Factors Modulating AP-1 Activity
This chapter focuses on these modifications, which take place in the absence of protein synthesis, and on auxiliary factors involved in modulating activator protein (AP-1) function. The fact that components of the AP-1 transcription factor are involved as "third messengers" in several signal transduction pathways implies that their expression, DNA binding activity and transcriptional activity, is finely controlled. The tuning of AP-1 activity is necessary to allow a flexible regulation in response to different cellular stimuli. AP-1 activity also appears to be modulated by cellular translocation. The protein, termed IP-1, is present in both the cytoplasm and nucleus of cells and reduces AP-1 complex formation with DNA in a rapid and phosphorylation-dependent fashion. Changing the composition of the dimers can result in AP-1 proteins with a dramatically different transactivation potential. The excess Jun deregulated transactivation of the chimera by competing for an inhibitory factor and titrating it.