Specific interaction of TFII-I with an upstream element on the HIV-1 LTR regulates induction of latent provirus

The HIV-1 Transcriptional Program: From Initiation to Elongation Control

A large body of work in the last four decades has revealed the key pillars of HIV-1 transcription control at the initiation and elongation steps. Here, I provide a recount of this collective knowledge starting with the genomic elements (DNA and nascent TAR RNA stem-loop) and transcription factors (cellular and the viral transactivator Tat), and later transitioning to the assembly and regulation of transcription initiation and elongation complexes, and the role of chromatin structure. Compelling evidence support a core HIV-1 transcriptional program regulated by the sequential and concerted action of cellular transcription factors and Tat to promote initiation and sustain elongation, highlighting the efficiency of a small virus to take over its host to produce the high levels of transcription required for viral replication. I summarize new advances including the use of CRISPR-Cas9, genetic tools for acute factor depletion, and imaging to study transcriptional dynamics, bursting and the progression through the multiple phases of the transcriptional cycle. Finally, I describe current challenges to future major advances and discuss areas that deserve more attention to both bolster our basic knowledge of the core HIV-1 transcriptional program and open up new therapeutic opportunities.

A Canadian Survey of Research on HIV-1 Latency-Where Are We Now and Where Are We Heading?

Worldwide, almost 40 million people are currently living with HIV-1. The implementation of cART inhibits HIV-1 replication and reduces viremia but fails to eliminate HIV-1 from latently infected cells. These cells are considered viral reservoirs from which HIV-1 rebounds if cART is interrupted. Several efforts have been made to identify these cells and their niches. There has been little success in diminishing the pool of latently infected cells, underscoring the urgency to continue efforts to fully understand how HIV-1 establishes and maintains a latent state. Reactivating HIV-1 expression in these cells using latency-reversing agents (LRAs) has been successful, but only in vitro. This review aims to provide a broad view of HIV-1 latency, highlighting Canadian contributions toward these aims. We will summarize the research efforts conducted in Canadian labs to understand the establishment of latently infected cells and how this informs curative strategies, by reviewing how HIV latency is established, which cells are latently infected, what methodologies have been developed to characterize them, how new compounds are discovered and evaluated as potential LRAs, and what clinical trials aim to reverse latency in people living with HIV (PLWH).

CDK8 inhibitors antagonize HIV-1 reactivation and promote provirus latency in T cells

Latent HIV-1 provirus represents the barrier toward a cure for infection and is dependent upon the host RNA Polymerase (Pol) II machinery for reemergence. Here, we find that inhibitors of the RNA Pol II mediator kinases CDK8/19, Senexin A and BRD6989, inhibit induction of HIV-1 expression in response to latency-reversing agents and T cell signaling agonists. These inhibitors were found to impair recruitment of RNA Pol II to the HIV-1 LTR. Furthermore, HIV-1 expression in response to several latency reversal agents was impaired upon disruption of CDK8 by shRNA or gene knockout. However, the effects of CDK8 depletion did not entirely mimic CDK8/19 kinase inhibition suggesting that the mediator kinases are not functionally redundant. Additionally, treatment of CD4+ peripheral blood mononuclear cells isolated from people living with HIV-1 and who are receiving antiretroviral therapy with Senexin A inhibited induction of viral replication in response to T cell stimulation by PMA and ionomycin. These observations indicate that the mediator kinases, CDK8 and CDK19, play a significant role for regulation of HIV-1 transcription and that small molecule inhibitors of these enzymes may contribute to therapies designed to promote deep latency involving the durable suppression of provirus expression. IMPORTANCE A cure for HIV-1 infection will require novel therapies that can force elimination of cells that contain copies of the virus genome inserted into the cell chromosome, but which is shut off, or silenced. These are known as latently-infected cells, which represent the main reason why current treatment for HIV/AIDS cannot cure the infection because the virus in these cells is unaffected by current drugs. Our results indicate that chemical inhibitors of Cdk8 also inhibit the expression of latent HIV provirus. Cdk8 is an important enzyme that regulates the expression of genes in response to signals to which cells need to respond and which is produced by a gene that is frequently mutated in cancers. Our observations indicate that Cdk8 inhibitors may be employed in novel therapies to prevent expression from latent provirus, which might eventually enable infected individuals to cease treatment with antiretroviral drugs.

Upstream Stimulatory Factors Regulate HIV-1 Latency and Are Required for Robust T Cell Activation

HIV-1 provirus expression is controlled by signaling pathways that are responsive to T cell receptor engagement, including those involving Ras and downstream protein kinases. The induction of transcription from the HIV-1 LTR in response to Ras signaling requires binding of the Ras-responsive element binding factor (RBF-2) to conserved cis elements flanking the enhancer region, designated RBE3 and RBE1. RBF-2 is composed minimally of the USF1, USF2, and TFII-I transcription factors. We recently determined that TFII-I regulates transcriptional elongation from the LTR through recruitment of the co-activator TRIM24. However, the function of USF1 and USF2 for this effect are uncharacterized. Here, we find that genetic deletion of USF2 but not USF1 in T cells inhibits HIV-1 expression. The loss of USF2 caused a reduction in expression of the USF1 protein, an effect that was not associated with decreased USF1 mRNA abundance. USF1 and USF2 were previously shown to exist predominately as heterodimers and to cooperatively regulate target genes. To examine cooperativity between these factors, we performed RNA-seq analysis of T cell lines bearing knockouts of the genes encoding these factors. In untreated cells, we found limited evidence of coordinated global gene regulation between USF1 and USF2. In contrast, we observed a high degree of genome-wide cooperative regulation of RNA expression between these factors in cells stimulated with the combination of PMA and ionomycin. In particular, we found that the deletion of USF1 or USF2 restricted T cell activation response. These observations indicate that USF2, but not USF1, is crucial for HIV-1 expression, while the combined function of these factors is required for a robust T cell inflammatory response.

HIV silencing and cell survival signatures in infected T cell reservoirs

Rare CD4 T cells that contain HIV under antiretroviral therapy represent an important barrier to HIV cure1-3, but the infeasibility of isolating and characterizing these cells in their natural state has led to uncertainty about whether they possess distinctive attributes that HIV cure-directed therapies might exploit. Here we address this challenge using a microfluidic technology that isolates the transcriptomes of HIV-infected cells based solely on the detection of HIV DNA. HIV-DNA+ memory CD4 T cells in the blood from people receiving antiretroviral therapy showed inhibition of six transcriptomic pathways, including death receptor signalling, necroptosis signalling and antiproliferative Gα12/13 signalling. Moreover, two groups of genes identified by network co-expression analysis were significantly associated with HIV-DNA+ cells. These genes (n = 145) accounted for just 0.81% of the measured transcriptome and included negative regulators of HIV transcription that were higher in HIV-DNA+ cells, positive regulators of HIV transcription that were lower in HIV-DNA+ cells, and other genes involved in RNA processing, negative regulation of mRNA translation, and regulation of cell state and fate. These findings reveal that HIV-infected memory CD4 T cells under antiretroviral therapy are a distinctive population with host gene expression patterns that favour HIV silencing, cell survival and cell proliferation, with important implications for the development of HIV cure strategies.

TRIM24 controls induction of latent HIV-1 by stimulating transcriptional elongation

Binding of USF1/2 and TFII-I (RBF-2) at conserved sites flanking the HIV-1 LTR enhancer is essential for reactivation from latency in T cells, with TFII-I knockdown rendering the provirus insensitive to T cell signaling. We identified an interaction of TFII-I with the tripartite motif protein TRIM24, and these factors were found to be constitutively associated with the HIV-1 LTR. Similar to the effect of TFII-I depletion, loss of TRIM24 impaired reactivation of HIV-1 in response to T cell signaling. TRIM24 deficiency did not affect recruitment of RNA Pol II to the LTR promoter, but inhibited transcriptional elongation, an effect that was associated with decreased RNA Pol II CTD S2 phosphorylation and impaired recruitment of CDK9. A considerable number of genomic loci are co-occupied by TRIM24/TFII-I, and we found that TRIM24 deletion caused altered T cell immune response, an effect that is facilitated by TFII-I. These results demonstrate a role of TRIM24 for regulation of transcriptional elongation from the HIV-1 promoter, through its interaction with TFII-I, and by recruitment of P-TEFb. Furthermore, these factors co-regulate a significant proportion of genes involved in T cell immune response, consistent with tight coupling of HIV-1 transcriptional activation and T cell signaling.

