Catalytically inactive protein phosphatase 2A can bind to polyomavirus middle tumor antigen and support complex formation with pp60(c-src)

• Published in: Journal of virology Vol. 73; no. 9; p. 7390
• Main Authors: Ogris, E, Mudrak, I, Mak, E, Gibson, D, Pallas, D C
• Format: Journal Article
• Language: English
• Published: United States 01-09-1999
• Subjects: 3T3 Cells; Amino Acid Sequence; Animals; Antigens, Polyomavirus Transforming - metabolism; Catalysis; Catalytic Domain; HeLa Cells; Humans; Mice; Molecular Sequence Data; Mutagenesis; Phosphoprotein Phosphatases - genetics; Phosphoprotein Phosphatases - metabolism; Protein Phosphatase 2; Proto-Oncogene Proteins pp60(c-src) - metabolism
• ISSN: 0022-538X
• DOI: 10.1128/jvi.73.9.7390-7398.1999

Interaction between the heterodimeric form of protein phosphatase 2A (PP2A) and polyomavirus middle T antigen (MT) is required for the subsequent assembly of a transformation-competent MT complex. To investigate the role of PP2A catalytic activity in MT complex formation, we undertook a mutational analysis of the PP2A 36-kDa catalytic C subunit. Several residues likely to be involved in the dephosphorylation mechanism were identified and mutated. The resultant catalytically inactive C subunit mutants were then analyzed for their ability to associate with a cellular (B subunit) or a viral (MT) B-type subunit. Strikingly, while all of the inactive mutants were severely impaired in their interaction with B subunit, most of these mutants formed complexes with polyomavirus MT. These findings indicate a potential role for these catalytically important residues in complex formation with cellular B subunit, but not in complex formation with MT. Transformation-competent MT is known to associate with, and modulate the activity of, several cellular proteins, including pp60(c-src) family kinases. To determine whether association of MT with an active PP2A A-C heterodimer is necessary for subsequent association with pp60(c-src), catalytically inactive C subunits were examined for their ability to form complexes containing pp60(c-src) in MT-expressing cells. Two catalytically inactive C subunit mutants that efficiently formed complexes with MT also formed complexes that included an active pp60(c-src) kinase, demonstrating that PP2A activity is not essential in cis in MT complexes for subsequent pp60(c-src) association.