list and the importance paid to position on a list significantly diminishes after the 2nd position. The derived value functions may be used by developers of clinical decision support applications to decide how best to organize medical knowledge for decision making and to create personalized evaluation measures that can augment typical measures used to evaluate information retrieval systems.

Clinical Decision Support System for Point of Care Use

Objectives: The objective of this research was to design a clinical decision support system (CDSS) that supports heterogeneous clinical decision problems and runs on multiple computing platforms. Meeting this objective required a novel design to create an extendable and easy to maintain clinical CDSS for point of care support. The proposed solution was evaluated in a proof of concept implementation.

Methods: Based on our earlier research with the design of a mobile CDSS for emergency triage we used ontology-driven design to represent essential components of a CDSS. Models of clinical decision problems were derived from the ontology and they were processed into executable applications during runtime. This allowed scaling applications’ functionality to the capabilities of computing platforms. A prototype of the system was implemented using the extended client-server architecture and Web services to distribute the functions of the system and to make it operational in limited connectivity conditions.

Results: The proposed design provided a common framework that facilitated development of diversified clinical applications running seamlessly on a variety of computing platforms. It was prototyped for two clinical decision problems and settings (triage of acute pain in the emergency department and postoperative management of radical pros-tatectomy on the hospital ward) and implemented on two computing platforms – desktop and handheld computers.

Conclusions: The requirement of the CDSS heterogeneity was satisfied with ontology-driven design. Processing of application models described with the help of ontological models allowed having a complex system running on multiple computing platforms with different capabilities. Finally, separation of models and runtime components contributed to improved extensibility and maintainability of the system.

BK Polyomavirus-Specific 9mer CD8 T Cell Responses Correlate With Clearance of BK Viremia in Kidney Transplant Recipients: First Report From the Swiss Transplant Cohort Study

BK polyomavirus (BKPyV) causes premature kidney transplant (KT) failure in 1-15% of patients. Because antivirals are lacking, most programs screen for BKPyV-viremia and, if positive, reduce immunosuppression. To evaluate the relationship of viremia and BKPyV-specific immunity, we examined prospectively cryopreserved plasma and peripheral blood mononuclear cells at the time of transplantation (T0) and at 6 mo (T6) and 12 mo (T12) after transplant from 28 viremic KT patients and 68 nonviremic controls matched for the transplantation period. BKPyV IgG seroprevalence was comparable between cases (89.3%) and controls (91.2%; p = 0.8635), but cases had lower antibody levels (p = 0.022) at T0. Antibody levels increased at T6 and T12 but were not correlated with viremia clearance. BKPyV-specific T cell responses to pools of overlapping 15mers (15mer peptide pool [15mP]) or immunodominant CD8 9mers (9mer peptide pool [9mP]) from the early viral gene region were not different between cases and controls at T0; however, clearance of viremia was associated with stronger 9mP responses at T6 (p = 0.042) and T12 (p = 0.048), whereas 15mP responses were not informative (T6 p = 0.359; T12 p = 0.856). BKPyV-specific T cells could be expanded in vitro from all patients after transplant, permitting identification of 78 immunodominant 9mer epitopes including 50 new ones across different HLA class I. Thus, 9mP-responses may be a novel marker of reconstituting CD8 T cell function that warrants further study as a complement of plasma BKPyV loads for guiding immunosuppression reduction.

Comparing predictions made by a prediction model, clinical score, and physicians: pediatric asthma exacerbations in the emergency department

BACKGROUND

Asthma exacerbations are one of the most common medical reasons for children to be brought to the hospital emergency department (ED). Various prediction models have been proposed to support diagnosis of exacerbations and evaluation of their severity.

OBJECTIVES

First, to evaluate prediction models constructed from data using machine learning techniques and to select the best performing model. Second, to compare predictions from the selected model with predictions from the Pediatric Respiratory Assessment Measure (PRAM) score, and predictions made by ED physicians.

DESIGN

A two-phase study conducted in the ED of an academic pediatric hospital. In phase 1 data collected prospectively using paper forms was used to construct and evaluate five prediction models, and the best performing model was selected. In phase 2 data collected prospectively using a mobile system was used to compare the predictions of the selected prediction model with those from PRAM and ED physicians.

MEASUREMENTS

Area under the receiver operating characteristic curve and accuracy in phase 1; accuracy, sensitivity, specificity, positive and negative predictive values in phase 2.

RESULTS

In phase 1 prediction models were derived from a data set of 240 patients and evaluated using 10-fold cross validation. A naive Bayes (NB) model demonstrated the best performance and it was selected for phase 2. Evaluation in phase 2 was conducted on data from 82 patients. Predictions made by the NB model were less accurate than the PRAM score and physicians (accuracy of 70.7%, 73.2% and 78.0% respectively), however, according to McNemar's test it is not possible to conclude that the differences between predictions are statistically significant.

CONCLUSION

Both the PRAM score and the NB model were less accurate than physicians. The NB model can handle incomplete patient data and as such may complement the PRAM score. However, it requires further research to improve its accuracy.

A task-based support architecture for developing point-of-care clinical decision support systems for the emergency department

OBJECTIVES

The purpose of this study was to create a task-based support architecture for developing clinical decision support systems (CDSSs) that assist physicians in making decisions at the point-of-care in the emergency department (ED). The backbone of the proposed architecture was established by a task-based emergency workflow model for a patient-physician encounter.

METHODS

The architecture was designed according to an agent-oriented paradigm. Specifically, we used the O-MaSE (Organization-based Multi-agent System Engineering) method that allows for iterative translation of functional requirements into architectural components (e.g., agents). The agent-oriented paradigm was extended with ontology-driven design to implement ontological models representing knowledge required by specific agents to operate.

RESULTS

The task-based architecture allows for the creation of a CDSS that is aligned with the task-based emergency workflow model. It facilitates decoupling of executable components (agents) from embedded domain knowledge (ontological models), thus supporting their interoperability, sharing, and reuse. The generic architecture was implemented as a pilot system, MET3-AE--a CDSS to help with the management of pediatric asthma exacerbation in the ED. The system was evaluated in a hospital ED.

CONCLUSIONS

The architecture allows for the creation of a CDSS that integrates support for all tasks from the task-based emergency workflow model, and interacts with hospital information systems. Proposed architecture also allows for reusing and sharing system components and knowledge across disease-specific CDSSs.

Triage of the child with abdominal pain: A clinical algorithm for emergency patient management

OBJECTIVE

To create a simplified clinical algorithm for the triage of children with abdominal pain.

DESIGN

Retrospective analysis.

SETTING

Emergency room at the Children's Hospital of Eastern Ontario, Ottawa, Ontario.

METHODS

A data mining methodology (rough sets analysis) was applied to a randomized data set obtained from 175 emergency room admission charts of patients. Patients were placed into two diagnostic decision classes: appendicitis confirmed by a pathological report, and resolution (this classification implied the resolution of all clinical complaints and physical findings, with no pathological diagnosis and no operative procedure).

RESULTS

Nine clinical symptoms and signs were identified as being important in the management of children with abdominal pain. A clinically based algorithm for the triage of such children was developed.

CONCLUSIONS

It is possible to develop a clinical algorithm for the triage of children with abdominal pain that can also be used by nonmedical professionals. A template for such an algorithm can be used as the basis for diagnosing other paediatric emergencies, such as chest pain, headaches and joint pain.

Purification of the eukaryotic 20S proteasome

The 20S proteasome is the catalytic core of the major extralysosomal proteolytic system of the cell. Combination of the 20S proteasome with a complex of regulatory proteins forms the 26S proteasome, which in turn is responsible for the recognition and degradation of ubiquitin-protein conjugates. As described in this unit, the constitutive form of the 20S proteasome can be conveniently purified as a stable and homogeneous preparation from bovine pituitaries. A support protocol details an enzyme assay used in evaluating proteasomal activity. The 20S proteasome is the catalytic core of the major extralysosomal proteolytic system of the cell.

Design and development of a mobile system for supporting emergency triage

OBJECTIVES

Our objective was to design and develop a mobile clinical decision support system for emergency triage of different acute pain presentations. The system should interact with existing hospital information systems, run on mobile computing devices (handheld computers) and be suitable for operation in weak-connectivity conditions (with unstable connections between mobile clients and a server).

METHODS

The MET (Mobile Emergency Triage) system was designed following an extended client-server architecture. The client component, responsible for triage decision support, is built as a knowledge-based system, with domain ontology separated from generic problem solving methods and used for the automatic creation of a user interface.

RESULTS

The MET system is well suited for operation in the Emergency Department of a hospital. The system's external interactions are managed by the server, while the MET clients, running on handheld computers are used by clinicians for collecting clinical data and supporting triage at the bedside. The functionality of the MET client is distributed into specialized modules, responsible for triaging specific types of acute pain presentations. The modules are stored on the server, and on request they can be transferred and executed on the mobile clients. The modular design provides for easy extension of the system's functionality. A clinical trial of the MET system validated the appropriateness of the system's design, and proved the usefulness and acceptance of the system in clinical practice.

CONCLUSIONS

The MET system captures the necessary hospital data, allows for entry of patient information, and provides triage support. By operating on handheld computers, it fits into the regular emergency department workflow without introducing any hindrances or disruptions. It supports triage anytime and anywhere, directly at the point of care, and also can be used as an electronic patient chart, facilitating structured data collection.

Increased local vascular endothelial growth factor expression associated with antitumor activity of proteasome inhibitor

Inhibition of the proteasome, a multicatalytic proteinase complex, is an attractive approach to cancer therapy. Here we report that a selective inhibitor of the chymotrypsin-like activity of the proteasome, PSI (N-benzyloxycarbonyl-Ile-Glu(O-t-butyl)-Ala-leucinal) may inhibit growth of solid tumors not only through apoptosis induction, but also indirectly--through inhibition of angiogenesis. Two murine tumors: colon adenocarcinoma (C-26) and Lewis lung carcinoma (3LL) were chosen to study the antitumor effect of PSI. In an in vivo model of local tumor growth, PSI exerted significant antitumor effects against C-26 colon carcinoma, but not against 3LL lung carcinoma. Retardation of tumor growth was observed in mice treated with both 10 nmoles and 100 nmoles doses of PSI and in the latter group prolongation of the survival time of tumor-bearing mice was observed. PSI inhibited angiogenesis in the C-26 growing tumors with no such effect in 3LL tumors. Unexpectedly, that activity was associated with upregulation of vascular endothelial growth factor (VEGF) at the level of mRNA expression and protein production in C-26 tumors treated with PSI. C-26 cells treated with PSI produced increased amounts of VEGF in vitro in a dose- and time-dependent manner. We demonstrated that in C-26 colon adenocarcionoma higher VEGF production may render endothelial cells susceptible to the proapoptotic activity of PSI and is associated with inhibition of tumor growth.

JLK isocoumarin inhibitors: Selective ?-secretase inhibitors that do not interfere with notch pathway in vitro or in vivo

gamma-Secretase activity is involved in the generation of Abeta and therefore likely contributes to the pathology of Alzheimer's disease. Blocking this activity was seen as a major therapeutic target to slow down or arrest Abeta-related AD progression. This strategy seemed more doubtful when it was established that gamma-secretase also targets other substrates including Notch, a particularly important transmembrane protein involved in vital functions, at both embryonic and adulthood stages. We have described previously new non-peptidic inhibitors able to selectively inhibit Abeta cellular production in vitro without altering Notch pathway. We show here that in vivo, these inhibitors do not alter the Notch pathway responsible for somitogenesis in the zebrafish embryo. In addition, we document further the selectivity of JLK inhibitors by showing that, unlike other described gamma-secretase inhibitors, these agents do not affect E-cadherin processing. Finally, we establish that JLKs do not inhibit beta-site APP cleaving enzymes (BACE) 1 and BACE2, alpha-secretase, the proteasome, and GSK3beta kinase. Altogether, JLK inhibitors are the sole agents to date that are able to prevent Abeta production without triggering unwanted cleavages of other proteins.

