Abstract
ATP7B utilizes lysosomal exocytosis to export copper from hepatocytes. We investigated the fate of ATP7B, post-copper export. At high copper ATP7B traffics to lysosomes and upon subsequent copper chelation, returns to Trans Golgi Network. At high copper, ATP7B co-localizes with lysosomal marker, Lamp1 and the core member of retromer complex, Vps35. Knocking down VPS35 did not alter copper-responsive vesicularization of ATP7B; rather upon subsequent copper chelation, ATP7B failed to relocalize to TGN that could be rescued by exogenously overexpressing wtVPS35. On testing a series of sorting-motif mutants of ATP7B, we found that deleting the conserved N-terminal motif NXXY, phenocopies trafficking phenotype of ATP7B in VPS35 KD condition and is the possible site of retrograde trafficking regulation. Using super-resolution microscopy we show that VPS35 and ATP7B are juxtaposed on the same lysosomal compartment and their interaction is indirect. We demonstrate that retromer regulates lysosome to TGN trafficking of a non-resident lysosomal cargo, viz., ATP7B and it is dependent upon cellular copper.