Transdominant mutants of I kappa B alpha block Tat-tumor necrosis factor synergistic activation of human immunodeficiency virus type 1 gene expression and virus multiplication

CD71+ Erythroid Cells Exacerbate HIV-1 Susceptibility, Mediate trans-Infection, and Harbor Infective Viral Particles

Immature red blood cells (erythroid precursors or CD71⁺ erythroid cells) have a wide range of immunomodulatory properties. In this study, we found that these erythroid precursors are abundant in the human cord blood/placental tissues, in the blood of HIV-infected and anemic individuals. We observed that these cells exacerbate HIV-1 replication/infection in target cells and even make HIV target cells more permissible to HIV infection. In addition, we found that HIV gets a free ride by binding on the surface of these cells and thus can travel to different parts of the body. In agreement, we noticed a positive correlation between the plasma viral load and the frequency of these cells in HIV patients. More importantly, we observed that infective HIV particles reside inside these erythroid precursors but not mature red blood cells. Therefore, these cells by harboring HIV can play an important role in HIV pathogenesis.

CD71⁺ erythroid cells (CECs) have a wide range of immunomodulatory properties. Here, we show that CECs are expanded in the peripheral blood of HIV patients, with a positive correlation between their frequency and the plasma viral load. CECs from HIV patients and human cord blood/placenta exacerbate HIV-1 infection/replication when cocultured with CD4⁺ T cells, and that preexposure of CD4⁺ T cells to CECs enhances their permissibility to HIV infection. However, mature red blood cells (RBCs) do not enhance HIV replication when cocultured with CD4⁺ T cells. We also found CECs express substantial levels of the NOX2 gene and via a mitochondrial reactive oxygen species (ROS)-dependent mechanism possibly upregulate NF-κB in CD4⁺ T cells once cocultured, which affects the cell cycle machinery to facilitate HIV-1 replication. The complement receptor-1 (CD35) and the Duffy antigen receptor for chemokines (DARC) as potential HIV target molecules are expressed significantly higher on CECs compared to mature red blood cells. Blocking CD35 or DARC substantially abolishes HIV-1 transmission by RBCs to uninfected CD4⁺ T cells but not by CECs. In contrast, we observed CECs bind to HIV-1 via CD235a and subsequently transfer the virus to uninfected CD4⁺ T cells, which can be partially blocked by the anti-CD235a antibody. More importantly, we found that CECs from HIV-infected individuals in the presence of antiretroviral therapy harbor infective viral particles, which mediate HIV-1 trans-infection of CD4⁺ T cells. Therefore, our findings provide a novel insight into the role of CECs in HIV pathogenesis as potential contributing cells in viral persistence and transmission.

Cellular RelB interacts with the transactivator Tat and enhance HIV-1 expression

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) Tat protein plays an essential role in HIV-1 gene transcription. Tat transactivates HIV-1 long terminal repeat (LTR)-directed gene expression through direct interactions with the transactivation-responsive region (TAR) element and other cis elements in the LTR. The TAR-independent Tat-mediated LTR transactivation is modulated by several host factors, but the mechanism is not fully understood.

RESULTS

Here, we report that Tat interacts with the Rel homology domain of RelB through its core region. Furthermore, RelB significantly increases Tat-mediated transcription of the HIV-1 LTR and viral gene expression, which is independent of the TAR. Both Tat and RelB are recruited to the HIV-1 promoter, of which RelB facilitates the recruitment of Tat to the viral LTR. The NF-κB elements are key to the accumulation of Tat and RelB on the LTR. Knockout of RelB reduces the accumulation of RNA polymerase II on the LTR, and decreases HIV-1 gene transcription. Together, our data suggest that RelB contributes to HIV-1 transactivation.

CONCLUSIONS

Our results demonstrate that RelB interacts with Tat and enhances TAR-independent activation of HIV-1 LTR promoter, which adds new insights into the multi-layered mechanisms of Tat in regulating the gene expression of HIV-1.

Multiple Inhibitory Factors Act in the Late Phase of HIV-1 Replication: a Systematic Review of the Literature

The use of lentiviral vectors for therapeutic purposes has shown promising results in clinical trials. The ability to produce a clinical-grade vector at high yields remains a critical issue. One possible obstacle could be cellular factors known to inhibit human immunodeficiency virus (HIV). To date, five HIV restriction factors have been identified, although it is likely that more factors are involved in the complex HIV-cell interaction. Inhibitory factors that have an adverse effect but do not abolish virus production are much less well described. Therefore, a gap exists in the knowledge of inhibitory factors acting late in the HIV life cycle (from transcription to infection of a new cell), which are relevant to the lentiviral vector production process. The objective was to review the HIV literature to identify cellular factors previously implicated as inhibitors of the late stages of lentivirus production. A search for publications was conducted on MEDLINE via the PubMed interface, using the keyword sequence "HIV restriction factor" or "HIV restriction" or "inhibit HIV" or "repress HIV" or "restrict HIV" or "suppress HIV" or "block HIV," with a publication date up to 31 December 2016. Cited papers from the identified records were investigated, and additional database searches were performed. A total of 260 candidate inhibitory factors were identified. These factors have been identified in the literature as having a negative impact on HIV replication. This study identified hundreds of candidate inhibitory factors for which the impact of modulating their expression in lentiviral vector production could be beneficial.

NF-κB regulates MICA gene transcription in endothelial cell through a genetically inhibitable control site

Endothelial cells form a barrier between blood and the underlying vessel wall, which characteristically demonstrates inflammatory damage in atherosclerotic disease. MICA is a highly polymorphic ligand for the activating immune receptor NKG2D and can be expressed on endothelial cells. We hypothesized that damaged vessel walls, such as those involved in atherosclerosis, might express MICA, which could contribute to the vascular immunopathology. Immune activation resulting from MICA expression could play a significant role in the development of vascular damage. We have demonstrated that TNFα up-regulates MICA on human endothelial cells. The up-regulation is mediated by NF-κB, and we have defined the regulatory control site responsible for this at -130 bp upstream of the MICA transcription start site. This site overlaps with a heat shock response element and integrates input from the two pathways. We have shown that in atherosclerotic lesions there is expression of MICA on endothelial cells. Using lentivirus-mediated gene delivery in primary human endothelial cells, we were able to inhibit the MICA response to TNFα with a truncated HSF1 that lacked a transactivation domain. This highlights the potential for transcription-based therapeutic approaches in atherosclerotic vascular disease to reduce immune-mediated endothelial and vessel wall damage.

HIV protein sequence hotspots for crosstalk with host hub proteins

HIV proteins target host hub proteins for transient binding interactions. The presence of viral proteins in the infected cell results in out-competition of host proteins in their interaction with hub proteins, drastically affecting cell physiology. Functional genomics and interactome datasets can be used to quantify the sequence hotspots on the HIV proteome mediating interactions with host hub proteins. In this study, we used the HIV and human interactome databases to identify HIV targeted host hub proteins and their host binding partners (H2). We developed a high throughput computational procedure utilizing motif discovery algorithms on sets of protein sequences, including sequences of HIV and H2 proteins. We identified as HIV sequence hotspots those linear motifs that are highly conserved on HIV sequences and at the same time have a statistically enriched presence on the sequences of H2 proteins. The HIV protein motifs discovered in this study are expressed by subsets of H2 host proteins potentially outcompeted by HIV proteins. A large subset of these motifs is involved in cleavage, nuclear localization, phosphorylation, and transcription factor binding events. Many such motifs are clustered on an HIV sequence in the form of hotspots. The sequential positions of these hotspots are consistent with the curated literature on phenotype altering residue mutations, as well as with existing binding site data. The hotspot map produced in this study is the first global portrayal of HIV motifs involved in altering the host protein network at highly connected hub nodes.

