THE EFFECTS OF MERCURIC-CHLORIDE ON GROWTH, CYTOKINE AND MHC CLASS-IIGENE-EXPRESSION IN A HUMAN LEUKEMIC MAST-CELL LINE

We have examined the effects of mercuric choride (HgCl2) on growth and IL-4, IL-8, TNF-alpha and MHC class II gene expression in the HMC-1 h uman leukemic mast cell line. Proliferation, measured by [H-3]thymidin e incorporation or production of a formazan product (MTT assay), was s ubstantially inhibited by HgCl2 at concentrations of 10(-6) M and abov e. Inspection of the DNA by agarose gel electrophoresis from HgCl2-tre ated cells revealed that it was intact, indicating inhibition of DNA s ynthesis, but not denaturation. HgCl2 inhibited expression of mRNA for IL-8, TNF-alpha and MHC class II at 4 x 10(-6) M and inhibited expres sion of IL-4 mRNA at 8 x 10(-6) M and above. At a concentration of 10( -5) M, HgCl2 almost completely blocked mRNA expression for IL-4, IL-8, TNF-alpha and MHC class Il, but produced negligible inhibition of exp ression of mRNA encoding the housekeeping gene beta-actin, thus demons trating selective toxicity for the cytokine and MHC class II genes stu died. Pre-exposure of the cells to human recombinant IL-4 prior to tre atment with HgCl2 had no effect on expression levels of any of the gen es examined. The effects seen in this study are consistent with previo us reports showing immunotoxic effects of HgCl2 on other cell types, t herefore, 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.