Regulation of Cellular Gene Expression and Function by the Human Immunodeficiency Virus Type 1 Tat Protein

Cannabinoid inhibits HIV-1 Tat-stimulated adhesion of human monocyte-like cells to extracellular matrix proteins

AIMS

The aim of this study was to assess the effect of select cannabinoids on human immunodeficiency virus type 1 (HIV-1) transactivating (Tat) protein-enhanced monocyte-like cell adhesion to proteins of the extracellular matrix (ECM).

MAIN METHODS

Collagen IV, laminin, or an ECM gel was used to construct extracellular matrix layers. Human U937 monocyte-like cells were exposed to Tat in the presence of ∆(9)-tetrahydrocannabinol (THC), CP55,940, and other select cannabinoids. Cell attachment to ECM proteins was assessed using an adhesion assay.

KEY FINDINGS

THC and CP55,940 inhibited Tat-enhanced attachment of U937 cells to ECM proteins in a mode that was linked to the cannabinoid receptor type 2 (CB2R). The cannabinoid treatment of Tat-activated U937 cells was associated with altered β1-integrin expression and distribution of polymerized actin, suggesting a modality by which these cannabinoids inhibited adhesion to the ECM.

SIGNIFICANCE

The blood-brain barrier (BBB) is a complex structure that is composed of cellular elements and an extracellular matrix (ECM). HIV-1 Tat promotes transmigration of monocytes across this barrier, a process that includes interaction with ECM proteins. The results indicate that cannabinoids that activate the CB2R inhibit the ECM adhesion process. Thus, this receptor has potential to serve as a therapeutic agent for ablating neuroinflammation associated with HIV-elicited influx of monocytes across the BBB.

Marijuana use and brain immune mechanisms

The recreational smoking of marijuana, or Cannabis sativa, has become widespread, including among adolescents. Marijuana contains a class of compounds known as phytocannabinoids that include cannabidiol (CBD) and Δ(9)-tetrahydrocannabinol (THC). THC is the major psychoactive component in marijuana, but also exhibits immunosuppressive activity. CBD, while not psychotropic, also modulates immune function, but its mechanism of action appears to differ from that of THC. Since both compounds are highly lipophilic, they readily passage the blood-brain barrier and access the central nervous system. Since CBD is not psychotropic, it has been considered as a candidate therapeutic compound for ablating neuropathological processes characterized by hyperinflammation. However, an unresolved question centers around the impact of these compounds on immune-competent cells within the CNS in relation to susceptibility to infection. There are accumulating data indicating that THC inhibits the migratory capability of macrophage-like cells resident in the CNS, such as microglia, toward nodes of microbial invasion. Furthermore, phytocannabinoids have been reported to exert developmental and long-term effects on the immune system suggesting that exposure to these substances during an early stage in life has the potential to alter the fundamental neuroimmune response to select microbial agents in the adult.

The effects of HIV Tat DNA on regulating the immune response of HIV DNA vaccine in mice

BACKGROUND

HIV trans-activator protein (Tat) is the crucial factor to control HIV transcription, and is usually considered as an important immunogen for the design of HIV vaccine. Recent studies reported some special bio-activities of Tat protein on immunoregulation. However, to date, few studies have focused on exploring the effects of Tat expression plasmid (pTat) on regulating the immune responses induced by HIV DNA vaccines. In this study, our main objective is to investigate the immunoregulation mediated by pTat in mice.

METHODS

Four gene-coding plasmids (pTat, pGag, pEnv and pPol) were constructed, and the gene expression was detected by western blot method. The effects of pTat on regulating the immune responses to antigens Gag, Env, Pol were assessed by enzyme-linked immunospot and enzyme-linked immunosorbent assay. The data was analysed by one-way analysis of variance.

RESULTS

After two immunizations, mice vaccinated with antigen expressing plasmid (pGag, pEnv or pPol) plus pTat exhibited significantly stronger IFN-gamma response than that vaccinated with the corresponding antigen alone. Moreover, mice receiving two injections of antigen plus pTat exhibited the same strong IFN-gamma response as those receiving three injections of antigen alone did. Furthermore, addition of pTat not only induced a more balanced Th1 and Th2 response, but also broadened IgG subclass responses to antigens Gag and Pol.

CONCLUSION

pTat exhibited the appreciable effects on modulating immune responses to HIV antigens Gag, Env and Pol, providing us interesting clues on how to optimize HIV DNA vaccine.

Inhibition of NF-κB activity by HIV-1 Vpr is dependent on Vpr binding protein

Numerous studies have reported that Vpr alters NF-κB signaling in various cell types, however, the findings have been largely conflicting with reports of both stimulatory and inhibitory effects of Vpr. Our aim was to investigate the role of Vpr signaling in myeloid cells using an adenovirus based expression and indicator system. Our results show that Vpr is inhibitory to NF-κB, however, this effect is dependent on the particular manner of NF-κB stimulation. Consistent with this notion, we report that Vpr has inhibitory effects that are specific to the TNF-α pathway, but not affecting the LPS pathway, suggesting that differential targets of Vpr may exist for NF-κB regulation. Further, we identify VprBP as one possible cellular component of Vpr's regulation of IκBα in response to TNF-α stimulation. We did not identify such a role for HSP27, which instead seems to inhibit Vpr functions. Chronically HIV-1 infected U1 cells with knockdown constructs for Vpr were unexpectedly less responsive to TNF-α mediated viral replication, perhaps suggesting that other HIV-1 components may antagonize these anti-NF-κB effects in infected cells. We hypothesize that Vpr may serve an important role in the context of viral infection and immune function in vivo, through its selective inhibition of NF-κB pathways.

Insights into the role of progranulin in immunity, infection, and inflammation

PGRN, a pleiotrophic growth factor, is known to play an important role in the maintenance and regulation of the homeostatic dynamics of normal tissue development, proliferation, regeneration, and the host-defense response and therefore, has been widely studied in the fields of infectious diseases, wound healing, tumorigenesis, and neuroproliferative and degenerative diseases. PGRN has also emerged as a multifaceted immune-regulatory molecule through regulating the signaling pathways known to be critical for immunology, especially TNF/TNFR signaling. In this review, we start with updates about the interplays of PGRN with ECM proteins, proteolytic enzymes, inflammatory cytokines, and cell-surface receptors, as well as various pathophysiological processes involved. We then review the data supporting an emerging role of PGRN in the fields of the "Cubic of I", namely, immunity, infection, and inflammation, with special focus on its regulation of autoimmune syndromes. We conclude with insights into the immunomodulating, anti-inflammatory, therapeutic potential of PGRN in treating diseases with an inflammatory etiology in a vast range of medical specialties.

