Protein aggregation and stress response in yeast defective for the ubiquitin-proteasome system

• Main Author: Thng, Yu Xuan
• Other Authors: Choe Young Jun
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Science::Biological sciences
• Online Access: https://hdl.handle.net/10356/166464
• Institution: Nanyang Technological University

Cdc48 is an ATPase chaperone for ER ubiquitinated protein translocation. Cim3 is a 19S regulatory ATPase subunit that unfolds polyubiquitylated substrates to feed them into the proteasomal catalytic core. The dynamic control of protein homeostasis via ubiquitin-proteasome system (UPS) is crucial to maintain optimal cellular encironments, and dysregulation can manifest as neurodegenerative diseases. Here, I explored the genetic interactions between CDC48 and CIM3 and their downstream effects following aberrant protein accumulation. Using temperature-sensitive cdc48-3, cim3-1 and cdc48-3/cim3-1 strains cell viability was examined. Unexpectedly, although cdc48-3 showed reduced growth compared to wild-type (WT), cdc48-3/cim3-1 reflected minimal change. Further, UPS impairment significantly activated unfolded protein response (UPR) and heat shock response (HSR). Protein aggregate formation is a hallmark of neurodegenerative proteinopathies. To investigate how protein quality control proceeds an impaired UPS, I followed the the fate of metastable proteins (LUCIDM-GFP and UBC9TS-GFP), which misfold at higher temperatures. Fluorescence microscopy revealed both proteins form persistent aggregates in all strains except UBC9TS-GFP in WT. Together, my results highlighted that although UPS-impaired cdc48-3/cim3-1 exhibits an overall suppression of misfolded protein clearance, alternative pathways that compensate impaired UPS and reduce cellular toxicity are likely present. Further investigations are necessary to elucidate the recovery effects in cdc48-3/cim-1.