Association between src-kinases and the polyoma virus oncogene middle T-antigen requires PP2A and a specific sequence motif.
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.
Glover
H R
HR
Department of Metabolic Medicine, Imperial College School of Medicine, London, UK.
Brewster
C E
CE
Dilworth
S M
SM
D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D002460:Cell Line; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D010766:Phosphorylation; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D019061:src-Family Kinases / Q000378:metabolism*
D000952:Antigens, Polyomavirus Transforming; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; D010749:Phosphoprotein Phosphatases