Preparative purification of the rat mast cell chymase: characterization and interaction with granule components

Impact of Mast Cell Chymase on Renal Disease Progression

Chymase, a serine protease found in mast cell granules, is released into the interstitium following injury or inflammation. Chymase is the primary ACE-independent pathway of angiotensin II formation, and also functions to activate TGF-beta and other promoters of extracellular matrix degradation, thereby playing a role in tissue remodeling. In the diseased kidney, chymase-containing mast cells markedly increase and their density correlates with tubulointerstitial fibrosis severity. Studies in humans support the pathologic role of chymase in diabetic nephropathy, while animal studies form the basis for the importance of increased chymase-dependent angiotensin II formation in progressive hypertensive, diabetic and inflammatory nephropathies. Moreover, humans with kidney disease express chymase in diseased blood vessels in concordance with significantly elevated plasma chymase levels. Conversely, specific chymase inhibitors attenuate angiotensin II production and renal fibrosis in animal models, suggesting their potential therapeutic benefit in human nephropathy, where chymase-containing mast cells accumulate and contribute to progressive disease.

Simultaneous development of acute disseminated encephalomyelitis and Guillain-Barré syndrome associated with H1N1 09 influenza vaccination

A 36-year-old man was admitted to our hospital because of urinary retention and muscle weakness affecting all 4 limbs after receiving a H1N1 09 influenza vaccination. Magnetic resonance imaging demonstrated multiple lesions in his brain and spinal cord. Furthermore, nerve conduction study showed acute sensorimotor neuropathy, and anti-GM2 antibodies were detected in his serum. Based on the temporal association and exclusion of alternative etiologies, we made a diagnosis of acute disseminated encephalomyelitis (ADEM) and Guillain-Barré syndrome (GBS). To our knowledge, this is the first case of co-morbid ADEM and GBS after influenza vaccination with positive anti-ganglioside antibodies.

Ovochymase in amphioxus Branchiostoma belcheri is an ovary-specific trypsin-like serine protease with an antibacterial activity

Ovochymases have been shown to be present in vertebrates; little information is available at present regarding ovochymase in invertebrates. Here we isolated a cDNA encoding an ovochymase homolog from amphioxus Branchiostoma belcheri, named BbOvc. The cDNA contained a 1248bp open reading frame corresponding to a deduced protein of 415 amino acids with a predicted molecular mass of approximately 44.4kDa. Phylogenetic analysis showed that BbOvc was located at the base of its vertebrate counterparts, suggesting that it represents the archetype of vertebrate ovochymases. BbOvc is found to display a tissue- and stage-specific expression pattern, with a predominant expression in the ovary of sexually matured females and in the early stage embryos (1-16-cell embryos). The recombinant ovochymase expressed in vitro shows a trypsin-like activity capable of hydrolysing the trypsin prototypic substrate N(a)-benzoyl-l-arginine ethyl ester (60UBAEE/mg), which can be inhibited by the trypsin-specific inhibitor soybean trypsin inhibitor. It also exhibits an antibacterial activity capable of inhibiting the growth of bacteria like E. coli and V. parahaemolyticus. Taken together, these data indicate that BbOvc is a novel ovochymase with an antibacterial activity and offer first clues to its role as an immune-relevant molecule which may protect the early embryos from pathogenic attacks.

Secretory granule proteoglycans of mast cells and natural killer cells

Proteoglycan research on cells that participate in immune responses has progressed from the early novel finding that heparin proteoglycans are present in the secretory granules of the connective tissue mast cell to the more recent findings that mucosal mast cells and natural killer (NK) cells possess chondroitin sulphate proteoglycans in their granules. Characterization studies of these intracellular proteoglycans have revealed that they all possess peptide cores which are very resistant to proteolytic degradation. Their glycosaminoglycans, however, differ in such parameters as the type of hexosamine, location of sulphation degree of sulphation, or extent of epimerization of the uronic acid. Amino acid compositional analyses of heparin proteoglycans from rat connective tissue mast cells and chondroitin sulphate E proteoglycans from mouse mucosal mast cells indicate that their peptide cores are homologous to, but possibly distinct from one another. It is not yet known if these differences reflect a species variation, are due to different post-translational proteolytic processing, or are the result of expression of distinct genes coding for different peptide cores. The proteoglycans of mast cells and natural killer cells are packaged in the granules with cationic proteins. In mast cells these proteins have been shown to be serine proteases, and when bound to the acidic proteoglycans their enzymic activity is inhibited. Since the type of glycosaminoglycan linked to the proteoglycan has been found to be a characteristic of that cell, the structure of the cell-associated proteoglycan has become one of the markers used to distinguish cells phenotypically. By following the expression of different proteoglycans during differentiation, the relationship of the two subclasses of mast cells has been determined.

Different mast cell mediators produced by different mast cell phenotypes

The activation of mast cells results in the release of a large variety of inflammatory mediators, many of which are preformed and stored within the secretory granules. Exocytosis of the secretory granule contents releases a macromolecular complex composed of proteoglycan and the neutral proteases. The proteases include both endo- and exopeptidases, suggesting the possibility of a concerted action on unknown substrates. Different proteases are expressed by different mast cells originally defined by histochemical and ultrastructural criteria. From adoptive transfer experiments it appears that the mast cell phenotype is profoundly influenced by the microenvironment. Understanding the development and regulation of the mast cell phenotype is being approached by the development of: (1) An in vitro system of differentiation using in vitro-differentiated mast cells which upon co-culture with fibroblasts demonstrate a phenotypic shift; (2) Kirsten virus-transformed mast cells exhibiting a spectrum of phenotypes. These reagents have allowed the isolation and characterization of the cDNAs of the various preformed protein mediators including the secretory granule proteoglycan peptide core, serine proteases and carboxypeptidase. These cDNAs have provided the first probes for the molecular characterization of the mast cell-associated proteoglycan peptide core, a carboxypeptidase A and a 28,000 Mr serine protease.

