The effects of mercuric chloride on growth, cytokine and MHC class II gene expression in a human leukemic mast cell line

Abstract

We have examined the effects of mercuric choride (HgCl 2) on growth and IL-4, IL-8, TNF-a and MHC class II gene expression in the HMC-1 human leukemic mast cell line. Proliferation, measured by [ 3H]thymidine incorporation or production of a formazan product (MTT assay), was substantially inhibited by HgCl 2 at concentrations of 10 −6 M and above. Inspection of the DNA by agarose gel electrophoresis from HgCl 2-treated cells revealed that it was intact, indicating inhibition of DNA synthesis, but not denaturation. HgCl 2 inhibited expression of mRNA for IL-8, TNF-a and MHC class II at 4 × 10 −6 M and inhibited expression of IL-4 mRNA at 8 × 10 −6 M and above. At a concentration of 10 −5 M, HgCl 2 almost completely blocked mRNA expression for IL-4, IL-8, TNF-a and MHC class II, but produced negligible inhibition of expression of mRNA encoding the housekeeping gene β-actin, thus demonstrating selective toxicity for the cytokine and MHC class II genes studied. Pre-exposure of the cells to human recombinant IL-4 prior to treatment with HgCl 2 had no effect on expression levels of any of the genes examined. The effects seen in this study are consistent with previous reports showing immunotoxic effects of HgCl 2 on other cell types, therefore, the HMC-1 mast cell line may prove useful in further studies of mast cell cytokine gene expression and the mechanisms involved in cytokine gene toxicity.