Molecules and Cells

Korean Society for Molecular and Cellular Biology (한국분자세포생물학회)
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N-recognins UBR1 and UBR2 as central ER stress sensors in mammals

  • Ly Thi Huong Luu Le (Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine) ;
  • Seoyoung Park (Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine) ;
  • Jung Hoon Lee (Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine) ;
  • Yun Kyung Kim (Center for Brain Disorders, Brain Science Institute, Korea Institute of Science and Technology (KIST)) ;
  • Min Jae Lee (Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine)
  • Received : 2023.10.20
  • Accepted : 2023.11.22
  • Published : 2024.01.31
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Abstract

In eukaryotes, a primary protein quality control (PQC) process involves the destruction of conformationally misfolded proteins through the ubiquitin-proteasome system. Because approximately one-third of eukaryotic proteomes fold and assemble within the endoplasmic reticulum (ER) before being sent to their destinations, the ER plays a crucial role in PQC. The specific functions and biochemical roles of several E3 ubiquitin ligases involved in ER-associated degradation in mammals, on the other hand, are mainly unknown. We identified 2 E3 ligases, ubiquitin protein ligase E3 component N-recognin 1 (UBR1) and ubiquitin protein ligase E3 component N-recognin 2 (UBR2), which are the key N-recognins in the N-degron pathway and participate in the ER stress response in mammalian cells by modulating their stability. Cells lacking UBR1 and UBR2 are hypersensitive to ER stress-induced apoptosis. Under normal circumstances, these proteins are polyubiquitinated through Lys48-specific linkages and are then degraded by the 26S proteasome. In contrast, when cells are subjected to ER stress, UBR1 and UBR2 exhibit greater stability, potentially as a cellular adaptive response to stressful conditions. Although the precise mechanisms underlying these findings require further investigation, our findings show that cytoplasmic UBR1 and UBR2 have anti-ER stress activities and contribute to global PQC in mammals. These data also reveal an additional level of complexity within the mammalian ER-associated degradation system, implicating potential involvement of the N-degron pathway.

Keywords

Acknowledgement

We thank T. Tasaki and Y. T. Kwon for UBR-related plasmids and MEFs. This work was supported by grants from the National Research Foundation of Korea (2021R1A2C2008023, 2020R1A5A1019023, and RS-2023-00261784 to M.J.L.; 2021R1I1A1A01051245 to J.H.L.).

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