An improved transfection assay for evaluating the effects of heavy metals

The transfection assay is an important tool for evaluating the health effects of industrial chemicals, with the reporter gene expression as an indicator. However, heavy metals often influence the expression of the reference plasmids used to correct variations in transfection efficiency between assay plates, reducing the reliability of this assay. We found that the target of heavy metals is the reporter, rather than the promoter used in the reference plasmid. Of the reporters we tested, luciferase (Luc) enzyme activity was affected by heavy metals, whereas gene product levels of the chloramphenicol acetyltransferase (CAT) or beta-galactosidase (betaGal) gene were not. Neither heavy metals nor extracts from cells exposed to heavy metals showed an effect when directly added to the Luc enzyme, suggesting that heavy metals act through an indirect mechanism. These data indicate that the use of CAT or betaGal as a reporter is appropriate for a reliable assay of heavy metal effects.