Susceptibility to virus-cell fusion at the plasma membrane is reduced through expression of HIV gp41 cytoplasmic domains

Analysis of Sigma-1 Receptor Antagonist BD1047 Effect on Upregulating Proteins in HIV-1-Infected Macrophages Exposed to Cocaine Using Quantitative Proteomics

HIV-1 infects monocyte-derived macrophages (MDM) that migrate into the brain and secrete virus and neurotoxic molecules, including cathepsin B (CATB), causing cognitive dysfunction. Cocaine potentiates CATB secretion and neurotoxicity in HIV-infected MDM. Pretreatment with BD1047, a sigma-1 receptor antagonist, before cocaine exposure reduces HIV-1, CATB secretion, and neuronal apoptosis. We aimed to elucidate the intracellular pathways modulated by BD1047 in HIV-infected MDM exposed to cocaine. We hypothesized that the Sig1R antagonist BD1047, prior to cocaine, significantly deregulates proteins and pathways involved in HIV-1 replication and CATB secretion that lead to neurotoxicity. MDM culture lysates from HIV-1-infected women treated with BD1047 before cocaine were compared with untreated controls using TMT quantitative proteomics, bioinformatics, Lima statistics, and pathway analyses. Results demonstrate that pretreatment with BD1047 before cocaine dysregulated eighty (80) proteins when compared with the infected cocaine group. We found fifteen (15) proteins related to HIV-1 infection, CATB, and mitochondrial function. Upregulated proteins were related to oxidative phosphorylation (SLC25A-31), mitochondria (ATP5PD), ion transport (VDAC2-3), endoplasmic reticulum transport (PHB, TMED10, CANX), and cytoskeleton remodeling (TUB1A-C, ANXA1). BD1047 treatment protects HIV-1-infected MDM exposed to cocaine by upregulating proteins that reduce mitochondrial damage, ER transport, and exocytosis associated with CATB-induced neurotoxicity.

Cellular defence or viral assist: the dilemma of HDAC6

Histone deacetylase 6 (HDAC6) is a unique cytoplasmic deacetylase that regulates various important biological processes by preventing protein aggregation and deacetylating different non-histone substrates including tubulin, heat shock protein 90, cortactin, retinoic acid inducible gene I and β-catenin. Growing evidence has indicated a dual role for HDAC6 in viral infection and pathogenesis: HDAC6 may represent a host defence mechanism against viral infection by modulating microtubule acetylation, triggering antiviral immune response and stimulating protective autophagy, or it may be hijacked by the virus to enhance proinflammatory response. In this review, we will highlight current data illustrating the complexity and importance of HDAC6 in viral pathogenesis. We will summarize the structure and functional specificity of HDAC6, and its deacetylase- and ubiquitin-dependent activity in key cellular events in response to virus infection. We will also discuss how HDAC6 exerts its direct or indirect histone modification ability in viral lytic-latency switch.

Overexpression of Histone Deacetylase 6 Enhances Resistance to Porcine Reproductive and Respiratory Syndrome Virus in Pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically relevant viral pathogens in pigs and causes substantial losses in the pig industry worldwide each year. At present, PRRSV vaccines do not effectively prevent and control this disease. Consequently, it is necessary to develop new antiviral strategies to compensate for the inefficacy of the available vaccines. Histone deacetylase 6 (HDAC6) is an important member of the histone deacetylase family that is responsible for regulating many important biological processes. Studies have shown that HDAC6 has anti-viral activities during the viral life cycle. However, whether HDAC6 overexpression enhances resistance to PRRSV in pigs remains unknown. In this study, we used a somatic cell cloning method to produce transgenic (TG) pigs that constitutively overexpress porcine HDAC6. These TG pigs showed germ line transmission with continued overexpression of HDAC6. In vitro, virus-challenged porcine alveolar macrophages (PAMs) overexpressed HDAC6, which suppressed viral gene expression and PRRSV production. In vivo, resistance to PRRSV in TG pigs was evaluated by direct or cohabitation mediated infection with a highly pathogenic PRRSV (HP-PRRSV) strain. Compared with non-TG (NTG) siblings, TG pigs showed a significantly lower viral load in the lungs and an extended survival time after infection with HP-PRRSV via intramuscular injection. In the cohabitation study, NTG pigs housed with challenged NTG pigs exhibited significantly worse clinical symptoms than the other three in-contact groups. These results collectively suggest that HDAC6 overexpression enhances resistance to PRRSV infection both in vitro and in vivo. Our findings suggest the potential involvement of HDAC6 in the response to PRRSV, which will facilitate the development of novel therapies for PRRSV.

