Effect of an antisense oligodeoxynucleotide to endothelin-converting enzyme-1c (ECE-1c) on ECE-1c mRNA, ECE-1 protein and endothelin-1 synthesis in bovine pulmonary artery smooth muscle cells

Ca2+ responses of pulmonary arterial myocytes to acute hypoxia require release from ryanodine and inositol trisphosphate receptors in sarcoplasmic reticulum

In pulmonary arterial smooth muscle cells (PASMC), acute hypoxia increases intracellular Ca(2+) concentration ([Ca(2+)](i)) by inducing Ca(2+) release from the sarcoplasmic reticulum (SR) and Ca(2+) influx through store- and voltage-operated Ca(2+) channels in sarcolemma. To evaluate the mechanisms of hypoxic Ca(2+) release, we measured [Ca(2+)](i) with fluorescent microscopy in primary cultures of rat distal PASMC. In cells perfused with Ca(2+)-free Krebs Ringer bicarbonate solution (KRBS), brief exposures to caffeine (30 mM) and norepinephrine (300 μM), which activate SR ryanodine and inositol trisphosphate receptors (RyR, IP(3)R), respectively, or 4% O(2) caused rapid transient increases in [Ca(2+)](i), indicating intracellular Ca(2+) release. Preexposure of these cells to caffeine, norepinephrine, or the SR Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA; 10 μM) blocked subsequent Ca(2+) release to caffeine, norepinephrine, and hypoxia. The RyR antagonist ryanodine (10 μM) blocked Ca(2+) release to caffeine and hypoxia but not norepinephrine. The IP(3)R antagonist xestospongin C (XeC, 0.1 μM) blocked Ca(2+) release to norepinephrine and hypoxia but not caffeine. In PASMC perfused with normal KRBS, acute hypoxia caused a sustained increase in [Ca(2+)](i) that was abolished by ryanodine or XeC. These results suggest that in rat distal PASMC 1) the initial increase in [Ca(2+)](i) induced by hypoxia, as well as the subsequent Ca(2+) influx that sustained this increase, required release of Ca(2+) from both RyR and IP(3)R, and 2) the SR Ca(2+) stores accessed by RyR, IP(3)R, and hypoxia functioned as a common store, which was replenished by a CPA-inhibitable Ca(2+)-ATPase.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Downregulated FKBP12.6 expression and upregulated endothelin signaling contribute to elevated diastolic calcium and arrhythmogenesis in rat cardiomyopathy produced by l-thyroxin

BACKGROUND

Dissociation of FKBP12.6 from RyR2 is considered as an important molecular event resulting in calcium leak and an increased risk in arrhythmogenesis. We hypothesized that augmented ventricular fibrillation (VF) on reperfusion of rat cardiomyopathy induced by l-thyroxin may result from elevated diastolic Ca(2+) levels due to dissociation (downregulation) of FKBP12.6 and upregulation of endothelin (ET-1) signaling pathway.

METHODS

Rats were treated with l-thyroxin (0.4 mg/kg, s.c.) for 10 days. Dajisentan (CPU0213), a dual endothelin receptor antagonist (100 mg/kg p.o.), or propranolol was administered on day 6 to 10. Susceptibility to VF was evaluated on ischemia/reperfusion episode. mRNA expression of FKBP12.6, and ET-1 levels were determined. Calcium transients and FKBP12.6 immunohistochemistry were measured by confocal microscopy in isolated cardiomyocytes from cardiomyopathy.

RESULTS

Cardiomyopathy induced by l-thyroxin resulted in an increased susceptibility to VF on ischemia/reperfusion. Upregulated mRNA expression of RyR2 and PKA in association with downregulated FKBP12.6 expression was found in l-thyroxin-treated rats compared to controls. Calcium transients evoked by field electrical stimulation showed an increase in Ca(2+) by +75% during diastole. An increase in ET-1 (ng/mg protein) (+36.6%) and mRNA abundance of preproET-1 were found in the left ventricle. A decreased mRNA ratio of FKBP12.6 to RyR2 likely reflected dissociation of FKBP12.6 in cardiomyopathy. These changes were normalized by Dajisentan, comparable to propranolol.

