Comparative studies of two cathepsin B isozymes from porcine spleen. Isolation, polypeptide chain arrangements, and enzyme specificity

Calcineurin orchestrates dimorphic transitions, antifungal drug responses and host-pathogen interactions of the pathogenic mucoralean fungus Mucor circinelloides

Calcineurin plays essential roles in virulence and growth of pathogenic fungi and is a target of the natural products FK506 and Cyclosporine A. In the pathogenic mucoralean fungus Mucor circinelloides, calcineurin mutation or inhibition confers a yeast-locked phenotype indicating that calcineurin governs the dimorphic transition. Genetic analysis in this study reveals that two calcineurin A catalytic subunits (out of three) are functionally diverged. Homology modeling illustrates modes of resistance resulting from amino substitutions in the interface between each calcineurin subunit and the inhibitory drugs. In addition, we show how the dimorphic transition orchestrated by calcineurin programs different outcomes during host-pathogen interactions. For example, when macrophages phagocytose Mucor yeast, subsequent phagosomal maturation occurs, indicating host cells respond appropriately to control the pathogen. On the other hand, upon phagocytosis of spores, macrophages fail to form mature phagosomes. Cytokine production from immune cells differs following exposure to yeast versus spores (which germinate into hyphae). Thus, the morphogenic transition can be targeted as an efficient treatment option against Mucor infection. In addition, genetic analysis (including gene disruption and mutational studies) further strengthens the understanding of calcineurin and provides a foundation to develop antifungal agents targeting calcineurin to deploy against Mucor and other pathogenic fungi.

Purification of bovine cathepsin B: proteomic characterization of the different forms and production of specific antibodies

Cathepsin B (EC 3.4.22.1) has been highly purified (14,225 fold) from bovine kidney by a rapid procedure that included the preparation of an enriched lysosomal extract, a selective fractionation with ammonium sulphate, size-exclusion chromatography, two cation-exchange chromatographies, and anion-exchange chromatography on diethylaminoethyl-Sephacel. After the last purification step, two hydrolytic peaks against Z-Phe-Arg-AMC were separated from each other, a minor peak corresponding to the cathepsin B single-chain form and a major one representing the double-chain form of cathepsin B. The single-chain form showed a molecular mass of 31 kDa on sodium dodecyl sulphate - polyacrylamide gel electrphoresis (PAGE) under reducing conditions, whereas the heavy chain of the double-chain form appeared as a doublet with molecular masses of 23.4 and 25 kDa, respectively. The identity of the different cathepsin B isoforms and the quality of the final enzyme preparation were confirmed by using two types of antibodies, one against a synthetic peptide sequence and one against purified cathepsin B. The proteomic study confirmed the identity of the different SDS-PAGE protein bands as cathepsin B isoforms and allowed the comparison and study of some structural differences between them at the level of their primary structures.

Miltpain, new cysteine proteinase from the milt of chum salmon, Oncorhynchus keta

A new cysteine proteinase, salmon miltpain, was isolated and purified from the milt of chum salmon (Oncorhynchus keta). Native molecular mass was estimated as 67,000 by gel filtration column chromatography (Shodex WS2003) and 22,300 by SDS-polyacrylamide gel electrophoresis. Isoelectoric point was determined to be 3.9 by isoelectric focusing. The first 15 amino acid residues in the N-terminal region were LPSFLY-AEMVGYNIL. The cysteine proteinase, which had a pH optimum of 6.0 for Z-Arg-Arg-MCA hydrolysis, required a thiol-reducing reagent for activation and was inhibited by E-64, iodacetamide, CA-074 Me, TLCK, TPCK and ZPCK. The cysteine proteinase exhibited unique substrate specificity toward paired basic residues such as Lys-Arg, Arg-Arg at the subsites of P2-P1 and had a K(m) of 16.3 microM and kcat of 20.3 s-1 with Z-Arg-Arg-MCA as substrate and a K(m) of 52.9 microM and kcat of 1.79 s-1 with Z-Phe-Arg-MCA. This proteinase was found to considerably hydrolyze basic proteins such as histone, salmine and clupaine but not milk casein.