Vasoconstrictor effect of the angiotensin-converting enzyme-resistant, chymase-specific substrate [Pro(11)(D)-Ala(12)] angiotensin I in human dorsal hand veins: in vivo demonstration of non-ace production of angiotensin II in humans

BACKGROUND

[Pro(11)(D)-Ala(12)] angiotensin I is an ACE-resistant substrate specific for chymase. We used this peptide to determine whether a functionally significant non-ACE angiotensin (Ang) II-generating pathway exists in human dorsal hand veins.

METHODS AND RESULTS

Using a modified Aellig technique, we studied the response to Ang I and [Pro(11)(D)-Ala(12)] Ang I in dorsal hand veins in vivo in patients with coronary heart disease. We measured the venoconstrictor effect of each peptide given before and after a 6.25-mg oral dose of the ACE inhibitor captopril or matching placebo. Placebo or captopril was given in a double-blind, randomized fashion. Ang I induced a mean+/-SEM venoconstrictor response of 45+/-11%, 40+/-10%, 55+/-8%, and 4+/-4% before placebo, after placebo, before captopril, and after captopril, respectively. Hence, the response to Ang I was reproducible and was reduced significantly only after treatment with captopril (P=0.002). [Pro(11)(D)-Ala(12)] Ang I induced a mean venoconstrictor response of 42+/-9%, 49+/-9%, 48+/-10%, and 54+/-11% before placebo, after placebo, before captopril, and after captopril, respectively. Hence, captopril had no significant effect on the response to [Pro(11)(D)-Ala(12)] Ang I.

CONCLUSIONS

We have demonstrated that [Pro(11)(D)-Ala(12)] Ang I is able to induce venoconstriction in humans in vivo. With this specific pharmacological probe, we have shown that a non-ACE pathway capable of generating Ang II exists in human veins in vivo and is potentially functionally important. This pathway is likely to involve the enzyme chymase.

Local angiotensin II-generating system in vascular tissues: the roles of chymase

Roles of each angiotensin II producing enzymes of each of the angiotensin II-producing enzymes were reviewed based on experimental models. In vascular tissues, angiotensin II is potentially cleaved from angiotensin I by angiotensin converting enzyme (ACE) and chymase. It has been confirmed that vascular tissues of humans, monkeys, dogs and hamsters have a chymase-dependent angiotensin II-forming pathway. Much like other hypertensive models, hamster hypertensive models show high levels of vascular ACE activity, but not chymase activity. In hypertensive hamsters, administration of either an ACE inhibitor or an angiotensin II type 1 (AT1) receptor antagonist resulted in similar reductions in blood pressure, suggesting that chymase is not involved in the maintenance of high blood pressure in this model. In monkeys fed a high-cholesterol diet, ACE activity was increased in the atherosclerotic lesions, and an ACE inhibitor and an AT1 receptor antagonist prevented atherosclerosis to a similar degree, suggesting that ACE may be mainly involved in the development of atherosclerosis. After balloon injury in dog vessels, both ACE and chymase activities were locally increased about 3-fold in the injured arteries, and an AT1 receptor antagonist was effective in preventing the intimal formation, but an ACE inhibitor was ineffective. In dog grafted veins, the activities of chymase were increased 15-fold, but those of ACE were increased only 2-fold, and the intimal formation was suppressed by either an AT1 receptor antagonist or a chymase inhibitor. In the normal vascular tissues, ACE plays a crucial role for angiotensin II production, whereas chymase is stored in mast cells in an inactive form. Chymase acquires the ability to form angiotensin II following mast cells activation followed by mast cells activation by a strong stimulus such as occurs in catheter-injury or grafting. Together, these results indicate that chymase plays a major role in the vascular angiotensin II-generating system, particularly in cases of vascular injury.

Role of chymase on vascular proliferation

In the normal state, vascular ACE regulates local angiotensin II formation and plays a crucial role in the regulation of blood pressure, whereas chymase is stored in secretory granules in mast cells and has no enzymatic effects such as angiotensin II-forming activity. Chymase has a maximal activity immediately upon release into the extracellular matrix in vascular tissues after mast cells have been activated by a strong stimulus such as experienced by catheter-injured and grafted vessels. Therefore, chymase plays an important role in forming local angiotensin II when vascular tissues are injured, and inhibition of chymase may be useful for preventing vascular proliferation in grafted vessels and after PTCA (Figure 6).

Chymase-dependent angiotensin II formation in human vascular tissue

BACKGROUND

Some reports have suggested that, in vitro, human heart chymase in homogenates contributes little to angiotensin (Ang) II formation in the presence of natural protease inhibitors such as alpha-antitrypsin. We studied whether chymase bound to heparin, resembling an in vivo form, could contribute to Ang II formation in the presence of natural protease inhibitors.

