Control of LMP7 expression in human endothelial cells by cytokines regulating cellular and humoral immunity

Formation of antigenic peptides by the multicatalytic proteinase complex (MPC, proteasome) is facilitated by incorporation of three subunits (LMP2, LMP7 and LMP10) that are inducible by IFN-gamma and TNF-alpha. These cytokines, or their functional homologues (e.g. TNF-beta), are released from many cells including Th(1)lymphocytes. To learn more about the relationship between control of cellular immunity and expression of LMP subunits, we measured LMP7 levels in human umbilical vein endothelial cells of cytokines promoting cellular immunity (IL-12, IFN-gamma, TNF-alpha) or humoral immunity (IL-10, IL-6). Little or no effect was seen when cells were exposed to IL-6, IL-10 or IL-12 alone. IFN-gamma upregulated LMP7 levels, as did TNF-alpha to a lesser extent. IL-10 downregulated IFN-gamma-induced increases in LMP7 levels, as did IL-12. The findings indicate that regulation of levels of LMP7 is similar to and may be coupled with that of other molecules required for MHC class I-dependent immunity, and depends primarily on cytokines released by Th(1)helper lymphocytes.

DNA vaccine encoding nucleocapsid and surface proteins of wild type canine distemper virus protects its natural host against distemper

Canine distemper virus (CDV), a member of the genus Morbillivirus induces a highly infectious, frequently lethal disease in dogs and other carnivores. Current vaccines against canine distemper consisting of attenuated viruses have been in use for many years and have greatly reduced the incidence of distemper in the dog population. However, certain strains may not guarantee adequate protection and others can induce post vaccinal encephalitis. We tested a DNA vaccine for its ability to protect dogs, the natural host of CDV, against distemper. We constructed plasmids containing the nucleocapsid, the fusion, and the attachment protein genes of a virulent canine distemper virus strain. Mice inoculated with these plasmids developed humoral and cellular immune responses against CDV antigens. Dogs immunized with the expression plasmids developed virus-neutralizing antibodies. Significantly, vaccinated dogs were protected against challenge with virulent CDV, whereas unvaccinated animals succumbed to distemper.

Up-regulation of the proteasome subunit LMP7 in tissues of endotoxemic rats

The proteasome has been implicated in systemic responses to infection or inflammatory stimuli including catabolism of skeletal muscle. Cytokines including tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) are known to be elevated systemically and locally under these conditions. They are also known to be potent inducers of three peptide subunits of the proteasome, including LMP7, that replace constitutively expressed subunits and change enzymatic properties. To determine whether endotoxemia alters the expression of inducible proteasome subunits, we examined the levels of LMP7 in tissues from rats 3 days after the injection of lipopolysaccharide (LPS) or normal saline solution (NS). By both immunoblotting and immunohistochemistry, significant increases in levels of LMP7 were observed in the heart, kidney, and lung of animals given LPS as compared with results in NS-treated animals, whereas immunoblotting revealed no changes in LMP7 levels in skeletal muscle or brain. Increased expression of LMP7 was limited to certain subpopulations of cells and was further localized at the subcellular level. Decreases in organ weight were also documented for organs in which the expression of LMP7 was up-regulated. Systemic or local release of cytokines or other proinflammatory mediators is suggested as the most likely mechanism for changes in LMP7 expression during endotoxemia. Changes in LMP7 expression may have functional consequences that contribute to organ dysfunction during systemic responses to infection and inflammatory stimuli.

Distribution of proteasomes and of the five proteolytic activities in rat tissues

Five peptidase activities (ChT-L, T-L, PGPH, BrAAP, and SNAAP) of the proteasome, and its caseinolytic activity, were measured in crude extracts of 10 rat tissues under experimental conditions simulating those found in vivo, thereby eliminating the alterations observed with the purified enzyme. The total and individual peptidase activities varied considerably from one tissue to another, whereas the proteolytic activity measured with [(14)C]methylcasein varied no more than twofold. The tissue-specific variations in individual peptidase activities may reflect tissue-specific differences in proteasome subunit composition, or the presence of regulators. Immunological assay using an antibody directed against the iota (alpha1) subunit showed that there was no correlation between protein abundance and peptidase activity. The results also show that the different peptidase activities are not representative of proteasome distribution in the different tissues.