HIV-1, interferon and the interferon regulatory factor system: an interplay between induction, antiviral responses and viral evasion

Thirty years after the first isolation of the etiological agent of AIDS, the virus HIV-1 is still a major threat worldwide with millions of individuals currently infected. Although current combination therapies allow viral replication to be controlled, HIV-1 is not eradicated and persists in drug- and immune system-insensitive reservoirs and a cure is still lacking. Pathogens such as HIV-1 that cause chronic infections are able to adapt to the host in a manner that ensures long term residence and survival, via the evolution of numerous mechanisms that evade various aspects of the innate and adaptive immune response. One such mechanism is targeted to members of the interferon (IFN) regulatory factor (IRF) family of proteins. These transcription factors regulate a variety of biological processes including interferon induction, immune cell activation and downstream pattern recognition receptors (PRRs). HIV-1 renders IRFs harmless and hijacks them to its own advantage in order to facilitate its replication and evasion of immune responses. Type I interferon (IFN), the canonical antiviral innate response, can be induced in both acute and chronic HIV-1 infection in vivo, but in the majority of individuals this initial response is not protective and can contribute to disease progression. Type I IFN expression is largely inhibited in T cells and macrophages in order to successfully establish productive infection, whereas sustained IFN production by plasmacytoid dendritic cells is considered an important source of chronic immune activation, a hallmark to AIDS progression.

HIV-1 targeting of IFN regulatory factors

Pathogens such as HIV-1 that cause chronic infections are particularly capable at adapting to the host in a manner that ensures long-term residence, and have evolved numerous mechanisms to evade various aspects of the innate and adaptive immune response. One of these mechanisms is the targeting of members of the IFN regulatory factor family. IFN regulatory factors are transcription factors that are implicated in the regulation of a variety of biological processes, including IFN induction and immune cell activation of downstream responses triggered by Toll-like receptors and other pattern-recognition receptors. Here, we report the specific targeting by HIV-1 of this class of cellular transcription factors, and describe how HIV-1 both makes them harmless and hijacks them, profoundly affecting their activity and turning them to its own advantage in order to facilitate its replication, survival, evasion of immune responses and spread.

Cannabinoids inhibit migration of microglial-like cells to the HIV protein Tat

Microglia are a population of macrophage-like cells in the central nervous system (CNS) which, upon infection by the human immunodeficiency virus (HIV), secrete a plethora of inflammatory factors, including the virus-specified trans-activating protein Tat. Tat has been implicated in HIV neuropathogenesis since it elicits chemokines, cytokines, and a chemotactic response from microglia. It also harbors a β-chemokine receptor binding motif, articulating a mode by which it acts as a migration stimulus. Since select cannabinoids have anti-inflammatory properties, cross the blood-brain barrier, and target specific receptors, they have potential to serve as agents for dampening untoward neuroimmune responses. The aim of this study was to investigate the effect of select cannabinoids on the migration of microglial-like cells toward Tat. Using a mouse BV-2 microglial-like cell model, it was demonstrated that the exogenous cannabinoids Delta-9-tetrahydrocannabinol (THC) and CP55940 exerted a concentration-related reduction in the migration of BV-2 cells towards Tat. A similar inhibitory response was obtained when the endogenous cannabinoid 2-arachidonoylglycerol (2-AG) was used. The CB(2) receptor (CB2R) antagonist SR144528, but not the CB(1) receptor (CB1R) antagonist SR141716A, blocked this inhibition of migration. Similarly, CB2R knockdown with small interfering RNA reversed the cannabinoid-mediated inhibition. In addition, the level of the β-chemokine receptor CCR-3 was reduced and its intracellular compartmentation was altered. These results indicate that cannabinoid-mediated inhibition of BV-2 microglial-like cell migration to Tat is linked functionally to the CB2R. Furthermore, the results indicate that activation of the CB2R leads to altered expression and compartmentation of the β-chemokine receptor CCR-3.

HIV-1 accessory protein Vpr: relevance in the pathogenesis of HIV and potential for therapeutic intervention

The HIV protein, Vpr, is a multifunctional accessory protein critical for efficient viral infection of target CD4⁺ T cells and macrophages. Vpr is incorporated into virions and functions to transport the preintegration complex into the nucleus where the process of viral integration into the host genome is completed. This action is particularly important in macrophages, which as a result of their terminal differentiation and non-proliferative status, would be otherwise more refractory to HIV infection. Vpr has several other critical functions including activation of HIV-1 LTR transcription, cell-cycle arrest due to DCAF-1 binding, and both direct and indirect contributions to T-cell dysfunction. The interactions of Vpr with molecular pathways in the context of macrophages, on the other hand, support accumulation of a persistent reservoir of HIV infection in cells of the myeloid lineage. The role of Vpr in the virus life cycle, as well as its effects on immune cells, appears to play an important role in the immune pathogenesis of AIDS and the development of HIV induced end-organ disease. In view of the pivotal functions of Vpr in virus infection, replication, and persistence of infection, this protein represents an attractive target for therapeutic intervention.

The oral commensal, Streptococcus gordonii, synergizes with Tat protein to induce HIV-1 promoter activation in monocytes/macrophages

Trans-activator of transcription (Tat) is an HIV-1 protein essential for viral replication. Oral periodontopathogens (e.g. Fusobacterium nucleatum) enhance HIV-1LTR promoter activation in monocytes/macrophages in absence of Tat; however, some oral commensals fail to trigger this response. We sought to determine the effect of Tat on HIV-1LTR promoter activation induced by the representative oral commensal Streptococcus gordonii in monocytes/macrophages. S. gordonii enhanced HIV-1LTR reactivation in THP89GFP (Tat(+)), but not in BF24 (Tat(-)) cells. Interestingly, S. gordonii, but not Streptococcus sanguinis enhanced HIV-1LTR activation in the presence of recombinant Tat in BF24 cells. This response correlated with IL-8 but not TNFα or IL-6 production, and was abrogated by the NFκB inhibitor BAY 11-7082. Kinetics of NFκB-RelA activation did not explain the S. gordonii-induced HIV-1LTR activation in presence of Tat. These results suggest that S. gordonii-induced HIV-1 reactivation in monocytes/macrophages is Tat-dependent and appears to involve NFκB activation.

A combination HIV vaccine based on Tat and Env proteins was immunogenic and protected macaques from mucosal SHIV challenge in a pilot study

HIV native Tat and V2 loop-deleted Env (EnvΔV2) proteins already proved safe and immunogenic in phase I clinical testing as single vaccine components. Further, a phase II vaccine trial with Tat showed intensification of the therapeutic effects of HAART in successfully treated HIV-infected individuals. Here a pilot study assessed the immunogenicity and protective efficacy of an HIV/AIDS vaccine based on the combination of Tat and EnvΔV2 proteins in cynomolgus macaques against homologous intrarectal challenge with 35 MID(50) (monkey infectious dose 50) of an R5 simian-human immunodeficiency virus (SHIV(SF162P4cy)). Upon challenge, three of four macaques immunized with Tat and EnvΔV2, and two of three monkeys immunized with EnvΔV2 alone were protected from infection. In contrast, all three control animals, which had been either administered with the adjuvants only or left untreated, and an additional monkey immunized with Tat alone became systemically infected. Protection of the macaques vaccinated with EnvΔV2 or Tat/EnvΔV2 correlated with higher peak titers of pre-challenge neutralizing antibodies obtained during the immunization period (between 70 and 3 weeks before challenge) and with anti-Env V3 loop binding antibodies assessed 3 weeks before challenge. Compared to EnvΔV2 alone, the Tat and EnvΔV2 combined vaccine elicited faster antibody responses (IgM) with a trend, early in the vaccination schedule, after the second immunization including EnvΔV2, towards broader anti-Env IgG epitope specificity and a higher ratio of neutralizing to Env-binding antibody titers. As the number of immunizations increased, vaccination with EnvΔV2 approached the immune response assessed after two inocula with the Tat/EnvΔV2 combined vaccine, even though some differences remained between groups, as indicated by anti-Env IgG epitope mapping. In fact, three weeks before challenge, plasma IgG of animals in the EnvΔV2 group showed a trend towards stronger specificity for the V1 loop and V5 loop-C5 regions of Env, whereas the Tat/EnvΔV2 group displayed an overall higher reactivity for epitopes within the Env V3 loop throughout the immunization period. Although differences in terms of protection rate were not found between the EnvΔV2 or Tat/EnvΔV2 vaccination groups in this pilot study, vaccination with Tat/EnvΔV2 appeared to accelerate the induction of potentially protective antibody responses to Env. In particular, antibodies to the Env V3 loop, whose levels at pre-challenge correlated with protection, were already higher early in the vaccination schedule in monkeys immunized with Tat/EnvΔV2 as compared to EnvΔV2 alone. Further studies including larger vaccination groups and fewer immunizations with these two vaccine candidates are needed to confirm these findings and to assess whether the Tat/EnvΔV2 vaccine may afford superior protection against infection.