Depicting HIV-1 Transcriptional Mechanisms: A Summary of What We Know

Despite the introduction of combinatory antiretroviral therapy (cART), HIV-1 infection cannot be cured and is still one of the major health issues worldwide. Indeed, as soon as cART is interrupted, a rapid rebound of viremia is observed. The establishment of viral latency and the persistence of the virus in cellular reservoirs constitute the main barrier to HIV eradication. For this reason, new therapeutic approaches have emerged to purge or restrain the HIV-1 reservoirs in order to cure infected patients. However, the viral latency is a multifactorial process that depends on various cellular mechanisms. Since these new therapies mainly target viral transcription, their development requires a detailed and precise understanding of the regulatory mechanism underlying HIV-1 transcription. In this review, we discuss the complex molecular transcriptional network regulating HIV-1 gene expression by focusing on the involvement of host cell factors that could be used as potential drug targets to design new therapeutic strategies and, to a larger extent, to reach an HIV-1 functional cure.

Cat and Mouse: HIV Transcription in Latency, Immune Evasion and Cure/Remission Strategies

There is broad scientific and societal consensus that finding a cure for HIV infection must be pursued. The major barrier to achieving a cure for HIV/AIDS is the capacity of the HIV virus to avoid both immune surveillance and current antiretroviral therapy (ART) by rapidly establishing latently infected cell populations, termed latent reservoirs. Here, we provide an overview of the rapidly evolving field of HIV cure/remission research, highlighting recent progress and ongoing challenges in the understanding of HIV reservoirs, the role of HIV transcription in latency and immune evasion. We review the major approaches towards a cure that are currently being explored and further argue that small molecules that inhibit HIV transcription, and therefore uncouple HIV gene expression from signals sent by the host immune response, might be a particularly promising approach to attain a cure or remission. We emphasize that a better understanding of the game of "cat and mouse" between the host immune system and the HIV virus is a crucial knowledge gap to be filled in both cure and vaccine research.

High-density genotyping of immune-related loci identifies new SLE risk variants in individuals with Asian ancestry

Systemic lupus erythematosus (SLE) has a strong but incompletely understood genetic architecture. We conducted an association study with replication in 4,478 SLE cases and 12,656 controls from six East Asian cohorts to identify new SLE susceptibility loci and better localize known loci. We identified ten new loci and confirmed 20 known loci with genome-wide significance. Among the new loci, the most significant locus was GTF2IRD1-GTF2I at 7q11.23 (rs73366469, Pmeta = 3.75 × 10(-117), odds ratio (OR) = 2.38), followed by DEF6, IL12B, TCF7, TERT, CD226, PCNXL3, RASGRP1, SYNGR1 and SIGLEC6. We identified the most likely functional variants at each locus by analyzing epigenetic marks and gene expression data. Ten candidate variants are known to alter gene expression in cis or in trans. Enrichment analysis highlights the importance of these loci in B cell and T cell biology. The new loci, together with previously known loci, increase the explained heritability of SLE to 24%. The new loci share functional and ontological characteristics with previously reported loci and are possible drug targets for SLE therapeutics.

Post-transcriptional gene silencing, transcriptional gene silencing and human immunodeficiency virus

While human immunodeficiency virus 1 (HIV-1) infection is controlled through continuous, life-long use of a combination of drugs targeting different steps of the virus cycle, HIV-1 is never completely eradicated from the body. Despite decades of research there is still no effective vaccine to prevent HIV-1 infection. Therefore, the possibility of an RNA interference (RNAi)-based cure has become an increasingly explored approach. Endogenous gene expression is controlled at both, transcriptional and post-transcriptional levels by non-coding RNAs, which act through diverse molecular mechanisms including RNAi. RNAi has the potential to control the turning on/off of specific genes through transcriptional gene silencing (TGS), as well as fine-tuning their expression through post-transcriptional gene silencing (PTGS). In this review we will describe in detail the canonical RNAi pathways for PTGS and TGS, the relationship of TGS with other silencing mechanisms and will discuss a variety of approaches developed to suppress HIV-1 via manipulation of RNAi. We will briefly compare RNAi strategies against other approaches developed to target the virus, highlighting their potential to overcome the major obstacle to finding a cure, which is the specific targeting of the HIV-1 reservoir within latently infected cells.

