text: Cellular differentiation AP-1 transcription is deeply involved in the modulation of gene expression. Changes in cellular gene expression in the initiation of DNA synthesis and the formation of differentiated derivatives can lead to cellular differentiation.  AP-1 has been shown to be involved in cell differentiation in several systems. For example, by forming stable heterodimers with c-Jun, the bZIP region of c-Fos increases the binding of c-Jun to target genes whose activation is involved in the differentiation of chicken embryo fibroblasts (CEF). It has also been shown to participate in endoderm specification.
  Apoptosis
  AP-1 transcription factor is associated with a broad range of apoptosis related interactions. AP-1 activity is induced by numerous extracellular matrix and genotoxic agents, suggesting involvement in programmed cell death. Many of these stimuli activate the c-Jun N-terminal kinases (JNKs) leading to the phosphorylation of Jun proteins and enhanced transcriptional activity of AP-1 dependent genes. Increases in the levels of Jun and Fos proteins and JNK activity have been reported in scenarios in which cells undergo apoptosis. For example, inactivated c-Jun-ER cells show a normal morphology, while c-Jun-ER activated cells have been shown to be apoptotic.
  Regulation of AP-1
  Increased AP-1 levels lead to increased transactivation of target gene expression. Regulation of AP-1 activity is therefore critical for cell function and occurs through specific interactions controlled by dimer-composition, transcriptional and post-translational events, and interaction with accessory proteins.