Abstract
Zerumbone, a sesquiterpene present in Zingiber zerumbet Smith, has been implicated as a promising chemopreventive agent. Interestingly, a number of studies have revealed that its potent bioactivities are dependent on the electrophilic moiety of its α,β-unsaturated carbonyl group, while our recent findings showed its chemical potential for binding to cellular proteins through a Michael reaction. In the present study, modifications of proteins by zerumbone led to their insolubilization in vitro. In living cell models, zerumbone induced ubiquitination and aggregation of cellular proteins, which demonstrated its substantial proteo-toxicity. On the other hand, it was also revealed that zerumbone possesses potential for activating intracellular proteolysis mechanisms of the ubiquitin-proteasome system and autophagy. Furthermore, it up-regulated expressions of pro-autophagic genes including p62, which is known as a cargo receptor of aggrephagy, the selective autophagic process for protein aggregates. Pretreatment of Hepa1c1c7 cells with zerumbone conferred a phenotype resistant to cytotoxicity and protein modifications by 4-hydroxy-2-nonenal, an endogenous lipid peroxidation product, in a p62-dependent manner. Together, these results suggest that protein modifications by zerumbone cause mild proteo-stress, thereby activating intracellular proteolysis machineries to maintain protein homeostasis. We consider these effects on proteolysis mechanisms to be hormesis, which provides beneficial functions through mild biological stresses.