title: The 26S proteasome drives trinucleotide repeat expansions.
abstract: Trinucleotide repeat (TNR) expansion is the causative mutation for at least 17 inherited neurological diseases. An important question in the field is which proteins drive the expansion process. This study reports that the multi-functional protein Sem1 is a novel driver of TNR expansions in budding yeast. Mutants of SEM1 suppress up to 90% of expansions. Subsequent analysis showed that Sem1 facilitates expansions via its function in the 26S proteasome, a highly conserved multi-subunit complex with both proteolytic and non-proteolytic functions. The proteolytic function of the 26S proteasome is relevant to expansions, as mutation of additional proteasome components or treatment of yeast with a proteasome inhibitor suppressed CTG•CAG expansions. The 26S proteasome also drives expansions in human cells. In a human astrocytic cell line, siRNA-mediated knockdown of 26S proteasome subunits PSMC5 or PSMB3 reduced expansions. This expansion phenotype, both in yeast and human cells, is dependent on the proteolytic activity of the proteasome rather than a stress response owing to depletion of free ubiquitin. Thus, the 26S proteasome is a novel factor that drives expansions in both yeast and human cells by a mechanism involving protein degradation.
authors.affiliation: Centre for Chromosome Biology, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland.
authors.forename: Claire
authors.initials: C
authors.lastname: Concannon
authors.forename: Robert S
authors.initials: RS
authors.lastname: Lahue
mesh_terms: D001253:Astrocytes / Q000201:enzymology; D002478:Cells, Cultured; D006801:Humans; D009154:Mutation; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D019680:Trinucleotide Repeat Expansion; D025801:Ubiquitin / Q000235:genetics
chemical_list: C117424:SEM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex