Cloning and sequence analysis of cDNA encoding the precursor of a human endothelium-derived vasoconstrictor peptide, endothelin: identity of human and porcine endothelin

Mouse preproendothelin-1 gene. cDNA cloning, sequence analysis and determination of sites of expression during embryonic development

Endothelin-1 (ET-1) is a peptide implicated in a wide variety of functions involving vascular and non-vascular systems. We have cloned the cDNA encoding the mouse prepro-endothelin-1 (PPET-1) and determined its nucleotide sequence. The putative PPET-1 peptide processing sites are all conserved and the deduced 21-amino-acid mature ET-1 peptide is identical to that of the rat, human, bovine, porcine and rabbit. Using the cloned cDNA as a probe for in situ hybridization, we detected PPET-1 mRNA in different tissues at different stages of mouse embryonic development. Embryos at a stage as early as 9.5 days postcoitum (E9.5) have very strong expression in the branchial epithelium, optic vesicle and the endothelial cells of large blood vessels, including the dorsal aorta and aortic arches. While the expression level in the branchial epithelium was decreasing towards the later stage of embryogenesis, the expression in the endothelial cells increased with age. At E10.5, PPET-1 mRNA was also detected in the otic vesicle as well as in the developing gut epithelium. At later stage of development, the expression of PPET-1 was primarily found in the vascular endothelial cells, cochlea, eye and the gut, with the highest level of PPET-1 mRNA in the endothelial cells of the lung. These data will be useful for analyzing the function of ET-1 in these organs.

Elevation of endothelin biosynthesis in human endothelial cells with mycoplasma infection

The effects of mycoplasma infection on the biosynthesis of endothelin-1 (ET-1) in cultured human vascular endothelial cell lines were examined to understand regulatory mechanisms of ET-1 biosynthesis and causes of angiopathy due to mycoplasma infection. The growth of normal endothelial cells from the umbilical cord vein and of an immortal endothelial cell line transfected with prepro ET-1 cDNA was decreased, while the secretion of ET-1 into the culture medium was enhanced by mycoplasma infection. However, the rate of ET-1 production in these cell cultures was much higher at the growing phase than at the stationary phase. Immunocytochemical studies with anti-ET-1 antibody and an autoradiographic examination of the labeled nuclei with 3H-TdR revealed that mycoplasma infection induced an elevation of ET-1 production in both S and non-S phase cells. The expression of prepro ET-1 mRNA as examined by in situ hybridization and by RNase protection assay was not altered by mycoplasma infection. Thus, the biosynthesis of ET-1 in vascular endothelial cells may be regulated at the posttranscriptional level.

Endothelial cell expression of vasoconstrictors and growth factors is regulated by smooth muscle cell-derived carbon monoxide

CO is produced in vascular smooth muscle cells (VSMC) by heme oxygenase-1 (HO-1). CO increases cGMP levels in VSMC; however, its possible additional roles in the vasculature have not been examined. We report that a product of HO, released from VSMC and inhibited by hemoglobin, has paracrine effects on endothelial cells: it increases endothelial cGMP content and decreases the expression of the mitogens, endothelin-1 (ET-1) and platelet-derived growth factor-B (PDGF-B). This product has the characteristics of CO, and its production is increased sevenfold under hypoxia. The VSMC-derived CO caused a fourfold rise in endothelial cell cGMP. In addition, it inhibited the hypoxia-induced increases in mRNA levels of the ET-1 and PDGF-B genes. Inhibitors of HO, and hemoglobin, a scavenger of CO, prevented the rise in cGMP and also restored the hypoxic response of these genes. The inhibition of ET-1 and PDGF-B mRNA by CO resulted in decreased production of these endothelial-derived mitogens, and in turn, inhibition of VSMC proliferation. These findings suggest an important physiologic role for VSMC-derived CO in modulating cell-cell interaction and cell proliferation in the vessel wall during hypoxia.

Hypoxia induces AP-1-regulated genes and AP-1 transcription factor binding in human endothelial and other cell types

Hypoxia results in differential expression of specific genes in certain cell types. In endothelial cells, hypoxia activates several genes that are known to be inducible by transcription factor AP-1, including endothelin-1 and platelet-derived growth factor-B (PDGF-B). In this study we demonstrated that other AP-1-inducible genes are activated by hypoxia in these cells, including collagenase IV and c-jun, and sought to correlate the activation of genes by hypoxia with the activation of transcription factor AP-1. Depending upon the type of cell studied, hypoxic exposure resulted in the induction of AP-1 transcription factor DNA-binding activity with wide variations in levels of binding. The magnitude of activation of transcription factor AP-1 by hypoxia did not always strictly correlate with the level of induction of AP-1-inducible genes. This finding indicates a requirement for additional mechanisms of controlling transcription beyond the simple activation of AP-1 factor DNA-binding activity for the activation of AP-1-inducible genes during hypoxia. Hypoxia has been reported to lower the intracellular redox potential. The effect of redox state changes on AP-1 transcription factor activity and on the activation of AP-1-inducible genes was also studied. PDTC, a potent reducing agent, activated the AP-1 transcription factor in HeLa cells, and also resulted in increased accumulation of c-jun mRNA in these cells. In contrast to PDTC-mediated activation of the AP-1 transcription factor and the subsequent induction of the AP-1-regulated c-jun gene, hypoxic activation of AP-1 transcription factor binding to its cognate DNA sequence did not activate the c-jun gene in HeLa cells, thus documenting distinct differences in signals generated by the reducing intracellular microenvironments created by hypoxia and PDTC. These results demonstrate the induction of AP-1 transcription factor activity by hypoxic environments, but suggest that additional factors or cell-specific signals are involved in the regulation of hypoxia-induced genes.

Cardiovascular and organ responses and adaptation responses to hypogravity in an experimental animal model

The head-down suspension (i.e. antiorthostatic hypokinesia) rat is used to simulate weightlessness. However, little is known about cardiovascular and organ adaptation responses which, over a long time, can become pathologically significant. The purpose of this study was therefore to evaluate regional changes in the hematology parameters. Endotheline-1 (ET-1) concentration and urinary excretion of N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30) (NAG) in an experimental antiorthostatic rat model. The data indicate significant variations in the plasma ET-1 level in time, in the superior and inferior cava vessel blood of animals maintained for 10 days in hypogravity with respect to controls. These changes do not seem to be due to hemoconcentration. The increase in urinary NAG was observed during the first 24h of experiment, indicating renal stress, probably due to adverse blood flow variations within the organ. We conclude that the plasma ET-1 level changes could be responsible, overall for the blood flow variations in the kidney and renal stress could be the consequence of extended antiorthostatic hypokinesia. The ET-1 behaviour and urinary NAG excretion in rats exposed to antiorthostatic hypokinetic hydynamia offer possibilities for understanding if these changes might be reversible or when they become pathological. This could give some relevant information about the effects of prolonged hypogravity during the space voyage.

Ultraviolet B irradiation increases endothelin-1 and endothelin receptor expression in cultured human keratinocytes

The effect of ultraviolet B (UVB) irradiation on endothelin-1 (ET-1) and ET receptor expression was examined using cultured normal human keratinocytes. Keratinocytes secreted ET-1 in the medium at a level of 2.1 pg/day/10(5) cells. UVB irradiation up to 10 mJ/cm2 increased ET-1 secretion 3-fold, and potentiated expression of mRNA for ET-1. Both ETA and ETB receptor mRNAs were detected in keratinocytes, and their expression was up-regulated by 5 mJ/cm2 UVB irradiation.

Vasoactive peptides and uterine vessels

Endothelins and atrial natriuretic peptide (ANP) are vasoactive peptides with effects on the human uterine and umbilical arteries. Endothelin (ET) contracts the vascular smooth muscle. Both ETA- and non-ETA-non-ETB-receptors seem to be involved. Autoradiography reveals binding of ET to vascular smooth muscle. ANP counteracts the contractile effects of angiotensin II in the human uterine artery. Head-down tilt results in elevation of plasma ANP in healthy pregnant women, while the same manoeuvre induces down-regulation of the reninangiotensin-aldosterone system in non-pregnant women and patients suffering from pre-eclampsia.

Processing of proendothelin-1 by human furin convertase

Endothelin-1 (ET-1) is the most potent vasoactive peptide known to date. The peptide is initially synthesized as an inactive precursor (proET-1) which undergoes proteolysis at specific pairs of basic amino acids to yield bigET-1. Production of ET-1 then proceeds by cleavage of bigET-1 by the endothelin converting enzyme (ECE). Here, we demonstrate that the in vitro cleavage of proET-1 by furin, a mammalian convertase involved in precursor processing, produced bigET-1. Upon further processing, bigET-1 was converted to biologically active ET-1. Furthermore, we demonstrate that the furin inhibitor, decanoyl-Arg-Val-Lys-Arg chloromethylketone, abolished production of ET-1 in endothelial cells.

Effects of bradykinin and endothelin-1 on the calcium homeostasis of mammalian cells

Ca2+ mobilization from intracellular stores is a major event in the signaling cascade triggered by peptide hormone receptors. The transient rise in intracellular free Ca2+ concentration ([Ca2+]i) is well characterized, but little is known about alterations of total cell Ca. Therefore we established a technique to determine changes in total cell Ca during hormone stimulation of 45Ca-loaded cells. Bradykinin and endothelin-1 reduced total cell Ca by up to 56% in HF-15 cells, COS-7 cells, and CHO K1 cells transfected with the rat B2 receptor cDNA. In Rat-1 cells and PC-12 cells, stimulation with endothelin-1 or bradykinin did not result in a net decrease in total cell Ca at physiological extracellular Ca2+ concentration. Decrease in total cell Ca was preceded by an increase in [Ca2+]i and blunting of the transient rise in [Ca2+]i by a Ca2+ chelator prevented the hormone-induced decrease in total cell Ca. Previous reduction of total cell Ca by one hormone suppressed the transient rise in [Ca2+]i induced by another. The data present evidence that the hormones bradykinin and endothelin-1 are capable of switching off the Ca(2+)-mobilizing signal transduction pathway in a cell by depleting intracellular Ca stores. This process is accompanied by a significant reduction of total cell Ca.

Decreased production of endothelin-1 in asthmatic children after immunotherapy

Endothelin-1 (ET-1) is an endothelium-derived peptide that may be the most potent vasoconstrictor and bronchoconstrictor yet known. To investigate the role of ET-1 in the pathogenesis of bronchial asthma and the effect of immunotherapy (IT) on endothelin production, we measured the in vivo and in vitro production of ET-1 in 24 asthmatic children before and after specific allergen IT for 2 years as well as in age-matched healthy controls. Our results showed that both the plasma concentrations and in vitro production of ET-1 from the supernatants of cultured mononuclear cells (MNCs) were significantly higher in asthmatic children than in control subjects. The mean plasma levels of ET-1 in asthmatic children before or after IT were significantly higher than in controls (49.4 +/- 26.5 and 30.6 +/- 20.7 ng/L vs. 13.2 +/- 8.5 ng/L, p < 0.05 and p < 0.01, respectively). When stimulated with phytohemagglutin (PHA) (1 microgram/ml) or mite extract (10 micrograms/ml) for 3 days, mononuclear cell from asthmatic children before IT produced significantly higher ET-1 than did those after IT (31.8 +/- 23.0 vs. 18.0 +/- 15.7 ng/L, stimulated with mite, and 67.9 +/- 22.4 vs. 25.0 +/- 13.3 ng/L, stimulated with PHA). The decreased production of ET-1 in MNCs culture supernatant of asthmatic children after IT indicated that immunotherapy may result in an immune nonresponsive state, which may reverse the abnormal secretory pattern of ET-1 production in asthmatic children and partly account for its clinical effectiveness in treating atopic patients.

