Interaction of musleblind, CUG-BP1 and hnRNP H proteins in DM1-associated aberrant IR splicing

In myotonic dystrophy (DM1), both inactivation of muscleblind proteins and increased levels of CUG‐BP1 are reported. These events have been shown to contribute independently to aberrant splicing of a subset RNAs. We demonstrate that steady‐state levels of the splice regulator, hnRNP H, are elevated in DM1 myoblasts and that increased hnRNP H levels in normal myoblasts results in the inhibition of insulin receptor (IR) exon 11 splicing in a manner similar to that observed in DM1. In normal myoblasts, overexpression of either hnRNP H or CUG‐BP1 results in the formation of an RNA‐dependent suppressor complex consisting of both hnRNP H and CUG‐BP1, which is required to maximally inhibit IR exon 11 inclusion. Elevated levels of MBNL1 show RNA‐independent interaction with hnRNP H and dampen the inhibitory activity of increased hnRNP H levels on IR splicing in normal myoblasts. In DM1 myoblasts, overexpression of MBNL1 in conjunction with si‐RNA mediated depletion of hnRNP H contributes to partial rescue of the IR splicing defect. These data demonstrate that coordinated physical and functional interactions between hnRNP H, CUG‐BP1 and MBNL1 dictate IR splicing in normal and DM1 myoblasts.