Mannose receptor is an HIV restriction factor counteracted by Vpr in macrophages

CRL4-DCAF1 Ubiquitin Ligase Dependent Functions of HIV Viral Protein R and Viral Protein X

The Human Immunodeficiency Virus (HIV) encodes several proteins that contort the host cell environment to promote viral replication and spread. This is often accomplished through the hijacking of cellular ubiquitin ligases. These reprogrammed complexes initiate or enhance the ubiquitination of cellular proteins that may otherwise act to restrain viral replication. Ubiquitination of target proteins may alter protein function or initiate proteasome-dependent destruction. HIV Viral Protein R (Vpr) and the related HIV-2 Viral Protein X (Vpx), engage the CRL4-DCAF1 ubiquitin ligase complex to target numerous cellular proteins. In this review we describe the CRL4-DCAF1 ubiquitin ligase complex and its interactions with HIV Vpr and Vpx. We additionally summarize the cellular proteins targeted by this association as well as the observed or hypothesized impact on HIV.

Help or Hinder: Protein Host Factors That Impact HIV-1 Replication

Interactions between human immunodeficiency virus type 1 (HIV-1) and the host factors or restriction factors of its target cells determine the cell's susceptibility to, and outcome of, infection. Factors intrinsic to the cell are involved at every step of the HIV-1 replication cycle, contributing to productive infection and replication, or severely attenuating the chances of success. Furthermore, factors unique to certain cell types contribute to the differences in infection between these cell types. Understanding the involvement of these factors in HIV-1 infection is a key requirement for the development of anti-HIV-1 therapies. As the list of factors grows, and the dynamic interactions between these factors and the virus are elucidated, comprehensive and up-to-date summaries that recount the knowledge gathered after decades of research are beneficial to the field, displaying what is known so that researchers can build off the groundwork of others to investigate what is unknown. Herein, we aim to provide a review focusing on protein host factors, both well-known and relatively new, that impact HIV-1 replication in a positive or negative manner at each stage of the replication cycle, highlighting factors unique to the various HIV-1 target cell types where appropriate.

Current status of mannose receptor-targeted drug delivery for improved anti-HIV therapy

In the pursuit of achieving better therapeutic outcomes in the treatment of HIV, innovative drug delivery strategies have been extensively explored. Mannose receptors, which are primarily found on macrophages and dendritic cells, offer promising targets for drug delivery due to their involvement in HIV pathogenesis. This review article comprehensively evaluates recent drug delivery system advancements targeting the mannose receptor. We have systematically described recent developments in creating and utilizing drug delivery platforms, including nanoparticles, liposomes, micelles, noisomes, dendrimers, and other nanocarrier systems targeted at the mannose receptor. These strategies aim to enhance drug delivery specificity, bioavailability, and therapeutic efficacy while decreasing off-target effects and systemic toxicity. Furthermore, the article delves into how mannose receptors and HIV interact, highlighting the potential for exploiting this interaction to enhance drug delivery to infected cells. The review covers essential topics, such as the rational design of nanocarriers for mannose receptor recognition, the impact of physicochemical properties on drug delivery performance, and how targeted delivery affects the pharmacokinetics and pharmacodynamics of anti-HIV agents. The challenges of these novel strategies, including immunogenicity, stability, and scalability, and future research directions in this rapidly growing area are discussed. The knowledge synthesis presented in this review underscores the potential of mannose receptor-based targeted drug delivery as a promising avenue for advancing HIV treatment. By leveraging the unique properties of mannose receptors, researchers can design drug delivery systems that cater to individual needs, overcome existing limitations, and create more effective and patient-friendly treatments in the ongoing fight against HIV/AIDS.

Antiviral factors and their counteraction by HIV-1: many uncovered and more to be discovered

Extensive studies on HIV-1 have led to the discovery of a variety of structurally and functionally diverse innate defense factors that target various steps of the retroviral replication cycle. Some of them, such as APOBEC3, tetherin, and SERINC5, are well established. Their importance is evident from the fact that HIV-1 uses its accessory proteins Vif, Vpu, and Nef to counteract them. However, the list of antiviral factors is constantly increasing, and accumulating evidence suggests that innate defense mechanisms, which restrict HIV-1 and/or are counteracted by viral proteins, remain to be discovered. These antiviral factors are relevant to diseases other than HIV/AIDS, since they are commonly active against various viral pathogens. In this review, we provide an overview of recently reported antiretroviral factors and viral countermeasures, present the evidence suggesting that more innate defense mechanisms remain to be discovered, and discuss why this is a challenging but rewarding task.

