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Nucleic Acids Res. 2014 Jun;42(11):7186-200. doi: 10.1093/nar/gku352. Epub 2014 May 3.

DDX6 regulates sequestered nuclear CUG-expanded DMPK-mRNA in dystrophia myotonica type 1.

Author information

1
Department of Biomedicine, Aarhus University, Wilhelm Meyers Allé 4, Building 1240, DK-8000 Aarhus C, Denmark.
2
Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, building 1131, DK-8000 Aarhus C, Denmark.
3
Department of Molecular Biology and Genetics, Aarhus University, C.F. Møllers Allé 3, building 1131, DK-8000 Aarhus C, Denmark cd@mb.au.dk.

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.

PMID:
24792155
PMCID:
PMC4066779
DOI:
10.1093/nar/gku352
[Indexed for MEDLINE]
Free PMC Article

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