Analysis of protein kinase C theta inhibitors for the control of HIV-1 replication in human CD4+ T cells reveals an effect on retrotranscription in addition to viral transcription

The Dynamic Linkage between Provirus Integration Sites and the Host Functional Genome Property Alongside HIV-1 Infections Associated with Antiretroviral Therapy

(1) Background: The HIV-1 latent reservoir harboring replication-competent proviruses is the major barrier in the quest for an HIV-1 infection cure. HIV-1 infection at all stages of disease progression is associated with immune activation and dysfunctional production of proinflammatory soluble factors (cytokines and chemokines), and it is expected that during HIV-1 infection, different immune components and immune cells, in turn, participate in immune responses, subsequently activating downstream biological pathways. However, the functional interaction between HIV-1 integration and the activation of host biological pathways is presently not fully understood. (2) Methods: In this work, I used genes targeted by proviruses from published datasets to seek enriched immunologic signatures and host biological pathways alongside HIV-1 infections based on MSigDb and KEGG over-representation analysis. (3) Results: I observed that different combinations of immunologic signatures of immune cell types and proinflammatory soluble factors appeared alongside HIV-1 infections associated with antiretroviral therapy. Moreover, enriched KEGG pathways were often related to "cancer specific types", "immune system", "infectious disease viral", and "signal transduction". (4) Conclusions: The observations in this work suggest that the gene sets harboring provirus integration sites may define specific immune cells and proinflammatory soluble factors during HIV-1 infections associated with antiretroviral therapy.

Nucleic acid recognition and antiviral activity of 1,4-substituted terphenyl compounds mimicking all faces of the HIV-1 Rev protein positively-charged α-helix

Small synthetic molecules mimicking the three-dimensional structure of α-helices may find applications as inhibitors of therapeutically relevant protein-protein and protein-nucleic acid interactions. However, the design and use of multi-facial helix mimetics remains in its infancy. Here we describe the synthesis and application of novel bilaterally substituted p-terphenyl compounds containing positively-charged aminoalkyl groups in relative 1,4 positions across the aromatic scaffold. These compounds were specifically designed to mimic all faces of the arginine-rich α-helix of the HIV-1 protein Rev, which forms deeply embedded RNA complexes and plays key roles in the virus replication cycle. Two of these molecules recognized the Rev site in the viral RNA and inhibited the formation of the RRE-Rev ribonucleoprotein complex, a currently unexploited target in HIV chemotherapy. Cellular assays revealed that the most active compounds blocked HIV-1 replication with little toxicity, and likely exerted this effect through a multi-target mechanism involving inhibition of viral LTR promoter-dependent transcription and Rev function. Further development of this scaffold may open new avenues for targeting nucleic acids and may complement current HIV therapies, none of which involve inhibitors interfering with the gene regulation processes of the virus.

Dasatinib protects humanized mice from acute HIV-1 infection

HIV-1 infection remains incurable despite the efficient combined antiretroviral therapy (cART) due to the formation of long-lived viral reservoirs that are mostly settled in CD4+T cells and maintained by homeostatic proliferation. The use of cytostatic drugs such as tyrosine kinase inhibitors (TKIs) as adjuvants to cART could be helpful to avoid the reservoir establishment and replenishment. We determined previously that TKI dasatinib, which is successfully used for treating chronic myeloid leukemia (CML), shows antiviral effect against HIV-1 infection of CD4⁺ T cells in vitro. HIV-infected subjects that developed CML may safely combine long-term treatment with TKIs and cART but there is no information about the effect of dasatinib on HIV-1 reservoir in vivo. Therefore, we analyzed the ability of dasatinib to protect NSG mice engrafted with human CD34⁺ hematopoietic stem cells from HIV-1 infection. Mice were randomly assigned to two groups that received dasatinib or placebo daily by oral gavage. After five days, all mice were infected intraperitoneally with HIV-1 and followed up for 21 days in the absence of cART. Daily administration of dasatinib decreased viral and proviral load in all treated mice, showing in 40% of these mice undetectable viral RNA or DNA in blood. Proviral HIV-1 DNA in gut-associated lymphoid tissue (GALT) was also reduced in all dasatinib-treated mice and under the limit of detection in one of these mice. Finally, treatment with dasatinib modified the distribution of CD4⁺ and CD8⁺ T-cell subpopulations, delaying their differentiation into memory T-cell subsets that are a major component of the viral reservoir. In conclusion, dasatinib afforded protection of NSG mice from HIV-1 intraperitoneal infection in the absence of cART.

