NF-kappa B and HIV: linking viral and immune activation

Differentiation into an Effector Memory Phenotype Potentiates HIV-1 Latency Reversal in CD4+ T Cells

By performing phenotypic analysis of latency reversal in CD4⁺ T cells from virally suppressed individuals, we identify the T_EM subset as the largest contributor to the inducible HIV reservoir. Differential responses of memory CD4⁺ T cell subsets to latency-reversing agents (LRAs) demonstrate that HIV gene expression is associated with heightened expression of transcriptional pathways associated with differentiation, acquisition of effector function, and cell cycle entry. In vitro modeling of the latent HIV reservoir in memory CD4⁺ T cell subsets identify LRAs that reverse latency with ranges of efficiency and specificity. We found that therapeutic induction of latency reversal is associated with upregulation of identical sets of T_EM-associated genes and cell surface markers shown to be associated with latency reversal in our ex vivo and in vitro models. Together, these data support the idea that the effector memory phenotype supports HIV latency reversal in CD4⁺ T cells.

During antiretroviral therapy (ART), human immunodeficiency virus type 1 (HIV-1) persists as a latent reservoir in CD4⁺ T cell subsets in central memory (T_CM), transitional memory (T_TM), and effector memory (T_EM) CD4⁺ T cells. We have identified differences in mechanisms underlying latency and responses to latency-reversing agents (LRAs) in ex vivo CD4⁺ memory T cells from virally suppressed HIV-infected individuals and in an in vitro primary cell model of HIV-1 latency. Our ex vivo and in vitro results demonstrate the association of transcriptional pathways of T cell differentiation, acquisition of effector function, and cell cycle entry in response to LRAs. Analyses of memory cell subsets showed that effector memory pathways and cell surface markers of activation and proliferation in the T_EM subset are predictive of higher frequencies of cells carrying an inducible reservoir. Transcriptional profiling also demonstrated that the epigenetic machinery (known to control latency and reactivation) in the T_EM subset is associated with frequencies of cells with HIV-integrated DNA and inducible HIV multispliced RNA. T_CM cells were triggered to differentiate into T_EM cells when they were exposed to LRAs, and this increase of T_EM subset frequencies upon LRA stimulation was positively associated with higher numbers of p24⁺ cells. Together, these data highlight differences in underlying biological latency control in different memory CD4⁺ T cell subsets which harbor latent HIV in vivo and support a role for differentiation into a T_EM phenotype in facilitating latency reversal.

IMPORTANCE By performing phenotypic analysis of latency reversal in CD4⁺ T cells from virally suppressed individuals, we identify the T_EM subset as the largest contributor to the inducible HIV reservoir. Differential responses of memory CD4⁺ T cell subsets to latency-reversing agents (LRAs) demonstrate that HIV gene expression is associated with heightened expression of transcriptional pathways associated with differentiation, acquisition of effector function, and cell cycle entry. In vitro modeling of the latent HIV reservoir in memory CD4⁺ T cell subsets identify LRAs that reverse latency with ranges of efficiency and specificity. We found that therapeutic induction of latency reversal is associated with upregulation of identical sets of T_EM-associated genes and cell surface markers shown to be associated with latency reversal in our ex vivo and in vitro models. Together, these data support the idea that the effector memory phenotype supports HIV latency reversal in CD4⁺ T cells.

