A Transformation-Defective Polyomavirus Middle T Antigen with a Novel Defect in PI3 Kinase Signaling.

摘要: Middle T antigen (MT), the principal oncoprotein of murine polyomavirus, transforms by association with cellular proteins. Protein phosphatase 2A (PP2A), YAP, Src family tyrosine kinases, Shc, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-γ1 (PLCγ1) have all been implicated in MT transformation. Mutant dl1015, deletion residues 338 to 347 C-terminal region, has an enigma, because basis for its transformation defect not apparent. This work probes dl1015 region MT. Because is proline rich, hypothesis that it targets homology domain 3 (SH3) domains was tested, but mutation putative SH3 binding motif did affect During this work, two point mutants, W348R E349K, were identified as defective. Extensive analysis E349K mutant described here. Similar wild-type MT, associates PP2A, PI3 kinase, PLCγ1. The examined determine mechanism defect. Assays cell localization membrane targeting showed no obvious difference localization. normal assayed vitro kinase phosphopeptide mapping. Shc activation confirmed phosphorylation. Association type 1 PI3K demonstrated coimmunoprecipitation, showing both subunits activity. Nonetheless, expression mutants failed lead known downstream PI3K, Akt Rac-1. Strikingly, despite cells expressing elevate (3,4,5)-trisphosphate (PIP3) mutant-expressing cells. These results indicate a novel unsuspected aspect control. IMPORTANCE gene coding middle (MT) polyomavirus oncogene most responsible tumor formation. Its study history uncovering aspects mammalian regulation. importance activity phosphorylation are examples insights coming from describes new unable transform like wild regulation signaling. Previous defective they bind enzyme bring membrane. recruit type, fail level PIP3, product used signal PI3K. As result, activate either or Rac1, explaining