[125I]endothelin binding in rat cerebellum is increased following L-2-chloropropionic-acid-induced granule cell necrosis

The systemic administration of L-2-chloropropionic acid (L-CPA) to rats produced a marked depletion of cerebellar granule cells (> 80% of the total) when administered in a single oral dose of 750 or 250 mg/kg/day for 3 days. The nature of the L-CPA-induced neurotoxicity is currently unknown but it exhibits a number of features in common with excitatory amino acid-induced neuronal cell death. We observed an increase in [125I]endothelin-1 (ET-1) binding in the cerebellar cortex, as measured by quantitative receptor autoradiography, which occurs at 48 h, but not 24 h, following the 750 mg/kg L-CPA dosing regimen. The increase in [125I]ET-1 binding did not parallel the cellular damage and resultant astrocyte proliferation, as measured by GFAP immunoreactivity, which was primarily confined to the granular layer of the cerebellar cortex. The increased [125I]ET-1 binding occurred in the molecular layer of the cerebellar cortex (controls 2.03 +/- 0.26 fmol/mg tissue; L-CPA-treated 6.69 +/- 0.45 fmol/mg tissue, n = 6; p < 0.01, Student's t-test) which appeared to contain astrocytic processes originating from the large increase in astrocyte number situated in the granular layer. Pretreatment of the rats with the irreversible NMDA receptor antagonist, MK-801, protected the cerebellar granule cells against the L-CPA neurotoxicity and also prevented the increase in [125I]ET-1 binding in the cerebellar cortex. The increased [125I]ET-1 binding in rat cerebellum appears to be linked to the reactive gliosis that occurs in association with neuronal cell injury.

Endothelin ETA receptor antagonist, BQ-123, blocks the vasoconstriction induced by sarafotoxin 6b in the heart but not in other vascular beds

1. The cardiovascular effects of SRT6b in control and BQ-123, a specific ETA receptor antagonist, pretreated rats were determined in anesthetized rats using a radioactive microsphere technique. 2. Infusion of SRT6b produced an increase in blood pressure and total peripheral resistance, decrease in cardiac output and stroke volume, and no change in heart rate of control or BQ-123 treated rats. 3. SRT6b induced a decrease in blood flow to the heart which was completely blocked by BQ-123 pretreatment. The decrease in blood flow to other organs by SRT6b was not affected by BQ-123 pretreatment. 4. This study indicates that ET receptors in the coronary blood vessels are of a different type (neither ETA nor ETB) to those in other vascular beds.

Endothelin 1-21 plasma levels in fetuses at 18-24 weeks of gestation

This study aimed to establish normal endothelin (ET) ranges in non malformed appropriate for gestational age fetuses of 18-24 weeks gestation and to investigate a possible correlation between maternal and fetal ET plasma levels. Twenty "mother-fetus" pairs were included in the study. The determination of ET 1-21 was performed by radioimmunoassay using 1 ml of fetal blood obtained by cordocentesis--indicated for various reasons--and in 2 ml of maternal venous blood. The statistical analysis involved the Wilcoxon test for pair differences and the Spearman rank correlation coefficient. Fetal and maternal ET 1-21 levels were respectively 11.39 +/- 2.22 pmol/L and 6.44 +/- 1.00 pmol/L. Fetal levels were significantly higher (p < 0.01) thus excluding passive ET transfer through the placenta, while no correlation between maternal and fetal levels was found. It is speculated that high fetal ET 1-21 levels result from increased ET production, which possess cell proliferative properties and/or decreased ET removal from the fetal circulation because of hypofunctioning lungs and kidneys. It can be assumed that the increased amounts of fetal ETs contribute to normal growth and development directly as well as by regulating vascular tonus and local blood flow.

Decreased expression of messenger RNAs encoding endothelin receptors and neutral endopeptidase 24.11 in endometrial cancer

In this study, we used reverse transcriptase-polymerase chain reaction (RT-PCR) to compare the expression of mRNAs encoding endothelin-1 (ET-1), endothelin receptors type A (ETA-R) and type B (ETB-R) and ET-1-degrading enzyme neutral endopeptidase 24.11 (NEP) in 15 endometrial cancer tissues and 13 normal endometrial tissues. The relative levels of ET-1 mRNA in endometrial cancer tissues did not differ from those in normal endometrium. Both ETA-R and ETB-R mRNA levels were significantly lower in endometrial cancer tissue than in normal endometrium (P < 0.001). The complete lack of NEP mRNA in endometrial cancer tissues was in marked contrast to results from normal endometrium (P < 0.001). In conclusion, differential expression of mRNAs encoding ET-R and NEP in normal endometrium and endometrial cancer suggests that ET action is altered in endometrial cancer compared with normal endometrium.