Effect of the redox state on HIV-1 tat protein multimerization and cell internalization and trafficking

The redox state of the cysteine-rich region of the HIV Tat protein is known to play a crucial role in Tat biological activity. In this article, we show that Tat displays two alternative functional states depending on the presence of either one or three reduced sulphydryl groups in the cysteine-rich region, respectively. Using different approaches, a disulfide pattern has been defined for the Tat protein and a specific DTT-dependent breaking order of disulfide bonds highlighted. The Tat redox state deeply influences macrophage protein uptake. Immunoistochemistry analysis shows that the oxidized protein does not enter cells, whereas partially reduced protein reaches the cytosol and, to a limited extent, the nucleus. Finally electrophoretic analysis shows Tat high-molecular weight multi-aggregation, resulting in the loss of biological activity. This is due to strong electrostatic and metal-binding interactions, whereas Tat dimerization involves metal-binding interactions as well as disulfide bond formation.

Macrophage signaling in HIV-1 infection

The human immunodeficiency virus-1 (HIV-1) is a member of the lentivirus genus. The virus does not rely exclusively on the host cell machinery, but also on viral proteins that act as molecular switches during the viral life cycle which play significant functions in viral pathogenesis, notably by modulating cell signaling. The role of HIV-1 proteins (Nef, Tat, Vpr, and gp120) in modulating macrophage signaling has been recently unveiled. Accessory, regulatory, and structural HIV-1 proteins interact with signaling pathways in infected macrophages. In addition, exogenous Nef, Tat, Vpr, and gp120 proteins have been detected in the serum of HIV-1 infected patients. Possibly, these proteins are released by infected/apoptotic cells. Exogenous accessory regulatory HIV-1 proteins are able to enter macrophages and modulate cellular machineries including those that affect viral transcription. Furthermore HIV-1 proteins, e.g., gp120, may exert their effects by interacting with cell surface membrane receptors, especially chemokine co-receptors. By activating the signaling pathways such as NF-kappaB, MAP kinase (MAPK) and JAK/STAT, HIV-1 proteins promote viral replication by stimulating transcription from the long terminal repeat (LTR) in infected macrophages; they are also involved in macrophage-mediated bystander T cell apoptosis. The role of HIV-1 proteins in the modulation of macrophage signaling will be discussed in regard to the formation of viral reservoirs and macrophage-mediated T cell apoptosis during HIV-1 infection.

HIV-1 Tat and AIDS-associated cancer: targeting the cellular anti-cancer barrier?

The acquired immunodeficiency syndrome (AIDS) is accompanied by a significant increase in the incidence of neoplasms. Several causative agents have been proposed for this phenomenon. These include immunodeficiency and oncogenic DNA viruses and the HIV-1 protein Tat. Cancer in general is closely linked to genomic instability and DNA repair mechanisms. The latter maintains genomic stability and serves as a cellular anti-cancer barrier. Defects in DNA repair pathway are associated with carcinogenesis.

This review focuses on newly discovered connections of the HIV-1 protein Tat, as well as cellular co-factors of Tat, to double-strand break DNA repair. We propose that the Tat-induced DNA repair deficiencies may play a significant role in the development of AIDS-associated cancer.

Intracellular HIV-1 Tat protein represses constitutive LMP2 transcription increasing proteasome activity by interfering with the binding of IRF-1 to STAT1

The Tat protein is the transcriptional activator of HIV-1 gene expression, which is not only essential for viral replication, but also important in the complex HIV-induced pathogenesis of AIDS, as both an intracellular and an extracellular released protein. Accordingly, Tat is able to profoundly affect cellular gene expression, regulating several cellular functions, also in non-infected cells. We showed recently that Tat induces modification of immunoproteasomes in that it up-regulates LMP7 (low-molecular-mass polypeptide 7) and MECL1 (multicatalytic endopeptidase complex-like 1) subunits and down-modulates the LMP2 subunit, resulting in a change in the generation and presentation of epitopes in the context of MHC class I. In particular, Tat increases presentation of subdominant and cryptic epitopes. In the present study, we investigated the molecular mechanism responsible for the Tat-induced LMP2 down-regulation and show that intracellular Tat represses transcription of the LMP2 gene by competing with STAT1 (signal transducer and activator of transcription 1) for binding to IRF-1 (interferon-regulatory factor-1) on the overlapping ICS-2 (interferon consensus sequence-2)-GAS (gamma-interferon-activated sequence) present in the LMP2 promoter. This element is constitutively occupied in vivo by the unphosphorylated STAT1-IRF-1 complex, which is responsible for the basal transcription of the gene. Sequestration of IRF-1 by intracellular Tat impairs the formation of the complex resulting in lower LMP2 gene transcription and LMP2 protein expression, which is associated with increased proteolytic activity. On the other hand, extracellular Tat induces the expression of LMP2. These effects of Tat provide another effective mechanism by which HIV-1 affects antigen presentation in the context of the MHC class I complex and may have important implications in the use of Tat for vaccination strategies.

The HIV-1 Tat protein enhances megakaryocytic commitment of K562 cells by facilitating CREB transcription factor coactivation by CBP

The human immunodeficiency virus type 1 (HIV-1) Tat protein regulates transcription factor functions and alters cellular gene expression. Because hematopoietic progenitor cell (HPC) differentiation requires activation of lineage-specific transcription factors, Tat may affect hematopoiesis in HIV-1-infected micro-environments. We have monitored the molecular effects of Tat on megakaryocytic differentiation in the HPC line, K562. Flow cytometry analysis of CD61 indicated that phorbol myristate acetate (PMA) (16 nM) stimulated megakaryocytic commitment of K562 cells was increased (3- to 4-fold) following exposure to Tat (1-100 ng/ml). Activation of the megakaryocytic transcription factor cAMP regulatory element binding protein (CREB) and its coactivation by the CREB binding protein (CBP) was subsequently monitored. CREB phosphorylation and DNA binding were measured by Western immunodetection and electrophoretic mobility shift assays (EMSA), respectively. Within 2 hrs after stimulation, Tat increased both CREB phosphorylation and DNA binding by 7- to 10-fold. Transient cotransfection with CREB reporter and CBP expression plasmids demonstrated that Tat treatment increases (3- to 4-fold) both PMA-stimulated and CBP-mediated transcription via the cAMP regulatory element. Histone acetyl transferase (HAT) activity was increased (8- to 10-fold) in Tat-stimulated cells, which suggested increased chromosomal accessibility of transcription factors. Two-hybrid cotransfection assays using reporter plasmid containing the GAL4 DNA-binding domain and expression plasmid coding for the GAL4-CBP fusion protein, showed that Tat increases (2-fold) CBP-mediated coactivation of CREB. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed that Tat treatment increases CBP gene expression (7- to 9-fold) and protein levels (5- to 7-fold) within 6-12 hrs after stimulation. Our findings indicated that Tat treatment increases both CREB function and CREB coactivation by CBP, which may facilitate megakaryocytic commitment of K562 cells. Induction of this molecular signaling by HIV-1 Tat protein may have relevance in understanding the HIV-induced hematologic manifestations and possibly in regulation of viral infectivity parameters in progenitor cell reservoirs.

Enhanced cellular immunity to SIV Gag following co-administration of adenoviruses encoding wild-type or mutant HIV Tat and SIV Gag

Among candidate antigens for human immunodeficiency virus (HIV) prophylactic vaccines, the regulatory protein Tat is a critical early target, but has a potential for immune suppression. Adenovirus (Ad) recombinants encoding wild-type HIV Tat (Tat-wt) and a transdominant negative mutant HIV Tat (Tat22) were constructed and administered to mice separately or together with Ad-SIVgag. Immunogenicity and effects on immune responses to the co-administered Gag immunogen were evaluated. Wild-type and mutant Tat recombinants elicited similar Tat-specific cellular and humoral immune responses. Co-administration of either Tat immunogen with Ad-SIVgag induced modest but significant enhancement of Gag-specific interferon-gamma secreting T cells and lymphoproliferative responses. Neither the Ad-recombinant encoding Tat-wt nor Tat22 suppressed induction of anti-Tat or anti-Gag antibodies. Based on the immune responses observed in mice, both recombinants appear to be suitable vaccine candidates. Their contribution to protective efficacy remains to be determined in a non-human primate model.

The binding affinity of double-stranded RNA motifs to HIV-1 Tat protein affects transactivation and the neutralizing capacity of anti-Tat antibodies elicited after intranasal immunization

In this study we examined the hypothesis that the binding affinity of two double-stranded (ds) RNA motifs to HIV-1 Tat protein might affect transactivation and the type of anti-Tat immune responses. Using surface plasmon resonance technology we demonstrated the capacity of the poly(A):poly(U) (pA:pU) motif to bind with high affinity to a totally synthetic Tat protein and to inhibit more efficiently the Tat/transactivation response element (TAR) RNA interaction as compared to the poly(I):poly(C) (pI:pC) motif. Furthermore, the pA:pU motif was tenfold more effective in inhibiting Tat-driven transactivation than the pI:pC motif. Following intranasal immunization of mice, both dsRNA motifs enhanced the antibody (serum and mucosal) and cellular responses to Tat. However, only the serum samples of mice immunized with Tat + pI:pC inhibited Tat-driven transactivation. The profile of serum antibody subclasses together with the secreted cytokines by Tat-stimulated splenocyte cultures indicated that both dsRNA motifs favored the induction of a balanced Th1 and Th2 immune response. The demonstration in this study that two dsRNA motifs had a marked effect on Tat/TAR RNA interaction and on the neutralizing capacity of anti-Tat specific antibody responses highlights their potential for biological applications and the importance of selecting the appropriate motif as an adjuvant for vaccine design.

Displacement of SATB1-bound histone deacetylase 1 corepressor by the human immunodeficiency virus type 1 transactivator induces expression of interleukin-2 and its receptor in T cells

One hallmark of human immunodeficiency virus type 1 (HIV-1) infection is the dysregulation of cytokine gene expression in T cells. Transfection of T cells with human T-cell leukemia type 1 or 2 transactivator results in the induction of the T-cell-restricted cytokine interleukin-2 (IL-2) and its receptor (IL-2Ralpha). However, no T-cell-specific factor(s) has been directly linked with the regulation of IL-2 and IL-2Ralpha transcription by influencing the promoter activity. Thymocytes from SATB1 (special AT-rich sequence binding protein 1) knockout mice have been shown to ectopically express IL-2Ralpha, suggesting involvement of SATB1 in its negative regulation. Here we show that SATB1, a T-cell-specific global gene regulator, binds to the promoters of human IL-2 and IL-2Ralpha and recruits histone deacetylase 1 (HDAC1) in vivo. SATB1 also interacts with Tat in HIV-1-infected T cells. The functional interaction between HIV-1 Tat and SATB1 requires its PDZ-like domain, and the binding of the HDAC1 corepressor occurs through the same. Furthermore, Tat competitively displaces HDAC1 that is bound to SATB1, leading to increased acetylation of the promoters in vivo. Transduction with SATB1 interaction-deficient soluble Tat (Tat 40-72) and reporter assays using a transactivation-negative mutant (C22G) of Tat unequivocally demonstrated that the displacement of HDAC1 itself is sufficient for derepression of these promoters in vivo. These results suggest a novel mechanism by which HIV-1 Tat might overcome SATB1-mediated repression in T cells.

The HIV-Tat protein induces chromosome number aberrations by affecting mitosis

To analyze the effects of the HIV-Tat-tubulin interaction, we microinjected HIV-Tat purified protein into Drosophila syncytial embryos. Following the Tat injection, altered timing of the cortical nuclear cycles was observed; specifically, the period between the nuclear envelope breakdown and anaphase initiation was lengthened as was the period between anaphase initiation and the formation of the next nuclear envelope. These two periods correspond to kinetochore alignment at metaphase and to mitosis exit, respectively. We also demonstrated that these two delays are the consequence of damage specifically induced by Tat on kinetochore alignment and on the timing of sister chromatid segregation at anaphase. Furthermore, we show that the expression of Tat in Drosophila larvae brain cells produces a significant percentage of polyploid and aneuploid cells. The results reported here indicate that Tat impairs the mitotic process and that Tat-tubulin interaction appears to be responsible for the observed defects. The presence of polyploid and aneuploid cells is consistent with a delay or arrest in the M phase of a substantial fraction of the cells expressing Tat, suggesting that mitotic spindle checkpoints are overridden following Tat expression.

HIV-1 Tat increases the adhesion of monocytes and T-cells to the endothelium in vitro and in vivo: implications for AIDS-associated vasculopathy

HIV-1-infected patients exhibit severe damages of the aortic endothelium, develop angioproliferative lesions such as Kaposi's sarcoma (KS), and have an increased risk of cardiovascular diseases and atherosclerosis. An increased adhesion of leukocytes to the endothelium is a common pathogenic parameter of AIDS-associated vascular diseases. Here we show that the HIV-1 Tat protein, a regulatory protein of HIV-1 released by infected cells, and TNF-alpha, a cytokine increased in sera and tissues of HIV-1-infected patients, activate synergistically the adhesion of leukocytes to endothelial cells both in vitro and in vivo. This effect is selectively mediated by HIV-1 Tat, since HIV-1 Nef, another HIV-1 regulatory protein, and the HIV-1 envelope protein gp41, had no effect. In vitro adhesion assays with PBMC and quantitative cell type analysis of adherent cells by FACS demonstrated that HIV-1 Tat selectively activates the adhesion of T-cells and monocytes but not of B-cells. Intravital microscopic studies in mice confirmed the synergistic activity of HIV-1 Tat and TNF-alpha on leukocyte adhesion to the endothelium in vivo. These data indicate that HIV-1 Tat in cooperation with TNF-alpha may contribute to the vascular damage and cardiovascular diseases observed in AIDS patients but also to the prominent extravasation of T-cells and monocytes which is a key process in the formation and progression of KS lesions.

HIV TAT basic peptide is not a high-affinity ligand for VEGF receptor 2

The 'transactivator of transcription' (TAT) protein of human immunodeficiency virus transforms cells in culture and promotes the development of tumors, so-called Kaposi's sarcoma, in AIDS patients. TAT induces growth and differentiation of blood vessels and has been suggested to directly activate VEGF receptor 2 expressed on endothelial cells through a peptide sequence located between amino acids 46 and 64, the so-called basic domain. This peptide mimics many aspects of TAT function when added to endothelial cells, even when expressed in the context of recombinant chimeric proteins. To define the exact sites of interaction between this peptide and VEGF receptor 2 we performed binding studies with recombinant proteins derived from the extracellular ligand binding domain of VEGF receptor 2. These in vitro binding studies showed that the TAT peptide binds with only low specificity to Ig-like domain 3 of the receptor, while VEGF interacts with receptor-derived proteins encompassing at least extracellular domains 1 through 3. The original concept that the angiogenic properties of TAT basic peptide result from specific, high-affinity interaction with VEGF receptor 2 must therefore be revised. Apparently this peptide interacts with cells in multiple ways: by directly activating acidic cell surface-exposed receptors, by releasing extracellular matrix-bound growth factors such as bFGF and VEGF which then bind to their cognate receptors, and by activating intracellular signalling molecules with which basic peptide interacts upon translocation into cells.

Long-term protection against SHIV89.6P replication in HIV-1 Tat vaccinated cynomolgus monkeys

Vaccination with a biologically active Tat protein or tat DNA contained infection with the highly pathogenic SHIV89.6P virus, preventing CD4 T-cell decline and disease onset. Here we show that protection was prolonged, since neither CD4 T-cell decline nor active virus replication was observed in all vaccinated animals that controlled virus replication up to week 104 after the challenge. In contrast, virus persisted and replicated in peripheral blood mononuclear cells and lymph nodes of infected animals, two of which died. Tat-specific antibody, CD4 and CD8 T-cell responses were high and stable only in the animals controlling the infection. In contrast, Gag-specific antibody production and CD4 and CD8 T-cell responses were consistently and persistently positive only in the monkeys that did not control primary virus replication. These results indicate that vaccination with Tat protein or DNA induced long-term memory Tat-specific immune responses and controlled primary infection at its early stages allowing a long-term containment of virus replication and spread in blood and tissues.

Multiple actions of the human immunodeficiency virus type-1 Tat protein on microglial cell functions

The human immunodeficiency virus type-1 (HIV-1) regulatory protein Tat is produced in the early phase of infection and is essential for virus replication. Together with other viral products, Tat has been implicated in the pathogenesis of HIV-1-associated dementia (HAD). As HIV-1 infection in the brain is very limited and macrophage/microglial cells are the only cellular type productively infected by the virus, it has been proposed that many of the viral neurotoxic effects are mediated by microglial products. We and others have shown that Tat affects the functional state of microglial cells, supporting the hypothesis that activated microglia play a role in the neuropathology associated with HIV-1 infection. This review describes the experimental evidence indicating that Tat stimulates microglia to synthesize potentially neurotoxic molecules, including proinflammatory cytokines and free radicals, and interferes with molecular mechanisms controlling cAMP levels, intracellular [Ca2+], and ion channel expression.

Human immunodeficiency virus type 1 Tat increases the expression of cleavage and polyadenylation specificity factor 73-kilodalton subunit modulating cellular and viral expression

The human immunodeficiency virus type 1 (HIV-1) Tat protein, which is essential for HIV gene expression and viral replication, is known to mediate pleiotropic effects on various cell functions. For instance, Tat protein is able to regulate the rate of transcription of host cellular genes and to interact with the signaling machinery, leading to cellular dysfunction. To study the effect that HIV-1 Tat exerts on the host cell, we identified several genes that were up- or down-regulated in tat-expressing cell lines by using the differential display method. HIV-1 Tat specifically increases the expression of the cleavage and polyadenylation specificity factor (CPSF) 73-kDa subunit (CPSF3) without affecting the expression of the 160- and 100-kDa subunits of the CPSF complex. This complex comprises four subunits and has a key function in the 3'-end processing of pre-mRNAs by a coordinated interaction with other factors. CPSF3 overexpression experiments and knockdown of the endogenous CPSF3 by mRNA interference have shown that this subunit of the complex is an important regulatory protein for both viral and cellular gene expression. In addition to the known CPSF3 function in RNA polyadenylation, we also present evidence that this protein exerts transcriptional activities by repressing the mdm2 gene promoter. Thus, HIV-1-Tat up-regulation of CPSF3 could represent a novel mechanism by which this virus increases mRNA processing, causing an increase in both cell and viral gene expression.

Multiple effects of HIV-1 trans-activator protein on the pathogenesis of HIV-1 infection

The HIV-1 trans-activator (Tat) protein is proposed as an important factor in the complex HIV-induced pathogenesis of AIDS. In this paper, multiple effects of this viral protein are described. Originally discovered as an intracellular activator of HIV-1 transcription, Tat was found to regulate viral reverse transcription as well. Trans-activator was found to be secreted by HIV-infected cells and taken up by neighbouring cells. In this way, Tat is able to affect both infected and uninfected cells. Intracellularly, Tat can deregulate the expression of several heterologous cellular and viral genes. Extracellular Tat can contribute to the spreading of HIV-1 and immunosuppression of uninfected cells. Finally, there is evidence that exogenous Tat is involved in AIDS-associated pathologies such as Kaposi's sarcoma and HIV-associated dementia. These capacities together accelerate the progression towards AIDS and make Tat an interesting candidate as a constituent of an anti-AIDS vaccine.

Interaction between HIV-1 Tat and pRb2/p130: a possible mechanism in the pathogenesis of AIDS-related neoplasms

Tat protein is an early nonstructural protein necessary for virus replication, which is secreted by infected cells and taken up by uninfected cells. Extensive evidence indicates that Tat may be a cofactor in the development of AIDS-related neoplasms. The molecular mechanism underlying Tat's oncogenic activity may include deregulation of cellular genes. Among these genes, it has recently been shown that pRb2/p130 oncosuppressor protein is one of the targets in the interaction between HIV gene product Tat and host proteins. However, whether the HIV-1 gene product Tat may inactivate the oncosuppressive function of pRb2/p130 has not yet been elucidated. Here, we show that mRNA levels of pRb2/p130 increase in the presence of Tat, whereas no change in the phosphorylation status of pRb2/p130 is observed. In addition, Tat can inhibit the growth control activity exerted by pRb2/p130 in the T98G cell line. Finally, Tat does not compete with E2F-4 in binding to pRb2/p130. The interaction between Tat and pRb2/p130 seems to result in the deregulation of the control exerted by pRb2/p130 on the cell cycle. Taken together, these results open a window on the role of pRb2/p130 in AIDS-related oncogenesis.

Pathologic aspects of AIDS malignancies

Since the emergence of the HIV pandemic, a close association between HIV infection and the development of a selected group of cancers has been acknowledged. The introduction of highly active antiretroviral therapy, however, has had a dramatic impact on the incidences of several AIDS-defining malignancies. This suggests the possibility of a direct and indirect role of HIV in HIV-related tumor genesis. The aim of this paper is to review the pathology of AIDS-related malignancies, taking into account the pathogenetic mechanisms and their potential for improving the treatment of these tumors.

Mucosal delivery of the human immunodeficiency virus-1 Tat protein in mice elicits systemic neutralizing antibodies, cytotoxic T lymphocytes and mucosal IgA

Human immunodeficiency virus (HIV)-1 Tat protein induces protection in non-human primates upon systemic vaccination. In view of the design of mucosal vaccines against HIV-1 we studied the immune response to native Tat (aa 1-86) in mice following intranasal delivery of the protein with two mucosal adjuvants, Escherichia coli heat-labile enterotoxin (LT) and LT-R72, a non-toxic mutant of LT. Immunization with Tat and the two adjuvants induced in BALB/c but not in C57BL/6 mice high and persistent levels of serum IgG and secretory IgA in vaginal and intestinal fluids. Mice sera neutralized Tat and recognized two epitopes mapping in the regions 1-20 and 46-60. Furthermore, their splenocytes proliferated and secreted IFN-gamma and IL-6 in response to Tat. Finally, CTLs were also elicited and they recognized an epitope localized within aa 11-40 of Tat.

The endocannabinoid system protects rat glioma cells against HIV-1 Tat protein-induced cytotoxicity. Mechanism and regulation

Cannabinoids modulate nitric oxide (NO) levels in cells of the central nervous system. Here we studied the effect of cannabinoid CB(1) and CB(2) receptor agonists on the release of NO and cell toxicity induced by the human immuno-deficiency virus-1 Tat protein (HIV-1 Tat) in rat glioma C6 cells. The CB(1) and CB(2) agonist WIN 55,212-2 inhibited the expression of inducible NO synthase (iNOS) and NO release caused by treatment of C6 cells with HIV-1 Tat and interferon-gamma (IFN-gamma). The effect of WIN 55,212-2 was uniquely due to CB(1) receptors, as shown by experiments carried out with selective CB(1) and CB(2) receptor agonists and antagonists. CB(1) receptor stimulation also inhibited HIV-1 Tat + IFN-gamma-induced and NO-mediated cell toxicity. Moreover, cell treatment with HIV-1 Tat + IFN-gamma induced a significant inhibition of CB(1), but not CB(2), receptor expression. This effect was mimicked by the NO donor GSNO, suggesting that the inhibition of CB(1) expression was due to HIV-1 Tat + IFN-gamma-induced NO overexpression. HIV-1 Tat + IFN-gamma treatment also induced a significant inhibition of the uptake of the endocannabinoid anandamide by C6 cells with no effect on anandamide hydrolysis. These findings show that the endocannabinoid system, through the modulation of the l-arginine/NO pathway, reduces HIV-1 Tat-induced cytotoxicity, and is itself regulated by HIV-1 Tat.

Human immunodeficiency virus type 1 (HIV-1) tat induces nitric-oxide synthase in human astroglia

Human immunodeficiency virus type 1 (HIV-1) infection is known to cause neuronal injury and dementia in a significant proportion of patients. However, the mechanism by which HIV-1 mediates its deleterious effects in the brain is poorly defined. The present study was undertaken to investigate the effect of the HIV-1 tat gene on the expression of inducible nitric-oxide synthase (iNOS) in human U373MG astroglial cells and primary astroglia. Expression of the tat gene as RSV-tat but not that of the CAT gene as RSV-CAT in U373MG astroglial cells led to the induction of NO production and the expression of iNOS protein and mRNA. Induction of NO production by recombinant HIV-1 Tat protein and inhibition of RSV-tat-induced NO production by anti-Tat antibodies suggest that RSV-tat-induced production of NO is dependent on Tat and that Tat is secreted from RSV-tat-transfected astroglia. Similar to U373MG astroglial cells, RSV-tat also induced the production of NO in human primary astroglia. The induction of human iNOS promoter-derived luciferase activity by the expression of RSV-tat suggests that RSV-tat induces the transcription of iNOS. To understand the mechanism of induction of iNOS, we investigated the role of NF-kappaB and C/EBPbeta, transcription factors responsible for the induction of iNOS. Activation of NF-kappaB as well as C/EBPbeta by RSV-tat, stimulation of RSV-tat-induced production of NO by the wild type of p65 and C/EBPbeta, and inhibition of RSV-tat-induced production of NO by deltap65, a dominant-negative mutant of p65, and deltaC/EBPbeta, a dominant-negative mutant of C/EBPbeta, suggest that RSV-tat induces iNOS through the activation of NF-kappaB and C/EBPbeta. In addition, we show that extracellular signal-regulated kinase (ERK) but not that p38 mitogen-activated protein kinase (MAPK) is involved in RSV-tat induced production of NO. Interestingly, PD98059, an inhibitor of the ERK pathway, and deltaERK2, a dominant-negative mutant of ERK2, inhibited RSV-tat-induced production of NO through the inhibition of C/EBPbeta but not that of NF-kappaB. This study illustrates a novel role for HIV-1 tat in inducing the expression of iNOS in human astrocytes that may participate in the pathogenesis of HIV-associated dementia.

HIV-1 Tat-based vaccines: from basic science to clinical trials

Vaccination against human immunodeficiency virus (HIV)-1 infection requires candidate antigen(s) (Ag) capable of inducing an effective, broad, and long-lasting immune response against HIV-1 despite mutation events leading to differences in virus clades. The HIV-1 Tat protein is more conserved than envelope proteins, is essential in the virus life cycle and is expressed very early upon virus entry. In addition, both humoral and cellular responses to Tat have been reported to correlate with a delayed progression to disease in both humans and monkeys. This suggested that Tat is an optimal target for vaccine development aimed at controlling virus replication and blocking disease onset. Here are reviewed the results of our studies including the effects of the Tat protein on monocyte-derived dendritic cells (MDDCs) that are key antigen-presenting cells (APCs), and the results from vaccination trials with both the Tat protein or tat DNA in monkeys. We provide evidence that the HIV-1 Tat protein is very efficiently taken up by MDDCs and promotes T helper (Th)-1 type immune responses against itself as well as other Ag. In addition, a Tat-based vaccine elicits an immune response capable of controlling primary infection of monkeys with the pathogenic SHIV89.6P at its early stages allowing the containment of virus spread. Based on these results and on data of Tat conservation and immune cross-recognition in field isolates from different clades, phase I clinical trials are being initiated in Italy for both preventive and therapeutic vaccination.

Infection of simian B lymphoblastoid cells with simian immunodeficiency virus is associated with upregulation of CD23 and CD40 cell surface markers

Simian immunodeficiency virus (SIV) as well as human immunodeficiency virus (HIV) induce polyclonal B-cell activation and are associated with the appearance of lymphomas in their respective hosts in either the presence or the absence of other co-infecting viruses such as Epstein-Barr virus (EBV). However, the pathogenic role of these retroviruses in the development of lymphoproliferative disorders remains poorly understood. To explore the virus-B-cell interactions, two immortalized lymphoblastoid B-cell lines (SL-P1 and SL-691) were established from cynomolgus monkeys that were naturally co-infected with a simian type D retrovirus-2 (SRV-2) and with the herpes virus Macaca fascicularis (HVMF-1). We addressed their susceptibility to SIV infection and the phenotypic modifications associated with SIV infection. In response, both cell lines (1) were co-infected with HVMF-1 (latent infection) and with SRV-2 (productive infection), (2) had a transformed phenotype because they did not require exogenous growth factors, and (3) when injected into mice with severe combined immunodeficiency (SCID), generated serially transplantable tumors. The B-cell origin of SL cells was demonstrated by the presence of rearrangements of the IgH gene and by the expression of typical B-cell lineage markers, such as CD20. SL-P1 and SL-691 could be discriminated on the basis of different expressions of CD23 and CD40 and of kappa- and lambda-chains. Most importantly, SL-691 cells, but not SL-P1 cells, were susceptible to chronic noncytolytic SIV infection. This infection occurred in a CD4/CCR5/CXCR4-independent manner and was associated with the upregulated expression of CD23 and CD40 cell surface markers. In addition, CD20 expression, which progressively disappeared in SL-691 noninfected cells, was maintained in the SIV-infected counterpart. These findings support the hypothesis that SIV induce phenotypic perturbations in B cells that might eventually contribute to the development of lymphoproliferative disease.

Modulation of human immunodeficiency virus 1 replication by interferon regulatory factors

Transcription of the human immunodeficiency virus (HIV)-1 is controlled by the cooperation of virally encoded and host regulatory proteins. The Tat protein is essential for viral replication, however, expression of Tat after virus entry requires HIV-1 promoter activation. A sequence in the 5' HIV-1 LTR, containing a binding site for transcription factors of the interferon regulatory factors (IRF) family has been suggested to be critical for HIV-1 transcription and replication. Here we show that IRF-1 activates HIV-1 LTR transcription in a dose-dependent fashion and in the absence of Tat. This has biological significance since IRF-1 is produced early upon virus entry, both in cell lines and in primary CD4+ T cells, and before expression of Tat. IRF-1 also cooperates with Tat in amplifying virus gene transcription and replication. This cooperation depends upon a physical interaction that is blocked by overexpression of IRF-8, the natural repressor of IRF-1, and, in turn is released by overexpression of IRF-1. These data suggest a key role of IRF-1 in the early phase of viral replication and/or during viral reactivation from latency, when viral transactivators are absent or present at very low levels, and suggest that the interplay between IRF-1 and IRF-8 may play a key role in virus latency.

Native HIV-1 Tat protein targets monocyte-derived dendritic cells and enhances their maturation, function, and antigen-specific T cell responses

Vaccination of cynomolgus monkeys with the biologically active HIV-1 Tat protein induces specific Th1 responses, including CTLs. Similar responses are also induced by vaccination with tat DNA, but not by vaccination with inactivated Tat or Tat peptides. This suggested that the native Tat protein may act differently on APC as compared with inactivated Tat or peptide Ag. In this study, we show that biologically active Tat is very efficiently taken up by monocyte-derived dendritic cells (MDDC) in a time (within minutes)- and dose-dependent (starting from 0.1 ng/ml) fashion, whereas uptake is very poor or absent with other APC, including T cell blasts and B lymphoblastoid cell lines. Although maturation of MDDC reduces their pino/phagocytic activity, mature MDDC take up Tat much more efficiently than immature cells. In addition, Tat uptake is abolished or greatly hampered by oxidation/inactivation of the protein or by performing the experiments at 4 degrees C, suggesting that MDDC take up native Tat by a receptor-mediated endocytosis. After uptake, active Tat protein induces up-regulation of MHC and costimulatory molecules and production of IL-12, TNF-alpha, and beta chemokines, which drive Th1-type immune response. In contrast, these effects are lost by oxidation and inactivation of the protein. Finally, native Tat enhances Ag presentation by MDDC, increasing Ag-specific T cell responses. These data indicate that native Tat selectively targets MDDC, is taken up by these cells via specialized pathways, and promotes their maturation and Ag-presenting functions, driving Th1-type immune responses. Thus, Tat can act as both Ag and adjuvant, capable of driving T cell-mediated immune responses.

IRF regulation of HIV-1 long terminal repeat activity

Interferon (IFN) regulatory factors (IRF) constitute a family of transcriptional activators and repressors implicated in multiple biologic processes, including regulation of immune responses and host defense, cytokine signalling, cell growth regulation, and hematopoietic development. All members are characterized by well-conserved DNA binding domains at the N-terminal region that recognize similar DNA sequences termed IRF-binding element/IFN-stimulated response element (IRF-E/ISRE) present on the promoter of the IFN-alpha/beta genes and of some IFN-stimulated genes (ISG). Recently, a sequence homologous to the ISRE has been identified downstream of the 5' human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR). This sequence is a binding site for IRF-1 and IRF-2. Deletion of the LTR-ISRE results in impaired LTR promoter activity and decreased synthesis of viral RNA and proteins. Here, we briefly summarize characteristics of IRF-1 and IRF-2 binding to the HIV-1 LTR-ISRE and the data obtained to date on the functionality of this cis-element and on the role of IRF in the regulation of HIV-1 LTR transcriptional activity.

Human immunodeficiency virus type-1 Tat protein induces nuclear factor (NF)-kappaB activation and oxidative stress in microglial cultures by independent mechanisms

We have extended our previous findings and shown that human immunodeficiency virus Tat protein, in addition to nitric oxide (NO), stimulated rat microglial cultures to release pro-inflammatory cytokine interleukin-1beta and tumour necrosis factor-alpha in a nuclear factor (NF)-kappaB-dependent manner. At the same time, Tat stimulated the accumulation of free radicals, as indicated by the increased levels of isoprostane 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)), a reliable marker of lipid peroxidation and oxidative stress, by a mechanism unrelated to NF-kappaB activation. The presence of free radical scavengers abrogated Tat-induced 8-epi-PGF(2alpha) accumulation without affecting NO and cytokine production. Consistently, Tat-induced IkappaBalpha degradation - an index of NF-kappaB activation - was not affected by free radical scavengers, but was prevented by an NF-kappaB-specific inhibitor. Our observations indicate that NF-kappaB plays a key role in Tat-dependent microglial activation, and that oxidative stress and NF-kappaB activation induced by Tat occur by independent mechanisms.

