Transactivation of murine cyclin A by polyomavirus large and small T antigens.
Polyomavirus large and small T antigens cooperate in the induction of S phase in serum-deprived Swiss 3T3 cells. While the large T antigen is able to induce S phase-specific enzymes, we have recently shown that both T antigens contribute to the production of the cyclins E and A and that the small T antigen is essential for the induction of cyclin A-dependent cdk2 activity (S. Schüchner and E. Wintersberger, J. Virol. 73:9266-9273, 1999). Here we present our attempts to elucidate the mechanisms by which the large and the small T antigens transactivate the murine cyclin A gene. Using Swiss 3T3 cells carrying the T antigens and various mutants thereof under the hormone-inducible mouse mammary tumor virus promoter, as well as transient-cotransfection experiments with the T antigens and cyclin A promoter-luciferase reporter constructs, we found the following. The large T antigen activates the cyclin A promoter via two transcription factor binding sites, a cyclic AMP responsive element (CRE), and the major negative regulatory site called CDE-CHR. While an intact binding site for pocket proteins is required for the function of this T antigen at the CDE-CHR, its activity at the CRE is largely independent thereof. In contrast, an intact J domain and an intact zinc finger are required at both sites. The small T antigen also appears to have an influence on the cyclin A promoter through the CRE as well as the CDE-CHR. For this an interaction with protein phosphatase 2A is essential; mutation of the J domain does not totally eliminate but greatly reduces the transactivating ability.
Schüchner
S
S
Department of Medical Biochemistry, Division of Molecular Biology, University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
Nemethova
M
M
Belisova
A
A
Klucky
B
B
Holnthoner
W
W
Wintersberger
E
E
D016475:3T3 Cells; D051698:Activating Transcription Factor 2; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D011120:Polyomavirus / Q000276:immunology*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
D051698:Activating Transcription Factor 2; D000952:Antigens, Polyomavirus Transforming; D017362:Cyclic AMP Response Element-Binding Protein; D019925:Cyclin A; D014157:Transcription Factors