Interplay between viral Tat protein and c-Jun transcription factor in controlling LTR promoter activity in different human immunodeficiency virus type I subtypes

HIV-1 transcription depends on cellular transcription factors that bind to sequences in the long-terminal repeat (LTR) promoter. Each HIV-1 subtype has a specific LTR promoter configuration, and minor sequence changes in transcription factor binding sites (TFBSs) or their arrangement can influence transcriptional activity, virus replication and latency properties. Previously, we investigated the proviral latency properties of different HIV-1 subtypes in the SupT1 T cell line. Here, subtype-specific latency and replication properties were studied in primary PHA-activated T lymphocytes. No major differences in latency and replication capacity were measured among the HIV-1 subtypes. Subtype B and AE LTRs were studied in more detail with regard to a putative AP-1 binding site using luciferase reporter constructs. c-Jun, a member of the AP-1 transcription factor family, can activate both subtype B and AE LTRs, but the latter showed a stronger response, reflecting a closer match with the consensus AP-1 binding site. c-Jun overexpression enhanced Tat-mediated transcription of the viral LTR, but in the absence of Tat inhibited basal promoter activity. Thus, c-Jun can exert a positive or negative effect via the AP-1 binding site in the HIV-1 LTR promoter, depending on the presence or absence of Tat.

ZASC1 stimulates HIV-1 transcription elongation by recruiting P-TEFb and TAT to the LTR promoter

Transcription from the HIV-1 LTR promoter efficiently initiates but rapidly terminates because of a non-processive form of RNA polymerase II. This premature termination is overcome by assembly of an HIV-1 TAT/P-TEFb complex at the transactivation response region (TAR), a structured RNA element encoded by the first 59 nt of HIV-1 mRNA. Here we have identified a conserved DNA-binding element for the cellular transcription factor, ZASC1, in the HIV-1 core promoter immediately upstream of TAR. We show that ZASC1 interacts with TAT and P-TEFb, co-operating with TAT to regulate HIV-1 gene expression, and promoting HIV-1 transcriptional elongation. The importance of ZASC1 to HIV-1 transcription elongation was confirmed through mutagenesis of the ZASC1 binding sites in the LTR promoter, shRNAs targeting ZASC1 and expression of dominant negative ZASC1. Chromatin immunoprecipitation analysis revealed that ZASC1 recruits Tat and P-TEFb to the HIV-1 core promoter in a TAR-independent manner. Thus, we have identified ZASC1 as novel regulator of HIV-1 gene expression that functions through the DNA-dependent, RNA-independent recruitment of TAT/P-TEFb to the HIV-1 promoter.

An upstream YY1 binding site on the HIV-1 LTR contributes to latent infection

During HIV-1 infection a population of latently infected cells is established. This population is the major obstacle preventing total eradication of the virus from AIDS patients. HIV-1 latency is thought to arise by various mechanisms including repressive chromatin modifications. Transcription factors such as YY1 have been shown to facilitate repressive chromatin modifications by the recruitment of histone deacetylases. In this study, we identified a novel binding site for YY1 on the HIV-1 LTR, 120 nucleotides upstream of the transcription start site. We show that YY1 can bind to this site in vitro and in vivo and that binding to the LTR is dissociated upon T cell activation. Overexpression of YY1 causes an increase in the proportion of cells that produce latent infections. These observations, in combination with previous results, demonstrate that YY1 plays a prominent role in controlling the establishment and maintenance of latent HIV-1 provirus in unstimulated cells.

Establishment and molecular mechanisms of HIV-1 latency in T cells

Treatment of an HIV infected individual with antiretroviral drugs is a successful way to suppress the plasma viral RNA load below the limit of detection (50 copies HIV RNA/ml plasma). This can provide lifelong protection against virus-induced pathogenesis in drug-adherent patients. Unfortunately, even after many years of continuous treatment, the virus persists and the plasma viral load will rebound rapidly when therapy is interrupted. The reason for this rapid rebound is the presence of a long-lived reservoir of latent HIV-1 proviruses that can be reactivated in resting memory T cells. Attempts to eliminate these proviruses have thus far not been successful and this long-lived latent reservoir is therefore considered a major obstacle toward a cure for HIV-1. A detailed understanding of the molecular mechanisms causing HIV latency and knowledge on the establishment of this reservoir may give us clues for future strategies aiming at the eradication of this reservoir.

Evolution of general transcription factors

Three genes GTF2IRD1, GTF2I, and GTF2IRD2, which encode members of the GTF2I (or TFII-I) family of so-called general transcription factors, were discovered and studied during the last two decades. Chromosome location and similarity of exon-intron structures suggest that the family evolved by duplications. The initial duplication of ancestral proto-GTF2IRD1 gene likely occurred in early vertebrates prior to origin of cartilaginous fish and led to formation of GTF2I (>450 MYA), which was later lost in bony fish but successfully evolved in the land vertebrates. The second duplication event, which created GTF2IRD2, occurred prior to major radiation events of eutherian mammalian evolution (>100 MYA). During recent steps of primate evolution there was another duplication which led to formation of GTF2IRD2B (<4 MYA). Two latest duplications were coupled with inversions. Genes belonging to the family have several highly conservative repeats which are implicated in DNA binding. Phylogenetic analysis of the repeats revealed a pattern of intragenic duplications, deletions and substitutions which led to diversification of the genes and proteins. Distribution of statistically rare atypical substitutions (p ≤ 0.01) sheds some light on structural differentiation of repeats and hence evolution of the genes. The atypical substitutions are often located on secondary structures joining α-helices and affect 3D arrangement of the protein globule. Such substitutions are commonly traced at the early stages of evolution in Tetrapoda, Amniota, and Mammalia.

