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Transcription factor AP-2 mRNA and DNA binding activity are constitutively expressed in SV40-immortalized but not
1Department of Radiology, The University of Iowa, Iowa City, Iowa, 52242, USA.
Abstract:
Large T antigen (LT) expressed by the oncogenic DNA virus SV40 transforms cells by interacting with and perturbing the normal function of several important cellular proteins including P53, RB, c-MYC, and AP-2. AP-2 binds to regulatory elements within the SV40 enhancer and is therefore of particular interest for mechanisms relating to viral transcription, replication, and packaging. LT antigen has been previously shown to inhibit transcription factor AP-2 from binding to its cognate cis-element in DNA in vitro, and this is believed to occur through a direct physical interaction between the LT and AP-2 proteins. Recently LT and AP-2 were shown to interact at the protein level in vivo and this interaction appeared to mediated by the RB protein. Although LT inhibited AP-2 DNA binding in vitro, the effects of LT on AP-2 expression and DNA binding activity in vivo have not been previously reported. We report here that transcription factor AP-2alpha is constitutively expressed in SV40-transformed cells compared to their normal cell counterparts. The overexpression of AP-2alpha in SV40 transformed cells occurred at the levels of mRNA, protein, and DNA binding activity. The increase in AP-2 DNA binding in vivo was particularly interesting since previous studies in vitro would have predicted that AP-2 DNA binding should be decreased in the presence of LT. AP-2 is a plieotropic regulator of gene expression, activating some and repressing others. Thus, increased cellular AP-2 activity may be an important downstream effector for the transforming ability of SV40.
Insights
SV40 large T antigen (LT) transforms cells by altering cellular proteins. This study found that LT increases AP-2alpha expression and DNA binding activity in SV40-transformed cells, contrary to in vitro findings.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Large T antigen (LT) from SV40 oncogenic virus transforms cells by interacting with cellular proteins like P53, RB, c-MYC, and AP-2.
- AP-2 transcription factor is crucial for SV40 enhancer regulation, viral transcription, replication, and packaging.
- Previous in vitro studies indicated LT directly inhibits AP-2 DNA binding, but in vivo effects were unknown.
Purpose of the Study:
- To investigate the in vivo effects of SV40 LT on the expression and DNA binding activity of transcription factor AP-2alpha.
- To understand the role of AP-2alpha overexpression in SV40-mediated cellular transformation.
Main Methods:
- Comparison of AP-2alpha expression (mRNA, protein) and DNA binding activity between SV40-transformed cells and normal cell counterparts.
- Analysis of in vivo protein-protein interactions involving LT, AP-2, and RB.
Main Results:
- AP-2alpha was constitutively overexpressed in SV40-transformed cells compared to normal cells.
- Overexpression of AP-2alpha occurred at mRNA, protein, and DNA binding activity levels.
- In vivo AP-2alpha DNA binding activity increased in SV40-transformed cells, contradicting in vitro results.
Conclusions:
- SV40 LT induces overexpression of AP-2alpha in transformed cells, leading to increased DNA binding activity.
- This elevated AP-2alpha activity may be a key downstream mechanism contributing to SV40's transforming ability.
- The findings highlight a discrepancy between in vitro and in vivo effects of LT on AP-2, suggesting complex regulatory mechanisms.