Dentate granule neuron apoptosis and glia activation in murine hippocampus induced by trimethyltin exposure

We investigated the effect of trimethyltin (TMT), a well-known neurotoxicant, on murine hippocampal neurons and glial cells. Three days following intraperitoneal (i.p.) injection of TMT into 1-month-old Balb/c mice at a dose of 2.5 mg/kg body weight we detected damage of the dentate gyrus granular neurons. The dying cells displayed chromatin condensation and internucleosomal DNA fragmentation, which are the most characteristic features of apoptosis. To study, if prolyl oligopeptidase is engaged in neuronal apoptosis following TMT administration, we pretreated mice with the specific inhibitor--Fmoc-Pro-ProCN in doses of 5 and 10 mg/kg body weight (i.p. injection). Three days following injection we did not observe any attenuation of neurotoxic damage, regardless of inhibitor dose, indicating the lack of prolyl oligopeptidase contribution to neuronal injury caused by TMT. The neurodegeneration was associated with reactive astrogliosis in whole hippocampus, but particularly in injured dentate gyrus. The reactive astrocytes showed an increased nerve growth factor (NGF) expression in ventral as well as dorsal hippocampal parts. NGF immunoreactivity was also augmented in neurons of CA3/CA4 areas, which were almost totally spared after TMT intoxication. It suggested a role for this neurotrophin in protection of pyramidal cells from loss of connection between CA3/CA4 and dentate gyrus fields. The granule neurons' death was accompanied by increased histochemical staining with isolectin B4, a marker of microglia, in the region of neurodegeneration. The microglial cells displayed ramified and ameboid morphology, characteristic of their reactive forms. Activated microglia were the main source of interleukin 1beta (IL-1beta). It is possible that this cytokine may participate in neurodegeneration of granule cells. Alternatively, IL-1beta elaborated by microglia could play a role in increasing NGF expression, both in astroglia and in CA3/CA4 neurons.

Properties of the beta subunit of the proteasome activator PA28 (11S REG)

The proteasome activator PA28 (11S REG) is composed of two homologous subunits termed alpha and beta. The properties of the recombinant beta-subunit were explored and compared to the properties of the recombinant alpha-subunit. PA28beta produced in an Escherichia coli expression system migrates on a calibrated gel filtration column as an apparent heptamer (Mr = 250,000). Low concentrations of SDS (0.005%), dissociate the protein to a monomer (Mr = 33,000). PA28beta, has a complex effect on proteasome activity. At concentrations which favor oligomerization (> 2 microM), PA28beta is a strong proteasome activator although its affinity for the proteasome is about 10-fold less than recombinant PA28alpha. The catalytic properties of the PA28alpha and PA28beta-activated proteasome are similar. At low concentrations, PA28beta is a monomer and a potent allosteric proteasome inhibitor. These studies show that oligomerization of PA28beta is required for proteasome activation and that PA28beta monomers are potent proteasome inhibitors.

Properties of the nuclear proteasome activator PA28gamma (REGgamma)

PA28 or 11S REG is a proteasome activator composed of homologous alpha- and beta-subunits and predominantly found in the cytosol. A homologous protein originally known as the Ki antigen but now called PA28gamma or REGgamma is predominantly localized in the nucleus. To further characterize the biochemical properties of PA28gamma, we expressed and purified homogenous recombinant human protein with and without an N-terminal 6-His extension. PA28gamma is a heptamer based on the molecular masses of the native and monomeric proteins. The heptameric 6-His fusion protein can dimerize. Recombinant PA28y stimulates the proteasome-mediated hydrolysis of synthetic substrates containing hydrophobic, basic, and acidic amino acids in the P1 position. Stimulation is dependent on substrate size. PA28y only minimally stimulates degradation of the oxidized B chain of insulin. PA28gamma may facilitate the later stages of protein metabolism in the nucleus and/or have a more specialized role in controlling the levels of biologically active peptides in the nucleus.

Catalytic activities of the 20 S proteasome, a multicatalytic proteinase complex

The proteasome, a multisubunit, multicatalytic proteinase complex, is attracting growing attention as the main intracellular, extralysosomal, proteolytic system involved in ubiquitin-(Ub) dependent and Ub-independent intracellular proteolysis. Its involvement in the mitotic cycle, and control of the half-life of most cellular proteins, functions absolutely necessary for cell growth and viability, make it an attractive target for researchers of intracellular metabolism and an important target for pharmacological intervention. The proteasome belongs to a new mechanistic class of proteases, the N-terminal nucleophile hydrolases, where the N-terminal threonine residue functions as the nucleophile. This minireview focuses on the three classical catalytic activities of the proteasome, designated chymotrypsin-like, trypsin-like, and peptidyl-glutamyl-peptide hydrolyzing in eukaryotes and also the activities of the more simple Archaebacteria and Eubacteria proteasomes. Other catalytic activities of the proteasome and their possible origin are also examined. The specificity of the catalytic components toward synthetic substrates, natural peptides, and proteins and their relationship to the catalytic centers are reviewed. Some unanswered questions and future research directions are suggested.

Separation of cathepsin A-like enzyme and the proteasome: evidence that lactacystin/beta-lactone is not a specific inhibitor of the proteasome

Previous studies have described a human platelet cathepsin A-like enzyme with a number of similarities to the "acidic" and "neutral" chymotrypsin-like activities of the proteasome. This includes its strong inhibition by the highly specific proteasome inhibitor Lactacystin/beta-lactone, suggesting that either the Cbz-Phe-Ala-hydrolyzing activity attributed to cathepsin A was due to the chymotrypsin-like activity of the proteasome or that lactacystin was not a specific inhibitor of the proteasome. In the present study we discard the first possibility on the basis of the following findings: (a) human platelet cathepsin A, unlike proteasome, binds to concanavalin A, and does not bind to Heparin-Sepharose at pH 7.4; (b) neither the chymotrypsin-like activity of the proteasome, nor proteasome antigens are detected in the cathepsin A preparation; (c) purified proteasome does not exhibit Cbz-Phe-Ala-hydrolyzing activity; (d) Z-lle-Glu-(Ot-Bu)Ala-leucinal (PSI), a compound that selectively inhibits the chymotrypsin-like activity of the proteasome at a concentration of 10 microM has no inhibitory effect on the carboxypeptidase activity of cathepsin A; (e) cathepsin A, free of the proteasome, is completely inhibited by micromolar concentrations of lactacystin/beta-lactone. It is therefore concluded that lactacystin/beta-lactone is not a specific inhibitor of the proteasome.

