The influence of zinc status onp53 tumor suppressor gene expression and p53 target genes in human hepatoblastoma, bronchial epithelial, and aortic endothelial cells

Abstract

The influence of zinc status on the expression of p53, the human tumor suppressor gene as well as downstream target genes of p53 were examined in human cell lines. HepG2 cells were depleted of cellular zinc using a low-zinc media containing Chelex-100 treated serum. Cellular zinc levels were depleted to 64% of controls (4.0 μM zinc, comparable to normal media). p53 mRNA was increased in the zinc-depleted HepG2s as compared to control, however, p53 protein levels and DNA binding activity were not significantly different among treatment groups. NHBEs were depleted of zinc using a serum-free zinc-free media which contained residual amounts of zinc (0.4 μM, ZD). Other treatments included a control group at 4.0 μM of zinc (ZN), for comparison with normal media, 16.0 μM (ZA), for comparison with human serum levels of zinc, and 32.0 μM (ZS), an attainable level of zinc supplementation in humans. Zinc was reduced to 34% in the ZD group as compared to the ZN control group, however, the ZA group and ZS group were significantly higher than control, 240% and 446% respectively. Using RNase protection assays, p53 and gadd45 mRNA were increased almost 100% in the ZD group, as compared to ZN and was higher in the ZA and ZS groups. c-fos was increased 79% in the ZS group as compared to the control group. p53 protein levels were almost 500% higher in the ZD group, and the ZA and ZS groups were six-fold and 16-fold higher respectively, as compared to the ZN group. HAECs were depleted of zinc using a low-serum zinc-free media that contained residual amounts of zinc (0.8 μM, ZD). Other treatments included a control group at 3.0 μM of zinc (ZN), 16.0 μM (ZA), and 32.0 μM (ZS). p53 protein was increased 100% in both the ZD and ZS groups as compared to control, and almost 200% higher in the ZA group. p21, bax and bcl-2, showed significant increases in mRNA in the ZS group as compared to the ZN control group. Mcl-1 mRNA abundance also showed an increase in the ZS cells as compared to ZN control cells.