Processing of proendothelin-1 at the C-terminus of big endothelin-1 is essential for proteolysis by endothelin-converting enzyme-1 in vivo

Endothelin and the heart in health and diseases

Endothelin-1 (ET-1), a 21-amino acid peptide, was initially identified in 1988 as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. From human genomic DNA analysis, two other family peptides, ET-2 and ET-3, were found. They showed different effects and distribution, suggesting that each peptide may play separate roles in different organs. In the heart, ET-1 also causes positive inotropic and chronotropic responses and hypertrophic activity of the cardiomyocytes. ETs act via activation of two receptor subtypes, ET_A and ET_B receptors, both of which are coupled to various GTP-binding proteins depending on cell types. Endogenous ET-1 may be involved in progression of various cardiovascular diseases. ET antagonists are currently used clinically in the treatment for patients with pulmonary hypertension, and are considered to have further target diseases as heart failure, cardiac hypertrophy and other cardiac diseases, renal diseases, systemic hypertension, and cerebral vasospasm.

Substance P stimulates endothelin 1 secretion via endothelin-converting enzyme 1 and promotes melanogenesis in human melanocytes

Substance P (SP) is a well-known neuropeptide implicated in the wound-healing process. The wound occasionally causes a pigmented scar. In the present study, we examined whether increased levels of SP affected melanogenesis. When human melanocytes were treated with SP, the melanin content increased and the pigmentation process accelerated in a dose-dependent manner. In addition to melanogenesis-related genes, the expression of neurokinin 1 receptor, endothelin 1 (EDN1), and EDN receptor type B (EDNRB) also increased at both the messenger RNA and protein levels. Interestingly, secreted EDN1 was observed in the melanocyte culture medium, and this phenomenon was significantly enhanced by SP treatment. Through knockdown experiments using small interfering RNAs (siRNAs), we confirmed that endothelin-converting enzyme 1 (ECE1), EDN1, and EDNRB were involved in SP-induced pigmentation and found that EDN1 secretion was affected by ECE1 and EDN1 siRNAs, but not by EDNRB siRNA. These findings indicate that ECE1 is essential for EDN1 secretion in melanocytes and that EDNRB functions downstream of secreted EDN1 to increase the cAMP levels and activate the melanogenesis-related phosphorylation cascade. This study provides in vitro evidence for a melanogenic function of SP in the skin and suggests that the SP-related signal is a potent target for regulating stress- or wound-induced pigmentation.

An arterial-specific enhancer of the human endothelin converting enzyme 1 (ECE1) gene is synergistically activated by Sox17, FoxC2, and Etv2

Endothelin-converting enzyme-1 (Ece-1), a crucial component of the Endothelin signaling pathway, is required for embryonic development and is an important regulator of vascular tone, yet the transcriptional regulation of the ECE1 gene has remained largely unknown. Here, we define the activity and regulation of an enhancer from the human ECE1 locus in vivo. The enhancer identified here becomes active in endothelial progenitor cells shortly after their initial specification and is dependent on a conserved FOX:ETS motif, a composite binding site for Forkhead transcription factors and the Ets transcription factor Etv2, for activity in vivo. The ECE1 FOX:ETS motif is bound and cooperatively activated by FoxC2 and Etv2, but unlike other described FOX:ETS-dependent enhancers, ECE1 enhancer activity becomes restricted to arterial endothelium and endocardium by embryonic day 9.5 in transgenic mouse embryos. The ECE1 endothelial enhancer also contains an evolutionarily-conserved, consensus SOX binding site, which is required for activity in transgenic mouse embryos. Importantly, the ECE1 SOX site is bound and activated by Sox17, a transcription factor involved in endothelial cell differentiation and an important regulator of arterial identity. Moreover, the ECE1 enhancer is cooperatively activated by the combinatorial action of FoxC2, Etv2, and Sox17. Although Sox17 is required for arterial identity, few direct transcriptional targets have been identified in endothelial cells. Thus, this work has important implications for our understanding of endothelial specification and arterial subspecification.

