The Hsp70/90 cochaperone, Sti1, suppresses proteotoxicity by regulating spatial quality control of amyloid-like...

Area of Science:

• Cell Biology
• Neuroscience
• Biochemistry

Background:

• Conformational diseases involve protein misfolding into toxic, amyloid-like structures.
• Cellular mechanisms for managing these toxic proteins, such as protective aggregation, are not fully understood.
• The Hsp70 system is implicated in protein quality control.

Purpose of the Study:

• To investigate the role of the Hsp70 system in the spatial organization of toxic polyglutamine-expanded Huntingtin (Htt103Q).
• To identify cellular mechanisms that promote beneficial protein aggregation.
• To understand how Sti1 modulates the toxicity and cellular localization of amyloid-like proteins.

Main Methods:

• Utilized a high-copy suppressor screen in yeast to identify factors involved in Htt103Q aggregation.
• Manipulated Sti1 activity to observe effects on Htt103Q toxicity and foci formation.
• Assessed the impact of Sti1 on the yeast prion [RNQ+] and Rnq1 protein aggregation.
• Characterized Sti1-induced foci using thioflavin-T staining and microscopy.

Main Results:

• Sti1 modulates the aggregation and toxicity of Htt103Q; loss of Sti1 increases toxicity and hinders foci formation.
• Elevated Sti1 suppresses Htt103Q toxicity by promoting the formation of larger, benign protein assemblies.
• Sti1 also suppresses the toxicity of the yeast prion [RNQ+] by reorganizing Rnq1 into distinct foci.
• Sti1-dependent foci are perinuclear and contain amyloid-binding proteins.

Conclusions:

• Sti1, an Hsp70 cochaperone, plays a critical role in the spatial organization of amyloid-like proteins within the cytosol.
• Sti1 facilitates protective aggregation of toxic proteins into benign cellular structures.
• This regulation of protein spatial distribution by Sti1 buffers proteotoxicity, offering a potential therapeutic target for conformational diseases.