Molecular pathology of Wilson's disease: a brief.
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ABSTRACT: The copper transporter ATP7B plays a central role in the elimination of excess copper by the liver into the bile, yet the site of its action remains controversial. The studies reported here examine the correspondence between the site of ATP7B action and distribution and the pathways of copper disposal by the liver. Microscopy and cell fractionation studies of polarized Can 10 cells forming long-branched bile canaliculi have been used to study the cellular distribution of ATP7B. Copper excretion into the bile was studied in perfused rat liver. Copper excess provokes a massive download of the ATP7B retained in the trans-Golgi network into the bile canalicular membrane. Furthermore, a stable ATP7B pool is localized to the tight junctions that seal the bile canaliculi. The profile of Cu(64) excretion into the bile by isolated rat livers perfused under one-pass conditions provides evidence of copper excretion by 2 separate mechanisms, transcytosis across the hepatocyte and paracellular transport throughout the tight junctions. Whereas the ATP7B retained in the trans-Golgi-network is massively translocated to the bile canalicular membrane in response to increased copper levels, a pool of ATP7B associated with the tight junctions remains stable. In situ studies indicate that copper is excreted into the bile by 2 separate pathways. The results are discussed in the frame of the normal and impeded excretion of copper into the bile.Gastroenterology 04/2008; 134(4):1215-23. · 12.82 Impact Factor
Molecular pathology of Wilson’s disease: A brief
Vassiliki Lalioti1, Ignacio Sandoval1, Doris Cassio2,3, Jean-Charles Duclos-Vallée4,5,6,7,⇑
1Department of Cell Biology and Immunology, Centro de Biologia Molecular Severo Ochoa and Centro de Enfermedades Hepáticas y
Digestivas (CIBEREHD), Universidad Autónoma de Madrid, 28049 Madrid, Spain;2INSERM Unité 757, Orsay F-91400, France;3Université
Paris-Sud, UMR-S 757, Orsay F-91405, France;4AP-HP Hôpital Paul Brousse, Centre Hépato-Biliaire, Villejuif F-94800, France;5Université
Paris-Sud, UMR-S 785, Villejuif F-94800, France;6Inserm, Unité 785, Villejuif F-94800, France;7Centre de Référence de la maladie de Wilson
Centre Hépato-Biliaire Hôpital Paul Brousse, Villejuif, France
Wilson disease (WD) is a rare autosomal recessive disorder of Cu
metabolism linked to dysfunction of the Cu translocase ATP7B
expressed in hepatocytes . ATP7B is critical in the distribution
and elimination of excess Cu from the organism. Malfunctioning
of the translocase interferes with the distribution of Cu among
organs and tissues and results in the imbalance between Cu
absorption and excretion, thus causing Cu toxicosis.
The levels of Cu regulate the distribution and traffic of ATP7B
in the hepatocyte. While at normal Cu concentrations, ATP7B
remains in the TGN (trans-Golgi network) to supply Cu to the
newly synthesized cuproproteins; at Cu concentrations exceed-
ing the physiological limits it is transferred to the membranes
of the bile canaliculi to dissipate the toxic levels of Cu .
Proper cellular distribution and functioning of ATP7B requires
the coordinated interaction between its separate modules.
Whereas the six Cu+-binding domains in its long N-cytoplasmic
domain play a major role in the acceptance of Cu+and in control-
ling the phosphorylation, traffic, and activity of the translocase,
the clustering of its eight transmembrane helixes forms the Cu+
pore, and the connecting loops in the cytoplasmic side are
involved in the cyclic phosphorylation that controls the activity
of the translocase (Fig. 1A and B) . In addition, there is evi-
dence that the C-cytoplasmic domain may also play an important
role in the traffic and cellular distribution of the translocase [3,4].
Over 300 mutations in the ATP7B gene have been associated
with WD, the majority missense mutations (60%). Mutations
affecting to different extents the binding of Cu, the cyclic phos-
phorylation, traffic, and posttranslational modifications of ATP7B
as well as its physiological interaction with other proteins, may
potentially interfere with the dual role of ATP7B in excreting
excess Cu into the bile and in the biosynthesis of the ceruloplas-
min essential for proper iron (Fe) metabolism.
The most prevailing mutations in Wilson patients are
H1069Q/G in Europe and North America, and R778L in southeast
Asia . Though H1069 residue plays a critical role in the ATP-
binding to the N-domain of ATP7B, the demonstration that the
H1069Q mutant is retained and quickly degraded in the ER sug-
gests that this is the primary cause of the WD. The same traffic
defect has been found in studies of the R778L mutant . Besides,
the association of WD with more than 40 different mutations in
the N-site of ATP7B and the fact that only four of these mutations
affect residues implicated in ATP-binding, point to the impor-
tance of cooperation between a large number of residues in the
construction of a functional N-domain. The disruption of
ATP7B-trafficking and the hampering of its phosphorylation pro-
vokes its dysfunction in the hepatocyte and explains the inhibi-
tion of Cu elimination into the bile. Interestingly, the liver from
patients with G943S and M769V mutations, that inhibit the api-
cal trafficking of ATP7B without interfering with its retention in
the TGN, produces normal ceruloplasmin levels and as a result
may not develop severe CNS intoxication.
