PolyQ Proteins Interfere with Nuclear Degradation of Cytosolic Proteins by Sequestering the Sis1p Chaperone

Abstract

Dysfunction of protein quality control contributes to the cellular pathology of polyglutamine (polyQ) expansion diseases and other neurodegenerative disorders associated with aggregate deposition. Here we analyzed how polyQ aggregation interferes with the clearance of misfolded proteins by the ubiquitin-proteasome system (UPS). We show in a yeast model that polyQ-expanded proteins inhibit the UPS-mediated degradation of misfolded cytosolic carboxypeptidase Y(∗) fused to green fluorescent protein (GFP) (CG(∗)) without blocking ubiquitylation or proteasome function. Quantitative proteomic analysis reveals that the polyQ aggregates sequester the low-abundant and essential Hsp40 chaperone Sis1p. Overexpression of Sis1p restores CG(∗) degradation. Surprisingly, we find that Sis1p, and its homolog DnaJB1 in mammalian cells, mediates the delivery of misfolded proteins into the nucleus for proteasomal degradation. Sis1p shuttles between cytosol and nucleus, and its cellular level limits the capacity of this quality control pathway. Upon depletion of Sis1p by polyQ aggregation, misfolded proteins are barred from entering the nucleus and form cytoplasmic inclusions.

SOD1 aggregation in ALS mice shows simplistic test tube behavior

“…2B). Conformationwise, the precursor of SOD1 fibrillation seems, thus, equivalent to those of intrinsically disordered proteins, like α-synuclein (21), polyQ (30), and the Aβ-peptide (29,31). Changing by mutation the SOD1 stability in ALS mice yields similar results, manifested in an R 2 = 0.92 correlation between survival times and tissue concentration of unfolded SOD1 (Fig.…”

“…Involvement of D. Unlike other precursors of neurodegenerative disease (21,29,30), the SOD1 monomer is not at all times disordered but can hide its sticky sequence material by folding up into a well-ordered and perfectly soluble β-barrel structure (7) (Fig. 1C).…”

Intracellular Dynamics of the Ubiquitin-Proteasome-System

“…Through these non-invasive techniques, the localization of the proteasome in growing yeast and highly proliferating cancer cells has been elucidated to be primarily nuclear ( Enenkel et al , 1998; Laporte et al , 2008; McDonald & Byers, 1997; Russell et al , 1999). In line with this finding, increasing evidence in the literature suggests that certain misfolded proteins are imported from the cytoplasm into the nucleus solely for proteasomal degradation ( Park et al , 2013; Prasad et al , 2010). Conversely, transient nuclear proteins are exported into the cytoplasm for proteolysis, indicating a dynamic shift of proteasomal substrates between the nucleus and cytoplasm ( Chen & Madura, 2014a).…”

Novel insights into renal d-amino acid oxidase accumulation: propiverine changes DAAO localization and peroxisomal size in vivo

“…The latter, however, would imply that these proteins are actively imported as a result of the inhibition of their original function and thus were marked for protein degradation. Indeed, recent studies provide compelling evidence that cytosolic misfolded proteins are actively imported into the nucleus for proteasomal degradation (Prasad et al 2010;Park et al 2013;Shibata and Morimoto 2014). Having found that the major fraction of 20S proteasomes is located in nuclei of both placebo-and propiverinetreated F344 rats and that the BioGRID interaction database provides evidence that DAAO interacts with KLHL42, a substrate-specific adapter of an E3 ubiquitin-protein ligase, 1 we wanted to demonstrate that proteins, e.g., DAAO and catalase are imported into the nucleus for proteasomal degradation.…”