Lysozyme degradation by the bovine multicatalytic proteinase complex (proteasome): evidence for a nonprocessive mode of degradation

The multicatalytic proteinase complex (MPC, proteasome) is composed of 28 subunits organized into four rings surrounding a water-filled canal. The catalytic centers face the inner canal confining protein substrates to an enclosed space. Experimental findings obtained with MPC from archaebacteria suggest that degradation of proteins by the complex is processive and have led to the proposal that the lengths of the peptides formed during degradation depend on the distances between active sites in the catalytic chamber. To test whether these postulates are valid for the MPC from a higher organism, we examined the size distributions of products formed early versus late in the course of protein degradation using reduced carboxamidomethylated lysozyme (RCM-lysozyme) and MPC from bovine spleen and pituitary. The majority of final degradation products ranged in length from 6 to 20 amino acids without a clear predilection for peptides of a particular, uniform size. Our observations suggest that selection of cleavage sites is governed by the amino acid sequence specificity of the MPC catalytic sites rather than the distances between the active sites. Early in the course of degradation, peptides with masses between 5 and 10 kDa accumulated in more than 80-fold molar excess over the MPC, indicating dissociation of large, partially degraded intermediates. Initial cleavages occurred at distances between 10 and 44 amino acids from the N- or C-terminus of the molecule and often involved removal of a fragment from both the N- and C-termini of RCM-lysozyme. Our data indicate that degradation of proteins by MPCs from higher organisms involves a nonprocessive mechanism comprised of multiple, independent cleavages with dissociation of degradation intermediates. A general model for protein degradation by the MPC is discussed.

Components of the bovine pituitary multicatalytic proteinase complex (proteasome) cleaving bonds after hydrophobic residues

Two catalytic components of the multicatalytic proteinase complex (MPC, proteasome) designated as chymotrypsin-like (ChT-L) and branched chain amino acid preferring (BrAAP) cleave bonds after hydrophobic amino acids. The possible involvement of the ChT-L and peptidylglutamyl-peptide hydrolyzing (PGPH) activities in the cleavage of bonds attributed to the BrAAP component was examined. Several inhibitors of the ChT-L activity containing a phenylalaninal group did not affect the BrAAP activity at concentrations that were more than 150 times higher than their K(i) values for the ChT-L activity. Concentrations of lactacystin that inactivated more than 90% of the ChT-L activity had no effect on the BrAAP activity. Concentrations of 3,4-dichloroisocoumarin (DCI) that inactivated the ChT-L activity activated by up to 10-fold the BrAAP activity toward synthetic substrates and by more than 2-fold the degradation of the insulin B chain in a reaction not inhibited by Z-LGF-CHO, a selective inhibitor of the ChT-L activity. These findings are incompatible with any significant involvement of the ChT-L activity in the cleavage of BrAAP substrates. Both the native and DCI-treated MPC cleaved the insulin B chain mainly after acidic residues in a reaction inhibited by Z-GPFL-CHO, an inhibitor of the BrAAP and PGPH activities. DCI exposure did not result in acylation of the N-terminal threonine in the active site of the Y subunit. These results suggest involvement of the PGPH activity in the cleavage of BrAAP substrates, but this conclusion is incompatible with DCI activation of the BrAAP activity and inactivation of the PGPH activity, and with the finding that proteins inhibiting the PGPH activity had no effect on the BrAAP activity. Rationalization of these contradictions is discussed.

