JNK phosphorylation relieves HDAC3-dependent suppression of the transcriptional activity of c-Jun

The AP-1 transcription factor c-Jun is a prototypical nuclear effector of the JNK signal transduction pathway. The integrity of JNK phosphorylation sites at serines 63/73 and at threonines 91/93 in c-Jun is essential for signal-dependent target gene activation. We show that c-Jun phosphorylation mediates dissociation of an inhibitory complex, which is associated with histone deacetylase 3 (HDAC3). The subsequent events that ultimately cause increased mRNA synthesis are independent of c-Jun phosphorylation and its interaction with JNK. These findings provide an 'activation by de-repression' model as an explanation for the stimulatory function of JNK on c-Jun.