Subcellular distribution of zinc in the benign and malignant human prostate: evidence for a direct zinc androgen interaction

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Abstract
The subcellular distribution of zinc and its interaction with androgens has been examined in the benign and malignant human prostate. Endogenously, most of the zinc was associated with the nuclear fraction but significant concentrations were also found in the cytosol. Furthermore, the epithelium contained more zinc than that found in either the stroma or the intact gland. Zinc concentrations were lower in the subcellular fractions of the cancerous tissue when compared to hyperplastic specimens. In vitro uptake of zinc into prostatic homogenates was rapid and at equilibrium the binding was stable for both the 4°C and the 37°C incubations. At low zinc concentrations (≤ 5 mm) the uptake was higher in the nucleus, whereas at higher concentrations, the cancerous tissue exhibited a greater capacity for the metal which was predominantly retained by the cytosol. Our data suggest the presence of a saturable zinc retention mechanism in the nucleus. The zinc uptake was found to be independent of any added androgen. In contrast, the total androgen uptake by the prostate was significantly enhanced by the addition of zinc. This effect was not due to increases in the nuclear and cytosolic receptor binding since zinc inhibited the binding of the androgen to these receptors.