Synergistic antitumor effects of a selective proteasome inhibitor and TNF in mice

The ubiquitin-proteasome pathway is becoming an attractive target in cancer therapy. The inhibitors of proteasomes have recently been shown to induce apoptosis of tumor cells in vitro and to exert significant antitumor effects in murine tumor models in vivo. Proteasome inhibitors, also prevent NF-kappa B activation. Since this transcription factor is responsible for counteracting apoptosis induced by numerous agents, and proteasome inhibitors have already proved efficacious in increasing the proapoptotic activity of TNF in vitro, we decided to evaluate the antitumor effects of the combined PSI and TNF treatment against a murine C-26 carcinoma. Both agents separately exerted moderate antitumor efficacy. However, their combination proved to exert dramatic antitumor activity with retardation of tumor growth and prolongation of mice survival time. Moreover, 50% of the mice were completely cured by this drug combination. Unexpectedly, there was no potentiation of the cytostatic/cytotoxic effects of these drugs in in vitro assays which argues against the direct influence on C-26 cells. Similarly, the influence of these drugs on tumor induced angiogenesis does not seem to explain the observed antitumor effects. Further studies are necessary to explain the striking antitumor effects of the PSI and TNF combination.

Antinociceptive and behavioral activation responses elicited by d-Pro(2)-endomorphin-2 in the ventrolateral periaqueductal gray are sensitive to sex and gonadectomy differences in rats

Sex differences have been observed in antinociception after morphine administered into either the lateral ventricles, rostral ventromedial medulla, or ventrolateral periaqueductal gray such that male rats exhibit significantly greater antinociception than female rats. Adult gonadectomy produced small, but significant changes in morphine antinociception relative to same-sex sham-operated controls. The present study examined whether sex and adult gonadectomy differences were observed in antinociceptive responses after D-Pro(2)-Endomorphin-2 (1-50 microg) elicited from the ventrolateral periaqueductal gray (vlPAG) on the tail-flick and jump tests in rats, and compared these effects with morphine antinociception. D-Pro(2)-Endomorphin-2 antinociception in the vlPAG was significantly greater in estrous-phase, sham-operated and ovariectomized female rats relative to sham-operated and castrated male rats on the tail-flick, but not jump test that differed markedly from the greater magnitude of morphine antinociception noted for male rats on both tests. In testing whether D-Pro(2)-Endomorphin-2's antinociceptive sex differences were secondary to alterations in activity, similar decreases in the pattern of total activity were observed after D-Pro(2)-Endomorphin-2 in the vlPAG in male and female rats. In evaluating whether male and female rats differed in their behavioral activation responses after D-Pro(2)-Endomorphin-2 in the vlPAG, significantly more excessive grooming, seizures, barrel rolls and explosive running behaviors were observed after D-Pro(2)-Endomorphin-2 in male, but not female rats during the precise periods of time when they were failing to display robust antinociceptive responses on the tail-flick test. Thus, the different patterns of sex differences after D-Pro(2)-Endomorphin-2 in the vlPAG appear to be attributable to sex-dependent alterations in behavioral activation rather than nociceptive processing per se.

Early prepubertal ontogeny of pulsatile gonadotropin-releasing hormone (GnRH) secretion: I. Inhibitory autofeedback control through prolyl endopeptidase degradation of GnRH

GnRH[1-5], a subproduct resulting from degradation of GnRH by prolyl endopeptidase (PEP) and endopeptidase 24.15 (EP24.15) was known to account for an inhibitory autofeedback of GnRH secretion through an effect at the N-methyl-D-aspartate (NMDA) receptors. This study aimed at determining the possible role of such a mechanism in the early developmental changes in frequency of pulsatile GnRH secretion. Using retrochiasmatic explants from fetal male rats (day 20-21 of gestation), no GnRH pulses could be observed in vitro, whereas pulses occurred at a mean interval of 86 min from the day of birth onwards. This interval decreased steadily until day 25 (39 min), during the period preceding the onset of puberty. Based on GnRH[1-10] or GnRH[1-9] degradation and GnRH[1-5] generation after incubation with hypothalamic extracts, EP24.15 activity did not change with age, whereas PEP activity was maximal at days 5-10 and decreased subsequently until day 50. These changes were consistent with the ontogenetic variations in PEP messenger RNAs (mRNAs) quantitated using RT-PCR. Using fetal explants, the NMDA-evoked release of GnRH was potentiated in a dose-dependent manner by bacitracin, a competitive PEP inhibitor and the desensitization to the NMDA effect was prevented using 2 mM of bacitracin. At day 5, a higher bacitracin concentration of 20 mM was required for a similar effect. Pulsatile GnRH secretion from fetal explants was not caused to occur using bacitracin or Fmoc-Prolyl-Pyrrolidine-2-nitrile (Fmoc-Pro-PyrrCN), a noncompetitive PEP inhibitor. At postnatal days 5 and 15, a significant acceleration of pulsatility was obtained using 1 microM of Fmoc-Pro-PyrrCN or 2 mM of bacitracin. At 25 and 50 days, a lower bacitracin concentration of 20 microM was effective as well in increasing the frequency of GnRH pulsatility. We conclude that the GnRH inhibitory autofeedback resulting from degradation of the peptide is operational in the fetal hypothalamus but does not explain the absence of pulsatile GnRH secretion at that early age. After birth, PEP activity is high and may account for the low frequency of pulsatility. The potency of that effect decreases before the onset of puberty and may contribute to the acceleration of GnRH pulsatility.

S 17092-1, a highly potent, specific and cell permeant inhibitor of human proline endopeptidase

Several lines of evidence indicate that proline endopeptidase (PE) could participate to the symptomatology and/or etiology of Alzheimer's disease. Thus, proline endopeptidase appears to contribute to the degradation of neuropeptides involved in learning and memory and could also control the production of the amyloidogenic peptide Abeta. Therefore the design of potent, selective and permeant inhibitors of human PE should lead to potential probes to assess the genuine contribution of this enzyme in Alzheimer's pathology. A novel perhydroindol carboxylic derivative, S17092-1 inhibits the hydrolysis of Z-Gly-Pro-7AMC-hydrolysing activity present in human brain nuclei with a high affinity (Ki = 1 nM) and behaves as a highly potent (Ki = 1.5 nM) inhibitor of partially purified human PE. By contrast, S17092-1 is unable to affect a series of other peptidases including aminopeptidases B and M, dipeptidylaminopeptidase IV, endopeptidases 3.4.24.11, 3.4.24.15, 3.4.24.16, calpains and angiotensin-converting enzyme. Furthermore, we show that the embryonic human kidney 293 cell line displays an intracellular PE-like activity that is blocked after preincubating cells with S17092-1, indicating that this inhibitor penetrates in HEK293 cells and could affect intracellular human PE. Altogether, we establish that S17092-1 behaves as a highly potent, specific and cell permeant inhibitor of human proline endopeptidase and can be seen as a probe to examine PE contribution in Alzheimer's disease.