The control of endothelin-1 secretion

1. The human endothelin-1 (ET-1) gene, which is located on chromosome 6, contains cis-regulatory elements in the 5'-flanking region including the TPA-responsive element, nuclear factor 1 binding element and GATA motif. 2. The expression of preproendothelin-1 (PPET-1) mRNA is regulated by a mechanism involving receptor mediated mobilization of intracellular Ca2+ and activation of protein kinase C in endothelial cells. 3. Activation of protein kinase C results in the synthesis of c-Jun protein and the rapid dephosphorylation of c-Jun protein. Consequently, the binding activity of c-Jun protein to the TPA-responsive element increases, and this causes the induction of PPET-1 mRNA. 4. The microtubular system seems to play some important roles in ET-1 secretion, especially in the process of transferring the synthesized ET-1 to the cell surface of the endothelial cells. 5. The secretion of ET-1 from endothelial cells is also regulated by intracellular Ca2+ released from the Ca2+ store and by Ca2+-calmodulin complex. The phosphorylation of the myosin light chain, elicited by myosin light chain kinase and activated by Ca2+-calmodulin complex, facilitates the formation of filamentous myosin and actin which probably participate in ET-1 secretion especially in transporting the ET-1-containing vesicles towards the cell membrane in the stimulated endothelial cells. 6. Many cultured cells, other than endothelial cells, also secret ET-1 into the culture medium and this secretion can be stimulated by a variety of agents.

High-yield production of human big endothelin-1 by a combination of chemical modification and proteolysis of a fusion protein in Escherichia coli

A protein modification method has been developed for the production of human big endothelin (ET)-1. Production of a large quantity of big ET-1 by the method described here is expected to facilitate future experiments such as X-ray crystallography and nuclear magnetic resonance studies, aimed at understanding the tertiary structure of big ET-1 and its dynamics. The plasmid pETB-50 used for the synthesis carries the gene for a fusion protein consisting of 34-amino acid (aa) residues of an N-terminal portion of beta-galactosidase and the 38-aa residues of big ET-1. The fusion protein ETB-50P contains an arginine residue in the big ET-1 portion at its second C-terminal site and three lysine residues including the C-terminal site in the beta-galactosidase portion, all of which are susceptible to trypsin. Tryptic digestion of the fusion protein quantitatively produced big ET-1 (1-37), which is depleted in the C-terminal serine. However, a treatment of the fusion protein with 1,2-cyclohexanedione prior to tryptic digestion gave full-length big ET-1 with N7, -N8-(1,2-dihydroxycyclohex-1,2- ylene)-arginine. This modification was reversed to the intact arginine residue when the modified big ET-1 was incubated in 0.5 M TRIS-HCl buffer, pH 8.0. Consequently, a combination of such a reversible protein modification and tryptic digestion gave 1.74 mg of recombinant big ET-1 from 2.01 of culture broth. The procedure described here may be applied to produce other arginine-containing peptides from fusion proteins.

Endothelin-1 conversion and receptor characterization in human placental arteries

Endothelin-1-(1-21), a potent pressor peptide, is transcribed as big endothelin-(1-38) and converted to active peptide by endothelin-converting enzyme. The current investigation tested the hypothesis that human fetoplacental blood vessels convert big endothelin-1 to active peptide and that fetoplacental blood vessels respond to endothelin-1 by binding of the peptide to specific receptor sites. In the isolated perfused placental cotyledon the addition of big endothelin-1 to the perfusate caused a time-dependent increase in perfusion pressure that corresponded to the appearance of endothelin-1 in the perfusate. The properties of human placental endothelin-1 receptors were defined in binding studies performed on a plasma membrane fraction of small arteries (<1.0 mm) dissected from the placenta. Binding was saturable, reached steady state by 3 h at 25 degrees C, and was linear with protein concentration. Scatchard analysis of binding data indicated a single class of high-affinity binding sites with a dissociation constant of 27.6 +/- 2.3 pM and a density of 856 +/- 119 fmol/mg protein (n = 5). The potency order for competitive inhibition of the binding of 125I-labeled endothelin-1 [endothelin-1 = endothelin-2 > endothelin-3 = sarafotoxin S6b >> big endothelin-1 (human) = big endothelin-1 (porcine)] is most consistent with a type A endothelin receptor subtype. Phenylephrine, bradykinin, norepinephrine, atrial natriuretic factor, diltiazem, U-46619, and angiotensin II did not displace 125I-endothelin-1 binding. Endothelin receptors were shown to have an approximate molecular weight of 36,600 by polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of mRNAs for endothelin-related proteins in human endometrium, myometrium and leiomyoma

The expression of mRNAs encoding endothelin-1 (ET-1) and its receptors (ETA-R and ETB-R) as well as the ET degrading enzyme, neutral endopeptidase 24.11 (NEP), was determined in tissue samples of endometrium, myometrium and leiomyoma by using a reverse transcriptase polymerase chain reaction (RT-PCR) technique. ET-1 mRNA was detected in all samples studied. The level of ET-1 mRNA was higher in endometrium than in myometrium (p < 0.01) and leiomyoma (p < 0.001). The ETA-R mRNA was more abundant in endometrium than in myometrium (p < 0.001). For ETB-R mRNA there was no difference between these tissues. In contrast to ETA-R mRNA, which was more abundant in leiomyoma than in myometrium (p < 0.01), the ETB-R mRNA was less abundant in leiomyoma (p < 0.01). The NEP mRNA was detected in all endometrial samples but not in myometrium and leiomyoma. Our results show that the expression and relative levels of mRNAs encoding ET-1, ETA-R, ETB-R, and NEP vary in different tissue compartments of the human uterus. Since the net biological action of ET-1 in a particular cell type presumably depends on the balance between the peptide itself, its receptors and degrading enzymes, these results suggest different roles for ET-1 action in uterine endometrium, myometrium and leiomyoma. The difference in relative abundance of ETA-R and ETB-R mRNAs between myometrium and leiomyoma suggests that an altered ET-R gene expression may be a contributing factor in myomal growth.

