title: Axotrophin/MARCH7 acts as an E3 ubiquitin ligase and ubiquitinates tau protein in vitro impairing microtubule binding.
abstract: Tau is the major microtubule-associated protein in neurons involved in microtubule stabilization in the axonal compartment. Changes in tau gene expression, alternative splicing and posttranslational modification regulate tau function and in tauopathies can result in tau mislocalization and dysfunction, causing tau aggregation and cell death. To uncover proteins involved in the development of tauopathies, a yeast two-hybrid system was used to screen for tau-interacting proteins. We show that axotrophin/MARCH7, a RING-variant domain containing protein with similarity to E3 ubiquitin ligases interacts with tau. We defined the tau binding domain to amino acids 552-682 of axotrophin comprising the RING-variant domain. Co-immunoprecipitation and co-localization confirmed the specificity of the interaction. Intracellular localization of axotrophin is determined by an N-terminal nuclear targeting signal and a C-terminal nuclear export signal. In AD brain nuclear localization is lost and axotrophin is rather associated with neurofibrillary tangles. We find here that tau becomes mono-ubiquitinated by recombinant tau-interacting RING-variant domain, which diminishes its microtubule-binding. In vitro ubiquitination of four-repeat tau results in incorporation of up to four ubiquitin molecules compared to two molecules in three-repeat tau. In summary, we present a novel tau modification occurring preferentially on 4-repeat tau protein which modifies microtubule-binding and may impact on the pathogenesis of tauopathies.
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Flach
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Ellen
authors.initials: E
authors.lastname: Ramminger
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Isabel
authors.initials: I
authors.lastname: Hilbrich
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Arsalan-Werner
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Albrecht
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Lydia
authors.initials: L
authors.lastname: Herrmann
authors.affiliation: MRC, Laboratory of Molecular Biology, Neurobiology Division, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Michel
authors.initials: M
authors.lastname: Goedert
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Arendt
authors.affiliation: Paul Flechsig Institute of Brain Research, Department of Molecular and Cellular Mechanisms of Neurodegeneration, University of Leipzig, 04109 Leipzig, Germany. Electronic address: holm@medizin.uni-leipzig.de.
authors.forename: Max
authors.initials: M
authors.lastname: Holzer
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism*; D016022:Case-Control Studies; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D051379:Mice; D018345:Mice, Knockout; D008870:Microtubules / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination; D016875:tau Proteins / Q000502:physiology*
chemical_list: C558298:Mapt protein, mouse; D011994:Recombinant Proteins; D025801:Ubiquitin; D016875:tau Proteins; C517824:MARCHF7 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: Alzheimer's disease; Microtubule binding; Mono-ubiquitination; Ring-variant domain; Tau protein; Yeast two-hybrid assay