Neoflavonoids as Inhibitors of HIV-1 Replication by Targeting the Tat and NF-κB Pathways

Twenty-eight neoflavonoids have been prepared and evaluated in vitro against HIV-1. Antiviral activity was assessed on MT-2 cells infected with viral clones carrying the luciferase reporter gene. Inhibition of HIV transcription and Tat function were tested on cells stably transfected with the HIV-LTR and Tat protein. Seven 4-phenylchromen-2-one derivatives showed HIV transcriptional inhibitory activity but only the phenylchrome-2-one 10 inhibited NF-κB and displayed anti-Tat activity simultaneously. Compounds 10, 14, and 25, inhibited HIV replication in both targets at concentrations <25 μM. The assays of these synthetic 4-phenylchromen-2-ones may aid in the investigation of some aspects of the anti-HIV activity of such compounds and could serve as a scaffold for designing better anti-HIV compounds, which may lead to a potential anti-HIV therapeutic drug.

miR-34a and its novel target, NLRC5, are associated with HPV16 persistence

Persistent infection with human papillomavirus (HPV), particularly type 16, is causally associated with cervical cancer and its precursors. The role of miRNAs in HPV16 persistence currently remains unclear. Preliminary analysis of miRNA profile demonstrated that HPV16 infection caused a striking downregulation of miR-34a. Through bioinformatics analysis and dual-luciferase assay with site-directed mutagenesis strategy, NLRC5, a negative regulator of NF-κB signaling, was identified to be a novel interactor of miR-34a. Transfection of miR-34a mimic strikingly downregulated NLRC5 in the HPV16-positive cervical cells, which might result in the nuclear accumulation of NF-κB p65. However, transfection of miR-34a inhibitor exhibited an opposite effect. The antagonistic expressions of NLRC5 and miR-34a were also observed in keratinocytes harboring HPV16 genome as well as in human cervical samples with persistent infection of HPV16. Our data uncover a previously unknown connection among HPV16 persistence, miR-34a and its interactor NLRC5.

Improving combination antiretroviral therapy by targeting HIV-1 gene transcription

INTRODUCTION

Combination Antiretroviral Therapy (cART) has not allowed the cure of HIV. The main obstacle to HIV eradication is the existence of quiescent reservoirs. Several other limitations of cART have been described, such as strict life-long treatment and high costs, restricting it to Western countries, as well as the development of multidrug resistance. Given these limitations and the impetus to find a cure, the development of new treatments is necessary. Areas covered: In this review, we discuss the current status of several efficient molecules able to suppress HIV gene transcription, including NF-kB and Tat inhibitors. We also assess the potential of new proteins belonging to the intriguing DING family, which have been reported to have potential anti-HIV-1 activity by inhibiting HIV gene transcription. Expert opinion: Targeting HIV-1 gene transcription is an alternative approach, which could overcome cART-related issues, such as the emergence of multidrug resistance. Improving cART will rely on the identification and characterization of new actors inhibiting HIV-1 transcription. Combining such efforts with the use of new technologies, the development of new models for preclinical studies, and improvement in drug delivery will considerably reduce drug toxicity and thus increase patient adherence.

Extracts from Acacia catechu suppress HIV-1 replication by inhibiting the activities of the viral protease and Tat

Background

Acacia catechu (Mimosa family) stem bark extracts have been used traditionally as a dietary supplement as well as a folk medicine given its reported anti-inflammatory, immunomodulatory, hepatoprotective, antioxidant, anti-microbial and anti-tumor activities. The present study was undertaken to evaluate the anti-HIV-1 activity of the extracts from stem bark of A. catechu.

Methods

The aqueous and 50% ethanolic extracts of A. catechu stem bark were prepared and 50% ethanolic extract was further fractioned by successively partitioning with petroleum ether, chloroform and n-butanol. All the extracts and fractions were evaluated for cytotoxicity and anti-HIV-1 activity using different in vitro assays. The active n-butanol fraction was evaluated for its inhibition against HIV-1 reverse transcriptase, integrase, protease, pro-viral genome integration and viral Tat protein mediated transactivation. The effect of n-butanol fraction on the induction of pro-inflammatory cytokines secretion in Vk2/E6E7 cells and transepithelial resistance in Caco-2 and HEC-1A cells was investigated.

