Related Experiment Videos
The transcriptional transactivation function of wild-type p53 is inhibited by SV40 large T-antigen and by HPV-16 E6
J A Mietz1, T Unger, J M Huibregtse
1Laboratory of Tumor Virus Biology, National Cancer Institute, Bethesda, MD 20892.
Abstract:
The observed interaction between p53 and the oncoproteins encoded by several DNA tumor viruses suggests that these viruses mediate their transforming activities at least in part by altering the normal growth regulatory function of p53. In this study we examined the effect of viral oncoprotein expression on the transcriptional transactivation function of wild-type p53 in human cells. Plasmids expressing human p53 were cotransfected with either SV40 large T-antigen or human papillomavirus (HPV) type 16 E6 expression plasmids and assayed for transactivation function using a reporter gene driven by a p53-responsive promoter containing multiple copies of the consensus p53 DNA binding motif, TGCCT. Both large T-antigen and E6 were able to inhibit transactivation by wild-type p53. Furthermore, SV40 T-antigen mutants that are defective for p53 binding were not able to inhibit transactivation and HPV E6 proteins that were either mutant or derived from non-oncogenic HPV types and unable to bind p53, had no effect on p53 transactivation. These results demonstrate the physiological relevance of the interaction of SV40 T-antigen and HPV E6 oncoproteins with p53 in vivo and suggest that the transforming functions of these viral oncoproteins may be linked to their ability to inhibit p53-mediated transcriptional activation.
Insights
Viral oncoproteins from SV40 and HPV16 inhibit the tumor suppressor p53. This interaction disrupts p53
Area of Science:
- Molecular Biology
- Virology
- Cancer Research
Background:
- The tumor suppressor protein p53 plays a critical role in regulating cell growth.
- Several DNA tumor viruses encode oncoproteins that interact with p53.
- This interaction is hypothesized to contribute to viral oncogenesis by disrupting p53's function.
Purpose of the Study:
- To investigate the impact of viral oncoprotein expression on the transcriptional activity of wild-type p53 in human cells.
- To determine if the interaction between viral oncoproteins and p53 is essential for inhibiting p53's function.
Main Methods:
- Co-transfection of human cells with plasmids expressing wild-type p53 and either SV40 large T-antigen or HPV type 16 E6.
- Assay of p53 transcriptional transactivation function using a reporter gene under the control of a p53-responsive promoter.
- Utilized mutant oncoproteins defective for p53 binding and E6 proteins from non-oncogenic HPV types to assess binding relevance.
Main Results:
- Both SV40 large T-antigen and HPV16 E6 significantly inhibited the transactivation function of wild-type p53.
- SV40 T-antigen mutants unable to bind p53 did not inhibit p53 transactivation.
- HPV E6 proteins that did not bind p53, including those from non-oncogenic HPV types, had no effect on p53 transactivation.
Conclusions:
- The interaction between SV40 T-antigen and HPV E6 oncoproteins with p53 is physiologically relevant in vivo.
- The ability of these viral oncoproteins to inhibit p53-mediated transcriptional activation is likely linked to their transforming functions.
- These findings underscore the importance of p53's transcriptional activity in tumor suppression and its subversion by viral agents.