Regulation of HIV-1 transcription

Human immunodeficiency virus type-1 (HIV-1) is a highly pathogenic lentivirus that requires transcription of its provirus genome for completion of the viral life cycle and the production of progeny virions. Since the first genetic analysis of HIV-1 in 1985, much has been learned about the transcriptional regulation of the HIV-1 genome in infected cells. It has been demonstrated that HIV-1 transcription depends on a varied and complex interaction of host cell transcription factors with the viral long terminal repeat (LTR) promoter. The regulatory elements within the LTR interact with constitutive and inducible transcription factors to direct the assembly of a stable transcription complex that stimulates multiple rounds of transcription by RNA polymerase II (RNAPII). However, the majority of these transcripts terminate prematurely in the absence of the virally encoded trans-activator protein Tat, which stimulates HIV-1 transcription elongation by interacting with a stem-loop RNA element (TAR) formed at the extreme 5' end of all viral transcripts. The Tat-TAR interaction recruits a cellular kinase into the initiation-elongation complex that alters the elongation properties of RNAPII during its transit through TAR. This review summarizes our current knowledge and understanding of the regulation of HIV-1 transcription in infected cells and highlights the important contributions human lentivirus gene regulation has made to our general understanding of the transcription process.

Chemokine gene activation in human bone marrow-derived osteoblasts following exposure to particulate wear debris

Particulate wear debris induces the expression of pro-inflammatory cytokine and chemokine genes in various cell types of the periprosthetic region. We have previously reported that titanium particles stimulate the selective induction of interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) chemokines in human osteoblast-like osteosarcoma cells. In this study, we characterize the human bone marrow-derived osteoblast chemokine response to titanium particles. We demonstrate that titanium particles result in enhanced IL-8 and MCP-1 protein secretion as well as differential chemokine gene activation. Osteoblast chemokine expression was regulated at the level of gene transcription, with a time-dependent induction of NF-kappaB activation. Inhibition studies with N-acetyl-L-cysteine (Nac) and MG-132 suggest that titanium particle activation of NF-kappaB activity and IL-8 chemokine expression involves oxidant signaling and IkappaBalpha-proteasomal degradation. Activation of the NF-kappaB transcription factor, as well as the IL-8 gene, are redox-regulated. We also demonstrate that while cytochalasin D, a potent inhibitor of phagocytosis, suppressed the titanium particle effect on IL-8 protein release in human bone marrow-derived osteoblasts, the inhibitor had no effect on IL-8 expression in MG-63 osteoblast-like cells. Collectively, these results provide insight into the potential mechanisms responsible for the particulate activation of osteoblast chemokine expression and suggest an important role for the osteoblast in the pathogenesis of periprosthetic osteolysis.

Chemokine IL-8 induction by particulate wear debris in osteoblasts is mediated by NF-kappaB

Chemokines, or chemotactic cytokines, are major regulators of the inflammatory response and have been identified as pathogenic factors in the periprosthetic soft tissue. Particulate wear debris induced NF-kappaB activation, the major transcriptional regulator of IL-8 and MCP-1 pro-inflammatory genes and, indeed, both IL-8 and MCP-1 chemokine gene expressions were upregulated in titanium particulate-stimulated human osteoblasts. Here, we demonstrate that phagocytosed particles activate the IL-8 gene promoter via a NF-kappaB-mediated mechanism. Transfection of a dominant negative mutant IkappaBalpha protein that cannot be serine phosphorylated led to suppression of IL-8 promoter activity. The p65/RelA NF-kappaB subunit activity was affected in both a time- and titanium particle concentration-dependent fashion. Titanium particles led to increased ERK, JNK, and p38 activation in MG-63 osteoblast cells, and IL-8 protein release was suppressed by specific inhibitors of the ERK and p38 MAPK pathways. Together, our results suggest that wear debris particles induce chemokine expression in osteoblasts via NF-kappaB-mediated transcriptional activation, which is controlled by the MAPK signal transduction pathway.

Elimination of background in film-based applications

Erase-It® Background Eliminator is a solution used directly on processed film to remove background or improve data resolution. Traditional methods, such as optimization of the scientific protocol or better estimation of exposure time, are tedious and uncertain. Nevertheless, autoradiography continues to be a simple, effective method to visualize data. Therefore, we evaluated the ability of Erase-It Working Solution to help solve background and resolution issues. To demonstrate the efficiency of the Background Eliminator, we analyzed the product's ability to remove signal evenly, performance on several brands of film, and usefulness with various detection methods. Even reduction of signal was demonstrated by performing densitometric analysis on film generated from a dot blot with serial dilutions of analyte. In addition, overexposed films from various suppliers were effectively treated to remove background and visualize data. Autoradiographs, generated with 32P-labeled probes, and chemiluminescent substrate were also processed resulting in clearer images. Our results demonstrate that film data can be treated quickly and conveniently without fear of artificial enhancement. We show the Background Eliminator to be a universal and timesaving tool to visualize results that otherwise may be difficult to interpret.

Concentration- and composition-dependent effects of metal ions on human MG-63 osteoblasts

Metal debris from implants has been shown to alter the function of osteoblasts in cell cultures. Its remains unclear, however, if specific forms of released ionic metals are involved in the pathogenesis of periprosthetic osteolysis. We evaluated the relative effects of ionic forms of implant metals by treating human osteoblast-like MG-63 osteosarcoma cells with eight concentrations (0.001-10.0 mM) of Cr(+3), Mo(+5), Al(+3), Ta(+5), Co(+2), Ni(+2), Fe(+3), Cu(+2), Mn(+2), Mg(+2), Na(+2), and V(+3) chloride solutions. The results demonstrated that the metal ions differentially affected osteoblast proliferation, viability, type-I collagen gene expression, and cytokine release. The metal ions were ranked in order from least to most toxic (based on a 50% reduction in viability) as follows: Na < Cr < Mg < Mo < Al < Ta < Co < Ni < Fe < Cu < Mn < V. Metal-induced decreases in osteoblast proliferation were similar in ranking. Nontoxic concentrations of metals had no effect on procollagen alpha1[I] gene expression; only at toxic concentrations did metals produce a decrease in gene expression. The most toxic metals (V, Mn, Fe, and Ni) were also the only metals found to induce IL-6 secretion on a per cell basis (of the cytokines tested, interleukin 6 (IL-6), interleukin beta 1 (IL-1beta), transforming growth factor beta 1 (TGF-beta1), and tumor necrosis factor alpha (TNF-alpha), only IL-6 was detectable in the culture medium after 48 h for any metal at any concentration). Less toxic metals (e.g., Co and Cr) had little effect on IL-6 release, even at high concentrations. In general, metal ions reduced osteoblast function (i.e., proliferation and collagen gene expression) in proportion to the degree of toxicity. These results support the hypothesis that adverse local cellular responses (particularly necrotic responses) associated with metal debris from implanted metallic devices may be due in part to metal ions released from implants or from particulate debris.

Shedding of the interleukin-6 (IL-6) receptor (gp80) determines the ability of IL-6 to induce gp130 phosphorylation in human osteoblasts

Human osteoblasts produce interleukin-6 (IL-6) and respond to IL-6 in the presence of soluble IL-6 receptor (sIL-6R), but the cell surface expression of IL-6R and the mechanism of sIL-6R production are largely unknown. Three different human osteoblast-like cell lines (MG-63, HOS, and SaOS-2) and bone marrow-derived primary human osteoblasts expressed both IL-6R and gp130 as determined by flow cytometry and immunoprecipitation. However, the membrane-bound IL-6R was nonfunctional, as significant tyrosine phosphorylation of gp130 did not occur in the presence of IL-6. Phorbol myristate acetate induced a dramatic increase of both IL-6R shedding (i.e. the production of sIL-6R) and IL-6 release in osteoblast cultures, but the cell surface expression of gp130 remained unchanged. IL-6 complexed with sIL-6R, either exogenously introduced or derived from the nonfunctional cell surface form by shedding, induced rapid tyrosine phosphorylation of gp130. This effect was inhibited by neutralizing antibodies to either sIL-6R or gp130, indicating that the gp130 activation was induced by IL-6/sIL-6R/gp130 interaction. Protein kinase C inhibitors blocked phorbol myristate acetate-induced and spontaneous shedding of IL-6R resulting in the absence of sIL-6R in the culture medium, which in turn also prevented the activation of gp130. In conclusion, human osteoblasts express cell surface IL-6R, which is unable to transmit IL-6-induced signals until it is shed into its soluble form. This unique mechanism provides the flexibility for osteoblasts to control their own responsiveness to IL-6 via the activation of an IL-6R sheddase, resulting in an immediate production of functionally active osteoblast-derived sIL-6R.

