Zinc status affects p53, gadd45, and c-fos expression and caspase-3 activity in human bronchial epithelial cells

Abstract

This study was designed to examine the influence of zinc depletion and supplementation on the expression of p53 gene, target genes of p53, and caspase-3 activity in normal human bronchial epithelial (NHBE) cells. A serum-free, low-zinc medium containing 0.4 μmol/l of zinc [zinc deficient (ZD)] was used to deplete cellular zinc over one passage. In addition, cells were cultured for one passage in media containing 4.0 μmol/l of zinc [zinc normal (ZN)], which represents normal culture concentrations (Clonetics); 16 μmol/l of zinc [zinc adequate (ZA)], which represents normal human plasma zinc levels; or 32 μmol/l of zinc [zinc supplemented (ZS)], which represents the high end of plasma zinc levels attainable by oral supplementation in humans. Compared with ZN cells, cellular zinc levels were 76% lower in ZD cells but 3.5-fold and 6-fold higher in ZA and ZS cells, respectively. Abundances of p53 mRNA and nuclear p53 protein were elevated in treatment groups compared with controls (ZN). For p53mRNA abundance, the highest increase (3-fold) was observed in ZD cells. In contrast, the highest increase (17-fold) in p53 nuclear protein levels was detected in ZS cells. Moreover, gadd45mRNA abundance was moderately elevated in ZD and ZA cells and was not altered in ZS cells compared with ZN cells. Furthermore, the only alteration in c-fos mRNA and caspase-3 activity was the twofold increase and the 25% reduction, respectively, detected in ZS compared with ZN cells. Thus p53, gadd45, and c-fos and caspase-3 activity appeared to be modulated by cellular zinc status in NHBE cells.