Potential transfer of aquatic organisms via ballast water with a particular focus on harmful and non-indigenous species: A survey from Adriatic ports

Ballast water discharges may cause negative impacts to aquatic ecosystems, human health and economic activities by the introduction of potentially harmful species. Fifty untreated ballast water tanks, ten in each port, were sampled in four Adriatic Italian ports and one Slovenian port. Salinity, temperature and fluorescence were measured on board. Faecal indicator bacteria (FIB), phyto- and zooplankton were qualitatively and quantitatively determined to identify the species assemblage arriving in ballast water. FIB exceeded the convention standard limits in 12% of the sampled tanks. Vibrio cholerae was not detected. The number of viable organisms in the size groups (minimum dimension) <50 and ≥10 μm and ≥50 μm resulted above the abundances required from the Ballast Water Management Convention in 55 and 86% of the samples, respectively. This is not surprising as unmanaged ballast waters were sampled. Some potentially toxic and non-indigenous species were observed in both phyto- and zooplankton assemblages.

Methodologic Problems Encountered in the Assay of Proteinases in Lewis Lung Carcinoma, a Mouse Metastasizing Tumor

The proteolytic activity in homogenates and extracts of subcellular fractions prepared from subcutaneous Lewis lung carcinoma was determined using proteins and synthetic peptides as substrates. The presence of cathepsin D, plasminogen activator, cathepsin B-, cathepsin G-and elastase-like enzymes was observed. No difference was revealed between the proteolytic activity in homogenates of Lewis lung carcinoma, at the growth stage examined, and in homogenates of normal lung. High specific activities were found in the lysosomal extract, whereas decreasing activities were found in the nuclear extract, the homogenate and the post-lysosomal mitochondrial supernatant; no active or trypsin-activatable collagenase activity was detected. The presence in the tumor tissue of these enzymatic activities is in agreement with their proposed role in the process of metastasis. The lack of differences between homogenates of tumor and normal lung tissue suggests that the use of whole cells is required to selectively study tumor proteinases specifically involved in tumor malignancy.

Bacterial community shift is induced by dynamic environmental parameters in a changing coastal ecosystem (northern Adriatic, northeastern Mediterranean Sea)--a 2-year time-series study

The potential link between the microbial dynamics and the environmental parameters was investigated in a semi-enclosed and highly dynamic coastal system (Gulf of Trieste, northern Adriatic Sea, NE Mediterranean Sea). Our comprehensive 2-year time-series study showed that despite the shallowness of this area, there was a significant difference between the surface and the bottom bacterial community structure. The bottom bacterial community was more diverse than the surface one and influenced by sediment re-suspension. The surface seawater temperature had a profound effect on bacterial productivity, while the bacterial community structure was more affected by freshwater-borne nutrients and phytoplankton blooms. Phytoplankton blooms caused an increase of Gammaproteobacteria (Alteromonadaceae, SAR86 and Vibrionaceae) and shift in dominance from SAR11 to Rhodobacteraceae taxon at the surface. Our results propose the importance of the water mass movements as drivers of freshwater-borne nutrients and of allochthonous microbial taxa. This study emphasizes the prediction power based on association networks analyses that are fed with long-term measurements of microbial and environmental parameters. These interaction maps offer valuable insights into the response of marine ecosystem to climate- and anthropogenic-driven stressors.

Selective targeting of tumor and stromal cells by a nanocarrier system displaying lipidated cathepsin B inhibitor

Cathepsin B (CtsB) is a lysosomal cysteine proteinase that is specifically translocated to the extracellular milieu during cancer progression. The development of a lipidated CtsB inhibitor incorporated into the envelope of a liposomal nanocarrier (LNC-NS-629) is described. Ex vivo and in vivo studies confirmed selective targeting and internalization of LNC-NS-629 by tumor and stromal cells, thus validating CtsB targeting as a highly promising approach to cancer diagnosis and treatment.

Microbial mechanisms coupling carbon and phosphorus cycles in phosphorus-limited northern Adriatic Sea

The coastal northern Adriatic Sea receives pulsed inputs of riverine nutrients, causing phytoplankton blooms and seasonally sustained dissolved organic carbon (DOC) accumulation-hypothesized to cause episodes of massive mucilage. The underlying mechanisms regulating P and C cycles and their coupling are unclear. Extensive biogeochemical parameters, processes and community composition were measured in a 64-day mesocosms deployed off Piran, Slovenia. We followed the temporal trends of C and P fluxes in P-enriched (P+) and unenriched (P-) mesocosms. An intense diatom bloom developed then crashed; however, substantial primary production was maintained throughout, supported by tightly coupled P regeneration by bacteria and phytoplankton. Results provide novel insights on post-bloom C and P dynamics and mechanisms. 1) Post-bloom DOC accumulation to 186 μM remained elevated despite high bacterial carbon demand. Presumably, a large part of DOC accumulated due to the bacterial ectohydrolytic processing of primary productivity that adventitiously generated slow-to-degrade DOC; 2) bacteria heavily colonized post-bloom diatom aggregates, rendering them microscale hotspots of P regeneration due to locally intense bacterial ectohydrolase activities; 3) Pi turnover was rapid thus suggesting high P flux through the DOP pool (dissolved organic phosphorus) turnover; 4) Alpha- and Gamma-proteobacteria dominated the bacterial communities despite great differences of C and P pools and fluxes in both mesocosms. However, minor taxa showed dramatic changes in community compositions. Major OTUs were presumably generalists adapted to diverse productivity regimes.We suggest that variation in bacterial ectohydrolase activities on aggregates, regulating the rates of POM→DOM transition as well as dissolved polymer hydrolysis, could become a bottleneck in P regeneration. This could be another regulatory step, in addition to APase, in the microbial regulation of P cycle and the coupling between C and P cycles.

