Canine endothelin-2: cDNA sequence for the mature peptide

Modulating effect of a selective endothelin A receptor antagonist on pulmonary endothelin system protein expression in experimental diaphragmatic hernia

BACKGROUND/PURPOSE

Previously, we reported that perinatal administration of atrasentan, a selective endothelin A receptor (ETA) antagonist, provided a beneficial effect on the cardiopulmonary profile under short-term conditions in newborn lambs with surgically induced congenital diaphragmatic hernia (CDH). We hypothesized that changes in the hemodynamic profile that we observed at birth in treated animals could be influenced by pulmonary modulation of the endothelin (ET) system.

METHODS

The effect of atrasentan on protein expression levels of ETs and ET receptors (ETA and ETB receptor) was investigated by immunohistochemistry in lung tissues of untreated control (n = 3), treated control (n = 6), untreated CDH (n = 6), and treated CDH newborn lambs (n = 8).

RESULTS

Right lung tissue of treated control lambs showed significantly higher ETA protein expression levels in both vascular adventitia and airway epithelia when compared with that of untreated control lambs (P < .05). In contrast, protein expression levels of ETA and ETB receptor were significantly lower in the vascular smooth muscle cells among other tissue subcompartments of the right lung of treated CDH newborn lambs vs CDH lambs (P < .02 and P = .005, respectively).

CONCLUSIONS

We speculate that rapid pulmonary modulation of ET system protein expression levels by atrasentan results from an indirect effect possibly dependent on ventilation and/or perfusion. In CDH groups, this could contribute to the beneficial effect of the treatment.

Cloning of full-length preproendothelin-2 cDNA and its expression in dog

Endothelin-2 (ET2) is a member of the endothelin family of 21-amino acid peptides with vasoconstrictive activity. We report here the molecular cloning of the canine full-length cDNA of the precursor form of ET2, prepro-ET2 (PPET2), from intestinal tissue by means of reverse transcription-polymerase chain reaction (RT-PCR) in conjunction with 5'- and 3'-rapid amplification of cDNA ends (RACE). Aside from the poly (A) tail the cDNA was found to be 1195 bp and included an open reading frame of 534 bp encoding a PPET2 polypeptide of 178 residues, in which the regions corresponding to bioactive mature ET2 peptide, an intermediate form big-ET2, and endothelin-like peptide are found. The organ distributions of PPET2 mRNA and a splicing variant were analyzed by RT-PCR. PPET2 transcript was detected in duodenum, colon, stomach, lung, liver, uterus, ovary, testis and kidney, but not in spleen. A splicing variant was found in none of the organs. Thus, based on the cloned cDNA sequence, we established a quantitative assay for dog PPET2 mRNA level using a real-time PCR system. Quantitative analysis by this method in various organs of the dog demonstrated that the dominant gene expression occurs in the intestine, with higher expression in large intestine than in small intestine.

Expression of endothelin-1 immunoreactivity in breast cancer

This study performed immunohistochemical staining for human ET-1, utilizing avidinbiotin-peroxidase complex detection to examine 47 surgically resected primary breast cancers. Positive immunoreactivity was demonstrated in 19 of the 47 breast cancers (40.4%). There was no significant relationship between the expression of ET-1 and clinicopathological findings. A significant difference was found between ET-1 positive and negative groups in the incidence of recurrence and distant metastasis (P < 0.05). The 5-year overall survival rate was significantly poorer in patients with ET-1-positive cancer (84.2%), compared to 96.4% in patients with ET-1 negative cancer (P < 0.01). The 5-year disease-free survival rate was significantly poorer in patients with ET-1-positive cancer (73.7%) compared to 96.4% in patients with ET-1-negative cancer (P < 0.05). These results suggest that the expression of ET-1 could be used as a possible indicator for predicting the metastatic potential of breast cancer.

Immunoreactive endothelin in human kidney

Using a sensitive and specific radioimmunoassay for endothelin, we examined immunoreactive endothelin in human kidney tissue obtained from three necropsy and three nephrectomy cases. Immunoreactive endothelin was present in high concentrations in human kidney inner medulla (necropsy cases: 1.08 +/- 0.47 pg/mg wet weight:mean +/- SE)(nephrectomy cases: 2.77 +/- 0.46). Characterization by reverse phase high performance liquid chromatography indicated that the only immunoreactive endothelin in human kidney inner medulla is endothelin-1, although immunoreactive endothelin in rat and pig kidney inner medulla comprises both isopeptides endothelin-1 and -3, suggesting that the genetic expression of endothelin differs according to species.

Distribution of endothelin-like immunoreactivity and mRNA in the developing and adult human lung

Localization and characterization of endothelin-producing cells in the developing (fetal and postnatal) and adult human lung was investigated using the technics of immunocytochemistry and in situ hybridization. Immunoreactivity for endothelin was seen mainly in pulmonary endocrine cells of developing human lung. Immunoreactivity was also seen in the airway epithelium in fewer cases (about 50%) of human adults. In situ hybridization with 35S- or 32P-labeled RNA probes complementary to endothelin-1, -2, and -3, showed that endothelin mRNAs were expressed in a number of cells that were in similar sites to endocrine cells. Immunocytochemistry and in situ hybridization employed on pairs of reverse-face serial sections showed the presence of endothelin immunoreactivity and mRNAs in the same endocrine cell. Correlative studies revealed that endothelin is co-localized with general endocrine markers (synaptophysin, chromogranin, protein gene product 9.5) and regulatory peptides (e.g., gastrin-releasing peptide). The density (cells/mm2) of endocrine cells containing immunoreactivity or mRNAs was highest during fetal life and started to decline before birth, and was minimal in adults. Endothelin-like immunoreactivity and mRNAs were also expressed in endothelial cells. From these results, it is concluded that endothelin is synthesized in endocrine cells of human lung and the change of developmental expression of this peptide suggests it may play a part in growth regulation in addition to its putative vasoconstrictor role in human lung.

