Zinc ion dyshomeostasis increases resistance of prostate cancer cells to oxidative stress via upregulation of HIF1α

Zinc ions (Zn(2+)) are known to influence cell survival and proliferation. However the homeostatic regulation of Zn(2+) and their role in prostate cancer (PC) progression is poorly understood. Therefore the subcellular distribution and uptake of Zn(2+) in PC cells were investigated. Inductively coupled plasma mass spectroscopy and fluorescent microscopy with the Zn(2+)-specific fluorescent probe FluoZin-3 were used to quantify total and free Zn(2+), respectively, in the normal prostate epithelial cell line (PNT1A) and three human PC cell lines (PC3, DU145 and LNCaP). The effects of Zn(2+) treatment on proliferation and survival were measured in vitro using MTT assays and in vivo using mouse xenografts. The ability of Zn(2+) to protect against oxidative stress via a HIF1α-dependent mechanism was investigated using a HIF1α knock-down PC3 model. Our results demonstrate that the total Zn(2+) concentration in normal PNT1A and PC cells is similar, but PC3 cells contain significantly higher free Zn(2+) than PNT1A cells (p < 0.01). PNT1A cells can survive better in the presence of high concentrations of Zn(2+) than PC3 cells. Exposure to 10 µM Zn(2+) over 72 hours significantly reduces PC3 cell proliferation in vitro but not in vivo. Zn(2+) increases PC3 cell survival up to 2.3-fold under oxidative stress, and this protective effect is not seen in PNT1A cells or in a HIF1α-KD PC3 cell model. A state of Zn(2+) dyshomeostasis exists in PC. HIF1α is an integral component of a Zn(2+)-dependent protective mechanism present in PC3 cells. This pathway may be clinically significant through its contribution to castrate-resistant PC survival.