Regulation of K562 cell transferrin receptors by exogenous iron

Abstract

Single-cell analysis of K562 human erythroleukemia cells by flow cytometry was used to demonstrate the specific role of iron in regulating transferrin receptors (TfRs) and to establish that TfR expression does not necessarily correlate with growth rate. Exogenous iron concentration in culture was manipulated by supplementing the medium with sera having different iron concentrations over the range 0.6 to 5.4 micrograms/ml, by the addition of iron in the form of FeCl3, iron-saturated serum, or diferric transferrin, and by the addition of the iron chelator Desferal (desferrioxamine). TfR expression was negatively correlated with exogenous iron content: any treatment that reduced exogenous iron supply by at least 15% resulted in as much as a 1.8-fold increase in external receptors, detected as binding by both transferrin and monoclonal anti-TfR antibodies, and a 1.5-fold increase in the pool of internal receptors, as detected by anti-TfR antibody binding. None of these treatments altered growth rate, total cellular protein content, protein synthetic rate, cell cycle distribution or cell size. The rapid (12 hr) and reversible induction of internal and external receptors by Desferal was inhibited by cycloheximide and therefore may have resulted from de novo synthesis and not just mobilization of internal receptor pool to the cell surface. The correlation between growth rate and TfR expression previously observed in these and other cells must be secondary to cellular mechanisms that maintain intracellular iron pools by regulating synthesis, recycling, and cell surface expression of TfRs.

Single‐cell analysis of the relationship among transferrin receptors, proliferation, and cell cycle phase in K562 cells

“…Relative size, estimated by LALS (n = 3) vitro, the observed decreases cannot be attributed to depletion of these components from the culture medium, for Tf is recycled to the cell after it is separated from the iron it carries (11,131 and iron deficiency reversibly induces TfR expression in K562 cells (24). Hence, decreased T f R density appears to be an early single-cell marker for changes in cell growth rate.…”

“…A third possibility, that iron uptake is regulated solely by differential rates of internalization of the W-receptor complex and not by changes in the number of surface receptors, does not explain decreased receptor expression with decreasing growth rate (Fig. 7) or the reversible induction of TfRs on K562 cells grown under conditions of iron deficiency (24). However, some of these questions can be addressed directly by real-time kinetic analysis of fluorescent Tf uptake as a function of DNA content.…”

“…The observation that the average number of TfRs per cell is correlated with relative cell growth rate of malignant and nonmalignant cells in vivo and in vitro (8,10,12,17,18,28) implies that these receptors may be useful as single-cell markers for proliferative rate. As part of our investigation of K562 human erythroleukemia cells as a model of erythroid differentiation in vitro (23,24), we have been using TfRs to develop correlated single-cell assays for the relationship between proliferation and hemoglobin induction.…”

Translation of ferritin light and heavy subunit mRNAs is regulated by intracellular chelatable iron levels in rat hepatoma cells.

“…Deferoxamine is the preferred iron chelator, because it enters the cell (7), whereas DTPA is restricted to extracellular chelation (21). Deferoxamine depletes the intracellular iron pool as evidenced by (i) a shift in transferrin receptor synthesis and display (21,23), (ii) depletion of intracellular ferritin iron (7,8), and (iii) the decrease in the iron-regulated rate of ferritin synthesis (24).…”

Comparison of Transferrin Receptors, Iron Content and Isoferritin Profile in Normal and Malignant Human Breast Cell Lines

“…It is well established that the principal mechanism for modulating cellular iron uptake is by regulation of ex pression of the Tf receptor [25][26][27][28][29], In the present inves tigation, it was shown that the rate of iron uptake by breast cancer cells was higher as compared to breast epi thelial cells, in spite of the identical rate of proliferation and lower number of Tf receptors. These results indicate that the number of Tf receptors on the cell surface was not in direct correlation with the cellular iron incorpora tion.…”