phosphoramidon and Adenocarcinoma

ABSTRACT The synthesis of the vasoconstrictor peptide endothelin-2 (ET-2) is dependent on hydrolysis of the biologically inactive intermediate big ET-2 by an endothelin-converting enzyme (ECE). Here, mechanisms inducing ET-2 synthesis have been investigated using the human renal adenocarcinoma cell line (ACHN). Synthesis of ET-2 by ACHN cells was inhibited by phosphoramidon (IC(50( congruent with11 microM). To determine whether ET-2 synthesis occurs in parallel with the metallopeptidase ECE-1, a putative processing peptidase for big ET-2, changes in the levels of their mRNAs were compared by semi-quantitative RT-PCR under conditions causing the upregulation of ET-2 synthesis. Tumour necrosis factor-alpha (TNFalpha), forskolin and a cell-permeable cAMP analogue (dibutyryl cAMP) caused concentration-dependent increases in ET-2 synthesis. Combination of forskolin or dibutyryl cAMP with TNFalpha produced a significantly greater increase in ET-2 production than these agents alone, indicating that adenylate cyclase and TNFalpha induce ET-2 synthesis by separate signalling pathways. Studies using receptor selective TNFalpha mutants, (125(I-TNFalpha binding and TNF receptor mRNA showed that type-1 TNF receptors mediate the ET-2 response to TNFalpha. PreproET-2 mRNA levels were increased by TNFalpha at 1 h and 2 h, but returned to control levels at 4 h. Treatment with forskolin significantly increased preproET-2 mRNA levels after 1 h and 4 h. ACHN cells expressed ECE-1b and ECE-1c, but not the ECE-1a isoform of this peptidase. RT-PCR for the combined isoforms ECE-1b/c/d showed TNFalpha to increase mRNA levels at 2 h and 4 h. Forskolin had no effect on ECE-1b/c/d mRNA levels. Thus, expression of ET-2 and ECE-1b/c/d mRNAs in ACHN cells do not display the co-ordinated regulation observed with typical peptide prohormone processing enzymes and their substrates.

Topics: Adenocarcinoma; Antigens, CD; Aspartic Acid Endopeptidases; Cyclic AMP; Endothelin-2; Endothelin-Converting Enzymes; Gene Expression Regulation, Neoplastic; Glycopeptides; Humans; Kidney Neoplasms; Metalloendopeptidases; Protease Inhibitors; Receptors, Tumor Necrosis Factor; Receptors, Tumor Necrosis Factor, Type I; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Transcription, Genetic; Tumor Cells, Cultured

This study was designed to characterize the endothelin pathway in an immortalized human adenocarcinoma-derived alveolar epithelial cell line (A549) and human umbilical vein endothelial cell line (HUVEC).. The release of ET-1 and big-ET-1 was measured in the incubation medium of both cell lines. The expression of mRNAs coding for the endothelin isoforms (hppET-1, -2, -3), the endothelin converting enzymes (hECE-1a, b, c, and d) and the hETA and hETB receptors was investigated using RT-PCR. The expression of ECE-1 mRNA in various human tissues and in A549 cells was investigated by Northern blot analysis and the subcellular localization of ECE-1 in A549 cells was investigated by immunoblotting using a polyclonal antibody.. Under control conditions, HUVEC release both ET-1 and big-ET-1 (ratio 5 to 1) while in A549 cells the big-ET-1 levels were below the threshold of detection. The release of these two peptides was minimally affected by various inhibitors of peptidases. However, in both cell lines phosphoramidon produced a concentration-dependent inhibition of ET-1 release and an enhanced accumulation of big-ET-1. Both HUVEC and A549 cells express the mRNAs for ppET-1, ET-A, and ET-B receptor subtypes and ECE-1 (isoforms ECE-1b, c and/or d). In addition, in HUVEC the mRNAs for ppET-2 and for the isoform ECE-1a were also detected. In A549 cells, ECE-1 had a preferential subcellular localization in the membrane fraction but was not detected in the cytosol.. Both A549 and HUVEC produce and release endothelin-1 through a specific enzymatic pathway, whether or not ECE-1 is the only enzyme involved remains to be determined. A549 might be used as a screening assay for drug discovery such as for inhibitors of endothelin-1 release.

