Regulation of human immunodeficiency virus infection: implications for pathogenesis

The next generation of HIV/AIDS drugs: novel and developmental antiHIV drugs and targets

There are presently 42 million people worldwide living with HIV/AIDS, the majority of which have limited access to antiretrovirals. Even if worldwide penetration was possible, our current chemotherapeutic strategies still suffer from issues of cost, patient compliance, deleterious acute and chronic side effects, emerging single and multidrug resistance, and generalized treatment and economic issues. Even our best antiretroviral therapeutic strategy, highly active antiretroviral therapy (HAART), falls short of completely suppressing HIV replication. Therefore, expansion of current therapeutic options by discovering new antiretrovirals and targets will be critical in the coming years. This review addresses the current status of reverse transcriptase and protease inhibitor development, and summarizes the progress in emerging classes of HIV inhibitors, including entry (T-20, T-1249), coreceptor (SCH-C, SCH-D), integrase (beta-Diketos) and p7 nucleocapsid Zn finger inhibitors (thioesters and PATEs). In addition, the processes of virus entry, PIC transport to the nucleus, HIV interaction with nuclear pores, Tat function, Rev function and virus budding (Tsg101 and ubiquitination) are examined, and proof of concept inhibitors and potential antiviral targets discussed.

Use of ATP analogs to inhibit HIV-1 transcription

Human immunodeficiency virus type 1 (HIV-1) is the etiological agent of AIDS. Chronic persistent infection is an important reason for the presence of "latent cell populations" even after Anti-Retroviral Therapy (ART). We have analyzed the effect of ATP analogs in inhibiting cdk9/T1 complex in infected cells. A third generation drug named CR8#13 is an effective inhibitor of Tat activated transcription. Following drug treatment, we observed a decreased loading of cdk9 onto the HIV-1 DNA. We found multiple novel cdk9/T1 complexes present in infected and uninfected cells with one complex being unique to infected cells. This complex is sensitive to CR8#13 in kinase assays. Treatment of PBMC with CR8#13 does not kill infected cells as compared to Flavopiridol. Interestingly, there is a difference in sensitivity of various clades to these analogs. Collectively, these results point to targeting novel complexes for inhibition of cellular proteins that are unique to infected cells.

Inhibition of human immunodeficiency virus type-1 by cdk inhibitors

Current therapy for human immunodeficiency virus (HIV-1) infection relies primarily on the administration of anti-retroviral nucleoside analogues, either alone or in combination with HIV-protease inhibitors. Although these drugs have a clinical benefit, continuous therapy with the drugs leads to drug-resistant strains of the virus. Recently, significant progress has been made towards the development of natural and synthetic agents that can directly inhibit HIV-1 replication or its essential enzymes. We previously reported on the pharmacological cyclin-dependent kinase inhibitor (PCI) r-roscovitine as a potential inhibitor of HIV-1 replication. PCIs are among the most promising novel antiviral agents to emerge over the past few years. Potent activity on viral replication combined with proliferation inhibition without the emergence of resistant viruses, which are normally observed in HAART patients; make PCIs ideal candidates for HIV-1 inhibition. To this end we evaluated twenty four cdk inhibitors for their effect on HIV-1 replication in vitro. Screening of these compounds identified alsterpaullone as the most potent inhibitor of HIV-1 with activity at 150 nM. We found that alsterpaullone effectively inhibits cdk2 activity in HIV-1 infected cells with a low IC₅₀ compared to control uninfected cells. The effects of alsterpaullone were associated with suppression of cdk2 and cyclin expression. Combining both alsterpaullone and r-roscovitine (cyc202) in treatment exhibited even stronger inhibitory activities in HIV-1 infected PBMCs.

Molecular modeling of the oxidized form of nuclear factor-κB suggests a mechanism for redox regulation of DNA binding and transcriptional activation

NF-kappa B is an important transcriptional regulator of numerous cellular genes, as well as viruses such as HIV-1. Oxidative stimuli in the cytosol are associated with nuclear translocation of NF-kappa B, whereas in the nucleus, reductive activation by thioredoxin is required for NF-kappa B to bind to DNA and activate target genes. Experimental structures of the reduced form of NF-kappa B bound to its DNA targets are available, from which we have modeled the oxidized form of NF-kappa B homodimer by removal of bound DNA, and modification via a hinge movement of a linker between the dimerization and DNA-binding domains of each subunit. These torsional motions enabled the formation of an inter-subunit disulfide bond between the Cys62 residues of each monomer; the resulting structure was refined using molecular dynamics simulation. The final model of oxidized, disulfide-bridged NF-kappaB is more compact than the open, reduced form. This may facilitate its nuclear translocation through small pores in the nuclear envelope, in response to oxidative stimuli in the cytosol. Furthermore, the inter-subunit disulfide blocks DNA from entering the active site of the oxidized dimer, explaining why subsequent reduction to the thiol form in the nucleus is essential for DNA binding and transcriptional activation to occur.

On the Role of Interferon Regulatory Factors in HIV-1 Replication

Interferons (IFNs) are pleiotropic cytokines that possess several biological activities and play a central role in basic and applied research as mediators of antiviral and antigrowth responses, modulators of the immune system, and therapeutic agents against viral diseases and cancer. Interferon regulatory factors (IRFs) have been identified together with signal transducers and activators of transcription (STAT) from studies on the type I IFN as well as IFN-stimulated (ISG) gene regulation and signaling. IRFs constitute a family of transcriptional activators and repressors implicated in multiple biological processes including regulation of immune responses and host defence, cytokine signaling, cell growth regulation, and hematopoietic development. All members share a well-conserved DNA binding domain at the NH(2)-terminal region that recognizes similar DNA sequences, termed IRF element (IRF-E)/interferon-stimulated response element (ISRE), present on the promoter of target genes. Recently, a sequence homologous to the ISRE has been identified downstream from 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. Here we briefly summarize the role of IRFs in the regulation of HIV-1 LTR transcriptional activity and virus replication. The overall effect of IRFs on HIV-1 replication will also be discussed in the context of strategies carried out by the virus to counteract the IFN-mediated host defences both in active replication and during the establishment of viral latency.

