Kappa B-type enhancers are involved in lipopolysaccharide-mediated transcriptional activation of the tumor necrosis factor alpha gene in primary macrophages

Cloning and characterization of human TNF alpha promoter region

We report the sequence of a 1.2-kb human tumor necrosis factor alpha (TNF alpha) promoter region, which was cloned using PCR. The sequence has several variations from two previous reports and exhibits many potential DNA-binding sites specific to mammalian gene regulatory proteins inducible by lipopolysaccharides.

Disruption in the AU motif of the mouse TNF-alpha 3' UTR correlates with reduced TNF production by macrophages in vitro

Many cytokine mRNAs exhibit a conserved, AU-rich motif in the 3'-untranslated region (UTR) of the molecule. Such sequence elements have been implicated in the regulation of mRNA turnover and as potential translational regulators. We report on the identification of a 3 base pair insertion which disrupts the AU motif of the TNF-alpha gene in the NZW, B10.KPA44, SM/J and Mus spretus mice and an insertion of an 8 base pair sequence into the 3' AU motif of the IL-10 gene in the Mus Spretus mouse. The mutation in the AU motif of the TNF-alpha gene correlates with reduced production of this cytokine by peritoneal macrophages from these mouse strains.

Electroporation and DNA-dependent cell death in murine macrophages

The difficulty of transfecting primary macrophages and macrophage cell lines has meant that relatively few studies on regulation of gene expression have been performed in these cells. This study has optimized an electroporation procedure for the macrophage cell line RAW 264, but shows that introduction of DNA into the cytoplasm of primary macrophages by electroporation is toxic to the cells. It is proposed that this cell death may have a physiological role in defence against certain viral infections which result in accumulation of cytoplasmic DNA. RAW 264 cells were efficiently transfected by electroporation, but electroporated bone marrow derived macrophages (BMM) showed large scale cell death over a period of 12 h. Electroporation without DNA was not toxic and DNase treatment of samples before transfection prevented cell death. The toxicity of DNA was concentration-dependent and sequence-independent. Synthetic, genomic and plasmid DNA all caused cell death. This sensitivity to DNA seems to be distinct from the antiviral state induced by double-stranded RNA and may be part of an uncharacterized viral defence system.

Nuclear factor kappa B, a mediator of lipopolysaccharide effects

Exposure of certain cell types to bacterial lipopolysaccharide (LPS) leads to activation of nuclear factor kappa B (NF-kappa B), an inducible transcription factor. One of NF-kappa B's unique properties is its posttranslational activation via release of an inhibitory subunit, called inhibitor of NF-kappa B (I kappa B), from a sequestered cytoplasmic form. This event is also triggered under various other conditions of biomedical importance. Other bacterial toxins, tumor necrosis factor-alpha (TNF), interleukin-1 (IL-1), T cell mitogens, UV light, gamma rays and oxidative stress were reported to induce NF-kappa B. The activated form of NF-kappa B, which is rapidly taken up into nuclei, initiates transcription from immediate early genes in a wide variety of cell types. Most of the target genes for NF-kappa B are of relevance for the immune response and can be grouped into those encoding cytokines, cell surface receptors, acute phase proteins and viral genomes, such as that of human immunodeficiency virus type 1 (HIV-1). We will discuss recent experimental evidences suggesting that LPS might share a pathway of NF-kappa B activation with other inducers of the factor. This common pathway may involve reactive oxygen intermediates (ROI) as messenger molecules.

Characterization of a new tissue-specific transcription factor binding to the simian virus 40 enhancer TC-II (NF-kappa B) element

We have biochemically and functionally characterized a new transcription factor, NP-TCII, which is present in nuclei from unstimulated T and B lymphocytes but is not found in nonhematopoietic cells. This factor has a DNA-binding specificity similar to that of NF-kappa B but is unrelated to this or other Rel proteins by functional and biochemical criteria. It can also be distinguished from other previously described lymphocyte-specific DNA-binding proteins.

