Down-Regulation of Proliferating Cell Nuclear Antigen Gene Expression Occurs during Cell Cycle Arrest Induced by Human Fecal Water in Colonic HT-29 Cells

Abstract

Cancer is a disease in which the cell cycle is altered, and the elucidation of the mechanisms by which constituents of human fecal water influence the cell cycle can lead to noninvasive measurement of colon cancer risk. The purpose of the present study was to investigate the effect of human fecal water on HT-29 cell-cycle progression with sodium selenite as a reference for comparison. Both human fecal water (2.5-5.0%) and selenite (3-4 micro mol/L) significantly inhibited cell growth. Cell-cycle analysis revealed that human fecal water decreased the proportion of S + G2 phase cells and increased that of G1 phase cells. In contrast, selenite decreased G1 phase cells and increased proportions of S and G2 phase cells. Both 5% human fecal water and 4 micro mol/L selenite greatly increased the mRNA level of the cyclin-dependent kinase inhibitor gene p21(waf1). Interestingly, the mRNA levels of cyclin A and proliferating cell nuclear antigen (PCNA) were dramatically decreased by 69 and 62%, respectively, in HT-29 cells treated with fecal water but not selenite. In contrast, the mRNA level of DNA damage-inducible transcript 1, gadd45, was significantly increased by 2.28-fold in HT-29 cells treated with selenite but not fecal water. Furthermore, a PCNA gene promoter was cloned into a luciferase reporter construct and its activity was significantly reduced in a dose-dependent manner in cells treated with fecal water but not selenite. Collectively, these results suggest that human fecal water and selenite can differentially induce growth arrest genes, and that PCNA gene expression is uniquely and highly sensitive to human fecal water.