Inhibition of RNA splicing triggers CHMP7 nuclear entry, impacting TDP-43 function and leading to the onset of ALS cellular phenotypes

Amyotrophic lateral sclerosis (ALS) is linked to the reduction of certain nucleoporins in neurons. Increased nuclear localization of charged multivesicular body protein 7 (CHMP7), a protein involved in nuclear pore surveillance, has been identified as a key factor damaging nuclear pores and disrupting transport. Using CRISPR-based microRaft, followed by gRNA identification (CRaft-ID), we discovered 55 RNA-binding proteins (RBPs) that influence CHMP7 localization, including SmD1, a survival of motor neuron (SMN) complex component. Immunoprecipitation-mass spectrometry (IP-MS) and enhanced crosslinking and immunoprecipitation (CLIP) analyses revealed CHMP7’s interactions with SmD1, small nuclear RNAs, and splicing factor mRNAs in motor neurons (MNs). ALS induced pluripotent stem cell (iPSC)-MNs show reduced SmD1 expression, and inhibiting SmD1/SMN complex increased CHMP7 nuclear localization. Crucially, overexpressing SmD1 in ALS iPSC-MNs restored CHMP7’s cytoplasmic localization and corrected STMN2 splicing. Our findings suggest that early ALS pathogenesis is driven by SMN complex dysregulation. [Display omitted] •CRaft-ID identifies key regulators of CHMP7 nuclear localization•CHMP7 interacts with snRNP assembly factors, SM proteins, and Gemin proteins•CHMP7 binds snRNAs and mRNAs that encode essential splicing factors•Inhibition of SMN complex triggers CHMP7 nuclear entry, affecting TDP-43 function Al-Azzam et al. reveal that SmD1, a member of the SMN complex, regulates CHMP7 translocation. Reduced SmD1 expression in sporadic ALS leads to CHMP7 nuclear translocation, while overexpression prevents it, highlighting SmD1’s role in ALS pathogenesis.