Titanium particles induce the immediate early stress responsive chemokines IL-8 and MCP-1 in osteoblasts

Exposure of human osteoblasts to ultrafine titanium (Ti) particles has been shown to alter osteoblast gene expression. We previously reported that Ti particles can increase IL-6 release and suppress the gene expression of procollagens alpha1[I] and alpha1[III] in human osteoblasts. In this study, we now demonstrate that Ti particles can rapidly induce the chemotactic cytokines interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1), two immediate early stress responsive chemokines important for the activation and chemotaxis of neutrophils and macrophages, respectively. In MG-63 osteosarcoma cells and bone marrow derived primary osteoblasts Ti particles selectively increased the steady state levels of IL-8 and MCP-1 mRNA in a time and concentration dependent manner. The increased chemokine mRNA correlated with increased secretion of IL-8 and MCP-1 protein. Actinomycin D, a potent RNA polymerase II inhibitor, blocked the Ti particle induction of IL-8 and MCP-1 mRNA expression, whereas cycloheximide, which inhibits protein synthesis, failed to inhibit chemokine gene expression suggesting Ti particles directly target activation of chemokine gene transcription. Consistent with a transcriptional mechanism not involving new protein synthesis, we demonstrate that Ti particles induce the binding of the p65 and p50 subunits of the latent transcription factor NF-kappaB to the IL-8 gene promoter. Taken together, these data demonstrate that Ti particles can activate transcription of the stress responsive chemokine genes IL-8 and MCP-1 in human osteoblasts.

Respiratory syncytial virus and TNF alpha induction of chemokine gene expression involves differential activation of Rel A and NF-kappa B1

BACKGROUND

Respiratory syncytial virus (RSV) infection of airway epithelial cells stimulates the expression and secretion of a variety of cytokines including the chemotactic cytokines interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), and RANTES (regulated upon activation, normal T cell expressed and secreted). Chemokines are important chemoattractants for the recruitment of distinct sets of leukocytes to airway sites of inflammation.

RESULTS

We have shown previously that chemokine expression is regulated in airway epithelial cells (A549) in a stimulus-specific manner in part through the redox-responsive transcription factors AP-1 and NF-kappaB. In this study, we examined the NF-kappaB-mediated effects of RSV and the proinflammatory cytokine TNFalpha on the induction of IL-8, MCP-1 and RANTES chemokine gene expression in A549 epithelial cells. The results demonstrate that RSV induces chemokine expression with distinct kinetics that is associated with a specific pattern of NF-kappaB binding activity. This distinction was further demonstrated by the differential effects of the NF-kappaB inhibitors dexamethasone (DEX) and N-acetyl-L-cysteine (NAC). NAC preferentially inhibited RSV induced chemokine expression, whereas DEX preferentially inhibited TNFalpha induced chemokine expression. DNA binding studies using NF-kappaB subunit specific binding ELISA demonstrated that RSV and TNFalpha induced different NF-kappaB binding complexes containing Rel A (p65) and NF-kappaB1 (p50). Both TNFalpha and RSV strongly induced Rel A the activation subunit of NF-kappaB, whereas only TNFalpha was able to substantially induce the p50 subunit. Consistent with the expression studies, RSV but not TNFalpha induction of Rel A and p50 were markedly inhibited by NAC, providing a mechanism by which TNFalpha and RSV can differentially activate chemokine gene expression via NF-kappaB.

CONCLUSIONS

These data suggest that RSV induction of chemokine gene expression, in contrast to TNFalpha, involves redox-sensitive NF-kappaB complexes containing predominantly Rel A.

Osteolysis: basic science

Since the recognition of aseptic loosening by Charnley in the early 1960s, much information has been gained on the basic science of periprosthetic bone loss. Initially termed cement disease, it now generally is accepted that, in most instances, osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris, possibly facilitated by local hydrodynamic effects. Tissue explant, animal, and cell culture studies have allowed us to compile an appreciation of the complexity of cellular interactions and chemical mediators involved in osteolysis. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular responses and effects on bone include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin 6. However, an increasing number of other proinflammatory and antiinflammatory cytokines, prostenoids, and enzymes have been shown to play important roles in this process. The ultimate goal of basic research is to develop novel strategies for evaluation and treatment of patients with osteolysis. Although initial animal studies are promising for possible pharmacologic treatment and prevention of osteolysis, well-controlled human trials are required before agents such as bisphosphonates can be recommended for general clinical use.

The potential role of the osteoblast in the development of periprosthetic osteolysis: review of in vitro osteoblast responses to wear debris, corrosion products, and cytokines and growth factors

Limited information is available on the responses of osteoblasts to wear debris, corrosion products, and cytokines and on the roles of altered osteoblast functions in the development of periprosthetic bone loss. Wear debris-challenged osteoblasts exhibit altered functions resulting in the loss of their capacity to produce bone matrix and to replace the resorbed bone. Also, osteoblasts may secrete cytokines, which act in a paracrine fashion to recruit inflammatory cells into the periprosthetic space and to stimulate osteoclastic bone resorption. These effects may be mediated in part by ionic metal dissolution products. We review the mechanisms by which altered osteoblast functions, in response to particulate wear debris, corrosion products, and cytokines and growth factors, may contribute to the development and the progression of periprosthetic osteolysis.

Oxidant stress and endothelial cell dysfunction

Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-kappaB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion. Particular emphasis is placed on the regulation of cell-cell and cell-surface adhesion molecules, the actin cytoskeleton, key protein kinases, and signal transduction events.

Down-regulation of procollagen alpha1[I]] messenger RNA by titanium particles correlates with nuclear factor kappaB (NF-kappaB) activation and increased rel A and NF-kappaB1 binding to the collagen promoter

Previously, we showed that exposure of human osteoblasts to titanium particles stimulates protein tyrosine phosphorylation (PTP), activates the transcription factor nuclear factor kappaB (NF-kappaB), and causes an approximately 50% decrease in the steady-state messenger RNA (mRNA) level of procollagen alpha1[I]. In this study, we identify three NF-kappaB binding sites within the human procollagen alpha1[I] gene promoter, show that titanium particles stimulate their binding of the NF-kappaB subunits Rel A (p65) and NF-kappaB1 (p50), and find NF-kappaB activation correlates with collagen gene suppression by titanium particles in osteoblasts. Protein tyrosine kinase (PTK) inhibitors, which significantly reduce the suppressive effect of titanium particles on collagen gene expression, inhibited NF-kappaB binding activity showing that titanium particle stimulation of PTK signals in osteoblasts are critical for both NF-kappaB activation and collagen gene expression. The antioxidant pyrrolidine dithiocarbamate (PDTC), which also inhibits the titanium particle suppression of collagen, abrogated the titanium particle activation of NF-kappaB, suggesting the involvement of redox signals in NF-kappaB-mediated collagen gene expression. The RNA polymerase II inhibitor actinomycin D (Act D) decreased procollagen alpha1[I] mRNA expression and effectively blocked the titanium-induced suppressive effect, suggesting that titanium particles activate a cascade of signals in osteoblasts, which result in a suppression of procollagen alpha1[I] mRNA. Collectively, these results show that titanium particles can activate NF-kappaB signaling in osteoblasts and suggest that NF-kappaB binding to the collagen gene promoter has a functional role in the down-regulation of procollagen alpha1[I] gene transcription.

The effects of particulate wear debris, cytokines, and growth factors on the functions of MG-63 osteoblasts

BACKGROUND

Particle-challenged cells release cytokines, chemokines, and eicosanoids, which contribute to periprosthetic osteolysis. The particle-induced activation of macrophages and monocytes has been extensively studied, but only limited information is available on the response of osteoblasts to particulate wear debris. This study examines the effects of particulate wear debris, proinflammatory cytokines, and growth factors on osteoblast functions.

METHODS

MG-63 osteoblasts were treated with metal particles (titanium, titanium alloy, and chromium orthophosphate) or polymeric particles (polyethylene and polystyrene) of phagocytosable sizes or were treated with exogenous cytokines and growth factors. The kinetics of particle phagocytosis and the number of engulfed particles were assessed with use of fluoresceinated particles. Cell proliferation was determined according to [3H]-thymidine incorporation, and cell viability was determined by either fluorescein diacetate uptake or trypan blue exclusion. Expressions of osteoblast-specific genes were quantified with Northern blot hybridization, and the secretions of osteoblast-specific proteins and cytokines were analyzed by enzyme-linked immunosorbent assays.

RESULTS

MG-63 osteoblasts phagocytosed particles and became saturated after twenty-four hours. A maximum of forty to sixty particles per cell were phagocytosed. Each type of particle significantly suppressed procollagen alpha1[I] gene expression (p<0.05), whereas other osteoblast-specific genes (osteonectin, osteocalcin, and alkaline phosphatase) did not show significant changes. Particle-stimulated osteoblasts released interleukin-6 (p<0.05) and a smaller amount of transforming growth factor-beta1. Particles reduced cell proliferation in a dose-dependent manner without affecting cell viability (p<0.05). Exogenous tumor necrosis factor-alpha also enhanced the release of interleukin-6 (p<0.01) and transforming growth factor-beta1 (p<0.05), whereas the secretion of transforming growth factor-beta1 was increased by insulin-like growth factor-I and prostaglandin E2 as well. Insulin-like growth factor-I and transforming growth factor-beta1 significantly increased procollagen alpha1[I] gene expression in osteoblasts (p<0.05), while tumor necrosis factor-alpha and prostaglandin E2 significantly suppressed procollagen alpha1[I] gene expression (p<0.01). In contrast, neither exogenous nor endogenous interleukin-6 had any effect on other cytokine secretion, on proliferation, or on procollagen alpha1[I] gene expression. The transcription inhibitor actinomycin D reduced both procollagen alpha1[I] transcription and interleukin-6 production. Inhibitors of protein synthesis (cyclohexamide) and intracellular protein transport (brefeldin A and monensin) blocked the release of interleukin-6, but none of these compounds influenced the suppressive effect of titanium on procollagen alpha1[I] gene expression.

CONCLUSIONS

MG-63 osteoblasts phagocytose particulate wear debris, and this process induces interleukin-6 production and suppresses type-I collagen synthesis. Osteoblast-derived interleukin-6 may induce osteoclast differentiation and/or activation, but the resorbed bone cannot be replaced by new bone because of diminished osteoblast function (reduced type-I collagen synthesis). Exogenous cytokines (tumor necrosis factor-alpha and interleukin-1beta), growth factors (insulin-like growth factor-I and transforming growth factor-beta1), and prostaglandin E2 can modify particulate-induced alterations of osteoblast functions.

The basic science of periprosthetic osteolysis

Despite improvements in the techniques, materials, and fixation of total joint replacements, wear and its sequelae continue to be the main factors limiting the longevity and clinical success of arthroplasty. Since Charnley first recognized aseptic loosening in the early 1960s, a tremendous amount of information has been gained on the basic science of osteolysis. Tissue explant, animal, and cell culture studies have allowed development of an appreciation of the complexity of cellular interactions and chemical mediators involved in these processes. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular interactions and effects on bone primarily include PGE2, TNF-alpha, IL-1, and IL-6. Recent and ongoing work in the field of signaling pathways will continue to advance our understanding of the mechanisms of periprosthetic bone loss. Although initial animal studies are promising for the development of possible pharmacologic agents for the treatment and prevention of osteolysis, well controlled human trials are required.

Particulate wear debris activates protein tyrosine kinases and nuclear factor kappaB, which down-regulates type I collagen synthesis in human osteoblasts

Particulate wear debris generated mechanically from prosthetic materials is phagocytosed by a variety of cell types within the periprosthetic space including osteoblasts, which cells with an altered function may contribute to periprosthetic osteolysis. Exposure of osteoblast-like osteosarcoma cells or bone marrow-derived primary osteoblasts to either metallic or polymeric particles of phagocytosable sizes resulted in a marked decrease in the steady-state messenger RNA (mRNA) levels of procollagen alpha1[I] and procollagen alpha1[III]. In contrast, no significant effect was observed for the osteoblast-specific genes, such as osteonectin and osteocalcin (OC). In kinetic studies, particles once phagocytosed, maintained a significant suppressive effect on collagen gene expression and type I collagen synthesis for up to five passages. Large particles of a size that cannot be phagocytosed also down-regulated collagen gene expression suggesting that an initial contact between cells and particles can generate gene responsive signals independently of the phagocytosis process. Concerning such signaling, titanium particles rapidly increased protein tyrosine phosphorylation and nuclear transcription factor kappaB (NF-kappaB) binding activity before the phagocytosis of particles. Protein tyrosine kinase (PTK) inhibitors such as genistein and the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly reduced the suppressive effect of titanium on collagen gene expression suggesting particles suppress collagen gene expression through the NF-kappaB signaling pathway. These results provide a mechanism by which particulate wear debris can antagonize the transcription of the procollagen alpha1[I] gene in osteoblasts, which may contribute to reduced bone formation and progressive periprosthetic osteolysis.

Expression of MHC class II in T cells is associated with increased HIV-1 expression

HIV-1 replicates in activated T cells at significantly higher levels than in resting cells. Thus, certain molecules up-regulated during T cell activation appear to be important for HIV-1 replication. In this study, we present evidence suggesting that expression of MHC class II (class II) molecules on CD4+ T cells facilitate HIV-1 replication. T cells that expressed class II supported greater virus replication than T cells lacking class II. The class II+ cells, when either infected with HIV-1 or transfected with an env-minus HIV-1 provirus plasmid, produced 10-20-fold greater virus expression than class II- cells. Anti-class II antibody markedly inhibited virus expression in class II+ cells (but not class II- cells) and also decreased the nuclear binding activity of AP-1, an inducible transcription factor important in T cell activation and HIV-1 expression. Most importantly, the induction of class II expression by transfection of the MHC class II transactivator (CIITA) stimulated HIV-1 replication in Jurkat T cells. Taken together, these data suggest that expression of MHC class II molecules and/or CIITA in T cells enhances HIV-1 transcription.

Cutting edge: activation of HIV-1 transcription by the MHC class II transactivator

Both macrophages and activated CD4+ T cells can be productively infected by HIV-1, and both cell types express MHC class II molecules. Expression of MHC class II proteins in these cells is regulated by a specific transcriptional coactivator, the class II transactivator (CIITA). In this study, we report for the first time that CIITA expression profoundly influences HIV-1 replication. Stable expression of CIITA in Jurkat cells markedly increased 1) HIV-1 replication as assessed by the p24 Ag production and 2) luciferase expression after transfection with full-length provirus or long terminal repeat constructs. Similarly, transient expression of CIITA increased provirus expression as well as long terminal repeat promoter activity in 293 and HeLa-T4 cells. In contrast, mutant forms of CIITA did not increase HIV-1 expression. This study shows that expression of CIITA increases HIV-1 replication through a transcriptional mechanism.

Transcriptional regulation of Fas gene expression by GA-binding protein and AP-1 in T cell antigen receptor.CD3 complex-stimulated T cells

Fas (CD95 or APO-1), a transmembrane cell surface receptor of the tumor necrosis factor receptor family, is up-regulated in activated T lymphocytes. Our present study identified an upstream enhancer element (between nucleotide positions -862 and -682) containing a GA-binding protein (GABP) site and a low affinity activating protein-1 (AP-1)-binding site. T cell activation increased the DNA binding of GABP and AP-1 to this enhancer site. The specificity of GABP and AP-1 binding was demonstrated by competition electrophoretic mobility shift assay and supershift electrophoretic mobility shift assay with antibodies against GABP and AP-1, respectively. Mutational analysis of Fas promoter revealed that both GABP- and AP-1-binding sites were required for initiating Fas gene transcription. We further show that anti-CD3 mAb, phorbol 12-myristate 13-acetate, and phorbol 12-myristate 13-acetate/ionomycin strongly activated promoters carrying multiple copies of the Fas enhancer, and mutation of either the GABP or AP-1 binding site severely reduced transcriptional activity. Taken together, these results suggest that the transcription factors GABP and AP-1 play a critical role in the induction of Fas gene expression in T cell antigen receptor.CD3-stimulated Jurkat cells.

Regulation of intercellular adhesion molecule-1 (CD54) gene expression

Intercellular adhesion molecule-1 (ICAM-1, CD54) is an inducible cell adhesion glycoprotein of the immunoglobulin supergene family expressed on the surface of a wide variety of cell types. ICAM-1 interactions with the beta2 integrins CD11a/CD18 (LFA-1) and CD11b/CD18 (MAC-1) on the surface of leukocytes are important for their transendothelial migration to sites of inflammation and their function as costimulatory molecules for T cell activation. ICAM-1 is constitutively expressed on the cell surface and is up-regulated in response to a variety of inflammatory mediators, including proinflammatory cytokines, hormones, cellular stresses, and virus infection. These stimuli increase ICAM-1 expression primarily through activation of ICAM-1 gene transcription. During the past decade much has been learned about the cell type- and stimulus-specific transcription of ICAM-1. The architecture of the ICAM-1 promoter is complex, containing a large number of binding sites for inducible transcription factors, the most important of which is nuclear factor-kappa B (NF-kappaB). NF-kappaB acts in concert with other transcription factors and co-activators via specific protein-protein interactions, which facilitate the assembly of distinct stereospecific transcription complexes on the ICAM-1 promoter. These transcription complexes presumably mediate the induction of ICAM-1 expression in different cell types and in response to different stimuli. In this review, we summarize our current understanding of ICAM-1 gene regulation with a particular emphasis on the transcription factors and signal transduction pathways critical for the cell type- and stimulus-specific activation of ICAM-1 gene transcription.

