Detection of early gene expression changes by differential display in the livers of mice exposed to dichloroacetic acid

Dichloroacetic acid (DCA) is a major by-product of water disinfection by ch lorination. Several studies have demonstrated the hepatocarcinogenicity of DCA in mice when administered in drinking water. The mechanism of DCA carci nogenicity is not clear and we speculate that changes in gene expression ma y be important. In order to analyze early changes in gene expression induce d by DCA treatment we used the differential display method. Mice were treat ed with 2 g/l DCA in drinking water for 4 weeks. Total RNAs were obtained f rom livers of both control and treated mice for analysis. Of similar to 48 000 bands on the differential display gels representing an estimated 96% of RNA species, 381 showed differences in intensity. After cloning and confir mation by both reverse-northern and northern analyses, six differentially e xpressed genes were found. The expression of five of these genes was suppre ssed in the DCA-treated mice while one was induced. After sequencing, four genes were identified and two were matched to expressed sequence tags throu gh the BLAST program. These genes are alpha-1 protease inhibitor, cytochrom e b5, stearoyl-CoA desaturase and carboxylesterase. Stearoyl-CoA desaturase was induced similar to3-fold in the livers of DCA-treated mice and the oth er three genes were suppressed approximately 3-fold. Stearoyl-CoA desaturas e, cytochrome b5 and carboxylesterase are endoplasmic reticulum membrane-bo und enzymes involved in fatty acid metabolism. The expression pattern of fo ur of these genes was similar in DCA-induced hepatocellular carcinomas and the 4 week DCA-treated mouse livers. The expression of stearoyl-CoA desatur ase and one of the unidentified genes returned to control levels in the car cinomas. Understanding the roles and interactions between these genes may s hed light on the mechanism of DCA carcinogenesis.