METHODS AND RESULTS

The Ang II formation was increased time-dependently after incubation in an extract (1 mg of protein/mL) of human vascular tissues containing Ang I. The concentration of Ang II in the extract after incubation for 30 minutes was 1.67+/-0.06 nmol/mL, and we regarded this quantity of Ang II as 100%. The Ang II formation was inhibited 10%, 95%, and 96% by 1 micromol/L lisinopril, 100 micromol/L chymostatin, and 0.1 g/L alpha-antitrypsin, respectively. The extract was applied to a heparin affinity column. After the column was washed with PBS, the eluted PBS contained a weak Ang II-forming activity, which was completely inhibited by lisinopril. The eluted PBS, to which >0.8 mol/L NaCl had been added, showed a strong Ang II-forming activity which was inhibited by chymostatin and alpha-antitrypsin. After the application of the extract, the column was washed with PBS and then an Ang I solution in PBS was applied to the column. The Ang II formation in the PBS eluted from the incubated column was increased time-dependently. The concentration of Ang II in the PBS (1 mL) eluted from the column after incubation for 30 minutes was 2.56+/-0.28 nmol/mL, and we regarded this quantity of Ang II as 100%. To study the effects of inhibitors, the extract (1 mg of protein/mL) was applied to a heparin affinity column (1 mL) which was preequilibrated with PBS (3 mL); 100 micromol/L chymostatin or 0.1 g/L alpha-antitrypsin in PBS (1 mL) was then applied to the column. After the column was washed with PBS (3 mL), Ang I solution (1 mg/mL) in PBS was applied to the column, and the column was incubated for 30 minutes. The Ang II formation in the PBS eluted from the column was suppressed up to 5% by application of chymostatin, although this was not affected by application of alpha-antitrypsin.

CONCLUSIONS

These findings suggest that human chymase bound to heparin plays a functional role in Ang II formation in the presence of natural protease inhibitors such as alpha-antitrypsin.

Functional role of chymase in angiotensin II formation in human vascular tissue

Recent reports suggested that human heart chymase contributed little to angiotensin (Ang) II formation in the presence of natural protease inhibitors such as alpha-antitrypsin. We studied whether chymase could contribute to Ang II formation in the presence of natural protease inhibitors in the homogenate, the extract, and slices of human vascular tissue, and whether these inhibitors affect Ang I-induced vasocontractile responses due to chymase. In the homogenate, lisinopril, chymostatin, and alpha-antitrypsin inhibited the formation of Ang II by 14, 92, and 74%, respectively. In the extract, the inhibition of Ang II formation by lisinopril, chymostatin, and alpha-antitrypsin was 18, 94, and 93%, respectively. In the slices, lisinopril and chymostatin inhibited Ang II formation by 5 and 90%, respectively. However, unlike the homogenate and the extract experiments, only 8% of the Ang II formation was suppressed by alpha-antitrypsin. In isolated human gastroepiploic artery, 30% of Ang I-induced vasoconstriction was blocked by lisinopril, and the rest was completely eliminated by a combination of lisinopril and chymostatin. On the other hand, alpha-antitrypsin was ineffective in blocking Ang I-induced vasoconstriction in the presence of lisinopril, which demonstrates that Ang II formation is dependent on chymase. These findings suggest that chymase in human vascular tissue plays a functional role in Ang II formation in the presence of natural protease inhibitors such as alpha-antitrypsin.

Effect of mast cell granules on the gene expression of nitric oxide synthase and tumour necrosis factor-alpha in macrophages

Previous studies have shown that mast cell granules (MCG) inhibit numerous macrophage functions including tumour cytotoxicity, superoxide and nitric oxide (NO) production, and FCgamma2a receptor-mediated phagocytosis. In this study, the effect of MCG on macrophage TNF alpha and nitric oxide synthase (iNOS) mRNA expression, and the production and fate of TNF alpha were examined. Upon activation with LPS+IFN gamma, macrophages expressed both TNF alpha and iNOS mRNA and produced both TNF alpha and NO. Co-incubation of LPS+IFN gamma-activated macrophages with MCG resulted in dose-dependent inhibition of iNOS mRNA expression. TNF alpha production in the activated macrophages was decreased by MCG, which was associated with a reduction in TNF alpha mRNA expression. MCG were also capable of degrading both macrophage-generated and recombinant TNF alpha. The direct effect of MCG on TNF alpha was partially reversed by a mixture of protease inhibitors. These results demonstrate that MCG decrease the production of NO and TNF alpha by inhibiting macrophage iNOS and TNF alpha gene expression. Furthermore, MCG post-transcriptionally alter TNF alpha levels via proteolytic degradation.

The isolation and purification of a dual specific mast cell-derived protease from parasitised caprine jejunal tissue

A mast cell granule protease has been isolated and purified from nematode-infected caprine jejunal homogenate by FPLC techniques and termed Goat Mast Cell Protease (GMCP). The purification steps were monitored for proteolytic activity against the synthetic substrate carboxybenzoyl-L-lysine thiobenzyl ester (BLT) and the presence of a homogenous protease preparation in the final sample was shown by SDS-PAGE electrophoresis. This protease was compared with enzymatic activity from isolated mucosal mast cells, which demonstrated the putative mast cell-derived source of the purified enzyme. Rabbit antiserum was raised against the protease and through the use of immunohistochemistry and Western blotting techniques the mast cell origin of the protease was confirmed. NH2-Terminal amino acid sequence analysis demonstrated a high degree of homology between GMCP and other previously isolated mast cell proteases including sheep mast cell protease (SMCP). Substrate analysis showed that GMCP also had an unusual dual chymotrypsin-like and trypsin-like activity similar to SMCP and bovine duodenase.

Induction of chymase that forms angiotensin II in the monkey atherosclerotic aorta

Chymase shows a catalytic efficiency in the formation of angiotensin (Ang) II. In the present study, the characterization and primary structure of monkey chymase were determined, and the pathophysiological role of chymase was investigated on the atherosclerotic monkey aorta. Monkey chymase was purified from cheek pouch vascular tissue using heparin affinity and gel filtration columns. The enzyme rapidly converted Ang I to Ang II (Km = 98 microM, k(cat) = 6203/min) but did not degrade several peptide hormones such as Ang II, substance P, vasoactive intestinal peptide and bradykinin. The primary structure, which was deduced from monkey chymase cDNA, showed a high homology to that of human chymase (98%). The mRNA levels of the aorta chymase were significantly increased in the atherosclerotic aorta of monkeys fed a high-cholesterol diet. These results indicate that monkey chymase has a highly specific Ang II-forming activity and may be related to the pathogenesis of atherosclerosis.

