The role of c-Jun protein in thrombin-stimulated expression of preproendothelin-1 mRNA in porcine aortic endothelial cells

Endothelin-1 in Health and Disease

Discovered almost 40 years ago, the potent vasoconstrictor peptide endothelin-1 (ET-1) has a wide range of roles both physiologically and pathologically. In recent years, there has been a focus on the contribution of ET-1 to disease. This has led to the development of various ET receptor antagonists, some of which are approved for the treatment of pulmonary arterial hypertension, while clinical trials for other diseases have been numerous yet, for the most part, unsuccessful. However, given the vast physiological impact of ET-1, it is both surprising and disappointing that therapeutics targeting the ET-1 pathway remain limited. Strategies aimed at the pathways influencing the synthesis and release of ET-1 could provide new therapeutic avenues, yet research using cultured cells in vitro has had little follow up in intact ex vivo and in vivo preparations. This article summarises what is currently known about the synthesis, storage and release of ET-1 as well as the role of ET-1 in several diseases including cardiovascular diseases, COVID-19 and chronic pain. Unravelling the ET-1 pathway and identifying therapeutic targets has the potential to treat many diseases whether through disease prevention, slowing disease progression or reversing pathology.

Orphan nuclear receptor Nur77 is a novel negative regulator of endothelin-1 expression in vascular endothelial cells

Endothelin-1 (ET-1) produced by vascular endothelial cells plays essential roles in the regulation of vascular tone and development of cardiovascular diseases. The objective of this study is to identify novel regulators implicated in the regulation of ET-1 expression in vascular endothelial cells (ECs). By using quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA), we show that either ectopic expression of orphan nuclear receptor Nur77 or pharmacological activation of Nur77 by 6-mercaptopurine (6-MP) substantially inhibits ET-1 expression in human umbilical vein endothelial cells (HUVECs), under both basal and thrombin-stimulated conditions. Furthermore, thrombin-stimulated ET expression is significantly augmented in both Nur77 knockdown ECs and aort from Nur77 knockout mice, suggesting that Nur77 is a negative regulator of ET-1 expression. Inhibition of ET-1 expression by Nur77 occurs at gene transcriptional levels, since Nur77 potently inhibits ET-1 promoter activity, without affecting ET-1 mRNA stability. As shown in electrophoretic mobility shift assay (EMSA), Nur77 overexpression markedly inhibits both basal and thrombin-stimulated transcriptional activity of AP-1. Mechanistically, we demonstrate that Nur77 specially interacts with c-Jun and inhibits AP-1 dependent c-Jun promoter activity, which leads to a decreased expression of c-Jun, a critical component involved in both AP-1 transcriptional activity and ET-1 expression in ECs. These findings demonstrate that Nur77 is a novel negative regulator of ET-1 expression in vascular ECs through an inhibitory interaction with the c-Jun/AP-1 pathway. Activation of Nur77 may represent a useful therapeutic strategy for preventing certain cardiovascular diseases, such as atherosclerosis and pulmonary artery hypertension.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.

Thrombin-stimulated proliferation is mediated by endothelin-1 in cultured rat gingival fibroblasts

Abstract Endothelin-1 (ET-1) appears to be involved in drug-induced proliferation of gingival fibroblasts. Thrombin induces proliferation of human gingival fibroblasts via protease-activated receptor 1 (PAR1). In this study, using cultured rat gingival fibroblasts, we investigated whether thrombin-induced proliferation of gingival fibroblasts is mediated by ET-1. Thrombin-induced proliferation (0.05-2.5 U/mL). Proliferation was also induced by a PAR1-specific agonist (TFLLR-NH(2,) 0.1-30 microm), but not by a PAR2-specific agonist (SLIGRL-NH(2)). Thrombin (2.5 U/mL) induced an increase in immunoreactive ET-1 expression, which was inhibited by cycloheximide (10 microg/mL), and an increase in preproET-1 mRNA expression, as assessed by reverse transcription polymerase chain reaction. TFLLR-NH(2) increased ET-1 release into the culture medium in both a concentration (0.01-10 microm)- and time (6-24 h)-dependent manner, as assessed by solid phase sandwich enzyme-linked immunosorbent assay. The thrombin (2.5 U/mL)-induced proliferation was inhibited by a PAR1-selective inhibitor, SCH79797 (0.1 microm) and an ET(A) antagonist, BQ-123 (1 microm), but not by an ET(B) antagonist, BQ-788 (1 microm). These findings suggest that thrombin, acting via PAR1, induced proliferation of cultured rat gingival fibroblasts that was mediated by ET-1 acting via ET(A).

Activation of ETB receptors regulates the abundance of ET-1 mRNA in vascular endothelial cells

BACKGROUND AND PURPOSE

The factors that influence the cellular levels of endothelin-1 (ET-1) include transcription, mRNA localization, stability and translation, post-translational maturation of preproET-1 and degradation of ET-1. We investigated the regulation of ET-1 mRNA abundance by extracellular ET-1 in porcine aortic endothelial cells (PAECs).

EXPERIMENTAL APPROACH

Passsage one cultures of PAECs were incubated in starving medium in the presence or absence of ET-1 and antagonists or pharmacological inhibitors. PreproET-1 mRNA, endothelin-1 promoter activity, Erk and p38 MAPK activation were determined.

KEY RESULTS

Exogenous ET-1 reduced cellular ET-1 mRNA content: a reduction of 10 000-fold was observed after 4 h. ET-1 simultaneously reduced the stability of ET-1 mRNA and increased the loading of RNA Polymerase II at the endothelin-1 promoter. In the absence of exogenous ET-1, the ETB-selective antagonist, BQ788, increased ET-1 mRNA. An ETA-selective antagonist had no effect. ET-1 mRNA returned to control levels within 24 h. Whereas activation of p38 MAPK induced by ET-1 peaked at 30 min and returned to control levels within 90 min, Erk1/2 remained active after 4 h of stimulation. Inhibition of p38 MAPK prevented the ET-1-induced decrease in ET-1 mRNA. In contrast, Erk1/2 inhibition increased ET-1 mRNA. Similarly, inhibition of receptor internalization increased ET-1 mRNA in the presence or absence of exogenous ET-1.

CONCLUSIONS AND IMPLICATIONS

These results suggest that extracellular ET-1 regulates the abundance of ET-1 mRNA in PAECs, in an ETB receptor-dependent manner, by modulating both mRNA stability and transcription via mechanisms involving receptor endocytosis and both ERK and p38 MAPK pathways.

[Endothelin-1 production and its involvement in cardiovascular diseases]

Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

Peripheral endothelin A receptor antagonism attenuates carcinoma-induced pain

In this study we investigated the role of endothelin-1 (ET-1) and its peripheral receptor (ET-A) in carcinoma-induced pain in a mouse cancer pain model. Tumors were induced in the hind paw of female mice by local injection of cells derived from a human oral squamous cell carcinoma (SCC). Significant pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, began at four days after SCC inoculation and lasted to 28 days, the last day of measurement. Intra-tumor expression of both ET-1 mRNA and ET-1 protein were significantly upregulated compared to normal tissue, and local administration of the ET-A receptor selective antagonist, BQ-123 (100 microM) significantly elevated withdrawal thresholds, indicating the induction of an antinociceptive effect. These findings support the suggestion that ET-1 and ET-A receptors contribute to the severity of carcinoma-induced soft tissue cancer pain.

Elevated salivary endothelin levels in oral cancer patients--a pilot study

The analysis of saliva has been proposed as a potentially rapid, non-invasive method to monitor and diagnose patients with oral disease. In this study we measured salivary endothelin-1 (ET-1) levels in patients diagnosed with oral squamous cell carcinoma (SCC) prior to treatment. We demonstrate significantly elevated salivary ET-1 levels in the oral SCC group (4.37+/-1.35pg/ml), relative to the control group (1.16+/-0.29pg/ml). ET-1 and ET-1 mRNA were also measured in oral SCC tissue specimens and compared to normal oral epithelial controls. The concentration of ET-1 in the oral SCC specimens was 17.87+/-4.0pg/ml and in the normal epithelial controls the concentration of ET-1 was 5.43+/-2.5pg/ml. ET-1 mRNA was significantly overexpressed in 80% (8/10) of the oral SCC specimens. Our results demonstrate the potential utility of salivary analysis for ET-1 levels to monitor patients at risk for oral SCC.