Siramesine triggers cell death through destabilisation of mitochondria, but not lysosomes

A sigma-2 receptor agonist siramesine has been shown to trigger cell death of cancer cells and to exhibit a potent anticancer activity in vivo. However, its mechanism of action is still poorly understood. We show that siramesine can induce rapid cell death in a number of cell lines at concentrations above 20 μM. In HaCaT cells, cell death was accompanied by caspase activation, rapid loss of mitochondrial membrane potential (MMP), cytochrome c release, cardiolipin peroxidation and typical apoptotic morphology, whereas in U-87MG cells most apoptotic hallmarks were not notable, although MMP was rapidly lost. In contrast to the rapid loss of MMP above 20 μM siramesine, a rapid increase in lysosomal pH was observed at all concentrations tested (5–40 μM); however, it was not accompanied by lysosomal membrane permeabilisation (LMP) and the release of lysosomal enzymes into the cytosol. Increased lysosomal pH reduced the lysosomal degradation potential as indicated by the accumulation of immature forms of cysteine cathepsins. The lipophilic antioxidant α-tocopherol, but not the hydrophilic antioxidant N-acetyl-cysteine, considerably reduced cell death and destabilisation of mitochondrial membranes, but did not prevent the increase in lysosomal pH. At concentrations below 15 μM, siramesine triggered cell death after 2 days or later, which seems to be associated with a general metabolic and energy imbalance due to defects in the endocytic pathway, intracellular trafficking and energy production, and not by a specific molecular event. Overall, we show that cell death in siramesine-treated cells is induced by destabilisation of mitochondria and is independent of LMP and the release of cathepsins into the cytosol. Moreover, it is unlikely that siramesine acts exclusively through sigma-2 receptors, but rather through multiple molecular targets inside the cell. Our findings are therefore of significant importance in designing the next generation of siramesine analogues with high anticancer potential.

The pH dependence of breakdown of various purified brain proteins by cathepsin D preparations

In a continuing study of control processes of cerebral protein catabolism we compared the activity of cathepsin D from three sources (rat brain, bovine brain, and bovine spleen) on purified CNS proteins (tubulin, actin, calmodulin, S-100 and glial fibrillary acidic protein). The pH optimum was 5 for hydrolysis with tubulin as substrate for all three enzyme preparations, and it was pH 4 with the other substrates. The pH dependence curve was somewhat variable, with S-100 breakdown relatively more active at an acidic pH range. The formation of initial breakdown products and the further catabolism of the breakdown products was dependent on pH; hence the pattern of peptides formed from glial fibrillary acidic protein was different in incubations at different pH's. The relative activity of the enzyme preparations differed, depending on the substrate: with tubulin and S-100 as substrates, rat brain cathepsin D was the most active and the bovine spleen enzyme was the least active. With calmodulin and glial fibrillary acidic protein as substrates, rat brain and spleen cathepsin D activities were similar, and bovine brain cathepsin D showed the lowest activity. Actin breakdown fell between these two patterns. The rates of breakdown of the substrates were different; expressed as ?g of substrate split per unit enzyme per h, with rat brain cathepsin D activity was 8-9 with calmodulin and S-100, 4 with glial fibrillary acidic protein, 1.8 with actin, and 0.9 with tubulin. The results show that there are differences in the properties of a protease like cathepsin D, depending on its source; furthermore, the rate of breakdown and the characteristics of breakdown are also dependent on the substrate. We recently measured the breakdown of brain tubulin by cerebral cathepsin D in a continuing study of the mechanisms and controls of cerebral protein catabolism (Bracco et al., 1982a). We found that tubulin breakdown is heterogeneous, that membrane-bound tubulin is resistant to cathepsin D but susceptible to thrombin (Bracco et al., 1982b), and that cytoplasmic tubulin was in at least two pools, one with a higher, another with a lower, rate of breakdown. The pH optimum of tubulin breakdown by cerebral cathepsin D differed significantly from the pH optimum of hemoglobin breakdown by the same enzyme. These findings showed that the properties of breakdown by a cerebral protease depend on the substrate. To further examine this dependence of properties of breakdown on the substrate, we now report measurements of pH dependence of breakdown of several purified proteins (tubulin, actin, calmodulin, S-100, glial fibrillary acidic protein [GFA]) from brain by cathepsin D preparations from three sources, rat brain, bovine brain, and bovine spleen. We also compare the rate of breakdown of the various proteins with the rate of hemoglobin breakdown.

MAGUKs, scaffolding proteins at cell junctions, are substrates of different proteases during apoptosis

A major feature of apoptotic cell death is gross structural changes, one of which is the loss of cell–cell contacts. The caspases, executioners of apoptosis, were shown to cleave several proteins involved in the formation of cell junctions. The membrane-associated guanylate kinases (MAGUKs), which are typically associated with cell junctions, have a major role in the organization of protein–protein complexes at plasma membranes and are therefore potentially important caspase targets during apoptosis. We report here that MAGUKs are cleaved and/or degraded by executioner caspases, granzyme B and several cysteine cathepsins in vitro. When apoptosis was induced by UV-irradiation and staurosporine in different epithelial cell lines, caspases were found to efficiently cleave MAGUKs in these cell models, as the cleavages could be prevented by a pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)fluoromethylketone. Using a selective lysosomal disrupting agent -leucyl--leucine methyl ester, which induces apoptosis through the lysosomal pathway, it was further shown that MAGUKs are also cleaved by the cathepsins in HaCaT and CaCo-2 cells. Immunohistological data showed rapid loss of MAGUKs at the sites of cell–cell contacts, preceding actual cell detachment, suggesting that cleavage of MAGUKs is an important step in fast and efficient cell detachment.

Why some adults with intellectual disability consult their general practitioner more than others

BACKGROUND

This research identifies factors affecting why some adults with intellectual disability (AWIDs) consult their general practitioner (GP) more than others. Little is known about these factors, despite AWIDs having higher health needs and reduced longevity. Current barriers to accessing health care need to be understood and overcome to achieve improved health outcomes.

METHODS

A secondary analysis of data obtained from a stratified randomised sample of AWIDs participating in a cluster randomised trial of hand held health records. The number of GP consultations was obtained retrospectively for the year preceding initial health interviews from GP records. AWIDs and their carers were given separate health interviews using identical/adapted questions where possible.

RESULTS

Two hundred and one AWIDs and or their carers from 40 practices participated (response rate 64.6%) with GP consultation data extracted for 187 AWIDs. Overall consulting levels were low, 3.2 per annum for women and 2.2 for men. Increased age, gender (women) and type of carer (paid) were all significantly associated with increased consultations. Carers reporting health problems, medications reported by AWIDs, medications recorded in GP records, and pain reported by AWIDs were also significant factors affecting consultations to GP practices after adjustment for age and type of carer.

