Antiprion drugs 6-aminophenanthridine and guanabenz reduce PABPN1 toxicity and aggregation in oculopharyngeal muscular dystrophy.
Bottom Line: We show that deletions of the ribosomal DNA locus reduce OPMD phenotypes and act synergistically with sub-effective doses of 6AP.In a complementary approach, we demonstrate that ribosomal RNA accelerates in vitro fibril formation of PABPN1 N-terminal domain.These results reveal the conserved role of ribosomal RNA in different protein aggregation disorders and identify 6AP and GA as general anti-aggregation molecules.
Affiliation: mRNA Regulation and Development, Institut de Génétique Humaine, CNRS UPR 1142, Montpellier Cedex 5, France.Show MeSH
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Mentions: The ribosomal RNA has been identified as a specific cellular target of both 6AP and GA. Both drugs bind specifically to several common positions in domain V of the large ribosomal RNA and these interactions prevent the ribosomal RNA-mediated activity in protein folding, as assessed in vitro and in an in vivo test in bacteria (Tribouillard-Tanvier et al, 2008b). If the beneficial effect of 6AP and GA on OPMD in Drosophila also results from a reduced activity of the large ribosomal RNA, a similar beneficial effect might be observed with mutants affecting ribosomal RNA activity. The ribosomal DNA locus, called bobbed (bb) in Drosophila, is composed of 120–240 tandem repeats on each of chromosomes X and Y. These repeats encode the 18S, 5.8S, 2S and 28S ribosomal RNA (Long & Dawid, 1980). We used bbN, a weak allele of bb, in which a small number of repeats is deleted, and Df(1)17-87, a complete deletion of the region including the whole bb locus, to determine whether genetically decreasing the copy number of ribosomal DNA repeats would affect OPMD phenotypes. We verified that none of the bb mutant combinations showed abnormal wing posture independently of OPMD. Each of the bb deletions alone had no significant effect on the percentage of OPMD flies with wing posture defects. However, when both deletions (bbN/Df(1)17-87) were combined in OPMD flies, we observed a significant decrease in the number of these flies showing wing position defects (Fig 6B). To determine whether the beneficial effect of 6AP on OPMD could occur through the modulation of ribosomal RNA activity, we analyzed if 6AP could act synergistically with a reduction of the copy number of ribosomal DNA repeats. Neither heterozygous bbN/+ and Df(1)17-87/+ mutations, nor 6AP at 250 µM had an effect on OPMD wing position defects (Fig 2A, 6B). However, the combination of both bbN/+ or Df(1)17-87/+ and 250 µM of 6AP strongly decreased the percentage of OPMD flies with wing posture defects (Fig 6C). This shows that 6AP and deletions of the ribosomal DNA locus act synergistically and strongly suggests that the ribosomal RNA is also a cellular target of 6AP in Drosophila. It should be noted that, because the survival of bbN/Df(1)17-87 flies raised on DMSO alone or 400 µM of 6AP was very low (<10%), wing position was not scored in these conditions.
Affiliation: mRNA Regulation and Development, Institut de Génétique Humaine, CNRS UPR 1142, Montpellier Cedex 5, France.