Implication of free radicals and glutathione in the mechanism of cadmium-induced expression of stress proteins in the A549 human lung cell-line

Cellular mechanisms underlying the expression of stress proteins (HSP) were studied in the human cell-line A549 submitted to a pollutant, cadmium, in the presence of several agents which modulate the glutathione level and, supposedly, the effects of this metal in the cell. It was observed that HSP 90, HSP 72 and HSP 27 are significantly over-expressed after exposure to cadmium chloride for 24 h. Low cadmium concentrations (i.e. from 1 to 10 microM) also triggered a slight accumulation of glutathione, whereas this compound was depleted after exposure to higher cadmium concentrations (25-100 microM). When 50 microM diethyl-maleate, which traps glutathione, was added together with cadmium, the over-expression of HSP 72 and HSP 90 was much stronger. Treatment of cells with 20 or 40 mM N-acetyl-L-cysteine, which traps free radicals, was found to increase by 30% the glutathione level and to suppress the HSP over-expression. From our results, it is suggested that HSP induction by cadmium in A549 cells is due, at least in part, to the oxidative stress consisting in formation of reactive oxygen species and inhibition of peroxides detoxification. Due to this oxidative status within the cell, more proteins would be damaged inducing the HSP over-expression.