FERRITIN IS A DEVELOPMENTALLY-REGULATED NUCLEAR-PROTEIN OF AVIAN CORNEAL EPITHELIAL-CELLS

We have now observed that one group of these antibodies reacts with a developmentally regulated component of corneal epithelial cell nuclei. This component is the heavy chain of ferritin, as determined by analy ses of immunoisolated cDNA clones and immunoblotting of the protein. I mmunoblotting also suggests that the nuclear ferritin may be in a supr amolecular form that is similar to the iron-binding ferritin complex f ound in the cytoplasm of many cells. In vitro cultures and transfectio n studies show that the nuclear localization depends predominantly on cell type but can be altered by the in vitro environment. The appearan ce of nuclear ferritin is at least partially under translational regul ation, as is known to be true for the cytoplasmic form of the molecule , The tissue and developmental distributions of the mRNA for the molec ule are much more extensive than the protein itself, and the removal o f iron from cultures of corneal epithelial cells with the iron chelato r deferoxamine prevents the appearance of nuclear ferritin. At present the functional role(s) of nuclear ferritin remain unknown, but previo us studies on cytoplasmic ferritin raise the possibility that it preve nts damage due to free radical generation (''oxidative stress'') by se questering iron, Although it remains to be tested whether nuclear ferr itin prevents oxidative damage, we find this an attractive possibility , Since the corneal epithelium is transparent and is constantly expose d to free radical-generating UV light, it is possible that the cells o f this tissue have evolved a specialized mechanism to prevent oxidativ e damage to their nuclear components.