Results

The aqueous and 50% ethanolic extracts of A. catechu showed IC₅₀ values of 1.8 ± 0.18 μg/ml and 3.6 ± 0.31 μg/ml, respectively in cell-free virus based assay using TZM-bl cells and HIV-1_NL4.3 (X-4 tropic). In the above assay, n-butanol fraction exhibited anti-HIV-1 activity with an IC₅₀ of 1.7 ± 0.12 μg/ml. The n-butanol fraction showed a dose-dependent inhibition against HIV-1_NL4.3 infection of the peripheral blood lymphocytes and against HIV-1_BaL(R-5-tropic) as well as two different primary viral isolates of HIV-1 infection of TZM-bl cells. The n-butanol fraction demonstrates a potent inhibitory activity against the viral protease (IC₅₀ = 12.9 μg/ml), but not reverse transcriptase or integrase. Further, in Alu-PCR no effect on viral integration was observed. The n-butanol fraction interfered with the Tat-mediated Long Terminal Repeat transactivation in TZM-bl cells, mRNA quantitation (qRT-PCR) and electrophoretic mobility shift assay (EMSA). The n-butanol fraction did not cause an enhanced secretion of pro-inflammatory cytokines in Vk2/E6E7 cells. Additionally, no adverse effects were observed to the monolayer formed by the Caco-2 and HEC-1A epithelial cells.

Conclusions

The results presented here show a potential anti-HIV-1 activity of A. catechu mediated by the inhibition of the functions of the viral protein and Tat.

3-Phenylcoumarins as inhibitors of HIV-1 replication

We have synthesized fourteen 3-phenylcoumarin derivatives and evaluated their anti-HIV activity. Antiviral activity was assessed on MT-2 cells infected with viral clones carrying the luciferase gene as reporter. Inhibition of HIV transcription and Tat function were tested on cells stably transfected with the HIV-LTR and Tat protein. Six compounds displayed NF-κB inhibition, four resulted Tat antagonists and three of them showed both activities. Three compounds inhibited HIV replication with IC₅₀ values < 25 µM. The antiviral effect of the 4-hydroxycoumarin derivative 19 correlates with its specific inhibition of Tat functions, while compound 8, 3-(2-chlorophenyl)coumarin, seems to act through a mechanism unrelated to the molecular targets considered in this research.

Small-molecule screening using a human primary cell model of HIV latency identifies compounds that reverse latency without cellular activation

The development of highly active antiretroviral therapy (HAART) to treat individuals infected with HIV-1 has dramatically improved patient outcomes, but HAART still fails to cure the infection. The latent viral reservoir in resting CD4+ T cells is a major barrier to virus eradication. Elimination of this reservoir requires reactivation of the latent virus. However, strategies for reactivating HIV-1 through nonspecific T cell activation have clinically unacceptable toxicities. We describe here the development of what we believe to be a novel in vitro model of HIV-1 latency that we used to search for compounds that can reverse latency. Human primary CD4+ T cells were transduced with the prosurvival molecule Bcl-2, and the resulting cells were shown to recapitulate the quiescent state of resting CD4+ T cells in vivo. Using this model system, we screened small-molecule libraries and identified a compound that reactivated latent HIV-1 without inducing global T cell activation, 5-hydroxynaphthalene-1,4-dione (5HN). Unlike previously described latency-reversing agents, 5HN activated latent HIV-1 through ROS and NF-kappaB without affecting nuclear factor of activated T cells (NFAT) and PKC, demonstrating that TCR pathways can be dissected and utilized to purge latent virus. Our study expands the number of classes of latency-reversing therapeutics and demonstrates the utility of this in vitro model for finding strategies to eradicate HIV-1 infection.