Modulators of the activation of the proteasome by PA28 (11S reg)

The degradation of chromogenic substrates and oligopeptides by the 20S proteasome is markedly enhanced and the generation of antigens for presentation by the MHC class-I system is facilitated by combination with an activator protein known as PA28 or 11S reg. We have described the properties of a PA28-proteasome modulator, N-benzyloxycarbonyl-Ile-Glu(O-t-Bu)-Ala-leucinol which shifts the pathway of peptide hydrolysis by the activated proteasome to products terminating in an acidic amino acid at the expense of products terminating in a hydrophobic amino acid. We now report that piperazinyl phenothiazines and several other antipsychotic drugs modulate the PA28-20S activated proteasome in an opposite manner. Fluphenazine, trifluoperazine and prochlorperazine antagonize the peptidylglutamyl peptide bond hydrolyzing activity of the activated proteasome much more strongly than the chymotrypsinlike activity. The chicken ovalbumin immunodominant epitope SIINFEKL is degraded by the activated proteasome to SIINFE and SIINF in approximately equimolar amounts. Piperazinyl phenothiazines promote formation of SIINF whereas Psi-ol promotes formation of SIINFE. PA28- proteasome modulators by modifying the profile of peptides produced by the activated proteasome, may either enhance or suppress the immune response.

Modulation of the PA28alpha-20S proteasome interaction by a peptidyl alcohol

The peptidyl alcohol N-benzyloxycarbonyl-Ile-Glu(O-t-Bu)-Ala-leucinol is a mild activator of the chymotrypsin-like activity of the proteasome. When added to an incubation mixture of recombinant PA28alpha plus 20S proteasome the peptidyl alcohol antagonizes the stimulation of the chymotrypsin-like activity by PA28alpha in a dose-dependent manner (IC50 = 30 microM). This effect is selective for the chymotrypsin-like activity. Stimulation of the peptidyl-glutamyl peptide bond hydrolyzing activity of the proteasome by PA28alpha is not affected by the peptidyl alcohol. The ovalbumin immunodominant epitope SIINFEKL is hydrolyzed by the PA28alpha-activated 20S proteasome to SIINF and SIINFE in approximately equimolar amounts. Addition of the peptidyl alcohol to an incubation mixture of PA28alpha, 20S proteasome and SIINFEKL shifts the ratio of products in favor of SIINFE. A similar shift in favor of postglutamyl cleavages occurs with the extended peptide LEQLESIINFEKLTE. By altering the ratio of products produced by the PA28alpha-activated proteasome, the peptidyl alcohol acts as a proteasome modulator. Proteasome modulators represent a novel class of molecules with a potential for altering the processing of antigens by the PA28-proteasome complex for presentation by the MHC class I system.

Changes in proteasome expression and activity during differentiation of neuronal precursor NTera 2 clone D1 cells

The effect of differentiation of the human neuronal progenitor cell line NTera 2 clone D1 (NT2/D1) by retinoic acid on components of the proteasome system was studied. The chymotrypsin-like and peptidylglutamyl peptide bond hydrolyzing activities of the proteasome increased five weeks after retinoic acid, and following treatment with mitotic inhibitors returned to levels detected in non-differentiated cells. A selective induction of the MHC class II region encoded LMP7 and LMP2 proteasome subunits occurred during differentiation, whereas there were no changes in the expression of the constitutive LMP2 counterpart (delta-subunit) or the constitutive C2 subunit. Immunofluorescence revealed marked LMP7 accumulation in fully differentiated cells, with no changes in the labeling pattern of the constitutive proteasome antigens. The expression of the alpha-subunit of the PA28 proteasome activator was down-regulated in fully differentiated neurons, but was not correlated with changes in enzymatic activity. Changes in proteasome activity and composition may contribute to the processes leading to differentiation of human neurons in vitro and to the properties of fully differentiated neurons.

Modulation of endomorphin-2-induced analgesia by dipeptidyl peptidase IV

The tetrapeptide, endomorphin-2 (Tyr-Pro-Phe-PheNH2) possesses high affinity for mu opioid receptors, and produces potent analgesia in mice. Its structure appears to satisfy the substrate requirements of the proteinase, dipeptidyl peptidase IV which removes dipeptides from the amino terminus of peptides containing proline as the penultimate amino acid. A potent, stable and specific inhibitor of this enzyme, Ala-Pyrrolidonyl-2-nitrile, has been described which should potentiate endomorphin-2-induced analgesia. Further, since dipeptidyl peptidase IV has an absolute requirement for l-Pro, a more metabolically-stable d-Pro2-endomorphin-2 analog should produce longer analgesic actions at lower doses. The present study found that endomorphin-2 was degraded approximately twice as fast than the chromogenic substrate, Ala-Pro-2naphthylamide, by dipeptidyl peptidase IV, whereas d-Pro2-endomorphin-2 was totally resistant to this enzyme's action. d-Pro2-endomorphin-2 (ED50=0.05 microg) was more potent than endomorphin-2 (ED50=30 microg) in significantly increasing tail-flick latencies with longer durations of action. Both the peptide and analogue were equipotent (ED50=0.5 microg) in significantly increasing jump thresholds. Ala-Pyrrolidonyl-2-nitrile (10-75 nmol) elicited a dose-dependent analgesia, and potentiated the analgesic actions of endomorphin-2, particularly on the tail-flick test. Whereas systemic naltrexone (2.5, 10 mg/kg) dose-dependently eliminated each of the three forms of analgesia on the jump test as well as the peak (15 min) effect on the tail-flick test, analgesia elicited by either endomorphin-2, d-Pro2-endomorphin-2 or Ala-Pyrrolidonyl-2-nitrile returned after 30-60 min in naltrexone-treated rats on the tail-flick test. These data strongly suggest that dipeptidyl peptidase IV plays a role in the inactivation of endomorphin-2 in vivo, and thereby modulates its central analgesic actions.