Clinical symptoms in WD include cirrhosis and chronic hepa-
titis that end in liver failure, neurological defects that course with
parkinsonian symptoms and seizures, and psychiatric features
. The Kayser–Fleischer ring, a deposition of Cu visible as a
golden ring in the periphery of the cornea, low serum levels of
ceruloplasmin, and high levels of Cu in the urine are helpful in
the diagnosis of the disease. The age of presentation of the WD
syndrome, the predominance of hepatic versus neurological
symptoms and their severity are strikingly variable. Excessive
Cu-derived oxidants produced by free Cu2+- catalyzed Fenton
reactions and reduced superoxide dismutase and glutathione
activities, appear to contribute decisively to the development
and progression of liver abnormalities in WD . Furthermore,
the toxic accumulation of Cu and the development of hepatic
abnormalities without neurological symptoms in a group of WD
patients is mimicked in the Cu toxicosis developed by the Long-
Evans cinnamon rat (50deletion) and the ‘toxic milk’ mouse.
Genotype variations in the mutations may partly explain the var-
iability behind the clinical symptoms but is also likely that this
also results from the activity of modifier genes and gene-environ-
ment interactions. Moreover, increased binding of Wilson’s dis-
ease ATP7B with COMMD1, a negative regulator of protein
stability involved in the quality control of ATP7B and absent in
Bedlington terriers suffering from copper toxicosis, results in a
decrease of their stability that may result in the amplification
of the mutation effects and partially explains the clinical hetero-
geneity observed in WD .
Journal of Hepatology 2010 vol. 53j1151–1153
Received 7 May 2010; received in revised form 9 July 2010; accepted 13 July 2010
⇑Corresponding author at: Centre Hépato-Biliaire, Hôpital Paul Brousse, 12,
Avenue Paul Vaillant Couturier, 94800 Villejuif, France. Tel.: +33 1 45 59 33 31;
fax: +33 1 45 59 38 57.
E-mail address: email@example.com (J.-C. Duclos-Vallée).
Cu + transfer from
Atox1 to ATP7B
Cu + loading/Initiation
Cu + translocation
Progression Cu + translocation
/Cu + binding to CPC
Cu + translocation
/Closing entrance channel
De phosphorylation P-domain
/Setting basal conditions
Fig. 1. Cyclic phosphorylation–dephosphorylation of ATP7B and vectorial transport of Cu through the ion channel. Five Cu binding domains (CBD) are aligned along
the N-cytoplasmic end of ATP7B. The chaperone Atox1 transfers Cu+to the CBD2 . The subsequent filling of CBDs1–4 with Cu+provokes structural changes that facilitate
the binding of ATP to the N-site , bringing bound ATP in close proximity to the phosphorylation site  and facilitating the binding of a Cu+atom by the two juxtaposed
Cys in the plane of the transmembrane domains TM1 and TM2 . Next, filling of CBDs5 and 6 with Cu+favours the transfer of a Cu+atom to the CPC motif in TM6 .
Phosphorylation of the Asp residue in the P-site  closes the access to the ion channel from the cytoplasm and facilitates the reception of the translocated Cu+by the
exofacial vestibule. Cu+is then released at the opposite side of the membrane and dephosphorylation of Asp-P by the phosphatase in the A-site  completes the phospho-
dephosphorylation cycle  and resets the channel to basal conditions. (B) Point mutations (
changes the levels, cellular distribution, and activity of ATP7B and results in Wilson disease (WD). (C) At physiological concentrations of Cu in the hepatocyte, ATP7B
transfers the Cu+donated by Atox1 to the newly synthesized cuproproteins (i.e. ceruloplasmin, CP) moving through the trans-Golgi network (TGN). The increase in Cu
concentration beyond physiological levels in the hepatocyte provokes the bulk translocation of ATP7B from the TGN to the membrane of the bile canaliculi where it
mediates the elimination of excess Cu into the bile. Restoration of the physiological levels of Cu results in recycling of ATP7B to the TGN; TJ: Tight junction, SA: serum
albumin. (D) Elimination of Cu by the hepatocyte into the bile is decreased in WD patients as compared to healthy individuals (N), causing Cu toxicosis. The main targets of
toxic Cu are the brain and liver. Low resorption of Cu in the kidney results in high levels of Cu in the urine. The volume of Cu flow into organs and body fluids is indicated by
the arrow size.
G85V, R778L, H1069Q, C1104F,V1262F, G1341V,S1363F)
Journal of Hepatology 2010 vol. 53j1151–1153
The capacity of Zn to induce metallothionein (MT) and the for-
mation of tight MT–Cu complexes in the intestinal mucosa
explains the effectiveness of the oral administration of Zn acetate
in reducing dietary Cu absorption and the levels of intestinal
haefestin, responses that ameliorate the clinical manifestations
associated with Cu and iron accumulation in WD patients .
Conflict of Interest
The authors who have taken part in this study declared that they
do not have anything to disclose regarding funding or conflict of
interest with respect to this manuscript.
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