title: Alpha4 is a ubiquitin-binding protein that regulates protein serine/threonine phosphatase 2A ubiquitination.
abstract: Multiple regulatory mechanisms control the activity of the protein serine/threonine phosphatase 2A catalytic subunit (PP2Ac), including post-translational modifications and its association with regulatory subunits and interacting proteins. Alpha4 is a PP2Ac-interacting protein that is hypothesized to play a role in PP2Ac ubiquitination via its interaction with the E3 ubiquitin ligase Mid1. In this report, we show that alpha4 serves as a necessary adaptor protein that provides a binding platform for both PP2Ac and Mid1. We also identify a novel ubiquitin-interacting motif (UIM) within alpha4 (amino acid residues 46-60) and analyze the interaction between alpha4 and ubiquitin using NMR. Consistent with other UIM-containing proteins, alpha4 is monoubiquitinated. Interestingly, deletion of the UIM within alpha4 enhances its association with polyubiquitinated proteins. Lastly, we demonstrate that addition of wild-type alpha4 but not an alpha4 UIM deletion mutant suppresses PP2Ac polyubiquitination. Thus, the polyubiquitination of PP2Ac is inhibited by the UIM within alpha4. These findings reveal direct regulation of PP2Ac polyubiquitination by a novel UIM within the adaptor protein alpha4.
authors.affiliation: Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600, USA.
authors.forename: Jamie L
authors.initials: JL
authors.lastname: McConnell
authors.forename: Guy R
authors.initials: GR
authors.lastname: Watkins
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Soss
authors.forename: Heidi S
authors.initials: HS
authors.lastname: Franz
authors.forename: Lisa R
authors.initials: LR
authors.lastname: McCorvey
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Spiller
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Chazin
authors.forename: Brian E
authors.initials: BE
authors.lastname: Wadzinski
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D015153:Blotting, Western; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000737:chemistry* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination / Q000235:genetics / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C490467:IGBP1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008868:Microtubule Proteins; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C109052:MID1 protein, human; D044767:Ubiquitin-Protein Ligases; D054648:Protein Phosphatase 2