Lactoferrin regulates the activity of heparin proteoglycan-bound mast cell chymase: characterization of the binding of heparin to lactoferrin

Rat mast cell protease 1 (RMCP-1) is a secretory granule serine protease (chymase) that is recovered in vivo in a macromolecular complex with heparin proteoglycan (PG). We have previously shown that heparin activates RMCP-1 and that RMCP-1, when bound to heparin PG, is largely resistant to inhibition by a variety of macromolecular protease inhibitors. In the search for alternative mechanisms in the regulation of RMCP-1 activity, we hypothesized that heparin antagonists, by interfering with the RMCP-1/heparin PG interaction, might influence the activity of heparin-bound mast cell chymase. In the present study, lactoferrin (LF), a heparin-binding protein, was assessed for RMCP-1 inhibiting activity. LF proved to decrease the activity of heparin PG-associated RMCP-1, although a portion of the enzyme activity was resistant to regulation. The mechanism of regulation was shown to involve the displacement of RMCP-1 from heparin PG, and LF caused an approx. 6-fold increase in the apparent Km of the RMCP-1-heparin PG complex for the chromogenic substrate S-2586. The interaction of LF with heparin was characterized. Pig mucosal heparin and endogenous heparin PG were equally effective in binding LF, whereas heparan sulphate bound with lower affinity. None of dermatan sulphate, chondroitin sulphate or hyaluronan were effective in binding LF. Further, the 6-O-, 2-O- and N-sulphate groups in heparin were of approximately equal importance for binding. Octasaccharides were the smallest heparin oligosaccharides showing significant binding to LF.

Mast cell chymase in complex with heparin proteoglycan is regulated by protamine

Protamines are polycationic proteins that are widely used for neutralisation of the anticoagulant action of heparin. However, several reports have shown adverse, mast cell-dependent reactions to protamine. The exact mechanism by which protamine causes these adverse effects is not clear. In the present study, the possibility that protamine may influence mast cell chymase function was investigated. Mast cell chymase is in vivo recovered in a macromolecular complex with heparin proteoglycan, and this interaction is essential for expression of optimal enzymatic activity. Protamine was shown to strongly reduce the activity of mast cell chymase by a mechanism that involved displacement of the chymase from heparin proteoglycan.

Packaging of proteases and proteoglycans in the granules of mast cells and other hematopoietic cells. A cluster of histidines on mouse mast cell protease 7 regulates its binding to heparin serglycin proteoglycans

Mouse mast cell protease 7 (mMCP-7) is a tryptase stored in the secretory granules of mast cells. At the granule pH of 5.5, mMCP-7 is fully active and is bound to heparin-containing serglycin proteoglycans. to understand the interaction of mMCP-7 with heparin inside and outside the mast cell, this trytase was first studied by comparative protein modeling. The "pro" form of mMCP-7 was then expressed in insect cells and studied by site-directed mutagenesis. Although mMCP-7 lacks known linear sequences of amino acis that interact with heparin, the three-dimensional model of mMCP-7 revealed an area on the surface of the folded protein away from the substrate-binding site that exhibits a strong positive electrostatic potential at the acidic pH of the granule. In agreement with this calculation, recombinant pro-mMCP-7 bound to a heparin-affinity column at pH 5.5 and readily dissociated from the column at pH > 6.5. Site-directed mutagenesis confirmed the prediction that the conversion of His residues 8,68, and 70 in the positively charged region into Glu prevents the binding of pro-mMCP-7 to heparin. Because the binding requires positively charged His residues, native mMCP-7 is able to dissociate from the protease/proteoglycan macromolecular complex when the complex is exocytosed from bone marrow-derived mast cells into a neutral pH environment. Many hematopoietic effector cells store positively charged proteins in granules that contain serglycin proteoglycans. The heparin/mMCP-7 interaction, which depends on the tertiary structure of the tryptase, may be representative of a general control mechanism by which hematopoietic cells maximize storage of properly folded, enzymatically active proteins in their granules.

The role of proteoglycans in hard and soft tissue repair

Healing of soft and hard tissues results from a progression of events initiated by injury and directed toward reestablishing normal structure and function. The ubiquity of proteoglycans in mammalian tissues virtually guarantees their involvement in tissue restitution. The dramatic advances in cellular and molecular biology in recent years have added significantly to understanding the specific roles played by proteoglycans in wound repair processes.

Inhibition of rat mast cell protease 1 by vitronectin

Rat mast cell protease 1 (RMCP-1) is a chymotrypsin-like serine protease specifically expressed by connective tissue-type mast cells. The enzyme is stored in the secretory granules in a macromolecular complex with heparin proteoglycan. In the present investigation it was shown that RMCP-1 is inhibited by vitronectin (VN), an RGD-containing adhesive glycoprotein with heparin-binding properties. RMCP-1 that had been separated from heparin proteoglycan was less susceptible to inhibition than RMCP-1 present in complex with heparin proteoglycan. Pre-incubation of VN with purified heparin partially blocked the RMCP-1 inhibiting activity of VN. Plasma VN had negligible RMCP-1-inhibiting activity. However, heat treatment of plasma VN, which is known to expose the heparin-binding domain, induced RMCP-1-inhibiting activity. Affinity chromatography on immobilized VN showed that RMCP-1 bound with high affinity to VN. The binding of RMCP-1 to VN was not heparin-dependent since free RMCP-1 bound with equal affinity to the immobilized VN as RMCP-1 present in complex with heparin. The inhibition of RMCP-1 by VN was shown to be reversible.