CONCLUSIONS

Overall consultation rates were lower than expected, and affected by age, gender and type of carer. Targeted interventions are needed to improve attendance and promote health.

Viral abundance and a high proportion of lysogens suggest that viruses are important members of the microbial community in the Gulf of Trieste

Epifluorescence microscopy and transmission electron microscopy were applied to study virioplankton community in the Gulf of Trieste (northern Adriatic Sea). The total viral abundance was in a range between 2.5 x 10(9)/L and 2.9 x 10(10)/L and was positively correlated with trophic status of the environment. Viruslike particles were significantly correlated with bacterial abundance in all samples studied. Correlations with other physicochemical or biological parameters were not significant. The data suggest that, because of the substantial fraction of tailed viruses present (26%), bacteriophages are an important component of the virioplankton community in the Gulf of Trieste. The abundance of viruslike particles in the seawater changed at hour intervals in a range from 1.3 x 10(9)/L to 5.1 x 10(9)/L. A significant fraction (71%) of the bacterial isolates was inducible in vitro by mitomycin C, and a high occurrence (51%) of lysogenic isolates with more than one phage morphotype present in the lysate was detected. The presence of lysogenic bacteria in the seawater was confirmed in situ with a mitomycin C induction experiment on the natural bacterial population. Results suggest that virioplankton is an abundant component of the microbial community in the Gulf of Trieste.

Inhibition of papain-like cysteine proteases and legumain by caspase-specific inhibitors: when reaction mechanism is more important than specificity

We report here that a number of commonly used small peptide caspase inhibitors consisting of a caspase recognition sequence linked to chloromethylketone, fluoromethylketone or aldehyde reactive group efficiently inhibit other cysteine proteases than caspases. The in vitro studies included cathepsins B, H, L, S, K, F, V, X and C, papain and legumain. Z-DEVD-cmk was shown to be the preferred irreversible inhibitor of most of the cathepsins in vitro, followed by Z-DEVD-fmk, Ac-YVAD-cmk, Z-YVAD-fmk and Z-VAD-fmk. Inactivation of legumain by all the inhibitors investigated was moderate, whereas cathepsins H and C were poorly inhibited or not inhibited at all. Inhibition by aldehydes was not very potent. All the three fluoromethylketones efficiently inhibited cathepsins in Jurkat and human embryonic kidney 293 cells at concentrations of 100 microM. Furthermore, they completely inhibited cathepsins B and X activity in tissue extracts at concentrations as low as 1 microM. These results suggest that data based on the use of these inhibitors should be taken with caution and that other proteases may be implicated in the processes previously ascribed solely to caspases.

Viral abundance and a high proportion of lysogens suggest that viruses are important members of the microbial community in the Gulf of Trieste

Epifluorescence microscopy and transmission electron microscopy were applied to study virioplankton community in the Gulf of Trieste (northern Adriatic Sea). The total viral abundance was in a range between 2.5 x 10(9)/L and 2.9 x 10(10)/L and was positively correlated with trophic status of the environment. Viruslike particles were significantly correlated with bacterial abundance in all samples studied. Correlations with other physicochemical or biological parameters were not significant. The data suggest that, because of the substantial fraction of tailed viruses present (26%), bacteriophages are an important component of the virioplankton community in the Gulf of Trieste. The abundance of viruslike particles in the seawater changed at hour intervals in a range from 1.3 x 10(9)/L to 5.1 x 10(9)/L. A significant fraction (71%) of the bacterial isolates was inducible in vitro by mitomycin C, and a high occurrence (51%) of lysogenic isolates with more than one phage morphotype present in the lysate was detected. The presence of lysogenic bacteria in the seawater was confirmed in situ with a mitomycin C induction experiment on the natural bacterial population. Results suggest that virioplankton is an abundant component of the microbial community in the Gulf of Trieste.

Effects of proteinase inhibitors on digestive proteinases and growth of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

The physiology of the gut lumen of the red flour beetle, T. castaneum, was studied to determine the conditions for optimal protein hydrolysis. Although the pH of gut lumen extracts from T. castaneum was 6.5, maximum hydrolysis of casein by gut proteinases occurred at pH 4.2. The synthetic substrate N-alpha-benzoyl-DL-arginine-rho-nitroanilide was hydrolyzed by T. castaneum gut proteinases in both acidic and alkaline buffers, whereas hydrolysis of N-succinyl-ala-ala-pro-phe rho-nitroanilide occurred in alkaline buffer. Inhibitors of T. castaneum digestive proteinases were examined to identify potential biopesticides for incorporation in transgenic seed. Cysteine proteinase inhibitors from potato, Job's tears, and sea anemone (equistatin) were effective inhibitors of in vitro casein hydrolysis by T. castaneum proteinases. Other inhibitors of T. castaneum proteinases included leupeptin, L-trans-epoxysuccinylleucylamido [4-guanidino] butane (E-64), tosyl-L-lysine chloromethyl ketone, and antipain. Casein hydrolysis was inhibited weakly by chymostatin, N-tosyl-L-phenylalanine chloromethyl ketone, and soybean trypsin inhibitor (Kunitz). The soybean trypsin inhibitor had no significant effect on growth when it was bioassayed alone, but it was effective when used in combination with potato cysteine proteinase inhibitor. In other bioassays with single inhibitors, larval growth was suppressed by the cysteine proteinase inhibitors from potato, Job's tears, or sea anemone. Levels of inhibition were similar to that observed with E-64, although the moles of proteinaceous inhibitor tested were approximately 1000-fold less. These proteinaceous inhibitors are promising candidates for transgenic seed technology to reduce seed damage by T. castaneum.

