Pertussis Toxin (PTX) B Subunit and the Nontoxic PTX Mutant PT9K/129G Inhibit Tat-Induced TGF-β Production by NK Cells and TGF-β-Mediated NK Cell Apoptosis

AP-1 transcription factors in cytotoxic lymphocyte development and antitumor immunity

The proper functioning of cytotoxic lymphocytes, such as natural killer and CD8+ T cells, is essential for effective cancer-immunity and immunotherapy responses. The differentiation of these cells is controlled by several transcription factors (TFs), including members of the activator protein (AP)-1 family. The activity of AP-1 family members is regulated by various immune signaling pathways, which can be triggered by activating or inhibitory receptors as well as cytokines. The target genes controlled by AP-1 TFs are central to generate immunity to pathogens or malignancies. Here, we provide an overview of the current understanding of how AP-1 TFs regulate cytotoxic lymphocytes.

Three-Dimensional Culture Models to Study Innate Anti-Tumor Immune Response: Advantages and Disadvantages

Several approaches have shown that the immune response against tumors strongly affects patients' clinical outcome. Thus, the study of anti-tumor immunity is critical to understand and potentiate the mechanisms underlying the elimination of tumor cells. Natural killer (NK) cells are members of innate immunity and represent powerful anti-tumor effectors, able to eliminate tumor cells without a previous sensitization. Thus, the study of their involvement in anti-tumor responses is critical for clinical translation. This analysis has been performed in vitro, co-incubating NK with tumor cells and quantifying the cytotoxic activity of NK cells. In vivo confirmation has been applied to overcome the limits of in vitro testing, however, the innate immunity of mice and humans is different, leading to discrepancies. Different activating receptors on NK cells and counter-ligands on tumor cells are involved in the antitumor response, and innate immunity is strictly dependent on the specific microenvironment where it takes place. Thus, three-dimensional (3D) culture systems, where NK and tumor cells can interact in a tissue-like architecture, have been created. For example, tumor cell spheroids and primary organoids derived from several tumor types, have been used so far to analyze innate immune response, replacing animal models. Herein, we briefly introduce NK cells and analyze and discuss in detail the properties of 3D tumor culture systems and their use for the study of tumor cell interactions with NK cells.

HIV-1 proteins gp120 and tat induce the epithelial-mesenchymal transition in oral and genital mucosal epithelial cells

The oral, cervical, and genital mucosa, covered by stratified squamous epithelia with polarized organization and strong tight and adherens junctions, play a critical role in preventing transmission of viral pathogens, including human immunodeficiency virus (HIV). HIV-1 interaction with mucosal epithelial cells may depolarize epithelia and disrupt their tight and adherens junctions; however, the molecular mechanism of HIV-induced epithelial disruption has not been completely understood. We showed that prolonged interaction of cell-free HIV-1 virions, and viral envelope and transactivator proteins gp120 and tat, respectively, with tonsil, cervical, and foreskin epithelial cells induces an epithelial-mesenchymal transition (EMT). EMT is an epigenetic process leading to the disruption of mucosal epithelia and allowing the paracellular spread of viral and other pathogens. Interaction of cell-free virions and gp120 and tat proteins with epithelial cells substantially reduced E-cadherin expression and activated vimentin and N-cadherin expression, which are well-known mesenchymal markers. HIV gp120- and tat-induced EMT was mediated by SMAD2 phosphorylation and activation of transcription factors Slug, Snail, Twist1 and ZEB1. Activation of TGF-β and MAPK signaling by gp120, tat, and cell-free HIV virions revealed the critical roles of these signaling pathways in EMT induction. gp120- and tat-induced EMT cells were highly migratory via collagen-coated membranes, which is one of the main features of mesenchymal cells. Inhibitors of TGF-β1 and MAPK signaling reduced HIV-induced EMT, suggesting that inactivation of these signaling pathways may restore the normal barrier function of mucosal epithelia.

