Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P15088 (mast cell)
 14,925 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human chymase and rat chymase-1 are mast cell serine proteases involved in angiotensin II (Ang II) formation and degradation, respectively. Previous studies indicate that both these enzymes have similar P1 and P2 preferences, which are the major determinants of specificity. Surprisingly, despite the occurrence of optimal P2 and P1 residues at the Phe8 downward arrow and Tyr4 downward arrow bonds (where downward arrow, indicates the scissile bond in peptide substrates) in Ang I (DRVYIHPFHL), human chymase cleaves the Phe8 downward arrow bond with an approximately 750-fold higher catalytic efficiency (kcat/Km) than the Tyr4 downward arrow bond in Ang II (DRVYIHPF), whereas rat chymase-1 cleaves the Tyr4 downward arrow bond with an approximately 20-fold higher catalytic efficiency than the Phe8 downward arrow bond. Differences in the acyl groups IHPF and DRVY at the Phe8 downward arrow and Tyr4 downward arrow bonds, respectively, are chiefly responsible for the preference of human chymase for the Phe8 downward arrow bond. We show that the IHPF sequence forms an optimal acyl group, primarily through synergistic interactions between neighboring acyl group residues. In contrast to human chymase, rat chymase-1 shows a preference for the Tyr4 downward arrow bond, mainly because of a catalytically productive interaction between the enzyme and the P'1 Ile5. The overall effect of this P'1 Ile interaction on catalytic efficiency, however, is influenced by the structure of the acyl group and that of the other leaving group residues. For human chymase, the P'1 Ile interaction is not productive. Thus, specificity for Ang II formation versus Ang II degradation by these chymases is produced through synergistic interactions between acyl or leaving group residues as well as between the acyl and leaving groups. These observations indicate that nonadditive interactions between the extended substrate binding site of human chymase or rat chymase-1 and the substrate are best explained if the entire binding site is taken as an entity rather than as a collection of distinct subsites.
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PMID:Distinct multisite synergistic interactions determine substrate specificities of human chymase and rat chymase-1 for angiotensin II formation and degradation. 900 43

The enzymatic pathways for local angiotensin II (Ang II) formation in the heart have been studied both in vivo and in vitro, but the results of these experiments have been discrepant. Thus, the experiments in vivo with intact hearts, both in humans and in animal models, have unequivocally demonstrated that the major Ang II-forming enzyme is angiotensin-converting enzyme (ACE). In contrast, the experiments in vitro with both human or animal heart preparations, have unequivocally demonstrated that the major Ang II-forming enzyme is chymase, a mast cell-derived chymotrypsin-like serine protease. The in vitro approach, however, seems to involve several pitfalls, which tend to overestimate the contribution of chymase as compared to that of ACE. It seems evident that in vivo the chymase-mediated Ang II formation is subjected to local inhibition, a fact that has been overlooked in most of the studies performed in vitro. Accordingly, human chymase, even in its natural form as a protease-proteoglycan complex, is highly sensitive to the protease inhibitors naturally present in the interstitial fluid (IF). We found that if human heart tissue preparations are incubated in vitro in the presence of IF, the chymase-mediated Ang II formation is almost totally suppressed. As the heart interstitium is constantly bathed by IF with its protease inhibitors in concentrations sufficiently high to ensure efficient inhibition of this enzyme, the protease inhibitor-mediated suppression of chymase should also be effective in vivo. Thus, the local production of Ang II in the human heart appears to be regulated by ACE rather than by chymase.
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PMID:Angiotensin II formation in the human heart: an ACE or non-ACE-mediated pathway? 980 Aug 78

