active transport of the ubiquitin ligase mid1 along the microtubules is regulated by protein phosphatase 2a主动运输的泛素连接酶mid1沿着微管是由蛋白磷酸酶2 a.pdfVIP

Active Transport of the Ubiquitin Ligase MID1 along the Microtubules Is Regulated by Protein Phosphatase 2A ´ 1. 1. 1 1 2 Beatriz Aranda-Orgilles , Johanna Aigner , Melanie Kunath , Rudi Lurz , Rainer Schneider , Susann Schweiger1,3* 1 Max-Planck Institute for Molecular Genetics, Berlin, Germany, 2 Institute of Biochemistry, University Innsbruck, Innsbruck, Austria, 3 Division of Pathology and Neuroscience, Ninewells Hospital, University of Dundee, Dundee, United Kingdom 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), a4, 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 a4 binding domain still bind the microtubules but cannot be actively transported. Likewise, knock-down of the a4 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