Dirk Wildeboer

The Metalloprotease Disintegrin ADAM8 PROCESSING BY AUTOCATALYSIS IS REQUIRED FOR PROTEOLYTIC ACTIVITY AND CELL ADHESION

ADAMs (a disintegrinand metalloprotease domains) are metalloprotease and disintegrin domain-containing transmembrane glycoproteins with proteolytic, cell adhesion, cell fusion, and cell signaling properties. ADAM8 was originally cloned from monocytic cells, and its distinct expression pattern indicates possible roles in both immunology and neuropathology. Here we describe our analysis of its biochemical properties. In transfected COS-7 cells, ADAM8 is localized to the plasma membrane and processed into two forms derived either by prodomain removal or as remnant protein comprising the extracellular region with the disintegrin domain at the N terminus. Proteolytic removal of the ADAM8 propeptide was completely blocked in mutant ADAM8 with a Glu330 to Gln exchange (EQ-A8) in the Zn2+ binding motif (HE330LGHNLGMSHD), arguing for autocatalytic prodomain removal. In co-transfection experiments, the ectodomain but not the entire MP domain of ADAM8 was able to remove the prodomain from EQ-ADAM8. With cells expressing ADAM8, cell adhesion to a substrate-bound recombinant ADAM8 disintegrin/Cys-rich domain was observed in the absence of serum, blocked by an antibody directed against the ADAM8 disintegrin domain. Soluble ADAM8 protease, consisting of either the metalloprotease domain or the complete ectodomain, cleaved myelin basic protein and a fluorogenic peptide substrate, and was inhibited by batimastat (BB-94, IC50∼50 nm) but not by recombinant tissue inhibitor of matrix metalloproteinases 1, 2, 3, and 4. Our findings demonstrate that ADAM8 processing by autocatalysis leads to a potential sheddase and to a form of ADAM8 with a function in cell adhesion.

Metalloproteinase Disintegrins ADAM8 and ADAM19 Are Highly Regulated in Human Primary Brain Tumors and their Expression Levels and Activities Are Associated with Invasiveness

Patients with primary brain tumors have bleak prognoses and there is an urgent desire to identify new markers for sensitive diagnosis and new therapeutic targets for effective treatment. A family of proteins, the disintegrin and metalloproteinases (ADAMs or adamalysins), are cell surface and extracellular multidomain proteins implicated in cell-cell signaling, cell adhesion, and cell migration. Their putative biological and pathological roles make them candidates for promoting tumor growth and malignancy. We investigated the expression levels of 12 cerebrally expressed ADAM genes in human primary brain tumors (astrocytoma WHO grade I-III, glioblastoma WHO grade IV, oligoastrocytoma WHO grade II and III, oligodendroglioma WHO grade II and III, ependymoma WHO grade II and III, and primitive neuroectodermal tumor WHO grade IV) using real-time PCR. The mRNAs of the five ADAMs 8, 12, 15, 17, and 19 were significantly upregulated. The ADAM8 and ADAM19 proteins were mainly located in tumor cells and in some tumors in endothelia of blood vessels. In brain tumor tissue, ADAM8 and ADAM19 undergo activation by prodomain removal resulting in active proteases. By using specific peptide substrates for ADAM8 and ADAM19, respectively, we demonstrated that the proteases exert enhanced proteolytic activity in those tumor specimens with the highest expression levels. In addition, expression levels and the protease activities of ADAM8 and ADAM19 correlated with invasive activity of glioma cells, indicating that ADAM8 and ADAM19 may play a significant role in tumor invasion that may be detrimental to patients survival.

The ADAM10 Prodomain Is a Specific Inhibitor of ADAM10 Proteolytic Activity and Inhibits Cellular Shedding Events

ADAM10 is a disintegrin metalloproteinase that processes amyloid precursor protein and ErbB ligands and is involved in the shedding of many type I and type II single membrane-spanning proteins. Like tumor necrosis factor-α-converting enzyme (TACE or ADAM17), ADAM10 is expressed as a zymogen, and removal of the prodomain results in its activation. Here we report that the recombinant mouse ADAM10 prodomain, purified from Escherichia coli, is a potent competitive inhibitor of the human ADAM10 catalytic/disintegrin domain, with a Ki of 48 nm. Moreover, the mouse ADAM10 prodomain is a selective inhibitor as it only weakly inhibits other ADAM family proteinases in the micromolar range and does not inhibit members of the matrix metalloproteinase family under similar conditions. Mouse prodomains of TACE and ADAM8 do not inhibit their respective enzymes, indicating that ADAM10 inhibition by its prodomain is unique. In cell-based assays we show that the ADAM10 prodomain inhibits betacellulin shedding, demonstrating that it could be of potential use as a therapeutic agent to treat cancer.