Nuclear factor-kappa B family member RelB inhibits human immunodeficiency virus-1 Tat-induced tumor necrosis factor-alpha production

Human Immunodeficiency Virus-1 (HIV-1)-associated neurocognitive disorder (HAND) is likely neuroinflammatory in origin, believed to be triggered by inflammatory and oxidative stress responses to cytokines and HIV protein gene products such as the HIV transactivator of transcription (Tat). Here we demonstrate increased messenger RNA for nuclear factor-kappa B (NF-κB) family member, transcription factor RelB, in the brain of doxycycline-induced Tat transgenic mice, and increased RelB synthesis in Tat-exposed microglial cells. Since genetic ablation of RelB in mice leads to multi-organ inflammation, we hypothesized that Tat-induced, newly synthesized RelB inhibits cytokine production by microglial cells, possibly through the formation of transcriptionally inactive RelB/RelA complexes. Indeed, tumor necrosis factor-alpha (TNFα) production in monocytes isolated from RelB deficient mice was significantly higher than in monocytes isolated from RelB expressing controls. Moreover, RelB overexpression in microglial cells inhibited Tat-induced TNFα synthesis in a manner that involved transcriptional repression of the TNFα promoter, and increased phosphorylation of RelA at serine 276, a prerequisite for increased RelB/RelA protein interactions. The Rel-homology-domain within RelB was necessary for this interaction. Overexpression of RelA itself, in turn, significantly increased TNFα promoter activity, an effect that was completely blocked by RelB overexpression. We conclude that RelB regulates TNFα cytokine synthesis by competitive interference binding with RelA, which leads to downregulation of TNFα production. Moreover, because Tat activates both RelB and TNFα in microglia, and because Tat induces inflammatory TNFα synthesis via NF-κB, we posit that RelB serves as a cryoprotective, anti-inflammatory, counter-regulatory mechanism for pathogenic NF-κB activation. These findings identify a novel regulatory pathway for controlling HIV-induced microglial activation and cytokine production that may have important therapeutic implications for the management of HAND.

Synergistic induction of inflammation by bacterial products lipopolysaccharide and fMLP: an important microbial pathogenic mechanism

A wide variety of stimuli have been shown to induce inflammation, but bacteria products/components are considered the major inducers during bacterial infections. We previously demonstrated that bacterial products/components such as LPS, a glycolipid component of the bacterial outer membrane, and formylated peptides (fMLP), a bacterial-derived peptide, induced proinflammatory cytokine gene expression in human peripheral blood monocytes. We now present evidence that mixtures of bacterial products/components LPS and fMLP behave synergistically in the induction of inflammation in vitro and in vivo. Furthermore, our results indicate that the TLR4 and the IKKbeta-IkappaBalpha signaling pathways are involved in the synergistic induction of inflammatory cytokines. The mechanism of synergistic activation of NF-kappaB is depended on nuclear translocation of p65 and phosphorylation of p65 at both Ser536 and Ser276 sites. These results demonstrate an important role for bacterial products/components from lysed bacteria in the pathogenesis of infectious diseases. We believe that this synergistic induction of inflammation by bacterial products LPS and fMLP represents an important pathogenic mechanism during bacterial infection, which may suggest novel therapeutic strategies or targets to minimize host injury following bacterial infection.

The roles of HIV-1 proteins and antiretroviral drug therapy in HIV-1-associated endothelial dysfunction

Since the emergence of highly active antiretroviral therapy (HAART), human immunodeficiency virus-1 (HIV-1)-infected patients have demonstrated dramatic decreases in viral burden and opportunistic infections, and an overall increase in life expectancy. Despite these positive HAART-associated outcomes, it has become increasingly clear that HIV-1 patients have an enhanced risk of developing cardiovascular disease over time. Clinical studies are instrumental in our understanding of vascular dysfunction in the context of HIV-1 infection. However, most clinical studies often do not distinguish whether HIV-1 proteins, HAART, or a combination of these 2 factors cause cardiovascular complications. This review seeks to address the roles of both HIV-1 proteins and antiretroviral drugs in the development of endothelial dysfunction because endothelial dysfunction is the hallmark initial step of many cardiovascular diseases. We analyze recent in vitro and in vivo studies examining endothelial toxicity in response to HIV-1 proteins or in response to the various classes of antiretroviral drugs. Furthermore, we discuss the multiple mechanisms by which HIV-1 proteins and HAART injure the vascular endothelium in HIV-1 patients. By understanding the molecular mechanisms of HIV-1 protein- and antiretroviral-induced cardiovascular disease, we may ultimately improve the quality of life of HIV-1 patients through better drug design and the discovery of new pharmacological targets.

Basal shuttle of NF-kappaB/I kappaB alpha in resting T lymphocytes regulates HIV-1 LTR dependent expression

Background

In HIV-infected T lymphocytes, NF-κB/Rel transcription factors are major elements involved in the activation of LTR-dependent transcription from latency. Most NF-κB heterodimer p65/p50 is sequestered as an inactive form in the cytoplasm of resting T lymphocytes via its interaction with IκB inhibitors. In these cells, both absolute HIV latency and low level ongoing HIV replication have been described. These situations could be related to differences in the balance between NF-κB and IκBα ratio. Actually, control of IκBα by cellular factors such as Murr-1 plays a critical role in maintaining HIV latency in unstimulated T lymphocytes. Formerly, our group demonstrated the presence of nuclear IκBα in T cells after PMA activation. Now we attempt to determine the dynamics of NF-κB/IκBα nucleocytosolic transport in absence of activation as a mechanism to explain both the maintenance of latency and the existence of low level ongoing HIV replication in resting CD₄⁺ T lymphocytes.

Results and conclusion

We show that the inhibition of the nuclear export by leptomycin B in resting CD₄⁺ T cells resulted in nuclear accumulation of both IκBα and p65/RelA, as well as formation of NF-κB/IκBα complexes. This proves the existence of a rapid shuttling of IκBα between nucleus and cytosol even in absence of cellular activation. The nuclear accumulation of IκBα in resting CD₄⁺ T lymphocytes results in inhibition of HIV-LTR dependent transcription as well as restrains HIV replication in CD₄⁺ T lymphocytes. On the other hand, basal NF-κB activity detected in resting CD₄⁺ T lymphocytes was related to low level HIV replication in these cells.

The RING finger ubiquitin ligase RNF125/TRAC-1 down-modulates HIV-1 replication in primary human peripheral blood mononuclear cells

CXCR4-using HIV-1 was previously shown to replicate more efficiently in a healthy donor-derived CD4(+) CD38(+) than in a CD4(+) CD38(-) T-cell subset after stimulation with interleukin (IL)-4. Here, we identified 3 cellular genes, which were expressed to a higher level in an IL-4-stimulated CD38(-) subset. One of the 3 genes, RNF125/TRAC-1, was involved in the down-regulation of HIV-1 replication not only in cell lines, but also in peripheral blood mononuclear cells. RNF125/TRAC-1 bears the RING finger domain, important for E3 ubiquitin protein ligase. Mutations in this domain of RNF125/TRAC-1 led to the loss of HIV-1 down-modulatory activity, suggesting that E3 ligase activity is necessary. In addition, the results of Northern blotting and reporter gene analysis indicated that RNF125/TRAC-1 function occurs at the viral transcription step. These results suggest that RNF125/TRAC-1 could function to recruit host factor(s) controlling HIV-1 transcription to the ubiquitin-proteasome pathway.