Autoradiographic localization of endothelin-1 binding sites in porcine skin

Autoradiographic techniques and 125I-labeled endothelin-1 were used to study the distribution of endothelin-1 binding sites in porcine skin. Specific endothelin-1 binding sites were localized to blood vessels (capillaries, deep cutaneous vascular plexus, arteries, and arterioles), the deep dermal and connective tissue sheath of hair follicles, sebaceous and sweat glands, and arrector pili muscle. Specific binding was inhibited by endothelin-2 and endothelin-3 as well as endothelin-1. Non-specific binding was found in the epidermis and the medulla of hair follicles. No binding was found in connective tissue or fat. These vascular binding sites may represent endothelin receptors, in keeping with the known cutaneous vasoconstrictor actions of the peptide. If all binding sites are receptors, the results suggest that endothelin could also regulate the function of sweat glands and may have trophic effects in the skin.

Binding of [125I]-endothelin-1 to rat cerebellar homogenates and its interactions with some analogues

1. [125I]-endothelin-1, over the concentration range 6 pM-10 nM, bound to a single site in homogenates of rat cerebellum with high affinity (Kd = 2.8 +/- 0.6 x 10(-10) M). The site was present in a concentration of 321 +/- 58 fmol mg-1 protein. 2. The rates of association and dissociation of [125I]-endothelin-1 with the binding site were slow (at 25 degrees C, k+1 = 8.0 +/- 1.3 x 10(5) M-1s-1; k-1 = 2.6 x 10(-4)s-1) and, on addition of a maximally displacing concentration of endothelin-1 (100 nM), 94.0 +/- 8.4% of the [125I]-endothelin-1 was still bound after 14 h. 3. [125I]-endothelin-1 binding was inhibited by a number of naturally occurring or genetically encoded members of the endothelin/sarafotoxin family of peptides. The order of potency was endothelin-3 = sarafotoxin S6b greater than endothelin-2 = endothelin-1 much greater than porcine proendothelin1-39. 4. Binding was also inhibited by analogues in which either one or both of the cystine disulphide bridges had been replaced by substitution with 2 or 4 alanine residues. The tetra-alanyl substituted analogue, [Ala1,3,11,15]endothelin-1, was equipotent with endothelin-1 at inhibiting the binding of [125I]-endothelin-1. [Ala3,11]endothelin-1 and [Ala1,15]endothelin-1, analogues which each contained one of the disulphide bridges from the parent peptide, were respectively 3 and 14 times less potent than the parent peptide. An analogue in which the Glu10 residue had been anisylated was 25 fold less potent than endothelin-1. 5. It is concluded that the structural requirements for binding to the cerebellar sites for [1251]_ endothelin-1 do not require the presence of the disulphide bridges characteristic of the endothelin/ sarafotoxin family. Rather, the binding may be more sensitive to the presence of bulky side chain substituents, at least in the smaller intramolecular loop.

Detection of endothelin immunoreactivity and mRNA in pulmonary tumours

Paraffin sections of 66 surgically resected lung tumours were immunostained with antisera to human endothelin-1 and to the C-terminal peptide of big endothelin. With both antisera, strong immunoreactivity was demonstrated in 11 of 15 squamous cell carcinomas and 11 of 16 adenocarcinomas. Focal immunoreactivity was seen in small cell carcinoma (2/12), large cell carcinoma (2/5), and carcinoid tumours (2/11). Four lymphomas and three sarcomas did not show endothelin immunoreactivity. Cryostat sections of 22 of the 66 tumours were hybridized with radiolabelled complementary RNA probes prepared from the 3' non-coding region of endothelin-1 cDNA, and the chromosomal genes encoding endothelin-2 and -3. In situ hybridization demonstrated the presence of endothelin mRNAs in 4 of 7 squamous cell carcinomas and in 5 of 8 adenocarcinomas, in a pattern similar to that shown by immunocytochemistry. No hybridization signals were obtained from the other types of tumours. In lung tissue adjacent to the tumours, endothelin-like immunoreactivity and mRNA were detected in pulmonary endocrine cells and, in some cases, other epithelial cells, and in alveolar capillary endothelial cells. This study demonstrates the expression of endothelin in a number of pulmonary tumours and suggests a possible role for this peptide in the growth and/or differentiation of these tumours.

Two different forms of endothelin receptors in rat lung

We provided evidence for the presence of two distinct types of rat endothelin (ET) receptors having different molecular masses by affinity labelling of rat lung membranes with 125I-ET-1, ET-2 and ET-3 and SDS-PAGE followed by autoradiography. One type, which is 44 kDa has a higher affinity for ET-1 and -2 than ET-3, whereas the other type, which is 32 kDa, preferably interacts with ET-3 rather than ET-1 and -2.