Suppression of Carbonic Anhydrase III in Rat Liver by a Dioxin-Related Toxic Compound, Coplanar Polychlorinated Biphenyl, 3,3′,4,4′,5-Pentachlorobiphenyl

A coplanar polychlorinated biphenyl, 3,3′,4,4′,5-pentachlorobiphenyl (PenCB), significantly suppresses the expression of rat liver carbonic anhydrase III (CAIII), an enzyme which has recently been suggested to prevent from H2O2-inducible apoptosis. Marked changes in the CAIII levels of liver cytosol were observed in rats following doses of PenCB ranging from 0.5 to 25 mg/kg body weight and maximum suppression was observed at a dose of 10 mg/kg. Northern analysis revealed that the level of CAIII mRNA in rat liver was dramatically reduced by PenCB treatment while only weak suppression was observed in pair-fed controls. Two AU-rich elements, considered as a destabilizing signal of mRNA, were found in the 3′-untranslated region of CAIII sequenced after reverse transcription-PCR and 3′-rapid amplification of the cDNA end. Dramatic decrease of CAIII in rat liver by PenCB could account for the suppression of the defense system for oxidative stress.