Structure-activity relationship of resveratrol and its analogue, 4,4'-dihydroxy-trans-stilbene, toward the endothelin axis in human endothelial cells

Resveratrol inhibits endothelin-1, a vascular tension regulator. We synthesized the resveratrol analogue 4,4'-dihydroxy-trans-stilbene with 2 hydroxyl groups in the 4 and 4' position to obtain a molecule more active than resveratrol (3,4',5-trihydroxy-trans-stilbene). The results demonstrate that 4,4'-dihydroxy-trans-stilbene led to a significant decrease in total endothelin-1 secretion and in endothelin-1 messenger RNA (mRNA) levels in human endothelial cells. In addition, resveratrol and its analogue decreased endothelin-converting enzyme-1 mRNA levels and further reduced the activity of the enzyme. 4,4'-dihydroxy-trans-stilbene was more active than resveratrol because the new molecule exerted greater activity at the level of endothelin synthesis and conversion, even at a lower concentration. Although 4,4'-dihydroxy-trans-stilbene and resveratrol inhibited formation of reactive oxygen species and lipid peroxidation, the treatment of cells with different oxidant agents did not modify the endothelin-1 release. This finding suggests that the inhibition of endothelin-1 secretion is independent of the antioxidant properties of the 2 compounds. On the basis of these results, the resveratrol analogue 4,4'-dihydroxy-trans-stilbene could be a promising chemopreventive agent against cardiovascular diseases.

Teratogenic effects of blue cohosh (Caulophyllum thalictroides) in Japanese medaka (Oryzias latipes) are probably mediated through GATA2/EDN1 signaling pathway

Blue cohosh (Caulophyllum thalictroides) (BC) has been used widely to induce labor and to treat other uterine conditions. However, the safety and effectiveness of this herbal product has not yet been evaluated by the US Food and Drug Administration (FDA). Several conflicting reports indicated that the root extract of BC is a teratogen and, by some unknown mechanisms, is able to induce cardiovascular malfunctions in new-born babies. To understand the mechanism, we have used Japanese medaka (Oryzias latipes) embryo-larval development as the experimental model and the methanolic extract of BC root as the teratogen. The embryo mortality, hatching efficiency, and morphological abnormalities in craniofacial and cardiovascular systems are considered for the evaluation of BC toxicity. Our results indicate that BC is able to disrupt cardiovascular and craniofacial cartilage development in medaka embryo in a dose and developmental stage-specific manner. Moreover, embryos in precirculation are to some extent more resistant to BC than ones with circulation. By using subtractive hybridization, we have observed that gata2 mRNA was differentially expressed in the circulating embryos after BC treatment. As GATA-binding sequences are required for the expression of the endothelin1 (edn1) gene and edn1 expressed in blood vessels and craniofacial cartilages, we have extended our investigations to edn1 gene expression regulation by BC. We found that edn1, furin1, and endothelin receptor A (ednrA) genes are developmentally regulated; endothelin converting enzyme mRNA (ece1) maintained a steady-state level throughout development. Circulating medaka embryos (3 days post fertilization, dpf) exposed to BC (10 microg/mL) for 48 h have increased levels of gata2, ece1, and preproenodthelin (preproedn1) mRNA contents; however, other mRNAs (furin and ednrA) remained unaltered. Therefore, the enhanced expression of gata2 mRNA followed by ece1 and preproedn1 mRNA by BC might be able to induce vasoconstriction and cardiovascular defects and disrupt craniofacial cartilages in medaka embryos. We conclude that cardiovascular and craniofacial defects in medaka embryogenesis by BC are probably mediated through a GATA2-EDN1 signaling pathway.

Structure of human endothelin-converting enzyme I complexed with phosphoramidon

Endothelin-converting enzyme I (ECE-1) is a mammalian type II integral membrane zinc-containing endopeptidase. ECE-1 catalyzes the final step in the biosynthesis of endothelins in a rate-limiting fashion, through post-translational conversion of the biologically inactive big endothelins. Endothelin-1 overproduction has been implicated in a heterogeneous list of diseases including systemic and pulmonary hypertension, stroke and asthma, cardiac and renal failure. Therefore, ECE-1 is a prime therapeutic target for the regulation of endothelin-1 production in vivo and there is considerable interest in selective inhibitors of this enzyme. Here, we present the crystal structure of the extracellular domain (residues 90-770) of human ECE-1 (C428S) with the generic metalloprotease inhibitor phosphoramidon determined at 2.38 A resolution. The structure is closely related to that of human NEP, providing essential information for a detailed understanding of ligand-binding, specificity determinants as well as selectivity criteria. Selective inhibitors of ECE-1s should have beneficial effects for the treatment of diseases in which an overproduction of ETs plays a pathogenic role.

