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 DNAbinding 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 phosphorylationdependent 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 α, and Fas ligand promoter activities.
The transcriptional activity of the constitutively
active ATF2 mutant could be impaired by dominantnegative
forms of ATF2 or c-jun, indicating that ATF2
and c-jun utilize a similar dimerization code. In contrast,
a dominantnegative CREB2 mutant did not impair
ATF2-mediated transcriptional activation, suggesting
that CREB2 exhibits a different dimerization
specificity than ATF2 or c-jun.
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