C9orf72 Poly(PR) Dipeptide Repeats Disturb Biomolecular Phase Separation and Disrupt Nucleolar Function

Mol Cell. 2019 May 16;74(4):713-728.e6. doi: 10.1016/j.molcel.2019.03.019. Epub 2019 Apr 10.

Abstract

Repeat expansion in the C9orf72 gene is the most common cause of the neurodegenerative disorder amyotrophic lateral sclerosis (C9-ALS) and is linked to the unconventional translation of five dipeptide-repeat polypeptides (DPRs). The two enriched in arginine, poly(GR) and poly(PR), infiltrate liquid-like nucleoli, co-localize with the nucleolar protein nucleophosmin (NPM1), and alter the phase separation behavior of NPM1 in vitro. Here, we show that poly(PR) DPRs bind tightly to a long acidic tract within the intrinsically disordered region of NPM1, altering its phase separation with nucleolar partners to the extreme of forming large, soluble complexes that cause droplet dissolution in vitro. In cells, poly(PR) DPRs disperse NPM1 from nucleoli and entrap rRNA in static condensates in a DPR-length-dependent manner. We propose that R-rich DPR toxicity involves disrupting the role of phase separation by NPM1 in organizing ribosomal proteins and RNAs within the nucleolus.

Keywords: ALS; C9orf72; DPR; RNA; dipeptide repeat; intrinsically disordered region; liquid-liquid phase separation; nucleolus; nucleophosmin; ribosome.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics*
  • Amyotrophic Lateral Sclerosis / pathology
  • Arginine / genetics
  • C9orf72 Protein / genetics*
  • Cell Nucleolus / chemistry
  • Cell Nucleolus / genetics
  • Dipeptides / genetics
  • Humans
  • Nuclear Proteins / genetics*
  • Peptides / genetics
  • Poly A / genetics
  • RNA, Ribosomal / genetics
  • Repetitive Sequences, Amino Acid / genetics*

Substances

  • C9orf72 Protein
  • C9orf72 protein, human
  • Dipeptides
  • Nuclear Proteins
  • Peptides
  • RNA, Ribosomal
  • nucleophosmin
  • Poly A
  • Arginine