Nuclear ferritin: a ferritoid-ferritin complex in corneal epithelial cells.
OBJECTIVE
Ferritin is an iron storage protein that is generally cytoplasmic. However, in embryonic avian corneal epithelial (CE) cells, the authors previously observed that the ferritin was predominantly nuclear. They also obtained evidence that this ferritin protects DNA from oxidative damage by UV light and hydrogen peroxide and that the nuclear localization involves a tissue-specific nuclear transporter, termed ferritoid. In the present investigation, the authors have determined additional properties of the nuclear ferritoid-ferritin complexes.


METHODS
For biochemical characterization, a combination of molecular sieve chromatography, immunoblotting, and nuclear-cytoplasmic fractionation was used; DNA binding was analyzed by electrophoretic mobility shift assay.


RESULTS
The CE nuclear ferritin complex has characteristics that differentiate it from a "typical" cytoplasmic ferritin, including the presence of ferritin and ferritoid subunits; a molecular weight of approximately 260 kDa, which is approximately half that of cytoplasmic ferritin; its iron content, which is below our limits of detection; and its ability to bind to DNA.


CONCLUSIONS
Within CE cell nuclei, ferritin and ferritoid are coassembled into stable complex(es) present in embryonic and adult corneas. Thus, ferritoid not only serves transiently as a nuclear transporter for ferritin, it remains as a component of a unique ferritoid-ferritin nuclear complex.
Nurminskaya
Maria V
MV
Department of Anatomy and Cell Biology, Tufts University, Boston, MA 02111, USA.
Talbot
Christopher J
CJ
Nurminsky
Dmitry I
DI
Beazley
Kelly E
KE
Linsenmayer
Thomas F
TF
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D018929:Cell Culture Techniques; D002467:Cell Nucleus / Q000378:metabolism*; D002642:Chick Embryo; D002645:Chickens; D002850:Chromatography, Gel; D004268:DNA-Binding Proteins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D019573:Epithelium, Corneal / Q000196:embryology* / Q000378:metabolism; D005293:Ferritins / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D047468:Immunoprecipitation; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D026901:Membrane Transport Proteins; D009687:Nuclear Proteins; D005293:Ferritins; D007770:L-Lactate Dehydrogenase