ferric-ammonium-citrate and Leukemia--Erythroblastic--Acute

The mechanisms that regulate the expression of the H chain of the iron storage protein ferritin in Friend erythroleukemia cells (FLCs) after exposure to hemin (ferric protoporphyrin IX), protoporphyrin IX, and ferric ammonium citrate (FAC) have been investigated. Administration of hemin increases the steady-state level of ferritin mRNA about 10-fold and that of ferritin protein expression 20-fold. Experiments with the transcriptional inhibitor actinomycin D and transfection studies demonstrate that the increment in cytoplasmic mRNA content results from enhanced transcription of the ferritin H-chain gene and cannot be attributed to stabilization of preexisting mRNAs. In addition to transcriptional effects, translational regulation induces the recruitment of stored mRNAs into functional polyribosomes after hemin and FAC administration, resulting in a further increase in ferritin synthesis. Administration of protoporphyrin IX to FLCs produces divergent transcriptional and translational effects. It increases transcription but appears to suppress ferritin mRNA translation. FAC treatment increases the mRNA content slightly (about twofold), and the ferritin levels rise about fivefold over the control values. We conclude that in FLCs, hemin induces ferritin H-chain biosynthesis by multiple mechanisms: a transcriptional mechanism exerted also by protoporphyrin IX and a translational one, not displayed by protoporphyrin IX but shared with FAC.

Topics: Animals; Base Sequence; Deferoxamine; Ferric Compounds; Ferritins; Gene Expression Regulation, Neoplastic; Hemin; Leukemia, Erythroblastic, Acute; Mice; Molecular Sequence Data; Polyribosomes; Protein Biosynthesis; Protoporphyrins; Quaternary Ammonium Compounds; RNA, Messenger; Transcription, Genetic; Tumor Cells, Cultured

The effects of either iron salts or iron chelators on the biosynthesis of transferrin receptors in human erythroleukemic lines was investigated. Addition of these compounds induced a rapid and marked decrease (iron salts) or increase (iron chelators) in the level of transferrin receptors synthesis. Both phenomena were inhibited by actinomycin D. In contrast, the increase in the synthesis of ferritin induced in these cells by addition of iron salts was not inhibited by actinomycin D. These results suggest that iron salts modulate the synthesis of transferrin receptors and ferritin via different molecular mechanisms, of transcriptional and translation type, respectively.

Topics: Cell Line; Dactinomycin; Electrophoresis, Polyacrylamide Gel; Ferric Compounds; Ferritins; Humans; Iron; Leukemia, Erythroblastic, Acute; Picolinic Acids; Quaternary Ammonium Compounds; Receptors, Cell Surface; Receptors, Transferrin; Time Factors

The growth requirements of three human leukemic cell lines (K 562, HEL, U937) have been studied in the absence of serum. For growth in serum-free medium, the cells require insulin, transferrin, and albumin. Two highly water-soluble iron salts, ferric ammonium citrate and ferric ammonium sulfate, may completely replace transferrin for supporting the growth of these cell lines. Similar results were obtained when mitogen-stimulated lymphocytes were grown in serum-free media. Iron containing compounds, such as hemin or hemoglobin, were also able to replace transferrin. Experiments using 42/6 monoclonal antibody strongly suggest that free-iron salts are taken up by the cells by a mechanism that is completely independent from transferrin-receptors.

Topics: Cell Division; Cell Line; Ferric Compounds; Humans; Iron; Leukemia; Leukemia, Erythroblastic, Acute; Quaternary Ammonium Compounds; Transferrin