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Transformation and tumorigenic properties of a mutant polyomavirus containing a middle T antigen defective in Shc
1Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore 21201, USA.
Abstract:
Polyomavirus middle T antigen is phosphorylated on several tyrosine residues which act as binding sites for cellular proteins, including phosphatidylinositol 3-kinase, Shc, and phospholipase C-gamma. In this report we describe the transforming properties and tumor-inducing ability of a polyomavirus that contains a single-site mutation in middle T antigen which changes a tyrosine residue at amino acid position 250 to serine. This mutation disrupts the association of middle T with the transforming protein Shc. The mutant virus is weakly transforming, inducing foci which are smaller and of different morphology than those of the wild type. Although the virus induced tumors in close to 100% of inoculated mice, the spectrum of tumors and their morphology were altered compared to those of wild-type virus. The mutant virus induced a reduced frequency of kidney and thymic tumors. Both the mammary gland and the thymic tumors that were induced were histologically distinct from those induced by wild-type polyomavirus. These results demonstrate that the signal transduction pathway that is deregulated by the middle T-Shc association is important for full transformation of cells in culture and for tumor induction in some target tissues in the mouse-polyomavirus system.
Insights
A mutation in polyomavirus middle T antigen impairs its association with the Shc protein. This results in weakened cell transformation and altered tumor development in mice, highlighting the Shc pathway
Area of Science:
- Virology
- Molecular Biology
- Oncology
Background:
- Polyomavirus middle T antigen (MT) contains tyrosine phosphorylation sites crucial for binding cellular proteins like phosphatidylinositol 3-kinase and Shc.
- These interactions mediate cellular transformation and tumor development.
Purpose of the Study:
- To investigate the transforming properties and tumor-inducing ability of a polyomavirus with a mutation in MT.
- Specifically, to assess the impact of disrupting the middle T-Shc association on viral oncogenesis.
Main Methods:
- Generated a single-site mutant polyomavirus altering a key tyrosine residue (Y250) in middle T antigen to serine.
- Assessed viral transforming efficiency in cell culture by analyzing focus formation.
- Inoculated mice with the mutant virus to evaluate tumor induction, spectrum, and morphology.
Main Results:
- The Y250S mutation disrupted the association between middle T antigen and Shc.
- The mutant virus exhibited weak transforming activity with altered focus morphology.
- While inducing tumors in nearly all mice, the mutant virus showed altered tumor spectrum and morphology, with reduced kidney and thymic tumors.
Conclusions:
- The middle T-Shc association is critical for efficient cellular transformation in vitro.
- This interaction plays a significant role in the induction of specific tumor types in the mouse-polyomavirus model.
- The findings underscore the importance of the Shc-mediated signal transduction pathway in polyomavirus oncogenesis.