Reactive Oxygen Species Modulate Endothelin-I-Induced C-Fos Gene Expression in Cardiomyocytes

Objectives: Recent evidence indicates that reactive oxygen species (ROS) may act as second messengers in receptor- mediated signaling pathways. The possible role of ROS during Et-1 stimulation in cardiomyocytes was therefore investigated. Methods: Intracellular ROS levels were measured with fluorescence probe 2',7'-dichlorofluorescin diacetate by confocal microscopy in cultured neonatal rat cardiomyocytes. The ROS-inducible c- fos expression was analyzed by Northern blotting and promoter activity. Results : Et-1 applied to cardiomyocytes dose-dependently increased intracellular ROS levels. The increase of ROS levels was attenuated by pretreating cardiomyocytes with Et-A receptor antagonist-BQ485, but not with Et-B receptor antagonist. Cardiomyocytes pretreated with catalase or an antioxidant N- acetylcysteine (NAC) reduced Et-1-induced ROS levels. Et -1 or H2O2 treatment of cardiomyocytes rapidly induced the expression of an immediate early gene c-fos. Et-1-treated cardiomyocytes enhanced the c- fos gene expression as revealed by functional analysis using a reporter gene construct containing c-fos promoter region (-2.25 kb) and reporter gene chloramphenicol acetyltransferase. The induction of mRNA levels and the promoter activities of c- fos gene by Et-1 or H2O2 were abolished by pretreating cardiomyocytes with catalase or NAC.Cells transiently transfected with the dominant positive mutant of p21(ras) ( RasL61) led to a significant increase in intracellular ROS. Concomitantly, the mRNA levels and the promoter activities of c-fos were also induced. In contrast , cells transfected with the dominant negative mutant of Ras (RasN17) inhibited Et-1-induced ROS. Consistently, the increase of c-fos mRNA levels and promoter activities by Et-1 were also inhibited. Conclusions: These findings clearly indicate that Et-1 treatment to cardiomyocytes fan induce ROS via Ras pathway and the increased ROS are involved in the increase of c-fos expression. Our studies thus emphasize the importance of ROS as second messengers in Et-1-induced responses in cardiomyocytes. (C) 1999 Published by Elsevier Science B.V. All rights reserved.