HIV-1 long terminal repeat modulation by glucocorticoids in monocytic and lymphocytic cell lines

Reactivation of latent HIV-1 by the glucocorticoid receptor modulator AZD9567

One key determinant of HIV-1 latency reversal is the activation of the viral long terminal repeat (LTR) by cellular transcription factors such as NF-κB and AP-1. Interestingly, the activity of these two transcription factors can be modulated by glucocorticoid receptors (GRs). Furthermore, the HIV-1 genome contains multiple binding sites for GRs. We therefore hypothesized that glucocorticoids and other GR modulators may influence HIV-1 latency and reactivation. To investigate how GR signaling affects latent HIV-1 reservoirs, we assembled a representative panel of GR modulators including natural steroidal agonists, selective and non-selective GR modulators, and clinically approved GR-modulating drugs. The effects of these compounds on HIV-1 reactivation were assessed using latently HIV-1-infected cell lines and primary cells, as well as reporter assays that monitored GR and LTR activities. We found that AZD9567 (Mizacorat), a non-steroidal partial GR agonist, reactivates latent HIV-1 in both lymphoid and myeloid cell lines and primary CD4+ T cells. Conversely, the GR antagonist mifepristone suppresses HIV-1 LTR-driven gene expression. Mechanistic analyses revealed that AZD9567-mediated reactivation partially depends on both GR and AP-1 binding sites in the LTR. In summary, we, here, identify the GR modulator AZD9567 as novel latency-reversing agent that activates LTR-driven gene expression, which may aid in advancing current shock-and-kill approaches in the treatment of HIV-1 infection.IMPORTANCELatently infected cells of people living with HIV are constantly exposed to fluctuating levels of glucocorticoid hormones such as cortisol. In addition, many HIV-infected individuals regularly take corticosteroids as anti-inflammatory drugs. Although corticosteroids are known to affect the activity of the viral long terminal repeat (LTR) promoter and influence ongoing HIV-1 replication, relatively little is known about the effect of corticosteroid hormones and other glucocorticoid receptor (GR) modulators on latent HIV-1. By systematically comparing natural and synthetic GR modulators, we, here, identify a first first-in-class, oral, partial GR agonist that reactivates latent HIV-1 from different cell types. This drug, AZD9567, was previously tested in clinical trials for rheumatoid arthritis. Mutational analyses shed light on the underlying mode of action and revealed transcription factor binding sites in the HIV-1 LTR that determine responsiveness to AZD9567.

Therapeutic potential of salicylamide derivatives for combating viral infections

Since time immemorial human beings have constantly been fighting against viral infections. The ongoing and devastating coronavirus disease 2019 pandemic represents one of the most severe and most significant public health emergencies in human history, highlighting an urgent need to develop broad-spectrum antiviral agents. Salicylamide (2-hydroxybenzamide) derivatives, represented by niclosamide and nitazoxanide, inhibit the replication of a broad range of RNA and DNA viruses such as flavivirus, influenza A virus, and coronavirus. Moreover, nitazoxanide was effective in clinical trials against different viral infections including diarrhea caused by rotavirus and norovirus, uncomplicated influenza A and B, hepatitis B, and hepatitis C. In this review, we summarize the broad antiviral activities of salicylamide derivatives, the clinical progress, and the potential targets or mechanisms against different viral infections and highlight their therapeutic potential in combating the circulating and emerging viral infections in the future.

Modulation of the long terminal repeat promoter activity of small ruminant lentiviruses by steroids

Production and excretion of small ruminant lentiviruses (SRLVs) varies with the stage of the host reproductive cycle, suggesting hormonal involvement in this variation. Stress may also affect viral expression. To determine if hormones affect SRLV transcriptional activity, the expression of green fluorescent protein (GFP) driven by the promoters in the U3-cap region of the long terminal repeats (LTRs) of different strains of SRLV was assessed in cell culture. High concentrations of steroids (progesterone, cortisol and dehydroepiandrosterone) inhibited expression of GFP driven by SRLV promoters. This effect decreased in a dose-dependent manner with decreasing concentrations of steroids. In some strains, physiological concentrations of cortisol or dehydroepiandrosterone (DHEA) induced the expression of GFP above the baseline. There was strain variation in sensitivity to hormones, but this differed for different hormones. The presence of deletions and a 43 base repeat in the U3 region upstream of the TATA box of the LTR made strain EV1 less sensitive to DHEA. However, no clear tendencies or patterns were observed when comparing strains of different genotypes and/or subtypes, or those triggering different forms of disease.