Nuclear accumulation of cRel following C-terminal phosphorylation by TBK1/IKK epsilon

The NF-kappaB transcription factors are key regulators of immunomodulatory, cell cycle, and developmental gene regulation. NF-kappaB activity is mainly regulated through the phosphorylation of IkappaB by the IkappaB kinase (IKK) complex IKKalphabetagamma, leading to proteasome-mediated degradation of IkappaB, nuclear translocation of NF-kappaB dimers, DNA binding, and gene induction. Additionally, direct posttranslational modifications of NF-kappaB p65 and cRel subunits involving C-terminal phosphorylation has been demonstrated. The noncanonical IKK-related homologs, TNFR-associated factor family member-associated NF-kappaB activator (TANK)-binding kinase (TBK)1 and IKKepsilon, are also thought to play a role in NF-kappaB regulation, but their functions remain unclear. TBK1 and IKKepsilon were recently described as essential regulators of IFN gene activation through direct phosphorylation of the IFN regulatory factor-3 and -7 transcription factors. In the present study, we sought to determine whether IKKepsilon and TBK1 could modulate cRel activity via phosphorylation. TBK1 and IKKepsilon directly phosphorylate the C-terminal domain of cRel in vitro and in vivo and regulate nuclear accumulation of cRel, independently of the classical IkappaB/IKK pathway. IkappaBalpha degradation is not affected, but rather IKKepsilon-mediated phosphorylation of cRel leads to dissociation of the IkappaBalpha-cRel complex. These results illustrate a previously unrecognized aspect of cRel regulation, controlled by direct IKKepsilon/TBK1 phosphorylation.

Current status of gene therapy strategies to treat HIV/AIDS

Progress in developing effective gene transfer approaches to treat HIV-1 infection has been steady. Many different transgenes have been reported to inhibit HIV-1 in vitro. However, effective translation of such results to clinical practice, or even to animal models of AIDS, has been challenging. Among the reasons for this failure are uncertainty as to the most effective cell population(s) to target, the diffuseness of these target cells in the body, and ineffective or insufficiently durable gene delivery. Better understanding of the HIV-1 replicative cycle, host factors involved in HIV-1 infection, vector biology and application, transgene technology, animal models, and clinical study design have all contributed vastly to planning current and future strategies for application of gene therapeutic approaches to the treatment of AIDS. This review focuses on the newest developments in these areas and provides a strong basis for renewed optimism that gene therapy will have an important role to play in treating people infected with HIV-1.

Suppression of nuclear translocation of nuclear factor-kappaB and nuclear factor of activated T cells by Younggaechulgam-tang

Younggaechulgam-tang (YGCGT) is known to suppress inflammatory and autoimmune responses, and it has clinically been used among Oriental medical doctors in South Korea. We investigated YGCGT-mediated changes in downstream T cell signal transduction. The expression levels of nuclear factor-kappaB (NFkappaB) subunit RelA and nuclear factor of activated T cells (NFATc1) in cytoplasm and nucleus were examined by western blot analysis. Interlukin-2 (IL-2) expression in MOLT-4 cells activated by phytohemagglutinin (PHA) was determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. IL-2 secretion was measured by an enzyme-linked immunosorbent assay (ELISA). PHA-induced translocation of Rel A and NFATcl to the nucleus were markedly reduced by YGCGT treatment. Furthermore, IL-2 mRNA and protein levels and IL-2 secretion were significantly diminished by YGCGT treatment. In conclusion, YGCGT treatment of T cells inhibits selectively nuclear translocation of RelA and NFATc1, resulting in diminished production of IL-2. These results suggest that YGCGT may have potential as immunosuppressive drugs with improved efficacy and reduced side effects.

TNF-alpha activates MUC2 transcription via NF-kappaB but inhibits via JNK activation

The molecular mechanisms responsible for TNF-alpha-mediated MUC2 intestinal mucin up-regulation in HM3 colon adenocarcinoma cells were analyzed using promoter-reporter assays of the 5'-flanking region of the MUC2 gene. Chemical inhibitors, mutant reporter constructs, and EMSA confirmed I-kappaB/NF-kappaB pathway involvement. Wortmannin, LY294002 and dominant negative Akt, as well as dominant negative NF-kappaB-inducing kinase (NIK) inhibited MUC2 reporter transcription, indicating that both phosphatidylinositol-3-OH kinase (PI3K)/Akt signaling pathway and NIK pathways mediate the effects of TNF-alpha. Wortmannin inhibited NF-kappaB binding and transcriptional activity without inhibiting NF-kappaB translocation to the nucleus, indicating that PI3K/Akt signaling activates NF-kappaB transcriptional activity directly. Our results demonstrate that TNF-alpha up-regulates MUC2 in human colon epithelial cells via several signaling pathways, involving both NIK and PI3K/Akt, which converge at the common IKK/I-kappaB/NF-kappaB pathway. TNF-alpha activated JNK, but JNK inhibitor SP600125 and dominant negative cJun consistently activated transcription, revealing a negative role for this signaling pathway. Thus TNF-alpha causes a net up-regulation of MUC2 gene expression in cultured colon cancer cells because NF-kappaB transcriptional activation of this gene is able to counter-balance the suppressive effects of the JNK pathway. However, the existence of this inhibitory JNK pathways suggests a mechanism whereby--in the absence of NF-kappaB activation--TNF-alpha production during inflammation in vivo could actually inhibit MUC2 production, giving rise to the defective mucosal protection which characterizes inflammatory bowel disease.

Synergistic activation of NF-kappaB by nontypeable Haemophilus influenzae and tumor necrosis factor alpha

Nontypeable Haemophilus influenzae (NTHi) is an important human pathogen causing otitis media in children and exacerbation of chronic obstructive pulmonary disease in adults. Like most other bacterial infections, NTHi infections are also characterized by inflammation, which is mainly mediated by cytokines and chemokines such as tumor necrosis factor alpha (TNF-alpha). Among a variety of transcription regulators, NF-kappaB has been shown to play a critical role in regulating the expression of large numbers of genes encoding inflammatory mediators. In review of the current studies on NF-kappaB regulation, most of them have focused on investigating how NF-kappaB is activated by a single inducer at a time. However, in bacteria-induced inflammation in vivo, multiple inducers including both exogenous and endogenous mediators are present simultaneously. A key issue that has yet to be addressed is whether the exogenous inducers such as NTHi and the endogenous factors such as TNF-alpha activate NF-kappaB in a synergistic manner. We show that NTHi and TNF-alpha, when present together, synergistically induce NF-kappaB activation via two distinct signaling pathways: NF-kappaB translocation-dependent and -independent pathways. The NF-kappaB translocation-dependent pathway involves NF-kappaB-inducing kinase-IkappaB kinase beta/gamma-dependent phosphorylation and degradation of IkappaBalpha, whereas the NF-kappaB translocation-independent pathway involves mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase kinase 1-dependent activation of MAPK kinase 3/6-p38 MAPK pathway. In addition, the same signaling pathways are also involved in synergistic induction of TNF-alpha, IL-1beta, and IL-8. These studies should deepen our understanding of the molecular mechanisms underlying the combinatorial regulation of inflammation and lead to development of therapeutic strategies for NTHi-induced infections.

Tumor necrosis factor-alpha inhibits endothelial nitric-oxide synthase gene promoter activity in bovine aortic endothelial cells

Tumor necrosis factor-alpha (TNF-alpha) has been shown to reduce endothelial nitric-oxide synthase (eNOS) gene expression through post-transcriptional regulation of mRNA stability. The current study documented an independent effect of the cytokine on the eNOS gene promoter. TNF-alpha effected a time- and dose-dependent reduction in activity of a transiently transfected human -1197 eNOS-luciferase reporter. This reduction was inhibited by co-transfection of dominant negative IKKbeta as well as a nonphosphorylatable constitutively suppressive mutant of IkappaB implying involvement of the NFkappaB cascade in the inhibitory effect. The locus of the TNF-alpha-dependent inhibition was traced to two Sp1-binding sites positioned between -109 and -95 and -81 and -67 relative to the transcription start site. Electrophoretic mobility shift analysis and immunoperturbation studies showed evidence for Sp1 and Sp3 binding to each element. TNF-alpha treatment had no effect on the binding pattern to the downstream (-81 to -67) site but did suppress association of Sp1 and Sp3 to the upstream (-109 to -95) site. Collectively, these data indicate that TNF-alpha exerts transcriptional, as well as post-transcriptional, effects on eNOS gene expression and suggest a potential mechanism to account for the endothelial dysfunction that accompanies disorders such as diabetes mellitus and heart failure.

Airway epithelia regulate expression of human beta-defensin 2 through Toll-like receptor 2

The goal of this study is to investigate whether TLR2 mediates hBD2 induction through NF-kappaB in response to bacterial components in the human airway epithelia. We showed that hTLR2 is expressed in the airway epithelial cells by immunohistochemical staining and RT-PCR. The biology of hTLR2 in this context was studied initially in 293 cells transfected with a plasmid expressing hTLR2 together with an hBD2 promoter-driven luciferase reporter (hBD2-promoter-LUC). Upon incubation with lipoteichoic acid (LTA), the major cell wall component of gram-positive bacteria, luciferase activity was greatly increased compared with mock stimulation. Analysis of mutation constructs of the hBD2 promoter revealed that NF-kappaB sites are important for hTLR2-mediated hBD2 up-regulation upon LTA stimulation. When hBD2-promoter-LUC was transfected into primary human airway epithelia cells (EC), the luciferase activity was greatly increased upon LTA stimulation compared with mock stimulation. The hBD2 promoter mutation constructs were also tested in EC, which confirmed the studies in 293 cells. When a plasmid expressing a dominant-negative mutant of hTLR2 was co-transfected with hBD2-promoter-LUC into EC, LTA could not stimulate hBD2 expression. These data provide convincing evidence that up-regulation of hBD2 can be induced through hTLR2-mediated NFkappaB/IkappaB pathway in the human airway epithelial cells.

TRAF6-NF-kappaB pathway is essential for interleukin-1-induced TLR2 expression and its functional response to TLR2 ligand in murine hepatocytes

We have previously reported that the expressions of TLR2 and TLR4 mRNA are differentially regulated in mouse liver and in the parenchymal cells. In the present study, we investigated the mechanism of the up-regulatory effects of interleukin-1alpha (IL-1alpha), tumour necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS), or bacterial lipoprotein (BLP) on TLR2 mRNA expression in primary cultured murine hepatocytes. Although TLR2 mRNA stability was not affected, these treatments enhanced NF-kappaB activity and TLR2 gene transcription simultaneously. The up-regulation of TLR2 transcription in response to these reagents was completely inhibited by blocking the NF-kappaB activation pathway, demonstrating a pivotal role of NF-kappaB activation in the regulation of hepatocyte TLR2 transcription. The expression of TLR2 protein by hepatocytes was also remarkably up-regulated by IL-1alpha and, to a lesser extent, by TNF-alpha as well, but not by LPS or BLP. In addition, pretreatment of mice with IL-1alpha markedly increased the BLP (a ligand for TLR2)-induced serum level of serum amyloid A (SAA), an acute-phase protein predominantly produced by hepatocytes, indicating that IL-1alpha may also up-regulate functional TLR2 in vivo. These results demonstrate that IL-1alpha, through activating the TRAF6-NF-kappaB pathway, serves as the most potent inducer for TLR2 up-regulation, and plays an important role in the regulation of hepatocyte functions by augmenting the hepatocyte response to bacteria or bacterial products.

Transforming growth factor-beta -Smad signaling pathway cooperates with NF-kappa B to mediate nontypeable Haemophilus influenzae-induced MUC2 mucin transcription

Transforming growth factor-beta (TGF-beta) and related factors are multifunctional cytokines that regulate diverse cellular processes, including proliferation, differentiation, apoptosis, and immune response. The involvement of TGF-beta receptor-mediated signaling in bacteria-induced up-regulation of mucin, a primary innate defensive response for mammalian airways, however, still remains unknown. Here, we report that the bacterium nontypeable Haemophilus influenzae (NTHi), an important human respiratory pathogen, utilizes the TGF-beta-Smad signaling pathway together with the TLR2-MyD88-TAK1-NIK-IKKbeta/gamma-IkappaBalpha pathway to mediate NF-kappaB-dependent MUC2 mucin transcription. The NTHi-induced TGF-beta receptor Type II phosphorylation occurred at as early as 5 min. Pretreatment of NTHi with TGF-beta neutralization antibody reduced up-regulation of MUC2 transcription. Moreover, functional cooperation of NF-kappaB p65/p50 with Smad3/4 appears to positively mediate NF-kappaB-dependent MUC2 transcription. These data are the first to demonstrate the involvement of TGF-beta receptor-mediated signaling in bacteria-induced up-regulation of mucin transcription, bring insights into the novel role of TGF-beta signaling in bacterial pathogenesis, and may lead to new therapeutic intervention of NTHi infections.

HTLV-1 Tax-associated hTid-1, a human DnaJ protein, is a repressor of Ikappa B kinase beta subunit

hTid-1, a human DnaJ protein, is a novel cellular target for HTLV-1 Tax. Here, we show that hTid-1 represses NF-kappaB activity induced by Tax as well as other activators such as tumor necrosis factor alpha (TNFalpha) and Bcl10. hTid-1 specifically suppresses serine phosphorylation of IkappaBalpha by activated IkappaB kinase beta (IKKbeta), but the activities of other serine kinases including p38, ERK2, and JNK1 are not affected. The suppressive activity of hTid-1 on IKKbeta requires a functional J domain that mediates association with heat shock proteins and results in prolonging the half-life of the NF-kappaB inhibitors IkappaBalpha and IkappaBbeta. Collectively, our data suggest that hTid-1, in association with heat shock proteins, exerts a negative regulatory effect on the NF-kappaB activity induced by various extracellular and intracellular activators including HTLV-1 Tax.

Glucocorticoids synergistically enhance nontypeable Haemophilus influenzae-induced Toll-like receptor 2 expression via a negative cross-talk with p38 MAP kinase

The recognition of invading microbes followed by the induction of effective innate immune response is crucial for host survival. Human surface epithelial cells are situated at host-environment boundaries and thus act as the first line of host defense against invading microbes. They recognize the microbial ligands via Toll-like receptors (TLRs) expressed on the surface of epithelial cells. TLR2 has gained importance as a major receptor for a variety of microbial ligands. In contrast to its high expression in lymphoid tissues, TLR2 is expressed at low level in epithelial cells. Thus, it remains unclear whether the low amount of TLR2 expressed in epithelial cells is sufficient for mediating bacteria-induced host defense and immune response and whether TLR2 expression can be up-regulated by bacteria during infection. Here, we show that TLR2, although expressed at very low level in unstimulated human epithelial cells, is greatly up-regulated by nontypeable Hemophilus influenzae (NTHi), an important human bacterial pathogen causing otitis media and chronic obstructive pulmonary diseases. Activation of an IKKbeta-IkappaBalpha-dependent NF-kappaB pathway is required for TLR2 induction, whereas inhibition of the MKK3/6-p38alpha/beta pathway leads to enhancement of NTHi-induced TLR2 up-regulation. Surprisingly, glucocorticoids, well known potent anti-inflammatory agents, synergistically enhance NTHi-induced TLR2 up-regulation likely via a negative cross-talk with the p38 MAP kinase pathway. These studies may bring new insights into the role of bacteria and glucocorticoids in regulating host defense and immune response and lead to novel therapeutic strategies for modulating innate immune and inflammatory responses for otitis media and chronic obstructive pulmonary diseases.

Inhibition of NF-kappaB-dependent T cell activation abrogates acute allograft rejection

Using a heterotopic model of transplantation, we investigated the role of T cell activation in vivo during allograft rejection in I-kappaB(DeltaN)-transgenic mice that express a transdominant inhibitor of NF-kappaB in T cells. Our results show indefinite prolongation of graft survival in the I-kappaB(DeltaN)-transgenic recipients. Interestingly, at the time of rejection of grafts in wild-type recipients, histology of grafts in the I-kappaB(DeltaN)-transgenic recipients showed moderate rejection; nevertheless, grafts in the I-kappaB(DeltaN) recipients survived >100 days. Analysis of acute phase cytokines, chemokine, chemokine receptors, and immune responses shows that the blockade of NF-kappaB activation in T cells inhibits up-regulation of many of these parameters. Interestingly, our data also suggest that the T cell component of the immune response exerted positive feedback regulation on the expression of multiple chemokines that are produced predominantly by non-T cells. In conclusion, our studies indicate NF-kappaB activation in T cells is necessary for acute allograft rejection.

