THE GENOTOXIC CARCINOGEN CHROMIUM(VI) ALTERS THE METAL-INDUCIBLE EXPRESSION BUT NOT THE BASAL EXPRESSION OF THE METALLOTHIONEIN GENE IN-VIVO

The ability of the carcinogen chromium(VI) to affect the basal and zin c-inducible expression of liver metallothionein was examined in 14- an d 18-day chicken embryos in vivo. Metallothionein expression varied wi th the stage of embryo development, with basal steady-state mRNA level s being approximately three times lower in livers of 18-day versus 14- day chicken embryos. Chromium(VI) treatment had no effect on the basal steady-state levels of metallothionein mRNA and protein in either 14- or 18-day chicken embryo liver. Treatment of 14-day embryos with zinc (II) resulted in a 3- to 5-fold increase in steady-state levels of met allothionein mRNA in liver. Pre-treatment of 14-day embryos with chrom ium(VI) inhibited the zinc(II)-induced increase in steady-state levels of metallothionein mRNA and protein in liver by 30-50%. In contrast, chromium(VI) and/or zinc(II) treatments had no effect on steady-state levels of beta-actin mRNA.