MARCH2, a T cell specific factor that restricts HIV-1 infection

Membrane-associated RING-CH (MARCH) 2 is a member of the MARCH protein family of RING-CH finger E3 ubiquitin ligases that play important roles in regulating the levels of proteins found on the cell surface. MARCH1, 2 and 8 inhibit HIV-1 infection by preventing the incorporation of the envelope glycoproteins into nascent virions. However, a better understanding of the mechanism utilized by MARCH proteins to restrict HIV-1 infection is needed. In this report, we identify an amino acid in human MARCH2, absent in mouse MARCH2, critical for its antiretroviral function. Moreover, we map the domains of human MARCH2 critical for restricting as well as binding to the HIV-1 envelope glycoproteins. In addition, we demonstrate that MARCH2 is present inside nascent virions and reduces particle infectivity by blocking virus entry in a RING-CH-independent manner. Finally, we show that MARCH2 acts as an HIV-1 restriction factor only in primary CD4+ T cells and can prevent cell-to-cell transmission of HIV-1. Our findings reveal important new aspects of the antiviral mechanism utilized by human MARCH2 to restrict HIV-1 that have potential implications to all MARCH proteins with antiviral functions and their viral targets.

HIV-1 Vpr combats the PU.1-driven antiviral response in primary human macrophages

HIV-1 Vpr promotes efficient spread of HIV-1 from macrophages to T cells by transcriptionally downmodulating restriction factors that target HIV-1 Envelope protein (Env). Here we find that Vpr induces broad transcriptomic changes by targeting PU.1, a transcription factor necessary for expression of host innate immune response genes, including those that target Env. Consistent with this, we find silencing PU.1 in infected macrophages lacking Vpr rescues Env. Vpr downmodulates PU.1 through a proteasomal degradation pathway that depends on physical interactions with PU.1 and DCAF1, a component of the Cul4A E3 ubiquitin ligase. The capacity for Vpr to target PU.1 is highly conserved across primate lentiviruses. In addition to impacting infected cells, we find that Vpr suppresses expression of innate immune response genes in uninfected bystander cells, and that virion-associated Vpr can degrade PU.1. Together, we demonstrate Vpr counteracts PU.1 in macrophages to blunt antiviral immune responses and promote viral spread.

HIV-1 Vpr combats the PU.1-driven antiviral response in primary human macrophages

HIV-1 Vpr promotes efficient spread of HIV-1 from macrophages to T cells by transcriptionally downmodulating restriction factors that target HIV-1 Envelope protein (Env). Here we find that Vpr induces broad transcriptomic changes by targeting PU.1, a transcription factor necessary for expression of host innate immune response genes, including those that target Env. Consistent with this, we find silencing PU.1 in infected macrophages lacking Vpr rescues Env. Vpr downmodulates PU.1 through a proteasomal degradation pathway that depends on physical interactions with PU.1 and DCAF1, a component of the Cul4A E3 ubiquitin ligase. The capacity for Vpr to target PU.1 is highly conserved across primate lentiviruses. In addition to impacting infected cells, we find that Vpr suppresses expression of innate immune response genes in uninfected bystander cells, and that virion-associated Vpr can degrade PU.1. Together, we demonstrate Vpr counteracts PU.1 in macrophages to blunt antiviral immune responses and promote viral spread.

Macrophages: Key Cellular Players in HIV Infection and Pathogenesis

Although cells of the myeloid lineages, including tissue macrophages and conventional dendritic cells, were rapidly recognized, in addition to CD4+ T lymphocytes, as target cells of HIV-1, their specific roles in the pathophysiology of infection were initially largely neglected. However, numerous studies performed over the past decade, both in vitro in cell culture systems and in vivo in monkey and humanized mouse animal models, led to growing evidence that macrophages play important direct and indirect roles as HIV-1 target cells and in pathogenesis. It has been recently proposed that macrophages are likely involved in all stages of HIV-1 pathogenesis, including virus transmission and dissemination, but above all, in viral persistence through the establishment, together with latently infected CD4+ T cells, of virus reservoirs in many host tissues, the major obstacle to virus eradication in people living with HIV. Infected macrophages are indeed found, very often as multinucleated giant cells expressing viral antigens, in almost all lymphoid and non-lymphoid tissues of HIV-1-infected patients, where they can probably persist for long period of time. In addition, macrophages also likely participate, directly as HIV-1 targets or indirectly as key regulators of innate immunity and inflammation, in the chronic inflammation and associated clinical disorders observed in people living with HIV, even in patients receiving effective antiretroviral therapy. The main objective of this review is therefore to summarize the recent findings, and also to revisit older data, regarding the critical functions of tissue macrophages in the pathophysiology of HIV-1 infection, both as major HIV-1-infected target cells likely found in almost all tissues, as well as regulators of innate immunity and inflammation during the different stages of HIV-1 pathogenesis.

Transcriptional regulation of the HIV-1 inhibitory factor human mannose receptor 1 by the myeloid-specific transcription factor PU.1

HIV-1 infection of human macrophages leads to the downmodulation of human mannose receptor 1 (hMRC1), a cell-surface glycoprotein that is involved in the host innate immune response. We previously reported that downmodulation of hMRC1 involves the transactivator of transcription (Tat)-dependent transcriptional silencing of the hMRC1 promoter. However, the inhibitory effect of Tat on hMRC1 transcription was indirect and involved inhibition of the transcriptional activator PU.1, which normally upregulates hMRC1 expression in macrophages and other myeloid cells. We cloned a 284-bp fragment of the hMRC1 promoter, and within it, we identified four PU.1 box elements. We assessed the relative contribution of each of the four PU.1 boxes to PU.1-dependent transcriptional regulation and, surprisingly, found that only one of the four PU.1 boxes [PU.1(b)] was critically required for PU.1-mediated upregulation of luciferase expression. Transfer of this PU.1 box to a heterologous promoter conferred PU.1 responsiveness to an otherwise PU.1 insensitive promoter. Electrophoretic mobility shift assays identified this PU.1 box as a direct binding site for PU.1 both in the context of the hMRC1 promoter and the heterologous promoter. Furthermore, mutational analysis of the PU.1 protein identified the C-terminal DNA-binding domain in PU.1 as the region responsible for interaction with the PU.1 box. Recombinant HIV-1 Tat protein did not bind to the hMRC1 promoter element but efficiently interfered with the binding of PU.1 protein to the hMRC1 promoter. Thus, Tat is likely to inhibit the formation of active PU.1 transcription complexes, presumably by binding to and depleting common transcriptional cofactors.IMPORTANCEHIV-1 infection of cells results in the modulation of cellular gene expression by virus-encoded proteins in a manner that benefits the virus. We reported that HIV-1 transactivator of transcription (Tat) dysregulates the expression of the human mannose receptor 1 (hMRC1). hMRC1 is involved in the innate immune response of macrophages to foreign pathogens. Tat does not act directly on the hMRC1 promoter but instead inhibits PU.1, a cellular transcription factor regulating hMRC1 gene expression. Here, we characterize the PU.1-dependent regulation of hMRC1 expression. We identified four potential PU.1 binding sites in the hMRC1 promoter region but found that only one, PU.1(b), functioned as a true binding site for PU.1. Transfer of the PU.1(b) box to a heterologous promoter did not activate this promoter per se but rendered it responsive to PU.1. Our results support the view that PU.1 acts as a transcriptional co-factor whose activity can be regulated by HIV-1 Tat.

Human Mannose Receptor 1 Attenuates HIV-1 Infectivity in a Virus Isolate-Specific Manner

