The mechanism(s) by which iron in blood is transported across the blood-brain barrier (BBB) remains controversial. Here we have examined the first step of this trans-cellular pathway, namely the mechanism(s) of iron uptake into human brain microvascular endothelial cells (hBMVEC). We show that hBMVEC actively reduce non-transferrin bound Fe-III (NTBI) and transferrin-bound Fe-III (TBI); this activity is associated with one or more ferrireductases. Efficient, exo-cytoplasmic ferri-reduction from TBI is dependent upon transferrin receptor (TfR), also. Blocking holo-Tf binding with an anti-TfR antibody significantly decreases the reduction of iron from transferrin by hBMVEC, suggesting that holo-Tf needs to bind to TfR in order for efficient reduction to occur. Ferri-reduction from TBI significantly decreases when hBMVEC are pre-treated with Pt-II, an inhibitor of cell surface reductase activity. Uptake of Fe-59 from Fe-59-Tf by endothelial cells is inhibited by 50 % when ferrozine is added to solution; in contrast, no inhibition occurs when cells are alkalinized with NH4Cl. This indicates that the iron reduced from holo-transferrin at the plasma membrane accounts for at least 50 % of the iron uptake observed. hBMVEC-dependent reduction and uptake of NTBI utilizes a Pt-II-insensitive reductase. Reductase-independent uptake of Fe-II by hBMVEC is inhibited up to 50 % by Zn-II and/or Mn-II by a saturable process suggesting that redundant Fe-II transporters exist in the hBMVEC plasma membrane. These results are the first to demonstrate multiple mechanism(s) of TBI and NTBI reduction and uptake by endothelial cells (EC) of the BBB.

By using subtraction and cDNA array hybridizations, we recently identified an anonymous transcript that was differentially expressed in benign prostate hyperplasia and prostate cancer cell line PC-3. Here, we report the cloning of the full-length cDNA of the gene, designated STEAP2 (six-transmembrane epithelial antigen of the prostate 2). The gene is located at the chromosomal region 7q21 and encodes for a 490-amino acid protein with six predicted transmembrane domains and is predominantly expressed in prostate epithelial cells. Green fluorescent protein fusion construct indicated that the STEAP2 protein is localized mainly in the plasma membrane. Real-time quantitative RT-PCR showed that the gene is expressed at levels more than 10 times higher in normal prostate than in other tissues studied. Of the prostate cancer cell lines, STEAP2 was expressed in significant levels only in androgen -responsive LNCaP. The expression of STEAP2 was significantly higher (P = 0.002) in both untreated primary and hormone-refractory prostate carcinomas than in benign prostate hyperplasias, suggesting that it may be involved in the development of prostate cancer. As a cell-surface antigen, STEAP2 is a potential diagnostic or therapeutic target in prostate cancer.