Oxidant stress regulation of IL-8 and ICAM-1 gene expression: differential activation and binding of the transcription factors AP-1 and NF-kappaB (Review)

Reactive oxygen species (ROS), generated either extracellularly or intracellularly through ligand-receptor interactions, can function as signal transduction molecules to activate the chemotactic cytokine interleukin-8 (IL-8) and the cell surface adhesion protein, intercellular adhesion molecule-1 (ICAM-1; CD54). Together, IL-8 and ICAM-1 orchestrate the transendothelial migration of neutrophils to sites of inflammation and injury. Recent results demonstrate that oxidant stress generated directly by exogenous H2O2 differentially induce IL-8 and ICAM-1 transcription in epithelial and endothelial cells. H2O2 induces IL-8 but not ICAM-1 in the A549 type-II-like epithelial cell line, whereas in a microvessel endothelial cell line (HMEC-1) as well as in primary endothelial cells, H2O2 induces ICAM-1 but not IL-8, which is spontaneously expressed. In contrast, the pro-inflammatory cytokine TNFalpha, whose activity is dependent on the generation of intracellular ROS, induces IL-8 and ICAM-1 in both cell types. The differential induction of IL-8 and ICAM-1 by H2O2 and TNFalpha suggest that the two inflammatory stimuli target distinct redox responsive signaling pathways to activate cell type-specific gene expression. In this regard, we found that the cell type-specific pattern of IL-8 and ICAM-1 gene expression was associated with the differential activation and promoter binding of the redox regulated transcription factors AP-1 and NF-kappaB. In this review, our current understanding of the redox regulation of the IL-8 and ICAM-1 genes is summarized, and the differential roles AP-1 and NF-kappaB play in their cell type-specific expression, with particular emphasis on the differential effects induced by TNFalpha and H2O2 is discussed.

Stimulation of neutrophil interleukin-8 production by eosinophil granule major basic protein

We evaluated the ability of eosinophil granule major basic protein (MBP) to stimulate interleukin (IL)-8 production by neutrophils. MBP over the concentration range of 0.1 to 10 microM stimulated the release of up to approximately 8 ng/ml IL-8. Incubation with 2 microM MBP showed that, after a 1 h lag, the level of IL-8 release increased with time for approximately 10 h. At the 2 microM concentration, eosinophil cationic protein, eosinophil-derived neurotoxin, and eosinophil peroxidase did not stimulate significant levels of IL-8 production. MBP stimulated 2-fold increases in IL-8 messenger RNA (mRNA) after 1 and 3 h of incubation, which were blocked by pretreatment with actinomycin D. However, stimulation with MBP did not produce an increase in the binding activity of nuclear factor (NF)-kappaB or activator protein-1. No NF-IL-6 binding activity was detected in the same nuclear extracts. In addition, stimulation with MBP prolonged the stability of IL-8 mRNA. MBP also induced transient increases in mRNA for macrophage inflammatory protein (MIP)-1alpha and MIP-1beta, but did not stimulate the release of either chemokine. These findings indicate that MBP is selective among the eosinophil granule proteins as a stimulus for neutrophil IL-8 release and, further, that stimulation of neutrophil IL-8 release by MBP involves both transcriptional and posttranscriptional regulation. We postulate that MBP-induced release of IL-8 by neutrophils may contribute to the pathophysiology of acute asthma and other inflammatory lung diseases.

Bacterial vaginosis-associated microflora isolated from the female genital tract activates HIV-1 expression

Alteration of cervicovaginal microbial flora can lead to vaginosis, which is associated with an increased risk of HIV-1 transmission. We recently characterized a soluble HIV-inducing factor (HIF) from the cervicovaginal lavage (CVL) samples of women. The goals of this study were to determine the effect of cervicovaginal microflora on HIV-1 expression and to elucidate the relationship between HIF activity and microflora. Physiologically relevant microorganisms, Mycoplasma, diphtheroid-like bacteria, Gardnerella vaginalis, Streptococcus agalactiae, and Streptococcus constellatus, cultured from the CVL of a representative woman with a clinical condition of bacterial vaginosis and possessing HIF activity, induced HIV-1 expression. The magnitude of virus induction varied widely with the greatest stimulation induced by diphtheroid-like bacteria and Mycoplasma. The transcriptional induction by Mycoplasma was mediated by activation of the KB enhancer, an activation mechanism shared with HIF. Also as with HIF, Mycoplasma induced AP-1 dependent transcription. Polymerase chain reaction (PCR)-based speciation showed that the isolate was M. hominis. Our data indicate that bacterial vaginosis-associated microflora can enhance HIV-1 transcription and replication and identify M. hominis as a potential source for HIF activity. The virus-enhancing activities associated with the microflora and HIF may increase genital tract viral load, potentially contributing to HIV transmission.

Regulation of interleukin-8 gene expression

Interleukin-8 (IL-8), a member of the CXC chemokine family, is an important activator and chemoattractant for neutrophils and has been implicated in a variety of inflammatory diseases. IL-8 is secreted in a stimulus-specific manner by a wide variety of cell types and is regulated primarily at the level of gene transcription. Functional studies indicate that IL-8 transcriptional responses to proinflammatory mediators are rapid and require only 100 nucleotides of 5'-flanking DNA upstream of the TATA box. Within the IL-8 promoter sequence are DNA binding sites for the inducible transcription factors AP-1, NF-IL-6, and NF-kappaB. Transcription factors in these families bind the IL-8 promoter as dimers, and several distinct subunit combinations have been identified as important for IL-8 transcription. In addition, these factors can act in concert to synergistically activate the IL-8 promoter. AP-1 and NF-IL-6 physically interact with NF-kappaB, and functional cooperativity among the factors appears to be critical for optimal IL-8 promoter activity in different cell types. IL-8 transcription appears to be activated by a promoter recruitment mechanism where inducible transcription factor binding to the IL-8 promoter is required for binding of constitutively active TATA box-binding proteins and formation of a stable preinitiation complex. This review discusses the regulatory role these higher-order synergistic interactions play in IL-8 transcription and in generation of the stimulus-specific and cell type-specific patterns of IL-8 expression.

Human immunodeficiency virus type 1 (HIV-1) infection and expression in intestinal epithelial cells: role of protein kinase A and C pathways in HIV-1 transcription

Human immunodeficiency virus (HIV) can infect human colon epithelial cell lines by both CD4-dependent and -independent mechanisms. The present studies assessed cellular factors that are important for HIV-1 transcription in human colon epithelial cells. The HIV-1 long terminal repeat (LTR) was shown to contain functional DNA cis-regulatory elements downstream of the viral transactivator-responsive element in the transcribed noncoding 5' leader sequence. These downstream regulatory elements, termed DSE, can bind c-Fos and JunD and transmit protein kinase C activation signals to the HIV LTR. Moreover, specific Jun and Fos transcription factors can transactivate HIV-1 provirus in human colon epithelial cells. The DSE also bind related proteins of the CREB/ATF family. In this regard, the DSE behave as 12-0-tetradecanoylphorbol 13-acetate responder element-like cAMP-responsive elements because they bind both AP-1 and CREB/ATF transcription factors, thereby permitting induction of the HIV-1 LTR by both protein kinase C and A activation signals.

Activation of human immunodeficiency virus type 1 expression by Gardnerella vaginalis

Bacterial vaginosis (BV) is associated with an increased rate of sexual transmission of human immunodeficiency virus (HIV) type 1, and Gardnerella vaginalis is frequently isolated from the genital tracts of women with BV. G. vaginalis lysates were found to significantly stimulate HIV expression in monocytoid cells. Stimulation was significantly higher when lysates were heated at 100 degrees C for 5 min but was reduced by treatment with lysozyme or protease. G. vaginalis lysates also activated HIV expression in certain T cell lines. G. vaginalis lysates activated HIV long-terminal repeat transcription in HIV-infected cells and increased NF-kappaB binding activity, indicating an effect by G. vaginalis on HIV transcription. The activation of HIV production by G. vaginalis suggests that genital tract infection with G. vaginalis increases the risk of HIV transmission by increasing HIV expression in the genital tract. This may explain, at least in part, the increased rate of HIV transmission in women with BV.

Stimulus-specific regulation of chemokine expression involves differential activation of the redox-responsive transcription factors AP-1 and NF-kappaB

The promoters of the IL-8, MCP-1, and RANTES genes contain binding sites for the redox-responsive transcription factors AP-1 and NF-kappaB, which have been shown to be important for their expression. In this overview, we present evidence from our laboratories that the stimulus-specific regulation of these chemokines by the reactive oxidant H2O2, the proinflammatory cytokine TNF-alpha, and respiratory syncytial virus (RSV) is mediated in a cell type-specific manner involving different patterns of AP-1 and NF-kappaB binding activity. Our results demonstrate that H2O2 induction of IL-8 gene expression is linked with the selective binding of AP-1 to the IL-8 promoter, whereas TNF-alpha and RSV induction of IL-8 correlates with the activation of NF-kappaB binding. We propose that the differential activation and binding of inducible transcription factors to the promoter regions of chemokine genes provides a critical regulatory mechanism by which the CXC and CC chemokines can be selectively expressed in a cell type-specific and stimulus-specific manner. Such a regulatory mechanism of differential chemokine expression could critically influence the site-specific recruitment of distinct subsets of leukocytes to sites of inflammation and injury.

Mycobacterium avium complex activates nuclear factor kappaB via induction of inflammatory cytokines

A variety of microorganisms has been reported to directly induce NF-kappaB, a critical step in the regulation of genes involved in the cellular immune response. In this study, we demonstrate that proinflammatory cytokines such as tumor necrosis factor alpha (TNFalpha) produced upon activation by the Mycobacterium avium complex (MAC) preceed NF-kappaB activity in U937, a human monocytoid cell line. MAC induction of TNFalpha mRNA expression was detected within 15 min after MAC infection, whereas enhanced NF-kappaB binding activity was not detected until 90 to 120 min postinfection. Supershift analysis revealed increased p50 in the MAC-induced NF-kappaB binding complexes. Consistent with an autocrine mechanism, anti-TNFalpha antibody and dexamethasone, a known cytokine inhibitor, both completely suppressed the effect of MAC on the induction of NF-kappaB. Taken together, these findings suggest that exposure of monocyte cell membranes to MAC induces endogenous TNFalpha, which in turn enhances NF-kappaB binding activity. The rapid induction of TNFalpha may be important in the initial host response to MAC infection.

H2O2 and tumor necrosis factor-alpha induce differential binding of the redox-responsive transcription factors AP-1 and NF-kappaB to the interleukin-8 promoter in endothelial and epithelial cells

We previously demonstrated that tumor necrosis factor-alpha (TNFalpha) and H2O2 differentially regulate interleukin-8 (IL-8) and intercellular adhesion molecule (ICAM-1) gene expression in endothelial and epithelial cells. H2O2 induced IL-8 expression in the A549 and BEAS-2B epithelial cell lines, but not in the human microvessel endothelial cell line, HMEC-1 or human umbilical vein endothelial cells. In contrast, H2O2 induced ICAM-1 only in endothelial cells. Unlike H2O2, the proinflammatory cytokine TNFalpha induced IL-8 and ICAM-1 in both cell types. In this study, we examine the role of the redox-responsive transcription factors AP-1 and nuclear factor-kappaB (NF-kappaB) in the differential expression of IL-8. DNA binding studies using nuclear protein extracts from HMEC-1 and A549 cells stimulated with H2O2 or TNFalpha demonstrated differential activation and promoter binding of AP-1 and NF-kappaB. H2O2 activated AP-1 but not NF-kappaB in A549, whereas TNFalpha activated AP-1 as well as NF-kappaB. In HMEC-1, TNFalpha activated NF-kappaB but not AP-1, while H2O2 did not activate either transcription factor. The differential activation of the factors was also reflected in their differential binding to the IL-8 promoter. Moreover, the H2O2 concentration dependent increase in epithelial IL-8 mRNA expression directly corresponded to the H2O2 concentration dependent binding of AP-1 to the IL-8 promoter. Supershift analysis revealed H2O2 as well as TNFalpha induced AP-1 complexes containing c-Fos and JunD. TNFalpha induced NF-kappaB complexes containing Rel A (p65). Immunohistochemical staining of HMEC-1 and A549 cells revealed TNFalpha stimulated nuclear localization of Rel A, whereas no translocation of Rel A was detected in either cell type stimulated by H2O2. These data indicate that the cell type-specific induction of IL-8 gene expression by H2O2 and TNFalpha in HMEC-1 and A549 cells can be explained by the differential binding of AP-1 and NF-kappaB to the IL-8 promoter.

Interleukin-10 enhances tumor necrosis factor-alpha activation of HIV-1 transcription in latently infected T cells

Interleukin-10 (IL-10) is elevated in HIV-1-infected individuals and has been implicated in disease progression. We previously reported that IL-10 cooperates with tumor necrosis factor-alpha (TNF-alpha) to activate HIV-1 expression synergistically in acutely infected monocyte-derived macrophages and the chronically infected U1 promonocytic cell line. To determine whether IL-10 also cooperates with TNF-alpha to activate latent HIV-I expression in lymphocytes, we examined the effects of IL-10 on proviral expression in the chronically infected T-cell line, ACH-2. Although IL-10 inhibited HIV-1 expression acting alone, in combination with suboptimal concentrations of TNF-alpha, IL-10 increased HIV-1 steady-state mRNA expression and p24 core antigen production in ACH-2 cells. Interestingly, IL-10 concentrations that synergistically induced virus also maximally stimulated endogenous TNF-alpha expression, suggesting that cell-derived TNF-alpha may contribute to cytokine synergy. Transfection studies in ACH-2 cells indicated that IL-10 combined with TNF-alpha to activate the HIV-1 long terminal repeat (LTR). IL-10 also cooperated with TNF-alpha to activate HIV-1 LTR in 1G5 cells, a Jurkat T-cell line stably transfected with an LTR-dependent luciferase reporter gene. Pyrrolidine dithiocarbamate, a potent transcriptional inhibitor of the viral LTR, abrogated the cytokine responses in both U1 and ACH-2 cells, suggesting a common TNF-alpha-mediated transcriptional mechanism in these cell types despite their different modes of provirus latency. Taken collectively, these data suggest that IL-10 enhances suboptimal TNF-alpha activation of HIV-1 transcription in chronically infected T-cells at least in part through induction of endogenous TNF-alpha expression.

A human immunodeficiency virus (HIV)-inducing factor from the female genital tract activates HIV-1 gene expression through the kappaB enhancer

Virus-enhancing factors present in the female genital tract may influence the transmission of human immunodeficiency virus type 1 (HIV-1). Previously, the presence of a heat-stable soluble factor in the cervicovaginal lavage (CVL) fluid of both HIV-infected and -uninfected women that induces HIV-1 expression in T cells and monocytes was reported. Now this CVL factor was shown to increase HIV-1 gene expression through the activation of the kappaB enhancer in the viral long terminal repeat (LTR). DNA binding studies, together with functional studies using mutant LTR reporter constructs, indicate the requirement for an NF-kappaB-dependent pathway in the CVL-mediated activation of HIV-1 expression. CVL samples that activated HIV-1 expression also stimulated AP-1-dependent transcription. These data demonstrate that an HIV-inducing factor, distinct from heat-labile cytokines, present in the female genital mucosa can activate AP-1 and NF-kappaB and increase HIV-1 gene expression through the kappaB enhancer, possibly contributing to HIV-1 transmission.

The cAMP-dependent protein kinase A and protein kinase C-beta pathways synergistically interact to activate HIV-1 transcription in latently infected cells of monocyte/macrophage lineage

The HIV-1 long terminal repeat (LTR) responds to a variety of cellular signal transduction pathways. We demonstrate that the cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) signaling pathways synergize to increase HIV-1 LTR-mediated transcription and viral replication in a latently infected promonocytic cell line (U1). The LTR-mediated synergy induced by cholera toxin (Ctx), a potent activator of the cAMP-dependent PKA pathway, and the PKC activator phorbol 12-myristate 13-acetate (PMA) was abrogated by a PKC-beta-specific inhibitor (LY333531). In contrast, the LTR-mediated synergy induced by Ctx and TNF alpha was not affected by LY333531. The synergy induced by Ctx and TNF alpha was also abrogated by mutation of the cAMP-responsive downstream sequence elements (DSE) in the 5' untranslated leader region, whereas the DSE mutations did not affect the synergy induced by Ctx and PMA. These distinctions indicate that Ctx cooperates differently with TNF alpha and PMA to activate the HIV-1 LTR. Ctx and PMA synergistically activated AP-1- and NF-kappa B-dependent transcription, even though no cooperative binding of AP-1 or NF-kappa B was observed in gel shift assays. An extensive mutational analysis of the HIV-1 LTR that included the NF-kappa B and AP-1 binding sites revealed no distinct cis-acting element or region within the HIV-1 LTR that was required for the transcriptional synergy. Ctx and PMA also synergistically interact to activate the HTLV-1 LTR. These results indicate that the transcriptional synergy elicited by Ctx and PMA targets multiple functional elements and promoters, requires a cooperative interaction between the PKA and PKC-beta pathways, and differs mechanistically from the transcriptional synergy induced by Ctx and TNF alpha.

Human immunodeficiency virus type-1 transcription: role of the 5'-untranslated leader region (review)

Human immunodeficiency virus type-1 (HIV-1) transcription is dependent on the interaction of host-cell transcription factors with cis-regulatory DNA elements within the viral long terminal repeat (LTR). Much attention has focused on the series of sequence elements upstream of the transcriptional initiation site in the U3 region of the LTR including the Sp1 and NF-kappaB binding sites. Recent studies, however, demonstrate that the transcribed 5'-untranslated leader region (5'-UTR) also contains important transcriptional elements. These regulatory elements situated downstream of transcription interact with constitutive and inducible transcription factors, mediate transmission of cellular activation signals, and are important for efficient HIV-1 transcription and replication. The 5'-UTR contains binding sites for the transcription factors AP-1, NF-kappaB, NF-AT, IRF, and Sp1. Mutations in these binding sites can interfere with the viral response to cell activation signals, decrease LTR transcription, and inhibit viral replication. The 5'-UTR also interacts with a specific nucleosome that is rapidly displaced during transcriptional activation of the latent provirus. We propose that the inducible transcription factor binding sites in the 5'-UTR comprise a downstream enhancer domain that can function independent of, or in concert with, the LTR promoter to rapidly increase latent proviral transcription in response to cell activation signals. In this review, we describe the host-cell transcription factors that interact with the 5'-UTR and discuss their role in the transcriptional regulation of HIV-1 gene expression.

Induction of HIV-1 replication by type 1-like cytokines, interleukin (IL)-12 and IL-15: effect on viral transcriptional activation, cellular proliferation, and endogenous cytokine production

Cytokine dysregulation is evident in HIV-1 infection and it may play an important role in HIV-1 pathogenesis. Administration of T helper cytokines potentially may restore the functional abnormalities to the HIV-1 immune response. Type 1-like cytokines, IL-2, IL-12, and IL-15, are candidates for immune-based therapy for HIV. Given their potential therapeutic use, we determined the effects of IL-2, IL-12, and IL-15 on HIV-1 replication in both primary blood mononuclear cells (PBMC) and the T-cell line, Kit 225-K6. We demonstrate that both IL-2 and IL-12 induce a similar level of HIV-1 replication (9- and 11-fold, respectively) in mitogen-stimulated PBMC. The effect of IL-2 plateaued by day 6, while that of IL-12 continued to increase HIV-1 expression. IL-15 induced a 2.5-fold increase in HIV-1 expression that remained at the same level through day 6. In Kit 225-K6, an IL-2-dependent T cell line, IL-12 and IL-15 enhanced HIV-1 replication by 5- and 3.5-fold over IL-2-treated cultures, respectively. IL-2-, IL-12-, and IL-15-mediated induction of HIV was independent of direct HIV-1 LTR activation, since none of the cytokines induced LTR activity from transfected reporter gene constructs. The cytokine-mediated induction of HIV-1 expression was also independent of cellular proliferation. In PBMC, the IL-12-mediated effect was partially mediated by endogenous cytokine production of IL-1beta and IL-7, whereas in Kit 225-K6, TNFalpha, INFgamma, IL-1beta, and IL-7 did not contribute significantly to the IL-12-mediated effect. IL-15 effect on HIV-1 in PBMC was independent of endogenous cytokine production. However, in Kit 225-K6, neutralizing antibodies to IL-7 had a significant effect on HIV-1 expression. These data suggest that IL-2, IL-12, and IL-15 increase HIV-1 replication predominantly through a posttranscriptional mechanism that may be enhanced by endogenous cytokine production.

Differential regulation of interleukin-8 and intercellular adhesion molecule-1 by H2O2 and tumor necrosis factor-alpha in endothelial and epithelial cells

The reactive oxygen intermediate H2O2 can function as a signaling molecule to activate gene expression. In this study, we demonstrate that oxidant stress induced by tumor necrosis factor alpha (TNFalpha) or H2O2 differentially regulates intercellular adhesion molecule-1 (ICAM-1) and interleukin-8 (IL-8) gene expression in endothelial and epithelial cells. Northern blot analysis revealed that TNFalpha induced both ICAM-1 and IL-8 expression in either the A549 lung epithelial cell line or the human microvessel endothelial cell line (HMEC-1). In contrast, H2O2 selectively induced only ICAM-1 in HMEC-1 and only IL-8 in A549. This cell type-specific pattern of IL-8 expression was also observed in several other endothelial and epithelial cells. TNFalpha induced greater IL-8 gene expression as compared with H2O2, but the kinetics of induction were similar. The induction of epithelial IL-8 message was accompanied by a corresponding increase in functional IL-8 protein secretion as determined by a neutrophil motility assay. The increased neutrophil motility stimulated by conditioned media from H2O2- or TNFalpha-exposed A549 cells was completely inhibited by an anti-IL-8 antibody. TNFalpha and H2O2 also induced a differential pattern of CC chemokine expression in A549. While TNFalpha induced both RANTES and MCP-1, H2O2 induced only MCP-1. These data suggest that epithelial cells under oxidant stress contribute to the inflammatory cytokine network by selective production of IL-8, MCP-1, and RANTES, which may critically influence the site-specific recruitment of leukocyte subsets.

Inhibition of cytokine-driven human immunodeficiency virus type 1 replication by protease inhibitor

Protease inhibitors block virus maturation and prevent the spread of human immunodeficiency virus (HIV)-1 in vitro. HIV-1-positive persons produce higher levels of proinflammatory cytokines that up-regulate HIV-1 replication. For the protease inhibitor to be effective in vivo, it must be able to suppress cytokine-induced HIV-1 replication. The in vitro efficacy of protease inhibitor to block tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-1alpha, and IL-1beta induction of HIV-1 was investigated. While 100 U/mL of the respective cytokines induced a 208- to 22-fold increase in HIV-1 p24 production, addition of protease inhibitor completely inhibited this virus induction. The kinetics indicated a sustained HIV-1 inhibition despite high levels of endogenous TNF-alpha induction. Dilution of protease inhibitor led to increased HIV-1 replication. These results show that while protease inhibitor can prevent cytokine induction of HIV-1 replication, a continual effective dose is required for the inhibition to be sustained.

TNFalpha cooperates with the protein kinase A pathway to synergistically increase HIV-1 LTR transcription via downstream TRE-like cAMP response elements

Activating protein-1 (AP-1) binding TPA responsive elements (TRE) are located downstream of the transcription initiation site in the U5 region of the HIV-1 long terminal repeat (LTR). These downstream sequence elements, termed DSE, can bind both AP-1 and CREB/ATF transcription factors. Recently, we demonstrated that the DSE are also cAMP-responsive elements (CRE), since they mediated activation signals elicited by cholera toxin (Ctx), a potent activator of the cAMP-dependent protein kinase A (PKA) signal transduction pathway. In the present study, we demonstrate that the HIV-1 DSE can mediate the transcriptional synergy elicited by the combination of Ctx and TNFalpha. Ctx combined with TNFalpha or IL-1beta to produce a synergistic increase in p24 antigen production in U1 promonocytic cells. Transfection studies of LTR reporter constructs indicated that mutation of the DSE sites abrogated the LTR-mediated synergy induced by Ctx and TNFalpha, whereas the synergy induced by Ctx and IL-1beta was unaffected, suggesting TNFalpha and IL-1beta cooperate differently with the cAMP/PKA activation pathway to induce HIV-1 expression in U1 cells. Because the DSE are also TRE sites, we assessed the effect of the agonist combinations on AP-1-dependent transcription. TNFalpha as well as IL-1beta cooperated with Ctx to produce a synergistic activation of AP-1-mediated transcription. These data indicate that the TRE-like cAMP-responsive DSE sites within the 5'-untranslated leader can mediate the transcriptional cooperativity between TNFalpha and the cAMP/PKA pathway. Since the DSE and TRE sites cannot bind CREB/ATF homodimers, we propose a mechanism in which the HIV-1 DSE bind heterodimers composed of both AP-1 and CREB/ATF proteins.

A potent activator of HIV-1 replication is present in the genital tract of a subset of HIV-1-infected and uninfected women

OBJECTIVE AND DESIGN

To determine whether the female genital tract contains factors that affect HIV-1 replication. Cervicovaginal lavage (CVL) samples were collected from HIV-1-seropositive and seronegative women and added to cell cultures.

METHODS

HIV p24 production was used to measure the effects of CVL on replication of HIVMN in a T-cell line, of a primary isolate in peripheral blood mononuclear cells, or on HIV expression by the latently-infected monocytic U1 cell line. The effects of CVL on the HIV long terminal repeat (LTR) were determined in 1G5 T cells by measuring luciferase activity.

RESULTS

Increased replication of HIVMN and a primary isolate were observed in T cells cultured with CVL samples from three out of 38 HIV-infected women, one out of four uninfected high-risk women, and none of 12 low-risk women. The CVL factor increased replication by enhancing virus expression via activation of the HIV LTR. The HIV-inducing activity was highly stable to heat but was sensitive to proteases, indicating that the activity was distinct from heat-labile cytokines including tumour necrosis factor-alpha.