Identification of candidate substrates for ectodomain shedding by the metalloprotease-disintegrin ADAM8

Abstract ADAM proteases are type I transmembrane proteins with extracellular metalloprotease domains. As for most ADAM family members, ADAM8 (CD156a, MS2) is involved in ectodomain shedding of membrane proteins and is linked to inflammation and neurodegeneration. To identify potential substrates released under these pathologic conditions, we screened 10-mer peptides representing amino acid sequences from extracellular domains of various membrane proteins using the ProteaseSpot™ system. A soluble ADAM8 protease containing a pro- and metalloprotease domain was expressed in E. coli and purified as active protease owing to autocatalytic prodomain removal. From 34 peptides tested in the peptide cleavage assay, significant cleavage by soluble ADAM8 was observed for 14 peptides representing membrane proteins with functions in inflammation and neurodegeneration, among them the β-amyloid precursor protein (APP). The in vivo relevance of the ProteaseSpot™ method was confirmed by cleavage of full-length APP with ADAM8 in human embryonic kidney 293 cells expressing tagged APP. ADAM8 cleaved APP with similar efficiency as ADAM10, whereas the inactive ADAM8 mutant did not. Exchanging amino acids at defined positions in the cleavage sequence of myelin basic protein (MBP) revealed sequence criteria for ADAM8 cleavage. Taken together, the results allowed us to identify novel candidate substrates that could be cleaved by ADAM8 in vivo under pathologic conditions.

Tumor Necrosis Factor-α (TNF-α) Regulates Shedding of TNF-α Receptor 1 by the Metalloprotease-Disintegrin ADAM8: Evidence for a Protease-Regulated Feedback Loop in Neuroprotection

Tumor necrosis factor α (TNF-α) is a potent cytokine in neurodegenerative disorders, but its precise role in particular brain disorders is ambiguous. In motor neuron (MN) disease of the mouse, exemplified by the model wobbler (WR), TNF-α causes upregulation of the metalloprotease-disintegrin ADAM8 (A8) in affected brain regions, spinal cord, and brainstem. The functional role of A8 during MN degeneration in the wobbler CNS was investigated by crossing WR with A8-deficient mice: a severely aggravated neuropathology was observed for A8-deficient WR compared with WR A8+/− mice, judged by drastically reduced survival [7 vs 81% survival at postnatal day 50 (P50)], accelerated force loss in the forelimbs, and terminal akinesis. In vitro protease assays using soluble A8 indicated specific cleavage of a TNF-α receptor 1 (p55 TNF-R1) but not a TNF-R2 peptide. Cleavage of TNF-R1 was confirmed in situ, because levels of soluble TNF-R1 were increased in spinal cords of standard WR compared with wild-type mice but not in A8-deficient WR mice. In isolated primary neurons and microglia, TNF-α-induced TNF-R1 shedding was dependent on the A8 gene dosage. Furthermore, exogenous TNF-α showed higher toxicity for cultured neurons from A8-deficient than for those from wild-type mice, demonstrating that TNF-R1 shedding by A8 is neuroprotective. Our results indicate an essential role for ADAM8 in modulating TNF-α signaling in CNS diseases: a feedback loop integrating TNF-α, ADAM8, and TNF-R1 shedding as a plausible mechanism for TNF-α mediated neuroprotection in situ and a rationale for therapeutic intervention.

Rapid detection of Escherichia coli in water using a hand-held fluorescence detector

The quantification of pathogenic bacteria in an environmental or clinical sample commonly involves laboratory-based techniques and results are not obtained for 24-72 h after sampling. Enzymatic analysis of microbial activity in water and other environmental samples using fluorescent synthetic substrates are well-established and highly sensitive methods in addition to providing a measure of specificity towards indicative bacteria. The enzyme beta-d-glucuronidase (GUD) is a specific marker for Escherichia coli and 4-methylumbelliferone-beta-D-glucuronide (MUG) a sensitive substrate for determining the presence of E. coli in a sample. However, currently used procedures are laboratory-based and require bench-top fluorimeters for the measurement of fluorescence resulting from the enzyme-substrate reaction. Recent developments in electronic engineering have led to the miniaturisation of fluorescence detectors. We describe the use of a novel hand-held fluorimeter to directly analyse samples obtained from the River Thames for the presence of E. coli. The results obtained by the hand-held detector were compared with those obtained with an established fluorescent substrate assay and by quantifying microbial growth on a chromogenic medium. Both reference methods utilised filtration of water samples. The miniaturised fluorescence detector was used and incubation times reduced to 30 min making the detection system portable and rapid. The developed hand-held system reliably detected E. coli as low as 7 cfu/mL river water sample. Our study demonstrates that new hand-held fluorescence measurement technology can be applied to the rapid and convenient detection of bacteria in environmental samples. This enables rapid monitoring to be carried out on-site. The technique described is generic and it may, therefore, be used in conjunction with different fluorescent substrates which allows the assessment of various target microorganisms in biological samples.

Specific protease activity indicates the degree of Pseudomonas aeruginosa infection in chronic infected wounds.

