title: Transformation by Polyomavirus Middle T Antigen Involves a Unique Bimodal Interaction with the Hippo Effector YAP.
abstract: Murine polyomavirus has repeatedly provided insights into tumorigenesis, revealing key control mechanisms such as tyrosine phosphorylation and phosphoinositide 3-kinase (PI3K) signaling. We recently demonstrated that polyomavirus small T antigen (ST) binds YAP, a major effector of Hippo signaling, to regulate differentiation. Here we characterize YAP as a target of middle T antigen (MT) important for transformation. Through a surface including residues R103 and D182, wild-type MT binds to the YAP WW domains. Mutation of either R103 or D182 of MT abrogates YAP binding without affecting binding to other signaling molecules or the strength of PI3K or Ras signaling. Either genetic abrogation of YAP binding to MT or silencing of YAP via short hairpin RNA (shRNA) reduced MT transformation, suggesting that YAP makes a positive contribution to the transformed phenotype. MT targets YAP both by activating signaling pathways that affect it and by binding to it. MT signaling, whether from wild-type MT or the YAP-binding MT mutant, promoted YAP phosphorylation at S127 and S381/397 (YAP2/YAP1). Consistent with the known functions of these phosphorylated serines, MT signaling leads to the loss of YAP from the nucleus and degradation. Binding of YAP to MT brings it together with protein phosphatase 2A (PP2A), leading to the dephosphorylation of YAP in the MT complex. It also leads to the enrichment of YAP in membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that may depart from YAP's canonical oncogenic transcriptional activation functions.
  
  
  
  The highly conserved Hippo/YAP pathway is important for tissue development and homeostasis. Increasingly, changes in this pathway are being associated with cancer. Middle T antigen (MT) is the primary polyomavirus oncogene responsible for tumor formation. In this study, we show that MT signaling promotes YAP phosphorylation, loss from the nucleus, and increased turnover. Notably, MT genetics demonstrate that YAP binding to MT is important for transformation. Because MT also binds PP2A, YAP bound to MT is dephosphorylated, stabilized, and localized to membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that depart from YAP's canonical oncogenic transcriptional activation functions.
authors.affiliation: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA.|Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, Massachusetts, USA.
authors.forename: Cecile
authors.initials: C
authors.lastname: Rouleau
authors.affiliation: Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.|Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Arun T
authors.initials: AT
authors.lastname: Pores Fernando
authors.affiliation: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA.|Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, Massachusetts, USA.
authors.forename: Justin H
authors.initials: JH
authors.lastname: Hwang
authors.affiliation: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Faure
authors.affiliation: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
authors.affiliation: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: White
authors.affiliation: Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA thomas_roberts@dfci.harvard.edu brian.schaffhausen@tufts.edu.|Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Roberts
authors.affiliation: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, Massachusetts, USA thomas_roberts@dfci.harvard.edu brian.schaffhausen@tufts.edu.|Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, Massachusetts, USA.
authors.forename: Brian S
authors.initials: BS
authors.lastname: Schaffhausen
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000821:virology; D005455:Fluorescent Antibody Technique; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D009154:Mutation / Q000235:genetics; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011120:Polyomavirus / Q000276:immunology*; D027601:Polyomavirus Infections / Q000276:immunology* / Q000378:metabolism / Q000821:virology; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014412:Tumor Virus Infections / Q000276:immunology* / Q000378:metabolism / Q000821:virology
chemical_list: D000952:Antigens, Polyomavirus Transforming; D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D054648:Protein Phosphatase 2; D012333:RNA, Messenger; D014157:Transcription Factors; C456659:YY1AP1 protein, human