Endothelin-1 activates c-Jun NH2-terminal kinase in mesangial cells

Endothelin-1 (ET-1) is known to induce the contraction and proliferation of glomerular mesangial cells. ET-1 has been shown to activate p42 and p44 mitogen-activated protein kinases (MAPKs), also known as extracellular signal regulated kinases (ERKs), through both protein kinase C (PKC) and protein tyrosine kinase (PTK)-dependent pathways. However, an involvement of c-Jun NH2-terminal kinase (JNK), one of members of the MAPK family, in ET-1 signaling in mesangial cells has not yet been elucidated. To clarify this point, we examined whether ET-1 could activate JNK and the mechanism of activation in cultured mesangial cells. ET-1 enhanced the activities of JNK in a dose-dependent (10(-8) M maximum) and time-dependent manner, with a peak at 15 minutes. ET-1-induced activation of JNK was blocked by BQ-123, an antagonist for the ETA receptor. The depletion of PKC by prolonged treatment with phorbol 12,13 dibutyrate or the inhibition of PKC by GF 109203X failed to inhibit ET-1-induced activation of JNK. In contrast, ET-1-induced activation of JNK was significantly reduced by calcium chelation (with BAPTA/AM and EGTA). In addition, ionomycin, a calcium ionophore, and thapsigargin, an intracellular calcium-rising agent, were able to induce the activation of JNK. ET-1-induced activation of JNK was also inhibited by PTK inhibitors (herbimycin A and genistein). Furthermore, ET-1 increased the DNA-binding activity of AP-1 containing c-Jun and c-Fos proteins. These results indicate that ET-1 is able to activate JNK in glomerular mesangial cells through PKC-independent and PTK-dependent pathways and intracellular calcium is necessary to the activation of JNK.