The development of immune-modulating compounds to disrupt HIV latency

Antiretroviral therapy (ART) has proved highly effective in suppressing HIV-1 replication and disease progression. Nevertheless, ART has failed to eliminate the virus from infected individuals. The main obstacle to HIV-1 eradication is the persistence of cellular viral reservoirs. Therefore, the "shock-and-kill" strategy was proposed consisting of inducing HIV-1 escape from latency, in the presence of ART. This is followed by the elimination of reactivated, virus-producing cells. Immune modulators, including protein kinase C (PKC) activators, anti-leukemic drugs and histone deacetylase inhibitors (HDACis) have all demonstrated efficacy in the reactivation of latent virus replication. This review will focus on the potential use of these small molecules in the "shock and kill" strategy, the molecular basis for their action and the potential advantages of their immune-modulating activities.

Cdk8 regulates stability of the transcription factor Phd1 to control pseudohyphal differentiation of Saccharomyces cerevisiae

The yeast Saccharomyces differentiates into filamentous pseudohyphae when exposed to a poor source of nitrogen in a process involving a collection of transcription factors regulated by nutrient signaling pathways. Phd1 is important for this process in that it regulates expression of most other transcription factors involved in differentiation and can induce filamentation on its own when overproduced. In this article, we show that Phd1 is an unstable protein whose degradation is initiated through phosphorylation by Cdk8 of the RNA polymerase II mediator subcomplex. Phd1 is stabilized by cdk8 disruption, and the naturally filamenting Σ1278b strain was found to have a sequence polymorphism that eliminates a Cdk8 phosphorylation site, which both stabilizes the protein and contributes to enhanced differentiation. In nitrogen-starved cells, PHD1 expression is upregulated and the Phd1 protein becomes stabilized, which causes its accumulation during differentiation. PHD1 expression is partially dependent upon Ste12, which was also previously shown to be destabilized by Cdk8-dependent phosphorylations, but to a significantly smaller extent than Phd1. These observations demonstrate the central role that Cdk8 plays in initiation of differentiation. Cdk8 activity is inhibited in cells shifted to limiting nutrient conditions, and we argue that this effect drives the initiation of differentiation through stabilization of multiple transcription factors, including Phd1, that cause activation of genes necessary for filamentous response.

The Suv39H1 methyltransferase inhibitor chaetocin causes induction of integrated HIV-1 without producing a T cell response

Latent HIV-1 (human immunodeficiency virus-1) provirus is unaffected by current AIDS (acquired immunodeficiency syndrome) therapies. We show here that chaetocin, an SUV39H1 histone methyltransferase inhibitor, causes 25-fold induction of latent HIV-1 expression, while producing minimal toxicity and without causing T cell activation. Induction is associated with loss of histone H3 lysine 9 (H3K9) trimethylation at the long terminal repeat (LTR) promoter, and a corresponding increase in H3K9 acetylation. The effect of chaetocin is amplified synergistically in combination with histone deacetylase (HDAC) inhibitors. These results indicate that chaetocin may provide a therapy to purge cells of latent HIV-1, possibly in combination with other chromatin remodeling drugs.

Identification and functional analysis of a second RBF-2 binding site within the HIV-1 promoter

Transcription from the HIV-1 long terminal repeat (LTR) is mediated by numerous host transcription factors. In this study we characterized an E-box motif (RBE1) within the core promoter that was previously implicated in both transcriptional activation and repression. We show that RBE1 is a binding site for the RBF-2 transcription factor complex (USF1, USF2, and TFII-I), previously shown to bind an upstream viral element, RBE3. The RBE1 and RBE3 elements formed complexes of identical mobility and protein constituents in gel shift assays, both with Jurkat T-cell nuclear extracts and recombinant USF/TFII-I. Furthermore, both elements are regulators of HIV-1 expression; mutations in LTR-luciferase reporters and in HIV-1 molecular clones resulted in decreased transcription, virion production, and proviral expression in infected cells. Collectively, our data indicate that RBE1 is a bona fide RBF-2 binding site and that the RBE1 and RBE3 elements are necessary for mediating proper transcription from the HIV-1 LTR.

