hnRNP A1 and A/B Interaction with PABPN1 in Oculopharyngeal Muscular Dystrophy

Abstract

Autosomal dominant oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disease that presents in the fifth or sixth decade. The disease is characterized by progressive eyelid drooping (ptosis), swallowing difficulties (dysphagia) and proximal limb weakness. [1][2][3][4][5][6] Pathological studies showed the presence of unique intranuclear filamentous inclusions in skeletal muscle fibers of OPMD patients. 7,8 The OPMD locus was mapped by linkage analysis to chromosome 14q11.1 9-11 and the gene was identified as PABPN1, encoding the poly(A) binding protein nuclear 1 (PABPN1, PABP2, PAB II). 12 Dominant OPMD is caused by expansion of a short GCG ABSTRACT: Background: Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive ptosis, dysphagia and proximal limb weakness. The autosomal dominant form of this disease is caused by short expansions of a (GCG) 6 repeat to (GCG) [8][9][10][11][12][13] in the PABPN1 gene. The mutations lead to the expansion of a polyalanine stretch from 10 to 12-17 alanines in the N-terminus of PABPN1. The mutated PABPN1 (mPABPN1) induces the formation of intranuclear filamentous inclusions that sequester poly(A) RNA and are associated with cell death. Methods: Human fetal brain cDNA library was used to look for PABPN1 binding proteins using yeast two-hybrid screen. The protein interaction was confirmed by GST pull-down and co-immunoprecipitation assays. Oculopharyngeal muscular dystrophy cellular model and OPMD patient muscle tissue were used to check whether the PABPN1 binding proteins were involved in the formation of OPMD intranuclear inclusions. Results: We identify two PABPN1 interacting proteins, hnRNP A1 and hnRNP A/B. When co-expressed with mPABPN1 in COS-7 cells, predominantly nuclear protein hnRNP A1 and A/B colocalize with mPABPN1 in the insoluble intranuclear aggregates. Patient studies showed that hnRNP A1 is sequestered in OPMD nuclear inclusions. Conclusions: The hnRNP proteins are involved in mRNA processing and mRNA nucleocytoplasmic export, sequestering of hnRNPs in OPMD intranuclear aggregates supports the view that OPMD intranuclear inclusions are "poly(A) RNA traps", which would interfere with RNA export, and cause muscle cell death. RÉSUMÉ: Interaction de hnRNP A1 et A/B avec PABPN1 dans la dystrophie musculaire oculopharyngée. Introduction: La dystrophie musculaire oculopharyngée (DMOP) est une maladie de l'âge adulte caractérisée par une ptose progressive des paupières, une dysphagie et une faiblesse musculaire proximale. La forme autosomique dominante est causée par de courtes expansions d'une répétition (GCG)6 à (GCG)8-13 dans le gène PABPN1. Les mutations donnent lieu à une expansion d'un tractus de polyalanine de 10 à 12-17 alanines dans la partie N-terminale de PABPN1. Le gène PABPN1 muté (PABPN1m) induit la formation d'inclusions filamenteuses intranucléaires qui séquestrent l'ARN poly(A) et entraînent la mort cellulaire. Méthodes: Une librairie d'ADNc provenant de cerveau foetal humain a été utilisée pour chercher...

Regulation of the Nuclear Poly(A)-binding Protein by Arginine Methylation in Fission Yeast

“…6, lane 4). These results are consistent with previous observations indicating that nuclear poly(A)-binding proteins form oligomers (15,51,52). Analysis of Myc immunoprecipitates prepared from extracts of rmt1-null cells that were previously transformed with plasmids expressing Myc-Pab2 and GFP-Pab2 showed a 10-fold increase in the level of GFP-Pab2 that copurified with Myc-tagged Pab2 (Fig.…”

“…Studies using cell culture models indeed correlate PABP2 oligomerization, aggregate formation, and cellular toxicity (20,51,72). Significantly, our data extend these results and describe the importance of arginine methylation in the control of Pab2 oligomerization and cellular toxicity.…”

“…binding studies indicate that the C-terminal domain of mammalian PABP2 promotes self-association (15,51). Because our data (Fig.…”

“…Interestingly, the extent of PAPB2 oligomerization is a key factor associated with the formation of nuclear aggregates found in cells of OPMD-afflicted individuals (20,51). Having established that Pab2 oligomerization was modulated by arginine methylation (Fig.…”

“…Arginine Methylation Modulates Pab2 OligomerizationOligomerization of PABP2 has been linked to the formation of nuclear aggregates and cell toxicity (51). Interestingly, in vitro 1, 4, and 7), GST-Pab2 (lanes 2, 5, and 8), and a truncated version of GST-Pab2 lacking the C-terminal arginine-rich domain (GST-Pab2⌬C28; lanes 3, 6, and 9) were incubated with poly(A)-Sepharose beads.…”