Characterization of a new tissue-specific transcription factor binding to the simian virus 40 enhancer TC-II (NF-kappa B) element

We have biochemically and functionally characterized a new transcription factor, NP-TCII, which is present in nuclei from unstimulated T and B lymphocytes but is not found in nonhematopoietic cells. This factor has a DNA-binding specificity similar to that of NF-kappa B but is unrelated to this or other Rel proteins by functional and biochemical criteria. It can also be distinguished from other previously described lymphocyte-specific DNA-binding proteins.

trans activation of the tumor necrosis factor alpha promoter by the human T-cell leukemia virus type I Tax1 protein

In a cotransfection assay, the human T-cell leukemia virus type I Tax1 gene product specifically activated transcription from the mouse tumor necrosis factor alpha promoter. The activation patterns of 5' deletion mutants, artificial enhancer constructs, and point mutations in the promoter indicate that the major Tax1-responsive element is a site at position -655 which binds the NF-kappa B/rel and NF-GMa transcription factors.

Interleukin-1 beta induction of TNF-alpha gene expression: involvement of protein kinase C

In the human astroglioma cell line CH235-MG, interleukin-1 beta (IL-1 beta) induces transcriptional activation of the tumor necrosis factor-alpha (TNF-alpha) gene, resulting in expression of TNF-alpha mRNA and biologically active TNF-alpha protein. This study was undertaken to elucidate intracellular signaling pathways involved in IL-1 beta induction of the TNF-alpha gene. We demonstrated that the protein kinase C (PKC) activator 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) in concert with Ca++ ionophore A23187 induced expression of TNF-alpha mRNA and protein, whereas an inactive PMA analogue (alpha PMA) had no effect. Various cyclic nucleotide activators such as 8-Bromo cAMP, cholera toxin, and forskolin had no effect on TNF-alpha production. Two PKC inhibitors, H7 and staurosporine (SS), abrogated IL-1 beta induced TNF-alpha expression in a dose-dependent fashion. Treatment of CH235-MG cells with a high concentration of PMA (1 microM) for an extended period of time (48 h) caused a greater than 90% reduction in total PKC activity. Further strengthening a role for PKC in this cytokine response is the fact that IL-1 beta was no longer able to induce TNF-alpha expression in these PKC depleted cells. Last, IL-1 beta treatment produced an increase of total PKC activity in CH235-MG cells. Taken together, these data demonstrate that IL-1 beta induces TNF-alpha gene expression in CH235-MG cells in a PKC-dependent manner.

Chromatin structure and DNase I hypersensitivity in the transcriptionally active and inactive porcine tumor necrosis factor gene locus

We have analyzed the chromatin structure of the porcine tumor necrosis factor gene locus (TNF-alpha and TNF-beta). Nuclei from porcine peripheral blood mononuclear cells were digested with different nucleases. As assessed with micrococcal nuclease, the two TNF genes displayed slightly faster digestion kinetics than bulk DNA. Studies with DNaseI revealed distinct DNaseI hypersensitive sites (DH-sites) within the porcine TNF locus. Four DH-sites could be observed in the promoter and mRNA leader regions of the TNF-beta gene. Two DH-sites could be observed for the TNF-alpha gene, one located in the promoter region close to the TATA-box and the other site in intron 3. This pattern of DH-sites was present independently of the activation state of the cells. Interestingly in a porcine macrophage-like cell line, we found that the TNF-alpha promoter DH-site disappeared and another DH-site appeared in the region of intron 1. Additionally, the DH-site of intron 3 could be enhanced by PMA-stimulation in these cells. TNF-beta sites were not detected in this cell line. However, DH-sites were totally absent in fibroblasts (freshly isolated from testicles) and in porcine kidney cells (PK15 cell line) both of which do not transcribe the TNF genes. Therefore, the pattern of DH-sites corresponds to the transcriptional activity of analyzed cells.

Proliferation-dependent HIV-1 infection of monocytes occurs during differentiation into macrophages

Requirements for the establishment of productive infection with the human immunodeficiency virus type 1 (HIV-1) in primary monocytes were investigated. In vitro, monocytes rendered susceptible for infection after at least a 2-d culture, but when cultured in the presence of differentiation-inducing agent IL-4, accelerated susceptibility was seen. Complete resistance to HIV-1 infection was observed in monocytes that had been treated for 5 d with rIL-4, and comparable results were obtained with other differentiation inducers such as dexamethasone or 1,25(OH)2 vitamin D3 (1,25(OH)2vitD3). The inhibition of productive infection was not caused by downregulation of CD4 expression or HIV-1 transcription, nor by intracellular accumulation of virions. Since treatment with rIL-4, dexamethasone, or 1,25(OH)2vitD3 also resulted in complete inhibition of monocyte proliferation, we studied whether establishment of productive infection in monocytes is proliferation dependent. Irradiation or mitomycin-C treatment within 24 h after inoculation prevented productive HIV-1 infection of monocytes, suggesting a proliferation-dependent step early in the virus replication cycle. Polymerase chain reaction (PCR) analysis revealed the presence of only incomplete proviral DNA species in non-proliferating monocytes, indicating restriction of viral replication at the level of reverse transcription. Thus, in analogy with HIV-1 infection of CD4+ T cells, proliferation of monocytes during differentiation into macrophages is a prerequisite for productive infection with HIV.

