Direct inhibition of c-Jun N-terminal kinase in sympathetic neurones prevents c-jun promoter activation and NGF withdrawal-induced death

c-Jun N-terminal kinases (JNKs) regulate gene expression by phosphorylating transcription factors, such as c-Jun. Studies with Jnk knockout mice sugge st that JNK activity may be required for excitotoxin-induced apoptosis in t he adult hippocampus and for apoptosis in the developing embryonic neural t ube. Here we investigate the role of JNKs in classical neurotrophin-regulat ed developmental neuronal death by using nerve growth factor (NGF)-dependen t sympathetic neurones. In this system, NGF withdrawal leads to an increase in JNK activity, an increase in c-Jun protein levels and c-Jun N-terminal phosphorylation before the cell death commitment point, and c-Jun activity is required for cell death. To inhibit JNK activity in sympathetic neurones we have used two different JNK inhibitors that act by distinct mechanisms: the compound SE 203580 and the JNK binding domain (JBD) of JNK interacting protein 1 (JIP-1). We demonstrate that JNK activity is required for c-Jun phosphorylation, c-jun promoter activation and NGF withdrawal-induced apopt osis. We also show that ATF-2, a c-Jun dimerization partner that can regula te c-jun gene expression, is activated following NGF deprivation. Finally, by cc-expressing the JBD and a regulatable c-Jun dominant negative mutant w e demonstrate that JNK and AP-1 function in the same pro-apoptotic signalli ng pathway after NGF withdrawal.