Related Experiment Videos
Association between src-kinases and the polyoma virus oncogene middle T-antigen requires PP2A and a specific sequence
H R Glover1, C E Brewster, S M Dilworth
1Department of Metabolic Medicine, Imperial College School of Medicine, London, UK.
Abstract:
Polymoma virus encodes a potent oncogene, the middle T-antigen (MT), that induces cell transformation by copying the actions of tyrosine kinase associated growth factor receptors. A crucial component of MT transformation is its ability to bind and stimulate the activity of src-family kinases. However, the mechanism by which this is achieved remains unclear. Tyrosine phosphorylation of MT by src-kinases then provides binding sites for SH2 and PTB domain containing molecules in a paradigm of receptor action. We present evidence here that the MT/src complex contains equi-molar amounts of PP2A, and that phosphatase activity may be required for the interaction of MT with both PP2A and the src-family. PP2A, then, is a necessary component of the MT-src complex. We also show that two motifs in the 185 to 210 region of MT, each consisting of a basic area followed by a serine or threonine, are essential for interaction with src-kinases, but not PP2A. The spacing between the serine or threonine and the basic sequence also appears to be important. Substituting a cysteine residue in place of Thr203 in MT has no affect on the binding of pp60c-src, showing that these sites interact with src-kinases by a novel mechanism that does not require phosphorylation.
Insights
Polyoma virus middle T-antigen (MT) transformation involves binding src-family kinases. This study reveals PP2A is essential for the MT-src complex, with specific MT motifs mediating kinase interaction via a novel, non-phosphorylation-dependent mechanism.
Area of Science:
- Molecular Biology
- Virology
- Oncogenesis
Background:
- Polyoma virus middle T-antigen (MT) is a potent oncogene that mimics tyrosine kinase-associated growth factor receptors.
- MT induces cell transformation by interacting with and activating src-family kinases.
- The precise mechanism of MT interaction with src-kinases remains incompletely understood.
Purpose of the Study:
- To elucidate the mechanism by which polyoma virus middle T-antigen (MT) interacts with and activates src-family kinases.
- To investigate the role of protein phosphatase 2A (PP2A) in the MT-src complex.
- To identify specific regions and motifs within MT critical for src-kinase interaction.
Main Methods:
- Biochemical assays to analyze protein-protein interactions within the MT-src complex.
- Analysis of MT mutants to determine the role of specific amino acid motifs in kinase binding.
- Investigation of the requirement for phosphatase activity in MT-src complex formation.
Main Results:
- The MT-src complex contains stoichiometric amounts of PP2A, indicating PP2A is a necessary component.
- Specific motifs (basic region followed by serine/threonine) in the MT 185-210 region are crucial for src-kinase interaction but not PP2A binding.
- The spacing within these motifs and the interaction mechanism with src-kinases do not require MT phosphorylation.
Conclusions:
- PP2A is an integral and essential component of the MT-src oncogenic complex.
- MT interacts with src-kinases through a novel mechanism involving specific sequence motifs that does not rely on tyrosine phosphorylation.
- These findings provide new insights into the molecular mechanisms of viral oncogenesis and kinase regulation.