Endotoxin tolerance: in vivo regulation of tumor necrosis factor and interleukin-1 synthesis is at the transcriptional level

Endotoxin tolerance is associated with a decreased production of many inflammatory mediators following stimulus-induced desensitization. The mechanisms involved in the regulation of tumor necrosis factor (TNF) and interleukin-1 (IL-1) beta expression were investigated in peritoneal macrophages from endotoxin tolerant mice. The absence of a serum TNF peak in tolerant mice correlated with a significant reduction in both TNF and IL-1 beta mRNA accumulation in macrophages from these animals. The reduction in both IL-1 and TNF mRNA was consistent with a decrease in transcriptional activity by nuclear run-on assays for both cytokines and a reduced amount of the nuclear-associated transcription factor NF-KB. Therefore, the hyporesponsive state associated with endotoxin tolerance is characterized by transcriptional regulation of both TNF and IL-1 synthesis.

Membrane potential modulates release of tumor necrosis factor in lipopolysaccharide-stimulated mouse macrophages

Lipopolysaccharide (LPS)-mediated synthesis of macrophage gene products such as tumor necrosis factor (TNF) is controlled by different signaling pathways. We investigated intracellular free Ca2+ (Ca2+ic) and the membrane potential as early cellular responses to LPS and their role in the synthesis and release of TNF. In peritoneal macrophages and in the RAW 269 mouse macrophage cell line, LPS and its biologically active moiety lipid A stimulated TNF synthesis but exerted no significant effects on these early cellular responses using Fura-2/Indo-1 to measure Ca2+ic and bis-oxonol, as well as the patch-clamp technique to monitor membrane potential. In contrast, the platelet-activating factor transiently induced both an increase in Ca2+ic and cell membrane depolarization but no significant TNF release. Increased extracellular K+ concentrations or K(+)-channel blockers, such as quinine, tetraethylammonium, or barium chloride, inhibited the LPS-stimulated release of TNF alpha, as well as the accumulation of cell-associated TNF alpha as found by enzyme-linked immunosorbent assay analysis, but did not inhibit TNF alpha mRNA accumulation. Concentrations of quinine (greater than 125 microM) or of enhanced extracellular K+ (25-85 mM) required to inhibit TNF production both significantly depolarized macrophages. These results indicate a lack of ion transport activities as early cellular responses of macrophages to LPS but suggest an important regulatory role of the membrane potential on the posttranscriptional synthesis and release of TNF in macrophages.

In vitro desensitization to lipopolysaccharide suppresses tumour necrosis factor, interleukin-1 and interleukin-6 gene expression in a similar fashion

Like blood monocytes, the human monocytic cell line Mono Mac 6 can be stimulated by lipopolysaccharide (LPS) at 1 microgram/ml to produce high levels of cytokines. When Mono Mac 6 cells are stimulated for 4-6 hr at 1 x 10(6)/ml, supernatants contain tumour necrosis factor (TNF) at an average of 60 U/ml and interleukin-6 (IL-6) at an average of 1000 U/ml. IL-1 is not detected in the supernatant, but after three freeze-thaw cycles cell-associated IL-1 can be detected (100 U/ml) and with similar amounts of IL-alpha and -beta. Preculture of Mono Mac 6 cells with LPS at 10 ng/ml for 3 days results in cells refractory to subsequent stimulation by LPS at 1 microgram/ml. In the refractory desensitized cells, production of all three cytokines is down-regulated, with a more than 10-fold reduction in protein production. For all three cytokines, this desensitization appears to be regulated at the transcript level, with a strong reduction in specific mRNA as detected by Northern blot analysis. Furthermore, Mono Mac 6 cells can be stimulated by Staphylococcus aureus (LPS contamination less than 10 pg/ml) to produce cytokines. This type of stimulus is unable to overcome desensitization, in that the secretion of TNF in LPS-precultured Mono Mac 6 cells was 10- to 100-fold lower than in Mono Mac 6 cells without LPS preculture. These data show that desensitization in Mono Mac 6 cells affects all three cytokines tested and that it extends to other activating signals, such as staphylococci.