Angiotensin II (Ang II) has powerful modulatory actions on cardiovascular function that are mediated by specific receptors located on neurons within the hypothalamus and brain stem. Incubation of neuronal cocultures of rat hypothalamus and brain stem with Ang II elicits an Ang II type 1 (AT1) receptor-mediated inhibition of total outward K+ current that contributes to an increase in neuronal firing rate. However, the exact K+ conductance(s) that is inhibited by Ang II are not established. Pharmacological manipulation of total neuronal outward K+ current revealed a component of K+ current sensitive to quinine, tetraethylammonium, and 4-aminopyridine, with IC50 values of 21.7 micromol/L, 1.49 mmol/L, and 890 micromol/L, respectively, and insensitive to alpha-dendrotoxin (100 to 500 nmol/L), charybdotoxin (100 to 500 nmol/L), and mast cell degranulating peptide (1 micromol/L). Collectively, these data suggest the presence of Kv2.2 and Kv3.1b. Biophysical examination of the quinine-sensitive neuronal K+ current demonstrated a macroscopic conductance with similar biophysical properties to those of Kv2.2 and Kv3.1b. Ang II (100 nmol/L), in the presence of the AT2 receptor blocker PD123,319, elicited an inhibition of neuronal K+ current that was abolished by quinine (50 micromol/L). Reverse transcriptase-polymerase chain reaction analysis confirmed the presence of Kv2.2 and Kv3.1b mRNA in these neurons. However, Western blot analyses demonstrated that only Kv2.2 protein was present. Coexpression of Kv2.2 and the AT1 receptor in Xenopus oocytes demonstrated an Ang II-induced inhibition of Kv2.2 current. Therefore, these data suggest that inhibition of Kv2.2 contributes to the AT1 receptor-mediated reduction of neuronal K+ current and subsequently to the modulation of cardiovascular function.
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PMID:Angiotensin II type 1 receptor-mediated inhibition of K+ channel subunit kv2.2 in brain stem and hypothalamic neurons. 1002 10

The effects of cold-restraint stress, repeated over 3 days, and treatment of rats with vasoactive intestinal peptide (VIP) on the contractile responses of isolated aorta to vasoconstrictors, and on aortic adventitial mast cells were investigated. Stress significantly reduced the contractile response of rat aorta smooth muscle to norepinephrine (NE), angiotensin II (Ang II) and vasopressin (VP). Decreased sensitivity to NE, Ang II and VP may result from decreased receptor density, and affinity or reduced effector efficacy. Stress induced degranulation, decreased the number and changed the granular content of mast cells; all degranulated mast cells were stained with alcian blue, and the percentage of safranin staining cells was decreased. Given prior to stress, VIP reversed the reduced contractile responses and sensitivity of aorta to NE and Ang II but had no effect on VP subsensitivity. VIP also inhibited stress-induced degranulation of mast cells, and after VIP only alcian blue-stained mast cells were seen. When VIP was given to non-stressed rats, the contractile response of the aorta to NE, but not Ang II or VP, was increased compared with control. Mast cell count was decreased in the adventitia of non-stressed VIP treated rats. The results indicate that stress decreases the heparin content of mast cells and VIP has an additive effect. In conclusion, VIP modulates both stress-induced mast cell activity and reduced sensitivity of aorta smooth muscle to NE and Ang II. It can be suggested that VIP may moderate some effects of stress on vascular pathophysiology.
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PMID:The effect of stress and in vivo vasoactive intestinal peptide (VIP) treatment on the response of isolated rat aorta to norepinephrine, angiotensin II and vasopressin, and adventitial mast cells. 1134 95

