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Inhibition of SV40 large T antigen induced apoptosis by small T antigen
T Kolzau1, R S Hansen, D Zahra
1Department of Pathology, Dunedin School of Medicine, University of Otago, Box 913, Dunedin, New Zealand.
Abstract:
It is well established that the expression of simian virus 40 (SV40) early gene products causes oncogenic transformation of rodent cells. An important aspect of this process is the inactivation of the p53 and retinoblastoma (pRb) tumour suppressor proteins through interaction with the SV40 large tumour antigen (LT). In addition, the SV40 small tumour antigen (ST) may enhance LT induced transformation. Here we show that LT induces apoptotic cell death in rat embryo fibroblast (REF) cells and that ST functions to inhibit this effect by a mechanism which is different from other known anti-apoptotic proteins. Mutational analysis of LT indicates that mutants defective in the pRb-binding domain are unable to induce apoptosis whereas LT mutants defective in the p53-binding domain are still competent to induce apoptosis. Thus, interaction between LT and one or more pRb family members must occur for induction of apoptosis and that binding of p53 by LT is insufficient to inhibit LT induced apoptosis in REFs. The data presented herein suggest that the anti-apoptotic function of ST may explain, at least in part, how ST contributes to SV40 early region induced transformation of REF cells.
Insights
Simian virus 40 (SV40) large tumor antigen (LT) induces cell death by interacting with pRb proteins. Small tumor antigen (ST) inhibits this apoptosis, contributing to cell transformation.
Area of Science:
- Molecular Biology
- Virology
- Cancer Research
Background:
- Simian virus 40 (SV40) early gene products are known to cause oncogenic transformation.
- SV40 large tumor antigen (LT) inactivates p53 and retinoblastoma (pRb) tumor suppressors.
- SV40 small tumor antigen (ST) may enhance LT-induced transformation.
Purpose of the Study:
- To investigate the role of SV40 LT and ST in apoptosis.
- To determine the mechanism by which ST inhibits LT-induced apoptosis.
- To elucidate the specific interactions of LT with p53 and pRb family members in apoptosis induction.
Main Methods:
- Expression of SV40 early gene products in rat embryo fibroblast (REF) cells.
- Mutational analysis of LT to assess the importance of pRb and p53 binding domains.
- Assays to detect and quantify apoptotic cell death.
- Characterization of ST's anti-apoptotic mechanism.
Main Results:
- LT induces apoptotic cell death in REF cells.
- Mutants of LT lacking pRb-binding domains are unable to induce apoptosis.
- LT mutants defective in p53 binding remain competent to induce apoptosis.
- ST inhibits LT-induced apoptosis via a novel mechanism.
Conclusions:
- Interaction between LT and pRb family members is essential for LT-induced apoptosis.
- LT binding to p53 is insufficient to inhibit LT-induced apoptosis in REFs.
- ST's anti-apoptotic function likely contributes to SV40-induced cell transformation.