The question is: "How does copper get exported from the cell?" We have also traced the pathway taken by endogenous ATP7B in liver. It also remains largely intracellular but in vesicles just underneath the apical membrane. By tagging wild type and mutant constructs of ATP7B with Green Fluorescent Protein (GFP), we have followed the copper-dependent dynamics of the protein in polarized WIF-B cells. We recently identified an apical targeting signal in the N-terminus of ATP7B that is necessary for the protein's copper-sensitive trafficking. Our work has implications for two human genetic diseases, which are caused by mutations in the ATP7B and ATP7A genes and lead to copper overload in the liver (Wilson Disease), due to the failure to excrete copper into the bile, and copper deficiency in many organs (Menkes Disease), due to the failure to deliver intestinal copper to the blood.
Barnes, N., Bartee, M.Y., Braiterman, L., Gupta,A., Ustiyan, V., Zuzel, V., Kaplan, J.H., Hubbard, A.L., Lutsenko, S. 2009. Cell specific trafficking suggests a new role for renal ATPB in intracellular copper storage. Traffic 10:767-779.
Braiterman, L., Nyasae, L., Guo, L., Bustos, R., Lutsenko, S., Hubbard, A. 2009. Apical targeting and golgi retention signals reside within a 9-amino acid sequence in the copper-ATPase, ATP7B. Am. J. Physiol. Gastrointest. Liver Physiology, 296(2):G433-444.
Nyasae, L., Bustos, R., Braiterman, L., Eipper, B., A. Hubbard. 2007. Dynamics of endogenous ATP7A (Menkes protein) in intestinal epithelial cells: copper-dependent redistribution between two intracellular sites. Am J Physiol Gastrointest Liver Physiol. 292(4):G1181-94.
Guo, Y, L. Nyasae, L. T. Braiterman, and A. L. Hubbard. 2005. N-terminal signals in ATP7B Cu-ATPase mediate its Cu-dependent anterograde traffic in polarized hepatic cells. Amer J. Physiol., GI/Liver 289(5):G904-16.