We investigated the degradation of angiotensin I (Ang I) by guinea pig aqueous humor at physiological pH (pH 7.4) and assessed the activity of responsible enzymes using various enzyme inhibitors. The aqueous humor was incubated with Ang I in the presence or absence of an enzyme inhibitor at 37 degrees C for the appropriate time period. The resulting peptides were analyzed by a Beckman HPLC system with a Waters microBondapak C18 analytical column using a 30-min increasing linear gradient of 10 to 40% acetonitrile containing 0.05% trifluoroacetic acid (TFA) and H2O containing 0.05% TFA at a flow rate of 1 mL/min. Detection was done by absorbance at 214 nm. Angiotensin II (Ang II) was a major product (39.3+/-4.10 nmol x h(-1) mL(-1), n = 5) of Ang I hydrolysis. Traces of angiotensin 1-9, angiotensin IV, and angiotensin 1-7 were also produced. Chymostatin (0.05 mmol/L), EDTA (1 mmol/L), enalaprilat (0.1 mmol/L), and ebelacton B (0.01 mmol/L) inhibited generation of Ang II from Ang I by guinea pig aqueous humor by 89+/-4.6, 56+/-7.6, 33+/-5.1, 20+/-6.5%, respectively. Our findings indicate that guinea pig aqueous humor contains several enzymes that can form Ang II. The chymostatin-sensitive type of enzyme was the most active one found in guinea pig aqueous humor. Angiotensin I converting enzyme, carboxypeptidase A, and deamidase may also contribute to angiotensin II formation in guinea pig ocular fluid.
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PMID:Metabolism of angiotensin I by guinea pig aqueous humor. 1147 97

In this study we demonstrate that carboxypeptidase A (CPA)-like enzyme is expressed in rat kidney. The major metabolites of angiotensin (Ang) I by the rat renal mesangial cell extract at 37 degrees C, pH 7.4, were Ang 1-9 and Ang II. Quinaprilat did not influence the formation of Ang 1-9, but it inhibited formation of Ang II. The formation of Ang 1-9 was inhibited by potato carboxypeptidase inhibitor, 1,10-phenanthroline or EDTA. Lowering the pH from 7.4 to 4.0 also inhibited the formation of this nonapeptide. These findings suggest that a metallocarboxypeptidase is responsible for Ang 1-9 production. Using monoclonal antibodies to CPA, Western blot showed the presence of CPA-like enzyme in the extracts prepared from the mesangial cells or kidney cortex of the rat. Immunohistochemistry showed that CPA-like enzyme is localized in the mesangial glomerular cells and adventitia of kidney blood vessels, whereas it was absent in the renal tubules. Our data suggest that a CPA-like enzyme could be added to a repertoire of enzymes present in the rat mesangial cells and adventitia of renal blood vessels.
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PMID:Localization of carboxypeptidase A-like enzyme in rat kidney. 1461 96

Chymase is a chymotrypsin-like serine protease secreted from mast cells. Mammalian chymases are classified into two subgroups (alpha and beta) according to structure and substrate specificity; human chymase is an alpha-chymase. An important action of chymase is the ACE-independent conversion of Ang I to Ang II, but chymase also degrades the extracellular matrix, activates TGF-beta1 and IL-1beta, forms 31-amino acid endothelins and is involved in lipid metabolism. Under physiological conditions, the role of chymase in blood vessels is uncertain. In pathological situations, however, chymase may be important. In animal models of hypertension and atherosclerosis, chymase may be involved in lipid deposition and intimal and smooth muscle hyperplasia, at least in some vessels. In addition, chymase has pro-angiogenic properties. In human diseased blood vessels (e.g. atherosclerotic and aneurysmal aorta; remodeled pulmonary blood vessels), there are increases in chymase-containing mast cells and/or in chymase-dependent conversion of Ang I to Ang II. These findings have raised the possibility that inhibition of chymase may have a role in the therapy of vascular disease. The effects of chymase can theoretically be attenuated either by reducing availability of the enzyme, with a mast cell stabiliser, or alternatively with specific chymase inhibitors. The mast cell stabiliser, tranilast, was shown to be beneficial in animal models of atherosclerosis, where a prevention protocol was used, but was not effective in clinical trials where it was administered after angioplasty. Chymase inhibitors could have the advantage of being effective even if used after injury. Several orally active inhibitors, including SUN-C8257, BCEAB, NK3201 and TEI-E548, are now available. These have yet to be tested in humans, but promising results have been obtained in animal models of atherosclerosis and angiogenesis. It is concluded that orally active inhibitors of chymase may have a place in the treatment of vascular diseases where injury-induced mast cell degranulation contributes to the pathology.
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PMID:Vascular chymase: pathophysiological role and therapeutic potential of inhibition. 1498 62