Altered properties of the branched chain amino acid-preferring activity contribute to increased cleavages after branched chain residues by the "immunoproteasome"

The multicatalytic proteinase complex (MPC, proteasome) is assembled from 14 nonidentical protein subunits. It expresses five distinct proteolytic activities, including a chymotrypsin-like activity, cleaving after hydrophobic residues, and a branched chain amino acid-preferring component (BrAAP), cleaving preferentially after branched chain residues. Exposure of cells to interferons leads to replacement of the X, Y, and Z subunits by the LMP2, LMP7, and MECL1 subunits. This "immunoproteasome" is critical to processing of certain antigens. The enzymatic basis for enhanced antigen processing has not been determined. To gain insight into this question, we examined sites and relative rates of cleavage of bonds in denatured, reduced, carboxyamidomethylated lysozyme, a 129-amino acid protein, by MPC from bovine spleen, in which the X, Y, and Z subunits are replaced by LMP2, LMP7, and MECL1. We compared cleavages to those catalyzed by MPC from bovine pituitary, which contains only the X, Y, and Z subunits. We found marked increases in the rates and number of cleavages after branched chain residues in reduced, carboxyamidomethylated lysozyme by the spleen MPC. This was largely due to accelerated cleavages of bonds after a Phi-X-Br motif, where Phi is a hydrophobic residue, X is a small neutral or polar residue, and Br is a branched chain residue. Inhibitors with these structural properties were selective and potent inhibitors of the BrAAP activity of the spleen MPC. The above findings indicate that alterations in activity and substrate specificity of the BrAAP activity are important factors underlying the altered cleavages after hydrophobic residues associated with incorporation of interferon-inducible subunits. The potential relevance of the findings to antigen processing functions of MPC is discussed.

Induction of acute and chronic pancreatitis with the use of the toxin of the scorpion Tityus serrulatus: experimental model in rats

We observed that the purified venom of the Tityus serrulatus scorpion (T1 fraction), injected i.v. in rats, in a single dose of 0.5 mg/kg, produces: acute pancreatitis, characterized by degranulation and acinar cell vacuolization, necrosis and an inflammatory reaction, 24, 48 and 96 hours after the injection; chronic pancreatitis, characterized by interstitial fibrosis, lymphocyte infiltration, ductal and ductular dilation, acinar cell atrophy, periductal ductular hyperplasia, 20 days after injection: hyperplasia of Langerhans' islets and nesidioblastosis, associated to chronic pancreatitis. The absence of deaths in the experimental group is an interesting finding: the dose used preserved the animals from death and allowed the safe follow-up of the progression of the provoked pancreatitis. The results led us to conclude that the toxin of Tityus serrulatus scorpion is an agent of considerable efficacy in the induction of pancreatitis in rats providing an experimental model of acute and chronic form of this disease.

Reactions of [14C]-3,4-dichloroisocoumarin with subunits of pituitary and spleen multicatalytic proteinase complexes (proteasomes)

Exposure to [14C]-3,4-dichloroisocoumarin (DCI) of multicatalytic proteinase complexes (MPC) isolated from bovine pituitary and spleen leads to label incorporation into several beta-type subunits, to rapid inactivation of the chymotrypsin-like (ChT-L) activity, and to a slower inactivation of other activities of the MPC. The pituitary and spleen MPCs differ in that the first contains almost exclusively the X, Y, and Z subunits, whereas in the latter these subunits are largely replaced by LMP2, LMP7, and MECL1. Preincubation with two peptidyl aledhyde inhibitors of the ChT-L activity protected the X subunit in the pituitary MPC and unexpectedly the LMP2 subunit in the spleen MPC from label incorporation, despite the greater amino acid sequence homology of the LMP7 subunit to that of the X subunit. Losses in the yield of amino acids in both subunits, shown by amino acid sequencing, and lability of the DCI-protein bond indicated formation of an acyl derivative by reaction of DCI with the threonine OH group. Brief exposure to [14C]-DCI led to preferential incorporation of label into the LMP2 and X subunits, consistent with the high inactivation rate constants of the ChT-L activity. Z-LLF-CHO, an inhibitor of ChT-L activity, but not Z-GPFL-CHO, an inhibitor of the branched chain amino acid preferring component, prevented incorporation of radioactivity into the X subunits, whereas both inhibitors prevented label incorporation into LMP2, indicating differences in susceptibility to inhibition between the two components. These and other data are consistent with involvement of the X and LMP2 subunits in expression of the ChT-L activity in the pituitary and spleen MPC, respectively, and suggest the catalytic functions of two other beta-subunits.

