HIV-1 Tat binds to SH3 domains: cellular and viral outcome of Tat/Grb2 interaction

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.

Th17 CD4+ T-Cell as a Preferential Target for HIV Reservoirs

Among CD4+ T-cells, T helper 17 (Th17) cells play a sentinel role in the defense against bacterial/fungal pathogens at mucosal barriers. However, Th17 cells are also highly susceptible to HIV-1 infection and are rapidly depleted from gut mucosal sites, causing an imbalance of the Th17/Treg ratio and impairing cytokines production. Consequently, damage to the gut mucosal barrier leads to an enhanced microbial translocation and systemic inflammation, a hallmark of HIV-1 disease progression. Th17 cells’ expression of mucosal homing receptors (CCR6 and α4β7), as well as HIV receptors and co-receptors (CD4, α4β7, CCR5, and CXCR4), contributes to susceptibility to HIV infection. The up-regulation of numerous intracellular factors facilitating HIV production, alongside the downregulation of factors inhibiting HIV, helps to explain the frequency of HIV DNA within Th17 cells. Th17 cells harbor long-lived viral reservoirs in people living with HIV (PLWH) receiving antiretroviral therapy (ART). Moreover, cell longevity and the proliferation of a fraction of Th17 CD4 T cells allow HIV reservoirs to be maintained in ART patients.

Combination of HIV-1 and Diabetes Enhances Blood Brain Barrier Injury via Effects on Brain Endothelium and Pericytes

Despite combined antiretroviral therapy (ART) achieving efficient HIV replication control, HIV-associated neurocognitive disorders (HAND) continue to be highly prevalent in HIV-infected patients. Diabetes mellitus (DM) is a well-known comorbidity of HAND in HIV-infected patients. Blood brain barrier (BBB) dysfunction has been linked recently to dementia development, specifically in DM patients. BBB injury exists both in HIV and DM, likely contributing to cognitive decline. However, its extent, exact cellular targets and mechanisms are largely unknown. In this report, we found a decrease in pericyte coverage and expression of tight junction proteins in human brain tissues from HIV patients with DM and evidence of HAND when compared to HIV-infected patients without DM or seronegative DM patients. Using our in vitro BBB models, we demonstrated diminution of barrier integrity, enhanced monocyte adhesion, changes in cytoskeleton and overexpression of adhesion molecules in primary human brain endothelial cells or human brain pericytes after exposure to HIV and DM-relevant stimuli. Our study demonstrates for the first-time evidence of impaired BBB function in HIV-DM patients and shows potential mechanisms leading to it in brain endothelium and pericytes that may result in poorer cognitive performance compared to individuals without HIV and DM.

Cellular levels of Grb2 and cytoskeleton stability are correlated in a neurodegenerative scenario

Alzheimer's disease (AD) manifests as neuronal loss. On the premise of Grb2 overexpression in AD mouse brain and brain tissues of AD patients, our study primarily focuses on the stability of cytoskeletal proteins in the context of degenerative AD-like conditions. Two predominant molecular features of AD, extracellular accumulation of β-amyloid oligomers and intracellular elevation of amyloid precursor protein intracellular domain levels, have been used to closely inspect the series of signalling events. In their presence, multiple signalling pathways involving ROCK and PAK1 proteins lead to disassembly of the cytoskeleton, and Grb2 partially counterbalances the cytoskeletal loss. Increased Grb2-NOX4 interactions play a preventive role against cytoskeletal disassembly, in turn blocking the activity of nitrogen oxides and decreasing the expression of slingshot homolog 1 (SSH-1) protein, a potent inducer of cytoskeleton disassembly. This study unravels a unique role of Grb2 in protecting the cytoskeletal architecture in AD-like conditions and presents a potential new strategy for controlling neurodegeneration.

The anticancer drug sunitinib promotes autophagyand protects from neurotoxicity in an HIV-1 Tat model of neurodegeneration

