Establishment and characterization of a human acute monocytic leukemia cell line (THP-1)

Phosphatidylinositol 3-kinase is involved in the induction of macrophage growth by oxidized low density lipoprotein

Early atherosclerotic lesions are characterized by the presence of cholesterol-rich, macrophage-derived foam cells. It has recently been shown that macrophage proliferation occurs during the development of early lesions and that oxidized low density lipoprotein (LDL) stimulates macrophage growth. Possible mechanisms for this induction of macrophage growth include potentiation of mitogenic signal transduction by a component of oxidized LDL following internalization and degradation, interaction with integral plasma membrane proteins coupled to signaling pathways, or direct or indirect activation of growth factor receptors on the cell surface (e.g. GM-CSF receptor) through an autocrine/paracrine mechanism. The present study was undertaken to characterize some of the early intracellular signaling events by which oxidized LDL mediates macrophage cell growth. Extensively oxidized LDL increased protein-tyrosine phosphorylation and caused a 2-fold increase in phosphatidylinositol (PI) 3-kinase activity in phorbol ester-pretreated THP-1 cells (a human monocyte-like cell line). Similar concentrations of native LDL had no effect. Oxidized LDL also stimulated growth of resident mouse peritoneal macrophages, and this effect was reduced by 40-50% in cells treated with PI 3-kinase inhibitors (100 nM wortmannin or 20 microM LY294002). These results suggest that PI 3-kinase mediates part of the mitogenic effect of oxidized LDL, but parallel pathways involving other receptors and signal transduction pathways are likely also involved.

CD14-Dependent Internalization of Bacterial Lipopolysaccharide (LPS) Is Strongly Influenced by LPS Aggregation But Not by Cellular Responses to LPS

We analyzed the impact of ligand aggregation and LPS-induced signaling on CD14-dependent LPS internalization kinetics in human monocytic THP-1 cells and murine macrophages. Using two independent methods, we found that the initial rate and extent of LPS internalization increased with LPS aggregate size. In the presence of LPS binding protein (LBP), large LPS aggregates were internalized extremely rapidly (70% of the cell-associated LPS was internalized in 1 min). Smaller LPS aggregates were internalized more slowly than the larger aggregates, and LPS monomers, complexed with soluble CD14 in the absence of LBP, were internalized very slowly after binding to membrane CD14 (5% of the cell-associated LPS was internalized in 1 min). In contrast, the initial aggregation state had little or no effect on the stimulatory potency of the LPS. Previous studies suggest that LPS-induced signal responses may influence the intracellular traffic and processing of LPS. We found that elicited peritoneal macrophages from LPS-responsive (C3H/HeN) and LPS-hyporesponsive (C3H/HeJ) mice internalized LPS with similar kinetics. In addition, pre-exposure of THP-1 cells to LPS had no effect on their ability to internalize subsequently added LPS, and pre-exposure of the cells to the LPS-specific inhibitor, LA-14-PP, inhibited stimulation of the cells without inhibiting LPS internalization. In these cells, LPS is thus internalized by a constitutive cellular mechanism(s) with kinetics that depend importantly upon the physical state in which the LPS is presented to the cell.

Glatiramer acetate blocks the activation of THP-1 cells by interferon-gamma

Glatiramer acetate (previously known as copolymer 1) is a synthetic copolymer of four amino acids that has been approved for use in the treatment of multiple sclerosis. It has been shown to suppress myelin antigen specific T cell activation by competing with these antigens at the major histocompatibility complex class II binding site and by inducing antigen specific suppressor T cells. In this study we investigated the effects of glatiramer acetate on the human monocytic cell line, THP-1, activated by lipopolysaccharide and interferon-gamma as a model for macrophages. At non-toxic concentrations of glatiramer acetate there were dose dependent reductions in the percentage of cells expressing human leukocyte DR and DQ antigen as well as in mean fluorescence intensity by flow cytometry. Production of tumor necrosis factor-alpha and the lysosomal cysteine proteinase cathepsin B were markedly inhibited, but production of interleukin-1 increased. These results suggest that glatiramer acetate might alter macrophage effector function and suggest that further studies in human monocytes and macrophages are warranted.

Acquisition of secretion of transforming growth factor-beta 1 leads to autonomous suppression of scavenger receptor activity in a monocyte-macrophage cell line, THP-1

Macrophage cells derived from the human monocytic leukemia cell line, THP-1, accumulate esterified cholesterol when cultivated in the presence of acetylated low density lipoprotein (Ac-LDL) through scavenger receptors (ScR). In the present study, we isolated a subtype of THP-1 cells that failed to accumulate esterified cholesterol when cultivated in the presence of Ac-LDL. The cells had negligible amounts of cell association and degradation of Ac-LDL compared with the parent THP-1 cells. The subtype THP-1 cells did not express ScR mRNA as well as that of lipoprotein lipase. In contrast, the expression of apolipoprotein E mRNA was greater than that found in parent THP-1 cells. The culture medium of subtype THP-1 cells treated with 12-O-tetradecanoylphorbol-13-acetate inhibited the uptake of Ac-LDL and the expression of ScR in parent THP-1 cells. After a 48-h incubation in the culture medium containing 12-O-tetradecanoylphorbol-13-acetate, the culture medium of differentiated subtype THP-1 cells contained 6.9 ng/ml transforming growth factor (TGF)-beta 1, while that of parent THP-1 cells secreted below detection level, which was less than 3 ng/ml. This inhibitory effect of the conditioned medium on the expression of ScR in parent THP-1 cells was abolished by pretreatment of the culture medium with anti-TGF-beta 1 antibodies. Parent THP-1 cells expressed as much TGF-beta 1 mRNA as sTHP-1 cells after stimulation of differentiation. Although the precursor forms of TGF-beta 1 that were synthesized in both parent and subtype THP-1 cells were of similar size and were expressed at similar levels, latent TGF-beta 1-binding protein, which is necessary for the secretion of TGF-beta 1, could only be co-immunoprecipitated with anti-TGF-beta 1 antibody from subtype THP-1 cells. This suggests that subtype THP-1 cells secrete TGF-beta 1 into the medium by forming a functional complex with the latent TGF-beta 1-binding protein. We conclude that subtype THP-1 cells could not take up Ac-LDL because ScR was inhibited (leading to a loss of function) caused by the secreted TGF-beta 1.

Lipoarabinomannan of Mycobacterium tuberculosis promotes protein tyrosine dephosphorylation and inhibition of mitogen-activated protein kinase in human mononuclear phagocytes. Role of the Src homology 2 containing tyrosine phosphatase 1

Lipoarabinomannan (LAM) is a putative virulence factor of Mycobacterium tuberculosis that inhibits monocyte functions, and this may involve antagonism of cell signaling pathways. The effects of LAM on protein tyrosine phosphorylation in cells of the human monocytic cell line THP-1 were examined. LAM promoted tyrosine dephosphorylation of multiple cell proteins and attenuated phorbol 12-myristate 13-acetate-induced activation of mitogen-activated protein kinase. To examine whether these effects of LAM could be related to activation of a phosphatase, fractions from LAM-treated cells were analyzed for dephosphorylation of para-nitrophenol phosphate. The data show that LAM induced increased phosphatase activity associated with the membrane fraction. The Src homology 2 containing tyrosine phosphatase 1 (SHP-1) is important for signal termination and was examined as a potential target of LAM. Exposure of cells to LAM brought about (i) an increase in tyrosine phosphorylation of SHP-1, and (ii) translocation of the phosphatase to the membrane. Phosphatase assay of SHP-1 immunoprecipitated from LAM-treated cells, using phosphorylated mitogen-activated protein kinase as substrate, indicated that LAM promoted increased activity of SHP-1 in vivo. LAM also activated SHP-1 directly in vitro. Exposure of cells to LAM also attenuated the expression of tumor necrosis factor-alpha, interleukin-12, and major histocompatibility class II molecules. These results suggest that one mechanism by which LAM deactivates monocytes involves activation of SHP-1.

Demethylation of ERV3, an endogenous retrovirus regulating the Krüppel-related zinc finger gene H-plk, in several human cell lines arrested during early monocyte development

The activation of H-plk (Human-proviral linked Krüppel), a human Krüppel-related zinc finger gene in organs such as placenta, adrenal cortex, and testis, is probably due to insertion of an endogenous retrovirus, ERV3, upstream of the gene. Several differently spliced transcripts originate from this locus, e.g., a transcript encoding the retroviral envelope protein and a few differentially spliced transcripts encoding both the env and the zinc finger protein. During a screening for zinc finger proteins expressed during monocyte differentiation, two H-plk encoding cDNA clones were isolated from the human monoblast cell line U-937. Northern blot analysis of a panel of human hematopoietic cell lines showed high levels of constitutive expression of this zinc finger transcript in two monocytic cell lines (U-937 and THP-1) but not in any of the other cell lines or tissues tested. In addition, the H-plk transcript was upregulated by the phorbolester PMA in U-937 and in an additional monocytic cell line, MonoMac 6. Genomic Southern blot analysis of a panel of hematopoietic cell lines, after cleavage with the methylation sensitive enzyme Xho I, led to the detection of tissue specific demethylation in all three monocytic cell lines. The Xho I site was mapped to a position just downstream of the regulatory region of the endogenous retrovirus. By analysis of the U-937 cell line with two additional restriction enzymes, Nar I and Sma I, the demethylation was shown to affect at least three independent CpG dinucleotides in this region of the gene. In summary, the present data provide evidence for specific demethylation of this genomic region, in cells of monocytic origin, resulting in enhanced transcription of the genetic regions derived from both the env region of the retrovirus and the Krüppel-related zinc finger gene.

Release of prostaglandin D2 by murine mast cells: importance of metabolite formation for antiproliferative activity

Prostaglandin (PG) D2, PGJ2 and delta12-PGJ2 are antiproliferative eicosanoids. We investigated the production of PGD2 by murine bone marrow-derived mast cells (BMMC) taking into consideration metabolism of PGD2 to PGD2 and delta12-PGJ2. PG-metabolites were quantified by high performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). Stimulated with calcium ionophore A23187 BMMC released eight-fold more PGJ2 and delta12-PGJ2 than PGD2. Conversion of endogenously produced PGD2 to PGJ2 and delta12-PGJ2 proceeded rapidly in contrast to metabolism of exogenously added PGD2. The antiproliferative potency of these prostaglandins is demonstrated in vitro. We conclude that determination of PGD2 production by mast cells must take into consideration rapid conversion to active derivatives, which may play a significant role in growth regulation.

Grain dust-induced lung inflammation is reduced by Rhodobacter sphaeroides diphosphoryl lipid A

To further determine the importance of endotoxin in grain dust-induced inflammation of the lower respiratory tract, we evaluated the efficacy of pentaacylated diphosphoryl lipid A derived from the lipopolysaccharide of Rhodobacter sphaeroides (RsDPLA) as a partial agonist of grain dust-induced airway inflammation. RsDPLA is a relatively inactive compound compared with lipid A derived from Escherichia coli (LPS) and has been demonstrated to act as a partial agonist of LPS-induced inflammation. To assess the potential stimulatory effect of RsDPLA in relation to LPS, we incubated THP-1 cells with RsDPLA (0.001-100 micrograms/ml), LPS (0.02 microgram endotoxin activity/ml), or corn dust extract (CDE; 0.02 microgram endotoxin activity/ml). Incubation with RsDPLA revealed a tumor necrosis factor (TNF)-alpha stimulatory effect at 100 micrograms/ml. In contrast, incubation with LPS or CDE resulted in TNF-alpha release at 0.02 microgram/ml. Pretreatment of THP-1 cells with varying concentrations of RsDPLA before incubation with LPS or CDE (0.02 microgram endotoxin activity/ml) resulted in a dose-dependent reduction in the LPS- or CDE-induced release of TNF-alpha with concentrations of RsDPLA of up to 10 micrograms/ml but not at 100 micrograms/ml. To further understand the role of endotoxin in grain dust-induced airway inflammation, we utilized the unique LPS inhibitory property of RsDPLA to determine the inflammatory response to inhaled CDE in mice in the presence of RsDPLA. Ten micrograms of RsDPLA intratracheally did not cause a significant inflammatory response compared with intratracheal saline. However, pretreatment of mice with 10 micrograms of RsDPLA intratracheally before exposure to CDE (5.4 and 0.2 micrograms/m3) or LPS (7.2 and 0.28 micrograms/m3) resulted in significant reductions in the lung lavage concentrations of total cells, neutrophils, and specific proinflammatory cytokines compared with mice pretreated with sterile saline. These results confirm the LPS-inhibitory effect of RsDPLA and support the role of endotoxin as the principal agent in grain dust causing airway inflammation.

The role of complement, antibody, and tumor necrosis factor alpha in the killing of Plasmodium falciparum by the monocytic cell line THP-1

Killing of Plasmodium falciparum blood forms by the differentiated human myelomonocytic THP-1Mo cell line was studied by a radiometric assay. Results showed that parasite killing was promoted by complement, antimalarial antibody, and the cytokines tumor necrosis factor alpha and gamma interferon. Differentiated THP-1Mo appears to be a useful monocytic cell line for the study of mechanisms of immunity to Plasmodium.

Activated lymphocytes increase expression of 5-lipoxygenase and its activating protein in THP-1 cells

The aim of this study was to investigate the regulation of the 5-lipoxygenase pathway of arachidonic acid metabolism by lymphocytes using the monocyte-like cell line, THP-1. When THP-1 cells were incubated over 4-7 days in 10% supernatant from lectin-activated human lymphocytes, their capacity to synthesize 5-lipoxygenase products was significantly increased. In contrast, the supernatant from nonactivated lymphocytes had no effect. The increase in capacity to synthesize 5-lipoxygenase products was mimicked by the addition of either granulocyte macrophage colony-stimulating factor (GM-CSF) or interleukin-3. These increases in synthetic capacity reflected increased enzymatic activity. Increased immunoreactive protein and mRNA for the enzymes 5-lipoxygenase and 5-lipoxygenase-activating protein were also found in cells conditioned with activated lymphocyte supernatants. Furthermore, the increase in mRNA for both enzymes was not blocked by cycloheximide, suggesting that the effect on steady-state mRNA levels does not require the synthesis of new protein. The increase in mRNA could be reproduced by GM-CSF. We conclude that lymphocytes can regulate the expression of 5-lipoxygenase in THP-1 cells over a period of days via the release of soluble factors.

Structure and function of the long terminal repeats of feline leukemia viruses derived from naturally occurring acute myeloid leukemias in cats

Long terminal repeats of feline leukemia viruses cloned from feline acute myeloid leukemias frequently contained direct repeats of 40 to 74 bp in the upstream region of the enhancer (URE). The repetitive URE conferred an enhancer function upon gene expression in myeloid cells, suggesting its association with tumorigenic potential in myeloid cells.

Modulation of platelet-activating-factor production by incorporation of naturally occurring 1-O-alkylglycerols in phospholipids of human leukemic monocyte-like THP-1 cells

1-O-Alkylglycerols (alkyl-Gro), naturally occurring compounds abundant in shark liver oil, protect patients from radiotherapy side-effects. However, the protection mechanism is not well understood. It might be mediated by alkyl-Gro incorporation into pools of platelet-activating factor (PAF) precursor and subsequent modification of PAF biosynthesis. Using a 3H-labelled or unlabelled natural alkyl-Gro mixture, in which prominent alkyl chains were C18:1(9) (54-65%), C16:1(7) (5-15.5%), and C16:0 (5-10%), we investigated the incorporation of alkyl-Gro into phospholipids of human leukemic monocyte-like THP-1 cells. Incubation of cells for 24 h with [3H]alkyl-Gro (10 microM) resulted in their incorporation into 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1097+/-25.1 pmol/2x10(6) cells) and into 1-alkyl-2-acyl-sn-glycero-3-phosphoethanolamine (640.4+/-12.5 pmol/2x10(6) cells) with a total yield of 6.5%. Such incorporation induced production of 1-O-[3H]alkyl-2-acetyl-sn-glycero-3-phosphocholine ([3H]PAF), which was increased after stimulation by the calcium ionophore A23187. HPLC analysis of the [3H]PAF molecular species indicated that the three major [3H]alkyl-Gro were used for [3H]PAF synthesis in ratios similar to that of the mixture. Total production of biologically active PAF, as measured by the platelet-aggregation bioassay, was also increased by alkyl-Gro incorporation in resting (+20%) and in A23187-stimulated (+59%) THP-1 cells. HPLC analysis of the [3H]PAF produced in the presence of [3H]acetate, confirmed that levels of PAF, but not of its 1-acyl analog, were increased by alkyl-Gro incorporation in resting and stimulated cells. However, the rise in [3H]acetyl-PAF, which resulted mainly from C16:0 PAF, was reduced by about 50% in the presence of the PAF-receptor antagonist SR 27417, providing evidence that stimulation of total PAF synthesis was caused by the increase in the precursor pool and autocrine amplification of PAF-induced PAF production. Thus, the supplementation of THP-1 cells in culture with naturally occurring alkyl-Gro led to the incorporation of alkyl-Gro into ether-containing phospholipids, which were subsequently used for PAF synthesis. Furthermore, alkyl-Gro incorporation resulted in a significant rise in PAF production by THP-1 cells under resting and stimulated conditions. These results may be of importance for modulating PAF production in several pathophysiological conditions, such as peroxysome deficiencies, that are associated with a lack of ether lipid synthesis.

Evidence for hormone-sensitive lipase mRNA expression in human monocyte/macrophages

The role of hormone-sensitive lipase (HSL) in the hydrolysis of adipose tissue triacylglycerol to provide free fatty acids for energy requirements has been well established. However, the role of HSL in other tissues, including macrophages, is not well understood. The demonstration that HSL is capable of hydrolyzing cholesteryl esters at approximately the same rate as triacylglycerol raised the possibility that HSL activity in macrophages may influence the accumulation of cholesteryl esters in foam cells of atherosclerotic lesions. We and others have previously demonstrated that HSL mRNA is expressed in murine peritoneal macrophages and macrophage cell lines; however, it was previously reported that HSL mRNA is absent in human monocyte-derived macrophages, suggesting that a species difference may exist. To clarify this point, we have further examined the issue of HSL mRNA expression in human macrophages. In the current study, we demonstrate that HSL mRNA is detectable in human monocyte-derived macrophages and in the THP-1 human monocyte cell line using reverse transcription coupled to polymerase chain reaction (RT-PCR). Specific amplification of cDNA derived from mRNA was ensured by using primers that span an intron within the human HSL gene, and the identity of PCR products as HSL was confirmed by hybridization to HSL cDNA and by DNA sequencing. Using a semiquantitative PCR assay, we establish that HSL mRNA levels in monocyte/macrophages are approximately 1/40 the levels in human adipose tissue. These results indicate that further studies addressing the role of HSL in macrophage metabolism and its potential role in development of foam cells in human atherosclerotic lesions are warranted.

Tumor necrosis factor-alpha production-inhibiting activity of phthalimide analogues on human leukemia THP-1 cells and a structure-activity relationship study

N-Substituted phthalimides (2-substituted 1H-isoindole-1,3-diones) were prepared and their inhibitory effects on tumor necrosis factor-alpha (TNF-alpha) production by human leukemia cell line THP-1 stimulated with 12-O-tetradecanoylphorbol 13-acetate (TPA) or okadaic acid (OA) were examined. A structure-activity relationship study of these phthalimide analogues revealed that their inhibitory effects on TPA- and OA-induced TNF-alpha production by THP-1 cells are well correlated to each other, i.e. they may involve the same target molecule(s). An analysis by the use of phthalimide analogue-immobilized affinity gels indicated the existence of several phthalimide-binding proteins in THP-1 cell extract.

Characterization of monoclonal antibody reactive with 10-hydroxy-12(Z)-octadecenoic acid (10-OHODA) and its demonstration in cultured human macrophages

10-Hydroxy-12(Z)-octadecenoic acid (10-OHODA) has an inhibitory effect on the tension of papillary muscles in isolated guinea-pig hearts. To establish an immunoassay for 10-OHODA a mouse monoclonal antibody (MoAb), YM-1, was produced. In order to evaluate the ability of this MoAb to recognize various 10-OHODA analogs including leukotoxin (9, 10-epoxy-12-octadecenoic acid, LTx), a sensitive enzyme-linked immunosorbent assay (ELISA) was developed using the avidin-biotin complex (ABC). The detection limit for 10-OHODA was as low as 0.5 ng in this system. In order to demonstrate the presence of 10-OHODA in living cells, macrophages derived from the human leukemia cell line THP-1 by adding 160nM phorbol 12-myristate 13-acetate (PMA) were exposed to 95% O2, and 5% CO2 for 24 h. 10-OHODA and other fatty acids were extracted from the exposed macrophages with diethylether after phospholipase A2 treatment. The 10-OHODA content was determined using the new ELISA, and 18.5 ng 10-OHODA was detected in the macrophages exposed to the high oxygen concentration (1 x 10(6) cells).

Dexamethasone and interleukin-1 potently synergize to stimulate the production of granulocyte colony-stimulating factor in differentiated THP-1 cells

The human monocytic leukemic cell line, THP-1, which differentiates toward macrophages in response to phorbol 12-myristate 13-acetate (PMA) was investigated for its ability to produce granulocyte colony-stimulating factor (G-CSF). G-CSF protein was neither produced during PMA-induced differentiation nor in response to dexamethasone (Dex) alone. However, when combined, PMA and Dex synergistically stimulated THP-1 cells to produce G-CSF. The synergistic interaction between PMA and Dex on G-CSF production appeared to be mediated through the production of interleukin-1 (IL-1) since neutralization of IL-1 activity completely inhibited G-CSF production. Further experiments demonstrated that in THP-1 cells pretreated with PMA, Dex potently synergized with IL-1 to stimulate G-CSF production.

Thioredoxin expression and localization in human cell lines: detection of full-length and truncated species

Thioredoxin (Trx) is an intracellular multifunctional 12-kDa protein with a reduction/oxidation (redox) active disulfide constitutively expressed by most cells of the human body. Trx can also be released by cells such as lymphocytes upon activation or oxidative stress exposure and exert a cocytokine and cytoprotective activity. In addition, a truncated 10-kDa form of Trx has been reported. In order to better understand the function of full-length and truncated Trx, we have produced, for the first time, specific monoclonal antibodies, which can discriminate between the two forms. Using these novel antibodies, designated alpha Trx1 to alpha Trx4, a panel of cell lines derived from human B and T lymphocytes, monocytes, granulocytes, and melanomas was analyzed by immunochemical techniques. The cellular distribution differed between the two forms. All lines contained full-length Trx, also located to a minor extent on the cell surface. One exception was the melanoma cell line FM28.4, which did not show any Trx expression. Truncated Trx was present in most cells in minimal amounts only, whereas the monocytic cell lines THP-1 and U-937 expressed high amounts on the cell surface, as shown by flow cytometric analysis of living cells and confocal laser-scanning microscopy. The biological importance and function of the short versus long forms of Trx as detected by the antibodies are discussed.

Lipoprotein(a) isoforms display differences in affinity for plasminogen-like binding to human mononuclear cells

Binding of lipoprotein(a) (Lp(a)) to membrane proteins of the monocyte-macrophage cell lineage may be an important event in atheroma formation. Since Lp(a) with distinct apolipoprotein(a) (apo(a)) isoforms may show differences in their affinity with regard to fibrin binding, the existence of such a functional behavior in the interaction of apo(a) in Lp(a) with these cells was explored using the monocytic cell line THP-1. Lp(a) preparations containing small size apo(a) isoforms (M(r) = 450,000 to 550,000) and high molecular mass isoforms (M(r) > or = 700,000) were purified from plasmas containing > 0.35 g/L of Lp(a) obtained from subjects (n = 14) with cardiovascular atherosclerotic disease. Binding of plasminogen to THP-1 cells was performed using the method of radioisotopic dilution. For binding of Lp(a) to cells, the THP-1 monocytic cells were incubated with varying concentrations of the different Lp(a) preparations; cells were then washed and the amount of Lp(a) bound was detected with a radiolabeled polyclonal antibody directed against apo(a). Binding due to kringle interactions with lysine residues was calculated by subtracting from the total bound the amount of Lp(a) bound (approximately 10%) in the presence of 6-aminohexanoic acid. Analysis of data with the Langmuir equation indicated identical and independent (non-interacting) sites and allowed evaluation of the Kd. Binding isotherms of small size isoforms showed saturation and a high affinity (Kd = 25.8 +/- 19 nmol/L) relative to that of plasminogen (Kd = 1750 +/- 760 nmol/L). A similar difference (Kd = 17.5 +/- 7.9 nmol/L versus Kd = 600 +/- 220 nmol/L) was found when binding experiments were performed with a fibrin surface. In contrast, binding isotherms of the high molecular mass isoforms did not show saturation at the highest Lp(a) concentrations used, thus indicating a lower affinity. In conclusion, these results show that apo(a) isoforms may display polymorphism-linked functional heterogeneity with regard to cell binding, which may explain the higher association with cardiovascular risk of small size isoforms. These qualitative differences in the binding of apo(a) isoforms to fibrin or cells may modulate the cardiovascular risk associated with high levels of Lp(a).

Expression of Prostacyclin Receptor in Human Megakaryocytes

Prostacyclin (prostaglandin I2, PGI2) is a potent vasodilator and inhibitor of platelet aggregation. Although it is well known that the specific receptor for prostacyclin (PGI2-R) is abundantly expressed on platelets, PGI2-R expression in megakaryocytes is poorly understood. In this study, we examined its expression in leukemic or normal megakaryocytes. PGI2-R mRNA was expressed in human leukemic cell lines of megakaryocytic nature as evaluated by Northern blot analysis. Phorbol 12-myristate 13-acetate (PMA), interleukin-1 (IL-1), IL-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF ), thrombopoietin (TPO), and tumor necrosis factor-α (TNF-α) enhanced PGI2-R mRNA expression. The enhancement of PGI2-R expression by PMA and TPO was associated with the upregulation of platelet factor 4 or glycoprotein IIb mRNA expression. Iloprost, an agonist of prostacyclin, induced significant cyclic (c)AMP synthesis in these leukemic cells indicating that interaction of PGI2-R and its ligand can induce postreceptor signal transduction. Furthermore, iloprost-induced cAMP synthesis was enhanced by the pretreatment with PMA or the cytokines that promoted PGI2-R expression. PMA and TPO also increased the specific binding of [3H]iloprost to these cells. Pooled normal megakaryocytic colonies from TPO-containing semisolid culture of purified human CD34+ cells expressed PGI2-R, which were increased as the megakaryocytes matured with the peak expression before proplatelet formation, as evaluated by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). These results indicate that PGI2-R is expressed in human megakaryocytes and is upregulated by cytokines involved in thrombopoiesis or inflammation. Also, it was indicated that megakaryocytic maturation accompanies enhancement of PGI2-R expression.

Expression of Prostacyclin Receptor in Human Megakaryocytes

Prostacyclin (prostaglandin I2, PGI2) is a potent vasodilator and inhibitor of platelet aggregation. Although it is well known that the specific receptor for prostacyclin (PGI2-R) is abundantly expressed on platelets, PGI2-R expression in megakaryocytes is poorly understood. In this study, we examined its expression in leukemic or normal megakaryocytes. PGI2-R mRNA was expressed in human leukemic cell lines of megakaryocytic nature as evaluated by Northern blot analysis. Phorbol 12-myristate 13-acetate (PMA), interleukin-1 (IL-1), IL-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF ), thrombopoietin (TPO), and tumor necrosis factor-α (TNF-α) enhanced PGI2-R mRNA expression. The enhancement of PGI2-R expression by PMA and TPO was associated with the upregulation of platelet factor 4 or glycoprotein IIb mRNA expression. Iloprost, an agonist of prostacyclin, induced significant cyclic (c)AMP synthesis in these leukemic cells indicating that interaction of PGI2-R and its ligand can induce postreceptor signal transduction. Furthermore, iloprost-induced cAMP synthesis was enhanced by the pretreatment with PMA or the cytokines that promoted PGI2-R expression. PMA and TPO also increased the specific binding of [3H]iloprost to these cells. Pooled normal megakaryocytic colonies from TPO-containing semisolid culture of purified human CD34+ cells expressed PGI2-R, which were increased as the megakaryocytes matured with the peak expression before proplatelet formation, as evaluated by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). These results indicate that PGI2-R is expressed in human megakaryocytes and is upregulated by cytokines involved in thrombopoiesis or inflammation. Also, it was indicated that megakaryocytic maturation accompanies enhancement of PGI2-R expression.

Molecular cloning of cDNA encoding a human TFEC isoform, a newly identified transcriptional regulator

TFEC is a transcriptional repressor originally identified in rat chondrosarcoma and contains a basic helix-loop-helix and leucine zipper (bHLH/LZ) structure. TFEC shares a closely related bHLH/LZ structure with microphthalmia-associated transcription factor (MITF) and TFE3. In the course of cDNA cloning for a factor structurally related to MITF which is also a regulator for cell differentiation, we have isolated cDNA clones from a THP-1 human monocytic leukemia cell line. These cDNAs encode a protein of 347 amino acids, termed TFECL, a human homolog of a putative rat TFEC isoform. TFECL contains an acidic domain that corresponds to a transcriptional activation domain of TFE3 but its equivalent region is deleted in rat TFEC. We explored a function of TFECL using a melanocyte-specific tyrosinase gene and a ubiquitously expressed heme oxygenase-1 gene, each promoter containing the cis-acting CANNTG motifs. By transient coexpression assays, we showed that TFECL is able to activate or inhibit transcription of a reporter gene linked to either the tyrosinase or the heme oxygenase-1 gene promoter, depending on cell types. These results suggest that TFECL may function as a transcriptional activator under certain conditions.

Human cytomegalovirus induces interleukin-8 production by a human monocytic cell line, THP-1, through acting concurrently on AP-1- and NF-kappaB-binding sites of the interleukin-8 gene

Cytomegalovirus (CMV) infection induced interleukin-8 (IL-8) gene transcription in a human monocytic cell line, THP-1 cells, leading to IL-8 secretion. The functional analysis of the IL-8 gene revealed that both AP-1- and NF-kappaB factor-binding elements were involved in conferring the responsiveness to CMV. Moreover, electrophoretic mobility shift assays demonstrated that CMV induced the formation of NF-kappaB and AP-1 complexes. These results suggest that CMV activates these transcriptional factors, resulting in IL-8 gene expression.

Distribution of endosomal, lysosomal, and major histocompatability complex markers in a monocytic cell line infected with Chlamydia psittaci

The intracellular fate of Chlamydia psittaci during infection of a monocytic cell line, THP1, was characterized. Cytochalasin D inhibited phagocytosis of latex beads but had no effect on infection by C. psittaci, and vacuoles expressed the transferrin receptor, suggesting accessibility to the endocytic pathway. Early Chlamydia-containing vacuoles expressed major histocompatibility complex (MHC) class I molecules, and most vacuoles fused with host cell lysosomes, since they expressed LAMP-1 and had acidic pHs. In cells prestimulated with gamma interferon, vacuoles also expressed MHC class II molecules, suggesting that the monocytes might effectively process Chlamydia-derived antigens for presentation by MHC class I and class II molecules.

Interleukin-1beta secreted from monocytic cells induces the expression of matrilysin in the prostatic cell line LNCaP

Matrilysin is a matrix metalloprotease that is overexpressed in cancer cells of epithelial origin and in normal tissues during events involving matrix remodeling such as the cycling endometrium. We previously observed that inflamed ductule and acinar epithelia in the prostate also overexpress matrilysin. The presence of infiltrating macrophages in these areas prompted us to determine if factors secreted from monocytes could induce matrilysin expression in a human prostatic cell line. Conditioned media collected from the monocyte cell line THP-1 following lipopolysaccharide treatment substantially induced matrilysin protein and mRNA expression in LNCaP prostate carcinoma cells. Matrilysin expression in LNCaP cells was also induced by recombinant interleukin (IL)-1 (50 pM), but not by equimolar concentrations of recombinant tumor necrosis factor-alpha or IL-6. The matrilysin-inducing activity of THP-1 conditioned medium was completely abrogated by preincubation with a neutralizing antibody to IL-1beta. Transient transfection analyses with a chimeric human matrilysin promoter-chloramphenicol acetyltransferase reporter construct demonstrated that IL-1beta activates transcription through the matrilysin promoter in LNCaP cells. This is the first report of matrilysin induction by an inflammatory cytokine in a cell line of epithelial origin, and the results suggest a potential mechanism for the overexpression of matrilysin in inflamed ducts and glands of the prostate.

Dexamethasone increases expression of 5-lipoxygenase and its activating protein in human monocytes and THP-1 cells

The aim of this study was to assess the effect of dexamethasone on 5-lipoxygenase pathway expression in human peripheral blood monocytes and the acute monocytic leukemia cell line, THP-1. Cells were conditioned over a period of days with dexamethasone, at concentrations relevant in vivo, to study the effect of the glucocorticoid on calcium-ionophore-stimulated 5-lipoxygenase product and arachidonic acid release. The effect of dexamethasone on levels of immunoreactive protein and steady-state messenger RNA encoding for 5-lipoxygenase and its activating protein (5-LAP) was also assessed. Dexamethasone increased the stimulated release of 5-lipoxygenase products from both monocytes and THP-1 cells in a dose-dependent fashion. The increase in product generation was not due to changes in the availability of arachidonic acid. However, immunoreactive protein and steady-state messenger RNA encoding for 5-lipoxygenase and 5-LAP were increased by conditioning with dexamethasone. There was no apparent effect of the glucocorticoid on LTA4-hydrolase-immunoreactive protein levels or specific activity. We conclude that dexamethasone increases 5-lipoxygenase pathway expression in both monocytes and in THP-1 cells. This effect is due, at least in part, to increases in immunoreactive protein and steady-state messenger RNA encoding for 5-lipoxygenase and 5-LAP. These results suggest a role for glucocorticoids in the regulation of 5-lipoxygenase pathway expression in mononuclear phagocytes.

Endotoxin induces increased intracellular cathepsin B activity in THP-1 cells

Macrophage cathepsin B (CB) is implicated in tissue injury in inflammatory diseases. Lipopolysaccharide (LPS) is an activator of macrophages whose effect on CB is unknown. This study was undertaken to investigate the potential of macrophages as a source of increased CB and to determine if exposure to LPS might stimulate CB levels. As a model we chose the macrophage-like tumor line, THP-1. Incubation with LPS led to a time and dose-dependent increase in CB activity. LPS potentiated interferon-gamma (IFN-gamma)-induced elevations of CB and led to an additive increase in CB activity. Pretreatment of the cells with LPS not only caused a marked stimulation of CB activity over that seen with IFN-gamma alone, but also decreased the concentration and exposure time to the cytokine necessary to achieve maximum induction of the enzyme. The LPS and IFN-gamma induced CB increases were abolished by cycloheximide or actinomycin D in the cultures, indicating that the increases in CB required increased RNA transcription and de novo protein synthesis. Direct measurement of CB mRNA showed increases. These data indicate that although LPS alone appears to induce the production of CB in THP-1 cells, it augments IFN-gamma induced increases, suggesting that two signals are necessary for maximum CB induction in this system.

Regulation of vimentin expression and protease-mediated vimentin degradation during differentiation of human monocytic leukemia cells

Terminal differentiation of human monocytic leukemia THP-1 cells is induced in vitro by 12-O-tetradecanoylphorbol-13-acetate (TPA). We investigated the effects of TPA on the expression of vimentin during the differentiation of THP-1 cells at both the mRNA and the protein level. On northern blotting analysis, a 2.1 kb vimentin mRNA was up-regulated by TPA. On western blotting, small vimentin molecules with a molecular mass of approximately 40 kDa were observed in the soluble fraction and increased with TPA-induction of cellular differentiation. Since larger, including intact, vimentin molecules were detectable at a high TPA dose, we assessed the possible existence of protease activity directed against vimentin in THP-1 cells. With incubation of the cellular lysates of THP-1 cells, the endogenous vimentin became increasingly smaller over time, suggesting the presence of a vimentin-degrading protease. Phenylmethylsulfonyl fluoride inhibited this apparent protease activity against vimentin, suggesting the enzyme involved to be a serine protease. Interestingly, the protease activity was down-regulated by TPA treatment. TPA-treated THP-1 cells were found to express a vimentin-filament network based on immunocytochemical analysis using an anti-vimentin monoclonal antibody, V9. Taken together, these observations suggest that post-translational mechanisms work in cooperation with transcriptional regulation to maintain the vimentin-intermediate filament structure in differentiated THP-1 cells.

An in vitro-differentiated human cell line as a model system to study the interaction of Neisseria gonorrhoeae with phagocytic cells

The extreme host specificity of pathogenic neisseriae limits investigations aimed at the analysis of bacterial-host interactions almost completely to the use of in vitro models. Although permanent epithelial and endothelial cell lines are already indispensable tools with respect to initial infection processes, studies concerning the interaction of neisseriae with phagocytic cells have been confined to primary human blood cells. We investigated the use of human leukemia-derived monocytic and myelomonocytic cell lines that can be differentiated in vitro towards phagocytic cells by a panel of chemical and biological reagents including cytokines, vitamin analogs, and antileukemia drugs. Whereas tumor necrosis factor alpha, gamma interferon, bufalin, or granulocyte-macrophage colony-stimulating factor only marginally increased the ability of monocytic MonoMac-6 and myelomonocytic JOSK-M cells to interact with the bacteria, retinoic acid and vitamin D3 treatment for 2 to 4 days led to highly phagocytic cells that internalized gonococci in an Opa protein-specific manner. This is comparable to the phagocytosis by primary monocytes from human blood, where more than 80% of cells are infected with intracellular bacteria. The increased phagocytic activity of JOSK-M cells following in vitro differentiation was paralleled by enhanced oxidative burst capacity. Whereas undifferentiated cells responded to neither phorbol 12-myristate 13-acetate nor other known soluble and particulate stimuli, cells incubated with retinoic acid and bufalin showed the same pattern and the same intensity of oxidative burst activity in response to Neisseria gonorrhoeae as primary cells: Opa-expressing gonococci elicited an oxidative burst, whereas Opa- gonococci did not. The surface expression of major histocompatibility complex (MHC) class II molecules was only slightly changed after retinoic acid treatment. Also, phagocytosis of gonococci had no influence on MHC class II surface expression. Taken together, our results demonstrate that in vitro-differentiated human myelomonocytic JOSK-M cells provide a suitable model for the study of a variety of aspects of the gonococcal interaction with phagocytes.

TRA1, a Novel mRNA Highly Expressed in Leukemogenic Mouse Monocytic Sublines But Not in Nonleukemogenic Sublines

Mouse monocytic Mm-A, Mm-P, Mm-S1, and Mm-S2 cells are sublines of mouse monocytic and immortalized Mm-1 cells derived from spontaneously differentiated, mouse myeloblastic M1 cells. Although these subline cells retain their monocytic characteristics in vitro, Mm-A and Mm-P cells are highly leukemogenic to syngeneic SL mice and athymic nude mice, whereas Mm-S1 and Mm-S2 cells are not or are only slightly leukemogenic. To better understand the molecular mechanisms of these levels of leukemogenicity, we investigated putative leukemogenesis-associated genes or oncogenes involved in the maintenance of growth, especially in vivo, by means of differential mRNA display. We isolated a fragment clone (15T01) from Mm-P cells. The mRNA probed with 15T01 was expressed at high levels in leukemogenic Mm-P and Mm-A cells but not in nonleukemogenic Mm-S1 and Mm-S2 cells. The gene corresponding to 15T01, named TRA1, was isolated from an Mm-P cDNA library. The longest open reading frame of the TRA1 clone predicts a peptide containing 204 amino acids with a calculated molecular weight of 23,049 D. The predicted TRA1 protein is cysteine-rich and contains multiple cysteine doublets. A putative normal counterpart gene, named NOR1, was also isolated from a normal mouse kidney cDNA library and sequenced. NOR1 cDNA predicts a peptide containing 234 amino acids. The sequence of 201 amino acids from the C-terminal NOR1 was completely identical to that of TRA1, whereas the remaining N-terminal amino acids (33 amino acids) were longer than that (3 amino acids) of TRA1 and the N-terminus of NOR1 protein contained proline-rich sequence. A similarity search against current nucleotide and protein sequence databases indicated that the NOR1/TRA1 gene(s) is conserved in a wide range of eukaryotes, because apparently homologous genes were identified in Caenorhabditis elegans and Saccharomyces cerevisiae genomes. Northern blotting using TRA1-specific and NOR1-specific probes indicated that TRA1 mRNA is exclusively expressed in leukemogenic but not in nonleukemogenic Mm sublines and normal tissues and also indicated that NOR1 mRNA is expressed in normal tissues, especially in kidney, lung, liver, and bone marrow cells but not in any Mm sublines. After leukemogenic Mm-P cells were induced to differentiate into normal macrophages by sodium butyrate, the normal counterpart, NOR1, was expressed, whereas the TRA1 level decreased. Furthermore, transfection of TRA1 converted nonleukemogenic Mm-S1 cells into leukemogenic cells. These results indicate that the TRA1 gene is associated at least in part with the leukemogenesis of monocytic Mm sublines.

Interferon-gamma induced increases in intracellular cathepsin B activity in THP-1 cells are dependent on RNA transcription

Interferon-gamma (IFN-gamma) treatment of human macrophages induces increased intracellular levels of cathepsin B (CB), a lysosomal cysteine proteinase which is implicated in inflammatory tissue injury. To determine the mechanism of the increase, we studied the macrophage-like cell line, THP-1. Dose and time dependent increases in intracellular CB were seen when cells primed with phorbol ester (PMA) were cultured with IFN-gamma. To determine whether protein synthesis was required for the increase, PMA primed cells were cultured in the presence of IFN-gamma and cycloheximide: The expected increase was inhibited. To determine whether RNA synthesis was required for the IFN-gamma induced increases, PMA primed cells were cultured in the presence of IFN-gamma and actinomycin D. Again the expected increases were not seen. Direct measurement of CB mRNA levels showed increases in cells not treated with inhibitors. These results suggest that the IFN-gamma induced increases in THP-1 cell CB are dependent on RNA and protein synthesis.

A recombinant fusion toxin targeted to the granulocyte-macrophage colony-stimulating factor receptor

Human granulocyte-macrophage colony stimulating factor (GMCSF) and its high affinity receptor function to regulate the proliferation and differentiation of myeloid lineage hematopoietic cells, and may participate in the pathogenesis of many malignant myeloid diseases. We have used genetic engineering based on the elucidated molecular structures of human granulocyte-macrophage colony-stimulating factor and diphtheria toxin (DT) to produce a recombinant fusion toxin, DTctGMCSF, that targets diphtheria toxin to high affinity GMCSF receptors expressed on the surface of blast cells from a large fraction of patients with acute myeloid leukemia (AML). DTctGMCSF was specifically immunoreactive with antidiphtheria toxin and anti-GMCSF antiseras, and exhibited the characteristic catalytic activity of diphtheria toxin, catalyzing the in vitro ADP-ribosylation of purified elongation factor 2. The cytotoxic effects of DTctGMCSF were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-tetrazolium (MTT) bromide assay of cell viability and in vivo assays of protein synthesis inhibition. DTctGMCSF were specifically cytotoxic to human leukemia cell lines bearing high affinity receptors for human GMCSF with IC50 of 10(-9) to 10(-11) M. It was not toxic to mammalian hematopoietic cell lines lacking human GMCSF (hGMCSF) receptors. In receptor positive cells, cytotoxicity can be specifically blocked by a large excess of hGMCSF, confirming that its cytotoxicity is mediated through the hGMCSF receptor. THough DTctGMCSF inhibited granulocyte-macrophage colony formation by committed myeloid progenitor cells (CFU-GM), it did not significantly affect erythroid burst formation by committed erythroid progenitor cells (BFU-E), or mixed granulocyte-erythroid-macrophage-megakaryocyte colony formation by pluripotent multilineage progenitor cells (CFU-GEMM). DTctGMCSF holds promise for the treatment of myeloid lineage malignancies, and is a useful reagent to study hematopoiesis.

Methylglyoxal-modified arginine residues--a signal for receptor-mediated endocytosis and degradation of proteins by monocytic THP-1 cells

Non-enzymatic glycosylation or glycation of proteins to form advanced glycation endproducts (AGE) has been proposed as a process which provides a signal for the degradation of proteins. Despite this, the AGE which act a recognition factor for receptor-mediated endocytosis and degradation of glycated proteins by monocytes and macrophages has not been identified. Methylglyoxal, a reactive alpha-oxoaldehyde and physiological metabolite, reacted irreversibly with arginine residues in proteins to form Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine and Ndelta-(5-methyl-4-imidazolon-2-yl)ornithine residues. Human serum albumin minimally-modified with methylglyoxal (MG(min)-HSA) was bound by cell surface receptors of human monocytic THP-1 cells in vitro at 4 degrees C: the binding constant K(d) value was 377 +/- 35 nM and the number of receptors per cell was 5.9 +/- 0.2 X 10(5) (n = 12). N alpha-Acetyl-Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)orni thine displaced MG(min)-HSA from THP-1 cells, suggesting that the Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine residue was the receptor recognition factor. At 37 degrees C, MG(min)-HSA was internalised by THP-1 cells and degraded. Similar binding and degradation of human serum albumin modified by glucose-derived AGE was found but only when highly modified. MG(min)-HSA, therefore, is the first example of a protein minimally-modified by AGE-like compounds that binds specifically to monocyte receptors. The irreversible modification of proteins by methylglyoxal is a potent signal for the degradation of proteins by monocytic cells in which the arginine derivative, Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine, is the receptor recognition factor. This factor is not present in glucose-modified proteins.

beta-Amyloid-induced IL-1 beta release from an activated human monocyte cell line is calcium- and G-protein-dependent

The proinflammatory cytokine, interleukin-1 (IL-1) is elevated in the Alzheimer's disease (AD) brain. Studies from our laboratory have demonstrated that beta-amyloid (A beta) 1-42, fibrillar A beta 1-40 and A beta 25-35 induce the release of IL-1 beta from activated THP-1 cells, a human monocyte cell line. A beta also is chemotactic for primary rodent microglia and peritoneal macrophages. We hypothesize that A beta is a chemokine and induces these responses by interaction with chemotactic receptors. If this is true, then these A beta-induced responses should be calcium-dependent and require activation of pertussis toxin-sensitive G-proteins. To test this hypothesis, THP-1 cells were grown in culture with lipopolysaccharide (LPS) and incubated with A beta 1-42 (5 muM) in the presence and absence of a calcium chelator, an inhibitor of intracellular calcium mobilization, a calcium channel blocker, or pertussis toxin, a bacterial endotoxin which uncouples G proteins from receptors by catalyzing the ADP ribosylation of cysteine near the carboxy-terminus of the alpha subunit. The media was collected and IL-1 beta present in the media was measured using an ELISA. Treatment of LPS-activated THP-1 cells with A beta 1-42 significantly elevated IL-1 beta released into the media as previously shown. Addition or ethylene glycol-bis (beta-aminothyl ether) N,N,N'N'-tetraacetic acid (EGTA) (0.5 mM), a calcium chelator, to the media blocked A beta-induced IL-1 beta release, but had no effect on LPS-activated THP-1 cell release of IL-1 beta. The presence of 3,4,5-trimethoxybenzoic acid 8-(diethyl amino)-octyl ester (TMB-8), an inhibitor of intracellular calcium mobilization, as well as nickel chloride, a non-specific calcium channel blocker, in the media also inhibited A beta-induced IL-1 release from LPS-activated THP-1 cells. IL- 1 beta release from activated THP-1 monocytes incubated with TMB-8 and nickel chloride without A beta remained at baseline values. Pretreatment of THP-1 monocytes with pertussis toxin for 4 h, followed by LPS activation and incubation with A beta, antagonized the release of IL-1 beta from these cells, but did not alter IL-1 beta release from activated THP-1 monocytes. These data suggest that A beta-induced IL-1 beta release from these cells is calcium-dependent and requires the activation of specific G-proteins. These findings are consistent with known second messengers that are activated following stimulation of chemotactic receptors.

Effects of cation substitutions on reverse transcriptase and on human immunodeficiency virus production

Reverse transcription is a key aspect of the retroviral life cycle. The enzyme reverse transcriptase requires divalent cations, manganese or magnesium, for function. In some cation-dependent systems substitution of a physiological metal by a nonphysiological metal has been shown to work. We investigated the effect of different cations on HIV reverse transcriptase activity. The studies established reaction conditions for assaying different cations. A variety of transition metals were used in in vitro assays with HIV recombinant RT homodimer and some were delivered to HIV-infected cells in vitro to study effects on virus production. Most metals substituted adequately for magnesium. However, palladium showed a marked nonreversible inhibition of RT activity in vitro that correlated with reduced HIV virus production in tissue culture. A more extensive range of transition metals and divalent cations was tested for their effects on detection of HIV RT from infected cell supernatants. In these complex phenotypes were seen. In some cases the RT activity appeared to be more easily detectable. This may relate to calcium-dependent nucleases in cell supernatants being inhibited, leading to an apparent enhancement of RT activity, or may be due to direct effects on RT processivity.

Human monocytes activate porcine endothelial cells, resulting in increased E-selectin, interleukin-8, monocyte chemotactic protein-1, and plasminogen activator inhibitor-type-1 expression

Monocytes (Mo) are thought to be important effector cells in early xenograft rejection. Effects of Mo-endothelial cell (EC) interactions on EC activation in vitro were studied by coculturing human Mo or human monocytoid cell lines, U937 and THP-1, with porcine EC. Without preactivation, U937 cells and Mo induced mRNA for the EC-specific adhesion receptor, E-selectin, expressed only on activated cells, after 2 hr. Surface protein was maximal when equal numbers of EC and Mo were cocultured. Increased mRNA expression of the chemokines, interleukin-8 and monocyte chemotactic protein-1, and the antifibrinolytic protein plasminogen activator inhibitor type-1, confirmed EC activation. Like E-selectin, plasminogen activator inhibitor type-1 mRNA was rapidly induced and returned to baseline after 24 hr, whereas chemokine gene expression was slower and more prolonged. Interleukin-1 receptor antagonist failed to modulate induction of E-selectin. Soluble tumor necrosis factor (TNF) alpha receptor inhibited E-selectin induced by TNF alpha, but not by U937 cells, and mRNA and protein on EC in Mo-EC mixtures cocultured at 1:1 ratios were not significantly reduced. The TNF alpha inhibitor did reduce E-selectin expression (30-40%), as well as induced chemokine gene expression (80%), at higher Mo-EC ratios. Despite this, minimal TNF alpha was detectable in supernatants. These results, along with the transwell experiments that confirmed a requirement for Mo-EC contact, suggest that membrane-bound TNF alpha may be involved. Thus, Mo-EC interactions in the porcine to human combination activated several EC functions, suggesting that initial Mo contact with the vessel wall of a xenogeneic graft may promote leukocyte recruitment, inflammation, and maintenance of thrombus, resulting in eventual organ destruction.

Identification of human and mouse GP-1, a putative member of a novel G-protein family

To identify genes induced in monocytes by interferon-gamma, we carried out PCR-based cDNA subtraction and subsequent differential display on mRNA isolated from a human monocytic leukemia cell line, THP-1. We detected a novel gene encoding a protein bearing GTP-binding motifs, the characteristics of GTP-binding proteins (G-proteins). We also identified the mouse homologue of this gene and designated the gene GP-1. The amino acid sequence of GP-1 deduced from the nucleotide sequence is highly conserved in human and mouse (97% identical over the entire protein), suggesting a fundamental physiological role for this molecule. As amino acid sequences of GTP-binding motifs of human and mouse GP-1 are practically identical to those of recently identified putative G-proteins of nematode, AGP-1 and CGP-1, these proteins are likely to be members of the same, novel G-protein family. GP-1 mRNA was readily detected in mouse brain, thymus, lung, and kidney, while GP-1 mRNA is rarely expressed in liver.