Diverse roles of HDAC6 in viral infection: Implications for antiviral therapy

Histone deacetylase 6 (HDAC6), a cytoplasmic enzyme important for many biological processes, has recently emerged as a critical regulator of viral infection. HDAC6 exerts this function either directly, via orchestrating various stages of the viral life cycle, or indirectly via modulating cytokine production by host cells. The broad influence of HDAC6 on viral pathogenesis suggests that this protein may represent an antiviral target. However, the feasibility of targeting HDAC6 and the optimal strategy by which this could be accomplished cannot simply be concluded from individual studies. The primary challenge in developing HDAC6-targeted therapies is to understand how its antiviral effect can be selectively harnessed. As a springboard for future investigations, in this review we recapitulate recent findings on the diverse roles of HDAC6 in viral infection and discuss its alluring potential as a novel antiviral target.

CDC42 Use in Viral Cell Entry Processes by RNA Viruses

The cellular actin cytoskeleton presents a barrier that must be overcome by many viruses, and it has become increasingly apparent many viral species have developed a diverse repertoire of mechanisms to hijack cellular actin-regulating signalling pathways as part of their cell entry processes. The Rho family GTPase Cdc42 is appreciated as a key moderator of cellular actin dynamics, and the development of specific Cdc42-inhibiting agents has given us an unprecedented ability to investigate its individual role in signalling pathways. However, investigative use of said agents, and the subsequent characterisation of the role Cdc42 plays in viral entry processes has been lacking. Here, we describe the current literature on the role of Cdc42 in human immunodeficiency virus (HIV)-1 cell entry, which represents the most investigated instance of Cdc42 function in viral cell entry processes, and also review evidence of Cdc42 use in other RNA virus cell entries, demonstrating prime areas for more extensive research using similar techniques.

The HDAC6/APOBEC3G complex regulates HIV-1 infectiveness by inducing Vif autophagic degradation

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) has evolved a complex strategy to overcome the immune barriers it encounters throughout an organism thanks to its viral infectivity factor (Vif), a key protein for HIV-1 infectivity and in vivo pathogenesis. Vif interacts with and promotes "apolipoprotein B mRNA-editing enzyme-catalytic, polypeptide-like 3G" (A3G) ubiquitination and subsequent degradation by the proteasome, thus eluding A3G restriction activity against HIV-1.

RESULTS

We found that cellular histone deacetylase 6 (HDAC6) directly interacts with A3G through its C-terminal BUZ domain (residues 841-1,215) to undergo a cellular co-distribution along microtubules and cytoplasm. The HDAC6/A3G complex occurs in the absence or presence of Vif, competes for Vif-mediated A3G degradation, and accounts for A3G steady-state expression level. In fact, HDAC6 directly interacts with and promotes Vif autophagic clearance, thanks to its C-terminal BUZ domain, a process requiring the deacetylase activity of HDAC6. HDAC6 degrades Vif without affecting the core binding factor β (CBF-β), a Vif-associated partner reported to be key for Vif- mediated A3G degradation. Thus HDAC6 antagonizes the proviral activity of Vif/CBF-β-associated complex by targeting Vif and stabilizing A3G. Finally, in cells producing virions, we observed a clear-cut correlation between the ability of HDAC6 to degrade Vif and to restore A3G expression, suggesting that HDAC6 controls the amount of Vif incorporated into nascent virions and the ability of HIV-1 particles of being infectious. This effect seems independent on the presence of A3G inside virions and on viral tropism.

CONCLUSIONS

Our study identifies for the first time a new cellular complex, HDAC6/A3G, involved in the autophagic degradation of Vif, and suggests that HDAC6 represents a new antiviral factor capable of controlling HIV-1 infectiveness by counteracting Vif and its functions.

The histone deacetylase inhibitor vorinostat (SAHA) increases the susceptibility of uninfected CD4+ T cells to HIV by increasing the kinetics and efficiency of postentry viral events

Latently infected cells remain a primary barrier to eradication of HIV-1. Over the past decade, a better understanding of the molecular mechanisms by which latency is established and maintained has led to the discovery of a number of compounds that selectively reactivate latent proviruses without inducing polyclonal T cell activation. Recently, the histone deacetylase (HDAC) inhibitor vorinostat has been demonstrated to induce HIV transcription from latently infected cells when administered to patients. While vorinostat will be given in the context of antiretroviral therapy (ART), infection of new cells by induced virus remains a clinical concern. Here, we demonstrate that vorinostat significantly increases the susceptibility of CD4(+) T cells to infection by HIV in a dose- and time-dependent manner that is independent of receptor and coreceptor usage. Vorinostat does not enhance viral fusion with cells but rather enhances the kinetics and efficiency of postentry viral events, including reverse transcription, nuclear import, and integration, and enhances viral production in a spreading-infection assay. Selective inhibition of the cytoplasmic class IIb HDAC6 with tubacin recapitulated the effect of vorinostat. These findings reveal a previously unknown cytoplasmic effect of HDAC inhibitors promoting productive infection of CD4(+) T cells that is distinct from their well-characterized effects on nuclear histone acetylation and long-terminal-repeat (LTR) transcription. Our results indicate that careful monitoring of patients and ART intensification are warranted during vorinostat treatment and indicate that HDAC inhibitors that selectively target nuclear class I HDACs could reactivate latent HIV without increasing the susceptibility of uninfected cells to HIV.

IMPORTANCE

HDAC inhibitors, particularly vorinostat, are currently being investigated clinically as part of a "shock-and-kill" strategy to purge latent reservoirs of HIV. We demonstrate here that vorinostat increases the susceptibility of uninfected CD4(+) T cells to infection with HIV, raising clinical concerns that vorinostat may reseed the viral reservoirs it is meant to purge, particularly under conditions of suboptimal drug exposure. We demonstrate that vorinostat acts following viral fusion and enhances the kinetics and efficiency of reverse transcription, nuclear import, and integration. The effect of vorinostat was recapitulated using the cytoplasmic histone deacetylase 6 (HDAC6) inhibitor tubacin, revealing a novel and previously unknown cytoplasmic mechanism of HDAC inhibitors on HIV replication that is distinct from their well-characterized effects of long-terminal-repeat (LTR)-driven gene expression. Moreover, our results suggest that treatment of patients with class I-specific HDAC inhibitors could induce latent viruses without increasing the susceptibility of uninfected cells to HIV.

The hematopoietic cell-specific Rho GTPase inhibitor ARHGDIB/D4GDI limits HIV type 1 replication

Rho GTPases are able to influence the replication of human immunodeficiency virus type 1 (HIV-1). However, little is known about the regulation of HIV-1 replication by guanine nucleotide dissociation inhibitors (GDIs), one of the three major regulators of the Rho GTPase activation cycle. From a T cell-based cDNA library screening, ARHGDIB/RhoGDIβ, a hematopoietic lineage-specific GDI family protein, was identified as a negative regulator of HIV-1 replication. Up-regulation of ARHGDIB attenuated the replication of HIV-1 in multiple T cell lines. The results showed that (1) a significant portion of RhoA and Rac1, but not Cdc42, exists in the GTP-bound active form under steady-state conditions, (2) ectopic ARHGDIB expression reduced the F-actin content and the active forms of both RhoA and Rac1, and (3) HIV-1 infection was attenuated by either ectopic expression of ARHGDIB or inhibition of the RhoA signal cascade at the HIV-1 Env-dependent early phase of the viral life cycle. This is in good agreement with the previous finding that RhoA and Rac1 promote HIV-1 entry by increasing the efficiency of receptor clustering and virus-cell membrane fusion. In conclusion, the ARHGDIB is a lymphoid-specific intrinsic negative regulator of HIV-1 replication that acts by simultaneously inhibiting RhoA and Rac1 functions.

Viral infection: Moving through complex and dynamic cell-membrane structures

Viruses have developed different survival strategies in host cells by crossing cell-membrane compartments, during different steps of their viral life cycle. In fact, the non-regenerative viral membrane of enveloped viruses needs to encounter the dynamic cell-host membrane, during early steps of the infection process, in which both membranes fuse, either at cell-surface or in an endocytic compartment, to promote viral entry and infection. Once inside the cell, many viruses accomplish their replication process through exploiting or modulating membrane traffic, and generating specialized compartments to assure viral replication, viral budding and spreading, which also serve to evade the immune responses against the pathogen. In this review, we have attempted to present some data that highlight the importance of membrane dynamics during viral entry and replicative processes, in order to understand how viruses use and move through different complex and dynamic cell-membrane structures and how they use them to persist.

HIV-1 requires Arf6-mediated membrane dynamics to efficiently enter and infect T lymphocytes

As the initial barrier to viral entry, the plasma membrane along with the membrane trafficking machinery and cytoskeleton are of fundamental importance in the viral cycle. However, little is known about the contribution of plasma membrane dynamics during early human immunodeficiency virus type 1 (HIV-1) infection. Considering that ADP ribosylation factor 6 (Arf6) regulates cellular invasion via several microorganisms by coordinating membrane trafficking, our aim was to study the function of Arf6-mediated membrane dynamics on HIV-1 entry and infection of T lymphocytes. We observed that an alteration of the Arf6-guanosine 5'-diphosphate/guanosine 5'-triphosphate (GTP/GDP) cycle, by GDP-bound or GTP-bound inactive mutants or by specific Arf6 silencing, inhibited HIV-1 envelope-induced membrane fusion, entry, and infection of T lymphocytes and permissive cells, regardless of viral tropism. Furthermore, cell-to-cell HIV-1 transmission of primary human CD4(+) T lymphocytes was inhibited by Arf6 knockdown. Total internal reflection fluorescence microscopy showed that Arf6 mutants provoked the accumulation of phosphatidylinositol-(4,5)-biphosphate-associated structures on the plasma membrane of permissive cells, without affecting CD4-viral attachment but impeding CD4-dependent HIV-1 entry. Arf6 silencing or its mutants did not affect fusion, entry, and infection of vesicular stomatitis virus G-pseudotyped viruses or ligand-induced CXCR4 or CCR5 endocytosis, both clathrin-dependent processes. Therefore we propose that efficient early HIV-1 infection of CD4(+) T lymphocytes requires Arf6-coordinated plasma membrane dynamics that promote viral fusion and entry.