Despite the success of antiretroviral therapies to control systemic HIV-1 infection, the prevalence of HIV-associated neurocognitive disorders (HANDs) has not decreased among aging patients with HIV. Autophagy pathway alterations, triggered by HIV-1 proteins including gp120, Tat, and Nef, might contribute to the neurodegenerative process in aging patients with HAND. Although no treatments are currently available to manage HAND, we have previously shown that sunitinib, an anticancer drug that blocks receptor tyrosine-kinase and cyclin kinase pathways, might be of interest. Studies in cancer models suggest that sunitinib might also modulate autophagy, which is dysregulated in our models of Tat-induced neurotoxicity. We evaluated the efficacy of sunitinib to promote autophagy in the CNS and ameliorate neurodegeneration using LC3-GFP-expressing neuronal cells challenged with low concentrations of Tat and using inducible Tat transgenic mice. In neuronal cultures challenged with low levels of Tat, sunitinib increased markers of autophagy such as LC3-II and reduced p62 accumulation in a dose-dependent manner. In vivo, sunitinib treatment restored LC3-II, p62, and endophilin B1 (EndoB1) levels in doxycycline-induced Tat transgenic mice. Moreover, in these animals, sunitinib reduced the hyperactivation of CDK5, tau hyperphosphorylation, and p35 cleavage to p25. Restoration of CDK5 and autophagy were associated with reduced neurodegeneration and behavioral alterations. Alterations in autophagy in the Tat tg mice were associated with reduced levels of a CDK5 substrate, EndoB1, and levels of total EndoB1 were normalized by sunitinib treatment. We conclude that sunitinib might ameliorate Tat-mediated autophagy alterations and may decrease neurodegeneration in aging patients with HAND.

Human immunodeficiency virus protein Tat induces oligodendrocyte injury by enhancing outward K+ current conducted by KV1.3

Brain white matter damage is frequently detected in patients infected with human immunodeficiency virus type 1 (HIV-1). White matter is composed of neuronal axons sheathed by oligodendrocytes (Ols), the myelin-forming cells in central nervous system. Ols are susceptible to HIV-1 viral trans-activator of transcription (Tat) and injury of Ols results in myelin sheath damage. It has been demonstrated that activation of voltage-gated K⁺ (K_V) channels induces cell apoptosis and Ols predominantly express K⁺ channel K_V1.3. It is our hypothesis that Tat injures Ols via activation of K_V1.3. To test this hypothesis, we studied the involvement of K_V1.3 in Tat-induced Ol/myelin injury both in vitro and ex vivo. Application of Tat to primary rat Ol cultures enhanced whole-cell K_V1.3 current recorded under voltage clamp configuration and confirmed by specific K_V1.3 antagonists Margatoxin (MgTx) and 5-(4-phenoxybutoxy) psoralen (PAP). The Tat enhancement of K_V1.3 current was associated with Tat-induced Ol apoptosis, which was blocked by MgTx and PAP or by siRNA knockdown of K_V1.3 gene. The Tat-induced Ol injury was validated in cultured rat brain slices, particularly in corpus callosum and striatum, that incubation of the slices with Tat resulted in myelin damage and reduction of myelin basic protein which were also blocked by aforementioned K_V1.3 antagonists. Further studies revealed that Tat interacts with K_V1.3 as determined by protein pull-down of recombinant GST-Tat with K_V1.3 expressed in rat brains and HEK293 cells. Such protein-protein interaction may alter channel protein phosphorylation, resultant channel activity and consequent Ol/myelin injury. Taken together, these results demonstrate an involvement of K_V1.3 in Tat- induced Ol/myelin injury, a potential mechanism for the pathogenesis of HIV-1-associated white matter damage.

HIV-1-Tat Protein Inhibits SC35-mediated Tau Exon 10 Inclusion through Up-regulation of DYRK1A Kinase

The HIV-1 transactivator protein Tat is implicated in the neuronal damage that contributes to neurocognitive impairment affecting people living with HIV/AIDS. Aberrant splicing of TAU exon 10 results in tauopathies characterized by alterations in the proportion of TAU isoforms containing three (3R) or four (4R) microtubule-binding repeats. The splicing factor SC35/SRSF2 binds to nuclear RNA and facilitates the incorporation of exon 10 in the TAU molecule. Here, we utilized clinical samples, an animal model, and neuronal cell cultures and found that Tat promotes TAU 3R up-regulation through increased levels of phosphorylated SC35, which is retained in nuclear speckles. This mechanism involved Tat-mediated increased expression of DYRK1A and was prevented by DYRK1A silencing. In addition, we found that Tat associates with TAU RNA, further demonstrating that Tat interferes with host RNA metabolism in the absence of viral infection. Altogether, our data unravel a novel mechanism of Tat-mediated neuronal toxicity through dysregulation of the SC35-dependent alternative splicing of TAU exon 10. Furthermore, the increased immunostaining of DYRK1A in HIV+ brains without pathology points at dysregulation of DYRK1A as an early event in the neuronal complications of HIV infection.