HIV-1 Nef inhibits lipopolysaccharide-induced IL-12p40 expression by inhibiting JNK-activated NFkappaB in human monocytic cells

Impaired cellular immunity caused by decreased production of Th1-type cytokines, including interleukin-12 (IL-12) is a major feature of HIV-1-associated immunodeficiency and acquired immunodeficiency syndrome. IL-12p40, an inducible subunit shared between IL-12 and IL-23, plays a critical role in the development of cellular immunity, and its production is significantly decreased during HIV infection. The mechanism by which HIV induces loss of IL-12p40 production remains poorly understood. We have previously shown that lipopolysaccharide (LPS)-induced IL-12p40 production in monocytic cells is regulated by NFkappaB and AP-1 transcription factors through the activation of two distinct upstream signaling pathways, namely the c-Jun-N-terminal kinase (JNK) and the calmodulin-dependent protein kinase-II-activated pathways. Herein, we show that intracellular nef expressed through transduction of primary monocytes and promonocytic THP-1 cells with retroviral-mediated nef gene inhibited LPS-induced IL-12p40 transcription by inhibiting the JNK mitogen-activated protein kinases without affecting the calmodulin-dependent protein kinase-II-activated pathway. In addition, nef inhibited JNK-activated NFkappaB without affecting the AP-1 activity. Overall, our results suggest for the first time that intracellular nef inhibited LPS-activated JNK, which may cause inhibition of IL-12p40 expression in human monocytic cells by selectively inhibiting NFkappaB activity.

PGJ2 antagonizes NF-kappaB-induced HIV-1 LTR activation in colonic epithelial cells

Intestinal epithelial cells play an important role in early stages of HIV-1 infection and long-term persistence of the virus. Here we determined the mechanism that regulates HIV-1 activation via prostaglandin J(2) (PGJ(2)) in Caco-2 cells. We showed that treatment of Caco-2 cells with PGJ(2) decreased the infectivity of a luciferase reporter virus, pHXB-luc, as well as HIV production following infection of cells with a X4-tropic virus by antagonizing sodium butyrate, a cellular activator known to induce HIV-1 transcription. Transfection of intestinal epithelial cells such as Caco-2, HT-29 and SW620 cells with full-length HIV-1 LTR (pLTR-luc) revealed that PGJ(2) reduced HIV-1 LTR-mediated reporter gene activity. The involvement of NF-kappaB in the PGJ(2)-dependent down-regulation of HIV-1 transcription was further assessed using the kappaB-regulated luciferase-encoding vectors. In Caco-2 cells, PGJ(2) decreased IKK activity, resulting in reduced NF-kappaB translocation to the nucleus. Since sodium butyrate has been associated with a chronic stress response in AIDS patients, our results suggest that addition of PGJ(2) in the environment of infected intestinal epithelial cells could reduce HIV-1 transcription.

Molecularly cloned SHIV-1157ipd3N4: a highly replication- competent, mucosally transmissible R5 simian-human immunodeficiency virus encoding HIV clade C Env

Human immunodeficiency virus type 1 (HIV-1) clade C causes >50% of all HIV infections worldwide, and an estimated 90% of all transmissions occur mucosally with R5 strains. A pathogenic R5 simian-human immunodeficiency virus (SHIV) encoding HIV clade C env is highly desirable to evaluate candidate AIDS vaccines in nonhuman primates. To this end, we generated SHIV-1157i, a molecular clone from a Zambian infant isolate that carries HIV clade C env. SHIV-1157i was adapted by serial passage in five monkeys, three of which developed peripheral CD4(+) T-cell depletion. After the first inoculated monkey developed AIDS at week 137 postinoculation, transfer of its infected blood to a naïve animal induced memory T-cell depletion and thrombocytopenia within 3 months in the recipient. In parallel, genomic DNA from the blood donor was amplified to generate the late proviral clone SHIV-1157ipd3. To increase the replicative capacity of SHIV-1157ipd3, an extra NF-kappaB binding site was engineered into its 3' long terminal repeat, giving rise to SHIV-1157ipd3N4. This virus was exclusively R5 tropic and replicated more potently in rhesus peripheral blood mononuclear cells than SHIV-1157ipd3 in the presence of tumor necrosis factor alpha. Rhesus macaques of Indian and Chinese origin were next inoculated intrarectally with SHIV-1157ipd3N4; this virus replicated vigorously in both sets of monkeys. We conclude that SHIV-1157ipd3N4 is a highly replication-competent, mucosally transmissible R5 SHIV that represents a valuable tool to test candidate AIDS vaccines targeting HIV-1 clade C Env.

