Differences in the cellular zinc content and 5′-nucleotidase activity of normal and acrodermatitis enteropathica (AE) fibroblasts

The acrodermatitis enteropathica (AE) mutation affects zinc (Zn) metabolism in human fibroblasts. We hypothesize that the mutation affects the cell Zn content, which subsequently affects the activity of various zinc-dependent enzymes, such as 5'-nucleotidase. Therefore, normal and AE fibroblasts were grown in normal medium containing physiological levels of Zn (16 mu mol/L) for similar to 24 h. The medium was replaced by normal medium (16 mu mol/L Zn), Zn-depleted medium (1.5 mu mol/L Zn), or Zn-supplemented medium (200 mu mol/L Zn) for another 24 h. Regardless of the Zn concentration of the growth medium, the AE fibroblasts contained significantly less Zn than normal fibroblasts grown in comparable medium. Nevertheless, growth of the fibroblasts in 200 mu mol/L Zn medium significantly increased the cell Zn content fourfold of both normal and AE fibroblasts. The activity of 5'-nucleotidase in the AE fibroblasts grown in 16 mu mol/L Zn or 1.5 mu mol/L Zn medium was also significantly lower than in normal fibroblasts. Changing the growth medium from 16 mu mol/L Zn to 1.5 mu mol/L Zn medium did not affect the activity of the enzyme in either genotype. Cells grown in 200 mu mol/L Zn medium exhibited threefold greater 5'-nucleotidase activity in AE fibroblasts, but had no affect on enzyme activity in normal cells. In summary altering the cell Zn content of normal fibroblasts did not result in a significant change in their 5'-nucleotidase activity. However, AE fibroblasts grown in 200 mu mol/L Zn medium exhibited recovery of their 5'-nucleotidase activity to normal levels. These results support the hypothesis that the AE mutation affects the cellular Zn content. The lower cell Zn content subsequently affects the activity of 5'-nucleotidase.