AP-1 is a well characterized transcription factor composed of many different combinations of homodimers and/or heterodimers of the Jun, Fos, ATRF (activating transcription factor), and MAF (musculoaponeurotic fibrosarcoma) protein families. AP-1 regulates the transcription of various genes that govern cellular processes, including proliferation and apoptosis. Strong evidence indicates that AP-1 plays a key role in cancer development and is up-regulated during tumor promotion and progression. Blocking tumor promoter-induced AP-1 activity inhibits neoplastic cell transformation and represses skin tumor promotion in vivo. However, several studies suggest that AP-1 can also act as a tumor suppressor, depending on the combination or the specific Jun or Fos protein that participates in the AP-1 complex. These data suggest that AP-1 and or its various components are promising targets for chemopreventive agents.
AP-1 regulates many genes that contain the specific DNA sequences in the promoter region collectively called the TPA response element. Once class of genes that AP-1 regulates is matrix metalloproteinases, which catalyze the proteolytic cleavage of extracellular matrix compoents.
The inhibition of AP-1 activation occurs through the inhibition of a dependent pathway.
EGCG has been reported to inhibit c-Jun protein phosphorylation which may result in lowered AP-1 activity in SV40 immortalized and Ha-ras gene transformed human bronchial epithelial cell lines.