Mechanism of Copper Uptake from Blood Plasma Ceruloplasmin by Mammalian Cells

• DOI: 10.1371/journal.pone.0149516
• Publication Date: 2016-03-02T18:36:42Z
• Authors: Danny Ramos; David Mar; Michael Ishida; Rebecca Vargas; Michaella Gaite; Aaron Montgomery; Maria C. Linder
• Keywords: Ceruloplasmin

Ceruloplasmin, the main copper binding protein in blood plasma, has been of particular interest for its role efflux iron from cells, but additional functions. Here we tested hypothesis that it releases cell uptake by interacting with a surface reductase and transporters, producing apoceruloplasmin. Uptake transepithelial transport ceruloplasmin was demonstrated mammary epithelial monolayers (PMC42) tight junctions grown bicameral chambers, purified human 64Cu-labeled secreted HepG2 cells. Monolayers took up virtually all 64Cu over 16h half into apical (milk) fluid. This partly inhibited Ag(I). The plasma 64Cu-injected mice accumulated linearly mouse embryonic fibroblasts (MEFs) 3-6h. Rates were somewhat higher Ctr1+/+ versus Ctr1-/- 3-fold lower at 2°C. ceruloplasmin-derived could not be removed extensive washing or trypsin treatment, most recovered cytosol. Actual (determined furnace atomic absorption) increased markedly upon 24h exposure to holoceruloplasmin. accompanied conversion holo apoceruloplasmin culture medium did occur during incubation absence Four different endocytosis inhibitors failed prevent ceruloplasmin. High concentrations non-radioactive Cu(II)- Fe(III)-NTA (substrates reductases), Cu(I)-NTA (to compete transporter uptake) almost eliminated MEFs had activity expressed Steap 2 (but Steaps 3 4 dCytB). However, six-day siRNA treatment insufficient reduce uptake. We conclude is circulating may interact Steap2 on surface, forming apoceruloplasmin, Cu(I) enters cells through CTR1 an unknown transporter.