Muscleblind-Like 1 and Muscleblind-Like 3 Depletion Synergistically Enhances Myotonia by Altering Clc-1 RNA Translation.
Loss of Muscleblind-like 1 (Mbnl1) is known to alter Clc-1 splicing to result in myotonia. Mbnl1(ΔE3/ΔE3)/Mbnl3(ΔE2) mice, depleted of Mbnl1 and Mbnl3, demonstrate a profound enhancement of myotonia and an increase in the number of muscle fibers with very low Clc-1 currents, where gClmax values approach ~ 1 mS/cm(2), with the absence of a further enhancement in Clc-1 splice errors, alterations in polyA site selection or Clc-1 localization. Significantly, Mbnl1(ΔE3/ΔE3)/Mbnl3(ΔE2) muscles demonstrate an aberrant accumulation of Clc-1 RNA on monosomes and on the first polysomes. Mbnl1 and Mbnl3 bind Clc-1 RNA and both proteins bind Hsp70 and eEF1A, with these associations being reduced in the presence of RNA. Thus binding of Mbnl1 and Mbnl3 to Clc-1 mRNA engaged with ribosomes can facilitate an increase in the local concentration of Hsp70 and eEF1A to assist Clc-1 translation. Dual depletion of Mbnl1 and Mbnl3 therefore initiates both Clc-1 splice errors and translation defects to synergistically enhance myotonia. As the HSA(LR) model for myotonic dystrophy (DM1) shows similar Clc-1 defects, this study demonstrates that both splice errors and translation defects are required for DM1 pathology to manifest.


BACKGROUND
Research in context: Myotonic Dystrophy type 1 (DM1) is a dominant disorder resulting from the expression of expanded CUG repeat RNA, which aberrantly sequesters and inactivates the muscleblind-like (MBNL) family of proteins. In mice, inactivation of Mbnl1 is known to alter Clc-1 splicing to result in myotonia. We demonstrate that concurrent depletion of Mbnl1 and Mbnl3 results in a synergistic enhancement of myotonia, with an increase in muscle fibers showing low chloride currents. The observed synergism results from the aberrant accumulation of Clc-1 mRNA on monosomes and the first polysomes. This translation error reflects the ability of Mbnl1 and Mbnl3 to act as adaptors that recruit Hsp70 and eEF1A to the Clc-1 mRNA engaged with ribosomes, to facilitate translation. Thus our study demonstrates that Clc-1 RNA translation defects work coordinately with Clc-1 splice errors to synergistically enhance myotonia in mice lacking Mbnl1 and Mbnl3.
Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, CA 90033, USA.
Jongkyu
J
Choi
Department of Rehabilitation Science and Program in Neuroscience, School of Public Health and Health Professions, University at Buffalo, Buffalo, NY 14214, USA.
Kirkwood E
KE
Personius
Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA.
Marino
M
DiFranco
Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, CA 90033, USA.
Warunee
W
Dansithong
Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA.
Carl
C
Yu
Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, CA 90033, USA.
Saumya
S
Srivastava
Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, CA 90033, USA.
Donald M
DM
Dixon
Department of Rehabilitation Science and Program in Neuroscience, School of Public Health and Health Professions, University at Buffalo, Buffalo, NY 14214, USA.
Darshan B
DB
Bhatt
Department of Microbiology and Immunology, University of Southern California, Los Angeles, CA 90033, USA.
Lucio
L
Comai
Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095, USA.
Julio L
JL
Vergara
Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, CA 90033, USA.
Sita
S
Reddy
D017398:Alternative Splicing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D057809:HEK293 Cells; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D009222:Myotonia / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D009223:Myotonic Dystrophy / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D020648:Peptide Elongation Factor 1 / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism
C086321:CLC-1 channel; D002352:Carrier Proteins; D018118:Chloride Channels; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; C522920:MBNL3 protein, mouse; C479922:Mbnl1 protein, mouse; D020648:Peptide Elongation Factor 1; D012333:RNA, Messenger; D016601:RNA-Binding Proteins
Clc-1; Muscleblind-like 1; Muscleblind-like 2; Myotonia; RNA translation