INVESTIGATION OF THE NOVEL INTERACTION BETWEEN THE HUMAN RECEPTOR FOR ACTIVATED C KINASE 1 (RACK1) AND 26S PROTEASOME

Abstract

The 26S proteasome is a highly conserved protein degradation complex. It facilitates ATP- and ubiquitin-dependent protein degradation and plays a central role in the ubiquitin-proteasome system (UPS). The proper function of the proteasome is essential for maintaining protein homeostasis by removing damaged and misfolded proteins as well as regulating protein turnover under various physiological and pathological conditions. RACK1, a highly conserved WD40 repeats scaffolding protein, is known for its ability to coordinate diverse protein-protein interactions. RACK1 is involved in the protein homeostasis network by serving as a platform for recruiting protein substrate or co-factors, as well as organizing protein complexes formation. Interestingly, RACK1’s involvement in the regulation of proteasome function has not been thoroughly explored. This study identified a novel interaction between RACK1 and the proteasome, shedding light on RACK1’s potential role in regulating proteasome activity. RACK1 was found to directly interact with 26S proteasome preferentially with 19S regulatory proteasome subcomplex through the N-terminal three WD repeat. RACK1 selectively enhances the proteasome’s trypsin-like activity in a purified protein system without affecting other catalytic activities. In the cellular context, RACK1 was shown to play a role in maintaining basal proteasome gene expression independently of NRF1 and NRF2 activation, the master transcription factors regulating proteasome genes. Furthermore, RACK1 was found to mitigate stress-induced NRF2 and proteasome gene expression, potentially through its role in maintaining proteasome activity and mitigating oxidative stress. These findings provide valuable insights into the regulatory interplay between RACK1 and the proteasome. In summary, this study establishes RACK1 as a novel and multifaceted regulator of proteasome activity, participating in both direct modulation and transcriptional regulation of proteasome function. These findings expand our understanding of the mechanisms governing proteasome function and highlight the potential of RACK1 as a therapeutic target in diseases associated with proteasome dysfunction and impaired protein homeostasis.