UC Irvine

Proteostasis networks are central to maintaining cellular homeostasis, and their dysregulation contributes to cancer, neurodegeneration, and aging-related pathologies. While proteasome inhibition has been widely explored therapeutically, comparatively little is understood about the biological consequences of small-molecule proteasome activation. This dissertation investigates how pharmacologic stimulation of the 20S proteasome reshapes stress response signaling, cellular metabolism, and proliferation, and evaluates induced-proximity strategies to enhance targeted protein degradation.We investigated whether small-molecule 20S proteasome activators could modulate IRE1 driven unfolded protein response (UPR) signaling through XBP1. Pre-treatment with a 20S activator prior to ER stress induction attenuated XBP1 signaling, whereas post-induction treatment had no effect. These results highlight a temporal window in which proteasome activation can bolster adaptive stress responses and modulate signaling outcomes. We then addressed concerns that enhanced 20S proteasome activity might promote uncontrolled cell proliferation or metabolic dysregulation. Using two 20S core particle (CP) stimulators, we measured proliferation rates and expression of growth- and metabolism-associated genes across low- and high-passage cell lines. xvii While younger cells showed no significant changes, older passages exhibited modest transcriptional responses without corresponding increases in proliferation. Collectively, these findings demonstrate that 20S CP stimulation does not inherently drive cellular overgrowth and suggest that proteasome enhancement can be achieved without compromising homeostasis. Additionally, we expanded the proof-of-concept ByeTAC strategy from BRD4 to a broader exploration of ubiquitin-independent proteasomal targeting. Systematic studies revealed that substrate degradability is governed by linker geometry, protein accessibility, and structural topology. These insights define the biophysical constraints that determine successful proteasome recruitment and inform the rational design of next-generation ByeTAC molecules capable of targeting new proteins. These studies advance our understanding of pharmacological proteasome modulation and direct proteasomal targeting. They demonstrate that the proteasome activation can selectively enhance stress adaptation, maintain cellular homeostasis, and support the rational design of targeted degradation platforms, providing a foundation for future therapeutic applications.