Hyunjoo Cha-Molstada† , Ji Eun Yuab† , Su Hyun Leec, Jung Gi Kima, Ki Sa Sungcd, Joonsung Hwanga, Young Dong Yooc, Yoon Jee Leec, Sung Tae Kimcd, Dae Hee Leee, Aaron Ciechanovercf, Bo Yeon Kima* & Yong Tae Kwoncg*
a World Class Institute, Korea Research Institute of Bioscience and Biotechnology, Ochang 363-883, Cheongwon, Korea.
b Department of Drug Discovery and Development, College of Pharmacy, Chungbuk National University, Cheongju 361-736, Chungbuk, Korea.
c Protein Metabolism Medical Research Center and Department of Biomedical Sciences, College of Medicine, Seoul National University, Seoul 110-799, Korea.
d Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh Pittsburgh, PA 15261, USA.
e Division of Oncology/Hematology, Department of Internal Medicine, Korea University College of Medicine, Seoul, Republic of Korea.
f The Polak Tumor and Vascular Biology Research Center, The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel
g Ischemic/Hypoxic Disease Institute, College of Medicine, Seoul National University, Seoul 110-799, Korea.
† These authors have contributed equally.
The N-end rule pathway is a proteolytic system, in which single N-terminal residues act as a determinant of a class of degrons, called N-degrons. In the ubiquitin (Ub)-proteasome system, specific recognition components, called N-recognins, recognize N-degrons and accelerate polyubiquitination and proteasomal degradation of the substrates. In this study, we show that the pathway regulates the activity of the macroautophagic receptor SQSTM1/p62 (sequestosome 1) through N-terminal arginylation (Nt-arginylation) of endoplasmic reticulum (ER)-residing molecular chaperones, including HSPA5/GRP78/BiP, CALR (calreticulin), and protein disulfide isomerases. The arginylation is co-induced with macroautophagy (hereafter autophagy) as part of innate immunity to cytosolic DNA and when misfolded proteins accumulate under proteasomal inhibition. Following cytosolic relocalization and arginylation, Nt-arginylated HSPA5 (R-HSPA5) is targeted to autophagosomes and degraded by lysosomal hydrolases through the interaction of its N-terminal Arg (Nt-Arg) with ZZ domain of SQSTM1. Upon binding to Nt-Arg, SQSTM1 undergoes a conformational change, which promotes SQSTM1self-polymerization and interaction with LC3, leading to SQSTM1 targeting to autophagosomes. Cargoes of R-HSPA5 include cytosolic misfolded proteins destined to be degraded through autophagy. Here, we discuss the mechanisms by which the N-end rule pathway regulates SQSTM1-dependent selective autophagy.
Key words : ATE1 R-transferase, N-end rule pathway, protein arginylation, protein quality control, proteolysis