Inactivation of thrombin by a complex between rat mast-cell protease 1 and heparin proteoglycan

Rat peritoneal mast cells were shown to inactivate thrombin rapidly. The thrombin-inactivating activity was purified to homogeneity by a combination of anion-exchange chromatography and h.p.l.c. on a Superdex 75 column. The purified thrombin inactivator had an apparent molecular mass of 29 kDa and an N-terminal amino acid sequence identical to rat mast-cell protease 1 (RMCP-1). After labelling of the mast cells in vivo with 35SO4(2-), RMCP-1 was recovered in a macromolecular complex with [35S]heparin proteoglycans. Dissociation of RMCP-1 from the heparin proteoglycans by Superdex 75 chromatography in the presence of 2 M NaCl resulted in a marked loss of the thrombin-inactivating activity displayed by the enzyme. When RMCP-1 was reconstituted with either endogenous [35S]heparin proteoglycans or standard pig mucosal heparin, the enzyme regained its thrombin-inactivating properties. Affinity chromatography of endogenous [35S]heparin on matrix-linked RMCP-1 demonstrated that all of the heparin molecules contained high-affinity binding sites for the mast-cell protease. In contrast, the endogenous mast-cell heparin showed low affinity for antithrombin, a protease inhibitor involved in the regulation of coagulation enzymes.

Effects of l-leucine methyl ester (Leu-OMe) on mouse peritoneal mast cells: Characterization of histamine release versus cytotoxicity

L-Leucine methyl ester (Leu-OMe), a lysosomotropic compound, has been found to eliminate several lysosome-rich cellular subtypes and all natural killer cell function from peripheral blood mononuclear cells. In this report, the effect of Leu-OMe on mouse peritoneal mast cells is described. The L-Leu-OMe induced the release of histamine from mouse peritoneal mast cells in a dose-dependent manner (0.25 to 3 mM), while its D-stereoisomer had no effect. L-Leu-OMe displayed also a potent histamine release effect on purified mast cells, indicating a direct effect on mast cells. The monitoring of radioactive chromium release versus histamine release showed that both processes may be unrelated for Leu-OMe concentrations inferior to 1.5 mM. At higher doses, L-Leu-OMe, but not its D-stereoisomer, exerted a potent cytotoxic effect on mast cells. The secretory effect of Leu-OMe was temperature- and energy-dependent. Experiments performed in the absence of extracellular calcium and magnesium demonstrated that these divalent cations were not necessary for the Leu-OMe-induced histamine release, and their deprivation even involved a higher histamine release. The secretory characteristics of the Leu-OMe-induced histamine release appeared to be different from those of the IgE-induced ones. These results support the conclusion that exposure of mouse peritoneal mast cells to high doses of L-Leu-OMe results in killing of these cells, that are new targets of this lysosomotropic agent.

Mast cell exocytosis: evidence that granule proteoglycan processing is not coupled to degranulation

It has been hypothesized that the dissolution of mast cell granules at the time of degranulation results from proteoglycan cleavage coupled to exocytosis. To address this hypothesis, we studied granule proteoglycan before and after exocytosis in dog mastocytoma cells, which solubilize granule contents during exocytosis. 35S-labeled proteoglycans were extracted from unstimulated whole cells and cell degranulation supernatant. Sequential anion-exchange and gel filtration chromatography, followed by specific glycosaminoglycan digestion, identified chondroitin sulfate and heparin glycosaminoglycan and proteoglycan in unstimulated cells and degranulated material alike. Glycosaminoglycan type and charge density in degranulation supernatant were unchanged compared with unstimulated cells. There was no decrease in proteoglycan size with cell activation and exocytosis. Thus, granule release and solubilization does not appear to require exocytosis-coupled degradation of granule proteoglycans. Release in association with high-m.w. proteoglycans may serve to limit rates of diffusion and activity of proteases and other mast cell mediators.

Identification of aminopeptidase activity in the secretory granules of mouse mast cells

Sonicates of mouse bone marrow-derived mast cells (BMMC) differentiated in vitro and of mouse serosal mast cells differentiated in vivo contained small but approximately equal amounts of aminopeptidase activity, as determined by cleavage of leucine-beta-naphthylamide and resolution of the reaction products by reverse-phase high-performance liquid chromatography. Aminopeptidase activity was exocytosed from antigen-activated, IgE-sensitized BMMC in proportion to the secretory granule enzyme beta-hexosaminidase, thereby localizing approximately 60% of the total cell-associated aminopeptidase activity to the secretory granules of the mast cells. A prominent secretory granule location for aminopeptidase was confirmed by activity measurement in subcellular fractions of disrupted BMMC. The secretory granule aminopeptidase had a pH optimum of 6.0-8.0 and a Km of 0.36 +/- 0.06 mM (mean +/- SD; n = 3) for leucine-beta-naphthylamide. When various amino acid beta-naphthylamides were used as substrates, the preference of the secretory granule enzyme was Ala greater than Leu greater than Phe much greater than Arg much greater than Asp = Tyr. Most of the aminopeptidase activity that was exocytosed from calcium ionophore-activated BMMC was bound to 35S-labeled proteoglycans in complexes of greater than 1 x 10(7) kDa as defined by exclusion during Sepharose CL-2B gel-filtration chromatography. We postulate that the amino-peptidase in the mast cell protease/proteoglycan complexes allows the removal of N-terminal amino acids from peptides that are generated by the action of mast cell endopeptidases.