Amyloid fibril formation by human stefin B: influence of the initial pH-induced intermediate state

The amyloid fibril field is briefly described, with some stress put on differences between various proteins and possible role for domain swapping. In the main body of the text, first, a short review is given of the folding properties of both human stefins, alpha/beta-type globular proteins of 53% identity with a known three-dimensional fold. Second, in vitro study of amyloid fibril formation by human stefin B (type I cystatin) is described. Solvents of pH 4.8 and pH 3.3 with and without 2,2,2-trifluoroethanol (TFE) were probed, as it has been shown previously that stefin B forms acid intermediates, a native-like and molten globule intermediate, respectively. The kinetics of fibrillation were measured by thioflavin T fluorescence and CD. At pH 3.3, the protein is initially in the molten globule state. The fibrillation is faster than at pH 4.8; however, there is more aggregation observed. On adding TFE at each pH, the fibril formation is further accelerated.

Invasion of ras-transformed breast epithelial cells depends on the proteolytic activity of cysteine and aspartic proteinases

It has been suggested that the lysosomal proteinases cathepsin B, L and D participate in tumour invasion and metastasis. Whereas for cathepsins B and L the role of active enzyme in invasion processes has been confirmed, cathepsin D was suggested to support tumour progression via its pro-peptide, rather than by its proteolytic activity. In this study we have compared the presence of active cathepsins B, L and D in ras-transformed human breast epithelial cells (MCF-10A neoT) with their ability to invade matrigel. In this cell line high expression of all three cathepsins was detected by immunofluorescence microscopy. The effect of proteolytic activity on cell invasion was studied by adding various natural and synthetic cysteine and aspartic proteinase inhibitors. The most effective compound was chicken cystatin, a general natural inhibitor of cysteine proteinases, (82.8+/-1.6% inhibition of cell invasion), followed by the synthetic inhibitor trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane (E-64). CLIK-148, a specific inhibitor of cathepsin L, showed a lower effect than chicken cystatin and E-64. Pepstatin A weakly inhibited invasion, whereas the same molar concentrations of squash aspartic proteinase (SQAPI)-like inhibitor, isolated from squash Cucurbita pepo, showed significant inhibition (65.7+/-1.8%). We conclude that both cysteine and aspartic proteinase activities are needed for invasion by MCF-10A neoT cells in vitro.

Lysosomal cysteine proteases: facts and opportunities

From their discovery in the first half of the 20th century, lysosomal cysteine proteases have come a long way: from being the enzymes non-selectively degrading proteins in lysosomes to being those responsible for a number of important cellular processes. Some of the features and roles of their structures, specificity, regulation and physiology are discussed.

The major cysteine proteinase of Trypanosoma cruzi: a valid target for chemotherapy of Chagas disease

Trypanosoma cruzi, the causative agent of the American Trypanosomiasis, Chagas disease, contains a major cysteine proteinase (CP), cruzipain (also known as cruzain, or GP57/51). The enzyme is a member of the papain C1 family of CPs, with a specificity intermediate between those of cathepsin L and cathepsin B. The enzyme, which is expressed at different levels by different parasite stages, is encoded by a high number of genes (up to 130 in the Tul2 strain), which code for a pre-pro-enzyme. Mature cruzipain consists of a catalytic moiety with high homology to cathepsins S and L, and a C-terminal domain, characteristic of Type I CPs of Trypanosomatids, and absent in all other C1 family CPs described so far. Irreversible inhibitors of cruzipain (peptidyl diazomethylketones, peptidyl fluoromethylketones, peptidyl vinyl sulphones) are able to block the differentiation steps in the parasite's life cycle, and effectively kill the organism. Recently, a vinyl sulphone derivative (N-piperazine-Phe-hPhe-vinyl sulphone phenyl) which is an efficient inhibitor of cruzipain and kills T. cruzi by inducing an accumulation of unprocessed cruzipain in the Golgi cisternae, interfering with the secretory pathway, has been tested in vivo in a mice model (J.H. McKerrow et al.). The curative effects observed, as well as the good bioavailability of the inhibitor and its apparent lack of undesirable side effects, make it a promising lead compound for the development of new drugs for the chemotherapy of Chagas disease.

Significance of cathepsin B accumulation in synovial fluid of rheumatoid arthritis

We measured and compared the activities of various kinds of proteinases, such as cysteine, serine, aspartic, and metalloproteinases, in synovial fluids of 16 patients with rheumatoid arthritis (RA) and 18 patients with osteoarthritis (OA). More than 19-fold higher activity of cathepsin B and about 6-fold higher activity of prolylendopeptidase, compared to those of OA, were accumulated in RA fluid. Moreover, levels of cathepsins B and S using the corresponding sandwich enzyme immunoassays were statistically higher in RA fluid than those in OA. Significant amounts of 41-kDa and 35-kDa procathepsin L were detected in RA fluid using gelatin zymography, while 41-kDa enzyme alone was detected in OA. Cathepsin B in RA fluid could degrade collagen, and this degradation was suppressed by the addition of CA-074, a specific inhibitor of cathepsin B. Therefore, cathepsin B may participate in joint destruction of RA, and its inhibitor may be effective for RA care.

Invasion of ras-transformed breast epithelial cells depends on the proteolytic activity of cysteine and aspartic proteinases

It has been suggested that the lysosomal proteinases cathepsin B, L and D participate in tumour invasion and metastasis. Whereas for cathepsins B and L the role of active enzyme in invasion processes has been confirmed, cathepsin D was suggested to support tumour progression via its pro-peptide, rather than by its proteolytic activity. In this study we have compared the presence of active cathepsins B, L and D in ras-transformed human breast epithelial cells (MCF-10A neoT) with their ability to invade matrigel. In this cell line high expression of all three cathepsins was detected by immunofluorescence microscopy. The effect of proteolytic activity on cell invasion was studied by adding various natural and synthetic cysteine and aspartic proteinase inhibitors. The most effective compound was chicken cystatin, a general natural inhibitor of cysteine proteinases, (82.8+/-1.6% inhibition of cell invasion), followed by the synthetic inhibitor trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane (E-64). CLIK-148, a specific inhibitor of cathepsin L, showed a lower effect than chicken cystatin and E-64. Pepstatin A weakly inhibited invasion, whereas the same molar concentrations of squash aspartic proteinase (SQAPI)-like inhibitor, isolated from squash Cucurbita pepo, showed significant inhibition (65.7+/-1.8%). We conclude that both cysteine and aspartic proteinase activities are needed for invasion by MCF-10A neoT cells in vitro.

