JunB is a basic region, leucine zipper (bZIP) transcription factor belonging to the Jun family that includes c-Jun and JunD. Jun family members homodimerize or heterodimerize with Fos and ATF proteins to form a functional transcription factor AP-1 (activator protein 1), whose activity is regulated by a variety of physiological and pathological stimuli such as growth factors, infections, and stress signals. While JunB sometimes antagonizes c-Jun transcriptional activity, it may functionally substitute for c-Jun during development in mice. JunB regulates hematopoietic stem cell number and plays an important role in the pathogenesis of chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML).