Nano-drug System Based on Hierarchical Drug Release for Deep Localized/Systematic Cascade Tumor Therapy Stimulating Antitumor Immune Responses

Inaccessibility of deep-seated malignant cells in the central region of tumors and uncontrollable tumor recurrence represent a significant challenge for conventional synergistic cancer therapy. Herein, we designed a novel nanoplatform based on hierarchical drug release for deep cascade cancer therapy including localized photothermal therapy, systematic chemotherapy, and elicited immune responses. Methods: The first-step chemotherapy could be carried out by polydopamine (PDA) releasing doxorubicin (DOX) in the specific microenvironment of lysosomes (pH 5.5). The branched gold nanoshells and PDA converted the light to heat efficiently to accomplish the second-step photothermal therapy and collapsed biomimetic vesicles (BVs) to release paclitaxel (PTX), which promoted the third-step of chemotherapy and triggered immune responses. Results: After 10 days of treatment, there were no obvious residual tumors in tumor-bearing mice. Significantly, 10 days after stopping treatment, mice in the drug immune-therapeutic group showed little tumor recurrence (1.5 times) compared to substantial recurrence (20 times) in the conventional treatment group. Conclusion: The hierarchical drug release and cascade therapeutic modality enhance the penetration of drugs deep into the tumor tissue and effectively inhibit recurrence. This cascade therapeutic modality provides a novel approach for more effective cancer therapy.

Role of Major Toxin Virulence Factors in Pertussis Infection and Disease Pathogenesis

Bordetella pertussis produces several toxins that affect host-pathogen interactions. Of these, the major toxins that contribute to pertussis infection and disease are pertussis toxin, adenylate cyclase toxin-hemolysin and tracheal cytotoxin. Pertussis toxin is a multi-subunit protein toxin that inhibits host G protein-coupled receptor signaling, causing a wide array of effects on the host. Adenylate cyclase toxin-hemolysin is a single polypeptide, containing an adenylate cyclase enzymatic domain coupled to a hemolysin domain, that primarily targets phagocytic cells to inhibit their antibacterial activities. Tracheal cytotoxin is a fragment of peptidoglycan released by B. pertussis that elicits damaging inflammatory responses in host cells. This chapter describes these three virulence factors of B. pertussis, summarizing background information and focusing on the role of each toxin in infection and disease pathogenesis, as well as their role in pertussis vaccination.

Contribution of pertussis toxin to the pathogenesis of pertussis disease

Pertussis toxin (PT) is a multisubunit protein toxin secreted by Bordetella pertussis, the bacterial agent of the disease pertussis or whooping cough. PT in detoxified form is a component of all licensed acellular pertussis vaccines, since it is considered to be an important virulence factor for this pathogen. PT inhibits G protein-coupled receptor signaling through Gi proteins in mammalian cells, an activity that has led to its widespread use as a cell biology tool. But how does this activity of PT contribute to pertussis, including the severe respiratory symptoms of this disease? In this minireview, the contribution of PT to the pathogenesis of pertussis disease will be considered based on evidence from both human infections and animal model studies. Although definitive proof of the role of PT in humans is lacking, substantial evidence supports the idea that PT is a major contributor to pertussis pathology, including the severe respiratory symptoms associated with this disease.

Pertussis toxin B-pentamer mediates intercellular transfer of membrane proteins and lipids

Pertussis toxin (PTx) is the major virulence factor of Bordetella pertussis. The enzymatic or active (A) subunit inactivates host G protein coupled receptor (GPCR) signaling pathways. The non-enzymatic binding (B) subunit also mediates biological effects due to lectin-like binding characteristics, including the induction of T cell receptor (TCR) signaling and subsequent down-regulation of chemokine receptor expression. Here we report another activity attributable to PTxB, facilitating transfer of membrane material between mammalian cells. This activity does not require the TCR, and does not require cell-to-cell contact or cellular aggregation. Rather, membrane vesicles are transferred from donor to recipient cells in a toxin-dependent fashion. Membrane transfer occurs in different cell types, including cultured human T cells, CHO cells, and human primary peripheral blood mononuclear cells. Transfer involves both lipid and integral membrane proteins, as evidenced by the transfer of T and B cell-specific receptor molecules to other PBMCs. Interestingly, membrane transfer activity is a property that PTx shares with some, but not all, cell-aggregating lectins that are mitogenic for human T cells, and appears to be related to the ability to bind certain host cell glycolipids. This phenomenon may represent another mechanism by which pertussis toxin disrupts mammalian intra- and inter-cellular signaling.