Activation of NF-kappa B by nontypeable Hemophilus influenzae is mediated by toll-like receptor 2-TAK1-dependent NIK-IKK alpha /beta-I kappa B alpha and MKK3/6-p38 MAP kinase signaling pathways in epithelial cells

Nontypeable Hemophilus influenzae (NTHi) is an important human pathogen in both children and adults. In children, it causes otitis media, the most common childhood infection and the leading cause of conductive hearing loss in the United States. In adults, it causes lower respiratory tract infections in the setting of chronic obstructive pulmonary disease, the fourth leading cause of death in the United States. The molecular mechanisms underlying the pathogenesis of NTHi-induced infections remain undefined, but they may involve activation of NF-kappa B, a transcriptional activator of multiple host defense genes involved in immune and inflammatory responses. Here, we show that NTHi strongly activates NF-kappa B in human epithelial cells via two distinct signaling pathways, NF-kappa B translocation-dependent and -independent pathways. The NF-kappa B translocation-dependent pathway involves activation of NF-kappa B inducing kinase (NIK)--IKK alpha/beta complex leading to I kappa B alpha phosphorylation and degradation, whereas the NF-kappa B translocation-independent pathway involves activation of MKK3/6--p38 mitogen-activated protein (MAP) kinase pathway. Bifurcation of NTHi-induced NIK-IKK alpha/beta-I kappa B alpha and MKK3/6--p38 MAP kinase pathways may occur at transforming growth factor-beta activated kinase 1 (TAK1). Furthermore, we show that toll-like receptor 2 (TLR2) is required for NTHi-induced NF-kappa B activation. In addition, several key inflammatory mediators including IL-1 beta, IL-8, and tumor necrosis factor-alpha are up-regulated by NTHi. Finally, P6, a 16-kDa lipoprotein highly conserved in the outer membrane of all NTHi and H. influenzae type b strains, appears to also activate NF-kappa B via similar signaling pathways. Taken together, our results demonstrate that NTHi activates NF-kappa B via TLR2-TAK1-dependent NIK--IKK alpha/beta-I kappa B alpha and MKK3/6--p38 MAP kinase signaling pathways. These studies may bring new insights into molecular pathogenesis of NTHi-induced infections and open up new therapeutic targets for these diseases.

NF-kappaB inducers upregulate cFLIP, a cycloheximide-sensitive inhibitor of death receptor signaling

The caspase 8 homologue FLICE-inhibitory protein (cFLIP) is a potent negative regulator of death receptor-induced apoptosis. We found that cFLIP can be upregulated in some cell lines under critical involvement of the NF-kappaB pathway, but NF-kappaB activation was clearly not sufficient for cFLIP induction in all cell lines. Treatment of SV80 cells with the proteasome inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG-132) or geldanamycin, a drug interfering with tumor necrosis factor (TNF)-induced NF-kappaB activation, inhibited TNF-induced upregulation of cFLIP. Overexpression of a nondegradable IkappaBalpha mutant (IkappaBalpha-SR) or lack of IkappaB kinase gamma expression completely prevented phorbol myristate acetate-induced upregulation of cFLIP mRNA in Jurkat cells. These data point to an important role for NF-kappaB in the regulation of the cFLIP gene. SV80 cells normally show resistance to TNF-related apoptosis-inducing ligand (TRAIL) and TNF, as apoptosis can be induced only in the presence of low concentrations of cycloheximide (CHX). However, overexpression of IkappaBalpha-SR rendered SV80 cells sensitive to TRAIL-induced apoptosis in the absence of CHX, and cFLIP expression was able to reverse the proapoptotic effect of NF-kappaB inhibition. Western blot analysis further revealed that cFLIP, but not TRAF1, A20, and cIAP2, expression levels rapidly decrease upon CHX treatment. In conclusion, these data suggest a key role for cFLIP in the antiapoptotic response of NF-kappaB activation.

The human immunodeficiency virus type 1 Vpu protein inhibits NF-kappa B activation by interfering with beta TrCP-mediated degradation of Ikappa B

The human immunodeficiency virus type 1 (HIV-1) Vpu protein binds to the CD4 receptor and induces its degradation by cytosolic proteasomes. This process involves the recruitment of human betaTrCP (TrCP), a key member of the SkpI-Cdc53-F-box E3 ubiquitin ligase complex that specifically interacts with phosphorylated Vpu molecules. Interestingly, Vpu itself, unlike other TrCP-interacting proteins, is not targeted for degradation by proteasomes. We now report that, by virtue of its affinity for TrCP and resistance to degradation, Vpu, but not a phosphorylation mutant unable to interact with TrCP, has a dominant negative effect on TrCP function. As a consequence, expression of Vpu in HIV-infected T cells or in HeLa cells inhibited TNF-alpha-induced degradation of IkappaB-alpha. Vpu did not inhibit TNF-alpha-mediated activation of the IkappaB kinase but instead interfered with the subsequent TrCP-dependent degradation of phosphorylated IkappaB-alpha. This resulted in a pronounced reduction of NF-kappaB activity. We also observed that in cells producing Vpu-defective virus, NF-kappaB activity was significantly increased even in the absence of cytokine stimulation. However, in the presence of Vpu, this HIV-mediated NF-kappaB activation was markedly reduced. These results suggest that Vpu modulates both virus- and cytokine-induced activation of NF-kappaB in HIV-1-infected cells.

Cardiac-specific abrogation of NF- kappa B activation in mice by transdominant expression of a mutant I kappa B alpha

Nuclear factor-kappaB (NF-kappa B) is a pleiotropic oxidant-sensitive transcription factor that is present in the cytosol in an inactive form complexed to an inhibitory kappaB (I kappa B) monomer. Various stimuli, including ischemia, hypoxia, free radicals, cytokines, and lipopolysaccharide (LPS), activate NF-kappa B by inducing phosphorylation of I kappa B. Phosphorylation of serine residues at positions 32 and 36 is critical for ubiquitination and degradation of I kappa B alpha with consequent migration of NF-kappa B to the nucleus. Although NF-kappa B is thought to contribute to numerous pathophysiologic processes, definitive assessment of its role has been hindered by the inability to achieve specific inhibition in vivo. Pharmacologic inhibitors of NF-kappa B are available, but their utility for in vivo studies is limited by their relative lack of specificity. Targeted ablation of genes encoding NF-kappa B subunits has not been productive in this regard because of fetal lethality in the case of p65 and functional redundancy in the Rel family of proteins. To overcome these limitations, we have created a viable transgenic mouse that expresses a phosphorylation-resistant mutant of I kappa B alpha (I kappa B alpha(S32A,S36A)) under the direction of a cardiac-specific promoter. Several transgenic lines were obtained with copy numbers ranging from one to seven. The mice exhibit normal cardiac morphology and histology. Total myocardial I kappa B alpha protein level is elevated 3.5- to 6.5-fold with a concomitant 50-60% decrease in the level of I kappa B beta. Importantly, expression of I kappa B(S32A,S36A) results in complete abrogation of myocardial NF-kappa B activation in response to tumor necrosis factor- alpha (TNF-alpha) and LPS stimulation. Thus, novel transgenic mice have been created that make it possible to achieve cardiac-specific and selective inhibition of NF-kappa B in vivo. These transgenic mice should be useful in studies of various cardiac pathophysiological phenomena that involve NF-kappa B activation, including ischemic preconditioning, heart failure, septic shock, acute coronary syndromes, cardiac allograft rejection, and apoptosis.

Endothelin-dependent and -independent components of strain-activated brain natriuretic peptide gene transcription require extracellular signal regulated kinase and p38 mitogen-activated protein kinase

The application of mechanical strain to cultured cardiac myocytes in vitro leads to activation of the brain natriuretic peptide (BNP) gene promoter, a marker of cardiac hypertrophy. We have previously shown that this activation results from both a direct mechanostimulatory event and an indirect autocrine/paracrine stimulation involving the sequential production of angiotensin II and endothelin (ET). In the present study, we examined the role of p38 mitogen-activated protein kinase (MAPK) and extracellular signal regulated kinase (ERK) in signaling the increase in promoter activity trafficking through each of these pathways. ET was shown to stimulate both p38 MAPK and ERK activity in these cultures and to activate human BNP (hBNP) promoter activity. Activation of the promoter was inhibited approximately 45% by SB-203580, a p38 MAPK inhibitor, and approximately 70% by PD98059, an inhibitor of the ERK-activating kinase MAPK kinase. The ET-independent (ie, direct) stimulation of the hBNP promoter by mechanical strain was inhibited approximately 70% by SB-203580 and approximately 60% by PD98059, implying that similar signaling circuitry is used, albeit to different degrees, by the direct and indirect pathways. The p38 MAPK component of both the ET-dependent and the ET-independent responses to strain appears to operate through a series of nuclear factor-kappaB binding, shear stress response element-like structures in the hBNP gene promoter. Collectively, these data suggest that activation of the BNP promoter by hypertrophic stimuli involves the participation of several independent signaling pathways. Such redundancy would help to guarantee generation of the full hypertrophic phenotype independently of the nature of the hypertrophic stimulus.

Mechanical strain activates BNP gene transcription through a p38/NF-kappaB-dependent mechanism

Application of mechanical strain to neonatal rat ventricular myocytes in culture evokes changes in gene expression reminiscent of those that occur with hypertrophy in vivo, such as stimulation of brain natriuretic peptide (BNP) gene expression. Here, we show that a major component of strain-dependent BNP promoter activation results from stimulation of p38 mitogen-activated protein kinase (MAPK) in the cardiac myocyte. Strain increased p38 activity in a time-dependent fashion. The p38 inhibitor SB203580 led to a reduction of approximately 60% in strain-activated human BNP (hBNP) promoter activity. Cotransfection of wild-type p38 increased both basal and strain-dependent promoter activity, while cotransfection with MKK6AL, a dominant-negative inhibitor of p38 MAPK kinase, resulted in partial inhibition of either p38- or strain-activated hBNP promoter activity. p38 MAPK increased hBNP promoter activity through activation of the transcription factor NF-kappaB. Activation of the hBNP promoter by either p38 or strain was mediated by DNA elements present in the 5' flanking sequence of the gene. Mechanical strain promoted assembly of NF-kappaB components on these DNA elements in vitro. Thus, induction of the hBNP promoter by mechanical strain depends, at least in part, on stimulation of p38 and subsequent activation of NF-kappaB. This activation may play an important role in signaling the increased BNP gene expression that accompanies hemodynamic overload and cardiac hypertrophy in vivo.

Lack of responsiveness of a nuclear factor-kappaB-regulated promoter to transactivation by human immunodeficiency virus 1 Tat in HeLa cells

Transcriptional activation by Tat protein is in large part dependent on interactions with the TAR RNA element located in the 5'-untranslated region of all human immunodeficiency virus type 1 (HIV-1) transcripts. In addition, Tat has been shown to induce nuclear translocation of nuclear factor-kappaB (NF-kappaB), potentially contributing to gene induction. The NF-kappaB responsive reporter construct, (PRDII)(4)-CAT, was used to explore transcription resulting from NF-kappaB activated by Tat. Tat did not activate (PRDII)(4)-CAT, whereas (PRDII)(4)-CAT was highly responsive to either transfected Rel A or to tumor necrosis factor-alpha (TNF-alpha). Despite its inability to directly induce, Tat enhanced the responsiveness of (PRDII)(4)-CAT to either transfected Rel A or to TNF-alpha by approximately 2.5-fold. High levels of CAT activity were seen with HIV-LTR-derived reporters that contained kappaB and TAR elements in response to transfected Tat in the absence of either transfected Rel A or exogenous TNF-alpha, and overexpression of IkappaBalpha with Tat inhibited CAT activity by 60% to 80%, suggesting that some activation of NF-kappaB by Tat was occurring. HIV-LTR reporter activities were enhanced three fold to sixfold compared with Tat alone when additional NF-kappaB was provided by transfection or by activation with TNF-alpha. These data indicate that Tat is unable to activate some NF-kappaB-responsive promoters but is able to synergize with NF-kappaB in the activation of both HIV-derived and non-HIV-derived promoters.

NF-kappaB activation and HIV-1 induced apoptosis

HIV infection leads to the progressive loss of CD4+ T cells and the near complete destruction of the immune system in the majority of infected individuals. High levels of viral gene expression and replication result in part from the activation of NF-kappaB transcription factors, which in addition to orchestrating the host inflammatory response also activate the HIV-1 long terminal repeat. NF-kappaB induces the expression of numerous cytokine, chemokine, growth factor and immunoregulatory genes, many of which promote HIV-1 replication. Thus, NF-kappaB activation represents a double edged sword in HIV-1 infected cells, since stimuli that induce an NF-kappaB mediated immune response will also lead to enhanced HIV-1 transcription. NF-kappaB has also been implicated in apoptotic signaling, protecting cells from programmed cell death under most circumstances and accelerating apoptosis in others. Therefore, activation of NF-kappaB can impact upon HIV-1 replication and pathogenesis at many levels, making the relationship between HIV-1 expression and NF-kappaB activation multi-faceted. This review will attempt to analyse the many faces and functions of NF-kappaB in the HIV-1 lifecycle.

Extracellular HIV type 1 Tat protein induces CD69 expression through NF-kappaB activation: possible correlation with cell surface Tat-binding proteins

The HIV-1 Tat protein, essential for HIV-1 gene expression and viral replication, is known to be secreted by infected cells and has pleiotropic effects on various cell functions. It seems that extracellular Tat may exert its functions on cellular targets by at least two different mechanisms, namely, by adsorptive endocytosis, and by a possible interaction with cell surface receptor(s). Here we report that extracellular Tat activates AIM/CD69 gene transcription through an NF-kappaB-dependent pathway in the erythroleukemia cell line K562. Tat induces NF-kappaB binding to DNA as a result of IkappaBalpha phosphorylation and degradation, which depend on the intracellular redox state. We found that the second Tat-coding exon is required for CD69 gene trans-activation, but not for HIV LTR gene transcription. Fluorescein-labeled Tat proteins were used to study cell surface binding sites and cellular uptake of the proteins. Full-length Tat protein has specific binding sites on the surface of K562 cells, whereas truncated Tat1-48, which is efficiently internalized by the cells, does not bind to the cell surface. Our results suggest that extracellular Tat may activate a cell surface-mediated pathway that induces intracellular signal transduction in K562 cells, leading to the activation of NF-kappaB and the transcription of NF-kappaB-dependent genes, such as CD69.

Interleukin-18 induces interferon-gamma production through NF-kappaB and NFAT activation in murine T helper type 1 cells

Interleukin-18 (IL-18) combined with anti-CD3 monoclonal antibody (mAb) induced interferon-gamma (IFN-gamma) production by T helper type 1 (Th1) cells. Neither IL-18 nor anti-CD3 mAb alone induced production of IFN-gamma. Although treatment with IL-18 alone induced full activation of NF-kappaB in Th1 cells, it was not sufficient for the production of IFN-gamma. To examine the importance of NF-kappaB activation in IFN-gamma production, we established Th1 cells which expressed a transdominant IkappaBalpha mutant. In these cells, activation of NF-kappaB and production of IFN-gamma by IL-18 were suppressed. On the other hand, we examined the T cell receptor (TCR)/CD3-mediated signaling pathway. FK506, an inhibitor of NFAT activation, inhibited IFN-gamma production by IL-18 without any effect on the NF-kappaB activation. We conclude that dual signaling consisting of IL-18-induced NF-kappaB activation and TCR/CD3-mediated NFAT activation is crucial for IFN-gamma production by IL-18 in murine Th1 cells.

Cell stress and MKK6b-mediated p38 MAP kinase activation inhibit tumor necrosis factor-induced IkappaB phosphorylation and NF-kappaB activation

Tumor necrosis factor (TNF) exerts many actions through activation of the transcription factor NF-kappaB. NF-kappaB is sequestered in the cytosol by an inhibitory subunit IkappaB, which is inducibly phosphorylated by an IkappaB kinase complex and subsequently degraded. Sodium salicylate (NaSal) can block NF-kappaB activation by inhibiting IkappaBalpha phosphorylation. Recently, we used the specific p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 to demonstrate that inhibition of TNF-induced IkappaBalpha phosphorylation requires NaSal-induced p38 activation. We demonstrate that NaSal similarly inhibits TNF-induced IkappaBbeta degradation in a p38-dependent manner. To further examine the role of p38, we determined whether other agents that activate p38 can block TNF-induced IkappaB phosphorylation and degradation. Sorbitol, H(2)O(2), and arsenite each blocked IkappaBalpha phosphorylation induced by TNF, and SB203580 reversed the inhibitory effects of sorbitol and H(2)O(2), but not arsenite. In addition, sorbitol and H(2)O(2) blocked TNF-induced but not interleukin-1-induced IkappaBalpha phosphorylation, whereas arsenite inhibited IkappaBalpha phosphorylation induced by TNF and interleukin-1. Transient expression of MAP kinase kinase (MKK) 6b(E), a constitutive activator of p38, reduced both TNF-induced phosphorylation of IkappaBalpha and NF-kappaB-dependent reporter activity. However, MKK7(D), a constitutive activator of c-Jun N-terminal kinases, failed to inhibit these TNF actions. Thus, sustained p38 activation by various stimuli inhibits TNF-induced IkappaB phosphorylation and NF-kappaB activation.

Nitric oxide inhibits HIV tat-induced NF-kappaB activation

To evaluate the roles of nitric oxide (NO) on human immunodeficiency virus (HIV) Tat-induced transactivation of HIV long terminal repeat (HIV-LTR), we examined the effect of NO in the regulation of nuclear factor (NF)-kappaB, a key transcription factor involved in HIV gene expression and viral replication. In the present study, we demonstrate that HIV Tat activates NF-kappaB and that this activation can be attenuated by endogenous or exogenous NO. Inhibition of endogenous NO production with the NO synthase (NOS) inhibitor L-NMMA causes a significant increase in Tat-induced NF-kappaB activity. In addition, NO attenuates signal-initiated degradation of IkappaBalpha, an intracellular inhibitor of NF-kappaB, and blocks the DNA binding activity of the NF-kappaB p50/p50 homodimer and p50/p65 heterodimer. To determine how NO is induced by HIV Tat, reverse transcription polymerase chain reaction was used to demonstrate the induction of NOS-2 and NOS-3 mRNA by Tat. Although a putative NF-kappaB binding site was identified in the -74 GGAGAGCCCCC -64 region of the NOS-3 gene promoter, gel mobility shift assays and site-directed mutation analyses suggest that the putative NF-kappaB site is not of primary importance. Rather, several Sp-1 sites adjoining the putative NF-kappaB binding site in the promoter region of NOS-3 gene are required for the induction of NOS-3 gene expression by Tat.

IkappaB-mediated inhibition of virus-induced beta interferon transcription

We have examined the consequences of overexpression of the IkappaBalpha and IkappaBbeta inhibitory proteins on the regulation of NF-kappaB-dependent beta interferon (IFN-beta) gene transcription in human cells after Sendai virus infection. In transient coexpression studies or in cell lines engineered to express different forms of IkappaB under tetracycline-inducible control, the IFN-beta promoter (-281 to +19) linked to the chloramphenicol acetyltransferase reporter gene was differentially inhibited in response to virus infection. IkappaBalpha exhibited a strong inhibitory effect on virus-induced IFN-beta expression, whereas IkappaBbeta exerted an inhibitory effect only at a high concentration. Despite activation of the IkappaB kinase complex by Sendai virus infection, overexpression of the double-point-mutated (S32A/S36A) dominant repressors of IkappaBalpha (TD-IkappaBalpha) completely blocked IFN-beta gene activation by Sendai virus. Endogenous IFN-beta RNA production was also inhibited in Tet-inducible TD-IkappaBalpha-expressing cells. Inhibition of IFN-beta expression directly correlated with a reduction in the binding of NF-kappaB (p50-RelA) complex to PRDII after Sendai virus infection in IkappaBalpha-expressing cells, whereas IFN-beta expression and NF-kappaB binding were only slightly reduced in IkappaBbeta-expressing cells. These experiments demonstrate a major role for IkappaBalpha in the regulation of NF-kappaB-induced IFN-beta gene activation and a minor role for IkappaBbeta in the activation process.

Nitric oxide inhibits HIV-1 replication in human astrocytoma cells

Astroglial cells represent a target for HIV infection in the central nervous system. In astrocytes, HIV infection is poorly productive, being characterized by a persistent state of viral latency. However, activation of the nuclear factor NF-kappaB and its binding to HIV long terminal repeat (LTR) can induce HIV replication. Moreover, nitric oxide (NO) can affect NF-kappaB activation in glial cells. Therefore, we hypothesize that NO may reduce HIV replication in human astroglial cells by inhibiting HIV-1 LTR transcriptional activity. In this respect, we show that NO donors reduce viral replication in HIV-1-infected human astrocytoma T67 cells, taken as an astroglial model. Furthermore, using transfected T67 cells, we demonstrate that NO donors inhibit HIV-1 LTR transcriptional activity. These results suggest that the use of NO-releasing drugs may represent a potential, novel approach in inhibiting HIV replication in the central nervous system.

A role for casein kinase II phosphorylation in the regulation of IRF-1 transcriptional activity

The Interferon Regulatory Factors (IRFS) play an important role in the transcriptional control of growth regulatory and immunoregulatory genes. The inducibility and availability of IRF-1 and IRF-2 are influenced by external stimuli, such as virus infection or interferon treatment. In the present study, we sought to examine the potential modulatory role of phosphorylation on IRF-1 transcriptional activity. During the purification of IRF recombinant proteins, a kinase activity copurified with IRF-1 (and IRF-2) from baculovirus infected Sf9 insect cell extracts, but not from E. coli extracts. The kinase activity was also identified in Jurkat T cells, specifically interacted with IRF proteins in GST affinity chromatography, and phosphorylated IRF-1 with high specificity in vitro. Using an in gel kinase assay with recombinant IRF-1 as substrate, two molecular weight forms of the kinase (43 and 38 kDa) were identified. Biochemical criteria identified the kinase activity as the alpha catalytic subunit of casein kinase II (CKII). Furthermore, far western analysis of protein-protein interactions demonstrated that casein kinase II directly interacted with IRF-1 protein. Deletion mutation analysis of IRF-1 revealed that IRF-1 was phosphorylated at two clustered sites, one located between amino acids 138-150, the other in the C-terminal acidic activation domain between amino acids 219-231. Cotransfection studies comparing wild type and point mutated forms of IRF-1 demonstrated that mutations of the four phosphoaceptor residues in the C-terminal transactivation domain, significantly decreased transactivation by IRF-1, indicating that casein kinase II may be involved in the regulation of IRF-1 function. Strikingly, the casein kinase II clusters in IRF-1 resemble the sites identified in the C-terminal PEST domain of IkappaBalpha. The present experiments, together with previously published studies with IkappaBalpha, c-Jun and other proteins, indicate a broad role for casein kinase II phosphorylation in the regulation of transcription factor activity.

