AP-1 proteins play a role in the expression of many genes involved in cellular proliferation and cell cycle progression. The transcription factor AP-1 is composed of a mixture of heterodimeric protein complexes derived from the Fos and Jun families, including c-Fos, FosB, Fra-1, Fra-2, c-Jun, JunB and JunD. AP-1 heterodimers bind to DNA on a serum response element with the 5´-TGA(C/G)TCA-3´ sequence. Jun proteins can bind to form transcriptionally active homodimers or heterodimers with CREB/ATF members to bind the CRE element. AP-1 expression is induced by multiple stimuli, including the presence of serum, growth factors, phorbol esters and oncogenes. Phosphorylation of AP-1 family members by kinases is required for transactivation activity.