Interleukin-1 beta induction of tumor necrosis factor-alpha gene expression in human astroglioma cells

Cells that produce tumor necrosis factor-alpha (TNF-alpha) require the presence of signaling molecules since this cytokine is not normally expressed in a constitutive manner. It has been demonstrated that glial cells can produce TNF-alpha; however, the specific inducing molecules and their mechanism(s) of action have not been clearly defined. In this study, we examined the effect of human recombinant interleukin-1 beta (IL-1 beta) on the expression of TNF-alpha by CH235-MG human malignant glioma cells. CH235-MG cells do not constitutively express TNF-alpha mRNA or protein; however, upon stimulation with IL-1 beta, these cells synthesize and secrete biologically active TNF-alpha. IL-1 beta induces the expression of a 1.9 kb TNF-alpha mRNA species. Kinetic analysis demonstrated optimum TNF-alpha mRNA expression after a 4 h exposure to IL-1 beta, and peak TNF-alpha protein production at 18 h. Cycloheximide (CHX), an inhibitor of protein synthesis, markedly increased expression of TNF-alpha mRNA in IL-1 beta stimulated CH235-MG cells, indicating that de novo protein synthesis is not required for astroglioma TNF-alpha gene expression. Nuclear run-off analysis demonstrates that IL-1 beta causes transcriptional activation of the TNF-alpha gene, and CHX enhances IL-1 beta-induced TNF-alpha transcription. Studies of TNF-alpha mRNA stability using actinomycin D show that IL-1 beta-induced TNF-alpha mRNA has a half-life of approximately 30 min, and CHX increases the half-life of IL-1 beta-induced TNF-alpha mRNA to approximately 210 min. These results indicate that IL-1 beta, a cytokine present in the central nervous system during some pathological disease states, is a potent inducer of TNF-alpha in human malignant glioma cells.

Constitutive activity of the tumor necrosis factor promoter is canceled by the 3' untranslated region in nonmacrophage cell lines; a trans-dominant factor overcomes this suppressive effect

The role of the mouse tumor necrosis factor (TNF) promoter, 5' untranslated region (UTR), and 3' UTR in TNF gene expression has been examined in three nonmacrophage cell lines (HeLa, NIH 3T3, and L-929). The TNF promoter is not macrophage-specific. On the contrary, it constitutively drives reporter gene expression in all three cell lines. Not only the full-length promoter but also truncated versions of the promoter, lacking NF-kappa B binding motifs, are active in each type of cell. The TNF 3' UTR effectively cancels reporter gene expression in HeLa cells and in NIH 3T3 cells but fails to block expression in L-929 cells. L-929 cells contain a factor that overcomes the inhibitory influence of the TNF 3' UTR. Its action depends upon the presence of sequences found in the TNF 5' UTR. Cell-fusion experiments reveal that this activator is trans-dominant. These studies highlight the essential role played by the TNF 3' UTR, which silences the TNF gene in cells that might otherwise express TNF. They also reveal the existence of an escape mechanism whereby inappropriate synthesis of TNF might occur.

Definition of microsatellite size variants for Tnfa and Hsp70 in autoimmune and nonautoimmune mouse strains

We have cloned and sequenced the upstream regulatory region of tumor necrosis factor alpha (Tnfa) gene in 12 different mouse strains and identified an allelic polymorphism in the upstream regulatory region of the mouse Tnfa gene. The TNF allele found in the NZW strain is distinct from those of all other H-2 haplotypes, supporting our previous suggestion that this allele may be associated with a regulatory or structural defect. In addition, simple tandem repeat sequences (microsatellites) within the promoter region of the Tnfa gene and the 3' untranslated region of one of the members of the HSP70 family (Hsp68c clone) were utilized as genetic markers. Ten TNF size variants and twelve HSP70 variants were identified in over forty mouse strains. Using these markers in a set of congenic mice, we mapped this member of the HSP70 family to the central portion of the H-2 complex, centromeric to the Tnfa gene. The NOD and NZW strains carry unique HSP70 alleles based on the variability in the length of this marker. These findings raise the possibility that this protein may play a role in the association of the major histocompatibility complex with these autoimmune diseases.

Regulation of NF-kappa B activity in murine macrophages: effect of bacterial lipopolysaccharide and phorbol ester

Nuclear factor kappa-B (NF-kappa B) has been shown to play an important role in LPS-mediated induction of several genes in macrophages. Several studies have implicated protein kinase C (PKC) or cAMP-dependent protein kinase in the regulation of NF-kappa B activity. In this study we have investigated the mechanism of NF-kappa B induction in murine macrophages. A chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the TNF-alpha NF-kappa B element was transfected into the RAW264 macrophage-like cell line and assessed for inducible CAT activity. LPS treatment of the transfected cells resulted in a significant induction of CAT activity. CAT activity was not induced by treatment with phorbol myristate acetate (PMA) or the cAMP analogue 8-bromo cAMP. To further study NF-kappa B induction, nuclear extracts were prepared from RAW264 cells. Extracts from RAW264 cells that were treated from 30 min to 2 hr with LPS had a significant increase in NF-kappa B binding activity as determined by the electrophoresis mobility shift assay (EMSA). Treatment of these cells from 30 min to 2 hr with PMA did not result in such binding activity. U.V. crosslinking analysis of the DNA-binding activity confirmed these results and indicated that LPS induced a 55 KD DNA-binding protein. Induction of this NF-kappa B binding activity was not inhibited by pretreatment with the PKC inhibitor H-7. H-7 did inhibit induction of TPA responsive element binding by either LPS or PMA. Prolonged exposure to phorbol ester, a treatment which down-regulates PKC, had no effect on LPS induction of NF-kappa B activity in these cells. These results suggest that the induction of NF-kappa B in macrophages by LPS is independent of PKC.

Lipopolysaccharide-mediated transcriptional activation of the human tissue factor gene in THP-1 monocytic cells requires both activator protein 1 and nuclear factor kappa B binding sites

Lipopolysaccharide (LPS) activation of cells of monocytic lineage leads to rapid and transient expression of a set of inflammatory gene products, including tissue factor (TF). This transmembrane receptor is the major cellular initiator of the blood coagulation cascades, and induced expression of TF is postulated to play a role in inflammation. Functional studies using transfected THP-1 monocytic cells revealed the presence of a 56-bp LPS response element (LRE) within the TF promoter that conferred LPS responsiveness to a heterologous promoter. LPS stimulation of these cells activated proteins that bound to nucleotide sequences within the LRE resembling consensus binding sites for activator protein 1 (AP-1) and nuclear factor kappa B (NF-kappa B). Induction of the TF gene may represent a prototypic example of gene activation in monocytic cells by assembly of transcription factor complexes, and may clarify the role of AP-1 and NF-kappa B in the regulation of other LPS-responsive genes.

The molecular action of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) is a polypeptide hormone newly synthesized by different cell types upon stimulation with endotoxin, inflammatory mediators (C5a anaphylatoxin), or cytokines such as interleukin-1 and, in an autocrine manner, TNF itself. The net biological effect of TNF-alpha may vary depending on relative concentration, duration of cell exposure and presence of other mediators which may act in synergism with this cytokine. TNF-alpha may be relevant either in pathological events occurring in cachexia and endotoxic shock and inflammation or in beneficial processes such as host defense, immunity and tissue homeostasis. The biological effects of TNF-alpha are triggered by the binding to specific cell surface receptors. The formation of TNF-alpha-receptor complex activates a variety of biochemical pathways that include the transduction of the signal at least in part controlled by guanine-nucleotide-binding regulatory proteins (G proteins), its amplification through activation of adenyl cyclase, phospholipases and protein kinases with the generation of second messenger pathways. The transduction of selected genes in different cell types determines the characteristics of the cell response to TNF-alpha. The full understanding of the molecular mechanisms of TNF-alpha will provide the basis for a pharmacological approach intended to inhibit or potentiate selected biological actions of this cytokine.