Identification of novel HIV-1 dependency factors in primary CCR4(+)CCR6(+)Th17 cells via a genome-wide transcriptional approach

BACKGROUND

The HIV-1 infection is characterized by profound CD4(+) T cell destruction and a marked Th17 dysfunction at the mucosal level. Viral suppressive antiretroviral therapy restores Th1 but not Th17 cells. Although several key HIV dependency factors (HDF) were identified in the past years via genome-wide siRNA screens in cell lines, molecular determinants of HIV permissiveness in primary Th17 cells remain to be elucidated.

RESULTS

In an effort to orient Th17-targeted reconstitution strategies, we investigated molecular mechanisms of HIV permissiveness in Th17 cells. Genome-wide transcriptional profiling in memory CD4(+) T-cell subsets enriched in cells exhibiting Th17 (CCR4(+)CCR6(+)), Th1 (CXCR3(+)CCR6(-)), Th2 (CCR4(+)CCR6(-)), and Th1Th17 (CXCR3(+)CCR6(+)) features revealed remarkable transcriptional differences between Th17 and Th1 subsets. The HIV-DNA integration was superior in Th17 versus Th1 upon exposure to both wild-type and VSV-G-pseudotyped HIV; this indicates that post-entry mechanisms contribute to viral replication in Th17. Transcripts significantly enriched in Th17 versus Th1 were previously associated with the regulation of TCR signaling (ZAP-70, Lck, and CD96) and Th17 polarization (RORγt, ARNTL, PTPN13, and RUNX1). A meta-analysis using the NCBI HIV Interaction Database revealed a set of Th17-specific HIV dependency factors (HDFs): PARG, PAK2, KLF2, ITGB7, PTEN, ATG16L1, Alix/AIP1/PDCD6IP, LGALS3, JAK1, TRIM8, MALT1, FOXO3, ARNTL/BMAL1, ABCB1/MDR1, TNFSF13B/BAFF, and CDKN1B. Functional studies demonstrated an increased ability of Th17 versus Th1 cells to respond to TCR triggering in terms of NF-κB nuclear translocation/DNA-binding activity and proliferation. Finally, RNA interference studies identified MAP3K4 and PTPN13 as two novel Th17-specific HDFs.

CONCLUSIONS

The transcriptional program of Th17 cells includes molecules regulating HIV replication at multiple post-entry steps that may represent potential targets for novel therapies aimed at protecting Th17 cells from infection and subsequent depletion in HIV-infected subjects.

The dual action of poly(ADP-ribose) polymerase -1 (PARP-1) inhibition in HIV-1 infection: HIV-1 LTR inhibition and diminution in Rho GTPase activity

Multifactorial mechanisms comprising countless cellular factors and virus-encoded transactivators regulate the transcription of HIV-1 (HIV). Since poly(ADP-ribose) polymerase 1 (PARP-1) regulates numerous genes through its interaction with various transcription factors, inhibition of PARP-1 has surfaced recently as a powerful anti-inflammatory tool. We suggest a novel tactic to diminish HIV replication via PARP-1 inhibition in an in vitro model system, exploiting human primary monocyte-derived macrophages (MDM). PARP-1 inhibition was capable to lessen HIV replication in MDM by 60–80% after 7 days infection. Tat, tumor necrosis factor α (TNFα), and phorbol 12-myristate 13-acetate (PMA) are known triggers of the Long Terminal Repeat (LTR), which can switch virus replication. Tat overexpression in MDM transfected with an LTR reporter plasmid resulted in a 4.2-fold increase in LTR activation; PARP inhibition caused 70% reduction of LTR activity. LTR activity, which increased 3-fold after PMA or TNFα treatment, was reduced by PARP inhibition (by 85–95%). PARP inhibition in MDM exhibited 90% diminution in NFκB activity (known to mediate TNFα- and PMA-induced HIV LTR activation). Cytoskeleton rearrangements are important in effective HIV-1 infection. PARP inactivation reduced actin cytoskeleton rearrangements by affecting Rho GTPase machinery. These discoveries suggest that inactivation of PARP suppresses HIV replication in MDM by via attenuation of LTR activation, NFκB suppression and its effects on the cytoskeleton. PARP appears to be essential for HIV replication and its inhibition may provide an effective approach to management of HIV infection.