Crosstalk Between Mesangial and Endothelial Cells: Angiotensin II Down-Regulates Endothelin-Converting Enzyme 1

OBJECTIVE

Since mesangial and endothelial cells interact in the kidney, the present experiments were designed to analyze the ability of human mesangial cells (HMC) to modulate endothelin-1 (ET-1) synthesis by human umbilical vein endothelial cells (HuVEC).

METHODS AND RESULTS

The supernatants of HuVEC/HMC contained significantly lower amounts of ET-1 than those of HuVEC alone. This effect was not due to a decreased prepro-ET-1 mRNA expression and was only partially the consequence of HMC-dependent ET-1 degradation. Therefore, we tested the influence of the coculture on endothelin-converting enzyme-1 (ECE-1), and found a significant reduction of its mRNA and protein levels as well as a decreased activity in HuVEC/HMC as compared to HuVEC alone. Using a pharmacological blockade approach (sulotrobam, BN52021, losartan or catalase), losartan was shown to completely abolish down-regulation of ECE-1 observed in HuVEC/HMC. Angiotensin II (AII) induced a dose and time-dependent inhibition of ECE-1 expression in HuVEC.

CONCLUSIONS

These results support the importance of cross-talk among different cell types in the regulation of vascular or renal function. ET-1, and particularly ECE-1, might constitute a target in this regulation. In addition, locally synthesized AII could be one of the mediators involved in the down-regulation of ECE-1.

Evaluation of the Lys198Asn and -134delA Genetic Polymorphisms of the Endothelin-1 Gene

Endothelin-1 (ET-1) is a potent vasoconstrictor and shows various pharmacological responses. Two single nucleotide polymorphisms in the ET-1 gene (EDN1) have been reported to be associated with blood pressure (BP). One is the Lys198Asn polymorphism, which showed a positive association with BP in overweight people. Another is the 3A/4A polymorphism (-134delA) located in the 5'-untranslated region. In this study, we investigated the expression of the Lys198Asn polymorphism in ET-1 in vitro, as well as the association between either of the two polymorphisms and the plasma ET-1 level. We expressed both the major (Lys-type) and minor type (Asn-type) preproET-1 in three different cell lines, and measured the levels of ET-1 and big ET-1 in the culture supernatant. There was no significant difference in the levels of ET-1 or big ET-1 between the Asn-type and Lys-type transfectant. In the association study, the plasma levels of ET-1 in 54 hypertensive patients having an amino acid substitution from Lys to Asn at position 198 were not different from those of hypertensives without the substitution. However, we found a significant difference in ET-1 levels between individuals with the 3A/3A and 3A/4A genotypes. Our transient expression study indicates that the Lys198Asn polymorphism may not directly affect ET-1 and big ET-1 production. Another variant in the EDN1 gene in linkage disequilibrium with the Lys198Asn polymorphism may be responsible for the association with BP, or the interaction between the EDN1 Lys198Asn polymorphism and other factors such as obesity may be involved in the mechanisms elevating BP in vivo.

Physiologic determinants of endothelin concentrations in human saliva

BACKGROUND

Salivary endothelin (ET) concentrations have been shown to correlate with disease severity in patients with chronic heart failure (CHF). We undertook the present study to evaluate the stability of salivary ET under different handling conditions to assess its suitability as a biochemical marker in screening, diagnosis, and management of CHF.

METHODS

Saliva samples were collected from healthy individuals and/or CHF patients, subjected to different handling conditions, and then stored at -80 degrees C until assayed by an ELISA for ET.

