Regulation of gene transcription by a constitutively active mutant of activating transcription factor 2 (ATF2).

Activating transcription factor 2 (ATF2) belongs to the family of basic region leucine zipper (bZIP) proteins that are characterized by the presence of a basic domain that functions as the DNA-binding domain and a leucine zipper domain that is required for dimerization. Together with bZIP proteins of the Fos and Jun families, ATF2 constitutes the AP-1 transcription factor complex. The biological activity of ATF2 is controlled by phosphorylation of two threonine residues within the N-terminal activation domain. Unphosphorylated ATF2 is trancriptionally silent, excluding simple overexpression studies to identify transcriptional targets of ATF2. We therefore decided to construct a constitutively active ATF2 mutant that would allow us to uncouple the investigation of transcriptional targets and biological functions of ATF2 from the variety of signaling pathways that lead to an activation of ATF2. We exchanged the phosphorylation-dependent activation domain of ATF2 with the constitutively active transcriptional activation domain of the transcription factor CREB2. In transient transfection experiments, this constitutively active ATF2 mutant stimulated c-jun, tumor necrosis factor alpha, and Fas ligand promoter activities. The transcriptional activity of the constitutively active ATF2 mutant could be impaired by dominant-negative forms of ATF2 or c-Jun, indicating that ATF2 and c-Jun utilize a similar dimerization code. In contrast, a dominant-negative CREB2 mutant did not impair ATF2-mediated transcriptional activation, suggesting that CREB2 exhibits a different dimerization specificity than ATF2 or c-Jun.