Harris E D, Qian Y, Tiffany-Castiglioni E, Lacy A R, Reddy M C
Department of Biochemistry and Biophysics and the Faculty of Nutrition, Texas A&M University, College Station 77843-2128, USA.
Am J Clin Nutr. 1998 May;67(5 Suppl):988S-995S. doi: 10.1093/ajcn/67.5.988S.
The movement of copper ions across membrane barriers of vital organs and tissues is a priority topic in nutrition and one for which there continues to be little understanding of the mechanism. Reports of membrane-bound, copper-transporting adenosine triphosphatases (Cu-ATPases) selective for copper ions have brought new focus to the problem and prompted fresh ideas. Using a cell culture model approach, we attempted to 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 rates of copper uptake and response to sulfhydryl reagents. BeWo cells, a human choriocarcinoma placental cell line, behaved as did Menkes fibroblasts by avidly absorbing copper but not releasing copper to the immediate environment. Further tests showed that BeWo cells did not express the transcript for the membrane-bound Cu-ATPase that has been identified with Menkes syndrome. Transcript induction, however, was achieved by growing BeWo cells on porous filters that allowed apical and basolateral surfaces to form. With transcript expression, the cells showed a capacity to release copper into the medium. BeWo cells also synthesized a form of ceruloplasmin whose structure differed from that of the plasma protein and hence may be a product of a different gene. BeWo cells may also express the gene for Wilson disease, thus linking Menkes and Wilson proteins to maternal delivery of copper. We constructed a model in which both ATPases work in concert in a vesicle-based transport mechanism. The vesicle model may help us understand the transport of copper across the placenta and all cells in general.
铜离子跨重要器官和组织的膜屏障转运是营养领域的一个重要课题，然而人们对其机制仍知之甚少。关于对铜离子具有选择性的膜结合型铜转运三磷酸腺苷酶（Cu - ATPases）的报道，为该问题带来了新的关注焦点，并引发了新的思考。我们采用细胞培养模型方法，试图了解铜离子进出细胞是否依赖于一种铜转运三磷酸腺苷酶。对成纤维细胞、脑胶质细胞、神经母细胞瘤细胞和胎盘细胞的转运动力学测量表明，这些细胞在铜摄取速率以及对巯基试剂的反应方面存在差异。BeWo细胞是一种人绒毛膜癌胎盘细胞系，其行为与门克斯病成纤维细胞相似，即能大量吸收铜但不会将铜释放到周围环境中。进一步测试表明，BeWo细胞不表达已被确定与门克斯综合征相关的膜结合型铜转运三磷酸腺苷酶的转录本。然而，通过将BeWo细胞培养在多孔滤器上，使细胞形成顶端和基底外侧表面，实现了转录本的诱导。随着转录本的表达，细胞表现出将铜释放到培养基中的能力。BeWo细胞还合成了一种铜蓝蛋白，其结构与血浆蛋白不同，因此可能是不同基因的产物。BeWo细胞也可能表达威尔逊病相关基因，从而将门克斯蛋白和威尔逊蛋白与母体铜转运联系起来。我们构建了一个模型，其中两种三磷酸腺苷酶在基于囊泡的转运机制中协同工作。该囊泡模型可能有助于我们理解铜在胎盘及所有细胞中的转运情况。