Mast cell proteases liberate stable encephalitogenic fragments from intact myelin

Protease-containing supernatants from activated rat mast cells were found to degrade purified rat myelin with a subsequent release of a stable encephalitogenic peptide. The two most abundant peptides were identified as residues 69-87 (GSLPQKSQRTQDENPVV) and residues 69-88 (GSLPQKSQRTQDENPVVH). While additional exposure to the mast cell supernatants removes the COOH terminal histamine from peptide 69-88 to yield peptide 69-87, additional proteolytic degradation of the 69-87 peptide was not detected. Immunization with this peptide emulsified in CFA caused the development of clinical experimental autoimmune encephalomyelitis (EAE) in Lewis rats. In addition this 69-87 sequence was found to activate resting encephalitogenic myelin basic protein-reactive T cell lines to adoptively transfer clinical EAE. The release of stable encephalitogenic peptides from the myelin sheath by mast cell proteases may play a role in activation of encephalitogen-specific T cells during the progression of EAE.

Evidence for in vivo degradation of C3a anaphylatoxin by mast cell chymase. I. Nonspecific activation of rat peritoneal mast cells by C3ades Arg

The anaphylatoxin C3a (125I-HC3a) is extensively degraded when exposed to isolated rat mast cells (RMC). Degradation occurs without prior stimulation of these cells. The protease responsible for C3a degradation has been identified as chymase. Mixed peritoneal cells, containing equal numbers of mast cells compared with incubates containing more highly purified RMC, promoted less degradation of the C3a molecule than did the purified RMC. These variable levels of spontaneous activation (ie, chymase release) of RMC in vitro were concluded to be a function of the cellular handling and isolation procedures. No degradation occurred when low levels of 125I-HC3ades Arg (10(-8) mol/l [molar]) were introduced in the peritoneum of a rat, unless the mast cells were stimulated by prior introduction of specific activators. Evidence that the enzyme being released in the peritoneal cavity of rats was chymase was provided both by its appearance after adding specific mast cell activators (ie, compound 48/80 and anti-IgE [gamma E immunoglobulin]) and by inhibition with chymostatin. Because 125I-HC3ades Arg at low levels (10(-8) mol/l) was not degraded in the rat peritoneum, expression of chymase by the rat mast cells could be monitored in situ during mast cell stimulation. 125I-HC3ades Arg was rapidly converted (in 2 to 5 minutes) to smaller fragments in the peritoneal cavity of the rat after either 10 micrograms of compound 48/80 or anti-IgE was injected. Introduction of higher levels of HC3a or HC3ades Arg (2.5 to 5.0 x 10(-6) mol/l) to the peritoneal cavity of the rat stimulated both chymase release and HC3a degradation without other mast cell activators being present. HC3ades Arg was equally as effective in vivo as HC3a in stimulating the rat peritoneal mast cell to release chymase. It was concluded that the mechanism of RMC activation by C3a (C3ades Arg) was nonspecific and similar to the process by which polyamines and polycations stimulate mast cells, as C3a is a highly cationic molecule. The fact that C3a may in turn be destroyed in minutes by the recruited protease (chymase) defines a potentially important physiologic control mechanism. This cellular control process, demonstrated here for rat mast cells, may function in other animals, including man, for regulating tissue levels of factors such as the anaphylatoxins that are potentially capable of mast cell activation through nonspecific (polycationic) mechanisms.

Oxidative degradation of rat mast-cell heparin proteoglycan

The susceptibility of rat mast-cell heparin to oxidative degradation was examined. Heparin as a component of intact mast-cell granules (MCG) was degraded following ingestion by normal human neutrophils. In contrast, neutrophils from patients with chronic granulomatous disease (CGD), which do not respond to stimulation with respiratory-burst activity, exhibited a greatly diminished ability to degrade phagocytosed MCG heparin. MCG-associated heparin also was cleaved by H2O2 plus Fe2+ (Fenton's reagent). Isolated heparin proteoglycan (average Mr approx. 750,000) was rapidly cleaved to smaller molecules similar in size to commercial pig heparin upon exposure to Fenton's reagent. This cleavage was inhibited by catalase and by the hydroxyl-radical (OH.)-scavenger mannitol, but not by superoxide dismutase (SOD). The cleavage products retained approx. 26% of the anticoagulant activity of the native molecule. The heparin proteoglycan was also cleaved by acetaldehyde/xanthine oxidase/FeSO4, a system that generates superoxide (O2.-), H2O2 and OH.. Whereas the cleavage at relatively high iron ion concentrations was inhibited by catalase and mannitol but not by SOD, at lower iron ion concentrations the cleavage was inhibited by catalase, mannitol and SOD. These findings suggest the involvement of OH., which at high Fe2+ concentrations is generated by Fenton's reagent (H2O2 plus Fe2+), and at low iron ion concentrations is generated by the iron-ion-catalysed interaction between O2.- and H2O2 (Haber-Weiss reaction). These studies suggest that oxygen radicals generated by activated phagocytes may contribute to the degradation in vivo of both solubilized and granule-associated proteoglycan heparin.

Characterization of the human gene that encodes the peptide core of secretory granule proteoglycans in promyelocytic leukemia HL-60 cells and analysis of the translated product

