Activation of CREB/ATF sites by polyomavirus large T antigen.
Polyomavirus large T antigen (LT) has a direct role in viral replication and a profound effect on cell phenotype. It promotes cell cycle progression, immortalizes primary cells, blocks differentiation, and causes apoptosis. While much of large T function is related to its effects on tumor suppressors of the retinoblastoma susceptibility (Rb) gene family, we have previously shown that activation of the cyclin A promoter can occur through a non-Rb-dependent mechanism. Here we show that activation occurs via an ATF/CREB site. Investigation of the mechanism indicates that large T can synergize with CREB family members to activate transcription. Experiments with Gal4-CREB constructs show that synergy is independent of CREB phosphorylation by protein kinase A. Examination of synergy with Gal4-CREB deletion constructs indicates that large T acts on the constitutive activation domain of CREB. Large T can bind to CREB in vivo. Genetic analysis shows that the DNA-binding domain (residues 264 to 420) is sufficient to activate transcription when it is localized to the nucleus. Further analysis of the DNA-binding domain shows that while site-specific DNA binding is not required, non-site-specific DNA binding is important for the activation. Thus, CREB binding and DNA binding are both important for large T activation of CREB/ATF sites. In contrast to previous models where large T transactivation occurred indirectly, these results also suggest that large T can act directly at promoters to activate transcription.
Love
Tara M
TM
Department of Biochemistry, Tufts University School of Medicine, Boston, MA 02111, USA.
de Jesus
Rowena
R
Kean
Jennifer A
JA
Sheng
Qing
Q
Leger
Andrew
A
Schaffhausen
Brian
B
D051696:Activating Transcription Factors; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D019925:Cyclin A / Q000096:biosynthesis / Q000235:genetics; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology; D015151:Immunoblotting; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D051696:Activating Transcription Factors; D000952:Antigens, Polyomavirus Transforming; D001798:Blood Proteins; C492004:Creb1 protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D019925:Cyclin A; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D004247:DNA; D017868:Cyclic AMP-Dependent Protein Kinases