Ras responsive element binding protein‐1 (RREB‐1) down‐regulates hZIP1 expression in prostate cancer cells

Abstract

Normal prostate accumulates extremely high levels of zinc compared to other soft tissues. In contrast, the level of zinc in the prostate decreases significantly in prostate cancer. We have shown that down-regulation of the expression of the zinc transporter hZIP1 in prostate cancer is an important event that is responsible for the decrease of zinc levels. However, the mechanism of hZIP1 down-regulation is not known. We have hypothesized that hZIP1 is down-regulated through transcriptional regulation. The hZIP1 promoter was studied using luciferase reporter assays, site-directed mutagenesis, gel shift, and ChIP assay. We have characterized a promoter region, downstream of the transcription start site, responsible for repression of hZIP1 transcription. We demonstrate that this region contains a binding site for the Ras-Responsive Element Binding protein 1 (RREB-1) and that the binding of RREB-1 to the hZIP1 promoter is involved in the decrease of hZIP1 transcription in PC-3 cells. The Ras pathway and activation of RREB-1 are involved in hZIP1 down-regulation and may play a role in the decrease of the transporter expression in prostate cancer.