Xanthoangelol D Isolated from the Roots of Angelica keiskei Inhibits Endothelin-1 Production through the Suppression of Nuclear Factor-.KAPPA.B

Transcription factor nuclear factor-kappa B (NF-kappaB) has been demonstrated to be important in regulating various gene expressions such as cytokines, adhesion molecules, and endothelin-1 (ET-1) in vascular endothelial cells. In the present study, we show the effects of xanthoangelol, xanthoangelol D, E, and F, which isolated from the root of Angelica keiskei KOIDZUMI (Umbelliferae), on NF-kappaB activation and ET-1 gene expression in cultured porcine aortic endothelial cells (PAECs). Treatments of xanthoangelol D but not xanthoangelol, xanthoangelol E and F markedly suppressed both of basal and tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation in PAECs. To clarify the mechanism of xanthoangelol D-induced suppression on NF-kappaB activation, we evaluated the effects of xanthoangelol D on phosphorylation and degradation of IkappaBalpha, an inhibitory protein bound to NF-kappaB, and obtained evidence that xanthoangelol D selectively suppresses the phosphorylation of IkappaBalpha rather than the degradation of phosphorylated IkappaBalpha. In addition, xanthoangelol D significantly attenuated basal and TNF-alpha-induced prepro ET-1 mRNA expression in PAECs. These results suggest that xanthoangelol D may be useful for the treatment of various vascular diseases involved NF-kappaB activation.

Eyeing endothelins: a cellular perspective

Endothelin is an endogenous vasoactive peptide that is considered among the most potent vasoconstrictor substances known. In addition to its vascular effects, endothelins and their receptors have been shown to be present in the eye and to have a number of ocular actions that may be important for ocular homeostasis, but, in excess can be a potential contributor to ocular neuropathy in glaucoma. The current review focuses on the cellular and molecular aspects of endothelins and its receptors in the eye with an emphasis on its relationship to ocular function and its potential role in the etiology of glaucoma pathophysiology.

Thrombin and phenotypic modulation of the endothelium

Thrombin signaling in the endothelium is linked to multiple phenotypic changes, including alterations in permeability, vasomotor tone, and leukocyte trafficking. The thrombin signal is transduced, at least in part, at the level of gene transcription. In this review, we focus on the role of thrombin signaling and transcriptional networks in mediating downstream gene expression and endothelial phenotype. In addition, we report the results of DNA microarrays in control and thrombin-treated endothelial cells. We conclude that (1) thrombin induces the upregulation and downregulation of multiple genes in the endothelium, (2) thrombin-mediated gene expression involves a multitude of transcription factors, and (3) future breakthroughs in the field will depend on a better understanding of the spatial and temporal dynamics of these transcriptional networks.

The role of nuclear factor-kappa B in the regulation of endothelin-1 production by nitric oxide

Nitric oxide (NO) has been reported to have an inhibitory effect on endothelin-1 production, but the detailed mechanisms are poorly understood. Our previous studies showed that a transcription factor nuclear factor-kappaB (NF-kappaB) plays an important role in endothelin-1 production. In the present study, we investigated the possible involvement of NF-kappaB in the inhibitory regulation of endothelin-1 production by NO. 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO), which is a well-known NO scavenger, remarkably increased both endothelin-1 production and NF-kappaB activation in cultured vascular endothelial cells. On the other hand, a spontaneous NO donor (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexanamide (FK409) significantly attenuated the basal and tumor necrosis factor-alpha-induced endothelin-1 production and NF-kappaB activation in endothelial cells. In addition, we found that FK409 suppressed NF-kappaB activation by the induction and stabilization of the inhibitory protein alpha, IkappaBalpha. Taken together, our results suggest that NO modulates the endothelial endothelin-1 production, possibly through the regulation of NF-kappaB activation.

Homocysteine decreases endothelin-1 expression by interfering with the AP-1 signaling pathway

The increased cardiovascular risk associated with hyperhomocysteinemia has been linked to homocysteine-induced endothelial cell (EC) dysfunction. Endothelin-1 is a vasoactive peptide, synthesized mainly by vascular ECs. We have previously shown that homocysteine decreases endothelin-1 biosynthesis. Here we addressed the molecular mechanism of endothelin-1 regulation by homocysteine. Experiments with the transcription inhibitor actinomycin D indicated that the decrease in preproendothelin-1 mRNA content in homocysteine-treated cells did not result from transcript destabilization. Transient transfection assays demonstrated that homocysteine downregulated endothelin-1 at the transcriptional level by decreasing preproendothelin-1 promoter activity. Mutation of the activator protein-1 (AP-1) site of the promoter eliminated the repression induced by homocysteine. Western blot analysis showed that the homocysteine-induced decrease in promoter activity was not associated with reduced expression of the AP-1 components c-Fos and c-Jun. The inhibitory action of homocysteine on preproendothelin-1 mRNA expression was not prevented by cycloheximide. Electrophoretic mobility shift assays demonstrated that homocysteine reduced the binding activity of ECs nuclear extracts to an AP-1 consensus site. These results indicate that homocysteine downregulates endothelin-1 synthesis by inhibiting AP-1 activity, and that the AP-1 signaling pathway may be of major importance in homocysteine-induced endothelial dysfunction.

Molecular regulation of the endothelin-1 gene by hypoxia. Contributions of hypoxia-inducible factor-1, activator protein-1, GATA-2, AND p300/CBP

Endothelin-1 (ET-1) is a peptide hormone with potent vasoconstrictor properties which is synthesized and secreted predominantly by vascular endothelial cells. Its production is regulated by numerous stimuli including ischemia and hypoxia, and the enhanced levels that occur during myocardial ischemia may contribute to the progression of heart failure. We reported previously a preliminary characterization of a hypoxia-inducible factor-1 (HIF-1) binding site in the human ET-1 promoter which contributed to the activation of ET-1 expression in endothelial cells. We report here that the HIF-1 binding site alone is not sufficient for the response to hypoxia but requires an additional 50 base pairs of flanking sequence that includes binding sites for the factors activator protein-1 (AP-1), GATA-2, and CAAT-binding factor (NF-1). Mutation of any one of these sites or the HIF-1 site eliminated induction by hypoxia. Mutations of the AP-1 and GATA-2 sites, but not the HIF-1 site, were complemented by overexpressing AP-1, GATA-2, HIF-1alpha, or the activator protein p300/CBP, restoring the response to hypoxia. Binding studies in vitro confirmed physical associations among GATA-2, AP-1, and HIF-1 factors. Overexpression or depletion of p300/CBP modulated the level of ET-1 promoter expression as well as the endogenous ET-1 transcript but did not change the fold induction by hypoxia in either case. Regulation of the ET-1 promoter by hypoxia in non-endothelial cells required overexpression of GATA-2 and HIF-1alpha. The results support essential roles for AP-1, GATA-2, and NF-1 in stabilizing the binding of HIF-1 and promoting recruitment of p300/CBP to the ET-1 hypoxia response complex.

Thrombin induces endothelin expression in arterial smooth muscle cells

Thrombin has been shown to stimulate endothelin release by endothelial cells, but the ability of thrombin to induce endothelin in nonendothelial cells is less well-known. Incubation of rat aortic smooth muscle cells with thrombin resulted in a stimulation of preproendothelin-1 (preproET-1) mRNA expression. This induction of preproET-1 mRNA expression by thrombin was accompanied by the release of immunoreactive peptide ET-1 into the extracellular medium. The synthetic thrombin receptor activator peptide (TRAP) confirmed ligand-specific receptor action to induce preproET-1 mRNA. Nuclear run-on analysis revealed that the transcriptional rate of preproET-1 mRNA increases twofold after 1 h of incubation with thrombin. In cells treated with thrombin, the half-life of preproET-1 mRNA was identical to that in untreated control cells. These results demonstrated that thrombin regulates endothelin synthesis at a transcriptional level but does not influence mRNA stability. Inhibition of protein kinase C (PKC) with selective inhibitors (chelerythrine and bisindolylmaleimide I) before thrombin stimulation failed to significantly inhibit preproET-1 gene expression. Inhibition of mitogen-activated protein (MAP) kinase kinase and protein tyrosine kinase decreased preproET-1 mRNA expression in thrombin-stimulated smooth muscle cells. Furthermore, addition of an activator of peroxisome proliferator-activated receptors-alpha (PPARalpha), fenofibrate, prevented the preproET-1 gene induction in response to thrombin. These results demonstrated that thrombin-induced endothelin gene transcription involved MAP kinase kinase rather than the PKC cascade in smooth muscle cells, which was repressed by PPARalpha stimulation.

Hypoxia regulates expression of the endothelin-1 gene through a proximal hypoxia-inducible factor-1 binding site on the antisense strand

Endothelin-1 (ET-1) is a peptide hormone with potent vasoconstrictor properties that is synthesized and secreted predominantly by vascular endothelial cells. Its production is regulated by numerous stimuli including ischemia and hypoxia, and the enhanced levels that occur during myocardial ischemia may contribute to the progression of heart failure. We previously reported that ET-1 expression was induced by both hypoxia and transition metals in endothelial cells (ECs). Here we define an element in the proximal promoter of the ET-1 gene that is responsible for this induction. By using deletions and site directed mutagenesis of the human ET-1 promoter, in combination with electrophoretic gel mobility shifts and transient expression assays in human ECs, we identified an active hypoxia-inducible factor 1 (HIF-1) binding site starting at position -118 upstream of the transcription start site on the non-coding DNA strand. Mutation of this site eliminated induction by hypoxia without affecting basal (aerobic) expression, and the mutated sequence did not display hypoxia-specific binding of HIF-1.

Transcriptional regulation of pre-pro-endothelin-1 gene by glucocorticoids in vascular smooth muscle cells

Endothelin is a potent vasoactive peptide involved in the maintenance of vascular tone and in pathophysiological states. Endothelin-1 synthesis is controlled at the transcriptional level. We report that glucocorticoids increase the pre-pro-endothelin-1 gene transcription rate in vascular smooth muscle cells. The effect of glucocorticoids is dose-dependent (EC50 approximately 2-3 nM) and completely blocked by co-incubation with the glucocorticoid antagonist RU 38486. The rise in pp-Et-1 steady state mRNA levels is rapid and transient with a maximal three-fold stimulation within one hour of glucocorticoid administration. Glucocorticoid treatment does not affect the half-life of pre-pro-endothelin-1 mRNA as shown by actinomycin D studies. Furthermore, cycloheximide treatment concomitantly with RU 28362 did not reverse the stimulatory effect of glucocorticoids on pre-pro-endothelin-1 mRNA levels. Nuclear run-on analysis shows that glucocorticoids increase the transcription rate of pre-pro-endothelin-1. Our results suggest a role for glucocorticoids in the regulation of biosynthesis and action of this important vasoactive peptide in vascular smooth muscle cells.

Regulation of endothelin-1 in human non-pigmented ciliary epithelial cells by tumor necrosis factor-alpha

Endothelins (ET) are potent vasoactive peptides present in many ocular structures and are formed from precursor Big endothelins (Big ET-1) by the action of an endothelin-converting enzyme (ECE). ET-1 is thought to decrease intraocular pressure by contracting the ciliary muscle thus enhancing the outflow of aqueous humor through the Canal of Schlemm and trabecular meshwork. However, the mechanisms involved in the regulation of endothelin-1 (ET-1) synthesis and release in ocular tissues have not been fully characterized. In this study we examined the effect of tumor necrosis factor-alpha(TNF-alpha; 10 nm), a proinflammatory cytokine, on the cellular mechanisms leading to ET-1 synthesis and release in SV-40 transformed human ciliary non-pigmented epithelial cells (HNPE). ET-1 and Big endothelin-1 (Big ET-1) immunoreactivity was time-dependently increased following TNF-alphatreatment. Phorbol esters (PMA), activators of PKC, also raised the immunoreactive levels of ET-1 and Big ET-1 while, staurosporine, a PKC inhibitor (20 nm), decreased ET-1 levels in TNF-alpha-stimulated cells. Pre-treatment with phosphoramidon (1 micron) an ECE-inhibitor, followed by TNF-alpha stimulation, decreased ir-ET-1 levels. Cycloheximide (9 micron), a protein synthesis inhibitor, decreased TNF-alpha-stimulated levels for ir-ET-1 and ir-Big ET-1, suggesting that TNF-alpha may be directly regulating ET-1 expression at the ET-1 gene. Our data indicates that TNF-alpha regulates ET-1 levels in HNPE cells possibly by activating PKC either to stimulate protein synthesis and/or to enhance ET-1 secretion. These results suggest that ET-1 released from the ciliary body may play an important role in aqueous humor dynamics following cytokine activation.

Endothelin expression in human megakaryoblastic leukemia cell lines and normal platelet precursors

The aim of the present investigation was to determine whether endothelin (ET) could be expressed in and released from the human leukemia megakaryoblastic cell lines HEL, MEG-01, DAMI and the normal human platelet progenitors. Using the reverse transcriptase-polymerase chain reaction (RT-PCR) on total RNA isolated from the cells, we amplified a cDNA of the expected size (453 bp). Southern-blotting hybridization revealed that RT-PCR products from the cell lines were specific of ET-1 mRNA. Immunocytochemical analyses highlighted immunoreactive ET-1 in the cytoplasm of these cells which also released the mature peptide. ET-1 release from the three cell lines was increased by thrombin exposure. Although MEG-01 cells express ET receptors, ET-1, the selective ETB agonist sarafotoxin 6C and the non-selective ET-receptor antagonist PD 142893 showed no proliferative or antiproliferative action in basal or stimulating medium. This indicated a lack of autocrine ET-mediated effect on growth. These results demonstrate for the first time that human megakaryoblastic leukemia cell lines and normal bone marrow platelet precursors express ET-1 mRNA and release the mature peptide.

Thrombin induces the preproendothelin-1 gene in endothelial cells by a protein tyrosine kinase-linked mechanism

Thrombin stimulates synthesis and secretion of endothelin-1 (ET-1), a vasoactive peptide that triggers responses in the vascular endothelium and smooth muscle. We investigated the signal transduction pathways by which thrombin stimulates preproET-1 gene expression and ET-1 peptide secretion in macrovascular cells (human umbilical vein endothelial cells [HUVECs] and bovine pulmonary artery endothelial cells [BPAECs]) and microvascular cells (human microvascular endothelial cell line [HMEC-1]). Thrombin (4 U/mL) stimulated maximal induction of ET-1 peptide secretion and preproET-1 mRNA after 2 hours in HUVECs and BPAECs and after 1 hour in HMEC-1. A synthetic thrombin receptor activator peptide confirmed ligand-specific receptor actions to induce preproET-1 mRNA. Protein kinase C (PKC) activation by phorbol ester transiently induced preproET-1 mRNA but had no effect on ET-1 peptide synthesis. PKC inhibitors sangivamycin and calphostin C and PKC depletion failed to suppress thrombin-stimulated preproET-1 mRNA. Adenylate cyclase and cAMP-dependent protein kinase did not participate in thrombin-induced preproET-1 gene activation. Thrombin stimulated a rapid increase in phosphotyrosine-containing proteins, suggesting a role for tyrosine phosphorylation in thrombin signaling. These data demonstrate that thrombin induces the preproET-1 gene and ET-1 peptide synthesis by a PKC-independent PTK-dependent pathway in macrovascular and microvascular endothelial cells. Protein tyrosine kinase inhibitors herbimycin A and genistein blocked thrombin-stimulated preproET-1 mRNA and peptide secretion, whereas daidzein, which lacks inhibitory activity, did not suppress thrombin-induced ET-1.

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.