Bovine spleen multicatalytic proteinase complex (proteasome). Replacement of X, Y, and Z subunits by LMP7, LMP2, and MECL1 and changes in properties and specificity

Amino acid sequencing of subunits of the multicatalytic proteinase complex (MPC) isolated from bovine spleen showed an almost complete replacement of the X, Y, and Z subunits, constitutively expressed in most tissues, by the interferon-gamma-inducible LMP7, LMP2, and MECL1 subunits. A comparison with the pituitary MPC found a decreased chymotrypsin-like activity, a depressed peptidylglutamyl-peptide hydrolyzing activity, and a highly active component with properties similar to, but not identical with, that of the pituitary branched chain amino acid preferring (BrAAP) component. Unlike the pituitary BrAAP component, that of the spleen MPC exhibited a greatly decreased Km, a highly increased catalytic efficiency (kcat), and a 80-180 times greater specificity constant (kcat/Km) toward substrates with either branched chain or aromatic amino acid residues in the P1 position. Also, unlike the pituitary BrAAP component, that of the spleen was sensitive to inactivation by 3,4-dichloroisocoumarin and sensitive to inhibition by peptidyl-aldehydes with either phenylalaninal or leucinal residues. Several phenylalaninal peptidyl-aldehydes were identified which selectively inhibited components of the spleen but not of the pituitary MPC. Two of the inhibitors are dipeptidyl-aldehydes, two others are tetrapeptidyl-aldehydes with a Pro residue in the P3 position. The possibility is discussed that the properties and specificity of the spleen MPC are a consequence of the presence of the interferon-gamma-inducible subunits.

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

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

Peptidase inhibitors potentiate lysylbradykinin-induced bronchoconstriction in the rat

To determine whether lysylbradykinin (LBK, kallidin) causes bronchoconstriction in animals and if peptidase inhibitors modulate the response, we studied the effects of LBK administered by aerosol in rats and assessed whether pretreatment with aerosolized solutions of enalaprilat, an inhibitor of angiotensin converting enzyme (ACE), or phosphoramidon, an inhibitor of endopeptidase 24.11 (EP 24.11, neutral endopeptidase), altered the response. Accordingly, LBK-induced bronchoconstriction was measured in anesthetized, mechanically ventilated, specific pathogen-free, Sprague-Dawley rats by body plethysmography and followed by continuous determination of lung resistance (RL) and maximal expiratory flow (MEF). Incremental doses of aerosolized LBK were administered by nebulization to obtain a concentration that caused a 5-15% increase in RL, which was designated the BC10 dose. We found that pretreatment with aerosolized enalaprilat (1 mM) 3 min prior to a BC10 dose of LBK significantly increased RL as compared to the BC10 dose alone (129 +/- 4.1% vs. 105 +/- 2.4%, P < 0.002, n = 4) and significantly decreased MEF (83 +/- 1.5% vs. 97 +/- 1.4%, P < 0.008, n = 4). Following pretreatment with aerosolized phosphoramidon (1 mM), significant increases in RL (113 +/- 1.4% vs. 106 +/- 1.6%, P < 0.019, n = 7) and decreases in MEF (92 +/- 0.9% vs. 95 +/- 0.9%, P < 0.035, n = 7) were observed (paired Student's t-test). The above findings demonstrate the effects of LBK on airway caliber for the first time in an animal model, and suggest that ACE and EP 24.11 contribute to degradation of the peptide in the airway.

