[show abstract][hide abstract] ABSTRACT: Alternative splicing and post-translational modifications are processes that give rise to the complexity of the proteome. The nuclear ATF7 and ATF2 (activating transcription factor) are structurally homologous leucine zipper transcription factors encoded by distinct genes. Stress and growth factors activate ATF2 and ATF7 mainly via sequential phosphorylation of two conserved threonine residues in their activation domain. Distinct protein kinases, among which mitogen-activated protein kinases (MAPK), phosphorylate ATF2 and ATF7 first on Thr71/Thr53 and next on Thr69/Thr51 residues respectively, resulting in transcriptional activation. Here, we identify and characterize a cytoplasmic alternatively spliced isoform of ATF7. This variant, named ATF7-4, inhibits both ATF2 and ATF7 transcriptional activities by impairing the first phosphorylation event on Thr71/Thr53 residues. ATF7-4 indeed sequesters the Thr53-phosphorylating kinase in the cytoplasm. Upon stimulus-induced phosphorylation, ATF7-4 is poly-ubiquitinated and degraded, enabling the release of the kinase and ATF7/ATF2 activation. Our data therefore conclusively establish that ATF7-4 is an important cytoplasmic negative regulator of ATF7 and ATF2 transcription factors.
PLoS ONE 01/2011; 6(8):e23351. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ubiquitous activating transcription factor (ATF) 7 binds as a homodimer to the cAMP response element/TPA response element motifs present in the promoters of its target genes. ATF7 is homologous to ATF2 and heterodimerizes with Jun or Fos proteins, modulating their DNA-binding specificities. We previously demonstrated that TAF12, a component of the TFIID general transcription factor, mediates ATF7 transcriptional activity through direct interactions between the two proteins. By contrast, ATF7, but not ATF2, is modified in vivo by sumoylation, which restricts its subcellular localization, thereby inhibiting its transcriptional activity. In the present study, we dissect the mechanism of this functional switch. We characterized the multisite phosphorylation of the ATF7 activation domain and identified one of the involved kinase, p38beta2 mitogen-activated protein kinase. In addition, we show that epidermal growth factor treatment results in a two-step modification mechanism of ATF7 activation domain. The Thr53 residue is phosphorylated first by a presently unknown kinase, allowing p38beta2 mitogen-activated protein kinase to modify the Thr51 residue, excluding the sumoylation of ATF7 protein. The resulting activation of transcription is related to an increased association of TAF12 with this phosphorylated form of ATF7. Our data therefore conclusively establish that sumoylation and phosphorylation of ATF7 are two antagonistic posttranslational modifications.
Journal of Molecular Biology 11/2008; 384(4):980-91. · 3.91 Impact Factor