The crystal structure of human endothelin

The three-dimensional structure of the vasoactive polypeptide endothelin, the most potent vasoconstrictor yet identified, has been determined by X-ray crystallography to 2.18 A resolution. This intermediate-sized structure was solved by molecular replacement techniques using a fragment of an NMR-derived model for initial phasing of the data. However, comparisons of the final X-ray structure with the many diverse models derived from NMR data indicate some important differences, especially in the carboxy-terminal region of the molecule: the entire carboxy terminal tail (residues 16-21) is helical in the crystal structure, but not in any of the NMR structures. This may be a functionally significant difference as this region is crucial for receptor binding and vasoactivity.

Endothelin-1 acts as an autocrine growth factor for normal human keratinocytes

Endothelin-1 (ET-1) is an endothelium-derived 21 amino acid vasoconstrictor peptide possessing two intrachain disulfide bridges. Recently it has become evident that isoforms of ET (ET-1, -2, and -3) have a wide range of pharmacological effects in various tissues and act as autocrine/paracrine factors. We demonstrate here that ET-1 is secreted from normal human keratinocytes and may work as an autocrine growth factor through a specific receptor. In this study, human foreskin keratinocytes were cultured in serum-free MCDB 153 medium. Cell growth and [3H] thymidine incorporation in low and high Ca++ concentration media was stimulated by ET-1, -2, and -3 with similar potencies. The strongest response was observed at 10 nM ETs, whereas stimulatory activity was reduced at 100 nM. ETs suppressed keratinocyte differentiation as measured by reactivity with involucrin antibody. Plasminogen activator activity (mainly urokinase) in the medium was also stimulated by the addition of 10 nM ETs. ET-1-like immunoreactivity measured by radioimmunoassay was 1.4 fmol/day/10(6) cells in non-treated condition medium. Among the various cytokines, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 alpha, and transforming growth factor-beta stimulated ET-1 secretion in a dose-dependent manner. The strongest response (ten-fold) was observed upon the addition of 10 ng/ml TNF-alpha. Scatchard plot analysis of [125I] ET-1 binding to keratinocytes revealed the presence of a single class of high affinity receptors (KD 50 pM, 9 x 10(3) sites/cell). Binding was competitively inhibited by the addition of unlabeled ET-1 and -2 with similar affinities and by ET-3 with weaker affinity. ET-1 mRNA expression in keratinocytes was detected by reverse transcription-polymerase chain reaction and was increased by treatment with 10 ng/ml TNF-alpha. These results suggest that ET-1 acts as an autocrine growth factor for keratinocytes through a specific receptor.

Endothelin family peptides in human plasma and urine: their molecular forms and concentrations

Molecular forms and concentrations of endothelin (ET) family peptides in normal human plasma and urine were investigated using five different sandwich-type enzyme immunoassays (sandwich-EIAs) and reverse-phase high performance liquid chromatography (RP-HPLC). We found that immunoreactive (IR-) big ET-3 and IR-big ET-2 were the major species in both plasma and urine from normal humans. Big ET-2(1-38) was found to be the major form of IR-big ET-2 in plasma. Urinary IR-big ET-2 and plasma and urinary IR-big ET-3 were heterogeneous, and the IR-big ET-3s were larger (M(r) 6,000-12,000) than authentic big ET-3. IR-big ET-1, IR-ET-1, and IR-ET-3 were found at relatively low concentrations in human plasma and urine, and their major forms were identical to authentic big ET-1, ET-1, and ET-3, respectively. Although ET-1 and other ET family peptides have often been measured using RIAs with board-spectrum antibodies, the presence of high concentrations of IR-big ET-2 and IR-big ET-3, but not IR-ET-1, in plasma and urine indicates that the clinical significance of ET family peptides should be investigated with assay methods specific to each ET and big ET.

Endothelin 1 in migraine and tension-type headache

We determined the plasma levels of ET1, both interictally and ictally, in 50 migraine patients, 20 with aura (MPA) and 30 without aura (MPWA), comparing them with the levels of 40 age-matched tension-type headache patients (20 episodic and 20 chronic) (ETTHP and CTTHP) and the levels of a group of 20 healthy control subjects (CS). No statistically significant difference was evident between the mean ET1 plasma levels of MPA and those of MPWA, assessed in headache-free periods. The mean ET1 plasma levels of MPA and MPWA, assessed interictally, were significantly higher than those of CS. However, the values of plasma ET1 in ETTP and in CTTHP did not differ statistically from those of CS. MPA and MPWA ET1 plasma levels increased significantly within 2 h from the onset of attacks (p < 0.0001) and remained significantly higher between 4 and 6 h from the onset. The ET1 plasma levels of ETTHP and CTTHP assessed during attacks did not differ statistically from those of the same patients assessed in the headache-free periods. The increase in ET1 levels in MPA and MPWA patients when assessed ictally, suggests that this peptide is involved in the haemodynamic changes and vascular tone modifications observed during migraine attacks, particularly in the first phase of the ictal period.

