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An unexpected role for p53 in augmenting SV40 large T antigen-mediated tumorigenesis
M Herzig1, M Novatchkova, G Christofori
1Research Institute of Molecular Pathology, Vienna, Austria.
Abstract:
Simian virus 40 large T antigen transforms cells by sequestration and inactivation of the tumor suppressor proteins p53, retinoblastoma gene product (pRb), and the pRb-related proteins p107 and p130. Thus, the absence of functional p53 is expected to promote T antigen-mediated tumorigenesis. However, in a transgenic mouse model of T antigen-mediated beta cell carcinogenesis (Rip1Tag2), tumor volumes are significantly diminished when these mice are intercrossed with p53-deficient mice. Whereas the incidence of beta tumor cell apoptosis is unaffected, their proliferation rate is reduced in p53-deficient beta cell tumors in vivo and in cell lines established from these tumors in vitro. Biochemical analyses reveal higher levels of T antigen in wild-type tumor cells as compared to p53-deficient tumor cells. The data indicate that p53 stabilizes SV40 large T antigen, thereby augmenting its oncogenic potential as manifested by increased proliferation rates in wild-type beta tumor cells as compared to p53-deficient beta tumor cells.
Insights
Simian virus 40 large T antigen promotes cell proliferation. However, p53 deficiency unexpectedly reduces tumor growth by stabilizing the T antigen, revealing a novel role for p53 in tumorigenesis.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Simian virus 40 large T antigen (SV40 T-ag) is known to transform cells by inactivating tumor suppressor proteins like p53 and retinoblastoma protein (pRb).
- The absence of functional p53 is generally expected to enhance T-ag-mediated tumorigenesis.
Purpose of the Study:
- To investigate the role of p53 in SV40 T-ag-mediated beta cell carcinogenesis using a transgenic mouse model (Rip1Tag2).
- To elucidate the underlying mechanisms by which p53 influences tumor development in this context.
Main Methods:
- Utilized a transgenic mouse model (Rip1Tag2) intercrossed with p53-deficient mice.
- Assessed tumor volumes, beta cell apoptosis, and proliferation rates in vivo and in vitro.
- Conducted biochemical analyses to quantify T antigen levels.
Main Results:
- Tumor volumes were significantly reduced in p53-deficient mice compared to wild-type.
- Beta cell tumor proliferation rates decreased in p53-deficient models, while apoptosis remained unaffected.
- Higher levels of SV40 T antigen were observed in wild-type tumor cells versus p53-deficient tumor cells.
Conclusions:
- p53 plays a crucial role in stabilizing SV40 large T antigen, thereby enhancing its oncogenic potential.
- Contrary to expectations, p53 deficiency diminishes beta cell tumor growth by reducing T antigen levels and proliferation.
- These findings reveal a novel, pro-tumorigenic function of p53 in SV40-induced carcinogenesis.