Immunochemical localisation of cathepsin S, cathepsin L and MHC class II-associated p41 isoform of invariant chain in human lymph node tissue

Antigen presentation by MHC class II molecules requires cysteine proteases (CP) for two convergent proteolytic processes: stepwise degradation of the invariant chain (Ii) and generation of immunogenic peptides. Their activity is controlled by intracellular CP inhibitors, including presumably the p41 isoform of invariant chain (p41 Ii), which is in vitro a potent inhibitor of cathepsin L but not of cathepsin S. In order to evaluate the inhibitory potential of p41 Ii in antigen-presenting cells (APC), these three proteins were stained in lymph node tissue using specific monoclonal and polyclonal antibodies. The most abundant labelling was observed in subcapsular (cortical) and trabecular sinuses of the lymph node. In this area the most frequent APC were macrophages, as confirmed by the CD68 cell marker. Using confocal fluorescence microscopy, co-localisation of p41 Ii with cathepsin S, but not with cathepsin L was found in these cells. Our results are consistent with the hypothesis that cathepsin S participates in degradation of the invariant chain, but they do not support the association between cathepsin L and p41 Ii in APC.

Anti-cathepsin L monoclonal antibodies that distinguish cathepsin L from cathepsin V

Cathepsin L is a lysosomal cysteine protease involved in intracellular protein degradation. Recently, several new cysteine proteases have been identified. Human cathepsin V, a thymus- and testis-specific human cysteine protease, shares 78% sequence identity with human cathepsin L. Due to the strong sequence similarity, highly selective reagents are needed to elucidate the physiological functions of the two enzymes. Monoclonal antibodies (mAbs) have been prepared against recombinant human cathepsin L. Antibodies produced by five clones reacted with procathepsin L and mature cathepsin L. They also reacted with cathepsin L in complex with a peptide fragment, which is identical to the alternatively spliced segment of the p41 form of MHC Class II associated invariant chain. Two mAbs, (M105 and H102) were specific for cathepsin L, while three (N135, B145 and D24) cross-reacted with cathepsin V. None of the mAbs cross-reacted with cathepsins B, H and S. We have developed a sandwich enzyme-linked immunosorbent assay (ELISA) for quantifying cathepsin L. This sandwich ELISA uses a combination of two monoclonal antibodies which recognize different, non-overlapping epitopes on the cathepsin L molecule. The lower detection limit of the sandwich ELISA was 5 ng of cathepsin L per ml.

Major differences in stability and dimerization properties of two chimeric mutants of human stefins

Stefins A and B are cysteine proteinase inhibitors that have considerable sequence similarity but marked differences in their stability and folding properties. Two chimeric proteins were designed to shed light on these differences. The chimeric mutants have been expressed in Escherichia coli and have been isolated. The first, A37B, consists of 37 residues of stefin A, comprising the N-terminal and the alpha-helix, joined to 61 residues of stefin B; the second, A61B, consists of 61 N-terminal residues of stefin A, followed by 37 residues of stefin B. Spectroscopic properties of the chimeric proteins (absorption, CD, and NMR spectra), together with activity measurements, have confirmed that both have well-defined tertiary structure and are active as cysteine proteinase inhibitors. Characterization consisted of GuHCl denaturation, ANS binding as a function of pH, and monitoring of dimerization under partially denaturing conditions. The c(m) values are 1.3 M GuHCl for A61B as compared with 2.7 M GuHCl for stefin A, and 2.1 M GuHCl for A37B as compared with 1.4 M GuHCl for stefin B (all at pH 7.5, 25 degrees C). However (G degrees (N-U) is lower for both chimeric proteins (18 +/- 3 kJ/mol) than for the parent stefins (28 +/- 3 kJ/mol). In pH denaturation, unlike stefin B, neither chimeric mutant unfolds to I(N) below pH 5.4. At pH 3, where stefin B forms a molten globule and stefin A is native, both A37B and A61B show increased ANS fluorescence and aggregate visibly. Dimers at pre-denaturation conditions are observed in all the proteins under study, but they remain "trapped" only in stefin A.

Human recombinant pro-dipeptidyl peptidase I (cathepsin C) can be activated by cathepsins L and S but not by autocatalytic processing

Human dipeptidyl peptidase I was expressed in the insect cell/baculovirus system and purified in its active (rhDPPI) and precursor (pro-rhDPPI) forms. RhDPPI was very similar to the purified enzyme (hDPPI) with respect to glycosylation, enzymatic processing, oligomeric structure, CD spectra, and catalytic activity. The precursor, which was a dimer, could be activated approximately 2000-fold with papain. Cathepsin L efficiently activated pro-rhDPPI in vitro at pH 4.5 (k(app) approximately 2 x 10(3) min(-)(1) M(-)(1)), and two cleavage pathways were characterized. The initial cleavage was within the pro region between the residual pro part and the activation peptide. Subsequently, the activation peptide was cleaved from the catalytic region, and the latter was cleaved into the heavy and light chains. Alternatively, the pro region was first separated from the catalytic region. Cathepsin S was a less efficient activating enzyme. Cathepsin B and rhDPPI did not activate pro-rhDPPI, and the proenzyme was incapable of autoactivation. Incubation of both pro-rhDPPI and rhDPPI with cathepsin D resulted in degradation. Cystatin C and stefins A and B inhibited rhDPPI with K(i) values in the nanomolar range (K(i) = 0.5-1.1 nM). The results suggest that cathepsin L could be an important activator of DPPI in vivo and that cathepsin D and possibly the cystatins may contribute to DPPI downregulation.

Lysosomal protease pathways to apoptosis. Cleavage of bid, not pro-caspases, is the most likely route

We investigated the mechanism of lysosome-mediated cell death using purified recombinant pro-apoptotic proteins, and cell-free extracts from the human neuronal progenitor cell line NT2. Potential effectors were either isolated lysosomes or purified lysosomal proteases. Purified lysosomal cathepsins B, H, K, L, S, and X or an extract of mouse lysosomes did not directly activate either recombinant caspase zymogens or caspase zymogens present in an NT2 cytosolic extract to any significant extent. In contrast, a cathepsin L-related protease from the protozoan parasite Trypanosoma cruzi, cruzipain, showed a measurable caspase activation rate. This demonstrated that members of the papain family can directly activate caspases but that mammalian lysosomal members of this family may have been negatively selected for caspase activation to prevent inappropriate induction of apoptosis. Given the lack of evidence for a direct role in caspase activation by lysosomal proteases, we hypothesized that an indirect mode of caspase activation may involve the Bcl-2 family member Bid. In support of this, Bid was cleaved in the presence of lysosomal extracts, at a site six residues downstream from that seen for pathways involving capase 8. Incubation of mitochondria with Bid that had been cleaved by lysosomal extracts resulted in cytochrome c release. Thus, cleavage of Bid may represent a mechanism by which proteases that have leaked from the lysosomes can precipitate cytochrome c release and subsequent caspase activation. This is supported by the finding that cytosolic extracts from mice ablated in the bid gene are impaired in the ability to release cytochrome c in response to lysosome extracts. Together these data suggest that Bid represents a sensor that allows cells to initiate apoptosis in response to widespread adventitious proteolysis.

Recombinant anti-stefin A Fab fragment: sequence analysis of the variable region and expression in Escherichia coli

Human stefin A is an inhibitor of lysosomal cysteine proteinases cathepsin B, H, L and S. In the present report we describe the cloning and expression of anti-stefin A Fab fragment A22 in E. coli. We have determined the nucleotide sequences of the antibody heavy and light chain and compared them to the murine immunoglobulin germ line sequences. Expression of the two antibody chains was achieved using a single vector with a PhoA promoter and coding regions placed after the signal sequences, directing them to the periplasmic space. The A22 Fab fragment was extracted from the periplasmic space and expression was confirmed by Western blot analysis. The recombinant A22 Fab fragment had an affinity for stefin A comparable to the original monoclonal antibody, as determined by ELISA.

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of approximately 33 kDa and pI 5.1-5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (Ki = 1.7-15.0 nM), but poorly or not at all by stefin B (Ki > 250 nM) and L-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1' position, although the enzyme cleaved all P1' residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (kcat/Km approximately 5.0 x 103 M-1.s-1) were degraded approximately 25-fold less efficiently than the carboxypeptidase substrates (kcat/Km approximately 120.0 x 103 M-1.s-1).

Saxiphilin, a saxitoxin-binding protein with two thyroglobulin type 1 domains, is an inhibitor of papain-like cysteine proteinases

The type 1 domain of thyroglobulin is a protein module (Thyr-1) that occurs in a variety of secreted and membrane proteins. Several examples of Thyr-1 modules have been previously identified as inhibitors of the papain family of cysteine proteinases. Saxiphilin is a neurotoxin-binding protein from bullfrog and a homolog of transferrin with a pair of such Thyr-1 modules located in the N-lobe. Saxiphilin is now characterized as a potent inhibitor of three cysteine proteinases as follows: papain, human cathepsin B, and cathepsin L. The stoichiometry of enzyme inhibition reveals that both Thyr-1 domains of saxiphilin inhibit papain (apparent K(i) = 1. 72 nm), but only one of these domains inhibits cathepsin B (K(i) = 1. 67 nm) and cathepsin L (K(i) = 0.02 nm). Physical association of saxiphilin and papain blocked from turnover at the active-site cysteine residue can be detected by cross-linking with glutaraldehyde. The rate of association of saxiphilin and cathepsin B is strongly pH-dependent with an optimum at pH 5.2, reflecting control by at least two H(+)-titratable groups. These results further demonstrate that various Thyr-1 domains are selective inhibitors of cysteine proteinases with utility in the study of protein interactions and degradation.

Equistatin, a protease inhibitor from the sea anemone actinia equina, is composed of three structural and functional domains

A cDNA encoding a precursor of equistatin, a potent cysteine and aspartic proteinase inhibitor, was isolated from the sea anemone Actinia equina. The deduced amino acid sequence of a 199-amino-acid residue mature protein with 20 cysteine residues, forming three structurally similar thyroglobulin type-1 domains, is preceded by a typical eukaryotic signal peptide. The mature protein region and those coding for each of the domains were expressed in the periplasmic space of Escherichia coli, isolated, and characterized. The whole recombinant equistatin and its first domain, but not the second and third domains, inhibited the cysteine proteinase papain (K(i) 0.60 nM) comparably to natural equistatin. Preliminary results on inhibition of cathepsin D, supported by structural comparison, show that the second domain is likely to be involved in activity against aspartic proteinases.

Crystal structure of cathepsin X: a flip-flop of the ring of His23 allows carboxy-monopeptidase and carboxy-dipeptidase activity of the protease

BACKGROUND

Cathepsin X is a widespread, abundantly expressed papain-like mammalian lysosomal cysteine protease. It exhibits carboxy-monopeptidase as well as carboxy-dipeptidase activity and shares a similar activity profile with cathepsin B. The latter has been implicated in normal physiological events as well as in various pathological states such as rheumatoid arthritis, Alzheimer's disease and cancer progression. Thus the question is raised as to which of the two enzyme activities has actually been monitored.

RESULTS

The crystal structure of human cathepsin X has been determined at 2.67 A resolution. The structure shares the common features of a papain-like enzyme fold, but with a unique active site. The most pronounced feature of the cathepsin X structure is the mini-loop that includes a short three-residue insertion protruding into the active site of the protease. The residue Tyr27 on one side of the loop forms the surface of the S1 substrate-binding site, and His23 on the other side modulates both carboxy-monopeptidase as well as carboxy-dipeptidase activity of the enzyme by binding the C-terminal carboxyl group of a substrate in two different sidechain conformations.

CONCLUSIONS

The structure of cathepsin X exhibits a binding surface that will assist in the design of specific inhibitors of cathepsin X as well as of cathepsin B and thereby help to clarify the physiological roles of both proteases.

Lysosomal cysteine proteases: more than scavengers

Lysosomal cysteine proteases were believed to be mainly involved in intracellular protein degradation. Under special conditions they have been found outside lysosomes resulting in pathological conditions. With the discovery of a series of new cathepsins with restricted tissue distributions, it has become evident that these enzymes must be involved in a range of specific cellular tasks much broader than as simple housekeeping enzymes. It is therefore timely to review and discuss the various physiological roles of mammalian lysosomal papain-like cysteine proteases as well as their mechanisms of action and the regulation of their activity.