Colocalization of vasoactive substances in the endothelial cells of human umbilical vessels

Human umbilical vessels are unique in lacking any innervation; thus endothelial cells may play the major role in local control and regulation of the blood flow. In the present study, we examined ultrathin sections of cultured human umbilical vein endothelial cells and tissue preparations of umbilical vein and artery, immunostained by the post-embedding colloidal gold double-labelling technique. We observed colocalization of atrial natriuretic peptide and neuropeptide Y, as well as colocalization of atrial natriuretic peptide and neuropeptide Y with other vasoactive substances, namely, vasoactive intestinal peptide, substance P, calcitonin gene-related peptide and arginine vasopressin. The functional significance of the colocalization of these vasoactive substances in the human umbilical vessel endothelial cells is discussed.

Sequence-directed recognition peptides: inhibition of endothelin generation via a substrate-depletion mechanism

Sequence-directed recognition peptides (SDRPs) were constructed on the basis of their hydropathic complementarity for big-endothelin (bigET). These peptides can inhibit in vitro the proteolytic cleavage that generates endothelin (ET) from its bigET precursor. Comparison of dissociation constants of the complexes SDRP:bigET with kinetic constants obtained for the cleavage of bigET by alpha-chymotrypsin (taken as a model proteinase) provides evidence of the potential of SDRPs. This is a novel application of SDRPs used as inhibitors of a proteolytic reaction.

Sarafotoxin expression in the bronchopulmonary tract: immunohistochemical occurrence and colocalization with endothelins

The immunohistochemical occurrence of sarafotoxin (SRTX), a snake venom peptide under strong evolutionary control, was investigated in the pulmonary diffuse neuroendocrine system (PDNES) of newborn cats and rats. By applying the avidin-biotin-peroxidase complex method on serial lung sections, we have demonstrated its distribution and colocalization with different endothelin (ET) isoforms. A light microscopic study revealed apparent immunostaining for SRTX in neuronal components and smooth muscle tissue and in neuroepithelial bodies (NEB), while isolated neuroendocrine cells (NEC) remain unlabelled. Comparison of the SRTX reactivity pattern with that of different ET peptides on adjacent lung sections showed colocalization of SRTX-b with ET-3 in NEB, intrapulmonary ganglion cells and nerve fibres, on the one hand, and with ET-1 in airway and vascular smooth muscle cells, on the other. These findings, in addition to the remarkable functional and structural similarities between SRTX and ET peptides, suggest a common evolutionary origin and biological significance of sarafotoxin and endothelins. Moreover, this is the first time that a toxic peptide has been demonstrated in the PDNES.

In situ hybridization of atrial natriuretic peptide mRNA in the endothelial cells of human umbilical vessels

The localization of mRNA encoding preproatrial natriuretic peptide (ANP) was investigated in cultured human umbilical vein endothelial cells (HUVEC) and tissue preparations of umbilical vein and artery. The techniques used were in situ hybridization and in situ hybridization combined with immunocytochemistry, using 32P-radiolabelled and non-radioactive digoxigenin labelled complementary RNA probes. Human ANP mRNAs are mainly localized in the endothelial cells of the umbilical vein and, to a lesser extent, in the endothelial cells of the umbilical artery. The autoradiographic labelling and the intensity of digoxigenin staining were significantly reduced by treatment with RNase before in situ hybridization. This study provides unequivocal evidence for the expression of the ANP gene in the endothelial cells of human umbilical vessels, confirming that these endothelial cells have the ability to synthesize this peptide. The functional significance of the presence of the ANP mRNA in the endothelial cells of human umbilical vessels is discussed.

The role of endothelin in the vessel wall

Endothelins (ETs) are a family of vasoactive peptides occurring in three isoforms (ET-1, ET-2, ET-3) encoded by three distinct genes in the human genome. ETs arise from precursor peptides (big-ETs) that are cleaved and released by an endothelin-converting enzyme. ET-1 secretion, which can be stimulated by various agents, is preferentially directed towards the abluminal site of endothelial cells, suggesting a local paracrine action of the peptide. ETs exert their actions through the activation of at least two receptor subtypes: ET-A receptors, which mediate the proliferative and vasoconstrictive effects, and ET-B receptors, which mediate vasorelaxation. Although, the potential roles of ETs are mostly hypothetical, considering their potent cardiovascular effects, it has been suggested that maintenance of a basal vascular tone and regulation of vascular growth and haemostasis may well represent the biological functions of this family of peptides. The recent discovery of specific receptor antagonists will provide a means to assess their physiological and pathophysiological roles.

Nitric oxide regulates the expression of vasoconstrictors and growth factors by vascular endothelium under both normoxia and hypoxia

The mechanisms by which hypoxia causes vasoconstriction in vivo are not known. Accumulating evidence implicates the endothelium as a key regulator of vascular tone. Hypoxia induces the expression and secretion of endothelin-1 (ET-1), a potent vasoconstrictor in cultured human endothelial cells. We report here that nitric oxide (NO), an endothelial-derived relaxing factor, modifies this induction of ET-1. Whereas low oxygen tension (PO2 = 20-30 Torr) increases ET-1 expression four- to eightfold above that seen at normal oxygen tension (PO2 = 150 Torr), sodium nitroprusside, which releases NO, suppresses this effect. This inhibition of hypoxia-induced ET-1 expression occurs within the first hour of exposure of cells to sodium nitroprusside. Moreover, when the endogenous constitutive levels of NO made by endothelial cells are suppressed using N-omega-nitro-L-arginine, a potent competitive inhibitor of NO synthase, the baseline levels of ET-1 produced in normoxic environments are increased three- to fourfold. The effects of hypoxia and the NO synthase inhibitor on ET-1 expression are additive. The regulation of ET-1 production by NO appears to be at the level of transcription. Similar effects of NO were observed on the expression of the PDGF-B chain gene. PDGF-B expression was suppressed by NO in a hypoxic environment and induced by N-omega-nitro-L-arginine in both normoxic and hypoxic environments. These findings suggest that in addition to its role as a vasodilator, NO may also influence vascular tone via the regulated reciprocal production of ET-1 and PDGF-B in the vasculature.

