Activating transcription factor 4 (ATF4) belongs to the ATF/CREB (activating 
transcription factor/cyclic AMP response element binding protein) family of 
basic region-leucine zipper (bZip) transcription factors, which have the 
consensus binding site cAMP responsive element (CRE). ATF4 has numerous 
dimerization partners. ATF4 is induced by stress signals including 
anoxia/hypoxia, endoplasmic reticulum stress, amino acid deprivation, and 
oxidative stress. ATF4 expression is regulated transcriptionally, 
translationally via the PERK pathway of eIF2alpha phosphorylation, and 
posttranslationally by phosphorylation, which targets ATF4 to proteasomal 
degradation. ATF4 regulates the expression of genes involved in oxidative 
stress, amino acid synthesis, differentiation, metastasis and angiogenesis. 
Transgenic studies have demonstrated ATF4 to be involved in hematopoiesis, lens 
and skeletal development, fertility, proliferation, differentiation, and 
long-term memory. ATF4 expression is upregulated in cancer. Since ATF4 is 
induced by tumour microenvironmental factors, and regulates processes relevant 
to cancer progression, it might serve as a potential therapeutic target in 
cancer.