Chaperone-mediated mechanisms of cellular proteostasis

PROJECT SUMMARY A broad range of major diseases ranging from diabetes to neurodegenerative disorders including Alzheimer's (AD), Parkinson's (PD) and Huntington's (HD) diseases have been linked to protein misfolding and aggregation. Normal protein homeostasis (proteostasis) in the cytosol and nucleus is maintained by networks of factors that promote protein folding (molecular chaperones) or clearance of terminally misfolded substrates (ubiquitin-proteasome system (UPS), autophagy). Cells grow and proliferate under the constant threat of intrinsic and extrinsic proteotoxic stressors including reactive oxygen species (ROS), exogenous oxidants and reactive electrophiles. However, the interface between proteostasis and cellular reduction-oxidation (redox) buffering pathways, namely the thioredoxin and glutathione systems, is not well understood. Our long-term goal is a comprehensive understanding of the biological roles of cytoprotective chaperones, the machinery employed to maintain redox balance and the interplay between them. In this MIRA application we define two independent themes that define our future research program. In the first line of investigation, we will examine redox modulation of cytoplasmic spatial protein quality control and degradation, empowered by our discoveries that the sequestrase Hsp42 accumulates with misfolded proteins and is required for optimal growth in redox-deficient yeast cells that lack a functional thioredoxin system. We have also uncovered a new arm of the endoplasmic reticulum-based unfolded protein response (UPR) pathway that is activated in thioredoxin-deficient cells and operates independently of the primary UPR transcription factor Hac1; we will elucidate the mechanism and biological relevance of this alternate cytoprotective system. The second broad direction will expand our studies of metazoan chaperone mechanisms with both biochemical and animal-based studies using Drosophila based on our discovery of a novel intrinsically disordered region (IDR) in fly and human Hsp110 chaperones with powerful anti-aggregation and anti-amyloid properties. The work outlined in this proposal will expand on our past successful studies of cellular redox and protein quality control networks, exploiting tractable yeast and fly model systems. These results in turn will guide future development of therapeutic interventions targeting ROS- and protein quality control-based disorders.