CONCLUSION

Increased susceptibility to VF in l-thyroxin-induced cardiomyopathy is related to increase in diastolic Ca(2+) levels, resulting from downregulated FKBP12.6 and upregulated ET system. ET antagonism might be useful in settings of FKBP12.6 dissociation.

A novel endothelin receptor antagonist CPU0213 improves diabetic cardiac insufficiency attributed to up-regulation of the expression of FKBP12.6, SERCA2a, and PLB in rats

The depressed sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) and Ca2+-release channels (ryanodine receptor RyR2) are involved in the diabetic cardiomyopathy. However, an implication of a down-regulation of FK506-binding protein or calstabin-2 (FKBP12.6) is undefined. It was hypothesized that the down-regulation of FKBP12.6 and SERCA2a of the intracellular calcium handling system is closely related to an up-regulated endothelin (ET) system. An ET receptor antagonist CPU0213 is newly discovered and expected to ameliorate cardiac insufficiency which is mediated by the depressed FKBP12.6 and SERCA2a in diabetic rat heart. Diabetes was developed in male Sprague-Dawley rats 8 weeks after an injection of streptozotocin (60 mg/kg IP), and CPU0213 was instituted 30 mg/kg, SC in the last 4 weeks. The assessment of the cardiac function, cardiac calcium handling proteins, endothelin system, and redox enzyme system were conducted. The compromised cardiac function in diabetic rats was accompanied by a significant down-regulation of expression of FKBP12.6 as well as SERCA2a and phospholamban. These were closely linked with an increased ET-1 and up-regulation of endothelin converting enzyme, PropreET1, and inducible nitric oxide synthase mRNA in diabetic cardiomyopathy. After 4-week treatment, CPU0213 was capable to attenuate completely the down-regulated FKBP12.6 and SERCA2a, and up-regulated ET system in association with a recovery of the cardiac insufficiency of diabetic cardiomyopathy.

CPU0213, a novel endothelin receptor antagonist, ameliorates septic renal lesion by suppressing ET system and NF-kappaB in rats

AIM

To examine whether a novel endothelin receptor antagonist, CPU0213, is effective in relieving the acute renal failure (ARF) of septic shock by suppressing the activated endothelin-reactive oxygen species (ET-ROS) pathway and nuclear factor kappa B (NF-kappaB).

METHODS

The cecum was ligated and punctured in rats under anesthesia. CPU0213 (30 mg .kg(-1).d(-1), bid, sc X 3 d) was administered 8 h after surgical operation.

RESULTS

In the untreated septic shock group, the mean arterial pressure and survival rate were markedly decreased (P<0.01), and heart rate, weight index of kidney, serum creatinine and blood urea nitrogen, 24 h urinary protein and creatinine were significantly increased (P<0.01). The levels of ET-1, total NO synthetase (tNOS), indusible nitric oxide synthetase (iNOS), nitric oxide (NO), and ROS in serum and the renal cortex were markedly increased (P<0.01). The upregulation of the mRNA levels of preproET-1, endothelin converting enzyme, ET(A), ET(B), iNOS, and tumor necrosis factor-alpha in the renal cortex was significant (P<0.01). The protein amount of activated NF-kappaB was significantly increased (P<0.01) in comparison with the sham operation group. All of these changes were significantly reversed after CPU0213 administration.

CONCLUSION

Upregulation of the ET signaling pathway and NF-kappaB play an important role in the ARF of septic shock. Amelioration of renal lesions was achieved by suppressing the ET(A) and ET(B) receptors in the renal cortex following CPU0213 medication.

Endothelin-converting Enzyme-1, Abundance of Isoforms a-d and Identification of a Novel Alternatively Spliced Variant Lacking a Transmembrane Domain

Endothelin-converting enzyme-1 (ECE-1) cleaves big endothelins, as well as bradykinin and beta-amyloid peptide. Several isoforms of ECE-1 (a-d) have been identified to date; they differ only in their NH(2) terminus but share the catalytic domain located in the COOH-terminal end. Using quantitative PCR, we found ECE-1d to be the most abundant type in several endothelial cells (EC) types. In addition to full-length ECE-1 forms we have identified novel, alternatively spliced mRNAs of ECE-1 b-d. These splice variants (SVs) lack exon 3', which codes for the transmembrane region and is present in full-length forms. SVs mRNA were highly expressed in EC derived from macro and microvascular beds but much less so in other, non-endothelial cells expressing ECE-1, which suggests that the splicing mechanism is cell-specific. Analyses of ECE-1d and its SV form in stably transfected HEK-293 cells revealed that both proteins were recognized by anti COOH-terminal ECE-1 antibodies, but anti NH(2)-terminal antibodies only bound ECE-1d. The novel protein, designated ECE-1 sv, has an apparent molecular mass of 75 kDa; by using site-directed mutagenesis its start site was identified in a region common to all ECE-1 forms suggesting that ECE-1 b-d SV mRNAs are translated into the same protein. In agreement with the findings demonstrating common COOH terminus for ECE-1sv and ECE-1d, both exhibited a similar catalytic activity. However, immunofluorescence staining and differential centrifugation revealed a distinct intracellular localization for these two proteins. The presence of ECE-1sv in different cellular compartments than full-length forms of the enzyme may suggest a distinct physiological role for these proteins.

Immunohistochemical Localization of Endothelin-Converting Enzyme-1 in Neuroendocrine Tumors and Normal Human Tissue

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final step in the process. In this study, we investigated the cellular distribution of ECE-1 in 19 normal human tissues and 16 neuroendocrine tumors using immunohistochemical staining with antigen retrieval. ECE-1 was expressed in vessel endothelial cells as well as nearly all epithelial cells, glands and duct cells in normal human tissues including the esophagus, stomach, small intestine, appendix, colon, liver, gallbladder, pancreas, endometrium, cervix, breast, skin, prostate, urinary bladder, lung, kidney, sympathetic ganglion, thyroid gland, and adrenal gland. The most interesting finding was that ECE-1 was expressed in normal neuroendocrine cells. ECE-1 was also expressed in all 16 neuroendocrine tumors, including three paragangliomas, five pheochromocytomas, three carcinoid tumors, four medullary carcinomas of the thyroid, and one islet cell tumor of the pancreas. In conclusion, ECE-1 is enriched in neuroendocrine cells and neuroendocrine tumors, suggesting an important biologic role for the enzyme in the neuroendocrine system.

Tumor necrosis factor alpha in the bovine oviduct during the estrous cycle: messenger RNA expression and effect on secretion of prostaglandins, endothelin-1, and angiotensin II

Tumor necrosis factor (TNF) alpha is an important physiological mediator of cell-to-cell communication. Recent observations suggest that TNFalpha is involved in the control of reproductive functions. The present study examined the role of TNFalpha in the secretion of factors involved in regulating smooth muscle contraction, such as prostaglandin E2 (PGE2), prostaglandin F2alpha (PGF2alpha), endothelin-1 (ET-1), and angiotensin II (Ang II), as it was in the original by the cow oviduct at different stages of the estrous cycle using an in vitro microdialysis system. Expression of mRNA for TNFalpha and its receptors (TNFalpha-R) was also evaluated. For microdialysis, the lumen of a portion (length, 10 cm) of the each oviductal segment was implanted with a dialysis capillary membrane, and TNFalpha (100 ng/ml) was infused for 4-8 h during a 16-h incubation period. The microdialysis system maintains cell-to-cell integrity and cell-to-cell communication, and it enables real-time observation of physiological changes in the luminal release of different substances. Concentrations of PG, ET-1, and Ang II in 4-h fractions were measured using second-antibody enzyme immunoassays. Infusion of TNFalpha stimulated oviductal secretion of PG, ET-1, and Ang II during the follicular and postovulatory stages, but not during the luteal stage. Expression of TNFalpha, TNFalpha-R type I, and TNFalpha-R type II mRNA was detected in the bovine oviduct by reverse transcription-polymerase chain reaction. High expression of both TNFalphaR types and ligands was detected during the follicular and postovulatory stages, whereas low expression was detected during the luteal stage. The results of the present study provide, to our knowledge, the first direct evidence that TNFalpha stimulates PG, ET-1, and Ang II secretion and that up-regulation of the TNFalpha system occurs in the cow oviduct during the periovulatory period. In conclusion, the TNFalpha system may optimize the release of contraction-related substances and modulate local contraction to regulate the oviductal transport of the gametes and embryo.

