Dietary factors play an important role in the pathogenesis of colorectal cancer (CRC), due in part to the influence of the bile acids. While the secondary bile acid, deoxycholic acid (DCA), has been associated with tumor promotion, one tertiary bile acid in particular, ursodeoxycholic acid (UDCA), has been demonstrated to exert chemopreventive properties in the colon. Although its efficacy against high-grade adenomas has already been demonstrated in phase III clinical trials, mechanisms by which UDCA suppresses colon tumorigenesis remain unclear. In order to gain further insight into the tumor modifying properties of the bile acids, we compared the effects of DCA and UDCA on human colon tumor cells (CaCo-2) using a combination of genomic and proteomic analyses. In the following study, CaCo-2 cells grown at 70% confluence were treated with either 10 µM deoxycholic acid (DCA) or 1 mM ursodeoxycholic acid (UDCA) for 72 hours. RNA was hybridized onto Illumina BeadArrays consisting of 500 human cancer-related genes. Approximately 15 genes showed significant differences in expression patterns between UDCA and DCA treatments. Interestingly, the levels of genes involved in cell cycle regulation and DNA repair were most differentially regulated. For proteomic analysis, protein was first fractionated by PF2D isochromatofocusing on a Beckman Coulter ProteomeLab PF2D platform. Fractions corresponding to a linear gradient between pH 8.0 and 4.0 were collected and processed through an automated autoloader for further separation by HPRP-PF2D reverse phase chromatography. Two dimensional protein expression maps displaying isoelectric point (pI) versus hydrophobicity were generated by the ProteoView/DeltaVue software package. Pairwise analysis of these complex protein chromatograms demonstrated common peak profiles (signatures) as well as unique peaks (fingerprints) characteristic of UDCA or DCA treatment. These protein peaks are prime candidates for identification by MALDI and tandem mass spectrometry sequencing. Further analyses using this combined approach will enable precise identification of differentially regulated cellular pathways controlled by bile acids.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA