ANALYSIS OF STEADY-STATE MESSENGER-RNA LEVELS OF CATALASE AND HEME OXYGENASE IN CULTURED RAT FAO CELLS TREATED WITH CHROMIUM(VI), USING SOLUTION HYBRIDIZATION

A sensitive solution hybridization assay was used to quantitate changes in the steady-state mRNA levels of two oxidative damage-inducible genes, catalase and heme oxygenase, in rat FAO cells treated with sodium dichromate [Cr(VI)], and two known oxidant compounds, hydrogen peroxide and heme. Both catalase and heme oxygenase mRNA levels were observed to be increased in cell cultures after a 4 h treatment with 5 muM Cr(VI). Catalase steady-state mRNA levels were induced approximately 4-fold while heme oxygenase mRNA levels were induced about 2-fold above basal expression. In comparison, treatment of FAO cell cultures with 200 muM hydrogen peroxide, a reactive intracellular oxidant, increased catalase mRNA levels 2-fold after 4 h of exposure. Induction of heme oxygenase for 8 h with 5 muM heme, an Fe(II)-containing natural inducer for this gene, was similar to Cr(VI) induction. Since the intracellular reduction of Cr(VI) to Cr(III) is believed to produce reactive intermediates, catalase and heme oxygenase induction in FAO cells by Cr(VI) may occur in response to an increase in cellular oxidative damage. The nature of Cr(VI)-mediated induction of oxidative damage-inducible gene expression and a detailed description of the solution hybridization assay is presented.