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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Endothelins (ETs) (ET-1, ET-2, and ET-3), a family of 21-amino acid peptides, mediate a host of biological responses by binding to specific cell surface receptors termed ETA and ETB. Because a role for ET in bone remodeling has been suggested, the present study was undertaken (a) to characterize ET receptors and their responses in the rat osteosarcoma cell line ROS 17/2.8 and (b) to study their regulation by 1,25-dihydroxy-vitamin D3. Binding studies using 125I-ET-1 (a nonselective agonist) and 125I-IRL-1620 (an ETB receptor-selective agonist) indicated that these cells display high affinity ETA and ETB receptors in the ratio of 3:1. Addition of ET-1 or sarafotoxin 6c to myo-[3H]inositol-labeled cells resulted in an increase in inositol phosphate accumulation as well as in intracellular Ca2+ release, suggesting that these receptors are coupled to phospholipase C. In addition, ET-1 but not sarafotoxin 6c induced a modest increase in the expression of osteocalcin protein that was completely blocked by BQ123 (an ETA receptor-selective antagonist), indicating that activation of ETA receptors plays a role in the induction of osteocalcin. Treatment of ROS osteoblasts with 10 nM 1,25-dihydroxy-vitamin D3 for 14 hr resulted in a significant (> 50%) decrease in 125I-ET-1 and 125I-IRL-1620 binding. This decrease in binding was shown to be due to a decrease in the number of ET receptors, with no change in affinity. Although both ETA and ETB receptors were down-regulated in response to 1,25-dihydroxy-vitamin D3, only ETA receptor mRNA levels were significantly decreased, with very little change in ETB mRNA levels. These data indicate that ROS osteoblasts display both ETA and ETB receptors that are functional. Induction of osteocalcin was primarily mediated by ETA receptors, and these receptors were also down-regulated at the mRNA level by 1,25-dihydroxy-vitamin D3.
Mol Pharmacol 1995 Feb
PMID:Identification and characterization of endothelin receptors on rat osteoblastic osteosarcoma cells: down-regulation by 1,25-dihydroxy-vitamin D3. 787 34

In estradiol-dominated rat myometrium, endothelin (ET)-1 caused contraction and increased the accumulation of [3H]inositol phosphates (EC50 = 70 nM), with the sequential generation of inositol trisphosphate, inositol bisphosphate, and inositol monophosphate. There was a coincident early decrease in phosphatidyl-inositol bisphosphate. The ET-1 stimulatory effect was pertussis toxin insensitive, suggesting an activation of phospholipase C via Gq/G11 proteins. ET-1 also inhibited the generation of cAMP induced by forskolin (EC50 = 30 nM). The inhibition was maintained in Ca(2+)-depleted medium and was prevented by pertussis toxin, suggesting G(i)-mediated inhibition of adenylyl cyclase. The rank order of potency for these various ET-1 effects [ET-1 > (Thr2)-sarafotoxin-b >> ET-3], as well as the inhibitory effect displayed by BQ123, a specific ETA receptor antagonist, provided evidence for the involvement of the ETA receptor subtype. Exposure to ET-1 (15 min) resulted in concentration-dependent and homologous desensitization (40%) of the inositol phosphate response triggered by ET-1. There was virtually no recovery of ET-1-mediated inositol phosphate responses in the desensitized tissue even after 180 min of incubation. In contrast, the persistent low level of ET-1 activity that was observed in spite of several washings and in the absence of rechallenge with ET-1 was progressively revsersed and totally eliminated by BQ123. The ET-1 inhibitory effect on cAMP was also desensitized, as evidenced by the attenuation of the inhibitory effect of ET-1 after 15 min of ET-1 pretreatment. The data indicate that in rat myometrium the ETA receptor is coupled, via two distinct G proteins, to two main signal transduction cascades, which both undergo rapid desensitization.
Mol Pharmacol 1994 Sep
PMID:Endothelin receptor type A signals both the accumulation of inositol phosphates and the inhibition of cyclic AMP generation in rat myometrium: stimulation and desensitization. 793 29

In adult rat cardiac myocytes, endothelin (ET) receptors couple to multiple signaling pathways, including stimulation of phosphoinositide hydrolysis (pertussis toxin insensitive) and inhibition of adenylyl cyclase via Gi. We have used ET-1 and congeners to characterize the subtypes of ET receptors on isolated rat myocytes. The rank orders of potency for stimulating phosphoinositide hydrolysis, inhibiting hormone-sensitive adenylyl cyclase, and competing with 125I-ET-1 for binding to myocytes are the same and show the pattern characteristic of an ETA receptor interaction, i.e., ET-1 approximately ET-2 > sarafotoxin 6b > ET-3; the corresponding EC50 values for the effects of ET on signal transduction are approximately 0.5 nM (ET-1), 0.7 nM (ET-2), 7 nM (sarafotoxin 6b), and 60 nM (ET-3). The ETA receptor antagonist BQ-123 abolishes the cellular responses to ET-1 and competes fully for 125I-ET-1 binding in a concentration-dependent manner. Sarafotoxin 6c, an ETB-specific agonist, does not diminish the responses to ET-1 or compete for 125I-ET-1 binding; no specific binding of the ETB-specific ligand 125I-IRL-1620 is detectable on myocytes. Myocytes express approximately 4 x 10(5) ET-1 binding sites/cell. The association of 125I-ET-1 with myocytes is largely irreversible, as are the biochemical responses to ET-1; thus, constants derived from analyses that assume reversible equilibria are in error. We conclude that the effects of ET on transmembrane signaling in rat ventricular myocytes result from occupation of ETA receptors and that the responses are likely to be long lived, compared with those of the readily dissociable neurotransmitters released by the autonomic nervous system.
Mol Pharmacol 1994 Jun
PMID:Coupling of the type A endothelin receptor to multiple responses in adult rat cardiac myocytes. 802 11

Endothelin (ET) peptides are growth factors that bind to G protein-coupled receptors and serve as a useful model to study mitogenic signal transduction by vasoactive peptides. To begin to define the molecular mechanisms underlying mitogenic signaling by ET-1, we analyzed expression of ET receptor subtypes in glomerular mesangial cells and antagonism of ET-1-induced mitogenic responses by ET receptor antagonists. Competitive displacement analysis of 125I-ET-1 binding revealed a shallow multicomponent curve consistent with the presence of two ET-1 binding sites (Kd values of 32 pM and 1.2 nM). Nonlinear regression analysis demonstrated that a two-site model fit the data better than a one-site model (p = 0.0063). Analysis of 125I-ET-1 binding sites by affinity cross-linking revealed incorporated radioactivity in two distinct protein bands in mesangial cell membranes. Both ETA-specific (BQ 123) and nonselective (PD 142893/PD 145065) receptor antagonists displaced 125I-ET-1 from the low affinity site. The Ki values for BQ 123 and PD 145065 were similar to the IC50 values for inhibition of ET-1-induced increases in the intracellular free Ca2+ concentration ([Ca2+]i) by these antagonists. The ETB-specific ligands S6c and [Ala1,3,11,15]ET-1(6-21) were unable to displace 125I-ET-1 from either low affinity or high affinity binding sites. Analysis of ET receptor mRNA by reverse transcription-polymerase chain reaction, using primers predicted from DNA sequences conserved through evolution in ETA and ETB genes, demonstrated that mesangial cells express a canonical ETA receptor. Collectively, these data suggest that the low affinity, high capacity 125I-ET-1 binding site is an ETA receptor and that the high affinity, low capacity site is not accounted for by canonical ET receptors. We further demonstrated that BQ 123 and PD 142893/PD 145065 inhibited ET-1-stimulated [3H]thymidine uptake but at higher concentrations than required for inhibition of [Ca2+]i increases. Preincubation (as opposed to coincubation) with antagonists was required to inhibit ETA-mediated increases in [Ca2+]i produced by ET-1. These results suggest that the unique, nearly irreversible binding of ET-1 to ETA receptors explains why high concentrations of ET receptor antagonists are required to block longer term actions such as mitogenesis.
Mol Pharmacol 1994 Jul
PMID:Characterization of endothelin receptors in mesangial cells: evidence for two functionally distinct endothelin binding sites. 805 55

To investigate the nuclear signalling pathway induced by endothelin (ET) isopeptides, we have established permanent Chinese hamster ovary (CHO) cell lines, CHO-ETA/fos-lacZ and CHO-ETB/fos-lacZ, that produce both a c-fos-beta-galactosidase fusion protein and either the type A or the type B human ET receptor. These cell lines permitted a colorimetric measurement of c-fos expression, which was induced by the signal transduction system with ET receptors and ET isopeptides. We found that the ET-1-dependent c-fos expression was so efficient that it could respond to low concentrations (even a physiological concentration) of ET-1. For example, CHO-ETA/fos-lacZ and CHO-ETB/fos-lacZ responded to ET concentrations of 5 x 10(-9) M and 5 x 10(-13) M respectively. Using this highly sensitive system, the H-7 sensitive protein kinase was found to be involved in signal transduction mediated by ETA, and also partly in the ETB-mediated pathway. These lines of evidence suggest that c-fos expression occurs through at least two different pathways, depending on the concentration of ET in plasma.
J Mol Endocrinol 1994 Apr
PMID:Differential regulation of c-fos gene expression by two types of human endothelin receptor in Chinese hamster ovary cells. 806 Apr 82

The two endothelin (ET) receptor subtypes (ETA and ETB) have been characterized in rat kidney from normal rats and rats with acute renal failure induced by hypertonic glycerol administration. In control rats, the total number of ET receptors in kidney cortex and medulla was 155 and 386 fmol/mg of protein, respectively. The ratio of ETA to ETB receptors was 54:46 in renal cortex and 35:65 in renal medulla. Treatment of rats with 10 ml/kg glycerol (50%, w/v) intramuscularly resulted in severe renal dysfunction; the serum urea concentration increased from 0.46 to 2.65 g/liter and the creatinine clearance decreased from 1.06 to 0.30 ml/min. Ligand binding studies showed that glycerol-induced acute renal failure was associated with a marked up-regulation of ETA and ETB receptor subtypes in both cortex and medulla. In glycerol-treated rats, the total ET receptor density in kidney cortex and medulla was increased to 294 and 1172 fmol/mg of protein, with ETA/ETB ratios of 52:48 and 31:69, respectively. The upregulatory effect of glycerol treatment was significantly more pronounced in renal medulla than renal cortex and affected ETB receptors preferentially, compared with ETA receptors. Subsequently, ETA and ETB receptor mRNA levels were markedly increased by glycerol administration in both kidney cortex and medulla, as assessed by polymerase chain reaction coupled to reverse transcription. These results suggest that up-regulation of renal ET receptors, particularly ETB receptors in kidney medulla, may account for or contribute to renal function impairment induced by glycerol, and they support a pathophysiological role for ET in acute renal failure.
Mol Pharmacol 1994 Feb
PMID:Endothelin receptor subtypes A and B are up-regulated in an experimental model of acute renal failure. 811 69

The objective of the present study was to characterize the binding and functional properties of endothelin (ET) receptor subtypes in the human prostate. Human prostatic tissue was obtained from male subjects undergoing radical prostatectomy for low-volume prostate cancer. The optimal assay conditions for characterizing human prostatic ET-1 binding sites on slide-mounted tissue sections were defined. Maximal specific 125I-ET-1 binding was achieved after a 10-min preincubation, a 120-min incubation, and a washing procedure that consisted of a brief rinse and a 1-min wash. The mean equilibrium dissociation constant (Kd) and density (Bmax) of ET-1 binding sites determined from six saturation studies were 0.72 +/- 0.13 nM and 40.4 +/- 6.9 fmol/mg of wet weight, respectively. The mean Hill coefficient was 0.99 +/- 0.01, indicating that 125I-ET-1 identifies a single population of binding sites. The pharmacology of 125I-ET-1 binding sites was characterized using competitive binding experiments. The competition plots for ET-1 were best fit by a one-binding site model, whereas the plots for sarafotoxin 6C (S6C) and BQ123 were consistently best fit by a two-site model. The mean Ki value of ET-1 was 0.34 +/- 0.12 nM. The mean Ki values for the high and low affinity S6C binding sites were 0.50 +/- 0.09 nM and 0.84 +/- 0.28 microM, respectively. The mean Ki values for the high and low affinity BQ123 binding sites were 5.51 +/- 1.05 nM and 24.9 +/- 6.5 microM, respectively. The ratio of ETA to ETB binding sites was approximately 2:1. The ET receptor subtype mediating prostatic smooth muscle tension was investigated using agonist-antagonist competition studies. ET-1, a nonselective ET agonist, elicited a potent contraction of prostate smooth muscle. The pA2 of BQ123 for inhibiting ET-1-mediated contraction was 6.84. S6C, a selective ETB agonist, also elicited a potent contraction of prostate smooth muscle. BQ123 at concentractions between 0.1 and 10 microM did not shift the S6C dose-response curve. These functional studies suggest that both ETA and ETB receptors mediate the tension of prostate smooth muscle. Endogenous ETS may be involved in the pathophysiology of bladder outlet obstruction in men with benign prostatic hyperplasia. If this is the case, then ET antagonists may represent effective treatment for benign prostatic hyperplasia.
Mol Pharmacol 1994 Feb
PMID:Binding and functional properties of endothelin receptor subtypes in the human prostate. 811 78