One base pair change abolishes the T cell-restricted activity of a kB-like proto-enhancer element from the interleukin 2 promoter

The inducible, T cell-specific enhancers of murine and human Interleukin 2 (Il-2) genes contain the kB-like sequence GGGATTTCACC as an essential cis-acting enhancer motif. When cloned in multiple copies this so-called TCEd (distal T cell element) acts as an inducible proto-enhancer element in E14 T lymphoma cells, but not in HeLa cells. In extracts of induced, Il-2 secreting El4 cells three individual protein factors bind to TCEd DNA. The binding of the most prominent factor, named TCF-1 (T cell factor 1), is correlated with the proto-enhancer activity of TCEd. TCF-1 consists of two polypeptides of about 50 kD and 105 kD; the former seems to be related to the 50 kD polypeptide of NF-kB. Purified NF-kB is also able to bind to the TCEd, but TCF-1 binds stronger than NF-kB to TCEd DNA. The conversion of the TCEd to a 'perfect' NF-kB binding site leads to a tighter binding of NF-kB to TCEd DNA and, as a functional consequence, to the activity of the 'converted' TCEd motifs in HeLa cells. Thus, the substitution of the underlined A residue to a C within the GGGATTTCACC motif abolishes its T cell-restricted activity and leads to its functioning in both El4 cells and HeLa cells. These results indicate that lymphocyte-specific factors binding to the TCEd are involved in the control of T cell specific-transcription of the Il-2 gene.

Tumor necrosis factor alpha in murine systemic lupus erythematosus disease models: implications for genetic predisposition and immune regulation

Recombinant tumor necrosis factor alpha (TNF-alpha) administration significantly delayed the development of lupuslike nephritis in the New Zealand black x New Zealand white (NZB x NZW)F1 and to a lesser extent in the MRL-lpr/lpr model systems. TNF-alpha treatment was effective when treatment was initiated at 2, 3, or 4 months of age but was ineffective if initiated as late as 6.5 months of age. Treatment of (NZB x NZW)F1 mice for 3 months was more effective than treatment continued for 6 months. Anti-TNF-alpha antibodies did not develop in these mice. Flow microfluorometry analysis showed no major effects on B, T, or monocyte cell population in cells from the peritoneum, spleen, lymph node, and thymus. A decrease in class II Ia expression on macrophages in the peritoneum of TNF-alpha-treated mice was noticed. A correlation between the level of TNF-alpha inducibility in vitro and the effect of TNF-alpha administration in vivo could be shown. Although a limited polymorphism could be shown by restriction fragment length polymorphism, using an amplified (AC)n microsatellite located in the 5' regulatory region of TNF-alpha, a much more extensive interallelic polymorphism was found. The AC microsatellite allele found in NZW mice was unique and different from other lupus strains and nonautoimmune strains. These results have possible implications to the pathogenesis of systemic lupus erythematosus.

Tissue factor mRNA in THP-1 monocytic cells is regulated at both transcriptional and posttranscriptional levels in response to lipopolysaccharide

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.

Tissue factor mRNA in THP-1 monocytic cells is regulated at both transcriptional and posttranscriptional levels in response to lipopolysaccharide

Tissue factor (TF) is transiently expressed in human monocytes exposed to the inflammatory agonist bacterial lipopolysaccharide (LPS). Since TF is the major cellular initiator of the coagulation protease cascades, it is inferred that its expression within the vasculature is strictly regulated. In this study, we investigated mechanisms which control TF mRNA expression in the human monocytic cell line THP-1. LPS induced a rapid and transient accumulation of the mature 2.2-kb TF mRNA, which was maximal at 2 h. After stimulation, the rate of transcription of the TF gene was increased (3.3 +/- 1.3)fold. In addition, we observed a significant change in TF mRNA stability: at 1 h after LPS stimulation, TF mRNA was stable during a 60-min period and had a half-life of greater than 120 min, whereas at 2 h, the half-life had declined to 25 +/- 5 min. Furthermore, a larger (3.4-kb) TF RNA species was induced in these cells; the size of this species and data from selective hybridizations with intron-specific probes are consistent with the presence of an unspliced copy of intron 1. These results demonstrate that the LPS-induced accumulation of TF mRNA levels in these monocytic cells is accomplished by both transcriptional and posttranscriptional control mechanisms.

The lack of receptors for atrial natriuretic peptides on human monocytes prevents a rise of cGMP and induction of tumor necrosis factor-alpha synthesis

Freshly harvested human monocytes were shown to produce tumor necrosis factor-alpha (TNF-alpha) in response to exogenously added or sodium nitroprusside-generated cGMP. In contrast, atrial natriuretic peptide (ANP) that acts by elevating cGMP in a variety of cells, was incapable of inducing TNF-alpha synthesis. This failure was due to a lack of ANP receptors and thus, to the inability of ANP to raise cGMP in human monocytes.

