title: Ubiquitin ligase E6AP mediates nonproteolytic polyubiquitylation of β-catenin independent of the E6 oncoprotein.
abstract: Recently, we showed that the ubiquitin ligase E6AP stabilizes β-catenin and activates its transcriptional activity. These activities were enhanced by the human papillomavirus (HPV) E6 protein. In the present study, we explored the function of E6AP, which increases β-catenin stabilization and transcriptional activation. Here, we report that E6AP interacts with β-catenin and mediates its nonproteolytic ubiquitylation, as evidenced in transiently transfected cell-based and in vitro reconstitution ubiquitylation assays. Overexpression of E6AP increased β-catenin polyubiquitylation and, consistent with that, knockdown or knock-out of E6AP expression reduced β-catenin polyubiquitylation. The ubiquitylation of β-catenin by E6AP was dependent on its E3 ubiquitin ligase activity, but it was proteasome-independent and did not require HPV-E6, phosphorylation of β-catenin by glycogen synthase kinase 3β (GSK3β) or activity of the β-catenin 'destruction complex'. We also show that transcriptional activation of β-catenin by E6AP is coupled with β-catenin protein stabilization, but not its ubiquitylation. In contrast to β-catenin ubiquitylation, β-catenin protein stability and its transcriptional activity were absolutely dependent on the activity of the destruction complex and phosphorylation by GSK3β. Collectively, our data uncover a dual role for E6AP in the regulation of β-catenin ubiquitylation, stability and transcriptional activity, with HPV-E6 enhancing only part of E6AP activities.
authors.affiliation: Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Kuslansky
authors.affiliation: Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Sophia
authors.initials: S
authors.lastname: Sominsky
authors.affiliation: Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Anna
authors.initials: A
authors.lastname: Jackman
authors.affiliation: Research Division, The Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville 3010, Victoria, Australia.
authors.forename: Cristina
authors.initials: C
authors.lastname: Gamell
authors.affiliation: Division of Systems Biology and Personalized Medicine, Walter and Eliza Hall Institute of Medical Research, Parkville 3052, Victoria, Australia.
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Monahan
authors.affiliation: Research Division, The Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville 3010, Victoria, Australia.
authors.forename: Ygal
authors.initials: Y
authors.lastname: Haupt
authors.affiliation: Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Rina
authors.initials: R
authors.lastname: Rosin-Arbesfeld
authors.affiliation: Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Levana
authors.initials: L
authors.lastname: Sherman
mesh_terms: D000071679:Glycogen Synthase Kinase 3 beta / Q000235:genetics / Q000378:metabolism; D054884:Host-Pathogen Interactions; D052162:Human papillomavirus 16 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D011485:Protein Binding; D055550:Protein Stability; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D051176:beta Catenin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D012097:Repressor Proteins; D051176:beta Catenin; C471639:UBE3A protein, human; D044767:Ubiquitin-Protein Ligases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta