title: New function for the RNA helicase p68/DDX5 as a modifier of MBNL1 activity on expanded CUG repeats.
abstract: Myotonic Dystrophy type I (DM1) is caused by an abnormal expansion of CTG triplets in the 3' UTR of the dystrophia myotonica protein kinase (DMPK) gene, leading to the aggregation of the mutant transcript in nuclear RNA foci. The expanded mutant transcript promotes the sequestration of the MBNL1 splicing factor, resulting in the misregulation of a subset of alternative splicing events. In this study, we identify the DEAD-box RNA helicase p68 (DDX5) in complexes assembled onto in vitro-transcribed CUG repeats. We showed that p68 colocalized with RNA foci in cells expressing the 3'UTR of the DMPK gene containing expanded CTG repeats. We found that p68 increased MBNL1 binding onto pathological repeats and the stem-loop structure regulatory element within the cardiac Troponin T (TNNT2) pre-mRNA, splicing of which is misregulated in DM1. Mutations in the helicase core of p68 prevented both the stimulatory effect of the protein on MBNL1 binding and the colocalization of p68 with CUG repeats, suggesting that remodeling of RNA secondary structure by p68 facilitates MBNL1 binding. We also found that the competence of p68 for regulating TNNT2 exon 5 inclusion depended on the integrity of MBNL1 binding sites. We propose that p68 acts as a modifier of MBNL1 activity on splicing targets and pathogenic RNA.
authors.affiliation: Centre de Génétique Moléculaire, CNRS, UPR 3404, Avenue de Terrasse, 91198 Gif-sur-Yvette, Université Paris-Sud, Orsay, France.
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Laurent
authors.forename: Alain
authors.initials: A
authors.lastname: Sureau
authors.forename: Arnaud F
authors.initials: AF
authors.lastname: Klein
authors.forename: François
authors.initials: F
authors.lastname: Trouslard
authors.forename: Erwan
authors.initials: E
authors.lastname: Gasnier
authors.forename: Denis
authors.initials: D
authors.lastname: Furling
authors.forename: Joëlle
authors.initials: J
authors.lastname: Marie
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D053487:DEAD-box RNA Helicases / Q000032:analysis / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D009223:Myotonic Dystrophy / Q000235:genetics; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D019680:Trinucleotide Repeat Expansion; D020107:Troponin T / Q000235:genetics / Q000378:metabolism
chemical_list: C585517:DMPK protein, human; C493663:MBNL1 protein, human; D016601:RNA-Binding Proteins; C545568:TNNT2 protein, human; D020107:Troponin T; D012313:RNA; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases; C102004:DDX17 protein, human; C506749:Ddx5 protein, human; D053487:DEAD-box RNA Helicases