Abstract 111: NEDD8 Ultimate Buster-1 Long (NUB1L) Protein Regulates Atypical Neddylation and Protects Against Myocardial Ischemia-reperfusion Injury

Abstract

Neddylation is a ubiquitination-like pathway that covalently conjugates NEDD8 to target proteins and involves in diverse cellular processes. Under stress conditions, NEDD8 forms a chain or mixes with ubiquitin to modify protein substrates in NEDD8 conjugating enzymes-independent manner (atypical neddylation). The functional consequence of atypical neddylation remains unexplored in any cell types including cardiomyocytes. Here we report that increased neddylated proteins were observed in desmin-related cardiomyopathic (DRC) mouse hearts, mouse hearts subjected to myocardial ischemia-reperfusion (I/R) and human failing hearts. In cultured cardiomyocytes, multiple cellular stresses induced atypical neddylation, which was attenuated by NUB1L overexpression but exaggerated by loss of NUB1L, revealing NUB1L as a negative regulator of atypical neddylation. Activation of atypical neddylation by forced expression of NEDD8 accumulated a proteasome surrogate substrate GFPu, while suppression of atypical neddylation by NUB1L overexpression enhanced the degradation of GFPu and a DRC-linking misfolded protein. NUB1L is necessary and sufficient to protect cardiomyocytes against proteotoxic stress-induced cell injury. In vivo, cardiac-specific overexpression of NUB1L (NUB1L-O/E) in mice dose-dependently reduced neddylated proteins and facilitated the degradation of the proteasome surrogate substrate. NUB1L-O/E mice displayed no discernible cardiac structural and functional abnormality at baseline, but exihibted reduced apoptotic cardiomyocytes, limited infarct sizes and preserved cardiac function in response to I/R. We therefore conclude that NUB1L suppresses atypical neddylation, enhances proteasome proteolytic function and protects against myocardial I/R injury. Targeting atypical neddylation could be a novel therapeutic strategy to treat cardiac ischemic cardiomyopathy.