Evidence for prothrombin production and thrombin expression by phorbol ester-treated THP-1 cells

With the addition of fibrinogen, fibrin clots form in serum-free culture medium recovered from phorbol ester-treated THP-1 cells. We attribute this coagulant activity to thrombin generated as a consequence of cell stimulation because the coagulant activity exists in serum-free culture medium from treated cells only, and it is inhibited by hirudin. The thrombin does not derive from a prothrombin/thrombin contaminant since no detectable prothrombin/thrombin preexists in either the serum-free culture medium or the fibrinogen preparations used for our experiments. We hypothesized that the thrombin is synthesized by the cells themselves. In support of this hypothesis, we found that prothrombin mRNA is expressed in THP-1 cells following their treatment with phorbol ester. Accompanying expression of this mRNA, prothrombin antigen becomes detectable in lysates of PMA-treated THP-1 cells, and thrombin antigen and activity become detectable in both lysates and culture medium of treated cells. These results are consistent with the notion that certain cells of myelomonocytic lineage are capable of synthesizing proteins relevant to coagulation.

Establishment and characterization of a novel human cell line exhibiting both immunophenotypic markers of monocyte/macrophage and natural killer cell lineages from peripheral blood of a patient with atopic dermatitis

Large amounts of homogeneous cells are not always available for in vitro studies of inflammatory skin disorders. Here we demonstrate that a novel cell line, termed YAA, has been established from peripheral blood mononuclear cells, which were separated by the Ficoll method, of a patient with atopic dermatitis. YAA cells were grown in suspension culture. The cytochemical staining showed a positive reaction for alpha-naphthyl butyrate esterase, which was completely inhibited by sodium fluoride, but a negative result for periodic acid-Schiff, peroxidase and alkaline phosphatase. A large population of YAA cells exhibited phenotype of CD33 and CD56 but neither of CD2 nor CD3. The phorbol ester-stimulated YAA cells produced a considerable amount of tumor necrosis factor-alpha. These findings suggest that YAA might be a monocytoid line with an additional phenotype specific for natural killer cells.

Human monocyte/macrophage response to cobalt-chromium corrosion products and titanium particles in patients with total joint replacements

The responses of human peripheral blood monocytes of 10 normal volunteers and 14 patients with total hip replacements to particles of commercially pure titanium and chromium orthophosphate (a corrosion product from cobalt-chromium alloy implants) were studied. In addition, these phagocytosable particles were added to cultured mononuclear cells isolated from the interfacial membrane of 14 patients with failed implants. Peripheral blood monocytes from patients who had had a total hip replacement produced significantly higher levels of interleukin-1 (both interleukin-1 alpha and interleukin-1 beta) and prostaglandin E2 following particulate stimulation than those from normal volunteers. Supernatants from both titanium and chromium orthophosphate-stimulated peripheral blood monocytes from the volunteers and patients with total hip replacement induced bone resorption (assayed in organ cultures of newborn mouse calvariae) and the proliferation of human fibroblasts. The levels of bone resorption were significantly higher (p < 0.05) in patients with implants than in normal volunteers. There were no significant differences in the responses of cells between patients with focal osteolysis and those without osteolysis. Interfacial membrane mononuclear cells also produced high levels of interleukin-1 alpha, interleukin-1 beta, and prostaglandin E2 and expressed bone resorptive activities following stimulation with either titanium or chromium orthophosphate. More importantly, interfacial membrane mononuclear cells "spontaneously" produced high levels of prostaglandin E2 that were comparable with the response of peripheral blood monocytes stimulated with particulate wear debris. The clinical relevance of this study is 2-fold. First, mononuclear cells from patients with total hip replacement were some-how "sensitized" to metal particles in comparison with mononuclear cells from individuals without an implant. Second, the chromium orthophosphate corrosion product was a potent macrophage/monocyte activator and may contribute to macrophage-mediated osteolysis and aseptic loosening.

Generation of reactive oxygen species is required for bucillamine, a novel anti-rheumatic drug, to induce apoptosis in concert with copper

Rheumatoid arthritis (RA) is considered to be a proliferative disorder of synovial tissue, which is composed of macrophage-like, fibroblast-like and dendritic cells. Bucillamine (BUC) is a novel disease-modifying anti-rheumatic drug, which is a structural analogue of cysteine. Some of the pharmacological actions of BUC have been shown to depend on the generation of reactive oxygen species (ROS) in the presence of copper. In this study, we examined whether BUC in concert with copper can induce apoptosis via generation of ROS. THP.1, a human monocytic cell line, was used as surrogate for synovial cells. We observed that BUC plus copper can induce THP.1 to undergo apoptosis, as evidenced by the presence of DNA degradation, which is preceded by ROS generation and increase in membrane permeability. Moreover, catalase rescued THP.1 from BUC-mediated cell death, indicating that generation of ROS is essential for the induction of apoptosis Red blood cells (RBC), probably acting as a scavenger of ROS, also rescued THP.1 from cell death mediated by BUC plus copper. Collectively, we suggest that ROS derived from BUC in the presence of copper may suppress the outgrowth of rheumatoid arthritis synovial cells in vivo through the induction of apoptosis.

Human Th1 cells preferentially induce interleukin (IL)-1beta while Th2 cells induce IL-1 receptor antagonist production upon cell/cell contact with monocytes

The role of human T cells in the induction and regulation, upon cell/cell contact, of inflammatory responses by monocytic cells was investigated. The production of interleukin (IL)-1beta and IL-1 receptor antagonist (IL-1Ra) by the monocytic THP-1 cell line was measured upon contact with either Th1 or Th2 cell clones. CD4+ T cell clones specific for purified protein derivative of Mycobacterium tuberculosis, predominantly Th1 [high interferon (IFN)-gamma and low IL-4 producers], or tetanus toxoid, predominantly Th2 (low IFN-gamma and high IL-4 producers), were generated. Cell membranes from antigen-stimulated, but not from resting T cell clones induced dose-dependent cytokine production by THP-1 cells. Th1 clones induced higher levels of IL-1beta production (484-806 pg/ml) than did Th2 clones (21-114 pg/ml). In contrast, Th1 clones induced lower levels of IL-IRa (0.9-7.8 ng/ml) than did Th2 clones (7.0-49.6 ng/ml). Similar results were obtained when T cell clones were activated by cross-linked CD3 and CD28. IL-1beta production by THP-1 cells correlated with IFN-gamma production by T cell clones but was unaffected by IFN-gamma neutralization. IL-1Ra production by THP-1 cells correlated with IL-4 production by T cells and was partially inhibited by IL-4 neutralization. These data indicate that activated Th1 and Th2 cells express different molecules on the cell surface able to induce distinct pro-inflammatory (IL-1beta) or anti-inflammatory (IL-1Ra) responses in monocytes. This differential induction of molecules with opposite effects on inflammation stresses the functional heterogeneity in CD4+ T cells.

Lipophosphoglycan from Leishmania suppresses agonist-induced interleukin 1 beta gene expression in human monocytes via a unique promoter sequence

Leishmania are parasites that survive within macrophages by mechanism(s) not entirely known. Depression of cellular immunity and diminished production of interleukin 1 beta (IL-1 beta) and tumor necrosis factor alpha are potential ways by which the parasite survives within macrophages. We examined the mechanism(s) by which lipophosphoglycan (LPG), a major glycolipid of Leishmania, perturbs cytokine gene expression. LPG treatment of THP-1 monocytes suppressed endotoxin induction of IL-1 beta steady-state mRNA by greater than 90%, while having no effect on the expression of a control gene. The addition of LPG 2 h before or 2 h after endotoxin challenge significantly suppressed steady-state IL-1 beta mRNA by 90% and 70%, respectively. LPG also inhibited tumor necrosis factor alpha and Staphylococcus induction of IL-1 beta gene expression. The inhibitory effect of LPG is agonist-specific because LPG did not suppress the induction of IL-1 beta mRNA by phorbol 12-myristate 13-acetate. A unique DNA sequence located within the -310 to -57 nucleotide region of the IL-1 beta promoter was found to mediate LPG's inhibitory activity. The requirement for the -310 to -57 promoter gene sequence for LPG's effect is demonstrated by the abrogation of LPG's inhibitory activity by truncation or deletion of the -310 to -57 promoter gene sequence. Furthermore, the minimal IL-1 beta promoter (positions -310 to +15) mediated LPG's inhibitory activity with dose and kinetic profiles that were similar to LPG's suppression of steady-state IL-1 beta mRNA. These findings delineated a promoter gene sequence that responds to LPG to act as a "gene silencer", a function, to our knowledge, not previously described. LPG's inhibitory activity for several mediators of inflammation and the persistence of significant inhibitory activity 2 h after endotoxin challenge suggest that LPG has therapeutic potential and may be exploited for therapy of sepsis, acute respiratory distress syndrome, and autoimmune diseases.