The effect of dexamethasone on lentiviral vector infection is associated with importin α

Importin α (Imα) plays an important role during the shuttling of the HIV-1 preintegration complex (PIC) from the cytoplasm to the nucleus. Imα may bind to the glucocorticoid receptor (GR), which is localized to nucleus following hormone binding. However, it remains unclear whether the binding of dexamethasone (Dex) to GR affects the Imα redistribution and, thus, alters PIC import. In our study, 293T cells were transfected with the lentiviral vector (LV) carrying the luciferase (Luci) gene following Dex or RU486 pretreatment. The Luci activity (LucA) in the Dex or RU486 group was significantly higher compared to that in the control group (P≤0.01). The effects of Dex and RU486 were inhibited by the Imα inhibitor Bimax1 (P≤0.01), although the inhibitory effect of Bimax1 was alleviated by increasing the Dex dose. Furthermore, it was observed that the LucA in the 30-min Dex treatment group was lower compared to that in the 30-min Dex pretreatment group (P≤0.01). These results suggested that Dex may improve PIC import via increasing the cytoplasmic Imα levels. Kunming mice were transfected in vivo with the LV, either 30 min or 15 h following an intraperitoneal injection of Dex. The LucA in the liver of the 30-min group mice was significantly lower compared to that of the 15-h group mice (P≤0.01), suggesting that the effect of Dex on LV infection depends mainly on the suppression of immune and inflammatory responses in vivo. Taken together, our data indicated that the effect of Dex on LV infection may be associated with Imα, constituting a novel signaling pathway mediating the effects of Dex on HIV-1 infection.

Systematic identification of synergistic drug pairs targeting HIV

The systematic identification of effective drug combinations has been hindered by the unavailability of methods that can explore the large combinatorial search space of drug interactions. Here we present a multiplex screening method named MuSIC (Multiplex Screening for Interacting Compounds), which expedites the comprehensive assessment of pair-wise compound interactions. We examined ~500,000 drug pairs from 1000 FDA-approved or clinically tested drugs and identified drugs that synergize to inhibit HIV replication. Our analysis reveals an enrichment of anti-inflammatory drugs in drug combinations that synergize against HIV, indicating HIV benefits from inflammation that accompanies its infection. Multiple drug pairs identified in this study, including glucocorticoid and nitazoxanide, synergize by targeting different steps of the HIV life cycle. As inflammation accompanies HIV infection, our findings indicate that inhibiting inflammation could curb HIV propagation. MuSIC can be applied to a wide variety of disease-relevant screens to facilitate efficient identification of compound combinations.

Nuclear receptor signaling inhibits HIV-1 replication in macrophages through multiple trans-repression mechanisms

Sexually transmitted pathogens activate HIV-1 replication and inflammatory gene expression in macrophages through engagement of Toll-like receptors (TLRs). Ligand-activated nuclear receptor (NR) transcription factors, including glucocorticoid receptor (GR), peroxisome proliferator-activated receptor gamma (PPARγ), and liver X receptor (LXR), are potent inhibitors of TLR-induced inflammatory gene expression. We therefore hypothesized that ligand-activated NRs repress both basal and pathogen-enhanced HIV-1 replication in macrophages by directly repressing HIV-1 transcription and by ameliorating the local proinflammatory response to pathogens. We show that the TLR2 ligand PAM3CSK4 activated virus transcription in macrophages and that NR signaling repressed both basal and TLR-induced HIV-1 transcription. NR ligand treatment repressed HIV-1 expression when added concurrently with TLR ligands and in the presence of cycloheximide, demonstrating that they act independently of new cellular gene expression. We found that treatment with NR ligands inhibited the association of AP-1 and NF-κB subunits, as well as the coactivator CBP, with the long terminal repeat (LTR). We show for the first time that the nuclear corepressor NCoR is bound to HIV-1 LTR in unstimulated macrophages and is released from the LTR after TLR engagement. Treatment with PPARγ and LXR ligands, but not GR ligands, prevented this TLR-induced clearance of NCoR from the LTR. Our data demonstrate that both classical and nonclassical trans-repression mechanisms account for NR-mediated HIV-1 repression. Finally, NR ligand treatment inhibited the potent proinflammatory response induced by PAM3CSK4 that would otherwise activate HIV-1 expression in infected cells. Our findings provide a rationale for studying ligand-activated NRs as modulators of basal and inflammation-induced HIV-1 replication.

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.

HIV-1 and the macrophage

Macrophages and CD4+ T cells are natural target cells for HIV-1, and both cell types contribute to the establishment of the viral reservoir that is responsible for continuous residual virus replication during antiretroviral therapy and viral load rebound upon treatment interruption. Scientific findings that support a critical role for the infected monocyte/macrophage in HIV-1-associated diseases, such as neurological disorders and cardiovascular disease, are accumulating. To prevent or treat these HIV-1-related diseases, we need to halt HIV-1 replication in the macrophage reservoir. This article describes our current knowledge of how monocytes and certain macrophage subsets are able to restrict HIV-1 infection, in addition to what makes macrophages respond less well to current antiretroviral drugs as compared with CD4+ T cells. These insights will help to find novel approaches that can be used to meet this challenge.

Dexamethasone and mifepristone increase retroviral infectivity through different mechanisms

Using adapted retroviruses for gene delivery is a modern and powerful tool in biological research as well as a promising approach for gene therapy. An important limitation for the extensive use of retroviral vectors is the low infection rate in target cells such as pulmonary vascular endothelial cells due to the insufficient infectivity of standard retrovirus supernatants that can only be overcome by complicated methods of virus concentration. This paper describes two easy methods to augment target cell infectivity, first by increasing the retroviral titer in the medium collected from packaging cells by stimulation of viral propagation with dexamethasone, and second, by increasing target cell sensitivity to retroviral infection by the glucocorticoid receptor antagonist, mifepristone. Using this method, we increased the infectivity of pulmonary microvascular endothelial cells from 16% to 85%. We demonstrate that mifepristone increased the susceptibility of target cells to retroviruses without increasing the viral titer of the supernatant. Dexamethasone, but not mifepristone, increased expression of delivered proteins such as GFP that are important for early identification of infected cells. Each, or both step(s), may be included in a standard protocol for retrovirus propagation and infection of target cells.

Prednisolone mediated suppression of HIV-1 viral load strongly correlates with C-C chemokine CCL2: In vivo and in vitro findings

CCL2 (MCP-1) is a proinflammatory chemokine induced in HIV-1 infection. We have previously demonstrated a significant correlation of CCL2 gene expression with HIV-1 viremia. In this study we investigated the effect of prednisolone on CCL2 gene expression and viral load in an HIV-1-infected patient receiving high-dose prednisolone for severe uveitis. We observed a >1 log reduction of HIV-1 viral load, associated with more than hundred fold reduction of CCL2 expression at day 3 of prednisolone treatment. In vitro HIV-1 infection of PBMC demonstrated reduced HIV-1 replication in the presence of prednisolone. Flow cytometric analysis revealed 50% reduction of LTR driven GFP activity by prednisolone in GHOST cells. These findings indicate that prednisolone suppresses both HIV-1 viral load and CCL2 mRNA expression, an association which might be exploited for future anti-inflammatory therapeutic strategies in HIV-1 infection.

