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Association of Polyomavirus middle tumor antigen with phospholipase C-gamma 1
W Su1, W Liu, B S Schaffhausen
1Division of Cellular and Molecular Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
Abstract:
Middle tumor antigen (MT) is the primary transforming protein of murine Polyomavirus. MT transforms by associating with and modulating the activities of cellular proteins involved in control of cell proliferation. MT binds to and is phosphorylated by cellular tyrosine kinases. The phosphorylated tyrosines become docking sites for SH2 (Src homology 2) domain-containing molecules. Tyrosine 322 of MT is known to be phosphorylated but has no known binding protein. We have found that phospholipase C-gamma 1 (PLC-gamma 1), a SH2 domain-containing protein, coimmunoprecipitates with MT. Tyrosine phosphorylation of PLC-gamma 1 is elevated in cells expressing MT, suggesting activation of this enzyme by MT. A Tyr-322-->Phe mutation in MT renders it defective in MT-PLC-gamma 1 interaction and in transformation. From the correlation between transformation and MT-PLC-gamma 1 interaction, we suggest that PLC-gamma 1 may play a role in transformation.
Insights
Murine Polyomavirus middle tumor antigen (MT) interacts with phospholipase C-gamma 1 (PLC-gamma 1). This interaction, particularly at tyrosine 322 of MT, is crucial for MT-mediated cell transformation.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Middle tumor antigen (MT) is a key protein in murine Polyomavirus, driving cell transformation.
- MT modulates cellular proteins controlling cell proliferation and interacts with tyrosine kinases.
- Phosphorylated tyrosines on MT serve as docking sites for SH2 domain-containing proteins.
Purpose of the Study:
- To identify binding proteins for the phosphorylated Tyrosine 322 of MT.
- To investigate the role of phospholipase C-gamma 1 (PLC-gamma 1) in MT-mediated transformation.
Main Methods:
- Coimmunoprecipitation assays to detect protein interactions.
- Analysis of tyrosine phosphorylation levels in cells expressing MT.
- Site-directed mutagenesis of MT (Tyr-322 to Phenylalanine).
Main Results:
- Phospholipase C-gamma 1 (PLC-gamma 1) was found to coimmunoprecipitate with MT.
- MT expression led to elevated tyrosine phosphorylation of PLC-gamma 1, suggesting enzyme activation.
- A Tyr-322 mutation in MT abolished MT-PLC-gamma 1 interaction and MT's transforming ability.
Conclusions:
- PLC-gamma 1 is a binding partner for MT.
- The interaction between MT and PLC-gamma 1, mediated by Tyr-322, is essential for Polyomavirus-induced cell transformation.
- PLC-gamma 1 likely plays a significant role in the transformation process driven by MT.