Lung cancer-associated protein: development and characterization of a new assay that detects a circulating lung cancer marker

A panel of murine monoclonal antibodies was generated against a high-molecular-weight glycoprotein produced by human lung cancer cells. This lung cancer-associated protein (LCAP) has been shown to circulate in the plasma of patients with lung cancer. Various combinations of MAbs were used in solid-phase enzyme-linked sandwich immunoassays to optimize the detection of LCAP in the plasma of these patients. One of these monoclonal antibodies, designated DF-L1, used both in the solid phase as well as the tracer, was selected to evaluate circulating levels of LCAP in normal subjects and in patients with lung cancer. In 341 normal subjects, the mean LCAP level was 7 units/ml, with 47 (13.8%) and 18 (5.3%) subjects having levels greater than or equal to 15 units/ml and 23 units/ml, respectively. In contrast, 27 of 35 (77.1%) patients with lung cancer had LCAP levels greater than or equal to 23 units/ml. A total of 16 of 19 (84.2%) patients with adenocarcinoma, four of seven (57.1%) patients with squamous cell carcinoma, and four of six (66.7%) patients with small cell carcinoma had levels greater than or equal to 23 units/ml. Moreover, in a small group of patients, serial LCAP levels correlated with clinical course during therapy. The LCAP assay is technically reproducible and unaffected by interfering substances in the blood or by variations in the handling of samples. These results indicate that LCAP is a new and potentially useful marker for the evaluation of patients with lung cancer.

Expression of the early growth response 1 and 2 zinc finger genes during induction of monocytic differentiation

Members of the early growth response (EGR) gene family are rapidly induced after mitogenic stimulation of diverse cell types. The present work has examined EGR gene expression during differentiation of myeloid leukemia cells along the monocytic lineage and in activated monocytes. Low levels of EGR-1 transcripts were detectable in untreated U-937 and HL-60 leukemia cells. In contrast, treatment of these cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) was associated with increases (within 1 h) in EGR-1 mRNA levels. The induction of monocytic differentiation by TPA and other agents was further associated with increases in EGR-2, but not EGR-3 or EGR-4, mRNA levels in these cells. Treatment of resting peripheral blood monocytes with the macrophage colony-stimulating factor (M-CSF) was also associated with rapid (within 15 min) increases in expression of the EGR-1 and EGR-2 genes. The results of nuclear run-on assays demonstrate that EGR-1 mRNA levels are increased in part by transcriptional activation of this gene in M-CSF-stimulated monocytes. The results also demonstrate that both EGR-1 and EGR-2 mRNA levels are regulated at the posttranscriptional level by a labile protein that destabilizes these transcripts. Finally, we demonstrate that dexamethasone, an inhibitor of monocytic differentiation, blocks the associated increases in EGR-1 and EGR-2 expression. Taken together, the results indicate that the EGR-1 and EGR-2 early response genes are involved in the induction of myeloid leukemia cell differentiation along the monocytic lineage and in the activation of human monocytes.

Ionizing radiation induces expression and binding activity of the nuclear factor kappa B

Recent studies have demonstrated that treatment of mammalian cells with ionizing radiation is associated with activation of gene expression. Although the signal transduction pathways stimulated by ionizing radiation remain unclear, our previous findings indicate that radiation induces specific genes at the transcriptional level. The present work has examined the effects of ionizing radiation on the transcription factor NF-kappa B. The results demonstrate that ionizing radiation activates DNA binding of nuclear factor (NF)kappa B. This effect was detectable at 2 grays (Gy) and reached a maximum at 5-20 Gy. At a dose of 20 Gy, the increase in NF-kappa B binding activity was maximal at 2-4 h and then declined to pretreatment levels. The results also demonstrate that ionizing radiation transiently increases NF-kappa B mRNA levels. However, the finding that induction of NF-kappa B binding to DNA occurs in the presence of cycloheximide indicates that ionizing radiation activates preexisting NF-kappa B protein. NF-kappa B exists as a cytoplasmic protein before activation. Thus, our results suggest that ionizing radiation induces transduction pathways which include cytoplasmic signaling events.

