Probable regulator of CREB1 transcriptional activity which is involved in adipose cells differentiation. May also play a regulatory role in the cell cycle. Identification in a chromosomal region frequently deleted in various cancers suggests that it might act as a tumor suppressor. Interacts with CREB1; regulates CREB1 phosphorylation, stability and transcriptional activity. Phosphorylated by AMPK. Belongs to the bZIP family. ATF subfamily.