Transcriptional and post-transcriptional mechanisms involved in the differential expression of LPS-induced IL-1 and TNF mRNA

The amplification of cytokine mRNA following incubation of macrophages with inflammatory stimuli and protein synthesis inhibitors has been related to stabilization of labile mRNA species containing the 3'AUUUA consensus sequence. In the present study, cycloheximide-treated lipopolysaccharide (LPS)-stimulated murine peritoneal macrophages had a five- to six-fold increase in tumour necrosis factor (TNF) mRNA when compared to parallel LPS-stimulated controls. Interleukin-1 beta (IL-1 beta) mRNA levels in these cells, however, were significantly lower than the LPS controls. The down-regulation of IL-1 beta by cycloheximide was not apparent for IL-1 alpha mRNA, which had a two- to three-fold increase in the LPS-stimulated cycloheximide-treated macrophages. A similar profile was observed in vivo in which up-regulation of TNF, but not IL-1 beta mRNA, was apparent in mice administered cycloheximide plus LPS relative to LPS alone. Cycloheximide-treated LPS-stimulated macrophages demonstrated a significant increase in transcriptional activity for TNF, but not IL-1 beta, by nuclear run-on transcription assays and an increase in the amount of the nuclear binding factor NFKB when compared to LPS controls. The cycloheximide-mediated increase in TNF mRNA was also related to an increased stability of the TNF message, while no significant increase in stability was apparent in IL-1 beta mRNA. Therefore, the differential expression of TNF and IL-1 beta mRNA in cycloheximide-treated macrophages involves both transcriptional and post-transcriptional regulatory mechanisms.

Activation of endothelial-leukocyte adhesion molecule 1 (ELAM-1) gene transcription

Leukocyte adherence to endothelium is in part mediated by the transient expression of endothelial-leukocyte adhesion molecule 1 (ELAM-1) on endothelial surfaces stimulated by tumor necrosis factor alpha (TNF), interleukin (IL) 1, or bacterial lipopolysaccharide (LPS). The intracellular factors controlling induction of ELAM-1 mRNA and protein are unknown. In nuclear runoff experiments with cultured human umbilical vein endothelial cells (HUVEC), we demonstrate that transcriptional activation of the ELAM-1 gene occurs following stimulation with TNF. Sequence analysis of the 5' flanking region of the ELAM-1 gene reveals consensus DNA-binding sequences for two known transcription factors, NF-kappa B and AP-1. Gel mobility shift assays demonstrate that TNF, IL-1, or LPS (but not IL-2, IL-4, IL-6, interferon gamma, histamine, or transforming growth factor beta) induces activation of NF-kappa B-like DNA binding activity in HUVEC. In contrast, neither TNF, IL-1, nor LPS activates proteins that bind to an AP-1 consensus sequence under these experimental conditions. Phorbol 12-myristate 13-acetate, a known activator of protein kinase C (PKC), weakly induces NF-kappa B-like activity, ELAM-1 mRNA, and ELAM-1 surface expression in HUVEC. However, TNF, IL-1, and LPS do not activate PKC in HUVEC at doses that strongly induce NF-kappa B-like protein activation and ELAM-1 gene expression. PKC blockade with H7 does not inhibit activation of these NF-kappa B-like proteins but does inhibit ELAM-1 gene transcription. We conclude that PKC-independent activation of NF-kappa B in HUVEC with TNF, IL-1, or LPS is associated with, but not sufficient for, activation of ELAM-1 gene transcription.

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.

