ER-trafficking triggers NRF1 ubiquitination to promote its proteolytic activation

ABSTRACT: The endoplasmic reticulum (ER) is a multifaceted organelle that plays an essential role in cellular processes such as protein folding, modification, and trafficking. It also acts as a proteostasis sensor and contributes to adaptation responses to maintain cellular homeostasis. The transcription factor NRF1 resides in the ER and is constantly transported from the ER to the cytosol for proteasomal degradation. However, when the proteasome function is defective, NRF1 escapes degradation and undergoes proteolytic cleavage by the protease DDI2, generating a transcriptionally active form that restores proteostasis, including proteasome function. Despite the importance of NRF1 in these processes, the mechanisms that regulate its proteolytic activation and transcriptional potential remain poorly understood. In this study, we utilized a functional molecular approach to elucidate the critical steps involved in NRF1 cleavage. Our results demonstrate that the ER is a crucial regulator of NRF1 function, orchestrating its ubiquitination by the ER-localized E3 ubiquitin ligase HRD1, a component of the ER-associated degradation (ERAD) pathway. Furthermore, we show that HRD1-mediated NRF1 ubiquitination is necessary for DDI2-mediated processing in cells. Notably, we found that the fusion of a ubiquitin moiety to NRF1 was sufficient to promote its proteolytic maturation by DDI2, thus bypassing the requirement for its trafficking to the ER. Our findings highlight the intricate mechanism by which NRF1 is activated by DDI2 and coordinates the transcriptional activity of an adaptation response in cells and suggest potential avenues for therapeutic interventions in conditions associated with proteasome impairment.

INSTRUMENT(S): Orbitrap Fusion, Q Exactive Plus

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Permanent Cell Line Cell

SUBMITTER: Manfredo Quadroni  

LAB HEAD: Fabio Martinon

PROVIDER: PXD041331 | Pride | 2023-09-05

REPOSITORIES: Pride