Characterization and localization of cathepsin B proteinases expressed by adult Ancylostoma caninum hookworms

The hookworm Ancylostoma caninum induces human eosinophilic enteritis (EE), probably via allergic responses to its secretions. Cysteine and metallo-proteinases may be the components of these secretions that elicit hypersensitivity reactions. In order to characterize genes encoding cysteine proteinases (CP) secreted by A. caninum, an adult hookworm cDNA library was constructed and screened with a cloned fragment of a hookworm CP gene. This fragment was obtained using consensus oligonucleotide, CP-gene-specific primers in the polymerase chain reaction. cDNAs encoding two CPs were obtained from the library and sequenced. The first gene, AcCP-1, encoded a cathepsin B-like zymogen CP of 343 amino acids (aa), predicted to be processed in vivo into a mature CP of 255 aa. Closest nucleotide identities were to Haemonchus contortus cysteine protease (61%) and to human cathepsin B (60%). The second gene, AcCP-2, encoded a mature CP of 254 aa, that showed 86% identity to AcCP-1, and 58% and 47% identity to bovine cathepsin B and human cathepsin B, respectively. Rabbit antisera raised against recombinant AcCP-1 reacted with esophageal, amphidial and excretory glands in formalin-fixed, paraffin embedded sections of both male and female adult hookworms, and with an antigen of approx. 40 kDa in Western blot analysis of excretory/secretory products from adult hookworms. Together, these immuno-hybridization results strongly suggest that the CP encoded by the AcCP-1 gene is secreted by hookworms. These are the first reported CP genes from hookworms. Proteinases encoded by these genes may be responsible for the CP activity that we have shown previously to be secreted by adult A. caninum.

Rat epidermal cathepsin B: purification and characterization of proteolytic properties toward filaggrin and synthetic substrates

The aim of this study was to purify epidermal cathepsin B from rat skin and investigate its proteolytic activities on filaggrin and several synthetic substrates. The molecular weight of purified monomeric cathepsin B was estimated to be 30 kDa by SDS-polyacrylamide gel electrophoresis. The amino acid composition, similar to that of liver cathepsin B, indicated the enzyme to be an acidic protease. The enzyme had strong hydrolytic activity toward N-benzyloxy-carbonyl-L-arginyl-L-arginine-7-amido-4-methylcoumarin (Z-Arg-Arg-MCA) (152 mU/mg) and N-benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methylcoumarin (424 mU/mg), but had no proteolytic activity toward L-arginine-7-amido-4-methylcoumarin. The Km value for Z-Arg-Arg MCA was 0.34 mM and pH optimum was 5.5. Cathepsin B degraded rat epidermal filaggrin into small fragments at pH 4.0 and 5.5., and was inhibited by a specific cysteine proteinase inhibitor, N-[N-(L-3-trans-carboxyoxirane-2-carbonyl)L-leucyl]- agmatin. This study demonstrated that filaggrin was susceptible to degradation by cathepsin B. Such an action may have relevance to skin differentiation in which acid proteases are thought to participate.

Nucleotide sequence of bovine preprocathepsin B. A study of polymorphism in the protein coding region

A cDNA encoding bovine procathepsin B was isolated. The deduced amino acid sequence revealed that a stop (TAG) codon, instead of a Trp-257 codon (TGG), generates in bovine a cathepsin B precursor four amino acids shorter than in other species. Because micro-heterogeneities were previously reported in the cathepsin B primary structure, sequence polymorphism in the protein coding region was then investigated by PCR sequencing of genomic fragments and RNase protection assays. Experiments performed with 12-15 animals of three breeds did not reveal any difference with our cDNA sequence. We conclude that sequence polymorphism in bovine cathepsin B is a rare event, and can only result from the expression of different alleles of a unique gene.