The mutation of Transportin 3 gene that causes limb girdle muscular dystrophy 1F induces protection against HIV-1 infection

The causative mutation responsible for limb girdle muscular dystrophy 1F (LGMD1F) is one heterozygous single nucleotide deletion in the stop codon of the nuclear import factor Transportin 3 gene (TNPO3). This mutation causes a carboxy-terminal extension of 15 amino acids, producing a protein of unknown function (TNPO3_mut) that is co-expressed with wild-type TNPO3 (TNPO3_wt). TNPO3 has been involved in the nuclear transport of serine/arginine-rich proteins such as splicing factors and also in HIV-1 infection through interaction with the viral integrase and capsid. We analyzed the effect of TNPO3_mut on HIV-1 infection using PBMCs from patients with LGMD1F infected ex vivo. HIV-1 infection was drastically impaired in these cells and viral integration was reduced 16-fold. No significant effects on viral reverse transcription and episomal 2-LTR circles were observed suggesting that the integration of HIV-1 genome was restricted. This is the second genetic defect described after CCR5Δ32 that shows strong resistance against HIV-1 infection.

HIV "shock and kill" therapy: In need of revision

The implementation of antiretroviral therapy 23 years ago has rendered HIV infection clinically manageable. However, the disease remains incurable, since it establishes latent proviral reservoirs, which in turn can stochastically begin reproducing viral particles throughout the patient's lifetime. Viral latency itself depends in large part on the silencing environment of the infected host cell, which can be chemically manipulated. "Shock and kill" therapy intends to reverse proviral quiescence by inducing transcription with pharmaceuticals and allowing a combination of antiretroviral therapy, host immune clearance and HIV-cytolysis to remove latently infected cells, leading to a complete cure. Over 160 compounds functioning as latency-reversing agents (LRAs) have been identified to date, but none of the candidates has yet led to a promising functional cure. Furthermore, fundamental bioinformatic and clinical research from the past decade has highlighted the complexity and highly heterogeneous nature of the proviral reservoirs, shedding doubt on the "shock and kill" concept. Alternative therapies such as the HIV transcription-inhibiting "block and lock" strategy are therefore being considered. In this review we describe the variety of existing classes of LRAs, discuss their current drawbacks and highlight the potential for combinatorial "shocktail" therapies for potent proviral reactivation. We also suggest investigating LRAs with lesser-known mechanisms of action, and examine the feasibility of "block and lock" therapy.

Restriction Factors: From Intrinsic Viral Restriction to Shaping Cellular Immunity Against HIV-1

Antiviral restriction factors are host cellular proteins that constitute a first line of defense blocking viral replication and propagation. In addition to interfering at critical steps of the viral replication cycle, some restriction factors also act as innate sensors triggering innate responses against infections. Accumulating evidence suggests an additional role for restriction factors in promoting antiviral cellular immunity to combat viruses. Here, we review the recent progress in our understanding on how restriction factors, particularly APOBEC3G, SAMHD1, Tetherin, and TRIM5α have the cell-autonomous potential to induce cellular resistance against HIV-1 while promoting antiviral innate and adaptive immune responses. Also, we provide an overview of how these restriction factors may connect with protein degradation pathways to modulate anti-HIV-1 cellular immune responses, and we summarize the potential of restriction factors-based therapeutics. This review brings a global perspective on the influence of restrictions factors in intrinsic, innate, and also adaptive antiviral immunity opening up novel research avenues for therapeutic strategies in the fields of drug discovery, gene therapy, and vaccines to control viral infections.

