| 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 (1-4). While JunB sometimes antagonizes c-Jun transcriptional activity, it may functionally substitute for c-Jun during development in mice (5-7). JunB regulates hematopoietic stem cell number and plays an important role in the pathogenesis of chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML) (8,9).JunB expression is selectively induced in T helper 2 (Th2) cells during T cell differentiation. JunB interacts with c-Maf, and the resulting complex functions synergistically to activate transcription of Interleukin-4 (IL-4), one of the signature cytokines secreted by Th2 cells. Transcriptional regulation of IL-4 was shown to be enhanced by JNK-mediated phosphorylation of JunB at Thr102 and Thr104 (10). Phosphorylation of these residues enhances DNA binding of the JunB/c-Maf complex at the P1 regulatory site of the IL-4 promoter, leading to Th2-restricted IL-4 expression. |
