FUNCTIONAL-ANALYSIS OF COPPER HOMEOSTASIS IN CELL-CULTURE MODELS - A NEW PERSPECTIVE ON INTERNAL COPPER TRANSPORT

The movement of copper ions across membrane barriers of vital organs a nd tissues is a priority topic in nutrition and one for which there co ntinues to be little understanding of the mechanism. Reports of membra ne-bound, copper-transporting adenosine triphosphatases (Cu-ATPases) s elective for copper ions have brought new focus to the problem and pro mpted fresh ideas. Using a cell culture model approach, we attempted t o learn whether transport into and out of cells depends on a Cu-ATPase . Measurement of transport kinetics in fibroblasts, brain glial cells, neuroblastoma cells, and placental cells showed differences in the ra tes of copper uptake and response to sulfhydryl reagents. Be Wo cells, a human choriocarcinoma placental cell line, behaved as did Menkes fi broblasts by avidly absorbing copper but not releasing copper to the i mmediate environment. Further tests showed that Be Wo cells did not ex press the transcript for the membrane-bound Cu-ATPase that has been id entified with Menkes syndrome. Transcript induction, however, was achi eved by growing Be Wo cells on porous filters that allowed apical and basolateral surfaces to form. With transcript expression, the cells sh owed a capacity to release copper into the medium. Be Wo cells also sy nthesized a form of ceruloplasmin whose structure differed from that o f the plasma protein and hence may be a product of a different gene. B e Wo cells may also express the gene for Wilson disease, thus linking Menkes and Wilson proteins to maternal delivery of copper. We construc ted a model in which both ATPases work in concert in a vesicle-based t ransport mechanism. The vesicle model may help us understand the trans port of copper across the placenta and all cells in general.