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Amino-terminal regions of polyomavirus middle T antigen are required for interactions with protein phosphatase 2A
1Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
Abstract:
Polyomavirus middle T antigen (MT) is the major transforming protein of the virus. It functions through interactions with a number of cellular proteins involved in cell proliferation. MT forms complexes with protein phosphatase 2A (PP2A), pp60c-src, phosphatidylinositol 3-kinase, and Shc. We introduced both deletion and point mutations into three regions of MT and examined their ability to associate with PP2A and pp60c-src. The first 25 amino acid residues of MT are required for association with PP2A and pp60c-src. Amino acids 105 to 111, comprising the sequence Cys-Arg-Met-Pro-Leu-Thr-Cys, is also required for complex formation between MT and PP2A. However, the sequence Asp-Lys-Gly-Gly (amino acids 44 to 47), also found in the B subunit of PP2A, is dispensable for complex formation between MT and PP2A. We find a strict correlation between the ability of MT to associate with PP2A and the ability of MT to associate with pp60c-src. One mutant, L5E, associates with a phosphatase other than PP2A, pp60c-src, and phosphatidylinositol 3-kinase in a manner similar to that of wild-type MT yet is reduced in its transforming ability on NIH 3T3 cells.
Insights
Polyomavirus middle T antigen (MT) mutations reveal key regions for binding protein phosphatase 2A (PP2A) and pp60c-src. These interactions are crucial for MT
Area of Science:
- Virology
- Molecular Biology
- Oncogenesis
Background:
- Polyomavirus middle T antigen (MT) is a key viral transforming protein.
- MT interacts with cellular proteins regulating cell proliferation, including PP2A and pp60c-src.
Purpose of the Study:
- To investigate the specific regions of MT essential for its association with PP2A and pp60c-src.
- To correlate these interactions with the transforming ability of MT.
Main Methods:
- Introduction of deletion and point mutations into three distinct regions of MT.
- Analysis of mutant MT protein complex formation with PP2A and pp60c-src.
Main Results:
- The N-terminal 25 amino acids of MT are essential for PP2A and pp60c-src association.
- Amino acids 105-111 (Cys-Arg-Met-Pro-Leu-Thr-Cys) are required for MT-PP2A complex formation.
- A strict correlation exists between MT's ability to associate with PP2A and pp60c-src.
- Mutant L5E showed altered phosphatase association but retained some wild-type interactions, with reduced transforming ability.
Conclusions:
- Specific amino acid sequences in MT are critical for binding PP2A and pp60c-src.
- The association with PP2A and pp60c-src is tightly linked and influences MT's transforming potential.
- Understanding these interactions provides insights into polyomavirus-mediated oncogenesis.