Evaluation of resistance to HIV-1 infection ex vivo of PBMCs isolated from patients with chronic myeloid leukemia treated with different tyrosine kinase inhibitors

Current antiretroviral treatment (ART) may control HIV-1 replication but it cannot cure the infection due to the formation of a reservoir of latently infected cells. CD4+ T cell activation during HIV-1 infection eliminates the antiviral function of the restriction factor SAMHD1, allowing proviral integration and the reservoir establishment. The role of tyrosine kinases during T-cell activation is essential for these processes. Therefore, the inhibition of tyrosine kinases could control HIV-1 infection and restrict the formation of the reservoir. A family of tyrosine kinase inhibitors (TKIs) is successfully used in clinic for treating chronic myeloid leukemia (CML). The safety and efficacy against HIV-1 infection of five TKIs was assayed in PBMCs isolated from CML patients on prolonged treatment with these drugs that were infected ex vivo with HIV-1. We determined that the most potent and safe TKI against HIV-1 infection was dasatinib, which preserved SAMHD1 antiviral function and avoid T-cell activation through TCR engagement and homeostatic cytokines. Imatinib and nilotinib showed lower potency and bosutinib was quite toxic in vitro. Ponatinib presented similar profile to dasatinib but as it has been associated with higher incidence of arterial ischemic events, dasatinib would be the better choice of TKI to be used as adjuvant of ART in order to avoid the establishment and replenishment of HIV-1 reservoir and move forward towards an HIV cure.

Promiscuous, Multi-Target Lupane-Type Triterpenoids Inhibits Wild Type and Drug Resistant HIV-1 Replication Through the Interference With Several Targets

Current research on antiretroviral therapy is mainly focused in the development of new formulations or combinations of drugs belonging to already known targets. However, HIV-1 infection is not cured by current therapy and thus, new approaches are needed. Bevirimat was developed by chemical modification of betulinic acid, a lupane-type pentacyclic triterpenoid (LPT), as a first-in-class HIV-1 maturation inhibitor. However, in clinical trials, bevirimat showed less activity than expected because of the presence of a natural mutation in Gag protein that conferred resistance to a high proportion of HIV-1 strains. In this work, three HIV-1 inhibitors selected from a set of previously screened LPTs were investigated for their targets in the HIV-1 replication cycle, including their maturation inhibitor effect. LPTs were found to inhibit HIV-1 infection acting as promiscuous compounds with several targets in the HIV-1 replication cycle. LPT12 inhibited HIV-1 infection mainly through reverse transcription, integration, viral transcription, viral proteins (Gag) production and maturation inhibition. LPT38 did it through integration, viral transcription or Gag production inhibition and finally, LPT42 inhibited reverse transcription, viral transcription or Gag production. The three LPTs inhibited HIV-1 infection of human primary lymphocytes and infections with protease inhibitors and bevirimat resistant HIV-1 variants with similar values of IC₅₀. Therefore, we show that the LPTs tested inhibited HIV-1 infection through acting on different targets depending on their chemical structure and the activities of the different LPTs vary with slight structural alterations. For example, of the three LPTs under study, we found that only LPT12 inhibited infectivity of newly-formed viral particles, suggesting a direct action on the maturation process. Thus, the multi-target behavior gives a potential advantage to these compounds since HIV-1 resistance can be overcome by modulating more than one target.

Elimination of cancer stem cells and reactivation of latent HIV-1 via AMPK activation: Common mechanism of action linking inhibition of tumorigenesis and the potential eradication of HIV-1

Although promising treatments are currently in development to slow disease progression and increase patient survival, cancer remains the second leading cause of death in the United States. Cancer treatment modalities commonly include chemoradiation and therapies that target components of aberrantly activated signaling pathways. However, treatment resistance is a common occurrence and recent evidence indicates that the existence of cancer stem cells (CSCs) may underlie the limited efficacy and inability of current treatments to effectuate a cure. CSCs, which are largely resistant to chemoradiation therapy, are a subpopulation of cancer cells that exhibit characteristics similar to embryonic stem cells (ESCs), including self-renewal, multi-lineage differentiation, and the ability to initiate tumorigenesis. Interestingly, intracellular mechanisms that sustain quiescence and promote self-renewal in adult stem cells (ASCs) and CSCs likely also function to maintain latency of HIV-1 in CD4⁺ memory T cells. Although antiretroviral therapy is highly effective in controlling HIV-1 replication, the persistence of latent but replication-competent proviruses necessitates the development of compounds that are capable of selectively reactivating the latent virus, a method known as the "shock and kill" approach. Homeostatic proliferation in central CD4⁺ memory T (T_CM) cells, a memory T cell subset that exhibits limited self-renewal and differentiation and is a primary reservoir for latent HIV-1, has been shown to reinforce and stabilize the latent reservoir in the absence of T cell activation and differentiation. HIV-1 has also been found to establish durable and long-lasting latency in a recently discovered subset of CD4⁺ T cells known as T memory stem (T_SCM) cells. T_SCM cells, compared to T_CM cells, exhibit stem cell properties that more closely match those of ESCs and ASCs, including self-renewal and differentiation into all memory T cell subsets. It is our hypothesis that activation of AMPK, a master regulator of cellular metabolism that plays a critical role in T cell activation and differentiation of ESCs and ASCs, will lead to both T cell activation-induced latent HIV-1 reactivation, facilitating virus destruction, as well as "activation", differentiation, and/or apoptosis of CSCs, thus inhibiting tumorigenesis. We also propose the novel observation that compounds that have been shown to both facilitate latent HIV-1 reactivation and promote CSC differentiation/apoptosis (e.g. bryostatin-1, JQ1, metformin, butyrate, etc.) likely do so through a common mechanism of AMPK activation.

Tyrosine kinase inhibitors: potential use and safety considerations in HIV-1 infection

INTRODUCTION

Infection caused by HIV-1 is nowadays a chronic disease due to a highly efficient antiretroviral treatment that is nevertheless, unable to eliminate the virus from the organism. New strategies are necessary in order to impede the formation of the viral reservoirs, responsible for the failure of the antiretroviral treatment to cure the infection. Areas covered: The purpose of this review is to discuss the possibility of using tyrosine kinase inhibitors (TKIs) for the treatment of HIV-1 infection. These inhibitors are successfully used in patients with distinct cancers such as chronic myeloid leukemia. The most relevant papers have been selected and commented. Expert opinion: The family of TKIs are directed against the activation of tyrosine kinases from the Src family. Some of these kinases are essential for the activation of CD4 + T cells, the major target of HIV-1. During acute or primary infection the CD4 + T cells are massively activated, which is mostly responsible for the generation of the reservoirs, the spread of the infection and the destruction of activated CD4 + T cells, infected or not. Consequently, we discuss the possibility of using TKIs as adjuvant of the antiretroviral treatment against HIV-1 infection mostly, but not exclusively, during the acute/recent phase.

FOXO3, IRF4, and xIAP Are Correlated with Immune Activation in HIV-1-Infected Men Who Have Sex with Men During Early HIV Infection

Forkhead box O (FOXO)1, FOXO3, interferon regulatory factor (IRF)4, X-linked inhibitor of apoptosis protein (xIAP), and E74-like factor (ELF)4 have been described as important regulators of T cell functions and differentiation. However, whether these molecules are associated with HIV-1 disease progression is still unknown. In this study, we showed that the levels of FOXO3, IRF4, and xIAP mRNA in rapid progressors (RPs) were significantly higher than in HIV-negative healthy controls (HCs). Moreover, FOXO3 expression was positively correlated with HIV-1 viral load and CD4⁺ T cell activation. Remarkably, increased CD4⁺ and CD8⁺ T cell activation was apparent in RPs compared with typical progressors and HCs. In addition, a profile of higher apoptosis, more CD8⁺ T_EM cells, and fewer CD4⁺ and CD8⁺ Naive T cells were observed in early HIV infection patients with low CD4⁺ T cell counts. Furthermore, in vitro, IRF4 and xIAP expression was enhanced in peripheral blood mononuclear cells from healthy people following T cell receptor stimulation. T cell activation was decreased by treatment with siRNA inhibiting FOXO3, IRF4, and xIAP. Our results show that significantly increased levels of FOXO3, IRF4, and xIAP mRNA in Chinese HIV-1-infected patients were related to T cell immune activation, implicating them as potential targets for developing new therapeutic avenues to slow down HIV-1 disease progression.

Pharmacological Inhibition of PKCθ Counteracts Muscle Disease in a Mouse Model of Duchenne Muscular Dystrophy

Inflammation plays a considerable role in the progression of Duchenne Muscular Dystrophy (DMD), a severe muscle disease caused by a mutation in the dystrophin gene. We previously showed that genetic ablation of Protein Kinase C θ (PKCθ) in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

Research in context

Duchenne muscular dystrophy (DMD) is a severe muscle disease affecting 1:3500 male births. DMD is caused by a mutation in dystrophin gene, coding for a protein required for skeletal and cardiac muscle integrity. Lack of a functional dystrophin is primarily responsible for the muscle eccentric contraction-induced muscle damage, observed in dystrophic muscle. However, inflammation plays a considerable role in the progression of DMD. Glucocorticoids, which have anti-inflammatory properties, are being used to treat DMD with some success; however, long term treatment with these drugs induces muscle atrophy and wasting, outweighing their benefit. The identification of specific targets for anti-inflammatory therapies is one of the ongoing therapeutic options. Although blunting inflammation would not be a “cure” for the disease, the emerging clue is that multiple strategies, addressing different aspects of the pathology, which may eventually converge, may be successful. In this context, we previously showed that genetic ablation of Protein Kinase C θ (PKCθ), an enzyme known to be involved in immune response, in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

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Immune-cell intrinsic PKCθ activity might play a hitherto unrecognized role of in the development of DMD.

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Mdx dystrophic mice were treated with the PKCθ inhibitor C20.

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C20 treatment prevents damage and inflammation in dystrophic muscle, while improving muscle regeneration.

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C20 treatment prevents drop in force and ameliorates fatigue resistance in dystrophic mice.

Oocyte activation and latent HIV-1 reactivation: AMPK as a common mechanism of action linking the beginnings of life and the potential eradication of HIV-1