Neuronal degeneration in brain stem nuclei in bovine spongiform encephalopathy

In 57% of 151 BSE positive brains of Swiss cattle, degenerating neurons were found in BSE predilection sites, either single scattered (34%) or involving large parts of brain stem nuclei (23%). The lesion consisted of central chromatolysis, shrinkage, karyolysis or nuclear pyknosis. In 43% of the BSE positive brains no neuronal changes besides vacuolation were present. Neuronal degeneration other than vacuolation alone is not pathognomonic for BSE but, according to our findings, seems to be of some importance together with the typical vacuolation of neuropil and neurons. There is no correlation between extent of these degenerative changes and accumulation of PrPSc protein, determined by immunohistochemistry. The significance remains obscure, yet as it had not been seen in cattle brains before the outbreak of BSE in Switzerland in 1990 it certainly is linked to the disease. Possible pathogenetic mechanisms are discussed.

Hydrolysis of N-formylmethionyl chemotactic peptides by endopeptidase 24.11 and endopeptidase 24.15

Endopeptidase 24.11 (EP 24.11), a membrane-bound cell surface enzyme, modulates chemotactic responsiveness of neutrophils to f-Met-Leu-Phe. It is unknown if the enzyme degrades potent formylmethionyl tetrapeptides or if an enzyme with similar activities, endopeptidase 24.15 (EP 24.15), degrades formylated chemotactic peptides. In a study of five formylmethionyl tetrapeptides and f-Met-Leu-Phe, we found that EP 24.11 had high affinity for all peptides evaluated, although it did not effectively degrade f-Met-Ile-Leu-Phe. EP 24.15 had high affinity for three of the tetrapeptides, and for f-Met-Leu-Phe, although, for unclear reasons, it did not degrade f-Met-Ile-Leu-Phe or f-Met-Leu-Phe, the apparent natural products of Staphylococcus aureus and Escherichia coli, respectively.

Differences in catalytic activities and subunit pattern of multicatalytic proteinase complexes (proteasomes) isolated from bovine pituitary, lung, and liver. Changes in LMP7 and the component necessary for expression of the chymotrypsin-like activity

Polyacrylamide gel electrophoresis and high performance liquid chromatography of multicatalytic proteinase complexes (MPC) isolated from bovine pituitary, lung, and liver showed marked differences in the pattern of subunits. The concentrations of LMP7 in the lung and liver were 10 and 5 times, respectively, greater than those in the pituitary, whereas the chymotrypsin-like activity and the amount of a subunit (BO2), necessary for its expression, were markedly decreased in the lung and moderately decreased in the liver. Lower trypsin-like, small neutral amino acid preferring, and peptidyl-glutamyl-peptide hydrolyzing activities were also found in the lung and liver. The activity of the branched chain amino acid preferring component (BrAAP), predominantly latent in the pituitary, was highly activated in the lung and liver, as evidenced by a greatly decreased Km and a 20-fold increase of the specificity constant Vmax/Km, indicating facilitated substrate access to its active site and increased affinity toward substrates with branched chain amino acids in the P1 position. It is suggested that overexpression of LMP7 in the lung is related to increased exposure of the airways to foreign antigens. The possible association between amounts of LMP7 and the activation of the BrAAP component needs further examination.

Degradation of lysylbradykinin by endopeptidase 24.11 and endopeptidase 24.15

Lysylbradykinin (LBK), a potent bioactive peptide with pleiotropic actions, is the major kinin generated in the extravascular space. To explore possible mechanisms of inactivation of this peptide in tissues, we evaluated its degradation by endopeptidase 24.11 (EP 24.11) and endopeptidase 24.15 (EP 24.15), two zinc metalloenzymes widely distributed in tissues. EP 24.11 cleaved LBK at the Gly5-Phe6 and Pro8-Phe9 bonds, whereas EP 24.15 cleaved the Phe6-Ser7 bond. Determination of kinetic constants for degradation of LBK by the two enzymes yielded kcat/Km ratios of 5.2 x 10(5) and 8.4 x 10(5) for EP 24.15 and EP 24.11, respectively, indicating that LBK is a good substrate for both enzymes. The findings demonstrate that both EP 24.11 and EP 24.15 efficiently degrade LBK and thus may contribute to the inactivation of this peptide in tissues.