Neuroprotective effects of the anti-cancer drug sunitinib in models of HIV neurotoxicity suggests potential for the treatment of neurodegenerative disorders

BACKGROUND AND PURPOSE

Anti-retrovirals have improved and extended the life expectancy of patients with HIV. However, as this population ages, the prevalence of cognitive changes is increasing. Aberrant activation of kinases, such as receptor tyrosine kinases (RTKs) and cyclin-dependent kinase 5 (CDK5), play a role in the mechanisms of HIV neurotoxicity. Inhibitors of CDK5, such as roscovitine, have neuroprotective effects; however, CNS penetration is low. Interestingly, tyrosine kinase inhibitors (TKIs) display some CDK inhibitory activity and ability to cross the blood-brain barrier.

EXPERIMENTAL APPROACH

We screened a small group of known TKIs for a candidate with additional CDK5 inhibitory activity and tested the efficacy of the candidate in in vitro and in vivo models of HIV-gp120 neurotoxicity.

KEY RESULTS

Among 12 different compounds, sunitinib inhibited CDK5 with an IC50 of 4.2 μM. In silico analysis revealed that, similarly to roscovitine, sunitinib fitted 6 of 10 features of the CDK5 pharmacophore. In a cell-based model, sunitinib reduced CDK5 phosphorylation (pCDK5), calpain-dependent p35/p25 conversion and protected neuronal cells from the toxic effects of gp120. In glial fibrillary acidic protein-gp120 transgenic (tg) mice, sunitinib reduced levels of pCDK5, p35/p25 and phosphorylated tau protein, along with amelioration of the neurodegenerative pathology.

CONCLUSIONS AND IMPLICATIONS

Compounds such as sunitinib with dual kinase inhibitory activity could ameliorate the cognitive impairment associated with chronic HIV infection of the CNS. Moreover, repositioning existing low MW compounds holds promise for the treatment of patients with neurodegenerative disorders.

Mechanisms of HIV-1 Tat neurotoxicity via CDK5 translocation and hyper-activation: role in HIV-associated neurocognitive disorders

The advent of more effective antiretroviral therapies has reduced the frequency of HIV dementia, however the prevalence of milder HIV associated neurocognitive disorders [HAND] is actually rising. Neurodegenerative mechanisms in HAND might include toxicity by secreted HIV-1 proteins such as Tat, gp120 and Nef that could activate neuro-inflammatory pathways, block autophagy, promote excitotoxicity, oxidative stress, mitochondrial dysfunction and dysregulation of signaling pathways. Recent studies have shown that Tat could interfere with several signal transduction mechanisms involved in cytoskeletal regulation, cell survival and cell cycle re-entry. Among them, Tat has been shown to hyper-activate cyclin-dependent kinase [CDK] 5, a member of the Ser/Thr CDKs involved in cell migration, angiogenesis, neurogenesis and synaptic plasticity. CDK5 is activated by binding to its regulatory subunit, p35 or p39. For this manuscript we review evidence showing that Tat, via calcium dysregulation, promotes calpain-1 cleavage of p35 to p25, which in turn hyper-activates CDK5 resulting in abnormal phosphorylation of downstream targets such as Tau, collapsin response mediator protein-2 [CRMP2], doublecortin [DCX] and MEF2. We also present new data showing that Tat interferes with the trafficking of CDK5 between the nucleus and cytoplasm. This results in prolonged presence of CDK5 in the cytoplasm leading to accumulation of aberrantly phosphorylated cytoplasmic targets [e.g.: Tau, CRMP2, DCX] that impair neuronal function and eventually lead to cell death. Novel therapeutic approaches with compounds that block Tat mediated hyper-activation of CDK5 might be of value in the management of HAND.

Identifying chemicals with potential therapy of HIV based on protein-protein and protein-chemical interaction network

Acquired immune deficiency syndrome (AIDS) is a severe infectious disease that causes a large number of deaths every year. Traditional anti-AIDS drugs directly targeting the HIV-1 encoded enzymes including reverse transcriptase (RT), protease (PR) and integrase (IN) usually suffer from drug resistance after a period of treatment and serious side effects. In recent years, the emergence of numerous useful information of protein-protein interactions (PPI) in the HIV life cycle and related inhibitors makes PPI a new way for antiviral drug intervention. In this study, we identified 26 core human proteins involved in PPI between HIV-1 and host, that have great potential for HIV therapy. In addition, 280 chemicals that interact with three HIV drugs targeting human proteins can also interact with these 26 core proteins. All these indicate that our method as presented in this paper is quite promising. The method may become a useful tool, or at least plays a complementary role to the existing method, for identifying novel anti-HIV drugs.