The transcription factor, activating protein-1(AP-1) plays an important role in the regulation of cell proliferation, cell survival and apoptosis. c-Jun is the major component of AP-1. The activity of c-Jun is up-regulated and down-regulated at three main levels: transcriptional control, posttranslational regulation (major by phosphorylation) and the modulation by interacting proteins. Eight sites of c-Jun can be phosphorylated by kinases such as JNK1, GSK3, CKII and Abl. Moreover, c-Jun is regulated through interacting with bZIP transcriptional factors, coactivators and other proteins via its N-terminal transcription-activation domain and C-terminal DNA-binding domain. Other molecules can regulate the AP-1 activity in a coactivator-dependent manner. So the regulatory mechanism of AP-1 activity is complicated.