Role of ferritin in the control of the labile iron pool in murine erythroleukemia cells.
In vitro studies have shown that ferritin iron incorporation is mediated by a ferroxidase activity associated with ferritin H subunits (H-Ft) and a nucleation center associated with ferritin L subunits (L-Ft). To assess the role played by the ferritin subunits in regulating intracellular iron distribution, we transfected mouse erythroleukemia cells with the H-Ft subunit gene mutated in the iron-responsive element. Stable transfectants displayed high H-Ft levels and reduced endogenous L-Ft levels, resulting in a marked change in the H:L subunit ratio from 1:1 in control cells to as high as 20:1 in some transfected clones. The effects of H-Ft overexpression on the labile iron pool were determined in intact cells by a novel method based on the fluorescent metallosensor calcein. H-Ft overexpression resulted in a significant reduction in the iron pool, from 1.3 microM in control cells to 0.56 microM in H-Ft transfectants, and in higher buffering capacity following iron loads. A fraction of the H-Ft-associated iron was labile, available to cell-permeant, but not cell-impermeant, chelators. The results of this study provide the first in vivo direct demonstration of the capacity of H-Ft to sequester cell iron and to regulate the levels of the labile iron pool.
Picard
V
V
INSERM U409, Faculté Xavier Bichat, BP416, 75870 Paris Cedex 18, France.
Epsztejn
S
S
Santambrogio
P
P
Cabantchik
Z I
ZI
Beaumont
C
C
D000818:Animals; D001052:Apoferritins; D002451:Cell Compartmentation; D015536:Down-Regulation; D005293:Ferritins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007501:Iron / Q000378:metabolism*; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D014162:Transfection; D014407:Tumor Cells, Cultured
D005293:Ferritins; D001052:Apoferritins; D007501:Iron