Placental ceruloplasmin homolog is regulated by iron and copper and is implicated in iron metabolism

We previously reported an endogenous, membrane-bound Cu oxidase with homology to ceruloplasmin in BeWo cells, a placental choriocarcinoma cell line. In this previous study, ceruloplasmin immunoreactivity was localized to the perinuclear region and non-brush-border membranes. Here, we show that azide-sensitive oxidase activity is enriched in the same fractions, correlating subcellular localization of enzyme activity with ceruloplasmin immunoreactivity. Expression of the placental Cu oxidase is inversely proportional to Fe status and directly proportional to Cu status at enzyme and protein levels. To identify a role for the Cu oxidase, cells were exposed to Fe-59-transferrin for 18 h in an environment of 20% O-2 or 5% O-2. At 5% O-2, Cu-deficient cells retain significantly more Fe-59 than control cells. This excess in Fe-59 accumulation is caused by a significant decrease in Fe-59 release. These results indicate that downregulation of the placental Cu oxidase in BeWo cells impairs Fe release. This effect is only apparent in an environment of limited O-2.