Kappa light chain predominance in serum and cerebrospinal fluid from human immunodeficiency virus type 1 (HIV-1)-infected patients

We measured kappa/lambda light chain ratios of Ig and IgG in 41 serum and 34 cerebrospinal fluid (CSF) samples from 47 patients at different clinical stages of human immunodeficiency virus type 1 (HIV-1) infection and in serum and CSF samples from control subjects. Both ratios were more elevated in HIV-1 seropositive subjects than controls. The elevation was more evident in samples from asymptomatic seropositive patients (ASP) than those from patients with acquired immunodeficiency syndrome (AIDS). In addition, there was a statistically significant elevation of Ig kappa/lambda ratios in ASP CSF compared to serum. We also delineated the light chain composition of oligoclonal IgG bands (OCB) by isoelectric focusing followed by immunofixation in CSF and serum samples from selected ASP and patients with AIDS who had neurological involvement. Five of six AIDS and all seven ASP samples had IgG OCB exclusively or predominantly of the kappa type. Four IgG OCB of the lambda type and one free lambda chain band were seen in CSF from a pediatric AIDS patient. The presence of an abnormally elevated kappa/lambda ratio correlated with the presence of IgG kappa OCB (p less than 0.02). We conclude that HIV-1 infection is associated with a kappa light chain predominance and with OCB mainly composed of kappa light chains.

Regulation of tumor necrosis factor gene expression by ionizing radiation in human myeloid leukemia cells and peripheral blood monocytes

Previous studies have demonstrated that ionizing radiation induces the expression of certain cytokines, such as TNF alpha/cachectin. However, there is presently no available information regarding the molecular mechanisms responsible for the regulation of cytokine gene expression by ionizing radiation. In this report, we describe the regulation of the TNF gene by ionizing radiation in human myeloid leukemia cells. The increase in TNF transcripts by x rays was both time- and dose-dependent as determined by Northern blot analysis. Similar findings were obtained in human peripheral blood monocytes. Transcriptional run-on analyses have demonstrated that ionizing radiation stimulates the rate of TNF gene transcription. Furthermore, induction of TNF mRNA was increased in the absence of protein synthesis. In contrast, ionizing radiation had little effect on the half-life of TNF transcripts. These findings indicate that the increase in TNF mRNA observed after irradiation is regulated by transcriptional mechanisms and suggest that production of this cytokine by myeloid cells may play a role in the pathophysiologic effects of ionizing radiation.

A CAT reporter construct allows ultrasensitive estimation of TNF synthesis, and suggests that the TNF gene has been silenced in non-macrophage cell lines

We have prepared a construct (designated CATTNF) in which the mouse TNF (cachectin) coding sequence is replaced by a sequence encoding chloramphenicol acetyltransferase (CAT), with preservation of the TNF promoter and 3'-untranslated sequences known to be important in the regulation of gene expression. When activated by LPS, permanently transfected RAW 264.7 (mouse macrophage) cells synthesize large quantities of CAT. Unlike TNF itself, CAT is nonsecreted and quite stable in the macrophage cytoplasm. Fewer than 1,000 LPS-induced macrophages can easily be detected by CAT assay. Cells maintain the ability to respond to LPS in vivo; as such, when injected intravenously, they accurately report conditions required for the production of TNF in diverse tissues. These cells may thus be used for the detection of cachectin/TNF synthesis in mice under conditions in which endogenously produced cachectin/TNF would be undetectable. Studies of the expression of CATTNF in nonmacrophage cell lines have revealed that the modified TNF gene is constitutively expressed in L-929 cells, but that its expression is tightly suppressed in HeLa cells and in NIH 3T3 cells. This finding would suggest that certain non-macrophage cells are potentially capable of utilizing the TNF promoter and translating the TNF mRNA; however, the endogenous gene has been developmentally silenced.

In situ detection of stage-specific genes and enhancers in B cell differentiation via gene-search retroviruses

We demonstrate that infection of an LPS-responsive pre-B cell line with transcriptionally-defective retroviruses containing a reporter gene (lacZ) can result in viral integrations where expression of lacZ is differentiation stage-dependent. Because expression of lacZ is dependent upon flanking cellular sequences these retroviral integrations represent in situ gene fusions with cellular enhancers (Enhsr1) and genes (Gensr1) which are either induced or repressed during LPS-stimulated differentiation. One of the well-documented effects of LPS upon pre-B cells is the induction of kappa light chain transcription via NF-kappa B. The identification of LPS-stimulated gene repression during B cell differentiation indicates that LPS has multiple effects upon gene expression during the pre-B to B cell transition. The identification of cellular enhancers and genes which are downregulated during the transition from the pre-B to the B cell stage indicates that other transcription factors, in addition to NF-kappa B, are required for this step in differentiation. Finally, we present some initial experiments which indicate the gene-search retroviruses can introduce expression of lacZ into normal hematopoietic cells in vitro and in vivo.