Sep15 and TR1 pathways in colon cancer promotion

Selenoproteins mediate the cancer-preventive properties of the essential nutrient selenium, but also have cancer-promoting effects. We examined the contributions of the 15-kDa selenoprotein (Sep15) and thioredoxin reductase 1 (TR1) to cancer development. Targeted down-regulation of either gene inhibited anchorage-dependent and anchorage-independent growth and cancer metastasis of mouse colon carcinoma CT26 cells. Surprisingly, combined deficiency of Sep15 and TR1 reversed the anti-cancer effects observed with down-regulation of each single gene. We found that inflammation-related genes regulated by Stat-1, especially the interferon-gamma-regulated guanylate-binding proteins, were highly elevated in Sep15-deficient cells. In contrast, the Wnt/Beta-catenin pathway was up-regulated in cells that lacked both TR1 and Sep15. These results suggest that Sep15 and TR1 participate in interfering regulatory pathways in colon cancer cells. Considering the variable expression levels of Sep15 and TR1 found within the human population, and controversial results of recent human clinical trials involving dietary selenium, our results are important to general public health. mRNA was isolated from plasmid-transfected control, shSep15, shTR1, and shTR1/shSep15 knockdown CT26 cells (four replicates of each). Microarray analysis was performed on Affymetrix Mouse 430_2 gene chips. Four arrays were analyzed from different mRNA samples for each construct.