Characteristics and expression of binding sites specific for ferritin H- chain on human cell lines

Abstract

Purified recombinant human ferritin composed solely of H subunit was radiolabeled and incubated with proerythroleukemic K562 human cells. A specific binding was detected, and it could be displaced only by ferritins, natural or recombinant, containing large proportion of the H subunit. The specific ferritin H-chain binding was saturable, and cells showed 17,000 to 23,000 binding sites per cell. The affinity constant measured at 37 degrees C was of 3 x 10(8) M-1. Treatment with pronase eliminated the specific binding. The binding sites were expressed in a high number during the cellular exponential phase of growth and progressively decreased to disappear when cells reached the plateau phase. Treatment of the cells with desferrioxamine increased recombinant H-ferritin binding, while iron had little effect. K562 cells induced to differentiate by hemin failed to bind ferritin H. Ferritin H-chain binding capacity is present on various cell lines such as HL60, lung cancer, and hepatoma cells. Analysis of the binding sites by western blotting showed a peptide with apparent mol wt of about 100 kd.

Ferritin is the key to dietary iron absorption and tissue iron detoxification inDrosophila melanogaster

“…Despite extensive biochemical, cytological, and genetic study of vertebrate and insect ferritins, their functions (in particular that of the secreted form of ferritin) at systemic, cellular, and molecular levels are not completely elucidated. A great deal of research effort has shown that mammalian serum ferritin can bind to a variety of cell types in a specific, saturable manner and undergo endocytosis with subsequent iron delivery (8,12,13). Several ferritin receptors on the surface of certain cell types or ferritin interaction proteins in plasma were even identified recently (12,14,15).…”

Iron‐binding Proteins

“…An immunosuppressive role for ferritin has also been proposed, based on !ts ability to inhibit mitogen-stimulated lymphocyte proliferation ( 121,122). The recent characterisation of ferritin receptors on a number of different cell types ( 123,124) supports the idea that ferritin may regulate certain cell functions.…”

Binding and suppressive activity of human recombinant ferritins on erythroid cells

“…for H-ferritin. Their expression was induced by cellular proliferation and iron depletion and in K562 cells it was suppressed by hemin induced differentiation [22]. A relation between the expression of H-ferritin binding sites and H-ferritin suppressive activity was suggested.…”

“…Ferritin binding was performed as described by Fargion et al [22]. Briefly, 2 X lo5 fetal liver erythroblasts and erythroblasts collected on the various days of BFU-E cultures, erythrocytes, and reticulocytes were incubated at 37°C for 60 min with saturating concentrations of radioiodinated rHF and rLF, in 50 ~1 of phosphate-buffered saline containing 1 mg/mL of bovine serum albumin.…”

“…Different studies with natural [2 11 and recombinant [22] ferritins showed that erythroleukemia K562 and other cell lines express membrane binding sites specific Morphologic examination was performed after May-Griinwald-Giemsa staining. The distribution of the different erythroblasts was calculated, based on cell size, cytoplasmic staining, and nuclear condensation.…”