Muscleblind Protein-Protein Interactions: Implications for RNA Biology and Myotonic Dystrophy Type 1 Pathogenesis

RNA granules are membrane-less condensates composed of various RNA-protein complexes, which are essential for post-transcriptional regulation of gene expression. However, RNA granules also have the potential to form the basis of disease pathogenesis, such as in Myotonic Dystrophy Type 1 (DM1). DM1 is a monogenic disorder in which CTG repeats in the gene DMPK are expanded. When transcribed, these CUG repeats form toxic RNA foci that sequester the Muscleblind-like (MBNL) family of RNA binding proteins (RBPs) in the nucleus. In a non-disease setting, MBNLs normally regulate alternative splicing (AS) and localize mRNA, though the mechanisms underlying the later had remained unclear. Using imaging and biochemical approaches, we demonstrated that kinesin motor proteins KIF1Bα and KIF1C selectively interact with and transport MBNL1 granules. This finding and the lack of a comprehensive MBNL interactome motivated us to conduct proteomics on immunoprecipitated MBNL1. In addition to numerous novel interactors, we found that MBNL interacts with itself. The exact forces that hold RNA granules together are not well understood despite their importance in RNA granule dynamics. We hypothesized that disulfide bonds are involved in MBNL dimerization, a process that influences MBNL1-mediated regulation of AS and DM1 pathogenesis. Here we identify the precise cysteine residues responsible for MBNL dimerization. We also use cysteine mutants and RNA sequencing to highlight the importance of MBNL1 dimerization in regulation of AS. Finally, we demonstrate that MBNL1 dimerization is needed to maintain DM1 foci integrity. These results provide insight into the pathological mechanisms of DM1 and suggest other RBPs might similarly dimerize to regulate function.

Date

2024-04-26

Resource Type

Text

Resource Subtype

Dissertation

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