Natural killer cell degranulation capacity predicts early onset of the immune reconstitution inflammatory syndrome (IRIS) in HIV-infected patients with tuberculosis

Immune reconstitution inflammatory syndrome (IRIS) is a common and potentially serious complication occurring in HIV-infected patients being treated for tuberculosis (TB) using combined antiretroviral treatment. A role of adaptive immunity has been suggested in the onset of IRIS, whereas the role of natural killer (NK) cells has not yet been explored. The present study sought to examine the involvement of NK cells in the onset of IRIS in HIV-infected patients with TB and to identify predictive markers of IRIS. A total of 128 HIV-infected patients with TB from the Cambodian Early versus Late Introduction of Antiretroviral Drugs (CAMELIA) trial were enrolled in Cambodia. Thirty-seven of the 128 patients developed IRIS. At inclusion, patients had low CD4 cell counts (27 cells/mm3) and high plasma viral load (5.76 and 5.50 log/mL in IRIS and non-IRIS patients, respectively). At baseline, NK-cell degranulation capacity was significantly higher in IRIS patients than in non-IRIS patients (9.6% vs 6.38%, P < .005). At IRIS onset, degranulation capacity did not differ between patients, whereas activating receptor expression was lower in IRIS patients. Patients with degranulation levels > 10.84% had a higher risk of IRIS (P = .002 by log-rank test). Degranulation level at baseline was the most important IRIS predictor (hazard ratio = 4.41; 95% confidence interval, 1.60-12.16). We conclude that NK-degranulation levels identify higher IRIS risk in HIV-infected patients with TB.

G(i/o) protein-dependent and -independent actions of Pertussis Toxin (PTX)

Pertussis toxin (PTX) is a typical A-B toxin. The A-protomer (S1 subunit) exhibits ADP-ribosyltransferase activity. The B-oligomer consists of four subunits (S2 to S5) and binds extracellular molecules that allow the toxin to enter the cells. The A-protomer ADP-ribosylates the α subunits of heterotrimeric G_i/o proteins, resulting in the receptors being uncoupled from the G_i/o proteins. The B-oligomer binds proteins expressed on the cell surface, such as Toll-like receptor 4, and activates an intracellular signal transduction cascade. Thus, PTX modifies cellular responses by at least two different signaling pathways; ADP-ribosylation of the Gα_i/o proteins by the A-protomer (G_i/o protein-dependent action) and the interaction of the B-oligomer with cell surface proteins (G_i/o protein-independent action).

Down regulation of human natural killer cell-mediated cytolysis induced by blood transfusion: role of transforming growth factor-β(1), soluble Fas ligand, and soluble Class I human leukocyte antigen

BACKGROUND

Human natural killer (NK) cells are thought to play a role in antiviral response and tumor immune surveillance. The molecular mechanisms of down regulation of NK-cell activity observed after red blood cell (RBC) transfusion is still undefined.

STUDY DESIGN AND METHODS

Both effects of blood transfusion (ex vivo) and supernatants (SNs) derived from RBC units unstored (RBC-0) or stored for 5 or 30 days (RBC-5 or -30, respectively) in vitro were analyzed on NK cell-mediated cytolytic activity.

RESULTS

We have found that NK cells isolated from transfused patients on Day 3 lysed the NK-sensitive target cells K562 to a lesser extent than before transfusion. This down regulation of NK-cell activation was evident also for NK-cell killing mediated through the engagement of NK cell-activating receptors as NKG2D, NKp30, NKp46, and CD16. Transfused patients reacquired NK cell-mediated cytolytic activity from Day 5 to Day 7 after transfusion. SN from RBC-30, but not from RBC-0 or RBC-5, strongly inhibited the generation of lymphokine-activated killer (LAK) cells and lysis of the NK-resistant target cell Jurkat in a dose-dependent manner. Transforming growth factor-β1 (TGF-β1) blocking antibodies partially restored the generation of LAK activity. In addition, the depletion of both soluble Class I human leukocyte antigens (sHLA-I) and soluble Fas ligand (sFasL) from SN of RBC-30 completely restored the generation of LAK activity.

CONCLUSIONS

Altogether, these findings would support the idea that blood transfusion-mediated down regulation of NK-cell activity is mediated by sHLA-I, sFasL, and TGF-β1.

Identification and characterization of the carbohydrate ligands recognized by pertussis toxin via a glycan microarray and surface plasmon resonance

Binding of pertussis toxin (PTx) was examined by a glycan microarray; 53 positive hits fell into four general groups. One group represents sialylated biantennary compounds with an N-glycan core terminating in alpha2-6-linked sialic acid. The second group consists of multiantennary compounds with a canonical N-glycan core, but lacking terminal sialic acids, which represents a departure from the previous understanding of PTx binding to N-glycans. The third group consists of Neu5Acalpha2-3(lactose or N-acetyllactosamine) forms that lack the branched mannose core found in N-glycans; thus, their presentation is more similar to that of O-linked glycans and glycolipids. The fourth group of compounds consists of Neu5Acalpha2-8Neu5Acalpha2-8Neu5Ac, which is seen in the c series gangliosides and some N-glycans. Quantitative analysis by surface plasmon resonance of the relative affinities of PTx for terminal Neu5Acalpha2-3 versus Neu5Acalpha2-6, as well as the affinities for the trisaccharide Neu5Acalpha2-8Neu5Acalpha2-8Neu5Ac versus disaccharide, revealed identical global affinities, even though the amount of bound glycan varied by 4-5-fold. These studies suggest that the conformational space occupied by a glycan can play an important role in binding, independent of affinity. Characterization of N-terminal and C-terminal binding sites on the S2 and S3 subunits by mutational analysis revealed that binding to all sialylated compounds was mediated by the C-terminal binding sites, and binding to nonsialylated N-linked glycans is mediated by the N-terminal sites present on both the S2 and S3 subunits. A detailed understanding of the glycans recognized by pertussis toxin is essential to understanding which cells are targeted in clinical disease.

Pertussis toxin and adenylate cyclase toxin: key virulence factors of Bordetella pertussis and cell biology tools

Pertussis toxin and adenylate cyclase toxin are two important virulence factors of Bordetella pertussis, the bacterial cause of the respiratory disease pertussis or whooping cough. In addition to studies on the structure, function and role in pathogenesis of these two toxins, they are both used as cell biology tools for a variety of applications owing to their ability to enter mammalian cells, perform enzymatic activities and modify cell signaling events. In this article, recent data from the research literature that enhance our understanding of the nature of these two toxins, their role in the pathogenesis of B. pertussis infection and disease, particularly in modulating host immune responses, and their use as tools for other areas of research will be outlined.

Pertussis toxin up-regulates angiotensin type 1 receptors through Toll-like receptor 4-mediated Rac activation

Pertussis toxin (PTX) is recognized as a specific tool that uncouples receptors from G(i) and G(o) through ADP-ribosylation. During the study analyzing the effects of PTX on Ang II type 1 receptor (AT1R) function in cardiac fibroblasts, we found that PTX increases the number of AT1Rs and enhances AT1R-mediated response. Microarray analysis revealed that PTX increases the induction of interleukin (IL)-1beta among cytokines. Inhibition of IL-1beta suppressed the enhancement of AT1R-mediated response by PTX. PTX increased the expression of IL-1beta and AT1R through NF-kappaB, and a small GTP-binding protein, Rac, mediated PTX-induced NF-kappaB activation through NADPH oxidase-dependent production of reactive oxygen species. PTX induced biphasic increases in Rac activity, and the Rac activation in a late but not an early phase was suppressed by IL-1beta siRNA, suggesting that IL-1beta-induced Rac activation contributes to the amplification of Rac-dependent signaling induced by PTX. Furthermore, inhibition of TLR4 (Toll-like receptor 4) abolished PTX-induced Rac activation and enhancement of AT1R function. However, ADP-ribosylation of G(i)/G(o) by PTX was not affected by inhibition of TLR4. Thus, PTX binds to two receptors; one is TLR4, which activates Rac, and another is the binding site that is required for ADP-ribosylation of G(i)/G(o).

HIV-1 Tat-specific IgG antibodies in high-responders target a B-cell epitope in the cysteine-rich domain and block extracellular Tat efficiently

Tat, an important regulatory protein of HIV-1, has been implicated in HIV-related pathogenesis. Immune responses to Tat, although underrepresented, confer protection against disease progression, in natural infection and experimental immunization, making Tat an attractive vaccine candidate. Information on immune responses to Tat from India which has the second largest HIV incidence has been lacking. Here we report a cross-sectional study evaluating the humoral response to Tat from a large number of samples from two southern states of India. 14% of the seropositive (63/447) and 4.6% of seronegative samples (7/150) harbored Tat-reactive antibodies. A significant number of the seropositive samples contained high levels of anti-Tat antibodies (31/447) which demonstrated class-switch to IgG1 and bound to Tat with high avidity. Cross-reactivity analysis showed that these antibodies interacted with Tat from different clades with variable degree with the highest interaction with subtype-AE and the least with subtype-B Tat. Importantly, a B-cell epitope in the cysteine-rich domain was found to be the most immunodominant one and antibodies interacting with this epitope blocked extracellular Tat efficiently. To the best of our knowledge this is the first report on immune responses to Tat from Indian populations and the data presented here could significantly contribute to HIV Tat vaccine design.

Pertussis toxin signals through the TCR to initiate cross-desensitization of the chemokine receptor CXCR4

Pertussis toxin (PTx) has been shown to exert a variety of effects on immune cells independent of its ability to ADP-ribosylate G proteins. Of these effects, the binding subunit of PTx (PTxB) has been shown to block signaling via the chemokine receptor CCR5, but the mechanism involved in this process is unknown. Here, we show that PTxB causes desensitization of a related chemokine receptor, CXCR4, and explore the mechanism by which this occurs. CXCR4 is the receptor for the chemokine stromal cell-derived factor 1alpha (SDF-1alpha) and elicits a number of biological effects, including stimulation of T cell migration. PTxB treatment causes a decrease in CXCR4 surface expression, inhibits G protein-associated signaling, and blocks SDF-1alpha-mediated chemotaxis. We show that PTxB mediates these effects by activating the TCR signaling network, as the effects are dependent on TCR and ZAP70 expression. Additionally, the activation of the TCR with anti-CD3 mAb elicits a similar set of effects on CXCR4 activity, supporting the idea that TCR signaling leads to cross-desensitization of CXCR4. The inhibition of CXCR4 by PTxB is rapid and transient; however, the catalytic activity of PTx prevents CXCR4 signaling in the long term. Thus, the effects of PTx holotoxin on CXCR4 signaling can be divided into two phases: short term by the B subunit, and long term by the catalytic subunit. These data suggest that TCR crosstalk with CXCR4 is likely a normal cellular process that leads to cross-desensitization, which is exploited by the B subunit of PTx.

Combined immunogene therapy of IL-6 and IL-15 enhances anti-tumor activity through augmented NK cytotoxicity

Many tumors evade host immunity by lowering expression of major histocompatibility complex (MHC) molecules. Theoretically, low MHC expression should activate natural killer (NK) cells and in some cases suppress tumor growth; nevertheless, some tumors also produce high concentrations of immunosuppressive cytokines, such as transforming growth factor (TGF)-beta, to inhibit the activity of NK cells. Using a canine transmissible venereal tumor (CTVT) model, we have previously demonstrated that IL-6 is a strong antagonist for TGF-beta. Herein, we found that IL-6 alone was unable to significantly promote TGF-beta-inhibited NK activities. Conversely, IL-15 alone strongly promoted NK activities; however, NK activities were inhibited to baseline levels following the addition of TGF-beta. Therefore, a new strategy using combined immunogene therapy of both IL-6 and IL-15 mediated by electroporation was used in this study. This combined IL-6 and IL-15 treatment effectively relieved the inhibitory effect of TGF-beta and activated NK cell cytotoxicity of lymphokine-activated killer (LAK) cells. Similarly, in isolated DX5+ NK cells, only IL-6 and IL-15 in combination significantly overcame the inhibitory effect of TGF-beta and promoted NK cytotoxicity. The group of BALB/c mice injected with plasmids with IL-6 and IL-15 genes (pIL-6/pIL-15) had the highest percentages of DX5+ NK cells as compared with either the pIL-6 or pIL-15 groups. Further, in SCID mice inoculated with CTVT, electroporation-mediated delivery of pIL-6/pIL-15 was significantly more efficient in suppressing both tumor establishment and tumor growth as compared with pIL-6 or pIL-15 inoculation alone. In addition, the anti-asialo GM-1 antibody abolished NK activities in SCID mice and resulted in outgrowth of the tumors. Together, these results suggest that the TGF-beta-associated inhibition of NK cytotoxicity cannot be adequately restored by simply antagonizing TGF-beta with IL-6: the co-existence of NK activating factors such as IL-15 is also important in restoring TGF-beta-inhibited cytotoxicity. This study highlights the therapeutic potential of the pIL-6/pIL-15 combination by inhibiting TGF-beta activity and enhancing NK cytotoxicity.

Tumor escape mechanisms: potential role of soluble HLA antigens and NK cells activating ligands

The crucial role played by human leukocyte antigen (HLA) antigens and natural killer (NK)-cell-activating ligands in the interactions of malignant cells with components of the host's immune system has stimulated interest in the characterization of their expression by malignant cells. Convincing evidence generated by the immunohistochemical staining of surgically removed malignant lesions with monoclonal antibodies recognizing HLA antigens and NK-cell-activating ligands indicates that the surface expression of these molecules is frequently altered on malignant cells. These changes appear to have clinical significance because in some types of malignant disease they are associated with the histopathological characteristics of the lesions as well as with disease-free interval and survival. These associations have been suggested to reflect the effect of HLA antigen and NK-cell-activating ligand abnormalities on the interactions of tumor cells with antigen-specific cytotoxic T lymphocytes (CTL) and with NK cells. Nevertheless, there are examples in which disease progresses in the face of appropriate HLA antigen and/or NK-cell-activating ligand as well as tumor antigen expression by malignant cells and of functional antigen-specific CTL in the investigated patient. In such scenarios, it is likely that the tumor microenvironment is unfavorable for CTL and NK cell activity and contributes to tumor immune escape. Many distinct escape mechanisms have been shown to protect malignant cells from immune recognition and destruction in the tumor microenvironment. In this article, following the description of the structural and functional characteristics of soluble HLA antigens and NK-cell-activating ligands, we will review changes in their serum level in malignant disease and discuss their potential role in the escape mechanisms used by tumor cells to avoid recognition and destruction.

Extracellular HIV-Tat induces cyclooxygenase-2 in glial cells through activation of nuclear factor of activated T cells

Both the HIV-1 protein Tat and cyclooxygenase-2 (COX-2) have been involved in the neuropathogenesis associated with HIV-1 infection. However, the relationship among them has not been addressed. Here, we found that extracellular Tat was able to induce COX-2 mRNA and protein expression and PGE2 synthesis in astrocytoma cell lines and primary human astrocytes. Moreover, Tat induced COX-2 promoter transcription. Deletion of NF-kappaB sites of the promoter did not diminish Tat-dependent transcription. Interestingly, Tat did not induce NF-kappaB activity, suggesting that NF-kappaB was not necessary to control COX-2 transcription induced by Tat. In contrast, deletion or mutation of the NFAT and/or AP-1 site abrogated COX-2 induction by Tat. Moreover, Tat induced transcription of NFAT- and AP-1-dependent reporter genes. Transfection of a dominant negative c-Jun mutant protein, TAM-67, or of a dominant negative version of NFAT, efficiently blocked the induction of COX-2 promoter by Tat, confirming the requirement of both transcription factors. Moreover, Tat induced NFAT translocation to the nucleus and binding to the distal site of the COX-2 promoter. The importance of NFAT and AP-1 in COX-2 induction and PGE2 synthesis by Tat was corroborated by using pharmacological inhibitors of the NFAlphaTau, ERK, and JNK pathways. In summary, our results indicate that HIV-1 Tat was able to induce COX-2 and PGE2 synthesis in astrocytic cells through an NFAT/AP-1-dependent mechanism.

Pertussis toxin B-oligomer suppresses human immunodeficiency virus-1 Tat-induced neuronal apoptosis through feedback inhibition of phospholipase C-beta by protein kinase C

Human immunodeficiency virus (HIV)-1 Tat is a multifunctional protein involved in viral replication, inflammation and apoptosis. Tat activates phospholipase C-beta (PLC-beta), presumably via a pertussis toxin (PTX) sensitive G(i) protein, which is critical for neuronal apoptosis. In this study, we show that Tat-mediated intracellular Ca(2+) release in rat pheochromocytoma (PC-12) cells and rat primary cortical neuronal cultures was abrogated by pretreatment with either pertussis toxin and/or its B-oligomer subunit (PTX-B), devoid of ADP ribosyltransferase activity. PTX-B pretreatment also inhibited intracellular Ca(2+) release by bradykinin and 2,4,6-trimethyl-N-(m-3-trifluoromethylphenyl) benzenesulfonamide (m-3M3FBS), a director activator of phospholipase C. Activation of protein kinase C (PKC) by phorbol 12,13-dibutyrate (PdBu) mimicked the PTX-B-mediated inhibition of m-3M3FBS-stimulated intracellular Ca(2+) increase, while inhibition of PKC by bisindolylmaleimide I hydrochloride (BIM) reversed the inhibitory action of PTX-B. Functionally, PTX-B reduced Tat-induced Bax and caspase-3 proteins and reduced cell apoptosis. We conclude that PTX inhibition of Tat-mediated intracellular Ca(2+) release is independent of ADP ribosylation of the G(i) protein via the A protomer, but mediated by the B-oligomer. Furthermore, PTX-B suppresses HIV-1 Tat-mediated apoptosis by reducing its activation of PLC-beta through a PKC activation pathway.