Chronic non-healing wounds are a major health problem with resident bacteria strongly implicated in their impaired healing. A rapid-screen to provide detailed knowledge of wound bacterial populations would therefore be of value and help prevent unnecessary and indiscriminate use of antibiotics—a process associated with promoting antibiotic resistance. We analysed chronic wound fluid samples, which had been assessed for microbial content, using 20 different fluorescent labelled peptide substrates to determine whether protease activity correlated with the bacterial load. Eight of the peptide substrates showed significant release of fluorescence after reaction with some of the wound samples. Comparison of wound fluid protease activities with the microbiological data indicated that there was no correlation between bacterial counts and enzyme activity for most of the substrates tested. However, two of the peptide substrates produced a signal corresponding with the microbial data revealing a strong positive correlation with Pseudomonas aeruginosa numbers. This demonstrated that short fluorescent labelled peptides can be used to detect protease activity in chronic wound fluid samples. The finding that two peptides were specific indicators for the presence of P. aeruginosa may be the basis for a diagnostic test to determine wound colonisation by this organism.

Characterization of bacterial proteases with a panel of fluorescent peptide substrates

Bacteria produce a range of proteolytic enzymes. In an attempt to detect and identify bacteria on the basis of their protease activity, a panel of protease substrates was investigated. Peptides conjugated to the fluorophore 7-amino-4-methylcoumarin (AMC) are well-established substrates for measuring protease activity. Although peptide-AMC substrates are generally not specific for a single protease, a unique pattern can be achieved for both highly specific enzymes and those with a broader substrate range by comparing different peptide substrates. The panel of 7 peptide-AMC substrates chosen exhibited a unique pattern for nine microbial proteases. The selected peptides were used to determine protease activity in cultured strains of Pseudomonas aeruginosa and Staphylococcus aureus. A signal pattern obtained with peptides with arginine, lysine, and tyrosine in the P1 position characterized the bacterial protease activities in these samples. The kinetic parameters for the three best substrates for the P. aeruginosa sample were calculated. Further information about substrate specificity was gained by the selective use of protease inhibitors. The results presented show that peptide-AMC substrates provide a simple and sensitive tool to characterize protease activity in microbiological samples and that they have the potential to identify and distinguish different bacterial species.

Use of antibody–hapten complexes attached to optical sensor surfaces as a substrate for proteases: real-time biosensing of protease activity

Fluorescent antibody protein (IgG) was attached to the surface of an integrated optical glass waveguide chip via specific binding to a covalently attached hapten and used as a substrate for the measurement of protease activities. Exposure of the optical chip to proteases resulted in digestion of the bound fluorescent antibody molecules and proportional decrease in the detectable fluorescence resulting from loss of fluorescence from the evanescent field. The bound fluorescent antibody protein was used as a unique universal protease substrate in which the combined biological activity and fluorescence signal were the basis of measurement. The action of proteases was monitored in real-time mode where the gradual decrease in evanescent fluorescence was recorded. The chip was regenerated by complete digestion of the antibody substrate by excess pepsin and recharged by incubation with a fresh sample of the labelled antibody. The biosensor was used to detect activity of several proteases including a bacterial protease preparation, Pronase E. The linear range of measurable Pronase E activity was from 0.03 to 2 units/mL. A measurement cycle took 40 min for samples with high protease concentration (>or=0.5 units/mL), when the concentration of the protease was less measurement times up to 100 min were required. The method demonstrates the principle of a new mode of real-time biosensing of proteases. The modular integrated optical glass waveguide biosensor system used in this study is compact and controlled by a laptop computer and could easily be miniaturised and utilized as a true probe device for detecting proteases with potential applications in a wide range of areas including research, clinical diagnostics, biotechnology processing and food and detergent manufacturing industries.

Mycoremediation of Heavy Metal/Metalloid-Contaminated Soil: Current Understanding and Future Prospects

In natural environments, heavy metals and metalloids are widely dispersed as a consequence of anthropogenic (e.g. mining) and geological (e.g. volcanic eruption) activities. The toxicity of these metals/metalloids could adversely affect the ecosystem as well as causing major human health concerns. Mycoremediation (remediation by fungi) has received attention from many researchers as an alternative to conventional chemical and physical methods in removing toxic metals and metalloids. A number of regulatory mechanisms to control the concentrations and counteract the toxicity of these pollutants have been observed in fungi. These mechanisms include: (i) precipitation or binding to cell surface materials, (ii) intracellular chelation and precipitation, (iii) biotransformation and (iv) control of membrane transport systems. This chapter examines the use of fungi to bioremediate metals and metalloids and their detoxification mechanisms, with special focus on an extremophilic fungus, Acidomyces acidophilus, isolated from a disused tin mine in the UK, to illustrate some of the mechanisms involved. Future biotechnological and nanotechnological prospects of metal/metalloids bioremediation using fungi are also discussed.