Human osteoclastomas contain multiple forms of cathepsin B

During bone resorption, the osteoclast secretes hydrolytic enzymes into the sealing zone which it creates between itself and the bone surface. Since this environment is acidic, proteinases active at low pH must therefore be responsible for degrading the bone matrix, which is largely composed of type I collagen. To investigate these enzymes, we have used human osteoclastomas as the starting material. Sequential chromatography on S-Sepharose, phenyl-Sepharose, heparin-Sepharose and Sephacryl S-200HR resulted in the separation of six cysteine proteinase activities. These proteinases have Mr values ranging from 20,000 to 42,000. The pH profiles of activity showed optima between 3.5-6.0 for both synthetic substrates and type I collagen. All the proteinases were able to degrade soluble and insoluble type I collagen. The kinetics of hydrolysis using Z-Phe-Arg-NHMec and Bz-Phe-Val-Arg-NHMec as substrates resulted in values within the range expected for cathepsin B. The six activities were all inhibited by the cysteine proteinase inhibitors antipain, chymostatin, leupeptin and E-64. The rate constants of inactivation using Z-Phe-Tyr-(O-t-Bu)CHN2 were also similar to the published rates for cathepsin B. Antibodies to cathepsin B reacted with all activities. These antibodies localised the enzyme activities to the osteoclast within the tumour. Northern blotting using a cDNA probe to cathepsin B revealed three species of mRNA transcripts. These results suggest that multiple forms of cathepsin B-like proteinases are involved in osteoclastic bone resorption.

The early and late processing of lysosomal enzymes: proteolysis and compartmentation

Lysosomal enzymes are subjected to a number of modifications including carbohydrate restructuring and proteolytic maturation. Some of these reactions support lysosomal targeting, others are necessary for activation or keeping the enzyme inactive before being segregated, while still others may be adventitious. The non-segregated fraction of the enzyme is secreted and can be isolated from the medium. It is considered that the secreted lysosomal enzymes fulfill certain physiological and pathophysiological roles. By comparing the secreted and the intracellular enzymes it is possible to distinguish between the reactions that occur before and after the segregation. In this review the reactions that may influence the segregation are referred to as the early processing and those characteristic for the enzymes isolated from lysosomal compartments as the late processing. The early processing is characterized mainly by modifications of carbohydrate side chains. In the late processing, proteolytic fragmentation represents the most conspicuous changes. The review focuses on the compartmentation of the reactions and the proteolytic fragmentation of lysosomal enzyme precursors. While a plethora of proteolytic reactions are involved, our knowledge of the proteinases responsible for the particular maturation reactions remains very limited. The review points also to work with cells from patients affected with lysosomal storage disorders, which contributed to our understanding of the lysosomal apparatus.

Cysteine endopeptidase activity levels in normal human tissues, colorectal adenomas and carcinomas

We have assayed cysteine endopeptidase activities in 17 types of normal human tissue and in matched sets of colorectal mucosa, adenoma and carcinoma samples. Our data indicate that cathepsin B enzyme levels vary 70-fold and cathepsin L enzyme levels vary 20-fold from one normal tissue to another. Cathepsin B specific activity in normal tissues fell into 3 categories. High activity, with a mean of 156.7 +/- 41.5 nmoles min-1 mg-1 protein, was measured in liver, thyroid, kidney and spleen; intermediate activity, with a mean of 60.2 +/- 8.3 nmoles min-1 mg-1 protein, was measured in heart, colon, adrenal and lung; and low activity, with a mean of 18.4 +/- 9.7 nmoles min-1 mg-1 protein, was measured in prostate, testis, nerve, stomach, pancreas, brain, skeletal muscle, skin and breast. Cathepsin L specific activity fell into 2 categories. High activity, with a mean of 51.1 +/- 4.9 nmoles min-1 mg-1 protein, was measured in thyroid, liver and kidney; and low activity, with a mean of 11.4 +/- 5.5 nmoles min-1 mg-1 protein, was measured in spleen, colon, heart, adrenal, lung, testis, brain, nerve, skin, stomach, pancreas, skeletal muscle, prostate and breast. Our characterization of these enzyme levels provides a reference standard for normal cathepsin B and L activities in human tissues that should enhance the detection of their deregulation in disease states. For example, in studies of colorectal carcinoma and normal mucosa, we observed a significant tumor-specific increase in cathepsin B and L activities with particularly high activity levels in earlier (Dukes' A and B) compared to later (Dukes' C and D) stages of colorectal cancer. In contrast, adenomas from colorectal cancer patients expressed normal levels of cathepsin B activity, providing evidence that the increase in expression of cathepsin B may be a sensitive marker for progression from the pre-malignant to the malignant state in the development of colorectal cancer.