Activation of the Adenosine A1Receptor Inhibits HIV-1 Tat-Induced Apoptosis by Reducing Nuclear Factor-κB Activation and Inducible Nitric-Oxide Synthase

Human immunodeficiency virus dementia (HIV-D) is a nonfocal central nervous system manifestation characterized by cognitive, behavioral, and motor abnormalities. The pathophysiology of neuronal damage in HIV-D includes a direct toxic effect of viral proteins on neuronal cells and an indirect effect caused by the release of inflammatory mediators and neurotoxins by activated macrophages/microglia and astrocytes, culminating into neuronal apoptosis. Previous studies have documented that the nucleoside adenosine mediates neuroprotection by activating adenosine A(1) receptor subtype (A(1)AR) linked to suppression of neuronal excitability. In this study, we show that A(1)AR activation protects against HIV-1 Tat-induced toxicity in primary cultures of rat cerebellar granule neurons and in rat pheochromocytoma (PC12) cell. In PC12 cells, HIV-1 Tat increased [Ca(2+)](i) levels, release of nitric oxide (NO), and expression of inducible nitric-oxide synthase (iNOS) and A(1)AR. Activation of A(1)AR suppressed Tat-mediated increases in [Ca(2+)](i) and NO. Furthermore, A(1)AR agonists inhibited iNOS expression in a nuclear factor-kappaB (NF-kappaB)-dependent manner. It is noteworthy that activation of the A(1)AR or inhibition of NOS protected against Tat-induced apoptosis in PC12 cells and cerebellar granule cells. Moreover, activation of the A(1)AR-inhibited Tat-induced increases in the levels of proapoptotic proteins Bax and caspase-3. Taken together, our results demonstrate that the A(1)AR protects against HIV-1 toxicity by inhibiting NF-kappaB, thereby reducing the expression of iNOS and NO radicals and neuronal apoptosis.

Pertussis toxin B-oligomer suppresses IL-6 induced HIV-1 and chemokine expression in chronically infected U1 cells via inhibition of activator protein 1

Pertussis toxin B-oligomer (PTX-B) inhibits HIV replication in T lymphocytes and monocyte-derived macrophages by interfering with multiple steps of the HIV life cycle. PTX-B prevents CCR5-dependent (R5) virus entry in a noncompetitive manner, and it also exerts suppressive effects on both R5- and CXCR4-dependent HIV expression at a less-characterized postentry level. We demonstrate in this study that PTX-B profoundly inhibits HIV expression in chronically infected promonocytic U1 cells stimulated with several cytokines and, particularly, the IL-6-mediated effect, a cytokine that triggers viral production in these cells independently of NF-kappaB activation. From U1 cells we have subcloned a cell line, named U1-CR1, with increased responsiveness to IL-6. In these cells, PTX-B neither down-regulated the IL-6R nor prevented IL-6 induced signaling in terms of STAT3 phosphorylation and DNA binding. In contrast, PTX-B inhibited AP-1 binding to target DNA and modified its composition with a proportional increases in FosB, Fra2, and ATF2. PTX-B inhibited IL-6-induced HIV-1 long-terminal repeat-driven transcription from A, C, E, and F viral subtypes, which contain functional AP-1 binding sites, but failed to inhibit transcription from subtypes B and D LTR devoid of these sites. In addition, PTX-B inhibited the secretion of IL-6-induced, AP-1-dependent genes, including urokinase-type plasminogen activator, CXCL8/IL-8, and CCL2/monocyte chemotactic protein-1. Thus, PTX-B suppression of IL-6 induced expression of HIV and cellular genes in chronically infected promonocytic cells is strongly correlated to inhibition of AP-1.