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The SV40 large T oncoprotein disrupts DNA-binding of the cell cycle-regulated transcriptional repressor CDF
J Zwicker1, K Körner, R Müller
1Institut für Molekularbiologie und Tumorforschung, Philipps-Universität Marburg, Germany.
Abstract:
A hallmark of neoplastic transformation by DNA tumor viruses is the deregulation of cell cycle genes. At least in some genes, this deregulation appears to be due to the oncoprotein-mediated disruption of complexes between E2F and pocket proteins and the ensuing generation of transcriptionally active free E2F. In the present study, we have analysed the effect of the SV40 large T oncoprotein (SV-LT) on the function of a different cell cycle-regulated transcriptional repressor, CDF, which is the principal regulator of the cdc25C, cyclin A and cdc2 genes. As shown by genomic footprinting of sorted G1 and G2 cell populations, transformation by SV-LT completely abrogated protection of the CDF binding site (CDE-CHR) in the cdc25C promoter. In agreement with this observation, expression of the SV-LT in fibroblasts led to a dramatic up-regulation of the cdc25C promoter in cells synchronized in G0. These findings indicate that the oncoprotein-mediated dissociation of the CDF repressor protein from its cognate DNA-binding site is a major mechanism in virus-induced transcriptional deregulation.
Insights
SV40 large T oncoprotein disrupts cell cycle regulation by dissociating the CDF repressor from DNA. This leads to up-regulation of key cell cycle genes, contributing to neoplastic transformation.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Neoplastic transformation by DNA tumor viruses involves cell cycle gene deregulation.
- This deregulation is often linked to oncoprotein disruption of E2F and pocket protein complexes.
- The CDF repressor regulates critical cell cycle genes including cdc25C, cyclin A, and cdc2.
Purpose of the Study:
- To investigate the effect of SV40 large T oncoprotein (SV-LT) on the CDF transcriptional repressor.
- To understand the mechanism of virus-induced transcriptional deregulation in cell cycle control.
Main Methods:
- Genomic footprinting of sorted G1 and G2 cell populations.
- Analysis of SV-LT expression in synchronized fibroblasts.
- Assessing the impact on the cdc25C promoter activity.
Main Results:
- SV-LT transformation abrogated protection of the CDF binding site (CDE-CHR) in the cdc25C promoter.
- SV-LT expression led to dramatic up-regulation of the cdc25C promoter in G0-synchronized cells.
- Demonstrated oncoprotein-mediated dissociation of the CDF repressor from its DNA-binding site.
Conclusions:
- SV-LT disrupts cell cycle gene regulation by releasing the CDF repressor.
- This dissociation is a key mechanism in virus-induced transcriptional deregulation.
- Findings provide insight into how DNA tumor viruses manipulate host cell machinery for transformation.