Amino-terminal regions of polyomavirus middle T antigen are required for interactions with protein phosphatase 2A.
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.
Glenn
G M
GM
Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, San Diego, California 92186-5800, USA.
Eckhart
W
W
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002461:Cell Line, Transformed; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011401:Promoter Regions, Genetic; D054648:Protein Phosphatase 2; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism
D000952:Antigens, Polyomavirus Transforming; D016760:Proto-Oncogene Proteins c-fos; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D016392:Proto-Oncogene Proteins pp60(c-src); D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2