title: DDX6 regulates sequestered nuclear CUG-expanded DMPK-mRNA in dystrophia myotonica type 1.
abstract: Myotonic dystrophy type 1 (DM1) is caused by CUG triplet expansions in the 3' UTR of dystrophia myotonica protein kinase (DMPK) messenger ribonucleic acid (mRNA). The etiology of this multi-systemic disease involves pre-mRNA splicing defects elicited by the ability of the CUG-expanded mRNA to 'sponge' splicing factors of the muscleblind family. Although nuclear aggregation of CUG-containing mRNPs in distinct foci is a hallmark of DM1, the mechanisms of their homeostasis have not been completely elucidated. Here we show that a DEAD-box helicase, DDX6, interacts with CUG triplet-repeat mRNA in primary fibroblasts from DM1 patients and with CUG-RNA in vitro. DDX6 overexpression relieves DM1 mis-splicing, and causes a significant reduction in nuclear DMPK-mRNA foci. Conversely, knockdown of endogenous DDX6 leads to a significant increase in DMPK-mRNA foci count and to increased sequestration of MBNL1 in the nucleus. While the level of CUG-expanded mRNA is unaffected by increased DDX6 expression, the mRNA re-localizes to the cytoplasm and its interaction partner MBNL1 becomes dispersed and also partially re-localized to the cytoplasm. Finally, we show that DDX6 unwinds CUG-repeat duplexes in vitro in an adenosinetriphosphate-dependent manner, suggesting that DDX6 can remodel and release nuclear DMPK messenger ribonucleoprotein foci, leading to normalization of pathogenic alternative splicing events.
authors.affiliation: Department of Biomedicine, Aarhus University, Wilhelm Meyers Allé 4, Building 1240, DK-8000 Aarhus C, Denmark.
authors.forename: Olof J
authors.initials: OJ
authors.lastname: Pettersson
authors.affiliation: Department of Biomedicine, Aarhus University, Wilhelm Meyers Allé 4, Building 1240, DK-8000 Aarhus C, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Aagaard
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, building 1131, DK-8000 Aarhus C, Denmark.
authors.forename: Diana
authors.initials: D
authors.lastname: Andrejeva
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, building 1131, DK-8000 Aarhus C, Denmark.
authors.forename: Rune
authors.initials: R
authors.lastname: Thomsen
authors.affiliation: Department of Biomedicine, Aarhus University, Wilhelm Meyers Allé 4, Building 1240, DK-8000 Aarhus C, Denmark.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Jensen
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, building 1131, DK-8000 Aarhus C, Denmark cd@mb.au.dk.
authors.forename: Christian K
authors.initials: CK
authors.lastname: Damgaard
mesh_terms: D020413:3' Untranslated Regions; D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D003593:Cytoplasm / Q000737:chemistry; D053487:DEAD-box RNA Helicases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005347:Fibroblasts / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D009223:Myotonic Dystrophy / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000032:analysis; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D019680:Trinucleotide Repeat Expansion
chemical_list: D020413:3' Untranslated Regions; C585517:DMPK protein, human; C493663:MBNL1 protein, human; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011972:Receptor, Insulin; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases; C094683:DDX6 protein, human; D053487:DEAD-box RNA Helicases