Myosin Vb mediates copper export in polarized hepatocytes

The cellular machinery responsible for copper-stimulated delivery of the Wilson Disease protein ATP7B to the apical domain of hepatocytes is poorly understood. We demonstrate that myosin Vb regulates the copper-stimulated delivery of ATP7B to the apical domain of polarized hepatic cells, and that disruption of the ATP7B-myosin Vb interaction reduces ATP7B apical surface expression. Myosin Vb tail overexpression, which competes for binding of subapical cargoes to myosin Vb bound to subapical actin, disrupted the surface expression of ATP7B, leading to reduced cellular copper export. The myosin Vb-dependent targeting step arose in parallel with hepatocyte-like polarity. If the myosin Vb tail was expressed acutely in cells just prior to the establishment of polarity, it appeared as part of an intracellular apical compartment, centered on gamma tubulin. ATP7B became arrested in this compartment selectively in high copper in the presence of myosin Vb tail, suggesting that these sites are precursors of donor-acceptor transfer stations for apically targeted myosin Vb cargoes. Our data suggest that reduced hepatic copper clearance in idiopathic Non-Wilsonian pathologies may be associated with the loss of myosin Vb function.