Regulation of jun-B expression by a cyclic AMP (cAMP)-dependent mechanism in human myeloid cells

The present studies have examined the regulation of the jun-B early response gene by cyclic AMP (cAMP)-dependent signaling pathways. The 2.0-kb jun-B transcript was at low but detectable levels in uninduced human HL-60 myeloid leukemia cells. In contrast, treatment with 1 mmol/L8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP) in the presence of isobutylmethylxanthine, an inhibitor of cAMP-dependent phosphodiesterase, was associated with increases in jun-B transcripts that were maximal by 1 hour and then decreased to near pretreatment levels by 6 hours. Similar findings were obtained with 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (8-CPT-cAMP) and N6,2'-0-dibutyryladenosine 3',5'-cyclic monophosphate (dBt-cAMP). jun-B transcripts were also increased with other agents that increase intracellular cAMP levels, such as prostaglandin E2 (PGE2) and forskolin. Moreover, inhibition of cAMP-dependent protein kinase by the isoquinolinesulfonamide H-8 blocked 8-Br-cAMP-induced increases in jun-B expression. The results of nuclear run-on assays demonstrate that treatment of HL-60 cells with PGE2, forskolin, 8-Br-cAMP, and dBt-cAMP is associated with increases in the rate of jun-B transcription. The present findings also demonstrate that the related jun-D gene is similarly regulated by a cAMP-dependent pathway. Taken together, these findings suggest that stimulation of cAMP-dependent protein kinase is involved in the induction of jun gene expression in myeloid leukemia cells.

Activation of the c-jun protooncogene in human myeloid leukemia cells treated with etoposide

The epipodophyllotoxin etoposide is an inhibitor of topoisomerase II. The effects of this agent on gene expression, particularly the transcriptional induction of genes implicated in growth control, are unknown. The present results demonstrate that etoposide induces expression of the c-jun protooncogene in HL-60 myeloid leukemia cells. This induction of c-jun expression was maximal at 3 hr and was transient. Similar findings were obtained in the human U-937 myeloid leukemia cell line. Nuclear run-on assays demonstrated that the induction of c-jun expression by etoposide is regulated at the transcriptional level. The results further demonstrate that etoposide-induced c-jun expression occurs in association with the appearance of c-fos transcripts. Moreover, the c-jun gene is induced by etoposide during periods of oligonucleosomal DNA cleavage, which is characteristic of programmed cell death. These findings suggest that transcriptional induction of c-jun expression represents a signaling pathway activated in the cellular response to etoposide-induced DNA damage.

Shaking HIV-1 infected cells indicates novel behavior of MN strain

The shaking method of harvesting human immunodeficiency virus type 1 (HIV-1) is a powerful method of obtaining high titer, highly infective virus solutions. In this method infected cells are suspended in a small volume of liquid and the mixture is shaken. Viral infectivity, measured by tissue culture infective dose (TCID50) studies, rises faster than virus titer, as measured by reverse transcriptase levels. It is postulated that this disproportionate increase in infectivity results from improved infectivity for the virus particles obtained from shaking the infected cells. Of the five strains of HIV-1 studied (IIIB, AL1212, 906, RJ4029, and MN), one strain, MN, behaved differently than the others. Upon shaking, its virus titer increased 18-fold, as opposed to the 5-10 fold increase demonstrated by the other strains. These results may indicate that MN virions are retained more on the surface of the infected cells, rather than budding off into the surrounding medium, than other HIV-1 strains. In support of this theory it was found that ratios of immunofluorescence assay scores to reverse transcriptase levels were higher for MN than for other strains.

Coexpression of the genes for platelet-derived growth factor B-chain receptor and macrophage colony-stimulating factor 1 receptor during monocytic differentiation

Receptors for platelet-derived growth factor (PDGF) have not been identified previously to our knowledge in human myeloid cells that also produce PDGF. Here we report that phorbol ester-treated myeloid cells differentiated along the monocytic lineage express both a full-length 5.5-kilobase (kb) mRNA and a predominant, truncated 4.6-kb mRNA coding for the PDGF B-chain receptor (PDGF-BR). PDGF-BR was identified in phorbol ester-differentiated myeloid cells by indirect immunofluorescence with an antibody specific to PDGF-BR. This anti-PDGF-BR was also used in immunoprecipitation studies to demonstrate that lysates of phorbol ester-differentiated myeloid cells contain PDGF-BR molecules of 37 kDa to 130 kDa. The results also show that the tandemly linked genes for PDGF-BR and the macrophage colony-stimulating factor 1 receptor are coexpressed in the phorbol ester-differentiated myeloid cells. Expression of these two receptor genes has not been shown previously in any cell type to our knowledge.

Protein kinase C mediates x-ray inducibility of nuclear signal transducers EGR1 and JUN

The cellular response to ionizing radiation includes growth arrest and DNA repair followed by proliferation. Induction of immediate early response genes may participate in signal transduction preceding these phenotypic responses. We analyzed mRNA expression for different classes of immediate early genes (JUN, EGR1, and FOS) after cellular x-irradiation. Increased expression of the EGR1 and JUN genes was observed within 0.5-3 hr following x-ray exposure. Preincubation with cycloheximide was associated with superinduction of JUN and EGR1 in x-irradiated cells. Inhibition of protein kinase C activity by prolonged stimulation with phorbol 12-myristate 13-acetate or the protein kinase inhibitor H7 prior to irradiation attenuated the increase in EGR1 and JUN transcripts. FOS expression was not coregulated with that of EGR1 following x-irradiation, suggesting a distinct regulatory pathway of this gene as compared with its regulation following serum and phorbol ester. These data implicate the EGR1 and JUN proteins as signal transducers during the cellular response to radiation injury and suggest that this effect is mediated in part by a protein kinase C-dependent pathway.

Induction of internucleosomal DNA fragmentation in human myeloid leukemia cells by 1-beta-D-arabinofuranosylcytosine

The present results demonstrate that treatment of human U-937 myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with DNA fragmentation at multiples of approximately 200 base pairs. The extent of ara-C-induced DNA fragmentation was dependent on drug concentration and time of exposure. This pattern of internucleosomal DNA cleavage has been observed during programmed cell death and was associated in the present studies with loss of clonogenic survival. The results also demonstrate that the c-jun protooncogene is induced by ara-C during periods of DNA cleavage. These findings suggest that ara-C activates a program involving both oligonucleosomal DNA fragmentation and changes in early response gene expression.

Expression of the jun-B gene during induction of monocytic differentiation

The AP-1 protein complex binds to specific DNA sequences that regulate transcription of genes responsive to certain growth factors and phorbol esters. This complex is composed of products of the jun and fos gene families. The present studies have examined the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the regulation of jun-B gene expression during induction of monocytic differentiation. Low levels of jun-B transcripts were present in uninduced HL-60 promyelocytic leukemia cells. In contrast, treatment with TPA was associated with rapid increases in jun-B mRNA levels that were maximal at 3 h and remained elevated at 48 h. The induction of jun-B expression by TPA in these cells preceded that of the c-jun and c-fos genes. Similar increases in jun-B transcripts were detectable in TPA-treated THP-1 and U-937 myeloid leukemia cells, although expression of this gene was transient in the more differentiated THP-1 cells. Run-on assays demonstrated low levels of jun-B gene activation in untreated HL-60 cells, whereas TPA treatment was associated with a 6-fold increase in the transcription rate of this gene. This induction of jun-B expression occurred in the absence of de novo protein synthesis. In contrast, inhibition of protein synthesis was associated with superinduction of TPA-induced jun-B mRNA levels and an increase in stability of this transcript. These findings suggest that jun-B gene expression is regulated at both the transcriptional and posttranscriptional levels during induction of monocytic differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of granulocyte-macrophage colony-stimulating factor on 3'-azido-3'-deoxythymidine uptake, phosphorylation and nucleotide retention in human U-937 cells

Previous studies have demonstrated that granulocyte-macrophage colony-stimulating factor (GM-CSF) both increases and decreases levels of 3'-azido-3'-deoxythymidine (AZT) nucleotides in certain human myeloid cells. The present studies have examined the effects of GM-CSF on AZT metabolism in U-937 cells. The results demonstrate that GM-CSF stimulated AZT nucleotide formation in these cells. This stimulation was detectable during concurrent exposure to GM-CSF and AZT or as a result of pretreatment with GM-CSF. The GM-CSF-induced enhancement in AZT nucleotide formation was associated with a 4-fold increase in AZT uptake. The finding that uptake of AZT into U-937 cells was only partially sensitive to 6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine (NBMPR) suggested a process primarily involving nonfacilitated diffusion. The results also demonstrate that treatment of U-937 cells with GM-CSF was associated with nearly a 2-fold increase in thymidine kinase activity. Moreover, the findings indicate that retention of AZT-MP and AZP-TP was prolonged significantly (P less than 0.05 and P less than 0.01 respectively) in association with GM-CSF treatment. Taken together, these results suggest that GM-CSF enhances the formation of AZT nucleotides by increasing AZT uptake and phosphorylation, as well as increasing retention of phosphorylated derivatives.

Regulation of c-jun gene expression by cAMP in HL-60 myeloid leukemia cells

Previous studies have demonstrated that expression of the c-jun proto-oncogene is induced by phorbol esters and other agents that activate protein kinase C. The present work has examined the involvement of cAMP-dependent signaling mechanisms in the regulation of c-jun gene expression. Low levels of c-jun transcripts were detectable in untreated HL-60 myeloid leukemia cells. In contrast, treatment of these cells with 8-bromoadenosine 3',5'-cyclic monophosphate was associated with increases in c-jun expression that were maximal at 3 h and then declined to pretreatment levels. Similar findings were obtained with N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate and 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, but not with 8-bromoguanosine 3',5'-cyclic monophosphate. c-jun transcripts were also increased with agents, such as prostaglandin E2 and forskolin, that increase intracellular cAMP levels. The effects of these agents on c-jun expression were associated with activation of cAMP-dependent protein kinase. Moreover, inhibition of this kinase activity with the isoquinolinesulfonamide derivative H8 was associated with a block in the induction of c-jun expression by cAMP. Nuclear run-on analysis further demonstrated that while c-jun transcription is a low levels in untreated HL-60 cells, treatment with cAMP analogs is associated with an increase in the transcriptional rate of this gene. Taken together, these findings suggested that, in addition to activation of protein kinase C, stimulation of cAMP-dependent protein kinase activity is also involved in the transcriptional induction of c-jun gene expression. The present results similarly demonstrate that c-fos gene transcription is induced in HL-60 cells through a mechanism involving cAMP-dependent protein kinase activity. Since heterodimers of the Jun and Fos proteins have been shown to bind to the phorbol ester-responsive element (AP-1-binding site), the present findings indicate that cAMP-induced signaling events may also regulate gene transcription through formation of Fos/Jun heterodimers and that interaction between phorbol ester- and cAMP-dependent pathways could occur through induction of the c-jun gene in these cells.

Induction of c-fos gene expression by arabinofuranosylcytosine in human KG-1 leukemia cells

Previous studies have demonstrated that the c-fos proto-oncogene is expressed during induction of differentiation and as an immediate early response to growth factors. The present results demonstrate that exposure of human KG-1 myeloid leukemic cells to 1-beta-D-arabinofuranosylcytosine (ara-C) was associated with increases in c-fos gene expression. This effect was dependent on the concentration and time of ara-C treatment. The level of c-fos transcripts was maximal after 6 hr of exposure to 5 x 10(-6) M ara-C and subsequently declined to that in untreated cells. Nuclear run-on assays demonstrated low to undetectable levels of c-fos gene transcription in untreated KG-1 cells. In contrast, treatment with 5 x 10(-6) M ara-C for 6 hr was associated with increases in transcription of this gene. Although superinduction of c-fos expression has been observed at the post-transcriptional level in the presence of protein synthesis inhibition, this effect was not detectable in ara-C-treated KG-1 cells. These combined results demonstrate that ara-C increased c-fos mRNA levels in KG-1 cells and that this effect was associated with transcriptional activation of the c-fos gene.

Detection and characterization of a high molecular weight human lung carcinoma-associated glycoprotein

We have defined a human lung carcinoma antigen using murine monoclonal antibodies (DF-L1 and DF-L2) prepared against a primary adenocarcinoma of the lung. This antigen is expressed on the surface of human lung carcinoma cell lines and has an apparent Mr of 350,000-420,000. Immunoperoxidase staining has demonstrated expression of the antigen in the cytoplasm and membranes of adenocarcinomas and squamous cell carcinomas but not small cell tumors of the lung. Immunoprecipitation of the antigen following radiolabeling has demonstrated the presence of both protein and carbohydrate. Antigen purified by immunoaffinity was used to study the epitopes defined by monoclonal antibodies DF-L1 and DF-L2. The results indicate that the DF-L1 epitope primarily involves a peptide structure, while the DF-L2 epitope is comprised in part by peptide and O-linked carbohydrate. In contrast, there was no detectable evidence for the presence of N-linked glycosylation. The results also demonstrate that this antigen circulates at elevated levels in patients with carcinoma of the lung. These findings are similar to previous reports of high molecular weight glycoproteins in breast and ovarian carcinomas. Indeed, the present results in lung cancer identify another member of this heterogeneous family of human carcinoma-associated glycoproteins.

Induction of monocytic differentiation by tumor necrosis factor in phorbol ester-resistant KG-1a cells

Tumor necrosis factor (TNF) is a regulatory cytokine that has pleiotropic effects on hematopoietic cell growth and differentiation. The present studies have examined the effects of TNF on the differentiation of phorbol-ester resistant human KG-la leukemia cells. Treatment with 100 U/mL of TNF or 33 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) had no detectable effect on the growth of KG-1a cells. In contrast, TNF, but not TPA, induced cellular aggregation and expression of the ICAM-1 adhesion molecule in KG-1a cells. Furthermore, KG-1a cells responded to TNF, but not to TPA, with a partial down-regulation of c-myc mRNA levels and induction of M-CSF gene transcription. Previous work suggested that TNF induces M-CSF gene expression through activation of phospholipase A2 and eicosanoid production. The present studies also demonstrate that TNF stimulated phospholipase A2 activity. In contrast, there was no detectable increase in phospholipase A2 activity following TPA treatment. These results indicate that: 1) certain characteristics of the differentiated monocytic phenotype were induced by TNF in the phorbol ester-resistant KG-1a line, and 2) treatment with TNF and not TPA was associated with activation of phospholipase A2 during induction of monocytic differentiation in these cells.

Regulation of jun-B gene expression by 1-beta-D-arabinofuranosyl-cytosine in human myeloid leukemia cells

The jun-B gene is a member of the jun family of immediate early response genes that regulate cellular responses to growth factors. The present studies have examined the effects of 1-beta-D-arabinofuranosylcytosine (ara-C) on jun-B expression in human KG-1 myeloid leukemia cells. The results demonstrate that ara-C increases jun-B mRNA levels. The level of jun-B transcripts was maximal after 12 hr of exposure to 10(-5) M ara-C and persisted through 72 hr. Nuclear run-on assays demonstrated that ara-C treatment is associated with an increased rate of jun-B gene transcription. The results also demonstrate that ara-C-induced jun-B mRNA levels are regulated by a posttranscriptional mechanism. The level of jun-B transcripts in ara-C-treated cells was superinduced by inhibition of protein synthesis. Moreover, cycloheximide prolonged the half-life of ara-C-induced jun-B transcripts. These results, thus, demonstrate that ara-C induces expression of the jun-B gene in KG-1 cells and that this effect is mediated by transcriptional and posttranscriptional mechanisms.

Colony-stimulating factor 1 activates protein kinase C in human monocytes

Colony-stimulating factor 1 (CSF-1) is required for the survival, proliferation and differentiation of monocytes. We previously demonstrated that the CSF-1 receptor is linked to a pertussis toxin-sensitive G protein and that the induction of Na+ influx by CSF-1 is a pertussis toxin-sensitive event. The present studies have examined activation of protein kinase C as a potential intracellular signaling event induced by the activated CSF-1 receptor. The results demonstrate that CSF-1 stimulates translocation of protein kinase C activity from the cytosol to membrane fractions. This activation of protein kinase C was sensitive to pretreatment of the monocytes with pertussis toxin. Lipid distribution studies demonstrated that phosphatidylcholine (PC) is the major phospholipid in human monocytes. Moreover, the results indicate that CSF-1 stimulation is associated with decreases in PC, but not in phosphatidylinositol (PI), levels. The absence of an effect of CSF-1 on PI turnover was confirmed by the lack of changes in inositol phosphate production. In contrast, CSF-1 stimulation was associated with increased hydrolysis of PC to phosphorylcholine and diacylglycerol (DAG) in both intact monocytes and cell-free assays. Furthermore, the increase in PC turnover induced by CSF-1 was sensitive to pertussis toxin. The results also demonstrate that the induction of Na+ influx by CSF-1 is inhibited by the protein kinase C inhibitors staurosporine and the isoquinoline derivative H7, but not by HA1004.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction between recombinant human tumor necrosis factor and radiation in 13 human tumor cell lines

Tumor necrosis factor (TNF) was cytotoxic at concentrations of 10 to 1000 units/ml to 12 of 14 human tumor cell lines. Synergistic or additive cell killing between TNF and radiation was observed in 7 of 10 tumor cell lines, while independent tumor cell killing by each agent occurred in two tumor cell lines. The maximum synergistic effect was observed when TNF was added 4-12 hr prior to irradiation. This interaction was absent when TNF was added after irradiation. TNF also reduced potentially lethal damage repair in 3 of 5 cell lines tested. Possible mechanisms of interaction of TNF and X rays including induction of hydroxyl radicals and subsequent DNA damage by TNF and radiation are discussed.

Transcriptional regulation of DF3 gene expression in human MCF-7 breast carcinoma cells

The DF3 gene codes for a high molecular weight human breast tumor-associated glycoprotein. The detection of this antigen in human milk has also suggested that its expression represents a differentiated function of mammary epithelium. The present studies have examined the regulation of DF3 gene expression in human MCF-7 breast carcinoma cells. These cells express two DF3 transcripts of 4.5 and 7.0 kb. Treatment of MCF-7 cells with 12-0-tetradecanoylphorbol-13-acetate (TPA) was associated with increases in levels of both DF3 mRNAs. When nuclear run-on assays were used, DF3 gene transcription was at low to undetectable levels in untreated MCF-7 cells and was increased after TPA exposure. TPA-induced increases in DF3 mRNA levels were also inhibited by actinomycin D (ACT). MCF-7 cells exposed to ACT further demonstrated that the half-lives of the 4.5 and 7.0 kb transcripts are 26 and 11 h, respectively. The results also demonstrate that the protein synthesis inhibitor, cycloheximide (CHX), increases DF3 mRNA levels in MCF-7 cells. These effects of CHX were sensitive to actinomycin D and not associated with stabilization of the DF3 transcripts. Taken together, these findings indicate that DF3 gene expression is controlled at a transcriptional level in TPA- and CHX-treated MCF-7 cells.

Effects of lipopolysaccharide on phospholipase A2 activity and tumor necrosis factor expression in HL-60 cells

LPS has been identified as a potent activator of mononuclear phagocytes. This activation is associated with TNF gene expression. The intracellular signaling mechanisms responsible for this effect, however, are unknown. The present studies demonstrate that LPS induces TNF transcripts in HL-60 promyelocytic leukemia cells. Because previous studies have demonstrated that eicosanoids are involved in the regulation of TNF gene expression in these cells, we examined the effects of LPS on activation of the arachidonic acid cascade. The results demonstrate that LPS stimulates phospholipase A2 activity and the hydrolysis of both 1,2-dipalmitoyl phosphatidylcholine and 1-steroyl 2-arachidonoyl phosphatidylcholine. In contrast, there was no detectable effect of LPS on activation of protein kinase C. We also demonstrate that inhibition of phospholipase A2 activity with bromophenacyl bromide or quinacrine blocks the induction of TNF transcripts by LPS. These findings suggested that LPS induces TNF gene expression through formation of arachidonic acid metabolites. Indeed, similar results were obtained with mellitin, a known activator of phospholipase A2 and eicosanoid production. Previous studies have also suggested that TNF mRNA levels are increased in HL-60 cells by the 5-lipoxygenase pathway and, in the present work inhibitors of this enzyme blocked LPS-induced TNF expression. Moreover, the cyclooxygenase metabolite, PGE2, as well as dibutyryl cAMP, inhibited the induction of TNF transcripts by LPS. Taken together, these results suggest that LPS induces TNF gene expression through activation of phospholipase A2 and that the level of this induction is regulated by activity of the 5-lipoxygenase and cyclooxygenase pathways.