A Drosophila model of HIV-Tat-related pathogenicity

To analyze the mechanism of Tat-mediated HIV pathogenicity, we produced a Drosophila melanogaster strain transgenic for HIV-tat gene and induced the expression of the protein during Drosophila development. By in vitro and in vivo experiments, we demonstrated that Tat specifically binds to tubulin via the MAP-binding domain of tubulin, and that this interaction delays the polymerization of tubulin and induces a premature stop to microtubule-dependent cytoplasmic streaming. The delay in the polymerization of microtubules, the tracks for the transport of the axes determinants, alters the positioning of the dorso-ventral axis as shown by the mislocalization of Gurken and Kinesin in oocyte of Drosophila after Tat induction. These results validate the use of Drosophila as a tool to study the molecular mechanism of viral gene products and suggest that Tat-tubulin interaction is responsible for neurodegenerative diseases associated with AIDS.

9-Nitrocamptothecin inhibits HIV-1 replication in human peripheral blood lymphocytes: a potential alternative for HIV-infection/AIDS therapy

The ability of the anti-cancer drug, 9-Nitrocamptothecin (9NC), to inhibit replication of HIV-1 in clinically relevant primary lymphocytic cells was studied. Primary peripheral blood lymphocytes (PBLs) from a non-infected donor were freshly infected with HIV-1 and treated with 9NC by using three different treatment schedules. Cells were monitored for cytotoxicity by the XTT metabolic cell proliferation assay and a sensitive flow cytometric assay that was capable of measuring cell cycle changes and apoptosis. 9NC inhibited replication of HIV-1 in PBLs by greater than 95% in a dose-dependent manner as measured by the level of extracellular HIV-1 p24 release. Similar results were observed, whether 9NC was applied in a single, double, or triple dose regimen. Minimal cytotoxicity was observed for both non-infected and infected PBLs, as determined by the XTT assay. Moreover, 9NC induced apoptosis within 24 hours of drug treatment in freshly infected, but not non-infected, PBLs. The data showed that 9NC reduced replication of HIV-1 in primary human lymphocytes; thus, it indicates the potential clinical utility of this drug as an alternative or adjunct therapy for HIV-infection/AIDS.

Characterization of HIV-1 Tat proteins mutated in the transactivation domain for prophylactic and therapeutic application

Previous work from our group showed that genetic immunization of mice with HIV-1 tat genes (tat22 and tat22/37), encoding Tat proteins mutated in the transactivation domain and lacking Tat-transactivating activity, evoke an immune response to wild-type Tat, both humoral and cellular. In the present work we report that the mutated Tat proteins localize within the cells, are released and taken up by the cells in a fashion similar to wild-type Tat. Moreover, the exogenous mutated Tat proteins interfere with the transactivating function of extracellular wild-type Tat. These results support the notion that tat22 and tat22/37 genes may represent good candidates for the development of an anti-HIV-1 vaccine, especially for HIV-1 infected patients.

Vaccination with DNA containing tat coding sequences and unmethylated CpG motifs protects cynomolgus monkeys upon infection with simian/human immunodeficiency virus (SHIV89.6P)

Recent evidence suggests that a CD8-mediated cytotoxic T cell response against the Tat protein of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) controls primary infection after pathogenic virus challenge, and correlates with the status of long-term nonprogressor in humans. Due to the presence of unmethylated CpG sequences, DNA vaccination can boost the innate immunity driving more potent T cell-mediated immune responses. Therefore, cynomolgus monkeys were vaccinated with a tat-expressing vector containing defined unmethylated CpG sequences (pCV-tat). Here it is shown that the intramuscular inoculation of the pCV-tat contained primary infection with the highly pathogenic SHIV89.6P virus preventing the CD4(+) T cell decline in all the vaccinated monkeys. Undetectable virus replication and negative virus isolation correlated in all cases with the presence of anti-Tat CTLs. However, a CD8-mediated non cytolytic antiviral activity was also present in all protected animals. Of note, this activity was absent in the controls but was present in the monkey inoculated with the CpG-rich vector alone that was partially protected against viral challenge (i.e. no virus replication but positive virus isolation). These results suggest that a CTL response against Tat protects against primary infection by blocking virus replication at its early stage, in the absence of sterilizing immunity. Nevertheless, the boost of the innate immunity by CpG sequences can contribute to this protection both by driving more potent CTL responses and by inducing other CD8-mediated antiviral activities. Thus, the CpG-rich tat DNA vaccine may represent a promising candidate for preventive and therapeutic vaccination against AIDS.

Immunization with a novel HIV-1-Tat multiple-peptide conjugate induces effective immune response in mice

We report here a novel, highly immunogenic synthetic, multiple-peptide conjugate comprising functional domains Tat(21-40) and Tat(53-68) from HIV-1 group M plus Tat(9-20) from HIV-1 group O of the HIV-Tat protein (HIV-1-Tat-MPC). Vaccination of mice with HIV-1-Tat-MPC induced an effective immune response to all three functional domains. The anti-HIV-1-Tat-MPC antibodies efficiently inhibited Tat-induced viral activation in monocytes infected with HIV(Ba-L) as well as with various clinical HIV-1 isolates, and reduced Tat-mediated cytopathicity in infected cells by 60-75%. Our results indicate that anti-HIV-1-Tat-MPC antibodies inhibit viral pathogenesis, possibly by blocking functional determinants of Tat and disrupting autocrine and paracrine actions of secreted Tat protein. This epitope-specific, synthetic Tat construct may, therefore, provide a subunit AIDS vaccine candidate for inducing an effective immunoprophylaxis response to reduce progression of HIV infection.

Analysis of HIV-1 Tat effects in Xenopus laevis embryos

Tat is one of the regulatory proteins of the HIV-1 virus. To date, besides the transactivation activity, a myriad of effects exerted by HIV-1 Tat on cellular and viral genes have been observed. The present study investigated the in vivo effects of HIV-1 Tat protein in the Xenopus embryo. We adopted the Xenopus system since expression of putative regulatory factors in the embryo has been widely used as a quick and effective first screen for protein function. Xenopus' early development is well characterized by stage-specific phenotypes, therefore, an in vivo HIV-1 Tat-mediated aberrant phenotype can easily be detected and analyzed. HIV-1 Tat protein expression through injection of synthetic mRNA into zygotes produced a marked delay in gastrulation leading to altered specification of the anterior-posterior axis and to partial or total loss of anterior structures. HIV-1 Tat effects resulted in a general suppression of gene expression, including that of Xbra and gsc, two early genes whose expression is required for proper gastrulation. The specificity of Tat effects was demonstrated by injecting a 'loss of function' mutant (Tat-C37S), lacking a single cysteine residue, which did not yield any effect. Both Tat and Tat-C37S were found to be localized mainly in the nucleus. The importance of subcellular targeting for the effects caused by HIV-1 Tat was demonstrated by injecting a second mutant (Tat-BDM), carrying an altered nuclear localization signal sequence. The Tat-BDM protein localized in the cytoplasm and accumulated at the cell membrane. Embryos injected with Tat-BDM mRNA did not develop beyond gastrulation. The importance of proper protein conformation and subcellular localization in determining Tat effects is discussed.