Estradiol negatively regulates HIV-LTR promoter activity in glial cells

HIV-associated dementia results from neuronal loss and an alteration of neuronal function due to a loss of synapses. While HIV infection in astrocytes is limited, astrocytes exhibit a chronic nonproductive infection that can lead to the release of neurotoxic proteins. Additionally, infection can disrupt the normal neurotrophic role of astrocytes that results in neuronal death. Gonadal steroid hormones are known to act as trophic and protective factors in the brain under a variety of normal and pathological conditions. In the present study, to determine if estrogen plays a role in the ability of Tat to function as a transcriptional activator within astrocytes, we examined the effect of estrogen on regulation of viral transcription. We utilized an immortalized human astrocyte cell line (SVGA) stably transfected with a reporter plasmid containing the HIV-1IIIB LTR driving the chloramphenicol acetyltransferase (CAT) gene. The amount of transcriptional activity was measured by quantifying the amount of CAT produced. We determined that 17beta-estradiol treatment (1 nM) had no effect on basal LTR activity. Following transfection with a Tat-expressing plasmid, there was a 100-fold increase in CAT production. This induction was reduced by 40% in cells pretreated with 17beta-estradiol. 17beta- Estradiol only suppressed transcription stimulated by Tat. Furthermore, we determined that this effect was specific to 17beta-estradiol and estrogen receptor agonists. This activity was limited to astrocytes as no effect was observed in a monocytic cell line. Finally, the mechanism of action did not involve an alteration in levels of Cdk9 or Cyclin T1 proteins necessary for Tat activation of the HIV-1 LTR. This study demonstrates a novel activity of 17beta-estradiol in glial cells that could play a role in the maintenance of neuronal health during HIV infection of the central nervous system.

Effect of 17beta-estradiol and progesterone on the expression of FeLV in chronically infected cells

In a previous study, it was found that even though more male cats were infected by feline leukaemia virus (FeLV), females seemed to progress easier to overt disease. To study the effect of female hormones, 17beta-estradiol and progesterone were added in different concentrations (10(-3) M to 10(-12) M) to a culture of persistently FeLV-infected cells. The effect of both hormones was very similar. After 24 h the cell viability was very low at 10(-3) M and 10(-4) M but similar to controls at the remaining concentrations. Liberation of viral particles was estimated by the reverse transcriptase activity (RT), which was the lowest also at 10(-3) M and 10(-4) M. However, low viability could not account for this low RT, as when cells were lysed with lysis buffer RT was high. Thus, cells were dying without freeing viral particles, suggestive of apoptosis. This possibility was confirmed by staining hormone-treated cells with annexin V and propidium iodide. The FeLV antigen p27 measured in the cultures had a maximum at 10(-3) M and 10(-4) M, higher than controls and lysed cells, so the presence of p27 in the supernatant was not only due to cell lysis but a consequence of hormone effect. In conclusion, 17beta-estradiol and progesterone induce death of FeLV-infected cells at high concentrations, probably through a process of apoptosis, which might limit the spread of the infection, as infective viral particles would be hampered from budding.

Interleukin-6 and platelet protagonists in T lymphocyte and virological response

The present cross-sectional study evaluated the status and relationship of interleukin-6, a platelet growth factor, with platelet counts, viral load, CD4 counts, and antiretroviral treatment in 75 HIV-infected subjects with thrombocytopenia and 50 gender-, race-, age- and antiretroviral treatment-matched controls without thrombocytopenia. Mean IL-6 production was significantly higher in thrombocytopenic participants (13 432+/-8596) than in non-thrombocytopenic subjects (12 859+/-3538 pg/10(5) Lym). Univariate analyses indicated, however, that thrombocytopenic patients were more likely to have <3000 pg of IL-6 than non-thrombocytopenic patients (OR=7 95% CI 1.3-12; P=0.01). For additional analyses, participants were dichotomized above and below 3000 pg of IL-6. Despite similar age, gender, drug use and antiretroviral treatment, thrombocytopenic participants had lower CD4 counts (186.5+/-149 vs. 401+/-286, P=0.005) than non-thrombocytopenic subjects. Thrombocytopenic participants with elevated IL-6, with or without HAART, were more likely to have higher HIV-replication (496 273+/-210 416; 34 656+/-25 332) than thrombocytopenic individuals with low IL-6 levels (105 332+/-42 699; 19 015+/-14 296 P=0.05). Non-thrombocytopenic patients with high IL-6 levels exhibited the highest CD4s (466.7+/-333) and the lowest viral burden (63 094+/-53 300) of the groups. Two distinct categories of HIV-associated thrombocytopenia exist: one accompanied by low IL-6, and another with compensatory elevations of IL-6. In thrombocytopenic individuals, the latter was associated with the poorest immunological and virological responses.

