Active transport of the Ubiquitin Ligase MID1 along the microtubules Is regulated by Protein Phosphatase 2A

Beatriz Aranda-Orgilles, Johanna Aigner, Melanie Kunath, Rudi Lurz, Rainer Schneider, Susann Schweiger

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    Abstract

    Mutations in the MID1 protein have been found in patients with Opitz BBB/G syndrome (OS), which is characterised by multiple malformations of the ventral midline. MID1 is a microtubule-associated protein that stabilizes microtubules and, in association with the regulatory subunit of protein phosphatase 2A (PP2A), alpha 4, provides ubiquitin ligase activity for the ubiquitin-specific modification of PP2A. Using Fluorescence Recovery After Photobleaching (FRAP) technology, we show here that MID1 is actively and bi-directionally transported along the microtubules, and that this movement is directly linked to its MAP kinase and PP2A-mediated phosphorylation status. Intact transport depends on both kinesins and dyneins and is inhibited upon colcemide treatments. MID1 proteins carrying missense mutations in the alpha 4 binding domain still bind the microtubules but cannot be actively transported. Likewise, knock-down of the alpha 4 protein, inhibition of PP2A activity by okadaic acid and fostriecin or the simulation of permanent phosphorylation at Ser96 in MID1 stop the migration of MID1-GFP, while preserving its microtubule-association. In summary, our data uncover an unexpected and novel function for PP2A, its regulatory subunit alpha 4 and PP2A/alpha 4/mTOR signaling in the active transport of the MID1 ubiquitin ligase complex along the cytoskeleton. Furthermore, a failure in the microtubule directed transport of this protein complex would be an attractive mechanism underlying the pathogenesis of OS in patients with B-box1 mutations.

    Original languageEnglish
    Article numbere3507
    Pages (from-to)-
    Number of pages8
    JournalPLoS ONE
    Volume3
    Issue number10
    DOIs
    Publication statusPublished - 24 Oct 2008

    Keywords

    • LINKED OPITZ-SYNDROME
    • SYNDROME GENE-PRODUCT
    • CATALYTIC SUBUNIT
    • NEURONAL POLARITY
    • MOTOR PROTEINS
    • G/BBB SYNDROME
    • MUTATIONS
    • BINDING
    • COMPLEX
    • DOMAIN

    Cite this

    Aranda-Orgilles, B., Aigner, J., Kunath, M., Lurz, R., Schneider, R., & Schweiger, S. (2008). Active transport of the Ubiquitin Ligase MID1 along the microtubules Is regulated by Protein Phosphatase 2A. PLoS ONE, 3(10), -. [e3507]. https://doi.org/10.1371/journal.pone.0003507