Topics: Adenocarcinoma; Aspartic Acid Endopeptidases; Cells, Cultured; Endothelin-1; Endothelin-Converting Enzymes; Endothelins; Endothelium, Vascular; Glycopeptides; Humans; Lung Neoplasms; Metalloendopeptidases; Protein Precursors; RNA, Messenger; Tumor Cells, Cultured; Umbilical Veins

Neutral endopeptidase (NEP; CALLA, CD10, EC 3.4.24.11) is a cell surface endopeptidase that hydrolyses bioactive peptides, including the bombesin-like peptides, as well as other neuropeptides. Bombesin-like peptides and other neuropeptides are autocrine growth factors for both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). Low expression of NEP has been reported in SCLC and NSCLC cell lines. NEP inhibition has been shown to increase proliferation in one cell line. To date, NEP expression has not been quantitatively evaluated in normal adult lung, SCLC or NSCLC tumors, paired uninvolved lung from the same patient, or in other pulmonary neoplasms such as mesotheliomas and carcinoids. We examined the expression of NEP in these tissues and human cell lines using immunohistochemistry, flow cytometry, enzyme activity, ELISA, Western blot, and reverse transcription (RT)-PCR. Uninvolved lung tissue from different individuals displayed considerable variation in NEP activity and protein. By immunohistochemistry, NEP expression was detectable in alveolar and airway epithelium, fibroblasts of normal lung, and in mesotheliomas, whereas it was undetectable in most SCLC, adenocarcinoma, squamous cell carcinoma, and carcinoid tumors of the lung. NEP activity and protein levels were lower in all SCLC and adenocarcinoma tumors when compared to adjacent uninvolved lung, often at levels consistent with expression derived from contaminating stroma. NEP expression and activity were reduced or undetectable in most SCLC and lung adenocarcinoma cell lines. NEP mRNA by RT-PCR was not expressed or was in low abundance in the majority of lung cancer cell lines. The majority of lung tumors did not express NEP by RT-PCR as compared with normal adjacent lung. In addition, recombinant NEP abolished, whereas an NEP inhibitor potentiated, the calcium flux generated by neuropeptides in some lung cancer cell lines, demonstrating potential physiological significance for low NEP expression. NEP, therefore, is a signal transduction and possibly a growth modulator for both SCLC and NSCLC, emphasizing the role of neuropeptides in the pathogenesis of the major histological forms of lung cancer.

Topics: Adenocarcinoma; Adult; Base Sequence; Blotting, Western; Bradykinin; Calcium; Carcinoma, Non-Small-Cell Lung; Carcinoma, Small Cell; Carcinoma, Squamous Cell; Cell Line; DNA Primers; Enzyme Inhibitors; Gastrin-Releasing Peptide; Gene Expression; Glycopeptides; Humans; Immunohistochemistry; Lung; Lung Neoplasms; Mesothelioma; Molecular Sequence Data; Neoplasm Metastasis; Neprilysin; Peptides; Polymerase Chain Reaction; Pulmonary Alveoli; Recombinant Proteins; RNA, Messenger; Signal Transduction; Tumor Cells, Cultured

From the membrane fraction of cultured human renal adenocarcinoma (ACHN) cells, two endothelin-2-converting enzymes (ECE-2A and ECE-2B) were solubilized with detergent Lubrol PX and separated by hydrophobic butyl fast-performance liquid chromatography. The pH range of the converting activity of ECE-2B for big endothelin-1 (big ET-1), big ET-2, or big ET-3, was very narrow, and the optimal pH for each substrate was significantly different; the pH optimum for big ET-1 was 6.8 and that for big ET-2 or big ET-3 was 6.4. The ET-converting activity was abolished by phosphoramidon, 1,10-phenanthroline and EDTA but was not inhibited by thiorphan, E-64, leupeptin, PCMS, p-APMSF, or pepstatin A. The conversion efficiency for big ET-2 or big ET-3 by ECE-2B was approximately one-eighth of that for big ET-1. The molecular weight of ECE-2B was estimated to be 400 kDa by gel filtration. Because these characteristics of ECE-2B are very similar to those of ET-1-converting enzyme (ECE-1) in endothelial cells, these results raise the possibility that ECE-2B is identical to ECE-1 and that a single ECE physiologically converts all big ETs to the corresponding ETs in ET-producing cells.

Topics: Adenocarcinoma; Aspartic Acid Endopeptidases; Chromatography, Gel; Chromatography, High Pressure Liquid; Endothelin-Converting Enzymes; Endothelins; Glycopeptides; Humans; Hydrogen-Ion Concentration; Kidney Neoplasms; Metalloendopeptidases; Molecular Weight; Protease Inhibitors; Radioimmunoassay; Tumor Cells, Cultured

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.

Topics: Adenocarcinoma; Aspartic Acid Endopeptidases; Chromatography, High Pressure Liquid; Cross Reactions; Endothelin-1; Endothelin-Converting Enzymes; Endothelins; Glycopeptides; Humans; Kidney Neoplasms; Metalloendopeptidases; Protein Precursors; Radioimmunoassay; Tumor Cells, Cultured