title: HuD interacts with survival motor neuron protein and can rescue spinal muscular atrophy-like neuronal defects.
abstract: Spinal muscular atrophy is an autosomal-recessive neuromuscular disease caused by disruption of the survival of motor neuron (SMN) gene, which promotes cytoplasmic assembly of the splicing core machinery. It remains unclear how a deficiency in SMN results in a disorder leading to selective degeneration of lower motor neurons. We report here that SMN interacts with RNA-binding protein HuD in neurites of motorneuron-derived MN-1 cells. This interaction is mediated through the Tudor domain of SMN and, importantly, naturally occurring Tudor mutations found in patients with severe spinal muscular atrophy (SMA) completely abrogate the interaction, underscoring its relevance to the disease process. We also characterized a regulatory pathway involving coactivator-associated arginine methyltransferase 1 (CARM1) and HuD. Specifically, we show that CARM1 expression is rapidly downregulated, at the protein level, following induction of differentiation through retinoid and neurotrophic signaling. Using purified proteins, we demonstrate that methylation of HuD by CARM1 reduces its interaction with the p21(cip1/waf1) mRNA, showing that CARM1 can directly influence RNA-binding activity. We further demonstrate that this CARM1-dependent regulatory switch mainly controls the activity of HuD in promoting cell-cycle exit, whereas the interaction between HuD and SMN is required for proper recruitment of HuD and its mRNA targets in neuronal RNA granules. Finally, we were able to rescue SMA-like defects in a hypomorphic Smn knockdown MN-1 cell line through overexpression of HuD. Together, these findings extend our understanding of specific role(s) of SMN in motor neurons and provide crucial insights into potential new avenues for SMA therapeutic strategies.
authors.affiliation: Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario,Canada K1H 8M5.
authors.forename: Lisa
authors.initials: L
authors.lastname: Hubers
authors.forename: Hector
authors.initials: H
authors.lastname: Valderrama-Carvajal
authors.forename: Janik
authors.initials: J
authors.lastname: Laframboise
authors.forename: Janie
authors.initials: J
authors.lastname: Timbers
authors.forename: Gabriel
authors.initials: G
authors.lastname: Sanchez
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Côté
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics; D002460:Cell Line; D051959:ELAV Proteins / Q000378:metabolism*; D000067779:ELAV-Like Protein 4; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D015151:Immunoblotting; D008745:Methylation; D051379:Mice; D009134:Muscular Atrophy, Spinal / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009414:Nerve Growth Factors; D016501:Neurites / Q000378:metabolism*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D054730:Protein Interaction Domains and Motifs; D011484:Protein-Arginine N-Methyltransferases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D012177:Retinol-Binding Proteins; D015398:Signal Transduction; D055533:Survival of Motor Neuron 1 Protein / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D051959:ELAV Proteins; D000067779:ELAV-Like Protein 4; C498011:Elavl4 protein, mouse; D009414:Nerve Growth Factors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012177:Retinol-Binding Proteins; C526472:Smn1 protein, mouse; D055533:Survival of Motor Neuron 1 Protein; D011484:Protein-Arginine N-Methyltransferases; C119966:coactivator-associated arginine methyltransferase 1