Monoubiquitination Promotes Calpain Cleavage of the Protein Phosphatase 2A (PP2A) Regulatory Subunit alpha 4, Altering PP2A Stability and Microtubule-associated Protein Phosphorylation

Guy R. Watkins, Ning Wang, Matthew D. Mazalouskas, Rey J. Gomez, Chris R. Guthrie, Brian C. Kraemer, Susann Schweiger, Benjamin W. Spiller, Brian E. Wadzinski

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    39 Citations (Scopus)


    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. alpha 4 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 alpha 4 triggers calpain-mediated cleavage and switches alpha 4's activity from protective to destructive, resulting in increased Tau phosphorylation. This regulatory mechanism appears important in MAP-dependent pathologies as levels of cleaved alpha 4 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 alpha 4, and dysregulation of alpha 4 cleavage may contribute to Opitz syndrome and Alzheimer disease.

    Original languageEnglish
    Pages (from-to)24207-24215
    Number of pages9
    JournalJournal of Biological Chemistry
    Issue number29
    Publication statusPublished - 13 Jul 2012

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