RESULTS

Salivary ET concentrations showed a time-dependent increase during storage at room temperature. After 72 h of incubation at room temperature, ET increased approximately 2.8-fold (P = 0.03). Simultaneously, salivary big ET showed a time-dependent 11.2-fold decrease (P <0.0001). This activity was blocked by an ET-converting enzyme (ECE) inhibitor, suggesting that these changes were attributable to ECE-dependent cleavage of endogenous big ET in saliva. Ex vivo conversion was also observed when samples were stored at 4 degrees C, but the magnitude of these changes was markedly smaller (P <0.0001). Posture also affected salivary ET concentrations in CHF patients. With a change from supine to seated rest, salivary ET concentrations increased 1.5- and 1.8-fold after 20 and 40 min, respectively (P = 0.01). With a return to supine rest, salivary ET concentrations returned to baseline concentrations (P = 0.008).

CONCLUSIONS

These data suggest that saliva sampling and handling conditions could markedly affect measurement of salivary ET. In particular, care should be taken to minimize ECE-dependent enzymatic conversion of endogenous big ET in saliva.

Synthesis and degradation of endothelin-1

The endothelin-converting enzyme (ECE) is the main enzyme responsible for the genesis of the potent pressor peptide endothelin-1 (ET-1). It is suggested that the ECE is pivotal in the genesis of ET-1, considering that the knockout of both genes generates the same lethal developments during the embryonic stage. Several isoforms of the ECE have been disclosed, namely ECE-1, ECE-2, and ECE-3. Within each of the first two groups, several sub-isoforms derived through splicing of single genes have also been identified. In this review, the characteristics of each sub-isoform for ECE-1 and 2 will be discussed. It is important to mention that the ECE is, however, not the sole enzyme involved in the genesis of endothelins. Indeed, other moieties, such as chymase and matrix metalloproteinase II, have been suggested to be involved in the production of ET intermediates, such as ET-1 (1-31) and ET-1 (1-32), respectively. Other enzymes, such as the neutral endopeptidase 24-11, is curiously not only involved in the degradation and inactivation of ET-1, but is also responsible for the final production of the peptide via the hydrolysis of ET-1 (1-31). In this review, we will attempt to summarize, through the above-mentioned characteristics, the current wisdom on the role of these different enzymes in the genesis and termination of effect of the most potent pressor peptide reported to date.

Heterodimerization of endothelin-converting enzyme-1 isoforms regulates the subcellular distribution of this metalloprotease

Endothelin-converting enzyme (ECE) is a membrane metalloprotease that generates endothelin from its direct precursor big endothelin. Four isoforms of ECE-1 are produced from a single gene through the use of alternate promoters. These isoforms share the same extracellular catalytic domain and contain unique cytosolic tails, which results in their specific subcellular targeting. We investigated the distribution of ECE-1 isoforms in transfected AtT-20 neuroendocrine cells. Whereas ECE-1a and 1c were present at the plasma membrane, ECE-1b and ECE-1d were retained inside the cells. We found that both intracellular isoforms were concentrated in the endosomal system: ECE-1d in recycling endosomes, and ECE-1b in late endosomes/multivesicular bodies. Leucine-based motifs were involved in the intracellular retention of these isoforms, and the targeting of ECE-1b to the degradation pathway required an additional signal in the N terminus. The concentration of ECE-1 isoforms in the endosomal system suggested new functions for these enzymes. Potential novel functions include redistribution of other isoforms through direct interaction. We have showed that ECE-1 isoforms could heterodimerize, and that in such heterodimers the ECE-1b targeting signal was dominant. Interaction of a plasma membrane isoform with ECE-1b resulted in its intracellular localization and decreased its extracellular activity. These data demonstrated that the targeting signals specific for ECE-1b constitute a regulatory domain per se that could modulate the localization and the activity of other isoforms.

Processing of proendothelin-1 by members of the subtilisin-like pro-protein convertase family

Endothelial cells (ECs) secrete numerous bioactive peptides that are initially synthesized as inactive precursor proteins. One of these, proendothelin-1 (proET-1), undergoes proteolysis at specific pairs of basic amino acids. Here, we wished to examine the role of mammalian convertases in this event. Northern blot analysis shows that only furin and PC7 are expressed in ECs. In vitro cleavage of proET-1 by furin or PC7 demonstrated that both enzymes efficiently and specifically process proET-1. These data reveal that furin and PC7 have similar specificities towards proET-1 and suggest that both enzymes may participate in the maturation of proET-1 in ECs.

Hydrogen peroxide regulation of bovine endothelin-converting enzyme-1

Vascular injury leads to the production of reactive oxygen species (ROS), but the mechanisms by which ROS contribute to vascular pathology are not completely understood. We hypothesized that ROS increase endothelin converting enzyme (ECE-1) expression. We found that glucose oxidase (GO) increases ECE-1 mRNA, protein, and activity in bovine aortic endothelial cells. Catalase abolishes this effect. Glucose oxidase treatment of endothelial cells transactivates the ECE-1 promoter. The ECE-1 promoter element that mediates this response to GO is located between -444 and -216 bp. This region contains a STAT response element, and GO activates STAT-3 binding to this STAT response element. Our data suggest that STAT3 mediates hydrogen peroxide induction of ECE-1 expression.

The mechanism of hyperpigmentation in seborrhoeic keratosis involves the high expression of endothelin-converting enzyme-1alpha and TNF-alpha, which stimulate secretion of endothelin 1

BACKGROUND

Seborrhoeic keratosis (SK) is a benign epidermal tumour with increased pigmentation. We have recently demonstrated that increased secretion of endothelin (ET)-1, a strong keratinocyte-derived mitogen and melanogen for human melanocytes, is intrinsically involved in the hyperpigmentation mechanism of SK.

OBJECTIVES

To examine whether the increased ET secretion results from cytokines that induce ET production and/or from differences in the processing of ET that lead to its final active, secreted form.

METHODS

We used immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) to determine whether ET-inducing enzymes and/or cytokines are also highly expressed in SK.

RESULTS

RT-PCR of mRNAs encoding interleukin (IL)-1alpha, tumour necrosis factor (TNF)-alpha and endothelin-converting enzyme (ECE)-1alpha demonstrated that there is an increased expression of TNF-alpha and ECE-1alpha mRNAs in SK, whereas the IL-1alpha transcript is rather downregulated in SK compared with that in perilesional normal epidermis. In parallel, immunohistochemical analysis of SK revealed marked immunostaining for TNF-alpha in basaloid cells at lower levels of the epidermis and in basal cells, and for ECE-1alpha in most basaloid and basal cells in comparison with their weak staining throughout the epidermis in perilesional normal controls. In contrast, immunostaining for IL-1alpha was almost negative in SK relative to distinctive staining throughout the epidermis in the perilesional normal controls.

CONCLUSIONS

These findings suggest that the increased secretion of ET-1 leading to enhanced pigmentation in SK results from the co-ordinated increased expression of TNF-alpha and ECE-1alpha.

Immunohistochemical localization of ECE-1 in the human placenta

Over the last several years, endothelin (ET-1) has emerged as an important mediator in the pathogenesis of pre-eclampsia and preterm labour, as well as in the normal function of gestational tissues. While the distribution of ET and its binding sites in the human placenta have been well studied, much less has so far been reported about the distribution of placental ET-1 processing enzymes. By immunohistochemical analysis and immunofluorescence, endothelin-converting enzyme-1 (ECE-1), the enzyme that synthesizes ET-1, is localized to five distinct cell populations in the human placenta: (1) the endothelial cells lining the maternal basal plate blood vessels, (2) the intermediate trophoblasts, (3) the endothelial cells lining the chorionic villous blood vessels, (4) the chorionic villous stromal cells and (5) the chorionic villous trophoblasts. The localization of ECE-1 corresponds with the previously reported distribution of ET-1 in the human placenta and is in accordance with the function of this enzyme in regulating vascular tone through synthesis of ET-1. The abundance of ECE-1 in the basal plate is consistent with a second possible function of this enzyme in affecting uterine contractions. ECE-1 may serve as a target for prognosis and therapy in states of pathologically altered vascular tone and/or altered myometrial smooth muscle tone in gestation.

