calcimycin and Leukemia--Monocytic--Acute

Stimulated leukocytes generate platelet-activating factor (PAF) from membrane 1-O-alkyl-2-acyl-sn-glycerophosphocholine through hydrolysis of fatty acid and subsequent acetylation at the sn2 position of glycerol. Since the enzymes involved in the hydrolysis step of PAF biosynthesis have relative selectivity for arachidonic acid (AA), the fatty acid composition of PAF precursors might modulate PAF production. We studied the effect of AA and eicosapentaenoic acid (EPA) incorporation on PAF biosynthesis, by measuring the incorporation of [(3)H]acetate, in Ca(2+) ionophore (A23187)-stimulated human leukemic monocyte-like cells, THP-1. Supplementation of THP-1 with AA (25 microM, 1 week) or EPA (25 microM, 1 week) led to their efficient incorporation, in comparable quantities and with similar distributions, into phosphatidylcholine and phosphatidylethanolamine, and to a lesser extent into phosphatidylinositol. THP-1 cells supplemented with AA or with EPA synthetized similar amounts of PAF and of acyl analog of PAF under resting condition. However, AA-supplemented cells responded to A23187 stimulation by important raises of PAF (+125.71%) and of acyl analog of PAF (+381.75%) productions, whereas the same stimulation had little effect or no effect at all in cells supplemented with EPA. These results show that both EPA and AA may influence PAF production through their incorporation into PAF precursors, indicating that PAF production might be modulated by the fatty acid composition of its precursors.

Topics: Acetates; Arachidonic Acid; Calcimycin; Eicosapentaenoic Acid; Humans; Ionophores; Leukemia, Monocytic, Acute; Phospholipids; Platelet Activating Factor; Tumor Cells, Cultured

The signal transduction pathway through which tumour necrosis factor (TNF) induces apoptosis in leukaemic cells may involve activation of cytosolic phospholipase A(2) (cPLA(2)). The steroids dexamethasone (Dex) and 1,25(OH)(2) D(3) both render U937 leukaemic cells resistant to TNF-induced apoptosis. In this study, we found that Dex inhibited both spontaneous and TNF-induced activation of cPLA(2). Dex had no direct effect on cellular cPLA(2) levels, but facilitated cPLA(2) degradation upon subsequent stimulation of cells with TNF. In addition, Dex increased synthesis of the endogenous cPLA(2) inhibitor lipocortin 1 (LC1). An antisense oligonucleotide to LC1 could completely abrogate Dex-induced resistance to the cytotoxic action of TNF. Constitutive LC1 levels were relatively higher in myeloid leukaemic blasts showing resistance to TNF than TNF-sensitive myeloid leukaemic cell lines. Our data suggest that Dex confers the resistance of U937 cells to TNF-induced apoptosis by upregulating intracellular levels of LC1 and by facilitating a negative-feedback loop, which is activated upon stimulation with TNF. High constitutive levels of LC1 in leukaemic blasts may protect them against immune-mediated killing.

Topics: Acute Disease; Annexin A1; Antineoplastic Agents, Hormonal; Apoptosis; Arachidonic Acid; Calcimycin; Cell Line; Cytosol; Dexamethasone; Enzyme Activation; Enzyme Inhibitors; Feedback; Humans; Ionophores; Leukemia; Leukemia, Monocytic, Acute; Leukemia, Myeloid; Oligonucleotides, Antisense; Phospholipases A; Signal Transduction; Stimulation, Chemical; Tumor Necrosis Factor-alpha

Topics: Calcimycin; Cell Differentiation; Cholecalciferol; Dinoprostone; Eicosanoids; Gene Expression Regulation, Neoplastic; Humans; Isoenzymes; Leukemia, Monocytic, Acute; Lipopolysaccharide Receptors; Lipopolysaccharides; Macrophage-1 Antigen; Neoplasm Proteins; Phagocytosis; Phospholipases A; Superoxides; Tetradecanoylphorbol Acetate; Tretinoin; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

The primary objective of this study was to explore if the CD23 antigen is a functional low affinity IgE receptor on macrophages for the release of thromboxane B2 (TXB2). The responsiveness of U937 monocytic cells and their macrophage-like inducible forms to platelet-activating factor (Paf), the chemotactic peptide fMLP, and low affinity IgE-receptor occupation was examined. Differentiation of U937 cells by phorbol myristate acetate (PMA) and a cancer cell line (HBT 5637) conditioned medium (5637-CM), but not INFg or IL4, resulted in a macrophage-like cell line which released TXB2. A high basal release of TXB2 with no significant response to Paf or fMLP challenge was seen following culture of cells with PMA. In 5637-CM-differentiated cells, Paf and fMLP induced a rapid release of TXB2, about 10 fold above basal activity. There was a slow Ca-independent response to short-term treatment with PMA and a rapid Ca-dependent response to the ionophore A23187. Both stimulants acted synergistically on TXB2 synthesis in 5637-CM differentiated cells. Although low affinity receptors for IgE (Fc epsilon RII/CD23) were induced by 5637-CM, no TXB2 was released in response to soluble or latex-bound IgE-antigen complexes or to anti-Fc epsilon RII/CD23-antibodies. IL4 and to a lesser extent INFg both induced Fc epsilon RII/CD23 receptor expression, but inhibited release of TXB2 in response to Paf, fMLP, or PMA. We conclude that the functional receptors for IgE on mature macrophages are most probably not Fc epsilon RII/CD23.

Topics: Antibodies, Anti-Idiotypic; Antigens, Differentiation, B-Lymphocyte; Calcimycin; Drug Synergism; Humans; Immunoglobulin E; Interferon-gamma; Interleukin-4; Leukemia, Monocytic, Acute; Lymphokines; N-Formylmethionine Leucyl-Phenylalanine; Platelet Activating Factor; Protein Binding; Receptors, Fc; Receptors, IgE; Tetradecanoylphorbol Acetate; Thromboxane B2; Tumor Cells, Cultured