Effect of elevated zinc chloride concentrations on protein synthesis in human lung cells

Effects of zinc chloride (ZnCl2) on protein synthesis were studied in cultured cells (16Lu) derived from human lung. High levels of ZnCl2 suppressed protein synthesis in fibroblast-like 16Lu cells as assessed by methionine incorporation into acid-precipitable material. IC50 values (zinc concentrations required for half-maximal inhibition of protein synthesis) were 120 mu M and 100 mu M for 5- and 7-hour incubation intervals, respectively. Cell-associated acid-soluble radioactivity was similar in control cells and cells exposed to 150 mu M ZnCl2 for 6 hours. This rules out a decreased availability of methionine. Two-dimensional protein maps from 16Lu cell homogenates showed. few striking differences between zinc-exposed cells and controls. A 28-kDa spot from lysates of zinc-exposed cells regularly lost its intensity as assessed by silver-stained polyacrylamide gels, but became detectable again when the cells were given fresh medium for 4 hours after a 1 hour ZnCl2 exposure. Addition of ZnCl2 to fresh lysates of control cells did not affect the 28 Ir]Da spot. When cells were switched to fresh medium the reappearance of the spot could be prevented by the addition of cycloheximide or puromycin. Similar changes were seen with CdCl2, but not with arsenic GAS), barium (Ba), cobalt (Go), iron (Fe), mercury (Hg), and manganese (Mn) salts. Autoradiographs of 16Lu cell homogenates obtained from ZnCl2-treated cells (up to 200 mu M over 6 hours) and using radiolabeled methionine as tracer were virtually blank, indicating a complete blocking of protein synthesis. When concentrations of ZnCl2 exceeded 100 mu M for more than 5 hours, cells became progressively damaged. Severe morphological alterations were seen after 24 hours (rounding oh, blebbing, cytolysis). Our results show that 16Lu cells are severely injured by moderate levels of zinc and apparently lack typical protective measures that have been observed after experimental zinc exposure in vitro and in vivo. Because 16Lu cells are nonmalignant fibroblast-like cells, this vulnerability may provide interesting clues to possible mechanisms involved in the complex response of pulmonary tissue to inhaled zinc-containing dust and fumes.