Endothelin-1 induces connective tissue growth factor expression in human lung fibroblasts by ET_AR-dependent JNK/AP-1 pathway

Endothelin-1 (ET-1) acts as a key mediator of vasoconstriction and tissue repair. Overproduction of connective tissue growth factor (CTGF) underlies the development of lung fibrosis. ET-1 induces expression of matrix-associated genes in lung fibroblasts, however, little is known about the signaling pathway of CTGF expression caused by ET-1. In this study, we found that ET-1 caused concentration- and time-dependently increases in CTGF expression in human embryonic lung fibroblast cell line (WI-38). ET-1-induced CTGF expression was inhibited by BQ123 (ETAR antagonist), but not BQ788 (ETBR antagonist). Moreover, ET-1-induced CTGF expression was significantly reduced by JNK inhibitor (SP600125), the dominant-negative mutants of JNK1/2 (JNK1/2 DN), and AP-1 inhibitor (curcumin). ET-1 induced phosphorylations of JNK and c-Jun in time-dependent manners. AP-1 luciferase activity was concentration-dependently increased by ET-1, and this effect was attenuated by SP600125. We also found that ET-1-induced CTGF expression was most controlled by the AP-1 binding region of CTGF promoter. ET-1-indiced CTGF luciferase activity was predominately controlled by the sequence -747 to -408 bp upstream of the transcription start site on the human CTGF promoter. Furthermore, ET-1 caused the formation of AP-1-specific DNA-protein complex and the recruitment of c-Jun to the CTGF promoter. Moreover, we found that ET-1 induced α-smooth muscle actin (α-SMA) expression, which was inhibited by BQ123, SP600125, curcumin, and anti-CTGF antibody. These results suggest that ET-1 stimulates expressions of CTGF and α-SMA through ETAR/JNK/AP-1 signaling pathway, and CTGF is required for ET-1-induced α-SMA expression in human lung fibroblasts.