Hyaluronan (HA) fragments induce chemokine gene expression in alveolar macrophages. The role of HA size and CD44

Hyaluronan (HA) is a glycosaminoglycan constituent of extracellular matrix. In its native form HA exists as a high molecular weight polymer, but during inflammation lower molecular weight fragments accumulate. We have identified a collection of inflammatory genes induced in macrophages by HA fragments but not by high molecular weight HA. These include several members of the chemokine gene family: macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, cytokine responsive gene-2, monocyte chemoattractant protein-1, and regulated on activation, normal T cell expressed and secreted. HA fragments as small as hexamers are capable of inducing expression of these genes in a mouse alveolar macrophage cell line, and monoclonal antibody to the HA receptor CD44 completely blocks binding of fluorescein-labeled HA to these cells and significantly inhibits HA-induced gene expression. We also investigated the ability of HA fragments to induce chemokine gene expression in human alveolar macrophages from patients with idiopathic pulmonary fibrosis and found that interleukin-8 mRNA is markedly induced. These data support the hypothesis that HA fragments generated during inflammation induce the expression of macrophage genes which are important in the development and maintenance of the inflammatory response.

Expression and cleavage of tumor necrosis factor-alpha and tumor necrosis factor receptors by human monocytic cell lines upon direct contact with stimulated T cells

Tumor necrosis factor-alpha (TNF-alpha) is a potent cytokine in inflammatory processes. A variety of mechanisms that modulate its activity have been described, one being its binding to soluble receptors (sTNFR). In this study, we demonstrate that human monocytic cells such as THP-1 respond to direct contact with a membrane preparation of stimulated HUT-78 cells by producing TNF-alpha and by releasing sTNFR-p75, but not sTNFR-p55, with different kinetics. TNF-alpha concentration peaked after 12 h of contact and then decreased, whereas sTNFR-p75 production increased progressively upon cell/cell contact. The decrease in TNF-alpha concentration is not due to trapping of TNF-alpha by its soluble receptors or other soluble or cell-associated molecules, but rather to a proteolytic activity associated to THP-1 cells. On the other hand, the increase in sTNFR-p75 release does not result from an increase in the cleavage of pre-existing cell-associated sTNFR-p75 but from an increase in TNFR-p75 expression, immediately followed by the cleavage of its extracellular domain. Phenylmethylsulfonylfluoride, a serine protease inhibitor, has a negative effect on both TNF-alpha degradation and sTNFR-p75 release by THP-1 cells. Thus, there may be an enzymatic activity associated to THP-1 cells that plays an important role in the neutralization of TNF-alpha activity both by degrading the molecule and by cleaving its receptors at the cell surface.

Regulation of platelet-derived growth factor receptor expression by cell context overrides regulation by cytokines

Immunocytochemical data has indicated that platelet-derived growth factor receptor beta-subunit (PDGFR beta) expression by connective tissue cells is up-regulated in many disease states. To investigate potential causes of this up-regulation, we have evaluated conditions that regulate PDGF receptor transcript levels in cultured diploid human fibroblast model systems. We found combinations of soluble mediators and cell "context," which can regulate receptor transcripts (and receptor protein) over a 50-fold range, with cell context factors being far more potent regulators than soluble mediators. For cells grown under standard monolayer conditions on plastic, levels of both PDGFR beta and PDGFR alpha increase 10-fold as culture density increases. Cells grown in suspension or in three-dimensional gels express 10- to 20-fold higher transcript levels than cells plated on plastic at comparable density and serum concentration. The soluble mediators tested, including 14 cytokines and conditioned medium from activated lymphocytes, have only modest effects on transcript levels. Lymph decreases PDGFR beta transcript expression 4-fold, suggesting that a component of interstitial fluid contributes to maintenance of the low basal level of expression in normal tissues. The mitogenic responsiveness of cells cultured at different densities parallels the level of PDGFR beta expression. Blocking anti-PDGF receptor antibodies decrease receptor availability and mitogenic responsiveness in parallel. In both cases, the striking overlap between the PDGF-BB binding and mitogenesis dose-response curves suggests that the level of PDGF receptor expression can limit responsiveness to PDGF. Overall, these results suggest that the up-regulation of PDGF receptor expression seen under pathological conditions may be due to disruption of the cell's normal environment/context/cell shape/cell attachment and that this could serve to ensure that a proliferative response to PDGF would occur only under conditions in which there had been significant tissue damage.

Absence of tumor necrosis factor alpha, interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor expression but presence of IL-1beta, IL-8, and IL-10 expression in human monocytes exposed to viable or killed Ehrlichia chaffeensis

Ehrlichia chaffeensis is a recently isolated minute gram-negative obligatory intracellular bacterium of monocytes/macrophages and is the etiologic agent of human monocytic ehrlichiosis. It is not known how macrophages respond when they encounter ehrlichiae in terms of cytokine production. In this study, we examined cytokine mRNA expression by incubating E. chaffeensis with THP-1 cells and performing competitive reverse transcription-PCR (RT-PCR). At 2 h postinfection, the levels of interleukin-1beta (IL-1beta), IL-8, and IL-10 mRNAs were significant but lower than those following Escherichia coli lipopolysaccharide (LPS) stimulation. Unlike the situation with E. coli LPS stimulation, however, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor alpha (TNF-alpha) mRNAs were not induced. Time course and dose-response studies confirmed the absence of IL-6, GM-CSF, and TNF-alpha mRNA induction with E. chaffeensis. Viable E. chaffeensis organisms were not required for IL-1beta IO, IL-8, and IL-10 mRNA induction, since heat-killed E. chaffeensis induced identical time course responses. IL-1beta, IL-8, and IL-10 mRNAs were detected for up to 21, 21, and 24 h postexposure with E. chaffeensis, respectively, which were shut off more rapidly than with LPS stimulation. Although heat treatment of E. chaffeensis had no effect, periodate treatment completely abolished the ability of E. chaffeensis to induce IL-1beta, IL-8, and IL-10 mRNAs. The capture enzyme-linked immunosorbent assay result corresponded with the RT-PCR results, showing that viable and heat-killed E. chaffeensis produced and secreted the same levels of IL-1beta and IL-8. IL-10 production was significantly reduced by heat treatment. Periodate-treated ehrlichiae did not induce production of any of the cytokines tested. Anti-CD14 monoclonal antibody and polymyxin B did not inhibit IL-1beta mRNA expression upon exposure to E. chaffeensis. The absence of TNF-alpha, IL-6, and GM-CSF mRNA induction may delay the development of a protective immune response, thereby allowing E. chaffeensis to set up residence in macrophages.

Regulation of plasminogen receptor expression on monocytoid cells by beta1-integrin-dependent cellular adherence to extracellular matrix proteins

Plasminogen binding sites function to arm cell surfaces with the proteolytic activity of plasmin, critical for degradation of extracellular matrices. We have assessed the effects of adhesion of the representative monocytoid cell lines, THP-1 and U937, to purified extracellular matrix proteins on their expression of plasminogen receptors. After adhesion to immobilized fibronectin, adherent and nonadherent subpopulations of cells were separated. Plasminogen binding to the nonadherent population of cells increased 3-fold, whereas binding to the adherent population decreased by 60%. These changes were due to differences in the plasminogen binding capacities of the cells, while the affinities of the cells for plasminogen were unchanged. The up-regulation of receptor expression in the nonadherent cell population was: 1) induced rapidly and reversibly, 2) independent of new protein synthesis, 3) required an interaction between adherent and nonadherent cell populations, and 4) associated with an enhanced ability of the cells to promote plasminogen activation and to degrade fibronectin. Other immobilized adhesive proteins, laminin and vitronectin, also supported up-regulation of plasminogen receptors in the nonadherent cells. Carboxypeptidase B treatment eliminated the increment in the plasminogen binding capacity of the nonadherent cells, suggesting that the increase in binding was due to exposure of new carboxyl-terminal lysyl residues on the cell surfaces. Furthermore, both the adherence of the cells and up-regulation of plasminogen binding sites was abolished by beta1-integrin monoclonal antibodies. These results suggest that proteins found in extracellular matrices have the capacity to modulate the expression of plasminogen binding sites, thus regulating local proteolysis and cell migration.

Transforming growth factor-beta2-mediated regulation of C3 gene expression in monocytes

In this report, we show that transforming growth factor-beta2 (TGF-beta2) regulates C3 gene expression in the human monocyte cell lines, U937 and THP-1, and human peripheral blood monocytes. Treatment of U937 or THP-1 cells with TGF-beta2 resulted in a dose-dependent induction of C3 protein and mRNA expression. Dose-dependent increases of C3 protein and mRNA levels were also detected in TGF-beta2-treated primary blood monocytes, demonstrating that TGF-beta2 can modulate C3 expression in nontransformed monocytes. Kinetic analysis demonstrated that TGF-beta2-mediated induction of C3 mRNA and protein could be detected within 8 hr, and the induction was continuous up to 72 hr. Exposure of cells to TGF-beta2 for as little as 2 hr was sufficient to induce C3 expression. TGF-beta2 did not significantly increase C3 mRNA stability as determined by mRNA half-life studies. Collectively, our results demonstrate that TGF-beta2 regulates the expression of C3 in monocytes and suggest that TGF-beta2 may play a role in modulating the synthesis of C3 during inflammatory responses.