title: HuR Mediates Changes in the Stability of AChR β-Subunit mRNAs after Skeletal Muscle Denervation.
abstract: Acetylcholine receptors (AChRs) are heteromeric membrane proteins essential for neurotransmission at the neuromuscular junction. Previous work showed that muscle denervation increases expression of AChR mRNAs due to transcriptional activation of AChR subunit genes. However, it remains possible that post-transcriptional mechanisms are also involved in controlling the levels of AChR mRNAs following denervation. We examined whether post-transcriptional events indeed regulate AChR β-subunit mRNAs in response to denervation. First, in vitro stability assays revealed that the half-life of AChR β-subunit mRNAs was increased in the presence of denervated muscle protein extracts. A bioinformatics analysis revealed the existence of a conserved AU-rich element (ARE) in the 3'-untranslated region (UTR) of AChR β-subunit mRNA. Furthermore, denervation of mouse muscle injected with a luciferase reporter construct containing the AChR β-subunit 3'UTR, caused an increase in luciferase activity. By contrast, mutation of this ARE prevented this increase. We also observed that denervation increased expression of the RNA-binding protein human antigen R (HuR) and induced its translocation to the cytoplasm. Importantly, HuR binds to endogenous AChR β-subunit transcripts in cultured myotubes and in vivo, and this binding is increased in denervated versus innervated muscles. Finally, p38 MAPK, a pathway known to activate HuR, was induced following denervation as a result of MKK3/6 activation and a decrease in MKP-1 expression, thereby leading to an increase in the stability of AChR β-subunit transcripts. Together, these results demonstrate the important contribution of post-transcriptional events in regulating AChR β-subunit mRNAs and point toward a central role for HuR in mediating synaptic gene expression.
  
  
  CONCLUSIONS
  Muscle denervation is a convenient model to examine expression of genes encoding proteins of the neuromuscular junction, especially acetylcholine receptors (AChRs). Despite the accepted model of AChR regulation, which implicates transcriptional mechanisms, it remains plausible that such events cannot fully account for changes in AChR expression following denervation. We show that denervation increases expression of the RNA-binding protein HuR, which in turn, causes an increase in the stability of AChR β-subunit mRNAs in denervated muscle. Our findings demonstrate for the first time the contribution of post-transcriptional events in controlling AChR expression in skeletal muscle, and points toward a central role for HuR in mediating synaptic development while also paving the way for developing RNA-based therapeutics for neuromuscular diseases.
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and.
authors.forename: Olivier R
authors.initials: OR
authors.lastname: Joassard
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and.
authors.forename: Guy
authors.initials: G
authors.lastname: Bélanger
authors.affiliation: CESEM, CNRS UMR 8194, University of Paris Descartes, F75270 Paris Cédex, France.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Karmouch
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and.
authors.forename: John A
authors.initials: JA
authors.lastname: Lunde
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and.
authors.forename: Anu H
authors.initials: AH
authors.lastname: Shukla
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and.
authors.forename: Angèle
authors.initials: A
authors.lastname: Chopard
authors.affiliation: CESEM, CNRS UMR 8194, University of Paris Descartes, F75270 Paris Cédex, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Legay
authors.affiliation: Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada, and jasmin@uottawa.ca.
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Jasmin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051959:ELAV Proteins / Q000235:genetics / Q000378:metabolism*; D000067780:ELAV-Like Protein 1; D005260:Female; D006614:Hindlimb / Q000294:innervation; D051379:Mice; D009121:Muscle Denervation; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation* / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism*
chemical_list: D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D021122:Protein Subunits; D011950:Receptors, Cholinergic
keywords: AChR β-subunit mRNA; HuR; p38 MAPK; skeletal muscle denervation