Zinc deficiency alters expression of genes involved in DNA damage response in normal human prostate epithelial cells and mouse prostates. Free

B52

Zinc is an essential mineral that is a component of multiple enzymes and transcription factors. Studies have shown that zinc status is compromised in cancer patients and zinc deficiency results in increased oxidative stress and DNA damage. The normal prostate accumulates high levels of zinc which is markedly decreased with cancer development. This data suggests that zinc could play an important role in protecting the prostate against cancer development. Since zinc is a critical component of many proteins involved in the DNA damage response, we hypothesized that zinc deficiency will result in the impairment of mechanisms involved in maintaining DNA integrity. This study examined the effect of zinc deficiency on DNA damage, global gene expression and transcription factor binding. Normal prostate epithelial cells, PrEC, were grown in either zinc deficient (ZnDF) or zinc adequate (ZnAD) media for 7 days. Zinc deficiency resulted in increased single-strand DNA breaks. Using the Affymetrix HG-U133A GeneChip, differential expression of genes involved in cell cycle, apoptosis, transcription and DNA damage response due to zinc deficiency in the prostate were identified. In particular, TP73, MRE11A, XRCC4 and BRCA2 were down-regulated and p53 was up-regulated with zinc deficiency. P53 is a transcription factor that is commonly mutated in many cancers, and contains zinc in its DNA binding site. Western blotting showed increased nuclear p53 expression in ZnDF compared to ZnAD cells. Despite increased p53 gene and nuclear protein expression, no significant change in p53 binding activity was observed by Transcription Factor Array and EMSA. Furthermore, no changes in gene expression of the downstream p53 targets, p21, GADD45 and BAX was observed. These data indicate that zinc deficiency may compromise DNA integrity in the prostate by impairing the function of p53, possibly through loss of zinc in the DNA binding region. To parallel the in vitro study an in vivo study was conducted in mice. Mice were fed zinc adequate or zinc deficient diet for 5 weeks to induce zinc deficiency. Global gene expression changes in the prostate were assessed using the Affymetrix Mouse 430 2.0 GeneChip. Similar classes of genes were differentially expressed. In particular genes involved in apoptosis, cell cycle regulation, transcription, and several genes known to possess zinc binding properties were differentially expressed. However, no change in p53 gene expression in mouse prostates was observed with zinc deficiency. Additional analysis of these data are planned and will include further analysis of p53, such as nuclear protein expression, binding activity and effects on downstream p53 targets. Together, these data strongly suggest that zinc plays an essential role in maintaining DNA integrity in the prostate. Loss of zinc due to zinc deficiency from critical zinc containing proteins, such as p53, may impair DNA damage response mechanisms, ultimately leading to increased risk for prostate cancer development.