Previously, we identified the heavy chain of ferritin as a development
ally regulated nuclear protein of embryonic chicken corneal epithelial
cells. The nuclear ferritin is assembled into a supramolecular form i
ndistinguishable from the cytoplasmic form of ferritin found in other
cell types and thus most likely has iron-sequestering capabilities. Fr
ee iron, via the Fenton reaction, is known to exacerbate UV-induced an
d other oxidative damage to cellular components, including DNA. Since
corneal epithelial cells are constantly exposed to UV light, we hypoth
esized that the nuclear ferritin might protect the DNA of these cells
from free radical damage. To test this possibility, primary cultures o
f cells from corneal epithelium and stroma, and from skin epithelium a
nd stroma, were UV irradiated, and DNA strand breaks were detected by
an in situ 3'-end labeling method. Corneal epithelial cells without nu
clear ferritin were also examined. We observed that the corneal epithe
lial cells with nuclear ferritin had significantly less DNA breakage t
han other cell types examined. Furthermore, increasing the iron concen
tration of the culture medium exacerbated the generation of UV-induced
DNA strand breaks in corneal and skin fibroblasts, but not in the cor
neal epithelial cells. Most convincingly, corneal epithelial cells in
which the expression of nuclear ferritin was inhibited became much mor
e susceptible to UV-induced DNA damage. Therefore, it seems that corne
al epithelial cells have evolved a novel, nuclear ferritin-based mecha
nism for protecting their DNA against UV damage.