Compartment-specific aggregases direct distinct nuclear and cytoplasmic aggregate deposition

• Published in: The EMBO journal Vol. 34; no. 6; pp. 778 - 797
• Main Authors: Miller, Stephanie BM, Ho, Chi-Ting, Winkler, Juliane, Khokhrina, Maria, Neuner, Annett, Mohamed, Mohamed YH, Guilbride, D Lys, Richter, Karsten, Lisby, Michael, Schiebel, Elmar, Mogk, Axel, Bukau, Bernd
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 12.03.2015; BlackWell Publishing Ltd
• Subjects: Amino Acid Transport Systems - metabolism; Amino Acid Transport Systems - physiology; Blotting, Western; Cell Compartmentation - physiology; chaperones; Cytoplasm; Cytosol - metabolism; Deoxyribonucleic acid; DNA; Enzymes; Heat-Shock Proteins - metabolism; Heat-Shock Proteins - physiology; HeLa Cells; Humans; Image Processing, Computer-Assisted; Microscopy, Fluorescence; Microscopy, Immunoelectron; Models, Biological; Protein Aggregates - physiology; protein aggregation; protein disaggregation; Protein Folding; proteostasis; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae - physiology; Saccharomyces cerevisiae Proteins - metabolism; Saccharomyces cerevisiae Proteins - physiology; Time-Lapse Imaging; ubiquitin-proteasome system; Ubiquitination; ubiquitin–proteasome system; protein disaggregation; proteostasis; chaperones; protein aggregation
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.201489524

Disruption of the functional protein balance in living cells activates protective quality control systems to repair damaged proteins or sequester potentially cytotoxic misfolded proteins into aggregates. The established model based on Saccharomyces cerevisiae indicates that aggregating proteins in the cytosol of eukaryotic cells partition between cytosolic juxtanuclear (JUNQ) and peripheral deposits. Substrate ubiquitination acts as the sorting principle determining JUNQ deposition and subsequent degradation. Here, we show that JUNQ unexpectedly resides inside the nucleus, defining a new intranuclear quality control compartment, INQ, for the deposition of both nuclear and cytosolic misfolded proteins, irrespective of ubiquitination. Deposition of misfolded cytosolic proteins at INQ involves chaperone‐assisted nuclear import via nuclear pores. The compartment‐specific aggregases, Btn2 (nuclear) and Hsp42 (cytosolic), direct protein deposition to nuclear INQ and cytosolic (CytoQ) sites, respectively. Intriguingly, Btn2 is transiently induced by both protein folding stress and DNA replication stress, with DNA surveillance proteins accumulating at INQ. Our data therefore reveal a bipartite, inter‐compartmental protein quality control system linked to DNA surveillance via INQ and Btn2. Synopsis ‘Juxtanuclear’ deposits of misfolded protein in fact reside in a new intranuclear quality control compartment (INQ). INQ formation is dependent on Btn2, while cytosolic protein deposition is mediated by the Hsp42 aggregase. Proteotoxic stress in yeast results in organized sequestration of misfolded proteins at cytosolic CytoQ and nuclear INQ (former JUNQ) deposition sites. INQ deposition does not rely on substrate ubiquitination and does not target sequestered proteins for degradation. CytoQ and INQ formation relies on compartment‐specific aggregases, the cytosolic Hsp42 and the nuclear Btn2. DNA replication stress triggers Btn2‐dependent protein sequestration, linking cellular mechanisms coping with protein and DNA stress. ‘Juxtanuclear’ deposits of misfolded protein in fact reside in a new intranuclear quality control compartment (INQ). INQ formation is dependent on Btn2, while cytosolic protein deposition is mediated by the Hsp42 aggregase.