CONCLUSIONS

This is the first study to show that a factor which can stimulate HIV-1 replication is present at biologically active levels in the reproductive tract of women. This factor could potentially affect sexual or vertical transmission of HIV-1 by altering genital tract virus load or virus expression.

U5 region of the human immunodeficiency virus type 1 long terminal repeat contains TRE-like cAMP-responsive elements that bind both AP-1 and CREB/ATF proteins

Activating protein-1 (AP-1) binding phorbol ester responsive elements (TRE) are located downstream of the transcription initiation site in the U5 region of the human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR). These downstream sequence elements, termed DSE, can bind cFos and junD and transmit protein kinase C (PKC) activation signals to the LTR. Further studies suggested the DSE might also bind AP-1-related proteins of the CREB/ATF family. Since enhanced HIV-1 expression is associated with activation of the cAMP-dependent protein kinase A (PKA) signaling pathway, we determined whether binding of CREB/ATF proteins to the DSE mediate cAMP/PKA activation of the HIV-1 LTR. In the present study. DSE binding complexes in nuclear protein extracta from colonic epithelial cells are shown to contain ATF-1, ATF-2, and CREB and transfection of either an ATF-2 or PKA expressing plasmid transactivated the DSE. Cholera toxin (Ctx), a potent activator of the cAMP/PKA pathway. Increased HIV-1 virus production from a latently infected promonocytic cell line, U1. Ctx increased LTR promoter activity and increased the CREB content of DSE binding complexes. Transfection of U1 cells with a series of mutant LTR reporter constructs demonstrated that the Ctx response was in large part mediated by the DSE. The Ctx response was also mediated by a heterologous promoter containing multiple TRE sites. Nuclear protein extracts from a T-cell line infected by HIV-1 contained higher levels of CREB/ATF proteins and manifested increased CREB/ATF binding activity. Collectively, these results indicate the DSE are TRE-like cAMP responsive elements that bind both AP-1 and CREB/ATF permitting induction of the HIV-1 LTR by both PKC and PKA activation signals.

Interleukin-10 inhibits interferon-gamma-induced intercellular adhesion molecule-1 gene transcription in human monocytes

Interleukin-10 (IL-10) is a potent monocyte regulatory cytokine that inhibits gene expression of proinflammatory mediators. In this study, we investigated the mechanism by which IL-10 downregulates expression of intercellular adhesion molecule-1 (ICAM-1) on the cell surface of normal human monocytes activated with interferon-gamma (IFN-gamma). IL-10 inhibition of IFN-gamma-induced ICAM-1 expression was apparent as early as 3 hours and was blocked by an anti-IL-10 antibody but not by an isotype-matched control antibody. Northern blot analysis showed that IL-10 reduced the accumulation of ICAM-1 mRNA in IFN-gamma-stimulated monocytes. IL-10 inhibition of ICAM-1 steady-state mRNA was detected at 3 hours and remained at 24 hours. Nuclear run-on transcription assays showed that IL-10 inhibited the rate of IFN-gamma-induced transcription of the ICAM-1 gene, and mRNA stability studies showed that IL-10 did not alter the half-life of IFN-gamma-induced ICAM-1 message. Thus, IL-10 inhibits IFN-gamma-induced ICAM-1 expression in monocytes primarily at the level of gene transcription. Activation of IFN-gamma-responsive genes requires tyrosine phosphorylation of the transcriptional factor STAT-1alpha (signal transducer and activator of transcription-1alpha). However, IL-10 did not affect IFN-gamma-induced tyrosine phosphorylation of STAT-1alpha or alter STAT-1alpha binding to the IFN-gamma response element (IRE) in the ICAM-1 promoter. Instead, IL-10 prevented IFN-gamma-induced binding activity at the NF-kappaB site of the tumor necrosis factor alpha (TNF-alpha)-responsive NF-kappaB/C-EBP composite element in the ICAM-1 promoter. These data indicate that IL-10 inhibits IFN-gamma-induced transcription of the ICAM-1 gene by a regulatory mechanism that may involve NF-kappaB.

Hepatocyte nuclear factor 3/fork head homolog 11 is expressed in proliferating epithelial and mesenchymal cells of embryonic and adult tissues

The hepatocyte nuclear factor 3alpha (HNF-3alpha) and 3beta proteins have homology in the winged helix/fork head DNA binding domain and regulate cell-specific transcription in hepatocytes and in respiratory and intestinal epithelia. In this study, we describe two novel isoforms of the winged helix transcription factor family, HNF-3/fork head homolog 11A (HFH-11A) and HFH-11B, isolated from the human colon carcinoma HT-29 cell line. We show that these isoforms arise via differential splicing and are expressed in a number of epithelial cell lines derived from tumors (HT-29, Caco-2, HepG2, HeLa, A549, and H441). We demonstrate that differentiation of Caco-2 cells toward the enterocyte lineage results in decreased HFH-11 expression and reciprocal increases in HNF-3alpha and HNF-3beta mRNA levels. In situ hybridization of 16 day postcoitus mouse embryos demonstrates that HFH-11 expression is found in the mesenchymal and epithelial cells of the liver, lung, intestine, renal cortex, and urinary tract. Although HFH-11 exhibits a wide cellular expression pattern in the embryo, its adult expression pattern is restricted to epithelial cells of Lieberkühn's crypts of the intestine, the spermatocytes and spermatids of the testis, and the thymus and colon. HFH-11 expression is absent in adult hepatocytes, but its expression is reactivated in proliferating hepatocytes at 4, 24, and 48 h after partial hepatectomy. Consistent with these findings, we demonstrate that HFH-11 mRNA levels are stimulated by intratracheal administration of keratinocyte growth factor in adult lung and its expression in an adult endothelial cell line is reactivated in response to oxidative stress. These experiments show that the HFH-11 transcription factor is expressed in embryonic mesenchymal and epithelial cells and its expression is reactivated in these adult cell types by proliferative signals or oxidative stress.

HIV-1 Tat protein can transactivate a heterologous TATAA element independent of viral promoter sequences and the trans-activation response element

OBJECTIVE

To determine whether the HIV-1 transactivator protein Tat acts as a DNA sequence-specific transcription factor and activates transcription from a heterologous TATAA element in the absence of the trans-activation response (TAR) element and other sequences in the HIV-1 long terminal repeat (LTR).

DESIGN

Activating protein-1 (AP-1) and Tat-induced transcription were assessed using Jun and hybrid Tat/Jun-expression plasmids and reporter gene constructs which contained AP-1 binding sites upstream of the rat prolactin TATAA element or an HIV-1 LTR construct in which AP-1 binding sites replaced the TAR element.

METHODS

Tat-induced transcription was determined following transient transfection of colon epithelial cell lines with reporter gene constructs and Tat/Jun-expression plasmids in which Tat was fused to the DNA binding domain of Jun. Activation of prolactin (PL) and LTR reporter genes was assessed by luciferase (LUC) or chloramphenicol acetyltransferase (CAT) activity in cellular extracts.

RESULTS

Cotransfection of cells with Tat/Jun and the AP-1 PL LUC or LTR AP-1 CAT reporter plasmid resulted in a marked increase in reporter gene activity which was comparable with that induced by transfection of cells with several different AP-1 expression plasmids (e.g., JunD, JunB, c-Fos), or that elicited by stimulation of the cells transfected with LTR AP-1 CAT plasmids with phorbol ester or tumor necrosis factor-alpha. Tat-induced transcription was DNA-mediated since both a Jun DNA binding domain fused to Tat as well as AP-1 binding sites within the promoter were required for the induction of CAT expression.

CONCLUSIONS

Tat-activated transcriptor can occur strictly through a heterologous TATAA element independent of TAR and Sp1 binding sites or other HIV-1 LTR sequences. Tat appears to increase transcription initiated through the TATAA element by mechanisms similar to that of DNA sequence-specific transcription factors.

Activating protein-1 cooperates with phorbol ester activation signals to increase HIV-1 expression

OBJECTIVE

To determine whether Jun and Fos, components of the activating protein-1 (AP-1) transcription factor, transactivate HIV-1 proviral expression.

DESIGN

The effects of phorbol myristate acetate (PMA) and Jun or Fos transcription factors on HIV-1 expression were investigated using a provirus clone and long terminal repeat (LTR)-reporter gene constructs. The influence of PMA stimulation on AP-1 binding activity was determined with antibodies in gel mobility shift assays.

METHODS

Activation of HIV-1 provirus and transcription of HIV-1 LTR sequences in response to cotransfection of Jun or Fos expression plasmids into a permissive colon cancer cell line, SW480, were assessed by p24 core antigen capture and reporter gene assays, respectively. The effect of protein kinase C activation was evaluated by comparing cells grown in the presence or absence of PMA (20 ng/ml).