The octapeptide angiotensin II (Ang II) exerts a wide range of effects on the cardiovascular system but has also been implicated in the regulation of cell proliferation, fibrosis, and apoptosis. Ang II is formed by cleavage of Ang I by angiotensin-converting enzyme, but there is also evidence for non-angiotensin-converting enzyme-dependent conversion of Ang I to Ang II. Here we address the role of mast cell proteases in Ang II production by using two different mouse strains lacking mast cell heparin or mouse mast cell protease 4 (mMCP-4), the chymase that may be the functional homologue to human chymase. Ang I was added to ex vivo cultures of peritoneal cells, and the generation of Ang II and other metabolites was analyzed. Activation of mast cells resulted in marked increases in both the formation and subsequent degradation of Ang II, and both of these processes were strongly reduced in heparin-deficient peritoneal cells. In the mMCP-4(-/-) cell cultures no reduction in the rate of Ang II generation was seen, but the formation of Ang-(5-10) was completely abrogated. Addition of a carboxypeptidase A (CPA) inhibitor to wild type cells caused complete inhibition of the formation of Ang-(1-9) and Ang-(1-7) but did not inhibit Ang II formation. However, when the CPA inhibitor was added to the mMCP-4(-/-) cultures, essentially complete inhibition of Ang II formation was obtained. Taken together, the results of this study indicate that mast cell chymase and CPA have key roles in both the generation and degradation of Ang II.
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PMID:Cooperation between mast cell carboxypeptidase A and the chymase mouse mast cell protease 4 in the formation and degradation of angiotensin II. 1517 64

Angiotensin I-converting enzyme (ACE) inhibitors are thought to lower blood pressure in hypertensive patients, mainly by decreasing angiotensin II (Ang II) formation. Chymase, a human mast cell protease, has recently been proposed to play a role in blood pressure regulation because of its Ang II-forming activity. Here we show that the predominant chymase mRNA species in the mouse aorta are those for types 4 and 5 isoforms, and that both are efficient Ang II-forming enzymes. Evaluation of ACE-dependent and ACE-independent Ang II-forming pathways in mast cell-deficient (Kit(w)/Kit(w-v)) mice and their mast cell-sufficient littermate (MC(+/+)) controls revealed that, in contrast to the latter, Kit(w)/Kit(w-v) mice fail to express chymase mRNAs in the vasculature and have almost no ACE-independent Ang II-forming activity in either isolated blood vessels or homogenates. Moreover, in MC(+/+) but not in Kit(w)/Kit(w-v) mice, a contribution of ACE-independent Ang II generation to blood pressure regulation was evident by a 1.6-fold greater maximal reduction in mean arterial pressure with acute ACE inhibition plus AT(1) receptor blockade than with ACE inhibition alone. Thus, mast cells are the source of the vascular ACE-independent pathway, and the antihypertensive benefit of combining ACE inhibitor therapy with AT(1) receptor antagonist therapy is most likely due to negation of chymase-catalyzed Ang II generation.
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PMID:Involvement of chymase-mediated angiotensin II generation in blood pressure regulation. 1523 18

The renin-angiotensin system (RAS) acts to regulate blood volume and arterial pressure, and has direct effects on the heart. Renin, released by the kidney, circulates and acts-in the rate-limiting step of angiotensin II (Ang II) production-to convert angiotensinogen to inactive angiotensin I (Ang I). Ang II constricts vessels, leading to increased arterial pressure, among other effects. Components of the RAS have been found in a number of extra-renal tissues. Recent research indicates that mast cells in the heart may produce renin, creating a cardiac-specific RAS that acts locally to produce Ang II. These results, however, are not without controversy. Others have searched for sites of renin production and have found no other significant source that was physiologically important or that could not be completely ruled out as a possible contaminant. How important is mast cell-synthesized renin for direct cardiac-related effects?
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PMID:Mast cells: the missing source of cardiac renin? 1573


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