Based upon the deduced amino acid sequence of a cDNA (cDNA-H4) that had been proposed to encode the peptide core of an eosinophil and a HL-60 cell secretory granule proteoglycan, a 16-amino acid peptide was synthesized. This peptide was then used to elicit rabbit antibodies for study of the translation and post-translational modification of this gene product in hematopoietic cells. When HL-60 cells were radiolabeled for 2 min with [35S]methionine, a protein that migrated in a sodium dodecyl sulfate-polyacrylamide electrophoresis gel with a Mr of 20,000 was immunoprecipitated with the IgG fraction of the anti-peptide serum. Kinetic experiments revealed that within 10 min this radiolabeled precursor protein was converted in HL-60 cells into an Mr approximately 150,000 chondroitin sulfate proteoglycan intermediate. After a 20-min to 1-h chase, this [35S]methionine- or [35S]sulfate-labeled proteoglycan intermediate lost its antigenicity, presumably due to proteolysis of its N terminus. A human genomic library was probed under conditions of high stringency with cDNA-H4 to isolate genomic clones that contain the gene that encodes this proteoglycan peptide core. This gene spans approximately 15 kilobases and consists of three exons. The first exon encodes the 5'-untranslated region of the mRNA transcript, as well as the entire 27-amino acid signal peptide of the translated molecule. The second exon encodes a 49-amino acid region of the peptide core, predicted to be the N terminus of the molecule after its proteolytic processing in the endoplasmic reticulum. The third exon encodes the remainder of the molecule, including its glycosaminoglycan attachment, serine-glycine repeat region. As assessed by S1 nuclease mapping and primer extension analysis, the transcription-initiation site in HL-60 cells for this gene resides 53 base pairs upstream from the translation-initiation site.

Different mouse mast cell populations express various combinations of at least six distinct mast cell serine proteases

Mouse serosal mast cells (SMCs) and Kirsten sarcoma virus-immortalized mast cells store large amounts of mast cell carboxypeptidase A and serine proteases in their secretory granules. Secretory granule proteins from 2.6 x 10(6) purified SMCs were separated by NaDodSO4/PAGE, trans-blotted to poly(vinylidine difluoride) membranes, and subjected to amino-terminal amino acid sequencing. Four distinct mast cell serine proteases were identified. With mast cell carboxypeptidase A, these serine proteases comprise the major proteins of mouse SMC secretory granules. Each of the four SMC serine proteases was distinct from the two serine proteases present in mucosal mast cells in the intestines of helminth-infected mice. The secretory granules of a Kirsten sarcoma virus-immortalized mast cell line contained three of the SMC-derived serine proteases and one of the mucosal mast cell-derived serine proteases. Thus, the family of mouse mast cell secretory granule serine proteases has at least six distinct members that can be expressed in different combinations in different mast cell populations.

Cloning of cDNAs that encode human mast cell carboxypeptidase A, and comparison of the protein with mouse mast cell carboxypeptidase A and rat pancreatic carboxypeptidases

Human skin and lung mast cells and rodent peritoneal mast cells contain a carboxypeptidase in their secretory granules. We have screened human lung cDNA libraries with a mouse mast cell carboxypeptidase A (MC-CPA) cDNA probe to isolate a near-full-length cDNA that encodes human MC-CPA. The 5' end of the human MC-CPA transcript was defined by direct mRNA sequencing and by isolation and partial sequencing of the human MC-CPA gene. Human MC-CPA is predicted to be translated as a 417 amino acid preproenzyme which includes a 15 amino acid signal peptide and a 94 amino acid activation peptide. The mature human MC-CPA enzyme has a predicted size of 36.1 kDa, a net positive charge of 16 at neutral pH, and 86% amino acid sequence identity with mouse MC-CPA. DNA blot analyses showed that human MC-CPA mRNA is transcribed from a single locus in the human genome. Comparison of the human MC-CPA with mouse MC-CPA and with three rat pancreatic carboxypeptidases shows that these enzymes are encoded by distinct but homologous genes.

Modulation of chymase-mediated rat serosal mast cell degranulation by trypsin or diisopropyl fluorophosphate

Exposure of rat serosal mast cells (RSMC) to chymase, an endogenous secretory granule serine protease, at 37 degrees results in exocytosis, as determined by beta-hexosaminidase release. As the number of RSMC is increased with a set amount of chymase, the net percentage beta-hexosaminidase release decreases linearly, implying a finite set of cellular interactions per chymase unit. Pretreatment of RSMC with trypsin at 37 degrees renders them refractory to subsequent exocytosis mediated by chymase in a dose- and time-dependent fashion, with complete refractiveness occurring by 15 min at 37 degrees with 2.5 micrograms trypsin/ml. Anti-IgE-mediated coupled activation-secretion of RSMC is not affected by the same trypsin pretreatment. When RSMC are pretreated with trypsin (2.5 micrograms/ml) for 0-120 min at 1 degree a progressive loss of sensitivity to activation by chymase at 37 degrees occurs. RSMC susceptibility to chymase-mediated degranulation after trypsin pretreatment can be partially regenerated by culturing the RSMC for about 24 hr in medium at 37 degrees. These findings suggest that a trypsin-sensitive constituent, possibly a receptor or substrate, is necessary for the functional interaction of chymase with RSMC. When added with diisopropyl fluorophosphate (DFP), chymase does not induce RSMC degranulation at 37 degrees. However, if the DFP is removed before addition of chymase at 37 degrees or is added after the chymase-priming event occurs at 1 degree, subsequent degranulation at 37 degrees is not inhibited. Thus, the induction and not the secretion phase is DFP-inhibitable in chymase-induced activation-secretion. In addition, the priming but not the exocytosis phase of chymase-initiated RSMC activation-secretion, which is not dependent on temperature and calcium ion concentration, involves a cellular trypsin-sensitive protein.