In all mammalian species studied to date, the initiation of oocyte activation is orchestrated through alterations in intracellular calcium (Ca(2+)) signaling. Upon sperm binding to the oocyte plasma membrane, a sperm-associated phospholipase C (PLC) isoform, PLC zeta (PLCζ), is released into the oocyte cytoplasm. PLCζ hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), which activates protein kinase C (PKC), and inositol 1,4,5-trisphosphate (IP3), which induces the release of Ca(2+) from endoplasmic reticulum (ER) Ca(2+) stores. Subsequent Ca(2+) oscillations are generated that drive oocyte activation to completion. Ca(2+) ionophores such as ionomycin have been successfully used to induce artificial human oocyte activation, facilitating fertilization during intra-cytoplasmic sperm injection (ICSI) procedures. Early studies have also demonstrated that the PKC activator phorbol 12-myristate 13-acetate (PMA) acts synergistically with Ca(2+) ionophores to induce parthenogenetic activation of mouse oocytes. Interestingly, the Ca(2+)-induced signaling cascade characterizing sperm or chemically-induced oocyte activation, i.e. the "shock and live" approach, bears a striking resemblance to the reactivation of latently infected HIV-1 viral reservoirs via the so called "shock and kill" approach, a method currently being pursued to eradicate HIV-1 from infected individuals. PMA and ionomycin combined, used as positive controls in HIV-1 latency reversal studies, have been shown to be extremely efficient in reactivating latent HIV-1 in CD4(+) memory T cells by inducing T cell activation. Similar to oocyte activation, T cell activation by PMA and ionomycin induces an increase in intracellular Ca(2+) concentrations and activation of DAG, PKC, and downstream Ca(2+)-dependent signaling pathways necessary for proviral transcription. Interestingly, AMPK, a master regulator of cell metabolism that is activated thorough the induction of cellular stress (e.g. increase in Ca(2+) concentration, reactive oxygen species generation, increase in AMP/ATP ratio) is essential for oocyte maturation, T cell activation, and mitochondrial function. In addition to the AMPK kinase LKB1, CaMKK2, a Ca(2+)/calmodulin-dependent kinase that also activates AMPK, is present in and activated on T cell activation and is also present in mouse oocytes and persists until the zygote and two-cell stages. It is our hypothesis that AMPK activation represents a central node linking T cell activation-induced latent HIV-1 reactivation and both physiological and artificial oocyte activation. We further propose the novel observation that various compounds that have been shown to reactivate latent HIV-1 (e.g. PMA, ionomycin, metformin, bryostatin, resveratrol, etc.) or activate oocytes (PMA, ionomycin, ethanol, puromycin, etc.) either alone or in combination likely do so via stress-induced activation of AMPK.

PKCθ and HIV-1 Transcriptional Regulator Tat Co-exist at the LTR Promoter in CD4(+) T Cells

PKCθ is essential for the activation of CD4⁺ T cells. Upon TCR/CD28 stimulation, PKCθ is phosphorylated and migrates to the immunological synapse, inducing the activation of cellular transcription factors such as NF-κB and kinases as ERK that are critical for HIV-1 replication. We previously demonstrated that PKCθ is also necessary for HIV-1 replication but the precise mechanism is unknown. Efficient HIV-1 transcription and elongation are absolutely dependent on the synergy between NF-κB and the viral regulator Tat. Tat exerts its function by binding a RNA stem-loop structure proximal to the viral mRNA cap site termed TAR. Besides, due to its effect on cellular metabolic pathways, Tat causes profound changes in infected CD4⁺ T cells such as the activation of NF-κB and ERK. We hypothesized that the aberrant upregulation of Tat-mediated activation of NF-κB and ERK occurred through PKCθ signaling. In fact, Jurkat TetOff cells with stable and doxycycline-repressible expression of Tat (Jurkat-Tat) expressed high levels of mRNA for PKCθ. In these cells, PKCθ located at the plasma membrane was phosphorylated at T⁵³⁸ residue in undivided cells, in the absence of stimulation. Treatment with doxycycline inhibited PKCθ phosphorylation in Jurkat-Tat, suggesting that Tat expression was directly related to the activation of PKCθ. Both NF-κB and Ras/Raf/MEK/ERK signaling pathway were significantly activated in Jurkat-Tat cells, and this correlated with high transactivation of HIV-1 LTR promoter. RNA interference for PKCθ inhibited NF-κB and ERK activity, as well as LTR-mediated transactivation even in the presence of Tat. In addition to Tat-mediated activation of PKCθ in the cytosol, we demonstrated by sequential ChIP that Tat and PKCθ coexisted in the same complex bound at the HIV-1 LTR promoter, specifically at the region containing TAR loop. In conclusion, PKCθ-Tat interaction seemed to be essential for HIV-1 replication in CD4⁺ T cells and could be used as a therapeutic target.

