The N-terminal cysteine is a dual sensor of oxygen and oxidative stress

  • Proc Natl Acad Sci U S A. 2021 Dec 14;118(50):e2107993118. doi: 10.1073/pnas.2107993118.
Ah Jung Heo  1  2  3 ,  Su Bin Kim  1  2 ,  Chang Hoon Ji  1  2  3 ,  Dohyun Han  4 ,  Su Jin Lee  1  2 ,  Su Hyun Lee  1  2 ,  Min Ju Lee  1  2 ,  Ji Su Lee  1  2 ,  Aaron Ciechanover  5 ,  Bo Yeon Kim  6 ,  Yong Tae Kwon  7  2  3  8
Affiliations
  • 1. Cellular Degradation Biology Center, College of Medicine, Seoul National University, Seoul 03080, Korea.
  • 2. Department of Biomedical Sciences, College of Medicine, Seoul National University, Seoul 03080, Korea.
  • 3. AUTOTAC Bio Inc., Jongno-gu, Seoul 03077, Korea.
  • 4. Transdisciplinary Department of Medicine & Advanced Technology, Seoul National University Hospital, Seoul 03082, Korea.
  • 5. The Rappaport Family Technion Integrated Cancer Center, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 3109601, Israel.
  • 6. World Class Institute, Anticancer Agents Research Center, Korea Research Institute of Bioscience and Biotechnology, Ochang, Cheongwon 28116, Korea; [email protected] [email protected].
  • 7. Cellular Degradation Biology Center, College of Medicine, Seoul National University, Seoul 03080, Korea; [email protected] [email protected].
  • 8. Ischemic/Hypoxic Disease Institute, College of Medicine, Seoul National University, Seoul 03080, Korea.
PMID: 34893540 DOI: 10.1073/pnas.2107993118
Abstract

Cellular homeostasis requires the sensing of and adaptation to intracellular oxygen (O2) and Reactive Oxygen Species (ROS). The Arg/N-degron pathway targets proteins that bear destabilizing N-terminal residues for degradation by the Proteasome or via Autophagy. Under normoxic conditions, the N-terminal Cys (Nt-Cys) residues of specific substrates can be oxidized by dioxygenases such as plant cysteine oxidases and cysteamine (2-aminoethanethiol) dioxygenases and arginylated by ATE1 R-transferases to generate Arg-CysO2(H) (R-CO2). Proteins bearing the R-CO2 N-degron are targeted via Lys48 (K48)-linked ubiquitylation by UBR1/UBR2 N-recognins for proteasomal degradation. During acute hypoxia, such proteins are partially stabilized, owing to decreased Nt-Cys oxidation. Here, we show that if hypoxia is prolonged, the Nt-Cys of regulatory proteins can be chemically oxidized by ROS to generate Arg-CysO3(H) (R-CO3), a lysosomal N-degron. The resulting R-CO3 is bound by KCMF1, a N-recognin that induces K63-linked ubiquitylation, followed by K27-linked ubiquitylation by the noncanonical N-recognin UBR4. Autophagic targeting of Cys/N-degron substrates is mediated by the autophagic N-recognin p62/SQTSM-1/Sequestosome-1 through recognition of K27/K63-linked ubiquitin (Ub) chains. This Cys/N-degron-dependent reprogramming in the proteolytic flux is important for cellular homeostasis under both chronic hypoxia and oxidative stress. A small-compound ligand of p62 is cytoprotective under oxidative stress through its ability to accelerate proteolytic flux of K27/K63-ubiquitylated Cys/N-degron substrates. Our results suggest that the Nt-Cys of conditional Cys/N-degron substrates acts as an acceptor of O2 to maintain both O2 and ROS homeostasis and modulates half-lives of substrates through either the Proteasome or lysosome by reprogramming of their Ub codes.

Keywords
Arg/N-degron pathway; Cys/N-degron pathway; N-degron pathway; oxidative stress sensor; oxygen sensor.