The glandular epithelial cells of the human prostate gland have the unique capability and function of accumulating the highest zinc levels of any soft tissue in the body. Zinc accumulation in the prostate is regulated by prolactin and testosterone; however, little information is available concerning the mechanisms associated with zinc accumulation and its regulation in prostate epithelial cells. In the present studies the uptake and accumulation of zinc were determined in the human malignant prostate cell lines LNCaP and PC-3. The results demonstrate that LNCaP cells and PC-3 cells possess the unique capability of accumulating high levels of zinc. Zinc accumulation in both cell types is stimulated by physiological concentrations of prolactin and testosterone. The studies reveal that these cells contain a rapid zinc uptake process indicative of a plasma membrane zinc transporter. Initial kinetic studies demonstrate that the rapid uptake of zinc is effective under physiological conditions that reflect the total and mobile zinc levels in circulation. Correspondingly, genetic studies demonstrate the expression of a ZIP family zinc uptake transporter in both LNCaP and PC-3 cells. The rapid zinc uptake transport process is stimulated by treatment of cells with physiological levels of prolactin and testosterone, which possibly is the result of the regulation of the ZIP-type zinc transporter gene. These zincaccumulating characteristics are specific for prostate cells. The studies support the concept that these prostate cells express a unique hormone-responsive, plasma membrane-associated, rapid zinc uptake transporter gene associated with their unique ability to accumulate high zinc levels.Zinc is an essential component of all cells. It is required for a variety of cellular activities such as metalloenzyme activity, nucleoprotein and nucleic acid structure, and transcription factor interactions. Typically, intracellular zinc is found predominantly (Ͼ 95%) bound to high molecular weight ligands such as metalloenzymes, metalloproteins, nucleoproteins, and nucleic acids. Very little zinc is available as free or loosely bound zinc, which we will refer to as " mobile reactive zinc" (for review, see Refs. 1-3).The prostate gland of humans and other animals is unique in that it accumulates much higher zinc levels than any other soft tissues in the body. For detailed and extensive reviews of zinc-citrate relationships in prostate, see Refs. 4 -6. The special functions associated with the high zinc level of the prostate have not been resolved. The ability of the prostate to accumulate high zinc levels is a function of the glandular secretory epithelial cells. Our recent studies (7) with rat prostate lobes have demonstrated that the epithelial cells contain high levels of intracellular zinc, and, most importantly, contain high levels of mitochondrial zinc. The accumulation of zinc results in the inhibition of mitochondrial aconitase activity which minimizes the ability of these cells to oxidize citrate (8). This is an important r...