Anti-HIV activity of stilbene-related heterocyclic compounds

Viral transcription has not been routinely targeted in the development of new antiviral drugs. This crucial step of the viral cycle depends on the concerted action of cellular and viral proteins such as NF-kappaB and Tat. In the present study, stilbene-related heterocyclic compounds including benzalphthalide, phthalazinone, imidazoindole and pyrimidoisoindole derivatives are tested for their anti-HIV activity. Original assays based on recombinant viruses were used to evaluate HIV replication inhibition and stably transfected cell lines were used to evaluate inhibition of Tat and NF-kappaB proteins. Some of the stilbene-related heterocyclic compounds analysed displayed anti-HIV activity through interference with NF-kappaB and Tat function. Moreover, compounds inhibiting both targets displayed a stronger activity on viral replication.

4-Phenylcoumarins as HIV transcription inhibitors

We have evaluated the anti-HIV activity of eleven natural 4-phenylcoumarins isolated from Marila pluricostata and three of their derivatives. Antiviral activity was assessed on MT-2 cells infected with viral clones carrying the luciferase gene as reporter. Inhibitions of HIV transcription and Tat function were tested on cells stably transfected with the HIV-LTR and Tat protein. Most of the coumarins tested displayed NF-kappaB inhibition. Two coumarins were also Tat antagonists and the presence of both activities correlated with a stronger inhibition of HIV replication. Our results show that antiviral effect of 4-phenylcoumarins can be related to the inhibition of NF-kappaB and Tat, and suggest that these types of compounds can be useful in the treatment of HIV infection as viral transcription inhibitors.

Cell cycle arrest in G2 induces human immunodeficiency virus type 1 transcriptional activation through histone acetylation and recruitment of CBP, NF-kappaB, and c-Jun to the long terminal repeat promoter

In human immunodeficiency virus type 1 (HIV-1)-infected cells, a cell cycle arrest in G(2) increases viral expression and may represent a strategy for the virus to optimize its expression. In latently infected cells, balance between viral silencing and reactivation relies on the nucleosomal organization of the integrated long terminal repeat (LTR). It is shown here that nucleosome nuc-1, which is located downstream of the TATA box, is specifically modified when latently infected cells are arrested in G(2) by chemical inducers. Notably, histones H3 and H4 are hyperacetylated, and this modification is associated with an increased LTR-driven transcription. nuc-1 hyperacetylation is also associated with the recruitment of histone acetyltransferase CBP and transcription factors NF-kappaB and c-Jun. NF-kappaB and/or c-Jun binding to the LTR in G(2)-arrested cells appears to be required for CBP recruitment as well as for nuc-1 remodeling and viral reactivation.

Administration of HDAC inhibitors to reactivate HIV-1 expression in latent cellular reservoirs: implications for the development of therapeutic strategies

The discovery of powerful antiviral compounds in the 90's raised the hope that the human immunodeficiency virus type 1 (HIV-1) might be eradicated. However, if these drugs succeed in decreasing and controlling viral replication, complete eradication of the virus is nowadays impossible. The persistence of virus even after long periods of highly active antiretroviral therapy (HAART) mainly results from the presence of cellular reservoirs that contain transcriptionally competent latent viruses capable of producing infectious particles after cellular activation. These latently infected cells are a permanent source for virus reactivation and lead to a rebound of the viral load after interruption of HAART. Activation of HIV gene expression in these cells combined with an effective HAART has been proposed as an adjuvant therapy that could lead to the elimination of the latently infected cells and then to the eradication of the infection. In this context, we have previously demonstrated that deacetylase inhibitors (HDACi) synergize with TNF-induced NF-kappaB to activate the HIV-1 promoter. The physiological relevance of the TNF/HDACi synergism was shown on HIV-1 replication in both acutely and latently HIV-infected cell lines. Based on these results, we propose the administration of deacetylase inhibitor(s) together with continuous HAART as a new potential therapeutic perspective to decrease the pool of latent HIV reservoirs by forcing viral expression.

