title: Cytoplasmic targeting of mutant poly(A)-binding protein nuclear 1 suppresses protein aggregation and toxicity in oculopharyngeal muscular dystrophy.
abstract: Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping, swallowing difficulties and proximal limb weakness. The autosomal dominant form of this disease is caused by a polyalanine expansion from 10 to 12-17 residues, located at the N-terminus of the poly(A)-binding protein nuclear 1 (PABPN1). A distinct pathological hallmark of OPMD is the presence of filamentous intranuclear aggregates in patients' skeletal muscle cells. Wildtype PABPN1 protein is expressed ubiquitously and was shown to be mostly concentrated in discrete nuclear domains called 'speckles'. Using an established cell- culture model, we show that most mutant PABPN1- positive (alanine expanded form) intranuclear aggregates are structures distinct from intranuclear speckles. In contrast, the promyelocytic leukaemia protein, a major component of nuclear bodies, strongly colocalized to intranuclear aggregates of mutant PABPN1. Wildtype PABPN1 can freely shuttle between the nucleus and cytoplasm. We determined whether the nuclear environment is necessary for mutant PABPN1 inclusion formation and cellular toxicity. This was achieved by inactivating the mutant PABPN1 nuclear localization signal and by generating full-length mutant PABPN1 fused to a strong nuclear export sequence. A green fluorescence protein tag inserted at the N-terminus of both wildtype PABPN1 (ala10) and mutant PABPN1 (ala17) proteins allowed us to visualize their subcellular localization. Targeting mutant PABPN1 to the cytoplasm resulted in a significant suppression of both intranuclear aggregates formation and cellular toxicity, two histological consequences of OPMD. Our results indicate that the nuclear localization of mutant PABPN1 is crucial to OPMD pathogenesis.
authors.affiliation: Center for Research in Neuroscience, McGill University, and the McGill University Health Center, 1650 Cedar Avenue, Montreal, Quebec, Canada H3G 1A4.
authors.forename: Aida
authors.initials: A
authors.lastname: Abu-Baker
authors.forename: Simon
authors.initials: S
authors.lastname: Laganiere
authors.forename: Xueping
authors.initials: X
authors.lastname: Fan
authors.forename: Janet
authors.initials: J
authors.lastname: Laganiere
authors.forename: Bernard
authors.initials: B
authors.lastname: Brais
authors.forename: Guy A
authors.initials: GA
authors.lastname: Rouleau
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002470:Cell Survival; D003593:Cytoplasm / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D002479:Inclusion Bodies / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000032:analysis / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D039141:Muscular Dystrophy, Oculopharyngeal / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D039122:Poly(A)-Binding Protein I / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D039122:Poly(A)-Binding Protein I; D007770:L-Lactate Dehydrogenase