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

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

Transcriptional mechanism of protein kinase C-induced isoform-specific expression of the gene for endothelin-converting enzyme-1 in human endothelial cells

Isoform-specific expression of endothelin-converting enzyme (ECE)-1, the major big endothelin-processing enzyme, is controlled by alternative promoters. Signaling pathways and transcriptional mechanisms of ECE-1 mRNA expression are largely unknown. To investigate ECE-1 isoform expression after protein kinase C (PKC) activation, we used phorbol 12-myristate 13-acetate (PMA) to stimulate primary cultured human umbilical vein endothelial cells and the related EA.hy926 cell line. ECE-1a mRNA was up-regulated (approximately 3-fold), whereas mRNA of alternative isoforms (b, c, and d) was unchanged, which was confirmed on the protein level. PMA effects on mRNA expression were suppressed by the PKC inhibitors H-7 and Calphostin C. Because increased ECE-1a expression was preceded by induction of the transcription factor Ets-1, we performed gel shift assays and demonstrated specific DNA/protein interactions involving the ETS binding motif GGAA. Luciferase reporter assays showed that PMA induced ECE-1a promoter activity about 2.5-fold in EA.hy926 cells. Similarly, coexpression of Ets-1 protein resulted in a dose-dependent increase in ECE-1a promoter activity (more than 8-fold). Using gel shift assays and mutation analysis, we identified two tandemly arranged Ets-1 binding sites (EBS) at -638 and -658, respectively, that are involved in transcriptional activation of the ECE-1a promoter by PMA or Ets-1. Moreover, we also found evidence for binding of a transcriptional repressor to EBS -638. The inhibitor of mitogen-activated protein kinase kinase, PD98059, inhibited PMA effects on ECE-1a mRNA expression and promoter activity, respectively. Our results provide the first detailed analysis of signaling pathways and transcriptional mechanisms involved in isoform-specific ECE-1 gene expression.

Vasoconstrictor activity of novel endothelin peptide, ET-1(1 - 31), in human mammary and coronary arteries in vitro

1. The ability of the putative chymase product of big endothelin-1 (big ET-1), ET-1(1 - 31), to constrict isolated endothelium-denuded preparations of human coronary and internal mammary artery was determined. 2. pD2 values in coronary and mammary artery respectively were 8.21+/-0.12 (n=14) and 8.55+/-0.11 (n=12) for ET-1, 6.74+/-0.11 (n=16) and 7.10+/-0.08 (n=16) for ET-1(1 - 31) and 6.92+/-0.10 (n=15) and 7.23+/-0.11 (n=12) for big ET-1. ET-1(1 - 31) was significantly less potent than ET-1 (P<0.001, Student's t-test) and equipotent with big ET-1. 3. Vasoconstrictor responses to 100 - 700 nM ET-1(1 - 31) were significantly (P<0.05, Student's paired t-test) attenuated by the ET(A) antagonist PD156707 (100 nM). 4. There was no effect of the ECE inhibitor PD159790 (30 microM), the ECE/NEP inhibitor phosphoramidon (100 microM) or the serine protease inhibitor chymostatin (100 microM) on ET-1(1 - 31) responses in either artery. 5. Radioimmunoassay detected significant levels of mature ET in the bathing medium of coronary (1.6+/-0.5 nM, n=14) and mammary (2.1+/-0.6 nM, n=14) arteries, suggesting that conversion of ET-1(1 - 31) to ET-1 contributed to the observed vasoconstriction. 6. ET-1(1 - 31) competed for specific [(125)I]-ET-1 binding to ET(A) and ET(B) receptors in human left ventricle with a pooled K(D) of 71.6+/-7.0 nM (n=3). 7. Therefore, in human arteries the novel peptide ET-1(1 - 31) mediated vasoconstriction via activation of the ET(A) receptor. The conversion of ET-1(1 - 31) to ET-1, by an as yet unidentified protease, must contribute wholly or partly to the observed constrictor response. Chymase generated ET-1(1 - 31) may therefore represent an alternative precursor for ET-1 production in the human vasculature.