Anti-HIV activity of some synthetic lignanolides and intermediates

The evaluation of the anti-HIV-1 activity of synthetic lignanolides and their intermediates is reported. The antiviral activity was studied through luciferase-based assays targeting the HIV-1 promoter activation induced by either, the HIV-1 Tat protein or the cellular transcription factor NF-kappaB, both known as crucial factors in HIV-1 replication. Among the compounds tested, three of them 2, 4 and 13 were further analysed for their anti-HIV-1 activity by recombinant virus assays, showing a suitable profile for development of novel anti-HIV-1 drugs.

Inhibition of herpesvirus-induced HIV-1 replication by cyclopentenone prostaglandins: role of IkappaB kinase (IKK)

OBJECTIVES

Herpes simplex virus (HSV) infections have been associated with reactivation of HIV-1 replication and increases of HIV-1-load in plasma of co-infected individuals. The present authors have previously reported that in epithelial cells HSV-1 induces the IkappaB-kinase (IKK) causing persistent activation of NF-kappaB, a critical regulator of HIV-1 replication. The present study was performed to investigate whether HSV-1-infection could induce IKK-mediated NF-kappaB activation and enhance HIV-1 expression in human T cells, and to analyze the effect of the IKK-inhibitor prostaglandin A1 (PGA1) and other prostanoids on the NF-kappaB-mediated HSV-HIV interaction.

DESIGN AND METHODS

Induction of IKK and NF-kappaB activity was determined in lymphoblastoid Jurkat cells and HIV-1 chronically-infected H9 and ACH-2 cells by kinase assay and electrophoretic mobility shift assay, respectively. The effect of HSV-1 and different prostanoids on HIV-1 expression and replication was determined in Jurkat cells transfected with HIV-1-LTR-driven reporter genes, and in H9 and ACH-2 cells by p24-antigen level evaluation. The role of NF-kappaB in HSV-1-induced HIV-1 expression was investigated by using the IkappaBalpha dominant-negative IkappaBalpha-AA in co-transfection experiments.

RESULTS

In human T lymphoblastoid cells HSV-1 potently induces IKK activity, causing a persistent induction of NF-kappaB. HSV-1-induced IKK and NF-kappaB function results in transactivation of HIV-1-LTR-regulated genes and induction of HIV-1 replication in chronically-infected T cells. The cyclopentenone PGA1 inhibits HSV-1-induced IKK and NF-kappaB activities, blocking HIV-1-LTR-driven expression and preventing HSV-1-induced HIV-1 replication in co-infected cells.

CONCLUSIONS

The results indicate that IKK is a key factor in triggering HSV-1-induced HIV-1 transcription in chronically-infected cells and identify cyclopentenone prostanoids as potent inhibitors of HSV-1-induced HIV-1 reactivation.

Expression of histone acetyltransferases was down-regulated in poly(ADP-ribose) polymerase-1-deficient murine cells

NF-kappaB-dependent, as well as human immunodeficiency virus type-1 (HIV-1) long terminal repeat (LTR)-dependent, reporter gene expression was significantly impaired in cells derived from poly(ADP-ribose) polymerase-1 (PARP-1)-knockout (PARP-1 -/-) mice. In addition, the level of protein acetylation was markedly lower in PARP-1 -/- cells than control (PARP-1 +/+) cells. Surprisingly, the expression levels of histone acetyltransferases (HATs), p300, cAMP response element-binding protein-binding protein (CBP), and p300/CBP-associated factor (PCAF), were significantly reduced in PARP-1 -/- cells, as compared with PARP-1 +/+ cells. These results suggest that PARP-1 is required for the proper expression of particular HATs. Since p300 and CBP are coactivators of NF-kappaB, we propose here that PARP-1 participates in NF-kappaB-dependent transcription by means of maintaining the expression of HATs.