Effects of lipopolysaccharide on phospholipase A2 activity and tumor necrosis factor expression in HL-60 cells

LPS has been identified as a potent activator of mononuclear phagocytes. This activation is associated with TNF gene expression. The intracellular signaling mechanisms responsible for this effect, however, are unknown. The present studies demonstrate that LPS induces TNF transcripts in HL-60 promyelocytic leukemia cells. Because previous studies have demonstrated that eicosanoids are involved in the regulation of TNF gene expression in these cells, we examined the effects of LPS on activation of the arachidonic acid cascade. The results demonstrate that LPS stimulates phospholipase A2 activity and the hydrolysis of both 1,2-dipalmitoyl phosphatidylcholine and 1-steroyl 2-arachidonoyl phosphatidylcholine. In contrast, there was no detectable effect of LPS on activation of protein kinase C. We also demonstrate that inhibition of phospholipase A2 activity with bromophenacyl bromide or quinacrine blocks the induction of TNF transcripts by LPS. These findings suggested that LPS induces TNF gene expression through formation of arachidonic acid metabolites. Indeed, similar results were obtained with mellitin, a known activator of phospholipase A2 and eicosanoid production. Previous studies have also suggested that TNF mRNA levels are increased in HL-60 cells by the 5-lipoxygenase pathway and, in the present work inhibitors of this enzyme blocked LPS-induced TNF expression. Moreover, the cyclooxygenase metabolite, PGE2, as well as dibutyryl cAMP, inhibited the induction of TNF transcripts by LPS. Taken together, these results suggest that LPS induces TNF gene expression through activation of phospholipase A2 and that the level of this induction is regulated by activity of the 5-lipoxygenase and cyclooxygenase pathways.

Effects of dexamethasone on induction of monocytic differentiation in human U-937 cells by dimethylsulfoxide

The present studies demonstrate that dimethylsulfoxide (DMSO) treatment of human U-937 myelomonocytic leukemia cells is associated with induction of monocytic differentiation. The DMSO-induced U-937 monocytic phenotype was associated with 1) growth inhibition, 2) loss of clonogenic survival, 3) increases in alpha-naphthyl acetate esterase (NSE) staining, and 4) increases in cell surface expression of the monocyte marker Mac-1. DMSO treatment of U-937 cells was also associated with down-regulation of c-myc and c-myb gene expression as well as with increases in tumor necrosis factor (TNF) mRNA levels. The results further demonstrate that induction of U-937 monocytic differentiation by DMSO is accompanied by increases in phospholipase A2 activity. Moreover, this stimulation of phospholipase A2 was sensitive to dexamethasone. We therefore studied the effects of dexamethasone on DMSO-induced differentiation of U-937 cells. Although dexamethasone had no effect on growth inhibition or loss of clonogenic survival by DMSO, this glucocorticoid blocked increases in NSE staining and cell surface Mac-1 expression. Dexamethasone also had no effect on the down-regulation of c-myc and c-myb expression but blocked the reappearance of c-myb transcripts after 6 hr of DMSO treatment. Finally, dexamethasone inhibited DMSO-induced increases in TNF gene expression. Taken together, the results demonstrate that dexamethasone inhibits multiple characteristics, including the stimulation of phospholipase A2 activity, associated with DMSO-induced monocytic differentiation of U-937 cells.

Sequence analysis of the 5' region of the human DF3 breast carcinoma-associated antigen gene

DF3 antigen is a high molecular weight glycoprotein detectable in human breast carcinomas. Recent studies have demonstrated that the gene coding for the DF3 core protein consists in part of highly conserved 60 base pair tandem repeats. The present work extends these findings by identifying the region of the DF3 gene 5' to the repeats. The results of primer extension studies demonstrate that the transcription start site of the cDNA is 384 base pairs upstream to the first tandem repeat. Comparison of the cDNA and genomic sequences has demonstrated that the sequences transcribed upstream to the repeats are interrupted by the presence of an intron at 124 bases after the start site. We have also identified the putative promoter region of the DF3 region. This region has several elements, including a TATA sequence and multiple GC boxes, that may be involved in the regulation of DF3 gene transcription.