In vivo expression of mutant preproendothelins: hierarchy of processing events but no strict requirement of Trp-Val at the processing site

Endothelin-1 (ET-1), a 21-residue vasoconstrictor peptide, originates in human cells from a 212-amino acid precursor (preproET-1). Big ET-1, an intermediate form of 38 amino acids, is generated by cleavage at basic-pair residues of proET-1, while a specific "ET-converting enzyme" was proposed to process the unusual Trp-Val site at positions 21 and 22 of big ET-1. We have previously shown that expression of synthetic RNA encoding human preproET-1 in Xenopus oocytes results in secretion of putative ET-1 and big ET-1. Here, to further dissect the processing pathway of preproET-1, we designed and expressed in oocytes a set of preproET-1 mutants. Four mutants affecting the Trp-Val site always originated putative ET-1(s) at levels comparable to the wild type, suggesting that there is only a conformational requirement for cleavage at this site. An Arg-->Ile mutation at the basic-pair site after the C terminus of big ET-1 fully inhibited the formation of both big ET-1 and ET-1, indicating that processing at this site is an early event and that big ET-1 is an obligate intermediate for the synthesis of ET-1 in vivo. Also, a truncated mutant bearing a stop codon after the C terminus of the big ET-1 sequence was totally stable and further processed into mature big ET-1 and ET-1, indicating that the second part of the precursor is not necessary for maturation.

Two preproendothelin 1 mRNAs transcribed by alternative promoters

Endothelin-1, initially identified as potent vasoconstrictor secreted by vascular endothelial cells, was subsequently found to have many effects on both vascular and nonvascular tissues. We have identified from a human placenta cDNA library a clone (cDNA-2) which corresponds to a novel 5'-extended preproendothelin 1 (preproET-1) mRNA. Comparison with the known preproET-1 mRNA (cDNA-1), showed that the two molecules share the same coding sequence but differ in the 5'-untranslated region. Interestingly, cDNA-2 extends upstream of promoter regions previously shown to be essential for full preproET-1 expression. Primer extension and PCR analysis of human placenta RNA demonstrated the presence of additional transcription initiation sites located upstream of the previously identified preproET-1 CAP site. Moreover, the two mRNAs show different pattern of expression. To elucidate the mechanisms controlling the production of alternative transcripts we transfected COS-1 cells with a series of preproET-1 promoter deletion mutants. This analysis revealed that the human preproET-1 gene can be transcribed from a proximal and a distal promoter element which has hitherto been undetected. In addition, we demonstrate the presence of a region in the down-epithelial specific expression.

Regulation of cortical collecting duct function: effect of endothelin

We recently showed that endothelin-1 (ET-1) increases cell Ca2+ in the mouse cortical collecting duct. To clarify the cellular action and target cell of ET-1, electrophysiologic techniques and cell Ca2+ measurement were applied to rabbit cortical collecting ducts perfused in vitro. When 10(-8) mol/L ET-1 was added to the bath, a transient increase followed by a sustained increase in cell Ca2+ was observed. A sustained increase in cell Ca2+ lasted 10 to 20 minutes and was associated with a decrease in lumen-negative transepithelial voltage. To confirm the target cell type of ET-1, confocal laser microscopy was used. An increase in cell Ca2+ was observed in the same cell, which also showed an increase in cell Ca2+ in response to arginine vasopressin (AVP), which indicated that the principal cell has ET-1 receptors in the basolateral membrane. When ET-1 was applied to the bath, total cellular membrane resistance (Ri) decreased initially and then gradually increased because of inhibition of the luminal Na+ channel. An initial decrease in Ri was considered an influx of Ca2+ from the basolateral membrane. To further determine the source of an increase in cell Ca2+, the effect of ET-1 was tested in the absence of external Ca2+ and in the presence of a Ca2+ channel blocker in the bath. Cell Ca2+ did not respond to ET-1 in the absence of external Ca2+, a condition in which an AVP-stimulated increase in cell Ca2+ was preserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin-1: immunocytochemistry, localization of binding sites, and contractile effects in human uteroplacental smooth muscle

OBJECTIVE

Our purpose was to study the localization, distribution of binding sites, and contractile effects of endothelin-1 in human uteroplacental smooth muscle.

STUDY DESIGN

The tissue localization of endothelin-1, the distribution of iodine 125-labeled endothelin-1 binding sites, and the mechanical effects of endothelin-1 were studied in isolated tissues from the human uterus and placenta by immunocytochemistry, autoradiography, and organ bath experiments.

RESULTS

No specific endothelin-1 immunoreactivity could be detected in fetal placental tissues or in myometrium or intramyometrial arteries from term pregnant and nonpregnant women. In placental tissues a high density of iodine 125-labeled endothelin-1 binding sites was found in vessels of various sizes and in the chorionic villi, whereas the density in the jelly of Wharton was low. In myometrial tissue from pregnant and nonpregnant women a high density of iodine 125-labeled endothelin-1 binding sites was found, which in myometrium from pregnant women was mainly located to the myometrium and vascular smooth muscle. Endothelin-1 produced marked contractile responses in maternal and fetal uteroplacental vessels and in myometrial preparations.

CONCLUSION

Endothelin-1 may be involved in the endogenous control of uteroplacental vascular and visceral smooth muscle.

Cloning and sequence analysis of a snake, Atractaspis engaddensis gene encoding sarafotoxin S6c

A 469 base pair genomic DNA, which encodes the mature region of a snake cardiotoxic peptide, sarafotoxin S6c, was isolated from the liver of the burrowing asp, Atractaspis engaddensis. The nucleotide sequence encoding the mature peptide region showed a high sequence homology with those of mammalian vasoconstrictor peptides, endothelin family as expected from the high homology of their amino acid sequences. In contrast, both of the upper and lower flanking sequences of sarafotoxin gene and the deduced amino acid sequence of the sarafotoxin precursor were quite different from those of endothelin family. These results suggest that the ancestral gene and biosynthetic pathway of sarafotoxins are different from those of endothelin.

Characterization and partial purification from pheochromocytoma cells of an endogenous equivalent of scyllatoxin, a scorpion toxin which blocks small conductance Ca(2+)-activated K+ channels

This work describes the partial purification of a heat-stable peptide which has the same properties as the scorpion toxin, scyllatoxin, a specific blocker of one class of Ca(2+)-activated K+ channels: (i) it competes with [125I]apamin for binding to the same site, (ii) like apamin and scyllatoxin, it blocks the after-potential hyperpolarization in skeletal muscle cells in culture, (iii) like apamin and scyllatoxin, it contracts guinea-pig taenia coli relaxed by epinephrine, (iv) it cross-reacts with antibodies raised against scyllatoxin but not with antibodies raised against apamin.

Effect of phosphoramidon on big endothelin-2 conversion into endothelin-2 in human renal adenocarcinoma (ACHN) cells. Analysis of endothelin-2 biosynthetic pathway

The biosynthetic pathway of endothelin (ET)-2 was analyzed in cultured ACHN cells. In the supernatant, we detected three ET-2-related peptides, ET-2, big ET-2(1-38) and big ET-2(22-38). Phosphoramidon decreased the amount of ET-2 and increased that of big ET-2(1-38) dose-dependently. The amount of big ET-2(1-37) did not significantly change. These results suggest that big ET-2 is composed of 38 and not 37 amino acid residues, and that a putative ET-2-converting enzyme (ECE-2) should be classified as a phosphoramidon-sensitive neutral metalloprotease, bearing a resemblance to the putative ET-1-converting enzyme (ECE-1) in endothelial cells.

Comparative effects of endothelin (ET-1) and U46619 on human saphenous vein and gastroepiploic artery, sources of human autologous grafts

The effects of endothelin (ET-1) on smooth muscle contractile activity were investigated and compared in human saphenous vein and gastroepiploic artery, vessels frequently used in revascularization procedures. ET-1 contracted saphenous vein and gastroepiploic artery in a concentration-dependent manner. The peptide produced a greater maximal effect in the vein than in the artery and, in both preparations, ET-1 was less efficacious than U46619, an agent which mimics the actions of thromboxane A2 at the thromboxane A2/prostaglandin H2 receptor. The contractile response to ET-1 declined spontaneously at a more rapid rate in the artery than in the vein. The present data indicate that ET-1 has significant contractile activity in both vessels which are used for coronary arterial bypass surgery and suggest that although, a weaker vasoconstrictor than U46619, the peptide could induce vasospasm in both graft vessels.

Endothelin-1 stimulates its own synthesis in human endothelial cells

We studied whether endothelin-1 (ET-1) would affect its own synthesis. Human umbilical cord vein endothelial cells in methionine-poor culture medium containing [35S] methionine were treated with synthetic ET-1 or ET-3. Immunoprecipitation of 35 S-labeled ET-1 was performed with rabbit ET-1 antiserum. ET-1 caused an 40 +/- 4% (mean +/- SEM) increase of immunoprecipitable 35 S-labeled ET-1 as confirmed by its elution point in reversed phase high power liquid chromatography (HPLC). ET-3 caused a 23 +/- 2% increase in ET-1 concentration. Amplification of cDNA by PCR showed both ET-1 and ETB receptor mRNAs in human cord vein endothelial cells. We conclude that ET-1 increases its own synthesis in endothelial cells. This suggests a positive autocrine feed-back action of ET-1 on its own synthesis, an effect which is probably mediated by non-specific ETB receptors.

Phosphoramidon-sensitive effects of big endothelins in the perfused rabbit kidney

The enzymatic conversion of human big endothelins (1, 2, and 3) to their respective active metabolites (endothelin-1, -2, and -3) was investigated in the perfused rabbit kidney through the pressor- and eicosanoid-releasing properties of these peptides. Intra-arterial bolus injections of endothelin-1 and -2 (5-50 pmol), endothelin-3 (100-250 pmol), and big endothelin-1 and -2 (100-250 pmol) into the kidney produced dose-dependent increases of perfusion pressure, whereas big endothelin-3 was inactive at doses up to 1,000 pmol. Endothelin-1 and -2 (10 nM), endothelin-3 (100 nM), and big endothelin-1 and -2 (100 nM) are potent enhancers of prostacyclin release without inducing any release of thromboxane B2 in the perfused kidney. In contrast, big endothelin-3 did not trigger the release of eicosanoids. A metalloprotease inhibitor, phosphoramidon (100 microM, 60 minutes), reduced the prostanoid release and pressor responses induced by big endothelin-1 and -2 without affecting the response induced by endothelin-1, -2, and -3. These results suggest the presence of a phosphoramidon-sensitive endothelin converting enzyme that converts the precursors of endothelin-1 and -2, but not of endothelin-3, in the renal vasculature of the rabbit.