Human mannose receptor 1 (hMRC1) is a transmembrane glycoprotein that belongs to the C-type lectin family and is expressed on the surface of most tissue macrophages. hMRC1 contributes to the binding and transmission of HIV-1 and is involved in the endocytic uptake of HIV-1 for subsequent antigen presentation. We previously reported that hMRC1 functions as an antiviral factor by inhibiting virus release through a BST-2-like mechanism. The inhibition of virus release was not virus isolate-specific and, surprisingly, was not Env-dependent. We now report on another hMRC1 antiviral function that affects the infectivity of viral particles. Unlike its effect on virus release, the inhibition of viral infectivity by hMRC1 was virus isolate-specific. An analysis of chimeric Env revealed that the Env V3 region was a critical determinant for the inhibitory effect of hMRC1. Of note, exogenously expressed hMRC1 was packaged into viral particles in an Env-independent manner. Co-immunoprecipitation studies revealed a strong interaction of the hMRC1-sensitive NL43 Env with hMRC1, while the hMRC1-insensitive Envs of AD8 and 49.5 isolates interacted poorly if at all with hMRC1. An analysis of a panel of Transmitted/Founder (T/F) viruses revealed that all of them were R5-tropic, and more than half of them were inhibited by hMRC1. The detailed mechanism of how hMRC1 inhibits viral infectivity remains to be investigated. However, the high-affinity binding of hMRC1 to Env may cause a conformational change around the Env V3 region or obstruct the Env V3 region and may make it inaccessible for subsequent interaction with the coreceptor during virus entry.

HIV-1 Vpr Induces Degradation of Gelsolin, a Myeloid Cell-Specific Host Factor That Reduces Viral Infectivity by Inhibiting the Expression and Packaging of the HIV-1 Env Glycoprotein

Gelsolin (GSN) is a structural actin-binding protein that is known to affect actin dynamics in the cell. Using mass spectrometry, we identified GSN as a novel Vpr-interacting protein. Endogenous GSN protein was expressed at detectable levels in monocyte-derived macrophages (MDM) and in THP-1 cells, but it was undetectable at the protein level in other cell lines tested. The HIV-1 infection of MDM was associated with a reduction in GSN steady-state levels, presumably due to the Vpr-induced degradation of GSN. Indeed, the coexpression of GSN and Viral protein R (Vpr) in transiently transfected HEK293T cells resulted in the Vpr-dependent proteasomal degradation of GSN. This effect was observed for Vprs from multiple virus isolates. The overexpression of GSN in HEK293T cells had no effect on Gag expression or particle release, but it reduced the expression and packaging of the HIV-1 envelope (Env) glycoprotein and reduced viral infectivity. An analysis of the HIV-1 splicing patterns did not reveal any GSN-dependent differences, suggesting that the effect of GSN on Env expression was regulated at a posttranscriptional level. Indeed, the treatment of transfected cells with lysosomal inhibitors reversed the effect of GSN on Env stability, suggesting that GSN reduced Env expression via enhanced lysosomal degradation. Our data identify GSN as a macrophage-specific host antiviral factor that reduces the expression of HIV-1 Env. IMPORTANCE Despite dramatic progress in drug therapies, HIV-1 infection remains an incurable disease that affects millions of people worldwide. The virus establishes long-lasting reservoirs that are resistant to currently available drug treatments and allow the virus to rebound whenever drug therapy is interrupted. Macrophages are long-lived cells that are relatively insensitive to HIV-1-induced cytopathicity and thus could contribute to the viral reservoir. Here, we identified a novel host factor, gelsolin, that is expressed at high levels in macrophages and inhibits viral infectivity by modulating the expression of the HIV-1 Env glycoprotein, which is critical in the spread of an HIV-1 infection. Importantly, the viral protein Vpr induces the degradation of gelsolin and thus counteracts its antiviral activity. Our study provides significant and novel insights into HIV-1 virus-host interactions and furthers our understanding of the importance of Vpr in HIV-1 infection and pathogenesis.

Characterization of effects of chitooligosaccharide monomer addition on immunomodulatory activity in macrophages

The present study aimed to investigate the effects of five chitooligosaccharide monomers of different molecular weights on immunomodulatory activity in macrophage-like RAW264.7 cells. The incubation of various chitooligosaccharide monomers enhanced phagocytosis and pinocytosis activity toward Staphylococcus aureus and Escherichia coli in RAW264.7 cells. The incorporation of chitooligosaccharide monomers significantly boosted the generation of reactive oxygen species and reactive nitrogen species, as well as the release of inflammatory cytokines. To further explore the mechanism of inflammation regulated by chitooligosaccharide, the activation inhibitors of NF-кB (CAPE) and TLR-4 (TAK-242) were utilized, the determination data demonstrated that chitobiose suppressed the expression of inflammatory cytokines and NF-кB p65. In addition, the investigation results revealed that the presence of the mannose receptor inhibitor (mannan) suppressed chitohexaose-induced phagocytic activity and inflammatory cytokines. These results suggested that the five distinct chitooligosaccharide monomers had inconsistent effects, the chitobiose and chitohexaose exhibiting the best biological activity in activating RAW264.7 cells, promoting cell proliferation, and increasing non-specific immunity.

The Myeloid-Specific Transcription Factor PU.1 Upregulates Mannose Receptor Expression but Represses Basal Activity of the HIV-LTR Promoter

Human mannose receptor 1 (MRC1) is a cell surface receptor expressed in macrophages and other myeloid cells that inhibits human immunodeficiency virus type 1 (HIV-1) particle release by tethering virions to producer cell membranes. HIV-1 counteracts MRC1 expression by inhibiting mrc1 transcription. Here, we investigated the mechanism of MRC1 downregulation in HIV-1-infected macrophages. We identified the myeloid cell-specific transcription factor PU.1 as critical for regulating MRC1 expression. In the course of our study, we recognized a complex interplay between HIV-1 Tat and PU.1 transcription factors: Tat upregulated HIV-1 gene expression but inhibited mrc1 transcription, whereas PU.1 inhibited HIV-1 transcription but activated MRC1 expression. Disturbing this equilibrium by silencing PU.1 resulted in increased HIV-1 gene expression and reduced MRC1 promoter activity. Our study identified PU.1 as a central player in transcriptional control, regulating a complex interplay between viral and host gene expression in HIV-infected macrophages. IMPORTANCE HIV-1 replication in primary human cells depends on the activity of virus-encoded proteins but also involves cellular factors that can either promote (viral dependency factors) or inhibit (host restriction factors) virus replication. In previous work, we identified human MRC1 as a macrophage-specific host restriction factor that inhibits the detachment of viral particles from infected cells. Here, we report that HIV-1 counteracts this effect of MRC1 by imposing a transcriptional block on cellular MRC1 gene expression. The transcriptional inhibition of the MRC1 gene is accomplished by Tat, an HIV-1 factor whose best-described function actually is the enhancement of HIV-1 gene expression. Thus, HIV-1 has evolved to use the same protein for (i) activation of its own gene expression while (ii) inhibiting expression of MRC1 and other host factors.

Host Restriction Factors Modulating HIV Latency and Replication in Macrophages

In addition to CD4⁺ T lymphocytes, myeloid cells and, particularly, differentiated macrophages are targets of human immunodeficiency virus type-1 (HIV-1) infection via the interaction of gp120Env with CD4 and CCR5 or CXCR4. Both T cells and macrophages support virus replication, although with substantial differences. In contrast to activated CD4⁺ T lymphocytes, HIV-1 replication in macrophages occurs in nondividing cells and it is characterized by the virtual absence of cytopathicity both in vitro and in vivo. These general features should be considered in evaluating the role of cell-associated restriction factors aiming at preventing or curtailing virus replication in macrophages and T cells, particularly in the context of designing strategies to tackle the viral reservoir in infected individuals receiving combination antiretroviral therapy. In this regard, we will here also discuss a model of reversible HIV-1 latency in primary human macrophages and the role of host factors determining the restriction or reactivation of virus replication in these cells.

Strategy and clinical application of up-regulating cross presentation by DCs in anti-tumor therapy

The cross presentation of exogenous antigen (Ag) by dendritic cells (DCs) facilitates a diversified mode of T-cell activation, orchestrates specific humoral and cellular immunity, and contributes to an efficient anti-tumor immune response. DCs-mediated cross presentation is subject to both intrinsic and extrinsic factors, including the homing and phenotype of DCs, the spatiotemporal trafficking and degradation kinetics of Ag, and multiple microenvironmental clues, with many details largely unexplored. Here, we systemically review the current mechanistic understanding and regulation strategies of cross presentation by heterogeneous DC populations. We also provide insights into the future exploitation of DCs cross presentation for a better clinical efficacy in anti-tumor therapy.