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.

Identification of T cell-signaling pathways that stimulate latent HIV in primary cells

Eradication of HIV infection depends on the elimination of a small, but stable population of latently infected T cells. After the discontinuation of therapy, activation of latent virus can rekindle infection. To purge this reservoir, it is necessary to define cellular signaling pathways that lead to activation of latent HIV. We used the SCID-hu (Thy/Liv) mouse model of HIV latency to analyze a broad array of T cell-signaling pathways and show in primary, quiescent cells that viral induction depends on the activation of two primary intracellular signaling pathways, protein kinase C or nuclear factor of activated T cells (NF-AT). In contrast, inhibition or activation of other important T cell stimulatory pathways (such as mitogen-activated protein kinase, calcium flux, or histone deacetylation) do not significantly induce virus expression. We found that the activation of NF-kappaB is critical to viral reactivation; however, all pathways that stimulate NF-kappaBdonot reactivate latent virus. Our studies further show that inhibition of NF-kappaB does not prevent activation of HIV by NF-AT, indicating that these pathways can function independently to activate the HIV LTR. Thus, we define several molecular pathways that trigger HIV reactivation from latency and provide evidence that latent HIV infection is maintained by the functional lack of particular transcription factors in quiescent cells.

Synergistic activation of human immunodeficiency virus type 1 promoter activity by NF-kappaB and inhibitors of deacetylases: potential perspectives for the development of therapeutic strategies

The transcription factor NF-kappaB plays a central role in the human immunodeficiency virus type 1 (HIV-1) activation pathway. HIV-1 transcription is also regulated by protein acetylation, since treatment with deacetylase inhibitors such as trichostatin A (TSA) or sodium butyrate (NaBut) markedly induces HIV-1 transcriptional activity of the long terminal repeat (LTR) promoter. Here, we demonstrate that TSA (NaBut) synergized with both ectopically expressed p50/p65 and tumor necrosis factor alpha/SF2 (TNF)-induced NF-kappaB to activate the LTR. This was confirmed for LTRs from subtypes A through G of the HIV-1 major group, with a positive correlation between the number of kappaB sites present in the LTRs and the amplitude of the TNF-TSA synergism. Mechanistically, TSA (NaBut) delayed the cytoplasmic recovery of the inhibitory protein IkappaBalpha. This coincided with a prolonged intranuclear presence and DNA binding activity of NF-kappaB. The physiological relevance of the TNF-TSA (NaBut) synergism was shown on HIV-1 replication in both acutely and latently HIV-infected cell lines. Therefore, our results open new therapeutic strategies aimed at decreasing or eliminating the pool of latently HIV-infected reservoirs by forcing viral expression.

Diversity of acetylation targets and roles in transcriptional regulation: the human immunodeficiency virus type 1 promoter as a model system

Persuasive evidence has accumulated that reversible acetylation of proteins is key post-translational modification regulating transcription in eukaryotes. Deacetylase inhibitors (such as trichostatin A) modulate the expression of approximately 2% of all cellular genes. We and others have demonstrated a marked transcriptional activation of the human immunodeficiency virus type 1 (HIV-1) promoter in response to deacetylase inhibitors. Deacetylation events seem to be an important mechanism of HIV-1 transcriptional repression during latency, whereas acetylation events play critical functional roles in HIV-1 reactivation from latency. These deacetylation/acetylation events are implicated in chromatin remodeling of the viral promoter region, as well as in modulating the functional properties of cellular and viral transcription factors binding to this promoter region. Thereby, the HIV-1 promoter constitutes a unique regulatory model system to study the complex relationship between acetylation processes and transcriptional activity.