Iron: Its Intracellular Localization and Possible Role in Cell Division

Abstract

Abstract. When HeLa cells are fixed with ethanol, extracted with 0.1 N HC1, and incinerated at 540'C, all organic constituents and all ions studied are removed with the exception of iron. The gross outlines of cell structures are preserved and high concentrations of residual ash in interphase nucleoli and mitotic chromosomes suggest that there may be a shift in iron salts during the cell cycle. Experiments with cells isotopically labeled in proteins, nucleic acids, lipids, and polysaccharides indicate that the iron is bound to a polysaccharide. Addition of iron chelating agents to living cells causes a selective inhibition of DNA synthesis. These data suggest that iron may play a crucial role in the mitotic process.Although inorganic elements are obviously essential in the cellular economy, their specific function in the mitotic process is unknown. Heilbrunn and others1-4 have suggested that calcium may be linked to chromosome structure and condensation. We have recently shown5 that hypertonic medium induces several mitotic-like phenomena in HeLa cells, including intranuclear condensation of chromosomes which at an ultrastructural level closely mimics that observed during prophase. The presence of Cu and Fe in chromosomes has been reported or suggested,6-8 and chelating agents such as a, a-dipyridyl, as well as EDTA cause chromosome breaks;9 however, the precise role of these elements in mitosis remains unexplored.We have examined the intracellular distribution of iron throughout the cell. The interphase nucleolus and the metaphase chromosomes are particularly enriched depots, and iron may move from one site to the other at different phases of the cell cycle. Depriving HeLa cells of extracellular iron by adding an ironchelating agent (Desferal, Ciba) rapidly inhibits DNA synthesis, and this in turn effectively prevents mitosis. In contrast, nondividing (contact-inhibited) diploid cells are unaffected by iron deprivation over a 4-day interval. It is of special interest that cellular iron binds preferentially to a material which can be labeled with isotopic glucose but not with amino acids, uridine, thymidine, or choline.Materials and Methods. Cells: HeLa (S3) cells were grown either as monolayers or suspension cultures in Eagle's medium supplemented with 7% fetal calf serum.10 Synchronized cells in mitosis were obtained by selective detachment from monolayers as previously described.11Microincineration: The basic method used is a modification of that described by Scott.12 Cell monolayers were cultured to near confluence on 3 X 1 in. glass slides 1244

Intracellular Iron-Binding Macromolecules in HeLa Cells

“…Addition of the iron-chelating agent, desferrioxamine (Desferal, Ciba), to HeLa cells selectively prevents entry of 55Fe (as citrate) and reversibly inhibits DNA synthesis, with little effect on RNA or protein synthesis (1). In the present paper we note that the concentration of desferrioxamine that just inhibits entry of iron into cells is precisely that concentration that also causes cessation of DNA synthesis, implying that perpetual addition or replacement of iron is critical for cell division.…”

“…Tables 1 and 2 illustrate that at all desferrioxamine concentrations above 0.05 mg/ml both DNA and iron uptake cease, while RNA and protein synthesis are only slightly affected. The precise correlation between the desferrioxamine concentration that inhibits iron uptake and that which inhibits DNA synthesis strongly suggests a causal relationship, especially since desferrioxamine does not affect transport of any other ion tested (1). However, while des- mim at 1000 and, similarly, 65% of the counts are in the 100,000 X g supernatant.…”

Identification of the molecular mechanisms underlying the cytotoxic action of a potent platinum metallointercalator

“…Iron and copper are required by proliferating cancer cells during carcinogenesis [32,39,59,77] and high levels of iron and copper were found in certain tumour cells and tissues, including breast cancer cells [17,33]. As iron and copper metabolism is up-regulated in neoplastic tumours [29,39,41,44,47,59,62,65,72], 56MESS and other complexes in this class should be assessed, in combination with cisplatin, in the cancer models that have elevated iron and copper metabolism. Indeed chelating cellular copper has recently been shown to selectively enhance the therapeutic efficacy of cisplatin in a mouse model of human cervical cancer [34].…”

Changes in Growth and Metabolism of Excised Pea Roots Associated With Iron Deficiency Ii. Changes in Nucleic Acids

“…They were unable to exclude, however, the alternative hypothesis that dePrt'ssion of cytochrome synthesis was a consequence of the absence of cell division. There is now accumulating evidence suggesting that iron is involved in nuclear processes (Amoore, 1963;Cohn, 1961;Robbins and Pederson, 1970).…”