Suppression of ATG4B by copper inhibits autophagy and involves in Mallory body formation

Autophagy is an evolutionarily conserved self-protecting mechanism implicated in cellular homeostasis. ATG4B plays a vital role in autophagy process via undertaking priming and delipidation of LC3. Chemical inhibitors and regulative modifications such as oxidation of ATG4B have been demonstrated to modulate autophagy function. Whether and how ATG4B could be regulated by metal ions is largely unknown. Copper is an essential trace metal served as static co-factors in redox reactions in physiology process. Excessive accumulation of copper in ATP7B mutant cells leads to pathology progression such as insoluble Mallory body (MB) in Wilson disease (WD). The clearance of MB via autophagy pathway was thought as a promising strategy for WD. Here, we discovered that copper ion instead of other ions could inhibit the activity of ATG4B followed by autophagy suppression. In addition, copper could induce ATG4B oligomers depending on cysteine oxidation which could be abolished in reduced condition. Copper also promotes the formation of insoluble ATG4B aggregates, as well as p62-and ubiquitin-positive aggregates, which is consistent with the components of MB caused by copper overload in WD cell model. Importantly, overexpression of ATG4B could partially reduce the formation of MB and rescue impaired autophagy. Taken together, our results uncovered for the first time a new damage mechanism mediated by copper and implied new insights of the crosstalk between the toxicity of copper and autophagy in the pathogenesis of WD.