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

Abstract

Zinc ions (Zn2+) are known to influence cell survival and proliferation. However the homeostatic regulation of Zn2+ and their role in prostate cancer (PC) progression is poorly understood. Therefore the subcellular distribution and uptake of Zn2+ in PC cells were investigated. Inductively coupled plasma mass spectroscopy and fluorescent microscopy with the Zn2+-specific fluorescent probe FluoZin-3 were used to quantify total and free Zn2+, respectively, in the normal prostate epithelial cell line (PNT1A) and three human PC cell lines (PC3, DU145 and LNCaP). The effects of Zn2+ treatment on proliferation and survival were measured in vitro using MTT assays and in vivo using mouse xenografts. The ability of Zn2+ 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 Zn2+ concentration in normal PNT1A and PC cells is similar, but PC3 cells contain significantly higher free Zn2+ than PNT1A cells (p < 0.01). PNT1A cells can survive better in the presence of high concentrations of Zn2+ than PC3 cells. Exposure to 10 µM Zn2+ over 72 hours significantly reduces PC3 cell proliferation in vitro but not in vivo. Zn2+ 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 Zn2+ dyshomeostasis exists in PC. HIF1α is an integral component of a Zn2+-dependent protective mechanism present in PC3 cells. This pathway may be clinically significant through its contribution to castrate-resistant PC survival.

Metformin may offer no protective effect in men undergoing external beam radiation therapy for prostate cancer

“…The data shown in Fig. C confirm our previous observation of a very low level of basal HIF1α in LNCaP cells . Importantly, metformin did not affect the expression of HIF1α, nor did it increase the sensitivity of LNCaP cells exposed to oxidative stress (25 μM H 2 O 2 ), as shown in Fig.…”

“…In both pathways, mTOR plays a key role in reducing tumour cell proliferation . HIF1α is a key transcription factor, regulated by mTOR, which promotes cancer growth, cell proliferation, angiogenesis, metastases and tumour cell survival , and is also thought to increase resistance to radiotherapy . However, in the present in vitro study, metformin failed to reduce expression of HIF1α and correspondingly failed to further sensitize PC3 cells against cytotoxic H 2 O 2 .…”

“…A, treatment of PC3 cells with increasing doses of metformin to a maximum concentration of 100 μM had no effect on HIF1α. In contrast, exogenous 10 μM ferric ions (Fe 2+ ) resulted in the degradation of HIF1α to 35 ± 7% in PC3 cells compared to untreated control cells, as demonstrated previously . Exposure of cells to ionizing radiation during radiotherapy generates oxidative stress via reactive oxygen species including H 2 O 2 .…”

“…Both pathways activate AMP‐activated protein kinase (AMPK), which in turn inhibits mammalian target of rapamycin (mTOR) and causes reduced cell proliferation . Hypoxia‐inducible factor 1‐α (HIF1α) is a transcription factor that promotes cancer growth, cell proliferation, angiogenesis, metastases and survival of PCa cells . In addition, HIF1α has been shown to increase resistance to radiotherapy , and targeting the mTOR/HIF1α pathway improves radio‐sensitivity in endometrial cancer .…”

Encapsulation and Storage of Therapeutic Fibrin-Homing Peptides using Conducting Polymer Nanoparticles for Programmed Release by Electrical Stimulation

“…Although the redox metabolism associated with Zn-S(Cys) complexes is involved in protein structure regulation, 58 alterations in the Zn 2+ regulation cause stress, even inducing cellular apoptosis. Considering that proliferation and survival of PC3 cells is known to be very sensitive to free Zn +2 , 59 it can be hypothesized that Zn-chelation through the formation Zn-S(Cys) complexes explains the effects of the studied peptides in this cell line.…”