Activation of NF-kappaB via a Src-dependent Ras-MAPK-pp90rsk pathway is required for Pseudomonas aeruginosa-induced mucin overproduction in epithelial cells

Cystic fibrosis (CF) is an autosomal recessive disorder, the most common lethal genetic disease in Caucasians. Respiratory disease is the major cause of morbidity and mortality. Indeed, 95% of CF patients die of respiratory failure. Pseudomonas aeruginosa, an opportunistic pathogen, chronically infects the lungs of over 85% of CF patients. It is ineradicable by antibiotics and responsible for airway mucus overproduction that contributes to airway obstruction and death. The molecular mechanisms underlying this pathology are unknown. Here we show that P. aeruginosa activates a c-Src-Ras-MEK1/2-MAPK-pp90rsk signaling pathway that leads to activation of nuclear factor NF-kappaB (p65/p50). Activated NF-kappaB binds to a kappaB site in the 5'-flanking region of the MUC2 gene and activates MUC2 mucin transcription. These studies bring new insight into bacterial-epithelial interactions and more specifically into the molecular pathogenesis of cystic fibrosis. Understanding these signaling and gene regulatory mechanisms opens up new therapeutic targets for cystic fibrosis.

Inducible expression of IkappaBalpha repressor mutants interferes with NF-kappaB activity and HIV-1 replication in Jurkat T cells

Human immunodeficiency virus (HIV-1) utilizes the NF-kappaB/Rel proteins to regulate transcription through NF-kappaB binding sites in the HIV-1 long terminal repeat (LTR). Normally, NF-kappaB is retained in the cytoplasm by inhibitory IkappaB proteins; after stimulation by multiple activators including viruses, IkappaBalpha is phosphorylated and degraded, resulting in NF-kappaB release. In the present study, we examined the effect of tetracycline-inducible expression of transdominant repressors of IkappaBalpha (TD-IkappaBalpha) on HIV-1 multiplication using stably selected Jurkat T cells. TD-IkappaBalpha was inducibly expressed as early as 3 h after doxycycline addition and dramatically reduced both NF-kappaB DNA binding activity and LTR-directed gene activity. Interestingly, induced TD-IkappaBalpha expression also decreased endogenous IkappaBalpha expression to undetectable levels by 24 h after induction, demonstrating that TD-IkappaBalpha repressed endogenous NF-kappaB-dependent gene transcription. TD-IkappaBalpha expression also sensitized Jurkat cells to tumor necrosis factor-induced apoptosis. De novo HIV-1 infection of Jurkat cells was dramatically altered by TD-IkappaBalpha induction, resulting in inhibition of HIV-1 multiplication, as measured by p24 antigen, reverse transcriptase, and viral RNA. Given the multiple functions of the NF-kappaB/IkappaB pathway, TD-IkappaBalpha expression may interfere with HIV-1 multiplication at several levels: LTR-mediated transcription, Rev-mediated export of viral RNA, inhibition of HIV-1-induced pro-inflammatory cytokines, and increased sensitivity of HIV-1-infected cells to apoptosis.

Inhibition of Proinflammatory Molecule Production by Adenovirus-Mediated Expression of a Nuclear Factor κB Super-Repressor in Human Intestinal Epithelial Cells

NF-κB plays a major role in the transcriptional regulation of many proinflammatory genes in multiple cell lineages, including intestinal epithelial cells (IEC). Activation of NF-κB requires both phosphorylation and degradation of its natural cytoplasmic inhibitor, IκB. We tested whether a super-repressor of NF-κB activity, which is a mutated nondegradable IκBα resistant to phosphorylation and degradation, could be delivered into IEC using an adenoviral vector (Ad5IκB) and determined the anti-inflammatory potential of this inhibitor following different stimuli. We showed for the first time that recombinant adenovirus efficiently infected (>80%) transformed as well as primary IEC. Cytoplasmic levels of the NF-κB super-repressor protein were more than 50-fold higher than those of endogenous IκB, and this mutated IκB was resistant to IL-1β-induced degradation. Immunofluorescent RelA nuclear staining was strongly inhibited in Ad5IκB-infected IEC compared with control Ad5LacZ, and NF-κB, but not AP-1 binding activity, was reduced by more than 70% as measured by electrophoretic mobility shift assay (EMSA). Induction of inducible nitric-oxide synthase (iNOS), IL-1β, and IL-8 genes by IL-1β, TNF-α, or PMA was blocked in Ad5IκB-infected cells but not in Ad5LacZ controls as assayed by RT-PCR and ELISA. In addition, IL-1β-induced IL-8 secretion was totally inhibited by Ad5IκB in primary colonic IEC. We conclude that an adenoviral vector efficiently transfers a nondegradable IκB in both transformed and native IEC. The strong inhibition of NF-κB activity and the resulting down-regulation of multiple proinflammatory molecules by Ad5IκB suggests an exciting approach for in vivo intestinal gene therapy and illustrates the key role of NF-κB in transcriptional regulation of the inflammatory phenotype of IEC.

Selective inhibition of l kappaB alpha phosphorylation and HIV-1 LTR-directed gene expression by novel antioxidant compounds

Oxidative stress activates the NF-kappaB/Rel transcription factors which are involved in the activation of numerous immunoregulatory genes and the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). In the present study, we examined the effects of established and novel compounds including antioxidants, ribonucleotide reductase inhibitors, and iron chelators on NF-kappaB activation and HIV LTR-mediated gene expression induced by TNF-alpha. N-Acetylcysteine (NAC), pyrrolidinedithiocarbamate (PDTC), and Trimidox (TD) at various concentrations inhibited TNF-alpha-induced NF-kappaB binding in Jurkat cells. Pretreatment of cells with these compounds prior to stimulation prevented I kappaB alpha degradation. Phosphorylation of I kappaB alpha, a prerequisite for its signal-induced degradation, was abrogated in these cells, indicating that oxidative stress is an essential step in the NF-kappaB activation pathway. On the other hand, iron chelators desferrioxamine, pyridoxal isonicotinoyl hydrazone (PIH), and salicylaldehyde isonicotinoyl hydrazone (SIH) showed no inhibition of TNF-alpha-induced NF-kappaB DNA-binding activity. Synergistic induction of HIV-1 LTR-mediated gene expression by TNF-alpha and the HIV-1 transactivator Tat in Jurkat cells was significantly suppressed in the presence of NAC and TD, but not PDTC. The inhibition of NAC and TD on LTR-directed gene expression was diminished when NF-kappaB-binding sites in the LTR were deleted, indicating that these compounds affected the NF-kappaB component of the synergism. Iron chelators PIH and SIH also showed some inhibitory effect on LTR-mediated gene activation, presumably through an NF-kappaB-independent mechanism. These experiments demonstrate that TD, at concentration 50 times lower than the effective concentration of NAC, potently inhibits NF-kappaB activity and suppresses HIV LTR expression.

Induction of CD4 expression and human immunodeficiency virus type 1 replication by mutants of the interferon-inducible protein kinase PKR

Replication of the human immunodeficiency virus type 1 (HIV-1) is inhibited by interferons (IFNs), and the IFN-inducible protein kinase PKR is thought to mediate this effect by regulating protein synthesis. Here we report that ectopic expression of dominant negative PKR mutants in Jurkat cells induces HIV-1 replication. Specifically, expression of CD4 is upregulated by the PKR mutants, and this correlates with an induction of HIV-1 binding and proviral DNA synthesis upon HIV-1 infection. Moreover, activation of NF-kappaB was induced by an RNA binding-defective mutant of PKR. Thus, it appears that PKR, in addition to translational control, is involved in HIV-1 replication by modulating virus binding through the regulation of CD4 expression and virus gene expression through the activation of NF-kappaB.