Indirubin-3′-oxime inhibits c-Jun NH2-terminal kinase: anti-apoptotic effect in cerebellar granule neurons

Abstract Previous studies have demonstrated that c-Jun NH 2 -terminal protein kinase (JNK) plays a crucial role in neuronal apoptosis. Here, we report that indirubin-3′-oxime, a known effective inhibitor of cyclin-dependent kinases (CDKs) and glycogen synthase kinase 3-beta (GSK-3β), has a significant inhibitory effect on JNK. Kinase assay showed that indirubin-3′-oxime directly inhibited the activity of all three isoforms of JNK (JNK1, and JNK3) in vitro, with half inhibition dose (IC 50 ) of 0.8 μM, 1.4 μM, and 1.0 μM, respectively. In cerebellar granule neurons (CGNs), indirubin-3′-oxime blocked c-Jun phosphorylation induced by potassium withdrawal and prevented CGNs from apoptosis in a dose dependent manner. However, inhibitors of CDKs and GSK-3β were ineffective in reducing c-Jun phosphorylation both in vitro and in vivo, suggesting that indirubin-3′-oxime prevents c-Jun phosphorylation independent of its inhibition on CDKs and GSK-3β. Our studies give further supports for JNK-targeting strategy in preventing neuronal apoptosis.