Inhibition of the proteolytic activity of the multicatalytic proteinase complex (proteasome) by substrate-related peptidyl aldehydes

Evidence indicates that a component of the multicatalytic proteinase complex (MPC) that preferentially cleaves bonds after branched chain amino acids (BrAAP) is a major factor responsible for the protein-degrading activity of the MPC. We report here the synthesis of substrate-related peptidyl aldehydes that inhibit the activity of this component toward both synthetic peptide substrates and proteins. The most potent of the inhibitors, Cbz-Gly-Pro-Phe-leucinal (Cbz-GPFL-CHO) inhibits competitively with a Ki of 1.5 microM. The peptidyl aldehydes also inhibit the small neutral amino acid preferring and the peptidylglutamyl-peptide hydrolyzing activities of the MPC. The chymotrypsin-like activity is only weakly inhibited, and the trypsin-like activity is moderately activated. The importance of a Pro residue in the P3 position and a leucinal residue in the P1 position for inhibition of the BrAAP component is indicated by the finding that replacement of these residues by a glycine or phenylalaninal, respectively, markedly increases the Ki. Cbz-GPFL-CHO inhibited the BrAAP activity with the same Ki both before and after activation of this component by exposure of the MPC to 3,4-dichloroisocoumarin, suggesting that the peptidyl aldehyde is an effective inhibitor of both the overt and latent proteolytic activities of the MPC. Incubation of a human breast cancer cell line (MCF-7) in culture with the inhibitors of the BrAAP component led to an accumulation of ubiquitin-protein conjugates, indicating inhibition of the ubiquitin-dependent proteolytic pathway.

Evidence that the nature of amino acid residues in the P3 position directs substrates to distinct catalytic sites of the pituitary multicatalytic proteinase complex (proteasome)

Cleavage of bonds after neutral amino acids by the multicatalytic proteinase complex (MPC) has been recently shown to be catalyzed by at least three distinct components [Orlowski, M., Cardozo, C., & Michaud, C. (1993) Biochemistry 32, 1563-1572]. One component, designated as chymotrypsin-like (ChT-L), cleaves peptide bonds on the carboxyl side of hydrophobic residues and is also active toward peptidyl-arylamide bonds. A second component, designated as branched-chain amino acid preferring (BrAAP), and a third component, designated as small neutral amino acid preferring (SNAAP), cleave preferentially bonds on the carboxyl side of branched-chain amino acids and between small neutral amino acids, respectively. Evidence indicates that the BrAAP component is a major factor responsible for degradation of protein by the MPC. The purpose of the present study was to identify the structural requirements that determine the involvement of these components in cleavage of peptides after different neutral amino acids. A series of substrates was synthesized with the aim of probing the role of residues beyond those flanking the scissile bond in directing substrates to defined catalytic sites. The data indicate that a proline or glycine residue in the P3 position directs the substrate to the catalytic site of the BrAAP component provided that a branched-chain amino acid is present in the P1 position. A proline residue in P3 is also important for involvement of the SNAAP component in substrate degradation. The presence of this residue interferes with substrate binding to the catalytic site of the ChT-L activity, even in the presence of a phenylalanine residue in the P1 position.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of endopeptidase 24.11 and endopeptidase 24.15 in human blood leukocytes

Endopeptidase 24.11 (EP 24.11; also called neutral endopeptidase, enkephalinase, CALLA, or CD10) and endopeptidase 24.15 (EP 24.15) are widely distributed neutral metalloendopeptidases that degrade a number of bioactive peptides including substance P, bradykinin, neurotensin, and chemotactic peptides. In this study we used sensitive substrates and specific inhibitors to quantitate the levels of these enzymes in purified peripheral human blood leukocytes obtained from healthy blood donors. We found that neutrophils did not contain detectable amounts of EP 24.15. In contrast, T lymphocytes, B lymphocytes, and monocytes contained significant amounts of the enzyme (446 +/- 248,314 +/- 183, and 484 +/- 212 nmol/mg protein/h, respectively). Neutrophils contained significant amounts of EP 24.11 (266 +/- 130 nmol/mg protein/h). Significantly lower levels of the enzyme were found in T lymphocytes, B lymphocytes, and monocytes (94 +/- 31, 87 +/- 38, and 20 +/- 13 nmol/mg protein/h, respectively). These findings suggest that the effects of some bioactive peptides on peripheral blood leukocyte function may be modulated by these enzymes.