The high stability of cruzipain against pH-induced inactivation is not dependent on its C-terminal domain

Unlike mammalian lysosomal cysteine proteases, the trypanosomal cysteine protease cruzipain contains a 130-amino acid residue C-terminal domain, in addition to the catalytic domain, and it is stable at neutral pH. The endogenous (with C-terminal domain) and recombinant (without C-terminal domain) cruzipains exhibit similar stabilities at both acid (k(inac)=3.1x10(-3) s(-1) and 4.4x10(-3) s(-1) at pH 2.75 for endogenous and recombinant cruzipain, respectively) and alkaline pH (k(inac)=3.0x10(-3) s(-1) and 3. 7x10(-3) s(-1) at pH 9.15 for endogenous and recombinant cruzipain, respectively). The pH-induced inactivation, which is a highly pH dependent first order process, is irreversible and accompanied by significant changes of secondary and tertiary structure as revealed by circular dichroism measurements. The different stability of cruzipain as compared to related proteases, is therefore due mainly to the different number, nature and distribution of charged residues within the catalytic domain and not due to addition of the C-terminal domain.

Cysteine proteinase cathepsin H in tumours and sera of lung cancer patients: relation to prognosis and cigarette smoking

In order to evaluate the role of cysteine peptidase cathepsin H (Cath H) in human lung cancer its protein levels were determined in 148 pairs of lung tumour tissue and adjacent non-tumourous lung parenchyma using the enzyme-linked immunosorbent assay technique. Additionally, Cath H levels were determined in sera of 171 patients with malignant tumours, 34 patients with benign lung diseases and 47 healthy controls. The median level of Cath H in tumour tissue was 0.64 times that in the corresponding lung parenchyma. Relating tumour levels with histological type we found higher Cath H levels in small-cell and adenocarcinomas and lower levels in squamous cell carcinoma, large-cell carcinoma and secondary tumours. A significant difference in Cath H level between lung tumour tissue and non-tumourous lung parenchyma was associated with the group of cigarette smokers (156 vs 263 ng mg(-1) protein, P < 0.001). For this group of patients Cath H tumour levels correlated with the survival rate, while for the entire patient population this was not the case. Smokers with high tumour levels of Cath H experienced poor survival. Cath H was significantly higher in sera of patients with malignant and benign lung diseases than in control sera (P < 0.001). The increase was significant for all histological types, being the highest in small-cell and squamous cell carcinomas. Our study reveals that in lung tumours there is different behaviour of Cath H compared with other cysteine peptidases, e.g. cathepsin B and cathepsin L. Variations between tissue and serum levels of Cath H indicate either reduced expression or enhanced secretion of this enzyme in lung tumours.

Structure-based development of pyridoxal propionate derivatives as specific inhibitors of cathepsin K in vitro and in vivo

We found that pyridoxal phosphate shows considerable inhibition of cathepsins. CLIK-071, in which the phosphate ester of position 3 of pyridoxal phosphate was replaced by propionate, strongly inhibited cathepsin B. Three new types of synthetic pyridoxal propionate derivatives showing specific inhibition of cathepsin K were developed. New synthetic pyridoxal propionate derivatives, -162, -163, and -164, in which the methyl arm of position 6 of CLIK-071 was additionally modified, strongly inhibited cathepsin K and cathepsin S weakly, but other cathepsins were not inhibited. CLIK-166, in which the position 4 aldehyde of CLIK-071 is replaced by a vinyl radical and position 5 is additionally modified, showed cathepsin K-specific inhibition at 10(-5) M. Pit formation due to bone collagen degradation by cathepsin K of rat osteoclasts was specifically suppressed by administration of CLIK-164, but not by inhibitors of cathepsin L or B.

Cloning and expression of functional equistatin

Equistatin is a 199-residue protein composed of three thyroglobulin type-1 domains. It strongly inhibits cysteine proteinases as well as the aspartic proteinase cathepsin D. In order to initiate structure-function studies by protein engineering, a cDNA library from sea anemone, Actinia equina, was screened. A positive clone of 888 nucleotides was shown to encode a protein of 231 amino acids, including the signal sequence. The mature protein region was amplified by PCR, cloned into the pET22b(+)cas expression vector and expressed in Escherichia coli. Isolation of active recombinant equistatin required only one purification step, the His-tag affinity column. The protein displays physical and inhibitory properties closely similar to the native inhibitor.

Inhibition mechanism of cathepsin L-specific inhibitors based on the crystal structure of papain-CLIK148 complex

Papain was used as an experimental model structure to understand the inhibition mechanism of newly developed specific inhibitors of cathepsin L, the papain superfamily. Recently, we developed a series of cathepsin L-specific inhibitors which are called the CLIK series [(1999) FEBS Lett. 458, 6-10]. Here, we report the complex structure of papain with CLIK148, which is a representative inhibitor from the CLIK series. The inhibitor complex structure was solved at 1.7 A resolution with conventional R 0.177. Unlike other epoxisuccinate inhibitors (E64, CA030, and CA074), CLIK148 uses both prime and nonprime sites, which are important for the specific inhibitory effect on cathepsin L. Also, the specificity for cathepsin L could be explained by the existence of Phe in the P2 site and hydrophobic interaction of N-terminal pyridine ring.

Autocatalytic processing of recombinant human procathepsin B is a bimolecular process

Cathepsin B and other lysosomal cysteine proteinases are synthesized as inactive zymogens, which are converted to their mature forms by other proteases or by autocatalytic processing. Procathepsin B autoactivation was shown in vitro at pH 4.5 to be a bimolecular process with K(s) and k(cat) values of 2.1+/-0.9 microM and 0.12+/-0.02 s(-1)6.0. However, in the presence of 0.5 microg/ml of dextran sulfate, relatively rapid processing is observed even at pH 6.5 (t(1/2) approximately 90 min), suggesting that glycosaminoglycans are involved in in vivo processing of lysosomal cysteine proteases.

