Submitted to: Biological Trace Element Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2010
Publication Date: 8/15/2010
Publication URL: http://handle.nal.usda.gov/10113/58196
Citation: Uthus, E.O., Begaye, A., Ross, S., Zeng, H. 2010. The von Hippel-Lindau (VHL) tumor-suppressor gene is down-regulated by selenium deficiency in Caco-2 cells and rat colon mucosa. Biological Trace Element Research. 2011 142:223-231. Interpretive Summary: The dietary nutrient selenium is known to have anticancer properties. It is also know that deficiency of selenium results in increased cancer in animal models. The reasons for selenium’s anticancer property and also why selenium deficiency results in increased cancer, are not completely understood. It is known that selenium affects the metabolism of the amino acid methionine.Methionine is important because it has a methyl group which it can donate to other compounds in the body. DNA is one such compound that can accept methyl groups from methionine. When these methyl groups are in particular regions, called promoter regions, of the DNA molecule, that portion of the DNA can be turned off. If genes (tumor suppressor genes) important in fighting cancer are turned off in this way, the incidence of cancer can increase. We wanted to see if selenium deficiency would methylate promoter regions from certain tumor suppressor genes. If this happened, it would be a possible mechanism that helps explain why there is an increase in cancer when selenium is deficient. We found that selenium deficiency resulted in the methylation of the promoter region of the von Hippel Lindau tumor suppressor gene in human cells. Further, we showed that this increase in gene methylation resulted in the expression of that gene being significantly reduced. Then, using an animal model we showed a decreased expression of the von Hippel Lindau gene expression in colon cell from the rats fed a selenium deficient diet. These studies confirm the importance of dietary selenium and may help provide other avenues of research that can be used to determine the mechanism of action of selenium in fighting cancer.
Technical Abstract: To test the hypothesis that selenium affects DNA methylation and hence gene regulation we employed a methylation array (Panomics) in the human colonic epithelial Caco-2 cell model. The array profiles DNA methylation from promoter regions of 82 human genes. After conditioning cells to repeatedly reduced concentrations of fetal bovine serum, a serum-free culture was established. Se-methylselenocysteine (SeMSC) was added at 0 (deficient Se) or 250 (control Se) nM to cells maintained in DMEM. After 7d cells were collected and stored at -80°C until analysis; experiments were replicated 3 times. GPx activity was significantly decreased in cells grown in low SeMSC. Cells grown in 250 nM SeMSC had maximal GPx activity. Of the genes profiled, VHL was most different by visual inspection of the arrays indicating that its promoter was hypermethylated in cells from the low-SeMSC media. To determine whether promoter methylation affected transcription, we isolated RNA from replicate samples and performed real-time RT PCR. VHL (mRNA) was down-regulated (fold change significantly <1) in cells grown in low SeMSC compared to cells grown in 250 nM SeMSC (fold change =1). We also show that (mRNA) Vhl expression is significantly reduced in mucosa from rats fed a diet deficient in Se. Our results suggest that low Se status affects DNA promoter region methylation and that this can result in down-regulation of the tumor suppressor gene VHL.