Bradykinin-induced airway microvascular leakage is potentiated by enalaprilat but not by phosphoramidon

The objective of the study was to determine if bradykinin-induced airway microvascular leakage in rats was altered by pretreatment of animals with enalaprilat, an inhibitor of angiotensin-converting enzyme (ACE), or phosphoramidon, an inhibitor of endopeptidase 24.11 (EP 24.11). We found that the intravascular infusion of bradykinin induced microvascular leakage of Evans blue dye in tracheal tissue (0.088 +/- 0.035 micrograms/mg tissue) that was significantly amplified by pretreatment with 3.27 mM enalaprilat (0.458 +/- 0.226 micrograms/mg tissue), but not by pretreatment with 10 mM phosphoramidon (0.082 +/- 0.0453 micrograms/mg tissue). Leakage in carinal tissue was also amplified by pretreatment with 3.27 mM enalaprilat (0.205 +/- 0.050 vs. 0.036 +/- 0.006 micrograms/mg tissue for bradykinin alone), whereas no amplification was observed in parenchymal tissue by pretreatment with either inhibitor. These findings indicate that in the rat, ACE, but not EP 24.11, modulates bradykinin-induced airway microvascular leakage following intravascular infusion of these agents.

Effects of peptidase inhibitors on bradykinin-induced bronchoconstriction in the rat

Objectives of this study were to determine if aerosolized bradykinin causes bronchoconstriction in anesthetized, mechanically ventilated rats, and if pretreatment with enalaprilat, an inhibitor of angiotensin-converting enzyme (ACE), or phosphoramidon, an inhibitor of endopeptidase 24.11 (EP 24.11), alters the response. We found that aerosolized bradykinin elicited a reproducible bronchoconstrictor response that was significantly amplified by pretreatment with aerosolized enalaprilat or phosphoramidon. Neither inhibitor alone affected airway tone or caused nonspecific airway hyperreactivity. These findings indicate that both ACE and EP 24.11 contribute to bradykinin degradation in rat airways.

Evidence that enzymatic conversion of N-[1(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate, a specific inhibitor of endopeptidase 24.15, to N-[1(R,S)-carboxy-3-phenylpropyl]-Ala-Ala is necessary for inhibition of angiotensin converting enzyme

N-[1(R,S)-Carboxy-3-phenylpropyl]-Ala-Ala-Phe-p-aminobenzoate (cFP-AAF-pAB) is a potent, substrate-related, specific inhibitor of endopeptidase 24.15, an enzyme involved in the metabolism of bioactive peptides including bradykinin, neurotensin, and proenkephalin, and prodynorphin-derived enkephalin precursors. The observation that this inhibitor causes a pronounced decrease in blood pressure after intravenous infusion into normotensive rats posed the question of the mechanism of this hypotensive response. It was suggested previously that cFP-AAF-pAB is an inhibitor of angiotensin converting enzyme (ACE) and that this function can account for the hypotensive response to the inhibitor. We present here evidence that cFP-AAF-pAB has no intrinsic ACE-inhibitory activity. The previously observed inhibition is shown to be dependent on cleavage of the Ala-Phe bond in the inhibitor by endopeptidase 24.11 (enkephalinase, EC 3.4.24.11), a contaminant of some ACE preparations.