Properties of the proteasome activator subunit PA28 alpha and its des-tyrosyl analog

The proteasome activator protein PA28 or 11 S regulator may play an important role in facilitating the generation of peptides for presentation by the MHC class I system. PA28 is composed of two homologous subunits termed alpha and beta. Removal of the carboxyl terminal tyrosine of the alpha subunit of PA28 abolishes activity (X. Song et al., 1997, J. Biol. Chem. 272, 27994-28000). To explore the structural basis of this effect the des-tyrosyl analog of PA28alpha prepared by site-directed mutagenesis and PA28alpha were expressed at high levels in a baculovirus system and purified by FPLC. Des-tyrosyl-PA28alpha neither stimulated the proteasome nor competed with PA28alpha for binding to the proteasome. Hydrophobic interaction chromatography revealed that the hydrophobicity of the mutant protein was considerably greater than PA28alpha. When the mutant protein was chromatographed on a calibrated Superose 6 column a mixture of approximately 25% oligomer and 75% monomer was found. The oligomer weakly stimulated the proteasome but this molecule was labile. Very low concentrations of SDS (0.005%) dissociated PA28alpha and abolished its stimulatory activity. It is concluded that the lack of activity of des-tyrosyl-PA28alpha is due to conformational changes resulting in dissociation and that the oligomeric form of PA28alpha is required for activation.

Proteasome activator (PA28) subunits, alpha, beta and gamma (Ki antigen) in NT2 neuronal precursor cells and HeLa S3 cells

The catalytic activity of the 20S proteasome can be modulated by endogenous proteins. A proteasome activator protein termed PA28 or 11S regulator, composed of two homologous subunits (alpha and beta) and a separate but related protein termed Ki antigen or PA28gamma have been characterized. To explore the functional relationship of these proteins, NT2 clone D1 human neuronal precursor cells, as well as HeLa S3 cells were labeled by immunofluorescence and immunoelectron microscopy with three different antisera directed against peptides derived from their sequences. It was found that both PA28alpha and PA28beta antisera label the cytoplasm and the nucleoli. In contrast, the PA28gamma antiserum labels the nucleus but not the nucleoli while in the cytoplasm it labels two different classes of structures identified as microtubular-like extensions and inclusion bodies that are most likely autophagosomes. The latter do not contain proteasome delta subunit antigen. The microtubular-like structures colocalize with beta-tubulin, are dispersed by nocodazole and are not affected by brefeldin A treatment. PA28alpha and PA28beta are co-localized in the cell whereas PA28gamma has a different distribution. PA28gamma complexed with the proteasome may serve a function other than or in addition to activation and may also have a proteasome-independent function.

Purification, characterization, and cloning of a cytosolic aspartyl aminopeptidase

An aminopeptidase with a preference for N-terminal aspartyl and glutamyl residues but distinct from glutamyl aminopeptidase (EC 3.4. 11.7) was purified to near homogeneity from rabbit brain cytosol. Its properties were similar to an enzyme described previously (Kelly, J. A., Neidle, E. L., and Neidle, A. (1983) J. Neurochem. 40, 1727-1734). Aspartyl aminopeptidase had barely detectable activity toward simple aminoacyl-naphthylamide substrates. Its activity was determined with the substrate Asp-Ala-Pro-naphthylamide in the presence of excess dipeptidyl-peptidase IV (EC 3.4.14.5). The native enzyme has a molecular mass of 440 kDa and migrates as a single band of 55 kDa after SDS-polyacrylamide gel electrophoresis. The sequences of three tryptic peptides were used to screen the GenBankTM data base of expressed sequence tags. Human and mouse clones described as "similar to a yeast vacuolar aminopeptidase" and containing full-length cDNAs were identified and sequenced. The human cDNA was expressed in Escherichia coli. The amino acid sequence has significant homology to yeast aminopeptidase I, placing it as the first identified mammalian member of the M18 family of metalloproteinases. Homologous sequences in Caenorhabditis elegans and in prokaryotes revealed three conserved histidines, three conserved glutamates and five conserved aspartates. Aspartyl aminopeptidase is found at relatively high levels in all mammalian tissues examined and is likely to play an important role in intracellular protein and peptide metabolism.

Production and properties of a recombinant soluble form of aminopeptidase A

Aminopeptidase A is a homodimeric membrane-bound zinc metallopeptidase anchored at the plasma membrane by a 22-amino-acid hydrophobic segment. The anchor segment separates a small N-terminal cytoplasmic domain from a large ectodomain that contains the active site. Site-directed mutagenesis was performed to investigate the role of the cytoplasmic domain of aminopeptidase A in membrane anchoring and routing of the enzyme. Expression in COS-7 cells of a mutant lacking the N-terminal cytoplasmic domain resulted in the efficient secretion of a catalytically active enzyme in the medium. The soluble mutated aminopeptidase A, purified from the medium of a stable cell line, exhibited similar biochemical features to those of the wild-type enzyme. Pulse/chase metabolic labeling experiments revealed that the soluble form is generated intracellularly at an early stage of biosynthesis, suggesting that the signal peptide/membrane anchor domain of aminopeptidase A is removed in the endoplasmic reticulum through the action of the signal peptidase.

[Strategies for identification of secretases implicated in Alzheimer's disease]

In Alzheimer's disease, cortical areas of affected patients are invaded by extracellular proteinous deposits called senile plaques, the main component of which is called amyloid beta-peptide or A beta. This peptide derives from the proteolytic attack of a precursor, the beta-amyloid precursor protein, by two enzymes called beta- and gamma-secretases. Alternatively, beta APP can be cleaved by an additional activity named alpha-secretase that occurs inside the A beta sequence, thereby precluding its formation, and concomitantly liberating a secreted fragment, namely APP alpha. Therefore, secretases seem to play a key role in the control of physiological and potentially pathogenic beta APP catabolites and could be envisioned as possible therapeutic targets in Alzheimer's disease. Here, we describe possible experimental approaches to identify such proteolytic activities.

