Wilson Disease Protein ATP7B Utilizes Lysosomal Exocytosis to Maintain Copper Homeostasis

Elena Polishchuk ,Giancarlo Parenti,Nunzia Pastore,Simona Paladino,Andrea Ballabio,Jefferson Chan,Angela Amoresano,Simona Iacobacci,Daniela Baldantoni,Antonietta Tarallo,Giancarlo Chesi,Pasquale Piccolo,Carmine Settembre,Mafalda Concilli,Piero Pucci,Christopher J Chang ,Sven C D Van Ijzendoorn ,Nicola Brunetti‐Pierri ,F Pane ,Roman Polishchuk

doi:10.1016/j.devcel.2014.04.033

Abstract

SummaryCopper is an essential yet toxic metal and its overload causes Wilson disease, a disorder due to mutations in copper transporter ATP7B. To remove excess copper into the bile, ATP7B traffics toward canalicular area of hepatocytes. However, the trafficking mechanisms of ATP7B remain elusive. Here, we show that, in response to elevated copper, ATP7B moves from the Golgi to lysosomes and imports metal into their lumen. ATP7B enables lysosomes to undergo exocytosis through the interaction with p62 subunit of dynactin that allows lysosome translocation toward the canalicular pole of hepatocytes. Activation of lysosomal exocytosis stimulates copper clearance from the hepatocytes and rescues the most frequent Wilson-disease-causing ATP7B mutant to the appropriate functional site. Our findings indicate that lysosomes serve as an important intermediate in ATP7B trafficking, whereas lysosomal exocytosis operates as an integral process in copper excretion and hence can be targeted for therapeutic approaches to combat Wilson disease.

Highlights

Copper is an indispensable micronutrient because a number of enzymes require it as a cofactor for fundamental metabolic processes such as respiration; free radical scavenging; pigmentation; and synthesis of collagen, elastin, and neurotransmitters (Lutsenko, 2010; Nevitt et al, 2012)
Our findings indicate that lysosomes serve as an important intermediate in ATP7B trafficking, whereas lysosomal exocytosis operates as an integral process in copper excretion and can be targeted for therapeutic approaches to combat Wilson disease
To stimulate ATP7B trafficking from the trans-Golgi network (TGN), bathocuproine disulphonate (BCS)-treated cells were washed and exposed to 200 mM CuSO4 for 2 hr

Summary

Introduction

Copper is an indispensable micronutrient because a number of enzymes require it as a cofactor for fundamental metabolic processes such as respiration; free radical scavenging; pigmentation; and synthesis of collagen, elastin, and neurotransmitters (Lutsenko, 2010; Nevitt et al, 2012). To avoid toxic accumulation of Cu, vertebrates developed a fine-tuned mechanism that allows excess Cu to be removed from the organism through the Cu-transporting ATPase ATP7B. When intracellular Cu levels increase, ATP7B is thought to traffic toward the biliary surface of hepatocytes and associated ‘‘vesicles’’ involved in the excretion of Cu into bile. Mutations in the ATP7B gene frequently result in the failure of its protein product to traffic to the sites of Cu excretion. This defect causes toxic accumulation of Cu in the liver and, as a consequence, development of Wilson disease that is fatal if not treated in time (Gupta and Lutsenko, 2009)

Results

Discussion

Conclusion