Endothelin-1 Inhibits Endothelin-Converting Enzyme-1 Expression in Cultured Rat Pulmonary Endothelial Cells

Abstract

Background-The lung expresses large amounts of endothelin-converting enzyme-1 (ECE-1), which catalyzes a step in the biosynthesis of potent vasoactive endothelin-1 (ET-1) from the inactive intermediate big ET-1. Because there has been no report concerning a possible relationship between ET-1 and ECE-1, we investigated the effects of ET-1 on ECE-1 expression in cultured rat pulmonary endothelial cells. Methods and Results-ECE-1 messenger RNA (mRNA) and protein expression in cultured endothelial cells were assayed by Northern and Western blotting, respectively. Incubation with ET-1 for 6 hours caused a significant decrease in ECE-1 mRNA expression. The action of ET-1 on ECE-1 mRNA expression was antagonized by pretreatment with BQ788, a specific ETB receptor antagonist, but not by pretreatment with BQ123, a specific ETA receptor antagonist. The expression of ECE-1 protein was also inhibited at 6 hours after incubation with ET-1. The effects of ET-1 on ECE-1 mRNA and protein expression were shown to be mimicked by ionomycin, a calcium ionophore, but not by 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C activator. Conclusions-The present results demonstrate that ET-1 suppressed ECE-1 protein levels by inhibiting ECE-1 mRNA expression through the ETB receptor, suggesting the existence of a feedback action of ET-1 on ECE-1 in pulmonary endothelial cells.(Circulation. 1998;97:234-236.)Key Words: endothelin Ⅲ endothelium Ⅲ receptors E ndothelin-1 is a potent vasoconstrictor peptide produced in vascular endothelial cells and is involved in pathophysiological conditions such as acute renal failure, 1 pulmonary hypertension, and systemic hypertension. ETA receptors are present on the vascular smooth muscle and mediate direct vasoconstriction, whereas ETB receptors are present on endothelial cells and produce vasodilation via the endothelininduced release of nitric oxide and prostacyclin. ET-1 is initially synthesized as preproET-1, which is processed to an inactive intermediate big ET-1. Mature ET-1 is produced from big ET-1. The final step is catalyzed by the endothelinconverting enzyme. An ECE-1 has recently been cloned 2,3 and is the major form of ECE in most tissues. A more recently cloned ECE-2 4 is a homologous protein that differs from ECE-1 in sensitivity to phosphoramidon, in optimal pH, and in tissue distribution and quantity.The lung is an organ that abundantly expresses ECE-1 2,3 as well as preproET-1 mRNA. The conversion of big ET-1 was reported to be more efficient in the lung than in the kidney or mesentery in isolated perfusion of rats.5 Increased pulmonary production of ET-1 has been demonstrated in pulmonary hypertension 6 and acute myocardial infarction. In such states, an elevation of ET-1 may not be beneficial to maintain pulmonary and systemic circulation. For the counterregulatory mechanism, ET-1 may act directly on ECE-1 expression. In the present study, we investigated the effects of ET-1 on ECE-1 expression in cultured rat pulmonary endothelial cells and evaluated whether those effects m...

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