Quantitation and regulation of pyroglutamyl peptidase II messenger RNA levels in rat tissues and GH3 cells

The distribution of the mRNA of the specific thyrotropin-releasing-hormone (TRH)-degrading enzyme pyroglutamyl peptidase II (EC 3.4.19.6) in rat tissues and brain regions and its regulation in rat tissues and in GH3 cells was studied by a reliable and quantitative solution hybridization ribonuclease protection assay. The distribution of pyroglutamyl peptidase II mRNA levels was uneven with the highest level of mRNA found in brain. Within brain the distribution of pyroglutamyl peptidase II mRNA was heterogeneous. A single dose of T3 markedly increased the level of pyroglutamyl peptidase II mRNA in the pituitary (p < 0.01) and in the liver (p < 0.05). In GH3 cells, exposure to T3 at concentrations from 10(-10) to 10(-6) M for time periods of 2-24 h, did not change pyroglutamyl peptidase II mRNA levels. Acute administration of TRH to rats had no effect on pyroglutamyl peptidase II mRNA levels. By contrast, TRH down-regulated pyroglutamyl peptidase II mRNA in GH3 cells. A similar effect was produced in GH3 cells by activators of protein kinase C. These studies reveal fundamental differences in the mechanism of regulation of pyroglutamyl peptidase II mRNA in pituitary and in GH3 cells. Elevation of pyroglutamyl peptidase II mRNA in liver by T3 suggests that this organ is the source of the enzyme in serum.

Neutral endopeptidase 24.11 loss in metastatic human prostate cancer contributes to androgen-independent progression

Neutral endopeptidase 24.11 (NEP) is a cell-surface enzyme expressed by prostatic epithelial cells that cleaves and inactivates neuropeptides implicated in the growth of androgen-independent prostate cancer (PC). We report that NEP expression and catalytic activity are lost in vitro in androgen-independent but not androgen-dependent PC cell lines. In vivo, NEP protein expression is commonly decreased in cancer cells of metastatic PC specimens from patients with androgen-independent but not androgen-dependent PC. Overexpression of NEP in androgen-independent PC cells or incubation with recombinant NEP inhibits PC cell growth. Furthermore, in androgen-dependent PC cells, expression of NEP is transcriptionally regulated by androgen and decreases with androgen withdrawal. These data suggest that decreased NEP expression, common in androgen-independent PCs, is facilitated by the elimination of androgens, and that NEP loss plays an important role in the development of androgen-independent PC by allowing PC cells to use mitogenic neuropeptides as an alternate source to androgen in order to stimulate cell proliferation.

Constitutive and protein kinase C-regulated secretory cleavage of Alzheimer's beta-amyloid precursor protein: different control of early and late events by the proteasome

The physiological processing of the beta-amyloid precursor protein (betaAPP) by a protease called alpha-secretase gives rise to APP alpha, a C-terminally truncated fragment of betaAPP with known neurotrophic and cytoprotective properties. Several lines of evidence indicate that protein kinase C (PKC)-mediated events regulate this physiological pathway. We show here that the proteasome multicatalytic complex modulates the phorbol 12,13-dibutyrate-stimulated APP alpha secretion at several levels in human kidney 293 (HK293) cells. Two blocking agents of the proteasome, namely, Z-IE(Ot-Bu)A-leucinal and lactacystin, elicit a dual effect on PKC-regulated APP alpha secretion by metabolically labeled HK293 cells. Thus, short periods of preincubation (2-5 h) of the cells with the inhibitors trigger a drastic potentiation of APP alpha recovery, whereas long-term treatment of the cells (15-20 h) with the blocking agents leads to an overall decrease in the secretion of APP alpha. Such a dual effect was not observed on constitutive APP alpha secretion and intracellular formation generated by HK293 cells, which both only increase upon inhibitor treatments. Similar effects on the constitutive and PKC-regulated APP alpha secretion were observed with PC12 cells. Altogether, these data suggest distinct mechanisms underlying basal and PKC-regulated APP alpha production, indicating that this multicatalytic complex appears as a key contributor of the alpha-secretase pathway.

Inhibition of human immunodeficiency virus type 1 infection in a T-cell line (CEM) by new dipeptidyl-peptidase IV (CD26) inhibitors

Phenylalanyl-pyrrolidine-2 nitrile (Phe-pyrr-2-CN) and arginyl(PMC)-pyrrolidine-2-nitrile (Arg(PMC)-pyrr-2-CN) are two dipeptidyl peptidase IV/CD26 (DPP-IV/CD26) inhibitors designed and synthesized by our group. These two compounds suppress the enzymatic activity of DPP-IV/CD26 in a competitive and reversible manner. Pretreatment of CEM cells with either of the compounds yielded a marked albeit transient reduction of HIV infection, as measured by HIV1 p24 production, RT activity and syncytium formation. The ID50 value of the Phe-Pyrr-2-CN and Arg(PMC)-pyrr-2-CN in HIV1 inhibition was 5.3 microM and 2.4 microM, respectively. Administration of either of the DPP-IV/CD26 inhibitors 1 h after HIV1 infection did not suppress HIV1 production. An analog whose inhibitory activity toward DPP-IV/CD26 was abolished by blocking the N-terminal of Phe-pyrr-2-CN with the 9-fluorenymethyloxycarbonyl (Fmoc) group had no effect on HIV1 infection. An additive effect of HIV1 inhibition was observed in combinations of either of the DPP-IV/CD26 inhibitors with CD4 monoclonal antibody. These results suggest that DPP-IV/CD26 enzymatic activity may play a role in facilitating HIV1 infection of human CD4+T cells at the entry process. DPP-IV/CD26 inhibitors may therefore have potential use in combination with other drugs to prevent HIV1 transmission.

Synthetic peptide-based activators of the proteasome

The development of small molecule peptide-based activators of the 20S proteasome or multicatalytic proteinase complex was initiated. The enhancement of antigen presentation by transfection of the protein activator PA28alpha into a mouse fibroblast cell line [10] supports the potential use of small molecule activators in stimulating the immune response. Four classes of peptide-based activators were synthesized, i.e. peptidyl alcohols, esters, p-nitroanilides and nitriles. These compounds markedly and reversibly stimulated the hydrolysis of suc-LLVY-MCA, Z-LLE-NA and Z-GPALG-p-aminobenzoate as well as hydrolysis of the decapeptide angiotensin I. Stimulation was due to a decrease in the Km and increase in the Vmax of the substrate. In general, the EC50 for activation ranged from 50-150 mM and maximal stimulation varied from 3 to 15 fold depending on the activity measured. Z-IE(Ot-Bu)AL-p-nitroanilide, a proteasome substrate, markedly stimulated the hydrolysis of Z-GPALG-pAB by binding to a saturable high affinity site distinct from its binding site as substrate. Since all effective activators contain hydrophobic groups in positions P1-P5, low aqueous solubility is a limitation of these compounds. Competition experiments suggest that these activators bind to the same site as PA28.