Sterol regulatory element-binding protein 2 couples HIV-1 transcription to cholesterol homeostasis and T cell activation

Cholesterol plays an essential role in the life cycle of several enveloped viruses. Many of these viruses manipulate host cholesterol metabolism to facilitate their replication. HIV-1 infection of CD4(+) T cells activates the sterol regulatory element-binding protein 2 (SREBP2) transcriptional program, which includes genes involved in cholesterol homeostasis. However, the role of SREBP2-dependent transcription in HIV-1 biology has not been fully examined. Here, we identify TFII-I, a gene critical for HIV-1 transcription in activated T cells, as a novel SREBP2 target gene. We found TFII-I expression increased after HIV-1 infection or activation of human primary CD4(+) T cells. We show that inhibition of SREBP2 activity reduced TFII-I induction in response to these stimuli. More importantly, small interfering RNA (siRNA)-mediated gene silencing of either SREBP2 or TFII-I significantly reduced HIV-1 production in CD4(+) T cells. We also found that TFII-I potentiates Tat-dependent viral gene expression, consistent with a role at the level of HIV-1 transcription. Collectively, our results demonstrate for the first time that HIV-1 transcription in T cells is linked to cholesterol homeostasis through control of TFII-I expression by SREBP2.

Curing HIV: Pharmacologic approaches to target HIV-1 latency

HIV-1 infection persists even after years of antiretroviral therapy (ART). Although ART can halt viral replication and thereby reduce viremia to clinically undetectable levels, proviral latency established within the host genome remains largely unaffected by ART and can replenish systemic infection following interruption of therapy. Pharmacologic strategies, which not only target viral replication but also deplete proviral infection, are required for successful clearance of HIV-1 infection. This review highlights the current understanding of molecular mechanisms that establish and maintain HIV-1 latency in its major reservoir, the resting memory CD4(+) T cell. We also identify the molecular targets that might be exploited to induce HIV-1 expression, remove epigenetic restrictions, or enhance effective transcription. Finally, we discuss the potential pharmacologic approaches toward targeting viral persistence in different cellular and anatomical reservoirs to achieve a cure of HIV-1 infection.

Molecular control of HIV-1 postintegration latency: implications for the development of new therapeutic strategies

The persistence of HIV-1 latent reservoirs represents a major barrier to virus eradication in infected patients under HAART since interruption of the treatment inevitably leads to a rebound of plasma viremia. Latency establishes early after infection notably (but not only) in resting memory CD4⁺ T cells and involves numerous host and viral trans-acting proteins, as well as processes such as transcriptional interference, RNA silencing, epigenetic modifications and chromatin organization. In order to eliminate latent reservoirs, new strategies are envisaged and consist of reactivating HIV-1 transcription in latently-infected cells, while maintaining HAART in order to prevent de novo infection. The difficulty lies in the fact that a single residual latently-infected cell can in theory rekindle the infection. Here, we review our current understanding of the molecular mechanisms involved in the establishment and maintenance of HIV-1 latency and in the transcriptional reactivation from latency. We highlight the potential of new therapeutic strategies based on this understanding of latency. Combinations of various compounds used simultaneously allow for the targeting of transcriptional repression at multiple levels and can facilitate the escape from latency and the clearance of viral reservoirs. We describe the current advantages and limitations of immune T-cell activators, inducers of the NF-κB signaling pathway, and inhibitors of deacetylases and histone- and DNA- methyltransferases, used alone or in combinations. While a solution will not be achieved by tomorrow, the battle against HIV-1 latent reservoirs is well- underway.

IL-2-inducible T-cell kinase (ITK) finds another (dance) partner...TFII-I

The signals that regulate T-cell activation have been studied for some time. We know that upon interaction with antigen/MHC complex, the TCR triggers the activation of a number of kinases, including tyrosine and serine/threonine kinases. The Tec family kinase IL-2- inducible T-cell kinase (ITK) plays a role in this response, but the signaling pathways that ITK regulates are less well known. Even less known are the binding partners and substrates of ITK. A paper in this issue of the European Journal of Immunology extends our knowledge on the subject by showing that ITK interacts with the transcriptional regulator TFII-I. The implications of this finding are discussed.