Localization of the Wilson's disease protein in human liver

Background & Aims: Wilson's disease is an autosomal-recessive disorder of c opper metabolism that results from the absence or dysfunction of a copper-t ransporting P-type adenosine triphosphatase that leads to impaired biliary copper excretion and disturbed holoceruloplasmin synthesis, To gain further insight into the role of the Wilson's disease protein in hepatic copper ha ndling, its localization in human liver was investigated, Methods: By use o f a specific antibody, localization of the Wilson's disease protein was stu died in liver membrane fractions and liver sections by immunoblotting, immu nohistochemistry, and double-label confocal scanning laser microscopy, Resu lts: The 165-kilodalton protein, found by immunoblotting, was most abundant mainly in isolated plasma membrane fractions enriched in canalicular domai ns, Immunohistochemistry revealed intracellular punctuate staining of hepat ocytes in certain regions of the liver, whereas a canalicular membrane stai ning pattern was observed in other regions. Double-labeling studies showed that in the latter regions the transporter is present mainly in vesicular s tructures just underneath the canalicular membrane that are positive for ma rkers of the trans-Golgi network. A weak staining of the canalicular membra ne, identified by staining for P-glycoprotein, was observed, Conclusions: T hese results show that in human liver the Wilson's disease protein is predo minantly present in trans-Golgi vesicles in the pericanalicular area, where as relatively small amounts of the protein appear to localize to the canali cular membrane, consistent with a dual function of the protein in holocerul oplasmin synthesis and biliary copper excretion.