Subcellular mechanisms of endothelin action in vascular system

To elucidate the role of endothelin in the regulation of vascular function, the cellular and subcellular mechanisms for the synthesis of endothelin and the function of endothelin-receptors have been studied extensively. In this article, recent results regarding these problems are reviewed. (1) Oxidatively modified low-density-lipoprotein (LDL) reduces nitric oxide (NO) release via inhibition of the high-affinity arginine transporter of endothelial cells. (2) Endothelin-1-induced vasoconstriction is mediated by Ca2+ influx through a non-selective cation channel sensitive to 1-[beta-[3-(4-methoxyphenyl) propoxyl]-4-methoxyphenethyl]-1H-imidazole HCl (SK & F96365). (3) A distinct domain of the endothelin-receptor is required for the coupling of different G(alpha)-proteins. (4) Endothelin ET(A) receptor-mediated mitogenic activity is mediated by two pathways, one classical protein kinase C(PKC)-dependent, and the other phosphoinositide 3-kinase dependent. Both stimulate mitogen-activated protein kinase (MAPK). Endothelin ET(B) receptor-mediated mitogenic activity is also mediated by the PKC-dependent pathway. In contrast, endothelin ET(B) receptor-mediates differentiation and apoptosis via G(alpha)i coupling.

Pathophysiology of endothelin in the cardiovascular system

In this article, we review the basic pharmacological and biochemical features of endothelin and the pathophysiological roles of endothelin in cardiovascular diseases. Development of receptor antagonists has accelerated the pace of investigations into the pathophysiological roles of endogenous endothelin-1 in various diseases, e.g. chronic heart failure, renal diseases, hypertension, cerebral vasospasm, and pulmonary hypertension. In chronic heart failure, the expression of endothelin-1 and its receptors in cardiomyocytes is increased, and treatment with an endothelin receptor antagonist improves survival and cardiac function. Endothelin receptor antagonists also improve other cardiovascular diseases. These results suggest that the interference with endothelin pathway either by receptor blockade or by inhibition of endothelin converting enzyme may provide novel therapeutic drugs strategies for multiple disease states.

Do the structures of big ET-1 and big ET-3 adopt a similar overall fold? Consequences for endothelin converting enzyme specificity

Big ET-1 and big ET-3 are precursor peptides which render endothelin-1 (ET-1) and endothelin-3 (ET-3) relatively unreactive and resistant to proteolytic cleavage. Big ET-1 is cleaved in vivo by ECE-1 (endothelin-converting enzyme), and big ET-3 is also cleaved but apparently to a significantly lesser extent by this enzyme. To shed light on the relation between structure and function, circular dichroism (CD) spectroscopy and homology modeling were used to determine whether big ET-1 and big ET-3 adopt similar secondary and tertiary structures. Analyses of the CD spectra and thermal denaturation indicate they have similar secondary structures and thermal stabilities. Superposition of the modeled coordinates of both peptides indicates that they can adopt the same overall fold except in the C-terminal residues, 34-38 in big ET-1 and 34-41 in big ET-3. This region corresponds to an area of complete sequence heterogeneity between the two peptides. A model has been developed which has a loop for residues 27-30 (HVVP in big ET-1), which have previously been demonstrated to be essential for eliciting efficient hydrolysis of the W21-V22 bond in big ET-1 and which have the sequence QTVP in big ET-3. Differences in affinity between big ET-1 and big ET-3 for ECE-1 thus appear to be due solely to sequence variations in the local region of the cleavage site.

Purification of a novel endothelin-converting enzyme specific for big endothelin-3

Endothelin-3 (ET-3), a potent vasoactive peptide, is considered to be produced from big ET-3 by endothelin-converting enzyme (ECE) like the other members of the endothelin family (ET-1 and ET-2). We purified a novel ECE from bovine iris microsomes. The purified enzyme, a 140 kDa protein by SDS-PAGE analysis, converted big ET-3 to ET-3 but not big ET-1, with a Km value of 0.14 microM for big ET-3. The conversion to ET-3 was confirmed with sandwich EIA by monoclonal antibodies, the elution profile of HPLC, and intracellular calcium mobilization in CHO-K1 cells expressing recombinant human ET(B) receptors. The conversion activity was inhibited by an inhibitor of neutral endopeptidase 24.11 (NEP) phosphoramidon. These results show that ECE-3 purified from bovine iris is a novel metalloprotease totally different from ECE-1 or ECE-2, in that the enzyme is highly specific for big ET-3.