Transcriptome analyses in normal prostate epithelial cells following exposure to low-dose cadmium

BACKGROUND: Cadmium is implicated in prostate carcinogenesis, but its oncogenic action remains unclear. OBJECTIVES: In this study we aimed to decipher changes in cell growth and the transcriptome in an immortalized human normal prostate epithelial cell line (NPrEC) following exposure to low-dose Cd. METHODS: Synchronized NPrEC cells were exposed to different doses of Cd and assayed for cell viability and cell-cycle progression. We investigated changes in transcriptome by global profiling and used Ingenuity Pathways Analysis software to develop propositions about functional connections among differentially expressed genes. A neutralizing antibody was used to negate the effect of Cd-induced up-regulation of tumor necrosis factor (TNF) in NPrEC cells. RESULTS: Exposure of NPrEC to 2.5 μM Cd enhanced cell viability and accelerated cell-cycle progression. Global expression profiling identified 48 genes that exhibited ≥ 1.5-fold changes in expression after 4, 8, 16, and 32 hr of Cd treatment. Pathway analyses inferred a functional connection among 35 of these genes in one major network, with TNF as the most prominent node. Fourteen of the 35 genes are related to TNF, and 11 exhibited an average of > 2-fold changes in gene expression. Real-time reverse transcriptase-polymerase chain reaction confirmed the up-regulation of 7 of the 11 genes (ADAM8, EDN1, IL8, IL24, IL13RA2, COX2/PTGS2, and SERPINB2) and uncovered a 28-fold transient increase in TNF expression in Cd-treated NPrEC cells. A TNF-neutralizing antibody effectively blocked Cd-induced elevations in the expression of these genes. CONCLUSIONS: Noncytotoxic, low-dose Cd has growth-promoting effects on NPrEC cells and induces transient overexpression of TNF, leading to up-regulation of genes with oncogenic and immunomodulation functions. KEY WORDS: carcinogenesis, cytokine, global expression profiling, heavy metals, immune response, inflammation, Ingenuity Pathway Analysis, knowledge-based analysis, prostate cancer. A total of 19 samples were analyzed, each experimental condition having two biological replicates, except Cadmium 4hr which has only 1 sample. Cadmium-treated and control samples were taken at 0, 4, 8, 16, and 32 hours.