RESULTS

Cotransfection of HIV-1 provirus and expression plasmids for c-Jun or JunB into SW480 cells resulted in increased p24 core antigen and this response was markedly increased following PMA stimulation of cells. c-Fos or JunD alone did not increase p24 production but markedly increased p24 production in PMA-stimulated cells. PMA increased c-Fos and JunD binding activity on an AP-1 binding site within the U5 region of the LTR, as shown in gel mobility shift assays. Functional analysis of this site by transient transfections demonstrated it was required to mediate c-Fos and JunD transactivation of the HIV-1 LTR.

CONCLUSIONS

Specific Jun and Fos transcription factors can transactivate the HIV-1 provirus and this response is markedly increased in cooperation with cellular activation signals elicited by PMA. Taken together, the data indicate that AP-1 binding sites downstream of the transcriptional start site in the HIV-1 LTR are capable of binding c-Fos and JunD and may contribute to transactivation of HIV-1 provirus.

IL-10 cooperates with TNF-alpha to activate HIV-1 from latently and acutely infected cells of monocyte/macrophage lineage

IL-10 is elevated in HIV-1-infected individuals and has been implicated in disease progression. In this study, we investigated the effects of IL-10 on the activation of HIV-1 from infected monocytes and macrophages. Although IL-10 alone did not induce HIV-1 replication, in the presence of TNF-alpha, IL-10 markedly enhanced virion production from a chronically infected promonocytic cell line (U1) and in acutely infected monocyte-derived macrophages. Neutralizing mAbs to IL-10 and TNF-alpha indicated that both cytokines were essential for the induction and were required to generate a synergistic increase in virus expression. The effects of the two cytokines were distinguishable functionally since pretreatment with TNF-alpha attenuated the cytokine cooperativity, while pretreatment with IL-10 potentiated their cooperativity, suggesting that IL-10 and TNF-alpha play different roles in the activation of virus. Northern blot analysis as well as Ab blocking and cytokine secretion studies indicated that the induction of either endogenous TNF-alpha or IL-10 was not involved in the cooperativity, nor was an up-regulation of TNF-alpha receptors. In combination with TNF-alpha, IL-10 stimulated activating protein-1 (AP-1) and nuclear factor (NF)-kappa B binding activities and cooperated to increase HIV-1 steady-state mRNA levels and enhance long terminal repeat-directed transcription through activation of the NF-kappa B binding sites, suggesting the IL-10 effect occurs at least in part at the transcriptional level. These results indicate that IL-10, in addition to down-regulating the cellular immune response to HIV-1, may also play a role in TNF-alpha-mediated activation of HIV-1 replication in the monocyte/macrophage lineage.

IL-10 cooperates with TNF-alpha to activate HIV-1 from latently and acutely infected cells of monocyte/macrophage lineage

IL-10 is elevated in HIV-1-infected individuals and has been implicated in disease progression. In this study, we investigated the effects of IL-10 on the activation of HIV-1 from infected monocytes and macrophages. Although IL-10 alone did not induce HIV-1 replication, in the presence of TNF-alpha, IL-10 markedly enhanced virion production from a chronically infected promonocytic cell line (U1) and in acutely infected monocyte-derived macrophages. Neutralizing mAbs to IL-10 and TNF-alpha indicated that both cytokines were essential for the induction and were required to generate a synergistic increase in virus expression. The effects of the two cytokines were distinguishable functionally since pretreatment with TNF-alpha attenuated the cytokine cooperativity, while pretreatment with IL-10 potentiated their cooperativity, suggesting that IL-10 and TNF-alpha play different roles in the activation of virus. Northern blot analysis as well as Ab blocking and cytokine secretion studies indicated that the induction of either endogenous TNF-alpha or IL-10 was not involved in the cooperativity, nor was an up-regulation of TNF-alpha receptors. In combination with TNF-alpha, IL-10 stimulated activating protein-1 (AP-1) and nuclear factor (NF)-kappa B binding activities and cooperated to increase HIV-1 steady-state mRNA levels and enhance long terminal repeat-directed transcription through activation of the NF-kappa B binding sites, suggesting the IL-10 effect occurs at least in part at the transcriptional level. These results indicate that IL-10, in addition to down-regulating the cellular immune response to HIV-1, may also play a role in TNF-alpha-mediated activation of HIV-1 replication in the monocyte/macrophage lineage.

H2O2 and tumor necrosis factor-alpha activate intercellular adhesion molecule 1 (ICAM-1) gene transcription through distinct cis-regulatory elements within the ICAM-1 promoter

We investigated the mechanisms by which H2O2 increases intercellular adhesion molecule 1 (ICAM-1; CD54) expression in endothelial cells. The H2O2-induced increase in ICAM-1 mRNA was inhibited by actinomycin D, by the antioxidant N-acetylcysteine, and by 3-amino-benzamide (which blocks oxidant-induced AP-1 activity), but not by pyrrolidine dithiocarbamate (which blocks oxidant-induced NF-kappa B activity). Nuclear run-on and transient transfections of ICAM-1 promoter constructs indicated that H2O2 stimulated ICAM-1 gene transcription by activation of a distinct region of the ICAM-1 promoter. The H2O2-responsive element was localized to sequences between -981 and -769 (relative to start codon). Located within this region are two 16-base pair repeats, each containing binding sites for the transcription factors AP-1 and Ets. A similar composite AP-1/Ets element isolated from the macrophage scavenger receptor gene conferred H2O2 responsiveness to a minimal promoter. Mutation of the 16-base pair repeats within the ICAM-1 promoter prevented H2O2-induced DNA binding activity, and their deletion abrogated the H2O2-induced transcriptional activity. In contrast, TNF alpha induced ICAM-1 transcription via activation of promoter sequences between -393 and -176, a region with C/EBP and NF-kappa B binding sites. The results indicate that H2O2 activates ICAM-1 transcription through AP-1/Ets elements within the ICAM-1 promoter, which are distinct from NF-kappa B-mediated ICAM-1 expression induced by TNF alpha.

Identification of c-fos-responsive elements downstream of TAR in the long terminal repeat of human immunodeficiency virus type-1

Activation of HIV-1 requires the binding of host cell transcription factors to cis elements in the proviral long terminal repeat (LTR). This study identifies c-fos-responsive sequence motifs in the U5 transcribed noncoding leader sequences downstream of the viral transactivator responsive (TAR) element. These DNA sequence motifs are the most downstream regulatory elements described thus far in the HIV-1 LTR. Functional studies, using human colon epithelial cell lines, demonstrate that the downstream elements are transactivated by expression of the c-fos protooncogene and can transmit PMA and TNF alpha activation signals to the viral LTR. Moreover, the c-fos-responsive elements mediate HIV-1 LTR transcription independent of Tat and the NF kappa B-binding enhancer element. Nuclear extracts of colon epithelial cells form distinct gel mobility shift complexes with the c-fos-responsive elements. These complexes comigrate with a gel shift complex formed on a classical CRE oligonucleotide and are competed by CRE oligonucleotides. These data indicate that the HIV-1 LTR contains previously unrecognized functional DNA cis-regulatory elements downstream of TAR in the transcribed noncoding 5' leader sequence and suggest that early response genes such as c-fos play a role in the activation of HIV-1 gene expression.

HIV-1 infection and expression in human colonic cells: infection and expression in CD4+ and CD4- cell lines

Three human colonic epithelial cell lines, SW620, HT29, and T84, were characterized with respect to HIV-1 infection and gene expression. SW620 and HT29, but not T84, could be infected with HIV-1. CD4 messenger RNA and its protein product were identified in SW620 cells but not in HT29 or T84 cells. Anti-CD4 antibody blocked infection of SW620 cells but had no effect on infection of HT29 cells. In SW620 and HT29 cells transfected with the HIV-1 long terminal repeat (LTR) linked to the chloramphenicol acetyl transferase (CAT) reporter gene, an intact HIV-1 enhancer element was required for stimulation of CAT activity by tumor necrosis factor alpha (TNF alpha) and phorbol ester. T84 was not able to mediate a TNF alpha or phorbol ester response. These studies provide further evidence that HIV-1 can infect cells by mechanisms other than those mediated by the CD4 receptor and describe complementary models for analyzing HIV-1 infection and expression in colonic epithelial cells.

Induction of an altered DNA conformation by an inversion rearrangement in the 5'-flanking DNA of a U1 RNA gene

The anomalous electrophoretic behavior of a 686 base pair restriction fragment containing an in vitro-generated inversion mutation within the enhancer region of a chicken U1 RNA gene was investigated. This DNA fragment migrated with an abnormally slow mobility in polyacrylamide gels but migrated normally in agarose gels relative to the wild type fragment of identical size and base composition. In polyacrylamide gels, the degree of retardation was enhanced at low temperature, a phenomenon associated with bent DNA. A putative site of bending was localized at or near one end of the inverted region. These data suggest that the altered DNA conformation results from the juxtaposition of two normally remote DNA sequences.