Abstract
Myotonic dystrophy type-1 (DM1) is the most prevalent form of muscular dystrophy in adults. This disorder is an RNA-dominant disease, caused by expansion of a CTG repeat in the DMPK gene that leads to a misregulation in the alternative splicing of pre-mRNAs. The longer muscleblind-like-1 (MBNL1) transcripts containing exon 5 and the respective protein isoforms (MBNL142–43) were found to be overexpressed in DM1 muscle and localized exclusively in the nuclei. In vitro assays showed that MBNL142–43 bind the Src-homology 3 domain of Src family kinases (SFKs) via their proline-rich motifs, enhancing the SFK activity. Notably, this association was also confirmed in DM1 muscle and myotubes. The recovery, mediated by an siRNA target to Ex5-MBNL142–43, succeeded in reducing the nuclear localization of both Lyn and MBNL142–43 proteins and in decreasing the level of tyrosine phosphorylated proteins. Our results suggest an additional molecular mechanism in the DM1 pathogenesis, based on an altered phosphotyrosine signalling pathway.
Highlights
MBNL1 exons encode for protein domains with different functions: exons 1, 2 and 4 are essential for RNA binding,[16] exons 5 and 6 for controlling the nuclear localization of MBNL1; exon 3 strongly enhances the affinity of MBNL1 for its pre-mRNA target sites; exons 3 and 6 encode for a splicing regulatory domain; and exon 7 enhances MBNL1 selfdimerization.[17]
The complete splicing pattern of the MBNL1 gene was first determined in muscle tissues from DM1 (n 1⁄4 8) patients compared with controls (n 1⁄4 4), by RT-PCR analysis
MBNL1 expression is crucial in the DM pathophysiology, and the loss of MBNL1 protein leads to the spliceopathy in the muscle tissues of DM patients and mouse models.[8,37]
Summary
MBNL1 exons encode for protein domains with different functions: exons 1, 2 and 4 are essential for RNA binding,[16] exons 5 and 6 for controlling the nuclear localization of MBNL1; exon 3 strongly enhances the affinity of MBNL1 for its pre-mRNA target sites; exons 3 and 6 encode for a splicing regulatory domain; and exon 7 enhances MBNL1 selfdimerization.[17]. MBNL142–43 proteins interact with SFKs in DM1 nuclei A Botta et al domains present in many signalling proteins (Supplementary Figure SF1). This observation suggests that the different MBNL1 isoforms might regulate the activity and/or localization of the tyrosine (Tyr) kinases of the Src family (SFKs), triggering a signalling cascade mediated by Tyr phosphorylation. Intracellular localization, regulation of the alternative splicing of model pre-mRNA, ability to interact with SFKs through SH2 and SH3 domains and susceptibility to Tyr phosphorylation of MBNL1 isoforms in DM1 muscle and myotubes were the aspects addressed by our investigation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