Biological functions of serine proteases in mast cells in allergic inflammation

Serine proteases in mast cell granules, such as chymase, atypical chymase, and tryptase, which are major proteins in the granules, may play important roles in the process of immunoglobulin E (IgE)-mediated degranulation and in pathobiological alterations in tissues. Indeed, inhibitors of chymase, substrate analogs, and antichymase F(ab')2, but not inhibitors of tryptase, markedly inhibited histamine release induced by IgE-receptor bridging but not that induced by Ca ionophore. In contrast, inhibitors of metalloprotease inhibited histamine release induced not only by IgE-receptor bridging but also by Ca ionophore. These results suggest that chymase and metalloprotease are involved at different steps in the process of degranulation. The extents of inhibition of histamine release were closely correlated with the amounts of the inhibitors of chymase accumulated in the granules. After degranulation, the released proteases may in part contribute to pathobiological alterations in allergic disorders through generations of C3a anaphylatoxin and thrombin by human and rat tryptase, respectively, and those of angiotensin II and a chemotactic factor of neutrophils by human and rat chymase, respectively. Moreover, chymase and atypical chymase from rat were shown to destroy type IV collagen, and human tryptase was found to hydrolyze various plasma proteins, such as fibrinogen and high-molecular-weight kininogen. The biological activities of tryptase and chymase from rat may be regulated by their dissociation from and association with trypstatin, an endogenous inhibitor of these proteases.

Tryptase in rat mast cells: properties and inhibition by various inhibitors in comparison with chymase

Previous studies with trans-4-(guanidinomethyl)cyclohexanecarboxylic acid 4-tert-butylphenyl ester (GMCHA-OPhBut), a trypsin inhibitor, strongly suggested the involvement of a trypsin-like protease in histamine release from mast cells induced by various secretagogues (Takei, M., Matumoto, T., Endo, K. & Muramatu, M. (1988) Agents and Actions, in press; Takei, M., Matumoto, T., Ito, T., Endo, K. & Muramatu, M.; Takei, M., Matumoto, T., Endo, K. & Muramatu, M. and Takei, M., Matumoto, T., Urashima, H., Endo, K. & Muramatu, M., unpublished results). Two serine proteases, chymase (Benditt, E.F. & Arase, M. (1959) J. Exp. Med. 110, 451-460) and tryptase Kido, H., Fukusen, N. & Katunuma, N. (1985) Arch. Biochem. Biophys. 239, 436-443) were demonstrated in rat peritoneal mast cells. Both enzymes were purified and the effects of inhibitors for trypsin and chymotrypsin on these proteases were examined. The trypsin-like protease was found in saline extract and purified by successive chromatographies on Sephadex G-100 and DEAE-cellulose columns. The molecular mass of this protease was apparently 120,000 Da. This protease showed maximal activity at pH 7.1 and was named pH 7 tryptase. Chymase was obtained from 1.5M NaCl extract. pH 7 Tryptase markedly hydrolysed Boc-Phe-Ser-Arg-NH-Mec and Boc-Val-Pro-Arg-NH-Mec among the various substrates containing arginyl and lysyl bonds but did not cleave Tos-Arg-OMe. Tos-Lys-CH2Cl and diisopropylfluorophosphate strongly inhibited this protease. Various inhibitors for trypsin inhibited pH 7 tryptase, and those for chymotrypsin inhibited chymase. Among the esters of GMCHA examined, GMCHA-OPhBut most strongly and competitively inhibited pH 7 tryptase but it had no effect on chymase.

Microwave fixation provides excellent preservation of tissue, cells and antigens for light and electron microscopy

It was demonstrated that microwave energy used simultaneously in combination with low concentrations of glutaraldehyde (0.05%) and formaldehyde (2.0%) rapidly preserved light microscopic histology and excellent fine structural details, as well as a variety of cytoplasmic and membrane-bound antigens. Specimen blocks up to 1 cm3 can be fixed in as brief a time as 26 ms using a specially designed microwave device (ultrafast microwave fixation method). The fast microwave fixation method, using a commercially available device, was successfully used to preserve granule-bound rat mast cell chymase which was subsequently detected by a postembedding immunogold procedure. Control of the following parameters is important to the microwave fixation method: (1) specimens with one dimension less than 1 cm; (2) irradiation temperatures lower than 50 degrees C; (3) irradiation times less than 50 s; (4) immediate replacement of the postirradiation solution with cold storage buffer; (5) fixing the specimen within 15 min after it is removed from its blood supply.

The question of chymase in cultured muscle cells

An alkaline proteinase, identical to mast cell chymase, has been described by a number of laboratories as being associated with myofibrils extracted from adult rat skeletal muscle tissue. A more recent study has indicated that chymase may be an intrinsic protein in the rat myocyte. The present study of rat myogenic cell lines, using more stringent controls and a probe of more highly defined specificity, supports the view that (i) chymase originates from mast cells of the interstitium and (ii) chymase from mast cells becomes adsorbed to myofibrils of adult muscle during homogenization of this complex tissue.

Purification and identification of two serine class proteinases from dog mast biochemically and immunologically similar to human proteinases tryptase and chymase

Serine class proteinases with trypsin-like and chymotrypsin-like specificity were purified from dog mastocytoma tissue. An antiserum was produced against the chymotrypsin-like proteinase. The antiserum reacted with mast cells in skin sections prepared from normal dogs consistent with the proteinase being a mast cell constituent. The antiserum also cross-reacted with the major chymotrypsin-like proteinase isolated from normal dog skin and partially cross-reacted with human skin chymase. No cross-reaction was detected with rat chymase. The trypsin-like proteinase from dog mastocytoma tissue was similar to tryptase isolated from human skin. It had a similar subunit structure, was not inhibited by many protein proteolytic enzyme inhibitors, bound to heparin, and reacted strongly with antiserum against human tryptase. Antiserum against human tryptase also reacted with mast cells in skin sections prepared from normal dog skin. No immunocytochemical labeling of rat skin mast cells was observed with anti-human tryptase. These studies establish the presence of a trypsin-like and chymotrypsin-like proteinase in dog skin mast cells and provide immunological evidence which suggests that both proteinases are more closely related to human than rat mast cell proteinases. These immunological and biochemical relationships are important when comparing the roles of these proteinases in different animals.