High-performance liquid chromatographic method for the simultaneous purification of cathepsins B, H and L from human liver

A high-performance liquid chromatographic procedure for the isolation of the three cysteine proteinases, namely cathepsins B, H and L, is described. The method is based on the following four steps. (1) A classical AcA 44 gel permeation separation with a 30-70% ammonium sulphate fraction from the human liver homogenate is used to remove the non-enzymic high-molecular-mass components. (2) Preparative cation-exchange chromatography on a CM-SW TSK column can separate the three proteinases. (3) An anion-exchange step on a semi-preparative DEAE-SW TSK column for the cathepsin H fraction is used to remove a small amount of cathepsins B and L activities. (4) The three separated enzymes are purified on an analytical TSK gel 2000 SW column. The purity of each enzyme is assessed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and electrofocusing on polyacrylamide gels. To check the activities of the purified proteinases, the kinetic constants [Michaelis constant (KM) and catalytic constant (Kcat)] and the ratio Kcat/KM against the fluorigenic substrates Arg-NH-Mec, Z-Arg-Arg-NH-Mec and Z-Phe-Arg-NH-Mec after active-site titration using E-64, were determined. Z-Phe-Phe-CNH2 was also used as a specific inhibitor of cathepsin L. This method requires only 6 g of human liver, and gives a high yield of the three lysosomal cysteine-proteinases: thus, about 150 micrograms of cathepsin B and 50 micrograms each of cathepsins L and H are obtained in a single run.

Molecular forms of cathepsin B in rat thyroid cells (FRTL5): comparison with molecular forms in liver (Hep G2) and insulin-secreting cells (HIT T15)

A radiolabelled peptide chloromethyl ketone (125I-tyrosyl-L-alanyl-L-lysyl-L-arginine chloromethyl ketone) was used to affinity-label proteinases in rat thyroid cells (FRTL5). Two major proteins of 34 kDa and 32 kDa were affinity-labelled. Inhibitor competition studies demonstrated that both proteins were cysteine proteinases. Over the range pH 5-8, they exhibited maximum activity against the affinity probe at pH 5. They were soluble rather than membrane-bound and were both glycosylated. The 32 kDa proteinase but not the 34 kDa proteinase was immunoprecipitated using an anti-rat liver cathepsin B antibody. The data suggested that these proteinases were molecular forms of cathepsin B. The affinity-labelled proteins in the thyroid were compared with those in an insulin-secreting cell line (HIT T15) and a liver cell line (Hep G2). Two molecular forms of cathepsin B of Mr 39,000 and 33,000 were identified in the insulin-secreting cell line and a single form of Mr 34,000 in the liver cell line. These molecular forms of cathepsin B may reflect the different functions and compartmentation of cathepsin B in these cells.

Action of rat liver cathepsin B on bradykinin and on the oxidized insulin A-chain

Rat liver cathepsin B was tested for its peptide-bond specificity against bradykinin and the oxidized insulin A-chain. Bradykinin was shown to be resistant to the action of cathepsin B. One possible reason for this resistance is the proline content of the peptide and the discrimination against proline residues at three or four subsites of cathepsin B. Oxidized insulin A-chain was degraded by a peptidyl dipeptidase activity. Three dipeptides were cleaved from the C-terminal part of the insulin A-chain after having been incubated for 2 h (molar ration E:S = 1:2800) and six dipeptides were released after a longer digestion (10 h, E:S = 1:575).