Dasatinib inhibits HIV-1 replication through the interference of SAMHD1 phosphorylation in CD4+ T cells

Massive activation of infected CD4+ T cells during acute HIV-1 infection leads to reservoir seeding and T-cell destruction. During T-cell activation, the antiviral effect of the innate factor SAMHD1 is neutralized through phosphorylation at T592, allowing HIV-1 infection. Dasatinib, a tyrosine kinase inhibitor currently used for treating chronic myeloid leukemia, has been described to control HIV-1 replication through its negative effect on T-cell proliferation and viral entry. We demonstrate that Dasatinib can actually interfere with SAMHD1 phosphorylation in human peripheral blood lymphocytes, preserving its antiviral activity against HIV-1. Dasatinib prevented SAMHD1 phosphorylation in vitro and ex vivo, impairing HIV-1 reverse transcription and proviral integration. This was the major mechanism of action because the presence of Vpx, which degrades SAMHD1, in HIV-1 virions impeded the inhibitory effect of Dasatinib on HIV-1 replication. In fact, infection with VSV-pseudotyped HIV-1 virions and fusion of BlaM-Vpr-containing HIV-1 viruses with activated PBMCs in the presence of Dasatinib suggested that Dasatinib was not acting at fusion level. Finally, PBMCs from patients on chronic treatment with Dasatinib showed a lower level of SAMHD1 phosphorylation in response to activating stimuli and low susceptibility to HIV-1 infection ex vivo. Consequently, Dasatinib is a compound currently used in clinic that preserves the antiviral function of SAMHD1. Using Dasatinib as adjuvant of antiretroviral therapy during early primary HIV-1 infection would contribute to reduce viral replication and spread, prevent reservoir seeding, and preserve CD4 counts and CTL responses. These events would create a more favorable virologic and immunologic environment for future interventional studies aiming at HIV-1 eradication.

PKC-Theta in Regulatory and Effector T-cell Functions

One of the major goals in immunology research is to understand the regulatory mechanisms that underpin the rapid switch on/off of robust and efficient effector (Teffs) or regulatory (Tregs) T-cell responses. Understanding the molecular mechanisms underlying the regulation of such responses is critical for the development of effective therapies. T-cell activation involves the engagement of T-cell receptor and co-stimulatory signals, but the subsequent recruitment of serine/threonine-specific protein Kinase C-theta (PKC-θ) to the immunological synapse (IS) is instrumental for the formation of signaling complexes, which ultimately lead to a transcriptional network in T cells. Recent studies demonstrated that major differences between Teffs and Tregs occurred at the IS where its formation induces altered signaling pathways in Tregs. These pathways are characterized by reduced recruitment of PKC-θ, suggesting that PKC-θ inhibits Tregs suppressive function in a negative feedback loop. As the balance of Teffs and Tregs has been shown to be central in several diseases, it was not surprising that some studies revealed that PKC-θ plays a major role in the regulation of this balance. This review will examine recent knowledge on the role of PKC-θ in T-cell transcriptional responses and how this protein can impact on the function of both Tregs and Teffs.

The Role of PKC-θ in CD4+ T Cells and HIV Infection: To the Nucleus and Back Again

Protein kinase C (PKC)-θ is the only member of the PKC family that has the ability to translocate to the immunological synapse between T cells and antigen-presenting cells upon T cell receptor and MHC-II recognition. PKC-θ interacts functionally and physically with other downstream effector molecules to mediate T cell activation, differentiation, and migration. It plays a critical role in the generation of Th2 and Th17 responses and is less important in Th1 and CTL responses. PKC-θ has been recently shown to play a role in the nucleus, where it mediates inducible gene expression in the development of memory CD4+ T cells. This novel PKC (nPKC) can up-regulate HIV-1 transcription and PKC-θ activators such as Prostratin have been used in early HIV-1 reservoir eradication studies. The exact manner of the activation of virus by these compounds and the role of PKC-θ, particularly its nuclear form and its association with NF-κB in both the cytoplasmic and nuclear compartments, needs further precise elucidation especially given the very important role of NF-κB in regulating transcription from the integrated retrovirus. Continued studies of this nPKC isoform will give further insight into the complexity of T cell signaling kinases.