Evidence for the presence of five distinct proteolytic components in the pituitary multicatalytic proteinase complex. Properties of two components cleaving bonds on the carboxyl side of branched chain and small neutral amino acids

Initial studies on the specificity of the multicatalytic proteinase complex (MPC; EC 3.4.99.46) led to the identification of three distinct proteolytic components designated as trypsin-like, chymotrypsin-like, and peptidylglutamyl-peptide hydrolyzing, all sensitive to inactivation by 3,4-dichloroisocoumarin (DCI), a general serine proteinase inhibitor. The three components cleave the peptidyl-arylamide bonds in the model synthetic substrates, Z-(D)-Ala-Leu-Arg-2-naphthylamide, Z-Gly-Gly-Leu-p-nitroanilide, and Z-Leu-Leu-Glu-2-naphthylamide, respectively. We report here evidence for the presence in the MPC of two additional distinct components, neither of them capable of cleaving the three model substrates. One of these components cleaves the Leu-Gly and the Leu-Ala bonds in the substrates Cbz-Gly-Pro-Ala-Leu-Gly-p-aminobenzoate and Cbz-Gly-Pro-Ala-Leu-Ala-p-aminobenzoate, respectively, and is activated by treatment of the MPC with DCI, N-ethylmaleimide, Mg2+, Ca2+, and low concentrations of sodium dodecyl sulfate and fatty acids. This component is apparently identical with the previously identified DCI-resistant component of the MPC that cleaves preferentially bonds on the carboxyl side of branched chain amino acids in natural peptides including neurotensin and proinsulin [Cardozo, C., Vinitsky, A., Hidalgo, M. C., Michaud, C., & Orlowski, M. (1992) Biochemistry 31, 7373-7380]. It is probably also identical with the component proposed to be the main factor responsible for the caseinolytic activity [Pereira, M. E., Nguyen, T., Wagner, B. J., Margolis, J. W., Yu, B., & Wilk, S. (1992a) J. Biol. Chem. 267, 7949-7955]. The designation "branched chain amino acid preferring" (BrAAP) is proposed for this component. The second component cleaves peptide bonds between the small neutral amino acids Ala-Gly and Gly-Gly in the substrates Cbz-Gly-Pro-Ala-Ala-Gly-p-aminobenzoate and Cbz-Gly-Pro-Ala-Gly-Gly-p-aminobenzoate, respectively. This component is sensitive to inactivation by DCI, N-ethylmaleimide, and organic mercurials, but unlike the BrAAP it is significantly activated neither by Mg2+ or Ca2+ nor by fatty acids or sodium dodecyl sulfate. The designation "small neutral amino acid preferring" (SNAAP) is proposed for this component. Both components are sensitive to inhibition by the peptidyl-aldehydes N-acetyl-Leu-Leu-norleucinal (Ac-LLnL-CHO; calpain inhibitor I) and N-acetyl-Leu-Leu-methioninal (Ac-LLM-CHO; calpain inhibitor II) but are resistant to inhibition by Z-LLF-CHO, a potent inhibitor of the chymotrypsin-like activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Catalytic components of the bovine pituitary multicatalytic proteinase complex (proteasome)

The multicatalytic proteinase complex (MPC), also called the proteasome, is a ubiquitous particle (19S) that is required for life. It is found in the cytoplasm and nucleus of all eukaryotic cells where it degrades selected cytosolic and nuclear proteins. It forms the proteolytic core of the 26S complex that represents the final step in the ubiquitin-dependent pathway of proteolysis. The MPC expresses at least five distinct proteolytic activities. Three activities preferring cleavages on the carboxyl side of neutral amino acids were described: an activity cleaving after branched chain residues, termed branched chain amino acid preferring, that is a major factor in the degradation of proteins, an activity preferring cleavages after bulky hydrophobic residues designated chymotrypsin-like, and an activity cleaving between small neutral amino acids. Activities cleaving after basic (trypsin-like) and acidic residues (peptidylglutamyl peptide-hydrolyzing) have also been described. The expression of multiple proteolytic activities with diverse specificities may provide a functional advantage that allows efficient hydrolysis of target proteins.