An HIV-1 encoded peptide mimics the DNA binding loop of NF-kappaB and binds thioredoxin with high affinity

Pro-fs is a human immunodeficiency virus type 1 (HIV-l)-encoded putative selenoprotein, predicted by a theoretical analysis of the viral genome; it is potentially expressed by a -1 frameshift from the protease coding region. Pro-fs has significant sequence similarity to the DNA binding loop of nuclear factor kappa B (NF-kappaB), which is known to bind thioredoxin (Trx). We hypothesize that the putative HIV-1 pro-fs gene product functions by mimicry of NF-kappaB via binding to Trx. The hypothesis was tested in vitro by co-immunoprecipitation and GST-pull down assays, using a purified mutant pro-fs protein, in which the two potential selenocysteine residues were mutated to cysteines, in order to permit expression in bacteria. Both experiments showed that pro-fs binds to human wild type Trx (Trx-wt) with high affinity. Mutation of the two conserved cysteine residues in the Trx active site redox center to serine (Ser) (Trx-CS) weakened but failed to abolish the interaction. In pro-fs-transfected 293T cells, using confocal microscopy and fluorescence resonance energy transfer (FRET), we have observed that pro-fs localizes in cell nuclei and forms oligomers. Upon stimulation by phorbol 12-myristate 13-acetate (PMA), Trx translocates into cell nuclei. Significant FRET efficiency was detected in the nuclei of PMA-stimulated 293T cells co-expressing fluorescence-tagged pro-fs and Trx-wt or Trx-CS. These results indicate that in living cells the double cysteine mutant of pro-fs binds to both Trx and Trx-CS with high affinity, suggesting that Trx-pro-fs binding is a structurally-specific interaction, involving more of the Trx molecule than just its active site cysteine residues. These results establish the capacity for functional mimicry of the Trx binding ability of the NF-kappaB/Rel family of transcription factors by the putative HIV-1 pro-fs protein.

Analysis of the signal transduction pathway leading to human immunodeficiency virus-1-induced interferon regulatory factor-1 upregulation

Interferon (IFN) regulatory factors (IRFs) constitute a family of transcriptional activators and repressors involved in the regulation of immune system, host defense, and cell growth. All members share conserved DNA-binding domains that recognize DNA sequences termed IRF-binding elements/IFN-stimulated response elements (IRF-E/ISRE) present on the promoter of IFN-alpha/beta and IFN-stimulated genes. An ISRE has been identified downstream of the transcription start site of the long terminal repeat (LTR) of human immunodeficiency virus-1 (HIV-1). Our previous results showed that among the IRF factors, IRF-1 is able to stimulate HIV-1 LTR transcription and its expression is induced by HIV-1, early, upon infection and before the expression of Tat. In this study we investigated the signal transduction pathway leading to HIV-1-induced IRF-1 expression. Key IRF-1 promoter elements that mediate the activation of transcription upon induction by inflammatory cytokines are IFN-gamma-activated sequences that bind members of the signal transducer and activator of transcription (STAT) family and binding sites for nuclear factor kappaB (NF-kappaB). Both STAT-1 and NF-kappaB activation were examined to determine putative molecular targets whose inhibition resulted in the inhibition of HIV-1 replication. The results show that at early time points after HIV-1 infection, NF-kappaB but not STAT-1 is activated. Moreover, a significant decrease in HIV-1 replication was observed upon de novo infection of Jurkat T cells expressing an NF-kappaB super-repressor (IkappaB-alpha 2NDelta4). These results suggest that in early phases of HIV-1 infection, before detectable cytokine production, NF-kappaB seems responsible for HIV-1-induced IRF-1 expression.

Repression of the human immunodeficiency virus type-1 long terminal repeat by the c-Myc oncoprotein

The effect of trans-acting factors on cis-acting DNA elements on the HIV-1 promoter are the principal determinant regulating transcriptional activation and repression. Host factors that limit viral replication can contribute to the emergence and maintenance of proviral reservoirs. The current paradigm is that this sub-population of latently infected cells confers a biological advantage to the virus by facilitating evasion of immunologic responses and therapeutic strategies resulting in life-long and persistent infection. In this report, we show that ectopic expression of the nuclear phosphoprotein, c-Myc can inhibit HIV-1 gene expression and virus production in CD4+ T-lymphocytes. The effect exerted does not appear to involve other known functions of c-Myc such as proliferation, or apoptosis. The mechanism does implicate c-Myc in a direct role. We have found evidence that c-Myc can specifically recognize the HIV-1 initiator element surrounding the start site of transcription and linker scanning mutagenesis experiments confirmed a loss of c-Myc-mediated repression in the absence of this region. Moreover, we show that c-Myc can interact with the initiator binding proteins YY-1 and LBP-1 and can cooperate with these factors to synergistically repress HIV-1 LTR transcription. Taken together, these results indicate that c-Myc is an important regulator of HIV-1 transcription that potentially contributes to the latent proviral state.

Natural bovine lentiviral type 1 infection in Holstein dairy cattle. I. Clinical, serological, and pathological observations

Clinical, serological, and pathological abnormalities observed in Holstein cows naturally infected with bovine lentivirus 1 bovine immunodeficiency virus (BIV) and other infections were progressive and most commonly associated with weight loss, lymphoid system deficiency, and behavioral changes. Clinical evidence of meningoencephalitis was dullness, stupor, and occasional head or nose pressing postures. The polymerase chain reactions associated the BIV provirus with the lesions in the central nervous system and lymphoid tissues. Multiple concurrent infections developed in retrovirally infected cows undergoing normal stresses associated with parturition and lactation. A major functional correlate of the lymphoreticular alterations was the development of multiple secondary infections which failed to resolve after appropriate antibacterial therapy. The chronic disease syndrome in dairy cows associated with BIV may be useful as a model system for investigation of the pathogenesis of the nervous system lesions and lymphoid organ changes that occur in humans with lentiviral infection.

Umbilical Cord Blood Mononuclear Cell HIV-1 LTR Binding Activities

Vertically transmitted HIV disease constitutes a significant problem in pediatrics. In order to characterize some of the possible host factors involved in HIV replication in fetuses and newborns, we surveyed the HIV-1 LTR binding factors present in nuclear extracts from cord blood mononuclear cells. A series of electrophoretic mobility shift assays (EMSAs) showed that protein extracts from cord blood interacted with several regions of the HIV LTR. The most prominent binding activities involved the NF-kB sites, but other regions of the LTR also showed factor binding with the cord blood extracts. Some of these cord blood extract binding activities displayed qualitative differences when compared to adult peripheral blood mononuclear cell extracts in EMSA and UV cross-linking studies. Transient transfection experiments indicated that the NF-kB and Sp1 sequences were important for wild type levels of expression in cord blood cells, but that additional sequences 5' to the NF-kB sites also contributed activity. Thus, factors that interact with many of the well-known HIV LTR regulatory sites are present in cord blood cells. However, certain qualitative differences distinguished cord blood and adult peripheral blood binding activities and these may contribute to pathogenesis of HIV infection in neonates.