Human Immunodeficiency Virus Type 1 Vpr Mediates Degradation of APC1, a Scaffolding Component of the Anaphase-Promoting Complex/Cyclosome

HIV-1 encodes several accessory proteins-Nef, Vif, Vpr, and Vpu-whose functions are to modulate the cellular environment to favor immune evasion and viral replication. While Vpr was shown to mediate a G2/M cell cycle arrest and provide a replicative advantage during infection of myeloid cells, the mechanisms underlying these functions remain unclear. In this study, we defined HIV-1 Vpr proximity interaction network using the BioID proximity labeling approach and identified 352 potential Vpr partners/targets, including several complexes, such as the cell cycle-regulatory anaphase-promoting complex/cyclosome (APC/C). Herein, we demonstrate that both the wild type and cell cycle-defective mutants of Vpr induce the degradation of APC1, an essential APC/C scaffolding protein, and show that this activity relies on the recruitment of DCAF1 by Vpr and the presence of a functional proteasome. Vpr forms a complex with APC1, and the APC/C coactivators Cdh1 and Cdc20 are associated with these complexes. Interestingly, we found that Vpr encoded by the prototypic HIV-1 NL4.3 does not interact efficiently with APC1 and is unable to mediate its degradation as a result of a N28S-G41N amino acid substitution. In contrast, we show that APC1 degradation is a conserved feature of several primary Vpr variants from transmitted/founder virus. Functionally, Vpr-mediated APC1 degradation did not impact the ability of the protein to induce a G2 cell cycle arrest during infection of CD4+ T cells or enhance HIV-1 replication in macrophages, suggesting that this conserved activity may be important for other aspects of HIV-1 pathogenesis. IMPORTANCE The function of the Vpr accessory protein during HIV-1 infection remains poorly defined. Several cellular targets of Vpr were previously identified, but their individual degradation does not fully explain the ability of Vpr to impair the cell cycle or promote HIV-1 replication in macrophages. Here, we used the unbiased proximity labeling approach, called BioID, to further define the Vpr proximity interaction network and identified several potentially new Vpr partners/targets. We validated our approach by focusing on a cell cycle master regulator, the APC/C complex, and demonstrated that Vpr mediated the degradation of a critical scaffolding component of APC/C called APC1. Furthermore, we showed that targeting of APC/C by Vpr did not impact the known activity of Vpr. Since degradation of APC1 is a conserved feature of several primary variants of Vpr, it is likely that the interplay between Vpr and APC/C governs other aspects of HIV-1 pathogenesis.

Size, shape, charge and "stealthy" surface: Carrier properties affect the drug circulation time in vivo

The present review sets out to discuss recent developments of the effects and mechanisms of carrier properties on their circulation time. For most drugs, sufficient in vivo circulation time is the basis of high bioavailability. Drug carrier plays an irreplaceable role in helping drug avoid being quickly recognized and cleared by mononuclear phagocyte system, to give drug enough time to arrive at targeted organ and tissue to play its therapeutic effect. The physical and chemical properties of drug carriers, such as size, shape, surface charge and surface modification, would affect their in vivo circulation time, metabolic behavior and biodistribution. The final circulation time of carriers is determined by the balance between macrophage recognitions, blood vessel penetration and urine excretion. Therefore, when designing the drug delivery system, we should pay much attention to the properties of drug carriers to get enough in vivo circulation time to arrive at target site eventually. This article mainly reviews the effect of carrier size, size, surface charge and surface properties on its circulation time in vivo, and discusses the mechanism of these properties affecting circulation time. This review has reference significance for the research of long-circulation drug delivery system.

Vpr counteracts the restriction of LAPTM5 to promote HIV-1 infection in macrophages

The HIV-1 accessory proteins Vif, Vpu, and Nef can promote infection by overcoming the inhibitory effects of the host cell restriction factors APOBEC3G, Tetherin, and SERINC5, respectively. However, how the HIV-1 accessory protein Vpr enhances infection in macrophages but not in CD4⁺ T cells remains elusive. Here, we report that Vpr counteracts lysosomal-associated transmembrane protein 5 (LAPTM5), a potent inhibitor of HIV-1 particle infectivity, to enhance HIV-1 infection in macrophages. LAPTM5 transports HIV-1 envelope glycoproteins to lysosomes for degradation, thereby inhibiting virion infectivity. Vpr counteracts the restrictive effects of LAPTM5 by triggering its degradation via DCAF1. In the absence of Vpr, the silencing of LAPTM5 precisely phenocopied the effect of Vpr on HIV-1 infection. In contrast, Vpr did not enhance HIV-1 infection in the absence of LAPTM5. Moreover, LAPTM5 was highly expressed in macrophages but not in CD4⁺ T lymphocytes. Re-expressing LAPTM5 reconstituted the Vpr-dependent promotion of HIV-1 infection in primary CD4⁺ T cells, as observed in macrophages. Herein, we demonstrate the molecular mechanism used by Vpr to overcome LAPTM5 restriction in macrophages, providing a potential strategy for anti-HIV/AIDS therapeutics.

Structural analysis of carbohydrate binding by the macrophage mannose receptor CD206

The human mannose receptor expressed on macrophages and hepatic endothelial cells scavenges released lysosomal enzymes, glycopeptide fragments of collagen, and pathogenic microorganisms and thus reduces damage following tissue injury. The receptor binds mannose, fucose, or N-acetylglucosamine (GlcNAc) residues on these targets. C-type carbohydrate-recognition domain 4 (CRD4) of the receptor contains the site for Ca2+-dependent interaction with sugars. To investigate the details of CRD4 binding, glycan array screening was used to identify oligosaccharide ligands. The strongest signals were for glycans that contain either Manα1-2Man constituents or fucose in various linkages. The mechanisms of binding to monosaccharides and oligosaccharide substructures present in many of these ligands were examined in multiple crystal structures of CRD4. Binding of mannose residues to CRD4 results primarily from interaction of the equatorial 3- and 4-OH groups with a conserved principal Ca2+ common to almost all sugar-binding C-type CRDs. In the Manα1-2Man complex, supplementary interactions with the reducing mannose residue explain the enhanced affinity for this disaccharide. Bound GlcNAc also interacts with the principal Ca2+ through equatorial 3- and 4-OH groups, whereas fucose residues can bind in several orientations, through either the 2- and 3-OH groups or the 3- and 4-OH groups. Secondary contacts with additional sugars in fucose-containing oligosaccharides, such as the Lewis-a trisaccharide, provide enhanced affinity for these glycans. These results explain many of the biologically important interactions of the mannose receptor with both mammalian glycoproteins and microbes such as yeast and suggest additional classes of ligands that have not been previously identified.

Retroviral Restriction Factors and Their Viral Targets: Restriction Strategies and Evolutionary Adaptations

The evolutionary conflict between retroviruses and their vertebrate hosts over millions of years has led to the emergence of cellular innate immune proteins termed restriction factors as well as their viral antagonists. Evidence accumulated in the last two decades has substantially increased our understanding of the elaborate mechanisms utilized by these restriction factors to inhibit retroviral replication, mechanisms that either directly block viral proteins or interfere with the cellular pathways hijacked by the viruses. Analyses of these complex interactions describe patterns of accelerated evolution for these restriction factors as well as the acquisition and evolution of their virus-encoded antagonists. Evidence is also mounting that many restriction factors identified for their inhibition of specific retroviruses have broader antiviral activity against additional retroviruses as well as against other viruses, and that exposure to these multiple virus challenges has shaped their adaptive evolution. In this review, we provide an overview of the restriction factors that interfere with different steps of the retroviral life cycle, describing their mechanisms of action, adaptive evolution, viral targets and the viral antagonists that evolved to counter these factors.

Vpr Is a VIP: HIV Vpr and Infected Macrophages Promote Viral Pathogenesis

HIV infects several cell types in the body, including CD4+ T cells and macrophages. Here we review the role of macrophages in HIV infection and describe complex interactions between viral proteins and host defenses in these cells. Macrophages exist in many forms throughout the body, where they play numerous roles in healthy and diseased states. They express pattern-recognition receptors (PRRs) that bind viral, bacterial, fungal, and parasitic pathogens, making them both a key player in innate immunity and a potential target of infection by pathogens, including HIV. Among these PRRs is mannose receptor, a macrophage-specific protein that binds oligosaccharides, restricts HIV replication, and is downregulated by the HIV accessory protein Vpr. Vpr significantly enhances infection in vivo, but the mechanism by which this occurs is controversial. It is well established that Vpr alters the expression of numerous host proteins by using its co-factor DCAF1, a component of the DCAF1-DDB1-CUL4 ubiquitin ligase complex. The host proteins targeted by Vpr and their role in viral replication are described in detail. We also discuss the structure and function of the viral protein Env, which is stabilized by Vpr in macrophages. Overall, this literature review provides an updated understanding of the contributions of macrophages and Vpr to HIV pathogenesis.