Probable regulator of CREB1 transcriptional activity which is involved in adipose cells differentiation. May also play a regulatory role in the cell cycle. Interacts with CREB1; regulates CREB1 phosphorylation, stability and transcriptional activity. Widely expressed with higher expression in adipose tissue, skeletal muscle, and liver (at protein level). Up-regulated during preadipocyte differentiation (at protein level). Phosphorylated by AMPK. Belongs to the bZIP family. ATF subfamily.