Proteasome contributes to the alpha-secretase pathway of amyloid precursor protein in human cells

A major histopathological hallmark in Alzheimer's disease consists of the extracellular deposition of the amyloid beta-peptide (A beta) that is proteolytically derived from the beta-amyloid precursor protein (beta APP). An alternative, nonamyloidogenic cleavage, elicited by a protease called alpha-secretase, occurs inside the A beta sequence and gives rise to APP alpha, a major secreted C-terminal-truncated form of beta APP. Here, we demonstrate that human embryonic kidney 293 (HK293) cells contain a chymotryptic-like activity that can be ascribed to the proteasome and that selective inhibitors of this enzyme reduce the phorbol 12,13-dibutyrate-sensitive APP alpha secretion by these cells. Furthermore, we establish that a specific proteasome blocker, lactacystin, also induces increased secretion of A beta peptide in stably transfected HK293 cells overexpressing wild-type beta APP751. Altogether, this study represents the first identification of a proteolytic activity, namely, the proteasome, contributing likely through yet unknown intracellular relays, to the alpha-secretase pathway in human cells.

Aminopeptidase A antiserum inhibits intracerebroventricular angiotensin II-induced dipsogenic and pressor responses

Angiotensin II increases drinking and blood pressure when administered intracerebroventricularly. Intracerebroventricular injections of antiserum with anticatalytic activity against aminopeptidase A, the principal enzyme that metabolizes angiotensin II to angiotensin III, reduced the drinking and blood pressure responses to 10 pmol angiotensin II by 73% and 59%, respectively. APA antiserum had no effect on responses to angiotensin III administered intracerebroventricularly. A Glu-thiol inhibitor of aminopeptidase A also reduced angiotensin II-induced drinking. These results suggest that metabolism of angiotensin II to angiotensin III is an obligatory activation step for the brain angiotensin system.

Apoptosis induced in L1210 leukaemia cells by an inhibitor of the chymotrypsin-like activity of the proteasome

Of a number of factors involved in apoptosis, protease activity may play a crucial role. We show that N-benzyloxycarbonyl-Ile-Glu( O-t-butyl)-Ala-leucinal (PSI), a selective inhibitor of the chymotrypsin-like activity of the proteasome, induces massive apoptosis in murine leukaemia L1210 cells. At 50 nM concentration, PSI induces a block of cytokinesis, while higher concentrations (500 nM) cause S phase block and massive apoptosis. Z-Leu-leucinal, a specific calpain inhibitor, did not induce apoptosis. In contrast to previous reports, TNF-alpha did not enhance apoptosis when combined with PSI. Our results suggest that proteasome inhibitors may be considered as potential anti-neoplastic agents.

Protein kinase A phosphorylation of the proteasome: a contribution to the alpha-secretase pathway in human cells

The beta-amyloid precursor protein undergoes a physiological cleavage by alpha-secretase that leads to the release of a secreted C-terminally truncated fragment called APP alpha and likely concomitantly reduces the formation of the amyloidogenic A beta peptide. Here we demonstrate that APP alpha secretion is increased by the protein kinase A (PKA) effectors 8-bromo cyclic AMP and forskolin in human embryonic kidney cells (HK293), and that this can be prevented by a proteasome inhibitor. Furthermore, we establish that PKA effectors but not protein kinase C agonists increase the chymotrypsin-like activity and phosphorylation state of the proteasome in vitro and in vivo in HK293 cells. Altogether, this report demonstrates that the alpha-secretase pathway is under the control of PKA in human cells and that the proteasome likely contributes, either directly or through yet unknown intermediates, to the PKA-stimulated APP alpha secretion in human cells.

Ubiquitin-mediated proteolysis centers in HeLa cells: indication from studies of an inhibitor of the chymotrypsin-like activity of the proteasome

HeLa cells growing in vitro were treated with the peptidyl aldehyde inhibitor of the chymotrypsin-like activity of the proteasome N-benzyloxycarbonyl-Ile-Glu(O-t-butyl)-Ala-leucinal (PSI). Immunofluorescence studies of treated cells revealed the formation of massive perinuclear aggregates rich in ubiquitin and proteasomal antigens, which on the ultrastructural level appeared as perinuclear aggregates of electron-dense material, usually in the vicinity of Golgi cisternae. Histochemical studies disclosed that these cells contained protein-rich perinuclear aggregates detected by amido black staining, while unusual accumulations of lipids, carbohydrates, or nucleic acids were not present. Inhibition of protein synthesis by cycloheximide prevented the formation of aggregates, whereas microtubule disruption by nocodazole induced a dispersion of the aggregates. We hypothesize that aggregates induced by PSI treatment correspond to accumulations of proteasome-substrate complexes in a well-defined region, where the proteolytic processes of the ubiquitin-proteasome pathway seem to be somehow centered. We propose to call this region the proteolysis center.

Cleavage of Pro-X and Glu-X bonds catalyzed by the branched chain amino acid preferring activity of the bovine pituitary multicatalytic proteinase complex (20S proteasome)

The multicatalytic proteinase complex or 20S proteasome is involved in the extralysosomal degradation of both long- and short-lived proteins. The eukaryotic enzyme is composed of 14 nonidentical subunits arranged as a complex dimer of the composition (alpha7beta7)2. Recent studies identify N-terminal threonines present on some beta-subunits as the active-site residues. It has been proposed that the molecule contains three or four proteolytically active subunits [Seemuller et al., Science 268, 579-582 (1995)]. Studies with synthetic substrates, activators, and inhibitors, however, have identified at least five distinct catalytic activities. To further characterize the specificity of the previously defined "peptidyl glutamyl peptide bond hydrolyzing activity," N-benzyloxycarbonyl-Leucyl-Leucyl-Glutamal was synthesized as a potential inhibitor. Surprisingly, this aldehyde most potently inhibited the "branched chain amino acid preferring activity" (BrAAP). To further explore BrAAP specificity, novel substrates containing internal prolyl and glutamyl residues were synthesized. Their use established that the BrAAP activity catalyzed both a postproline and a postglutamate cleavage and therefore has a broader specificity than previously recognized. These results help explain earlier observations on treatment of the multicatalytic proteinase complex with 3,4-dichloroisocoumarin. This reagent activates both the BrAAP activity and the degradation of beta-casein and inhibits the other catalytic activities.