Structure based development of novel specific inhibitors for cathepsin L and cathepsin S in vitro and in vivo

Specific inhibitors for cathepsin L and cathepsin S have been developed with the help of computer-graphic modeling based on the stereo-structure. The common fragment, N-(L-trans-carbamoyloxyrane-2-carbonyl)-phenylalanine-dimethyla mide, is required for specific inhibition of cathepsin L. Seven novel inhibitors of the cathepsin L inhibitor Katunuma (CLIK) specifically inhibited cathepsin L at a concentration of 10(-7) M in vitro, while almost no inhibition of cathepsins B, C, S and K was observed. Four of the CLIKs are stable, and showed highly selective inhibition for hepatic cathepsin L in vivo. One of the CLIK inhibitors contains an aldehyde group, and specifically inhibits cathepsin S at 10(-7) M in vitro.

Interaction of cystatin C variants with papain and human cathepsins B, H and L

Recombinant human cystatin C and two of its mutants were expressed in Escherichia coli. The recombinant inhibitor was found to be identical to authentic cystatin C as judged by isoelectric focusing (pI 9.2) and kinetics of inhibition of papain and human cathepsins B, H and L. N-terminal truncation of 8 residues resulted in a decrease of isoelectric point (pI 7.8), but the inhibitory properties were similar to those of recombinant cystatin C, suggesting that Leu9 is a critical residue for the inhibition. The mutation of Trp106 to Ser, however, resulted in a decreased affinity of the inhibitor for the enzymes tested, with the largest effect on cathepsin B inhibition (approximately 100-fold increase in Ki).

Differences in the effects of TFE on the folding pathways of human stefins A and B

Trifluoroethanol (TFE) has been used to probe differences in the stability of the native state and in the folding pathways of the homologous cysteine protein inhibitors, human stefin A and B. After complete unfolding in 4.5 mol/L GuHCl, stefin A refolded in 11% (vol/vol) TFE, 0.75 mol/L GuHCl, at pH 6.0 and 20 degrees C, with almost identical first-order rate constants of 4.1 s-1 and 5.5 s-1 for acquisition of the CD signal at 230 and 280 nm, respectively, rates that were markedly greater than the value of 0.11 s-1 observed by the same two probes when TFE was absent. The acceleration of the rates of refolding, monitored by tyrosine fluorescence, was maximal at 10% (vol/vol) TFE. Similar rates of refolding (6.2s-1 and 7.2 s-1 for ellipticity at 230 and 280 nm, respectively) were observed for stefin A denatured in 66% (vol/vol) TFE, pH 3.3, when refolding to the same final conditions. After complete unfolding in 3.45 mol/L GuHCl, stefin B refolded in 7% (vol/vol) TFE, 0.57 mol/L GuHCl, at pH 6.0 and 20 degrees C, with a rate constant for the change in ellipticity at 280 nm of 32.8 s-1; this rate was only twice that observed when TFE was absent. As a major point of distinction from stefin A, the refolding of stefin B in the presence of TFE showed an overshoot in the ellipticity at 230 nm to a value 10% greater than that in the native protein; this signal relaxed slowly (0.01 s-1) to the final native value, with little concomitant change in the near-ultraviolet CD signal; the majority of this changes in two faster phases. After denaturation in 42% (vol/vol) TFE, pH 3.3, the kinetics of refolding to the same final conditions exhibited the same rate-limiting step (0.01 s-1) but were faster initially. The results show that similarly to stefin A, stefin B forms its hydrophobic core and predominant part of the tertiary structure faster in the presence of TFE. The results imply that the alpha-helical intermediate of stefin B is highly structured. Proteins 1999;36:205-216.

The p41 fragment story

The discovery of a fragment from the p41 form of invariant chain tightly bound to cathepsin L provided the first direct link between MHC class II molecules and the regulation of activity of lysosomal cysteine proteases. We recently determined the crystal structure of this p41 invariant chain fragment in complex with cathepsin L [EMBO J. 18, 793-803 (1999)]. This structure explains the specificity of the observed interactions and actually provides a tool, which can be utilized by means of molecular biology, to explore and understand the specificity of thyroglobulin type I domains and thus allow the design of specific inhibitors of papain-like cysteine proteases. The structure further supports the hypothesis that the thyroglobulin type I and II domains present in various proteins, sometimes in multiple repeats, are regulatory elements of the processing of these proteins by proteolytic cleavage.

Mutational analysis of two stefin A epitopes

Stefin A, an intracellular inhibitor of cysteine proteinases, is expressed most abundantly in epithelial cells and in cells of lymphatic origin. In order to study its role in normal and pathological conditions we have prepared and characterized monoclonal antibodies against recombinant stefin A. Two high affinity monoclonal antibodies (mAbs) (A22 and C52) were tested for binding to free and papain-complexed stefin A and to a chimeric inhibitor, consisting of 61 amino acid residues of stefin A and 37 carboxy-terminal residues of stefin B. mAb A22 recognized not only free stefin A but also stefin A in complex with papain. The mAbs were further tested for their cross-reactivity against stefin A and B isolated from different mammalian species. On the basis of sequence similarity and tertiary structure of human stefin A we have prepared three mutants - Glu33Lys, Asp61Gly and Asn62Tyr and their reactivity with the mAbs was tested. The binding affinities of mAb A22 for the Asp61Gly and Asn62Tyr mutants were significantly lower, indicating thatthe two amino acids are part of the stefin A epitope recognized by A22. The binding of both mAbs to the mutants Gly4Arg and Gly4Glu was comparable to wild-type stefin A.

Cathepsin S and cruzipain are inhibited by equistatin from Actinia equina

Cathepsin S has been isolated for the first time from human tissue. It has a molecular mass of 24 kDa and an isoelectric point in the range of 8.2 to 8.6. The enzyme is inhibited by equistatin, which belongs to the thyropins, a new family of protein inhibitors, with an inhibition constant of Ki = 0.40 +/- 0.07 nM. Cruzipain, a cathepsin L-like enzyme sharing a 130 amino acid long C-terminal extension, is also strongly inhibited by equistatin (Ki = 0.028 +/- 0.006 nM). Together with previously reported data, these results further indicate that a functional heterogeneity exists among thyropin inhibitors, as demonstrated by their interaction with cathepsin S and cruzipain.