Regulation of HIV-1 gene transcription: from lymphocytes to microglial cells

Transcription is a crucial step for human immunodeficiency virus type 1 (HIV-1) expression in all infected host cells, from T lymphocytes, thymocytes, monocytes, macrophages, and dendritic cells in the immune system up to microglial cells in the central nervous system. To maximize its replication, HIV-1 adapts transcription of its integrated proviral genome by ideally exploiting the specific cellular environment and by forcing cellular stimulatory events and impairing transcriptional inhibition. Multiple cell type-specific interplays between cellular and viral factors perform the challenge for the virus to leave latency and actively replicate in a great diversity of cells, despite the variability of its long terminal repeat region in different HIV strains. Knowledge about the molecular mechanisms underlying transcriptional regulatory events helps in the search for therapeutic agents that target the step of transcription in anti-HIV strategies.

A glucocorticoid response element in the LTR U3 region of Friend murine leukaemia virus variant FIS-2 enhances virus production in vitro and is a major determinant for sex differences in susceptibility to FIS-2 infection in vivo

The nucleotide sequence of the Friend murine leukaemia virus variant FIS-2 LTR has high identity with the closely related Friend murine leukaemia virus (F-MuLV) LTR, except for the deletion of one direct repeat, a few point mutations and the generation of a glucocorticoid response element (GRE) in the U3 region. The GRE can mediate gene induction by glucocorticoids, mineral corticoids, progesterone and androgens, and it has been shown that incorporation of a GRE(s) within the LTR can increase the transcriptional activity of retroviral enhancers. We have previously reported an increased early virus replication in male mice compared with female mice when infected with a virus containing the FIS-2 LTR and have proposed that the GRE might contribute to this sex difference. In the present study, we introduced a single point mutation in the GRE and performed comparative studies in NIH 3T3 cells and in young adult male and female NMRI mice. We found that significantly more virus was produced from NIH 3T3 cells infected with wt FIS-2 than from cells infected with the FIS-2 GRE mutant and that this difference was further augmented by glucocorticoids. The glucocorticoid antagonist RU486 inhibited virus production in a dose-dependent manner. The wt FIS-2 disseminated significantly faster than the FIS-2 GRE mutant in both male and female mice. There was no significant difference in the dissemination rate between male and female mice infected with the FIS-2 GRE mutant. Hence, the GRE in the FIS-2 LTR is one determinant of the significant sex difference in susceptibility to FIS-2 infection.

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.

Glucocorticoids suppress human immunodeficiency virus type-1 long terminal repeat activity in a cell type-specific, glucocorticoid receptor-mediated fashion: direct protective effects at variance with clinical phenomenology

Glucocorticoid administration and/or excess secretion have been associated with increased Human Immunodeficiency Virus Type-1 (HIV-1) replication and AIDS progression. The HIV-1 long terminal repeat (LTR) promoter contains glucocorticoid-responsive element (GRE)-like sequences that could mediate a positive effect of glucocorticoids on HIV-1. In addition, we recently demonstrated that the HIV-1 accessory protein Vpr is a potent coactivator of the glucocorticoid receptor, which, like the host coactivator p300, potentiates the effect of glucocorticoids on GRE-containing, glucocorticoid-responsive genes. Such an effect may increase the sensitivity of several host target tissues to glucocorticoids by several fold, and may, thus, contribute to a positive effect of glucocorticoids on the HIV-1-LTR in infected host cells. In this study, we determined the direct effect of glucocorticoids on HIV-1-LTR by examining the ability of dexamethasone to modulate the activity of this promoter coupled to the luciferase reporter gene in human cell lines. Dexamethasone markedly inhibited Tat-stimulated, p300- or Vpr-enhanced luciferase activities in a cell-type specific, dose-dependent, and glucocorticoid receptor-mediated fashion. This effect of dexamethasone was not potentiated by Vpr, was antagonized by the glucocorticoid receptor antagonist RU 486 and required the DNA-binding domain of the receptor. These data suggest that the inhibitory effect of glucocorticoids on the HIV-1-LTR may be exerted via non-GRE-dependent inhibition of the strongly positive host transcription factor NF-kappaB, which interacts with the DNA- and ligand-binding domains of the receptor. Alternatively, it is also possible that dexamethasone-activated glucocorticoid receptor competes with other transcription factors for their binding sites on the promoter region or squelches transcription factors shared by HIV-1-LTR and glucocorticoid-responsive promoters. We conclude that glucocorticoids suppress, rather than stimulate, the HIV-1 promoter, thus acting, protectively for the host. Their apparent negative clinical association with AIDS is most likely due to immunosuppression of the host.