Glutamine/proline-rich PQE-1 proteins protect Caenorhabditis elegans neurons from huntingtin polyglutamine neurotoxicity

Abstract

Huntington's disease is a progressive neurodegenerative disease caused by a polyglutamine (polyQ) repeat expansion in the huntingtin protein [Huntington's Disease Collaborative Research Group (1993) Cell 72, 971-983]. To understand the mechanism by which polyQ repeats cause neurodegeneration and cell death, we modeled polyQ neurotoxicity in Caenorhabditis elegans. In our model, expression of N-terminal fragments of human huntingtin causes polyQ-dependent degeneration of neurons. We conducted a genetic screen to identify proteins that protect neurons from the toxic effects of expanded polyQ tracts. Loss of polyQ enhancer-1 (pqe-1) gene function strongly and specifically exacerbates neurodegeneration and cell death, whereas overexpression of a pqe-1 cDNA protects C. elegans neurons from the toxic effects of expanded huntingtin fragments. A glutamineproline-rich domain, along with a charged domain, is critical for PQE-1 protein function. Analysis of pqe-1 suggests that proteins exist that specifically protect neurons from the toxic effects of expanded polyQ disease proteins.

Fig. 1.

Alternative splicing of pqe-1 yields multiple protein isoforms. pqe-1 maps genetically to chromosome III (−1.91 map units) to the right of dpy-17. On the basis of our analysis, pqe-1 corresponds to F52C9.8 and encodes at least three different proteins generated by differential mRNA splicing. The exonic structures of pqe-1 splice forms are depicted. Exons encoding the Q/P-rich domain are illustrated as white boxes. Black boxes represent the exons encoding the charged region. Sequences corresponding to the exonuclease domain are illustrated as gray boxes. The approximate locations of pqe-1 mutations are labeled: * for stop codons, I for rt64 M1I, and N for rt67 S709N. The regions encoding putative nuclear localization signals are marked by #. The PQE-1A protein sequence is shown in Fig. 3, which is published as supporting information on the PNAS web site.

Fig. 2.

PQE-1B and PQE-1C are nuclear proteins. Subcellular localization of PQE-1B:GFP and PQE-1C:GFP was examined by using the osm-10 promoter to drive transgene expression. The PQE-1B:GFP and PQE-1C:GFP fusion proteins were detected in the nucleus of the ASH neurons of live animals (A and D, respectively). The cell bodies of the corresponding ASH neurons were visualized by dye filling with DiD (B and E, respectively). PQE-1B:GFP and PQE-1C:GFP were detected in the ASH nuclei of Bowin's fixed animals (35) by using affinity-purified antisera that recognize the C and N termini of PQE-1 (C and F, respectively). PQE-1B:GFP and PQE-1C:GFP are still localized to the nucleus in animals expressing Htn-Q150 (not shown). (Bar = 0.5 μm.)