Global analysis of the molecular targets of MBNL1 and CELF1 proteins and their potential role in DM1

Myotonic dystrophy type 1 (DM1) is caused by the nuclear accumulation of mutant DMPK mRNA containing CUG-repeat expansions, resulting in a trans-dominant effect on RNA processing by sequestration of MBNL1 and activation of CELF1 splicing regulators. Here, we present a comprehensive study of the MBNL1 and CELF1-regulated splicing in the HeLa cell line that may participate in the complex phenotype of the DM1 disease. We have performed human GeneChip Exon array experiments with RNAs extracted from HeLa cells in which MBNL1 or CELF1 were silenced or over-expressed. MBNL1 or CELF1-silenced HeLa cells showed changes in the expression of 170 probe sets (150 genes) and 893 probe sets (613 genes), whereas MBNL1 or CELF1 over-expression on these cells had 812 probe sets (589 genes) and 684 probe sets (531 genes) altered, respectively. In MBNL1-silenced cells we have found and validated by RT-qPCR the exclusion of RASIP1 exon 4 and of KIF13A exon 26 and the inclusion of MBNL2 exon 5. Furthermore, we have found exclusion of LCOR exon 6 and PIP4K2C exon 1, and inclusion TCF12 exon 16, with dependence on the silencing degree of MBNL1, In MBNL1 over-expressed HeLa cells we have found and validated by RT-qPCR a potent inclusion of CD44 exon 8, CD44 exon 11 and the 3UTR of TRAF2. We have then mimicked the misregulation of MBNL1 and CELF1 protein levels of DM1 in HeLa cells, finding new altered splicing events. These alterations were found in genes that encode proteins involved in myoblast differentiation and migration (CD44, RASIP1) and muscle development (TCF12 transcription factor), estrogen and thyroid receptor interactor (LCOR), as well as proteins involved in transduction signaling pathways (PIP4K2C, TRAF2) and intracellular trafficking (KIF13A). These results provide potential contributing genes that could help to explain the complex phenotype of the DM1 disease.

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