title: Monoubiquitination promotes calpain cleavage of the protein phosphatase 2A (PP2A) regulatory subunit α4, altering PP2A stability and microtubule-associated protein phosphorylation.
abstract: Multiple neurodegenerative disorders are linked to aberrant phosphorylation of microtubule-associated proteins (MAPs). Protein phosphatase 2A (PP2A) is the major MAP phosphatase; however, little is known about its regulation at microtubules. α4 binds the PP2A catalytic subunit (PP2Ac) and the microtubule-associated E3 ubiquitin ligase MID1, and through unknown mechanisms can both reduce and enhance PP2Ac stability. We show MID1-dependent monoubiquitination of α4 triggers calpain-mediated cleavage and switches α4's activity from protective to destructive, resulting in increased Tau phosphorylation. This regulatory mechanism appears important in MAP-dependent pathologies as levels of cleaved α4 are decreased in Opitz syndrome and increased in Alzheimer disease, disorders characterized by MAP hypophosphorylation and hyperphosphorylation, respectively. These findings indicate that regulated inter-domain cleavage controls the dual functions of α4, and dysregulation of α4 cleavage may contribute to Opitz syndrome and Alzheimer disease.
authors.affiliation: Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600, USA.
authors.forename: Guy R
authors.initials: GR
authors.lastname: Watkins
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Mazalouskas
authors.forename: Rey J
authors.initials: RJ
authors.lastname: Gomez
authors.forename: Chris R
authors.initials: CR
authors.lastname: Guthrie
authors.forename: Brian C
authors.initials: BC
authors.lastname: Kraemer
authors.forename: Susann
authors.initials: S
authors.lastname: Schweiger
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Spiller
authors.forename: Brian E
authors.initials: BE
authors.lastname: Wadzinski
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D006801:Humans; D047468:Immunoprecipitation; D013058:Mass Spectrometry; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000235:genetics / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability; D054875:Ubiquitination / Q000235:genetics / Q000502:physiology*
chemical_list: D008869:Microtubule-Associated Proteins; D054648:Protein Phosphatase 2