HIV-1 Tat-associated RNA polymerase C-terminal domain kinase, CDK2, phosphorylates CDK7 and stimulates Tat-mediated transcription

HIV-1 gene expression is regulated by a viral transactivator protein (Tat) which induces transcriptional elongation of HIV-1 long tandem repeat (LTR). This induction requires hyperphosphorylation of the C-terminal domain (CTD) repeats of RNA polymerase II (Pol II). To achieve CTD hyperphosphorylation, Tat stimulates CTD kinases associated with general transcription factors of the promoter complex, specifically TFIIH-associated CDK7 and positive transcription factor b-associated CDK9 (cyclin-dependent kinase 9). Other studies indicate that Tat may bind an additional CTD kinase that regulates the target-specific phosphorylation of RNA Pol II CTD. We previously reported that Tat-associated T-cell-derived kinase (TTK), purified from human primary T-cells, stimulates Tat-dependent transcription of HIV-1 LTR in vivo [Nekhai, Shukla, Fernandez, Kumar and Lamb (2000) Virology 266, 246-256]. In the work presented here, we characterized the components of TTK by biochemical fractionation and the function of TTK in transcription assays in vitro. TTK uniquely co-purified with CDK2 and not with either CDK9 or CDK7. Tat induced the TTK-associated CDK2 kinase to phosphorylate CTD, specifically at Ser-2 residues. The TTK fraction restored Tat-mediated transcription activation of HIV-1 LTR in a HeLa nuclear extract immunodepleted of CDK9, but not in the HeLa nuclear extract double-depleted of CDK9 and CDK7. Direct microinjection of the TTK fraction augmented Tat transactivation of HIV-1 LTR in human primary HS68 fibroblasts. The results argue that TTK-associated CDK2 may function to maintain target-specific phosphorylation of RNA Pol II that is essential for Tat transactivation of HIV-1 promoter. They are also consistent with the observed cell-cycle-specific induction of viral gene transactivation.

E-state modeling of HIV-1 protease inhibitor binding independent of 3D information

Data for HIV-1 protease inhibitors (in vitro enzyme binding) were used as a training set to develop a QSAR model based on topological descriptors, including two hydrogen E-state indices, along with a molecular connectivity chi and a kappa shape index. A statistically satisfactory four-variable model was obtained for the 32 compounds in the training set, r2 = 0.86, s = 0.60, and q2 = 0.79, without the use of information from 3D geometries or detailed interaction energy calculations. The model was validated through the prediction of 15 compounds in the external test set, yielding a mean absolute error, MAE, = 0.82. Structure interpretation is given for each variable to assist in the design of new compounds. Structure features emphasized in the model include hydrogen bond donating ability, nonpolar groups, skeletal branching, and molecular globularity. On the basis of these statistical criteria, this E-state model may be considered useful for prediction of pIC50 values for new HIV-1 protease inhibitors.

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.

Contribution of immune activation to the pathogenesis and transmission of human immunodeficiency virus type 1 infection

The life cycle of human immunodeficiency virus type 1 (HIV-1) is intricately related to the activation state of the host cells supporting viral replication. Although cellular activation is essential to mount an effective host immune response to invading pathogens, paradoxically the marked systemic immune activation that accompanies HIV-1 infection in vivo may play an important role in sustaining phenomenal rates of HIV-1 replication in infected persons. Moreover, by inducing CD4+ cell loss by apoptosis, immune activation may further be central to the increased rate of CD4+ cell turnover and eventual development of CD4+ lymphocytopenia. In addition to HIV-1-induced immune activation, exogenous immune stimuli such as opportunistic infections may further impact the rate of HIV-1 replication systemically or at localized anatomical sites. Such stimuli may also lead to genotypic and phenotypic changes in the virus pool. Together, these various immunological effects on the biology of HIV-1 may potentially enhance disease progression in HIV-infected persons and may ultimately outweigh the beneficial aspects of antiviral immune responses. This may be particularly important for those living in developing countries, where there is little or no access to antiretroviral drugs and where frequent exposure to pathogenic organisms sustains a chronically heightened state of immune activation. Moreover, immune activation associated with sexually transmitted diseases, chorioamnionitis, and mastitis may have important local effects on HIV-1 replication that may increase the risk of sexual or mother-to-child transmission of HIV-1. The aim of this paper is to provide a broad review of the interrelationship between immune activation and the immunopathogenesis, transmission, progression, and treatment of HIV-1 infection in vivo.

Effect of insulin-like growth factor I on HIV type 1 long terminal repeat-driven chloramphenicol acetyltransferase expression

In this study, we have investigated the ability of insulin-like growth factor I (IGF-I) to inhibit HIV long terminal repeat (LTR)-driven gene expression. Using COS 7 cells cotransfected with tat and an HIV LTR linked to a chloramphenicol acetyltransferase (CAT) reporter, we observed that physiological levels of IGF-I (10(-9) M) significantly inhibited CAT expression in a concentration- and time-dependent manner. IGF-I did not inhibit CAT expression in COS 7 cells transfected with pSVCAT, and did not affect CAT expression in the absence of cotransfection with tat. Transfection of HIV-1 proviral DNA into COS 7 cells +/- IGF-I resulted in a significant decrease (p < 0.05) in infectious virion production. Both IGF-I and Ro24-7429 inhibited LTR-driven CAT expression, while TNF-alpha-enhanced CAT expression was not affected by IGF-I. On the other hand, a plasmid encoding parathyroid hormone-related peptide exhibited dramatic additivity of inhibition of CAT expression in COS 7 cells. Finally, we show that in Jurkat or U937 cells cotransfected with HIVLTRCAT/tat, IGF-I significantly inhibited CAT expression. Further, interleukin 4 showed in U937 cells inhibition of CAT expression that was not additive to IGF-I induced inhibition. Our data demonstrate that IGF-I can specifically inhibit HIVLTRCAT expression. This inhibition may occur at the level of the tat/TAR interaction. Finally, this IGF-I effect is seen in target cell lines and similar paths of inhibition may be involved in the various cell types employed.

Human astrocytes inhibit HIV-1 expression in monocyte-derived macrophages by secreted factors

OBJECTIVE

To determine the effects of primary human fetal and adult astrocytes on HIV-1 replication in monocyte-derived macrophages (MDM).

DESIGN

HIV-1 can infect the brain in the early stage of systemic infection. The HIV-1-associated cognitive/motor complex develops later in the course of the disease, suggesting that brain cells may inhibit the early productive infection and the development of neurological disease. In this study, we established an in-vitro coculture system to determine whether astrocytes can modulate HIV-1 replication in MDM.

METHODS

Elutriated human monocytes were differentiated in culture, then infected with monocyte tropic HIV-1. One day after infection, MDM were co-cultured with primary astrocytes. Reverse transcriptase (RT) activity was used to monitor virus replication. RT-polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and bioassay were used to assess cytokine production.

RESULTS

Primary human astrocytes suppressed HIV-1 replication in MDM via the production of soluble factors. Cytokine inhibitors of HIV-1, such as IFN-gamma, IL-4, IL-10 and IL-13, were not detectable, whereas transforming growth factor beta (TGF-beta) was constitutively produced only in its latent form. Paraformaldehyde-fixed astrocytes, unable to secrete cytokines, failed to inhibit HIV-1. These cells caused enhanced virus replication, however, which correlated with an increase in macrophage colony stimulating factor (M-CSF) production.

CONCLUSIONS

Human astrocytes can increase and decrease HIV-1 expression in MDM. An imbalance between the positive and negative effects of astrocytes may contribute to the expression of virus in the brain, and the development of HIV-1-associated cognitive/motor complex.

Infection of T cell subsets by HIV-1 and the effects of interleukin-12

CD4+ lymphocytes constitute one of the major cell targets for human immunodeficiency virus type 1 (HIV-1) infection. The eventual loss of CD4+ lymphocytes contributes substantially to the pathogenesis of HIV-1 and development of acquired immunodeficiency syndrome (AIDS). CD4+ lymphocytes consist of the subgroups Th1, Th2, and Th0, which differ in their cytokine profile. Th1 cells produce cytokines that favor cell-mediated immune responses, whereas Th2 cells produce cytokines that favor humoral immunity. Th0 cells are precursors to the Th1 and Th2 subsets. A shift from a Th1 to a Th2 response has been reported for HIV-1-infected patients (Kannagi et al. 1990. J. Virol. 64, 3399-3406; Walker et al. 1986. Science 234, 1563-1566; Walker et al. 1991. J. Virol. 65, 5921-5927). For this reason, the potential role of cytokines in the development of AIDS has received a great deal of attention. Interleukin (IL)-12 is a disulfide-linked, 70-kDa heterodimeric cytokine produced by antigen-presenting cells. IL-12 has a central role in the development of the Th1-type immune responses. Therefore, we investigated the ability of T-tropic HIV-1 IIIB to replicate in Th1, Th2, and Th0 T cell clones and studied the effects of IL-12 on HIV-1 replication in these cells types. These studies demonstrate several points. (1) Th1, Th2, and Th0 T cell clones support HIV-1 IIIB replication nearly equally well, and it is, therefore, unlikely that differences in ability to support HIV-1 replication can explain changes in Th1, Th2, or Th0 subtype 1 following HIV-1 infection. (2) Using this model, we show that IL-12 can inhibit HIV-1 replication, consistent with a role for IL-12 in HIV-1 replication in T cells. (3) HIV-1 can form a persistent infection in T cell clones, providing a reservoir model for study of viral sanctuary and persistence in a system closely approximating the in vivo situation.

Inhibition of phosphodiesterase type IV suppresses human immunodeficiency virus type 1 replication and cytokine production in primary T cells: involvement of NF-kappaB and NFAT

Rolipram, a phosphosdiesterase type IV-specific inhibitor, prevented p24 antigen release from anti-CD3-activated human immunodeficiency virus (HIV)-infected T cells and CD4(+)-cell depletion associated with viral replication in a dose-responsive manner but minimally inhibited T-cell proliferation. Moreover, rolipram reduced the production of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) by HIV-infected T cells. The transcriptional ability of a luciferase reporter gene under control of the HIV long terminal repeat, induced by phorbol myristic acetate plus ionomycin or by TNF-alpha, in primary T and Jurkat cells was also inhibited by rolipram. Rolipram inhibited NF-kappaB and NFAT activation induced by T-cell activation in Jurkat and primary T cells, as measured by transient transfection of reporter genes and electrophoretic mobility shift assays. Exogenous addition of TNF-alpha in the presence of rolipram restored NF-kappaB but not NFAT activation or p24 release. Addition of dibutyryl-cyclic AMP (dBcAMP) mimicked the effects of rolipram on p24 antigen release, NF-kappaB activation, and TNF-alpha secretion, but it did not affect NFAT activation or IL-10 production. The protein kinase A inhibitor KT5720 prevented the inhibition of TNF-alpha secretion but not that of HIV type 1 (HIV-1) replication caused by rolipram. Our data indicate that blockade of phosphodiesterase type IV could be of benefit against HIV-1 disease by modulating cytokine secretion and transcriptional regulation of HIV replication, and they suggest an important role of NFAT in HIV replication in primary T cells. Some of those activities cannot be ascribed solely to its ability to increase cAMP.

The expression of the essential nuclear splicing factor SC35 is altered by human immunodeficiency virus infection

In order to identify cellular genes differentially expressed during human immunodeficiency virus 1 (HIV-1) infection, we conducted a screen using differential display. The sequence of one of the clones, 0085, was identical to a sequence present in the RNA splicing factor SC35. Since splicing is an essential point of control during HIV gene expression, we carried out additional experiments to examine SC35 expression during HIV infection. RNA blots confirmed that SC35 RNA was induced following HIV infection; a 2-3-fold increase in expression of SC35 RNA was detected by day 2 of HIV infection. Fluorescence-activated cell-sorting revealed concomitant increases in SC35 protein and double staining studies demonstrated that increases in SC35 protein occurred specifically in the HIV-infected cells. Laser scanning confocal microscopy revealed SC35 was associated with 2 microm 'nuclear speckles' in both infected and uninfected cells, suggesting that increases in SC35 accumulated in these nuclear structures and that HIV infection did not alter the intracellular distribution of SC35. These findings indicate that an essential splicing factor is induced after HIV infection, suggesting that the consequences of HIV infection include alterations in relative levels of a splicing factor.

Three-dimensional structure of HIV-1 Rev protein filaments

The HIV-1 Rev protein facilitates the export of incompletely spliced and unspliced viral mRNAs from the nucleus. Rev polymerizes into two types of filaments in vitro. In the presence of RNA, Rev forms poorly ordered structures, while in the absence of RNA it polymerizes into regular hollow filaments. We have determined the helical structure of the latter filaments by analysis of cryo-electron micrographs, taking into account STEM measurements of mass-per-unit-length. They are made up of Rev dimers, arranged in a six-start helix, with 31 dimers in 2 turns, a pitch angle of 45 degrees, and an interstrand spacing of 3.8 nm. Three-dimensional reconstruction at 2.1 nm resolution reveals a smooth outer surface and a featured inner surface, with outer and inner diameters of approximately 14.8 and approximately 10.4 nm, respectively. The Rev dimer has a "top-hat" shape with a cylinder approximately 3.2 nm in diameter and approximately 2.2 nm high, pointing inward: the thinner rim areas pack together to form the filament wall. Raman spectroscopy shows polymerized Rev to have approximately 54% alpha-helix and 20-24% beta-sheet content. Electron microdiffraction of aligned filaments reveals a broad meridional reflection at approximately (0.51 nm(-1, suggesting approximate alignment of the alpha-helices with the filament axis. Based on these data, a molecular model for the Rev filament is proposed.

Selective inhibition of mitogen-induced transactivation of the HIV long terminal repeat by carboxyamidotriazole. Calcium influx blockade represses HIV-1 transcriptional activation

Carboxyamidotriazole (CAI) is a calcium influx inhibitor that has both antiproliferative and antimetastatic activities. Pretreatment of human T-cells with micromolar concentrations of CAI causes a near complete inhibition of calcium-regulated mitogen-induced transcription from the human immunodeficiency virus (HIV) long terminal repeat (LTR). This inhibition is selective since other mitogen-activated gene regulatory elements, such as the 12-O-tetradecanoylphorbol-13-acetate response element, are not influenced by the drug. HIV LTR transcription inhibition is maximal at 1.0 microM CAI, requires a pretreatment interval of at least 8 h for optimum inhibition, and shows no acute interference with the growth properties of the cells. Moreover, the inhibition is rapidly reversible upon removal of the drug from the medium. Studies to identify enhancer elements within the HIV LTR that are functionally sensitive to low-dose long-term pretreatment with CAI indicate that the NF-kappaB-binding sites are among the major targets of drug action. In vitro DNA binding studies with nuclear extracts prepared from mitogen-induced T-cells stimulated in the presence of CAI indicate that the drug differentially influences the calcium-regulated downstream signal transduction pathways necessary for specific NF-kappaB DNA binding activity at the two kappaB sites within the HIV LTR. Studies with ionomycin and thapsigargin show that repression is specific for selected modes of inducible calcium entry and indicate that, in T-cells, a major mechanism of CAI action is to modulate calcium influx at a level that is proximal to the regulated release of calcium from intracellular stores. Measurement of calcium influx in CAI-treated cells reveals a dramatic and reversible inhibition of mitogen-induced calcium influx. These results indicate that CAI can be an important and effective pharmacological tool for analysis of the calcium-dependent modulation of HIV LTR transcription.

Selenium supplementation suppresses tumor necrosis factor alpha-induced human immunodeficiency virus type 1 replication in vitro

Selenium is a nutritionally essential trace element that is important for optimal function of the immune system. It is incorporated into selenoproteins as the amino acid selenocysteine and it is known to inhibit the expression of some viruses. In this study, we show that selenium supplementation for 3 days prior to exposure to tumor necrosis factor alpha (TNF-alpha) partially suppresses the induction of human immunodeficiency virus type 1 (HIV-1) replication in both chronically infected T lymphocytic and monocytic cell lines. In acute HIV-1 infection of T lymphocytes and monocytes in the absence of exogenous TNF-alpha, the suppressive effect of selenium supplementation was not observed. However, selenium supplementation did suppress the enhancing effect of TNF-alpha on HIV-1 replication in vitro in acutely infected human monocytes, but not in T lymphocytes. Selenium supplementation also increased the activities of the selenoproteins, glutathione peroxidase (GPx) and thioredoxin reductase (TR), which serve as cellular antioxidants. Taken together, these results suggest that selenium supplementation may prove beneficial as an adjuvant therapy for AIDS through reinforcement of endogenous antioxidative systems.

A human primary T-lymphocyte-derived human immunodeficiency virus type 1 Tat-associated kinase phosphorylates the C-terminal domain of RNA polymerase II and induces CAK activity

Tat protein mediates transactivation of human immunodeficiency virus type 1 (HIV-1), which results in more-efficient transcript elongation. Since phosphorylation of C-terminal domain (CTD) of RNA polymerase II correlates with its enhanced processivity, we studied the properties of a Tat-associated CTD kinase derived from mitogenically stimulated human primary T lymphocytes (TTK). TTK binds to full-length Tat and specifically phosphorylates CTD and CDK2. This dual kinase activity is characteristic of CDK-activating kinase (CAK). The CTD kinase activity is induced upon mitogenic stimulation of primary T lymphocytes. Fractionation of T-cell lysate demonstrates that Tat-associated CTD kinase activity elutes in two peaks. About 60% of Tat-associated CTD kinase copurifies with CDK2 kinase activity and contains the CAK components CDK7 and cyclin H. The rest of Tat-associated kinase is free of CDK2 kinase activity and the CAK components and thus may represent a novel CTD kinase. The kinase activities of TTK are blocked by the adenosine analog 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) as well as by the kinase inhibitor H8 at concentrations known to block transcript elongation. Importantly, the Tat-associated kinase markedly induced CAK. We suggest that the mechanism of Tat-mediated processive transcription of the HIV-1 promoter includes a Tat-associated CAK activator.

Simian immunodeficiency viruses containing mutations in the long terminal repeat NF-kappa B or Sp1 binding sites replicate efficiently in T cells and PHA-stimulated PBMCs

The long terminal repeats (LTRs) of primate lentiviruses contain conserved binding sites for the NF-kappa B and Sp1 cellular transcription factors. In order to study the role that these sites play in simian immunodeficiency virus (SIV) replication, we have introduced mutations that disrupt either the NF-kappa B or Sp1 binding sites in the LTR of an infectious molecular clone of SIVmac239. An additional mutation also disrupted the SF3 transcription factor binding site that overlaps the NF-kappa B site. Viruses containing point mutations or deletions of the NF-kappa B, SF3, or Sp1 binding sites retained the ability to replicate efficiently in the CEMx174 and MT4 cell lines, as well as in PHA-stimulated primary rhesus macaque peripheral blood mononuclear cells (PBMCs). Efficient replication of SIVs mutated in either NF-kappa B or Sp1 binding sites suggests that the SIV LTR promoter contains multiple functionally redundant elements capable of supporting sufficient transcription to allow productive viral replication.

Activation of HIV-1 long terminal repeat transcription and virus replication via NF-kappaB-dependent and -independent pathways by potent phosphotyrosine phosphatase inhibitors, the peroxovanadium compounds

Replication of human immunodeficiency virus type 1 (HIV-1) is increased by different cytokines and T cell activators, also known to modulate tyrosine phosphorylation levels. A novel class of protein tyrosine phosphatase (PTP) inhibitors, peroxovanadium (pV) compounds, were tested for a putative effect on HIV-1 long terminal repeat (LTR) activity. We found that these PTP inhibitors markedly enhanced HIV-1 LTR activity in 1G5 cells, a stably transfected cell line that harbors an HIV-1 LTR-driven luciferase construct. A direct correlation between the extent of tyrosine phosphorylation and the level of HIV-1 LTR inducibility was seen after treatment with three different pV compounds. Transient transfection experiments were carried out in several T cell lines, and after addition of pV, a marked increase in HIV-1 LTR activity was measured. Monocytoid cells were tested using U937-derived cell lines and were also found to be sensitive to the pV-mediated potentiating effect on HIV-1 LTR activity. A significant reduction of the pV-mediated increase in HIV-1 LTR activity was seen in cells transiently transfected with an HIV-1 LTR-driven luciferase construct bearing a mutation in both NF-kappaB binding sites although detectable levels of induction remained. Electrophoretic mobility shift assays allowed the identification of the nuclear translocation of the NF-kappaB p50.p65 heterodimer complex induced by pV compounds. A dominant negative version of the repressor IkappaBalpha mutated on serines 32 and 36 impeded pV-induced NF-kappaB-dependent luciferase activity. Western blot analysis showed a clear diminution in the protein level of IkappaBalpha starting 30 min after pV treatment of Jurkat E6.1 cells which is indicative of its degradation. On the other hand, no increase in tyrosine phosphorylation was observed on IkappaBalpha itself. Finally, we tested the PTP inhibitors on four cell lines latently infected with HIV-1 and showed a consistent pV-mediated increase in virion production. Thus, our studies suggest that pV-mediated activation of HIV-1 LTR activity is controlled by the nuclear translocation of the NF-kappaB transcription factor, which is mediated by IkappaBalpha serine phosphorylation and degradation, but also by a still undefined NF-kappaB-independent pathway.

Inhibition of recombinant human immunodeficiency virus type 1 replication by a site-specific recombinase

Current molecular genetic strategies to inhibit productive human immunodeficiency virus type 1 (HIV-1) replication have involved the generation of gene products which provide intracellular inhibition of essential virally encoded proteins or RNA structures. A molecular strategy to excise proviral DNA from HIV-1-infected cells and render these cells virus free would provide an attractive direct antiviral strategy, providing a mechanism to remove viral genes from infected cells. The potential of such a molecular genetic intervention was examined by using the Cre-loxP recombination system. A recombinant HIV-1 clone, designated HIV(lox), that contains loxP within a nonessential U3 region of the long terminal repeats was synthesized. The loxP motif was maintained during replication of HIV(lox) in CEM cells, as demonstrated by reverse transcriptase PCR analyses of genomic RNA isolated from virions. Two different types of HIV-1-permissive cells, CEM cells and 293 cells expressing the CD4 glycoprotein, were transformed with a Cre expression vector which was shown to encode Cre DNA binding and recombinase activities. HIV(lox) infection of CEM or CD4+ 293 cells expressing Cre resulted in a substantial reduction in virus replication compared to control cells, and evidence for the presence of the expected excision product was found. Site-specific excision of HIV-1 can therefore be achieved by using this model system with acute infection. These studies represent one step toward the development of a novel antiviral strategy for the treatment of AIDS.

Human chromosome 6- and 11-encoded factors support human immunodeficiency virus type 1 Rev function in A9 cells

The precise mechanism of Rev-mediated expression of human immunodeficiency virus (HIV-1) late genes is not well characterized. We recently proposed a requirement for HIV-1 Rev responsive element (RRE) RNA binding host nuclear proteins in Rev function. In this report, using a transient transfection assay of Rev function, we further demonstrate the role of host cell factors in HIV-1 Rev function. Murine A9 cells, which are inefficient in forming RRE-host protein ribonucleoprotein complexes, are also inefficient in supporting Rev function. We also show that host cell factor(s) encoded by human chromosomes 6 and 11 can support HIV-1 Rev-mediated expression of unspliced viral mRNAs in murine A9 cells.

Topoisomerase poisons activate the transcription factor NF-kappaB in ACH-2 and CEM cells

The nuclear factor kappaB (NF-kappaB) is involved in T cell activation and enhances HIV-1 gene expression. It is activated in response to numerous stimuli, including oxidative stress. Oxidative stress damages membrane lipids, proteins and nucleic acids. We have shown previously that oxidative DNA damage generated by photosensitization could trigger activation of NF-kappaB. We now show that a series of topoisomerase poisons (actinomycin D, camptothecin, daunomycin and etoposide) also activate NF-kappaB (NFKB1/RelA dimer) in ACH-2 and CEM cells. This activation is inhibited by pyrrolidine dithiocarbamate. In ACH-2 cells latently infected by HIV-1, camptothecin, daunomycin and etoposide are able to enhance virus production. Since topoisomerase poisons cause the formation of single- and double-strand breaks in DNA, these lesions might be capable of triggering NF-kappaB activation. Indeed, DNA damaging agents generating adducts (trans-platin and 4-nitroquinoline 1-oxide) and/or crosslinks in DNA (cisplatin and mitomycin C) do not or only weakly activate NF-kappaB in T cell lines.

2-Glycineamide-5-chlorophenyl 2-pyrryl ketone, a non-benzodiazepin Tat antagonist, is effective against acute and chronic HIV-1 infections in vitro

In the search for effective Tat-dependent transcription inhibitors using a screening assay system that has recently been developed, 2-glycineamide-5-chlorophenyl 2-pyrryl ketone (GCPK) has proved to be a potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) replication in vitro. This compound was inhibitory to HIV-1 replication in both acutely and chronically infected cells. The 50% effective concentration (EC50) of GCPK in acutely infected MOLT-4 and CEM cells was 0.62 and 0.13 microgram/ml, respectively. These values were similar to those of the known Tat-dependent transcription inhibitors Ro5-3335 and Ro24-7429. Like these inhibitors, GCPK could inhibit HIV-1 replication in MOLT-4/IIIB (MOLT-4 cells chronically infected with HIV-1) and tumor necrosis factor-alpha-(TNF-alpha)-induced viral activation in OM10.1 cells (a HL-60 clone latently infected with HIV-1). GCPK is distinct from Ro5-3335 and Ro24-7429 in that this novel Tat-dependent transcription inhibitor has no benzodiazepin ring.

The regulation of human immunodeficiency virus type-1 gene expression

Despite 15 years of intensive research we still do not have an effective treatment for AIDS, the disease caused by human immunodeficiency virus (HIV). Recent research is, however, revealing some of the secrets of the replication cycle of this complex retrovirus, and this may lead to the development of novel antiviral compounds. In particular the virus uses strategies for gene expression that seem to be unique in the eukaryotic world. These involve the use of virally encoded regulatory proteins that mediate their effects through interactions with specific viral target sequences present in the messenger RNA rather than in the proviral DNA. If there are no cellular counterparts of these RNA-dependent gene-regulation pathways then they offer excellent targets for the development of antiviral compounds. The viral promoter is also subject to complex regulation by combinations of cellular factors that may be functional in different cell types and at different cell states. Selective interference of specific cellular factors may also provide a route to inhibiting viral replication without disrupting normal cellular functions. The aim of this review is to discuss the regulation of HIV-1 gene expression and, as far as it is possible, to relate the observations to viral pathogenesis. Some areas of research into the regulation of HIV-1 replication have generated controversy and rather than rehearsing this controversy we have imposed our own bias on the field. To redress the balance and to give a broader view of HIV-1 replication and pathogenesis we refer you to a number of excellent reviews [Cullen, B. R. (1992) Microbiol. Rev. 56, 375-394; Levy, J. A. (1993) Microbiol. Rev. 57, 183-394; Antoni, B. A., Stein, S. & Rabson, A. B. (1994) Adv. Virus Res. 43, 53-145; Rosen, C. A. & Fenyoe, E. M. (1995) AIDS (Phila.) 9, S1-S3].

Two species of Rev proteins, with distinct N termini, are expressed by caprine arthritis encephalitis virus

Several cDNA clones representing alternatively spliced Rev-specific transcripts were isolated from a cDNA library prepared from Himalayan tahr cells infected with caprine arthritis encephalitis virus (CAEV). We previously characterized two rev-like cDNA species, d1 and d2, and a tat e1 cDNA containing the rev coding sequence downstream to the tat. In these cDNAs, the rev coding domain derives its amino terminus from the N terminus of env, which is spliced to the 3' open reading frame encoding the putative Rev protein. In this study, we report the genetic structure of a fourth rev-like cDNA (designated g1), which lacks the 5' env-derived sequences. All of these rev transcripts, including cDNA g1, increased the level of chloramphenicol acetyltransferase expression when cotransfected with a reporter plasmid containing the CAEV Rev-response element-spanning region downstream of the cat coding sequences. Western blot (immunoblot) analysis showed that each transfected cDNA species gave rise to a 16-kDa protein lacking env-encoded amino-terminal epitopes. In contrast, CAEV-infected Himalayan tahr cells expressed only a 20-kDa protein, whose N terminus, in contrast, is derived from the env. Moreover, only the 20-kDa protein was also detected in the mature CAEV virions. These observations suggest that the transcripts d1, d2, and e1 can potentially, in appropriate cellular context, encode two Rev isoforms differing in their N termini, whereas the g1 transcript encodes only the 16-kDa species. Elucidation of the significance of the 16-kDa Rev protein in CAEV biology must await further studies.

Encephalitis, lymphoid tissue depletion and secondary diseases associated with bovine immunodeficiency virus in a dairy herd

Encephalitis, lymphoid tissue depletion and secondary infections occurred over a 5-yr-period in Holstein cows infected with bovine immunodeficiency virus (BIV). There were 59 cattle studied, the majority during 1991, when a severe environmental stress occurred, each with one or more primary causes of death, natural or by euthanasia, and most with several secondary diseases. The encephalitis was characterized by meningeal, perivascular and parenchymal infiltration with lymphocytes, occasional plasma cells and macrophages with perivascular edema in some cows. Affected areas included the cerebrum, cerebellum, and spinal cord with no particular distribution pattern recognized. The lymphoid depletion was primarily an absence of follicular development in nodes draining regions with secondary infections such as chronic mastitis and chronic suppurative pododermatitis. Paucity of lymphocytes in thymic-dependent regions of lymph nodes and the spleen suggested a primary depletion of T cells. Secondary infections were often multiple with each cow having several minor conditions, usually considered short-term and treatable. These included mastitis and pododermatitis, with many cows having non-responding abscesses, cellulitis and myositis attributed to injection site infections. A large number of the cattle had parturition difficulties such as dystocia, obturator paralysis, and metritis. Pulmonary, cardiovascular, and intestinal disease were recognized as both primary and secondary disease conditions. There was a high level of infection with bovine leukemia virus with 4 of the 59 cattle having lymphosarcoma. Under practical conditions, the infection with BIV has a different effect on the host than has been observed under experimental conditions. The presence of BIV combined with the stresses associated with parturition and a modern dairy production system were considered causal for the development of untreatable secondary diseases in immunocompromised cattle. The peak incidence in 1991 was attributed to increased environmental stress during renovation of the barn facility. During this time the cattle were kept on open pasture, exposed to an extremely wet winter, and spring weather conditions. The effect of co-infection with bovine leukemia virus, the influence of immunocompromise on the chronicity of mastitis, the relationship with laminitis and pododermatitis, and several questions related to viral transmission, complementarism with bovine leukemia virus, viral reactivation and immunoprophylaxis all remain as viable avenues for future investigations.

Activation of the HIV long terminal repeat and viral production by H2O2-vanadate

The long terminal repeat (LTR) of human immunodeficiency virus type 1 (HIV-1) contains sequences required for the initiation of gene transcription. Among the substances known to activate the HIV-1 LTR is hydrogen peroxide (H2O2). We report here that H2O2-induced activation of the LTR in the macrophage cell line THP-1 and the lymphocyte cell line, Jurkat, is greatly increased by vanadate. Activation of the LTR by phorbol myristate acetate, tumor necrosis factor alpha, lipopolysaccharide, or Staphylococcus epidermidis extract was not increased by vanadate, indicating some selectivity for H2O2. H2O2 and vanadate also acted synergistically to increase the production of HIV-1 virions by the latently infected macrophage cell line U-1 as determined by p24 antigen release and the detection of intact virions by electron microscopy. Effects were observed at H2O2 and vanadate concentrations down to 3 x 10(-6) M, with high concentrations leading to cell toxicity. Catalase was strongly inhibitory when added prior to the interaction of H2O2 and vanadate, but was considerably less inhibitory when the H2O2 and vanadate were allowed to preincubate prior to the catalase addition. H2O2 reacts with vanadate to form peroxides of vanadate that have potent biological effects. Our findings suggest that among these is the activation of the HIV-1 LTR.

Selective infection of human T-lymphotropic virus type 1 (HTLV-1)-infected cells by chimeric human immunodeficiency viruses containing HTLV-1 tax response elements in the long terminal repeat

Previous studies have suggested that the human immunodeficiency virus long terminal repeat (HIV LTR) enhancer/promoter sequences contribute to the replication ability of HIV in different T-cell lines; mutation of these sequences can alter HIV tropism. We have utilized site-specific mutagenesis to generate variants of HIV that exhibit specific tropism for human T-lymphotropic virus type 1 (HTLV-1) Tax-expressing CD4+ T cells. The wild-type HIV LTR NF-kappa B and Sp1 sites in an infectious molecular clone of HIV type 1 were replaced with sequences derived from the 21-bp Tax response elements (TRE) from the HTLV-1 LTR to generate TRE-containing chimeric HIVs (TRE-HIVs). The TRE-HIVs exhibit selective replication and cell killing in HTLV-infected human CD4+ T cells, but not in HTLV-negative T cells. Transient transfections suggested that Tax-TRE interactions could account for the observed replication specificity. The TRE-containing HIV LTRs were synergistically activated by the HIV Tat and HTLV-1 Tax transactivators. These results demonstrate that it is possible to specifically target HIV replication and cytotoxicity to HTLV-1+, CD4+ human T cells, on the basis of Tax-TRE interactions, and provide a model for the development of specific, cytotoxic, retroviral gene therapy vectors for HTLV-1-infected cells based on alterations of the LTR transcriptional regulatory elements. They also suggest that HIV Tat can cooperate with heterologous transcriptional activators, such as Tax, which act through upstream binding sites without directly binding to DNA.

A human chromosome 12-associated 83-kilodalton cellular protein specifically binds to the loop region of human immunodeficiency virus type 1 trans-activation response element RNA

trans activation of human immunodeficiency virus type 1 (HIV-1) involves the viral trans-activator protein (Tat) and a cellular factor(s) encoded on human chromosome 12 (HuChr12) that targets the trans-activation response element (TAR) in the viral long terminal repeat. Because nascent TAR RNA is predicted to form a secondary structure that specifically binds cellular proteins, we investigated the composition of the TAR RNA-protein complex for HuChr12-specific proteins. UV cross-linking of TAR RNA-nuclear protein complexes formed in vitro identified an 83-kDa protein in human cells and in a human-hamster hybrid cell containing only HuChr12. The 83-kDa TAR RNA-binding protein was absent in the parental hamster cells. TAR RNA mutations that inhibited binding of the 83-kDa protein in vitro also inhibited HuChr12-dependent Tat trans activation. These TAR mutations changed the native sequence or secondary structure of the TAR loop. The TAR RNA binding activity of the 83-kDa protein also correlated with a HuChr12-dependent increase in steady-state HIV-1 RNA expression during Tat trans activation. Our results suggest that either a species-specific 83-kDa TAR RNA loop-binding protein is directly encoded on HuChr12 or a HuChr12 protein(s) induces the expression of an 83-kDa TAR-binding protein in nonprimate cells.

Regulation of human immunodeficiency virus type 1 and cytokine gene expression in myeloid cells by NF-kappa B/Rel transcription factors

CD4+ macrophages in tissues such as lung, skin, and lymph nodes, promyelocytic cells in bone marrow, and peripheral blood monocytes serve as important targets and reservoirs for human immunodeficiency virus type 1 (HIV-1) replication. HIV-1-infected myeloid cells are often diminished in their ability to participate in chemotaxis, phagocytosis, and intracellular killing. HIV-1 infection of myeloid cells can lead to the expression of surface receptors associated with cellular activation and/or differentiation that increase the responsiveness of these cells to cytokines secreted by neighboring cells as well as to bacteria or other pathogens. Enhancement of HIV-1 replication is related in part to increased DNA-binding activity of cellular transcription factors such as NF-kappa B. NF-kappa B binds to the HIV-1 enhancer region of the long terminal repeat and contributes to the inducibility of HIV-1 gene expression in response to multiple activating agents. Phosphorylation and degradation of the cytoplasmic inhibitor I kappa B alpha are crucial regulatory events in the activation of NF-kappa B DNA-binding activity. Both N- and C-terminal residues of I kappa B alpha are required for inducer-mediated degradation. Chronic HIV-1 infection of myeloid cells leads to constitutive NF-kappa B DNA-binding activity and provides an intranuclear environment capable of perpetuating HIV-1 replication. Increased intracellular stores of latent NF-kappa B may also result in rapid inducibility of NF-kappa B-dependent cytokine gene expression. In response to secondary pathogenic infections or antigenic challenge, cytokine gene expression is rapidly induced, enhanced, and sustained over prolonged periods in HIV-1-infected myeloid cells compared with uninfected cells. Elevated levels of several inflammatory cytokines have been detected in the sera of HIV-1-infected individuals. Secretion of myeloid cell-derived cytokines may both increase virus production and contribute to AIDS-associated disorders.

Interaction of nuclear protein p140 with human immunodeficiency virus type 1 TAR RNA in mitogen-activated primary human T lymphocytes

Several lines of evidence suggest that cellular proteins play a role during human immunodeficiency virus type 1 (HIV-1) Tat-mediated trans activation. A recent report from this laboratory has shown that a 140-kDa HeLa nuclear protein (p140) binds specifically to the lower stem region of the Tat response element, TAR RNA. Since HIV-1 trans activation is most efficient in proliferating T cells, we investigated the binding of p140 to TAR RNA in unstimulated and mitogen-activated, G1-phase primary T lymphocytes. TAR RNA/protein-binding activity was low in resting cells but increased significantly within 2 h of activation and remained elevated for at least 48 h. Corresponding increases in p140 protein levels were observed with most but not all donors, suggesting that an additional nuclear factor(s) may be required for efficient binding of this protein to TAR RNA in activated T cells.

Membrane permeabilization by different regions of the human immunodeficiency virus type 1 transmembrane glycoprotein gp41

The transmembrane glycoprotein (gp41) of human immunodeficiency virus type 1 (HIV-1) has been implicated in the cytopathology observed during HIV infection. The first amino acids located at the amino terminus are involved in membrane fusion and syncytium formation, while sequences located at the carboxy terminus have been predicted to interact with membranes and modify membrane permeability. The HIV-1 gp41 gene has been cloned and expressed in Escherichia coli cells by using pET vectors to analyze changes in membrane permeability produced by this protein. This system is well suited for expressing toxic genes in an inducible manner and for analyzing the function of proteins that modify membrane permeability. gp41 enhances the permeability of the bacterial membrane to hygromycin B despite the low level of expression of this protein. To localize the regions of gp41 responsible for these effects, a number of fragments spanning different portions of gp41 were inducibly expressed in E. coli. Two regions of gp41 were shown to increase membrane permeability: one located at the carboxy terminus, where two highly amphipathic helices have been predicted, and another one corresponding to the membrane-spanning domain. Expression of the central region of gp41 comprising this domain was highly lytic for E. coli cells and increased membrane permeability to a number of compounds. These findings are discussed in the light of HIV-induced cytopathology and gp41 structure.

Regulation of macrophage activation and human immunodeficiency virus production by invasive Salmonella strains

Salmonellae possess the ability to adhere to and invade macrophages and in so doing trigger a number of intracellular events that are associated with cellular activation. As an initial approach to defining the mechanisms by which invasive salmonellae alter macrophage function, we have explored the impact of Salmonella infection on the production of human immunodeficiency virus (HIV) in U1 cells, a promonocytic cell line latently infected with the virus. Infection of U1 cells with a pathogenic strain of Salmonella enteritidis resulted in a marked induction of macrophage activation and HIV production. The stimulatory effect of salmonellae was mediated by signals other than lipopolysaccharide. Salmonella mutants with specific defects in invasion or intracellular survival were markedly less effective in the induction of HIV production. In contrast to S. enteritidis, strains of Yersinia enterocolitica, Legionella pneumophila, and Escherichia coli did not induce HIV production. However, all of these bacteria induced comparable levels of gene expression mediated by the HIV long terminal repeat. The results of this study are consistent with the notion that invasive salmonellae possess the ability to activate the macrophage by at least one mechanism that is not shared with several other species of gram-negative bacteria. Furthermore, the expression of this unique property is maximal with Salmonella strains that are not only invasive but also capable of prolonged survival within the macrophage. Our results indicate that the U1 cell line may be a very useful model system with which to examine the biochemical pathways by which internalized salmonellae modulate the activation state of the macrophage.