title: Dimerization of Laforin is required for its optimal phosphatase activity, regulation of GSK3beta phosphorylation, and Wnt signaling.
abstract: Epilepsy of progressive myoclonus type 2 gene A (EPM2A) encodes a dual specificity protein phosphatase called Laforin. Laforin is also a tumor suppressor that dephosphorylates GSK3beta at the critical Ser9 position and regulates Wnt signaling. The epilepsy-causing mutations have a deleterious effect on phosphatase activity, regardless of whether they locate in the carbohydrate-binding domain (CBD) at the N terminus or the dual specificity phosphatase domain (DSPD) at the C terminus. How mutations outside the DSPD reduce the phosphatase activity of Laforin remains unexplained. Here we report that Laforin expressed in mammalian cells forms dimers that are highly resistant to SDS treatment. Deleting CBD completely abolished the dimerization and phosphatase activity of Laforin. Moreover, all of the naturally occurring Laforin mutations tested impaired laforin GSK3beta dephosphorylation at Ser9 dimerization, and beta-catenin accumulation in nucleus. Our results demonstrate a critical role of dimerization in Laforin function and suggest an important new dimension in protein phosphatase function and in molecular pathogenesis of Lafora's disease.
authors.affiliation: Division of Immunotherapy, Department of Surgery, Program of Molecular Medicine and Cancer Center, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Yin
authors.initials: Y
authors.lastname: Wang
authors.forename: Cindy
authors.initials: C
authors.lastname: Wu
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Pan
authors.initials: P
authors.lastname: Zheng
mesh_terms: D000818:Animals; D002460:Cell Line; D019281:Dimerization; D054637:Dual-Specificity Phosphatases; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D020836:Protein Structure, Quaternary; D017027:Protein Tyrosine Phosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D015398:Signal Transduction; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D051153:Wnt Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D054637:Dual-Specificity Phosphatases; C491989:Epm2a protein, mouse; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C114990:EPM2A protein, human