Specific binding sites for H-ferritin on human lymphocytes: modulation during cellular proliferation and potential implication in cell growth control

Abstract

Interactions between human recombinant H- and L-ferritins and human lymphocytes were studied in vitro by direct binding assays and by flow cytometry. L-ferritin did not cause detectable specific binding, whereas H-ferritin showed a specific and saturable binding that increased markedly in phytohemagglutinin (PHA)-stimulated cells. This ferritin bound up to 30% of CD4+ and CD8+ T-lymphocytes and most B cells, indicating that expression of ferritin binding sites is not related to cell lineage or function. Dual-color flow cytometry experiments showed that ferritin binding sites were present on cells expressing the proliferation markers HLA-DR, MLR3, interleukin 2 (IL- 2), and transferrin receptors (Tf-R). In addition, after PHA induction, the time course of the expression of H-ferritin binding sites was similar to those of the above proliferation markers. Ferritin binding sites were observed in lymphocytes at all cell cycle phases, including the early S-phase. H-Ferritin at nanomolar and picomolar concentrations had an inhibitory effect on PHA-induced blastogenesis. We propose that H-ferritin binding sites behave like proliferation markers, with the unusual function of downregulating proliferation.

Characterization and Distribution of Ferritin Binding Sites in the Adult Mouse Brain

“…Ferritin, specifically the H‐chain, may have a regulatory role in cellular development through suppression of cellular proliferation in several cell types, including lymphocytes (Fargion et al, 1991 a ), erythroid precursor cells (Fargion et al, 1992), and granulocyte macrophages (Broxmeyer et al, 1986). In addition, the expression of ferritin receptors has been shown to be cell cycle dependent (Fargion et al, 1988 ; Moss et al, 1992 a ).…”

“…Human recombinant H‐chain ferritin (rH‐ferritin) was generated as described previously (Levi et al, 1987). Amino acid sequences of ferritin H‐chains are highly conserved (90%) between various species (Harrison et al, 1987) and rH‐ferritin has been the standard form of ferritin used in binding studies (Broxmeyer et al, 1986 ; Fargion et al, 1988, 1991 a , b , 1992 ; Moss et al, 1992 a , b ). The recombinant protein has been shown to form the complete ferritin cage and can contain up to 3,200 iron atoms per molecule (Levi et al, 1988).…”

The endocytic pathway for H‐ferritin established in live MOLT‐4 cells by laser scanning confocal microscopy

“…The low iron content of H-ferritin (Arosio et al, 1986) suggests that its internalization is not an important means of delivering iron as a nutrient to the cell. H-ferritin may, however, fulfil a regulatory role, as it has previously been shown to down-modulate cellular proliferation (Broxmeyer et al 1991;Fargion et al, 1991Fargion et al, , 1992 and has been proposed to act as a regulatory cytokine (Broxmeyer, 1992). The ferroxidase activity of H-ferritin.…”

“…The iron requirements of most cells are met by the irontransport protein, transferrin, and its receptor. However, Hferritin has been proposed to play a role in the regulation of cellular proliferation by limiting cellular iron uptake (Fargion et al, 1991: Broxmeyer, 1992. H-ferritin, unlike L-ferritin, possesses ferroxidase activity (Levi et al 1988;Lawson et al, 1991) and this could theoretically allow H-ferritin to interfere with any reduction of transferrin-iron which occurred at the cell surface (Broxmeyer et nl, 1991).…”

TIM-2 is expressed on B cells and in liver and kidney and is a receptor for H-ferritin endocytosis

“…Thus, ferritin inhibits T cell proliferation in response to mitogens, it impairs the maturation of B cells in vitro (20,21), and it has immunosuppressive effects in vivo (22). Additionally, H-ferritin, but not L-ferritin, shows saturable binding to subsets of human T and B cells (23)(24)(25)(26). Despite the evidence for H-ferritin receptors on the cell surface, none had been identified.…”