Nuclear accumulation of expanded PABP2 gene product in oculopharyngeal muscular dystrophy

Autosomal dominant oculopharyngeal muscular dystrophy (OPMD) is an adult-on set disease caused by (GCG) repeat expansions in exon 1 of the poly(A) bind ing protein 2 gene (PABP2). To elucidate the molecular mechanism underlying the disease, we raised an antiserum against a synthetic peptide fragment p redicted from PABP2 cDNA. The peptide corresponded to amino acids 271-291 w here a cluster of posttranslational arginine methylation occurs. We examine d the subcellular localization of PABP2 in muscle specimens from five patie nts with OPMD, 14 patients with various neuromuscular disorders, and three normal controls. All Japanese patients with OPMD have been shown to have ex panded (GCG)(8, 9, or 11) mutations in PABP2, as well as intranuclear tubul ofilamentous inclusions (ITFI) of 8.5 nm. None of 50 separate Japanese cont rol individuals were shown to have expanded (GCG) repeat in PABP2. Positive immunoreaction for polyclonal PABP2 was confined to the intranuclear aggre gates of muscle fibers exclusively in patients with OPMD. Frequency of the nuclei positive for PABP2 (2%) was similar to that of ITFI detected by elec tron microscopy (2.5%). There was no apparent relationship between the freq uency of PABP2-positive intranuclear aggregates and the severity of muscle fiber damage. In contrast, nuclear immunoreaction was not detected in any s amples from normal controls or from other neuromuscular diseases. These res ults suggest the presence of molecular modification of the product of expan ded (GCG) repeat in PABP2, since the synthetic antigen peptide may not reco gnize a highly dimethylated cluster of arginine residues of the native PABP 2, but may recognize the mutated form. Nuclear accumulation of expanded PAB P2 product implies a causative role for ITFI. (C) 2000 John Wiley & Sons, I nc.