The vasoactive peptides endothelin-1 (ET-1) and angiotensin-II (AII) have been implicated in chronic hypertension and may play important roles in related vascular diseases such as restenosis and atherosclerosis. Using a rat aortic smooth muscle (RASM) cell model, both ET-1 and AII induced concentration-dependent delayed increases in DNA synthesis relative to that in the serum-deprived controls. Stimulation of DNA synthesis was maximal at 100 nM for each peptide. All treatment of RASM cells resulted in a greater mitogenic effect (4- to 7-fold) than that observed for ET-1 (3-fold). When added in the presence of AII, ET-1 had a supplemental effect on DNA synthesis (5- to 10-fold above control). Although RASM cells expressed both ETA and AT1 receptors, radioligand binding experiments indicated that approximately 10-fold as many AT1 receptors as ETA receptors were present. In signal transduction studies, ET-1 and AII each elicited concentration-dependent increases in the intracellular Ca2+ concentration. ET-1 and AII also stimulated phosphoinositide metabolism and phosphorylation of a specific substrate for protein kinase-C. The release of total inositol phosphates in response to ET-1 and AII was concentration dependent and inhibited by the ETA receptor-selective antagonist BQ-123 and the AT1 receptor-selective antagonist losartan, respectively. In addition, tyrosine phosphorylation of 120- and 75-kilodalton proteins as well as the mitogen-activated protein kinases p44mapk and p42mapk was observed within 5 min of the addition of either ET-1 or AII. Taken together, these data indicate that ET-1 and AII may promote smooth muscle cell growth through common intracellular signaling mechanisms.
Mol Endocrinol 1994 Feb
PMID:Endothelin-1 and angiotensin-II stimulate delayed mitogenesis in cultured rat aortic smooth muscle cells: evidence for common signaling mechanisms. 817 Apr 71

Endothelin (ET) receptors display subtype heterogeneity and so far three subtypes of ET receptors, namely ETA, ETB, and ETC, have been identified, cloned, sequenced, and characterized. Based on the binding profile of ET and related peptides, a novel ET receptor (ETAX) was identified in the follicular membranes of Xenopus laevis oocytes (Kumar, C. S., Nuthulaganti, P., Pullen, M., and Nambi, P. (1993). Mol. Pharmacol. 44, 153-157). Here we report the cloning and characterization of this ETAX subtype from X. laevis heart. A cDNA was isolated that encodes a protein of 415 amino acids that shares 74, 60, and 51% identities with human ETA, human ETB, and Xenopus ETC receptors, respectively. Competition binding studies of the cloned receptor expressed in COS cells using ET-related peptides suggested that this receptor is pharmacologically identical to that expressed in Xenopus oocyte follicular, heart, and lung membranes. Phosphoinositide turnover and oocyte electrophysiological studies indicated that the cloned receptor is functionally coupled to a second messenger system.
 ...
PMID:Cloning and characterization of a novel endothelin receptor from Xenopus heart. 817 72

The unique cyclic peptide designated RES-701-1 blocked the binding of 125I-labeled endothelin (ET)-1 to bovine cerebellar membranes. ETB receptors are predominant in bovine cerebellum. However, in bovine lung membranes, where both ETA and ETB receptors are expressed, RES-701-1 inhibited 125I-ET-1 binding by up to 70%; RES-701-1, in the presence of the ETA-selective antagonist BQ-123 at 1 microM, displaced 125I-ET-1 binding completely. With membranes from transfected Chinese hamster ovary cells expressing the human ETA or ETB receptors, RES-701-1 inhibited 125I-ET-1 binding to the ETB receptor with an IC50 value of 10 nM but had no effect on 125I-ET-1 binding to the ETA receptor. Thus, RES-701-1 is highly specific for the ETB receptor; it has no effect on a number of other receptors. RES-701-1 selectively inhibited the ET-1-induced increase in intracellular Ca2+ concentration in COS-7 cells expressing the ETB receptor but did not inhibit the Ca2+ transient in ETA-expressing cells. When injected intravenously (250 nmol/kg) into anesthetized rats, RES-701-1 abolished the initial depressor response to ET-1 but enhanced the subsequent pressor response. These results suggest that RES-701-1 is a potent and specific antagonist for the ETB receptor and that RES-701-1 will be a powerful tool for understanding the physiological roles of this receptor.
Mol Pharmacol 1994 Apr
PMID:RES-701-1, a novel, potent, endothelin type B receptor-selective antagonist of microbial origin. 818 52


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