Macrophage tropism determinants of human immunodeficiency virus type 1 in vivo

Novel small synthetic HIV-1 V3 crown variants: CCR5 targeting ligands

The CC chemokine receptor 5 (CCR5) antagonism represents a promising pharmacological strategy for therapeutic intervention as it plays a significant role in reducing the severity and progression of a wide range of pathological conditions. Here we designed and generated peptide ligands targeting the chemokine receptor, CCR5, that were derived from the critical interaction sites of the V3 crown domain of envelope protein glycoprotein gp120 (TRKSIHIGPGRAFYTTGEI) of HIV-1 using computational biology approach and the peptide sequence corresponding to this region was taken as the template peptide, designated as TMP-1. The peptide variants were synthesized by employing Fmoc chemistry using polymer support and were labelled with rhodamine B to study their interaction with the CCR5 receptor expressed on various cells. TMP-1 and TMP-2 were selected as the high-affinity ligands from in vitro receptor-binding assays. Specific receptor-binding experiments in activated peripheral blood mononuclear cells and HOS.CCR5 cells indicated that TMP-1 and TMP-2 had significant CCR5 specificity. Further, the functional analysis of TMP peptides using chemotactic migration assay showed that both peptides did not mediate the migration of responsive cells. Thus, template TMP-1 and TMP-2 represent promising CCR5 targeting peptide candidates.

Intra-host dynamics and co-receptor usage of HIV-1 quasi-species in vertically infected patients with phenotypic switch

HIV-1 infection through vertical transmission provides a good model to evaluate intra-host viral evolution and allows to gain insight into the dynamics of viral populations. Our aim was to assess the diversity and dynamics of X4- and R5-using HIV-1 variants in vertically infected children who presented a switch in SI/ NSI phenotype in MT-2 cell assays during chronic infection. Through molecular cloning and next generation sequencing of the C2-V5 env fragment, we investigated HIV-1 evolution and co-receptor usage based on V3 loop prediction bioinformatic tools of longitudinal samples obtained from 4 children. In all cases, the phylogenetic relationships were assessed by Maximum-Likelihood trees constructed with MEGA 6.0. In two cases, V3 loop sequences predicted exclusively R5-using and or X4-using strains, while in another two a higher degree of concordance was observed between the phenotypic and genotypic characteristics. In 3 of the 4 cases, C2-V5 env sequences from different time points were intermingled in phylogenetic trees, with no segregation neither by time or tropism. In only one case monophyletic clustering defined groups of sequences with different co-receptor usage. Comparison of amino acid frequency between isolates with SI and NSI phenotype allowed the identification of 9 possible genetic determinants in subtype F C2-V5 region of env associated to SI/ NSI phenotype in these patients, one of which had previously been reported for subtype B. Overall, we found a low degree of correlation between phenotypic and genotypic properties of HIV-1 quasispecies in patients under chronic infection. Whether HIV-1 subtype or other factors influence the evolution of HIV-1 in vivo will require further research.

HIV-1 Integrates Widely throughout the Genome of the Human Blood Fluke Schistosoma mansoni

Schistosomiasis is the most important helminthic disease of humanity in terms of morbidity and mortality. Facile manipulation of schistosomes using lentiviruses would enable advances in functional genomics in these and related neglected tropical diseases pathogens including tapeworms, and including their non-dividing cells. Such approaches have hitherto been unavailable. Blood stream forms of the human blood fluke, Schistosoma mansoni, the causative agent of the hepatointestinal schistosomiasis, were infected with the human HIV-1 isolate NL4-3 pseudotyped with vesicular stomatitis virus glycoprotein. The appearance of strong stop and positive strand cDNAs indicated that virions fused to schistosome cells, the nucleocapsid internalized and the RNA genome reverse transcribed. Anchored PCR analysis, sequencing HIV-1-specific anchored Illumina libraries and Whole Genome Sequencing (WGS) of schistosomes confirmed chromosomal integration; >8,000 integrations were mapped, distributed throughout the eight pairs of chromosomes including the sex chromosomes. The rate of integrations in the genome exceeded five per 1,000 kb and HIV-1 integrated into protein-encoding loci and elsewhere with integration bias dissimilar to that of human T cells. We estimated ~ 2,100 integrations per schistosomulum based on WGS, i.e. about two or three events per cell, comparable to integration rates in human cells. Accomplishment in schistosomes of post-entry processes essential for HIV-1replication, including integrase-catalyzed integration, was remarkable given the phylogenetic distance between schistosomes and primates, the natural hosts of the genus Lentivirus. These enigmatic findings revealed that HIV-1 was active within cells of S. mansoni, and provided the first demonstration that HIV-1 can integrate into the genome of an invertebrate.

Cellular minichromosome maintenance complex component 5 (MCM5) is incorporated into HIV-1 virions and modulates viral replication in the newly infected cells

The post-entry events of HIV-1 infection occur within reverse transcription complexes derived from the viral cores entering the target cell. HIV-1 cores contain host proteins incorporated from virus-producing cells. In this report, we show that MCM5, a subunit of the hexameric minichromosome maintenance (MCM) DNA helicase complex, associates with Gag polyprotein and is incorporated into HIV-1 virions. The progeny virions depleted of MCM5 demonstrated reduced reverse transcription in newly infected cells, but integration and subsequent replication steps were not affected. Interestingly, increased packaging of MCM5 into the virions also led to reduced reverse transcription, but here viral replication was impaired. Our data suggest that incorporation of physiological amounts of MCM5 promotes aberrant reverse transcription, leading to partial incapacitation of cDNA, whereas increased MCM5 abundance leads to reduced reverse transcription and infection. Therefore, MCM5 has the properties of an inhibitory factor that interferes with production of an integration-competent cDNA product.

Evolution of coreceptor utilization to escape CCR5 antagonist therapy

The HIV-1 envelope interacts with coreceptors CCR5 and CXCR4 in a dynamic, multi-step process, its molecular details not clearly delineated. Use of CCR5 antagonists results in tropism shift and therapeutic failure. Here we describe a novel approach using full-length patient-derived gp160 quasispecies libraries cloned into HIV-1 molecular clones, their separation based on phenotypic tropism in vitro, and deep sequencing of the resultant variants for structure-function analyses. Analysis of functionally validated envelope sequences from patients who failed CCR5 antagonist therapy revealed determinants strongly associated with coreceptor specificity, especially at the gp120-gp41 and gp41-gp41 interaction surfaces that invite future research on the roles of subunit interaction and envelope trimer stability in coreceptor usage. This study identifies important structure-function relationships in HIV-1 envelope, and demonstrates proof of concept for a new integrated analysis method that facilitates laboratory discovery of resistant mutants to aid in development of other therapeutic agents.

Phenyl-1-Pyridin-2yl-ethanone-based iron chelators increase IκB-α expression, modulate CDK2 and CDK9 activities, and inhibit HIV-1 transcription

HIV-1 transcription is activated by the Tat protein, which recruits CDK9/cyclin T1 to the HIV-1 promoter. CDK9 is phosphorylated by CDK2, which facilitates formation of the high-molecular-weight positive transcription elongation factor b (P-TEFb) complex. We previously showed that chelation of intracellular iron inhibits CDK2 and CDK9 activities and suppresses HIV-1 transcription, but the mechanism of the inhibition was not understood. In the present study, we tested a set of novel iron chelators for the ability to inhibit HIV-1 transcription and elucidated their mechanism of action. Novel phenyl-1-pyridin-2yl-ethanone (PPY)-based iron chelators were synthesized and examined for their effects on cellular iron, HIV-1 inhibition, and cytotoxicity. Activities of CDK2 and CDK9, expression of CDK9-dependent and CDK2-inhibitory mRNAs, NF-κB expression, and HIV-1- and NF-κB-dependent transcription were determined. PPY-based iron chelators significantly inhibited HIV-1, with minimal cytotoxicity, in cultured and primary cells chronically or acutely infected with HIV-1 subtype B, but they had less of an effect on HIV-1 subtype C. Iron chelators upregulated the expression of IκB-α, with increased accumulation of cytoplasmic NF-κB. The iron chelators inhibited CDK2 activity and reduced the amount of CDK9/cyclin T1 in the large P-TEFb complex. Iron chelators reduced HIV-1 Gag and Env mRNA synthesis but had no effect on HIV-1 reverse transcription. In addition, iron chelators moderately inhibited basal HIV-1 transcription, equally affecting HIV-1 and Sp1- or NF-κB-driven transcription. By virtue of their involvement in targeting several key steps in HIV-1 transcription, these novel iron chelators have the potential for the development of new therapeutics for the treatment of HIV-1 infection.

Spontaneous rearrangement of the β20/β21 strands in simulations of unliganded HIV-1 glycoprotein, gp120

Binding of the viral spike drives cell entry and infection by HIV-1 to the cellular CD4 and chemokine receptors with associated conformational change of the viral glycoprotein envelope, gp120. Crystal structures of the CD4-gp120-antibody ternary complex reveal a large internal gp120 cavity formed by three domains-the inner domain, outer domain, and bridging sheet domain-and are capped by CD4 residue Phe43. Several structures of gp120 envelope in complex with various antibodies indicated that the bridging sheet adopts varied conformations. Here, we examine bridging sheet dynamics using a crystal structure of gp120 bound to the F105 antibody exhibiting an open bridging sheet conformation and with an added V3 loop. The two strands of the bridging sheet β2/β3 and β20/β21 are dissociated from each other and are directed away from the inner and outer domains. Analysis of molecular dynamics (MD) trajectories indicates that the β2/β3 and β20/β21 strands rapidly rearrange to interact with the V3 loop and the inner and outer domains, respectively. Residue N425 on β20 leads the conformational rearrangement of the β20/β21 strands by interacting with W112 on the inner domain and F382 on the outer domain. An accompanying shift is observed in the inner domain as helix α1 exhibits a loss in helicity and pivots away from helix α5. The two simulations provide a framework for understanding the conformational diversity of the bridging sheet and the propensity of the β20/β21 strand to refold between the inner and outer domains of gp120, in the absence of a bound ligand.

Virus-producing cells determine the host protein profiles of HIV-1 virion cores

Background

Upon HIV entry into target cells, viral cores are released and rearranged into reverse transcription complexes (RTCs), which support reverse transcription and also protect and transport viral cDNA to the site of integration. RTCs are composed of viral and cellular proteins that originate from both target and producer cells, the latter entering the target cell within the viral core. However, the proteome of HIV-1 viral cores in the context of the type of producer cells has not yet been characterized.

Results

We examined the proteomic profiles of the cores purified from HIV-1 NL4-3 virions assembled in Sup-T1 cells (T lymphocytes), PMA and vitamin D₃ activated THP1 (model of macrophages, mMΦ), and non-activated THP1 cells (model of monocytes, mMN) and assessed potential involvement of identified proteins in the early stages of infection using gene ontology information and data from genome-wide screens on proteins important for HIV-1 replication. We identified 202 cellular proteins incorporated in the viral cores (T cells: 125, mMΦ: 110, mMN: 90) with the overlap between these sets limited to 42 proteins. The groups of RNA binding (29), DNA binding (17), cytoskeleton (15), cytoskeleton regulation (21), chaperone (18), vesicular trafficking-associated (12) and ubiquitin-proteasome pathway-associated proteins (9) were most numerous. Cores of the virions from SupT1 cells contained twice as many RNA binding proteins as cores of THP1-derived virus, whereas cores of virions from mMΦ and mMN were enriched in components of cytoskeleton and vesicular transport machinery, most probably due to differences in virion assembly pathways between these cells. Spectra of chaperones, cytoskeletal proteins and ubiquitin-proteasome pathway components were similar between viral cores from different cell types, whereas DNA-binding and especially RNA-binding proteins were highly diverse. Western blot analysis showed that within the group of overlapping proteins, the level of incorporation of some RNA binding (RHA and HELIC2) and DNA binding proteins (MCM5 and Ku80) in the viral cores from T cells was higher than in the cores from both mMΦ and mMN and did not correlate with the abundance of these proteins in virus producing cells.

Conclusions

Profiles of host proteins packaged in the cores of HIV-1 virions depend on the type of virus producing cell. The pool of proteins present in the cores of all virions is likely to contain factors important for viral functions. Incorporation ratio of certain RNA- and DNA-binding proteins suggests their more efficient, non-random packaging into virions in T cells than in mMΦ and mMN.

Vpx is critical for SIVmne infection of pigtail macaques

BACKGROUND

Viral protein X (Vpx) of SIV has been reported to be important for establishing infection in vivo. Vpx has several different activities in vitro, promoting preintegration complex import into the nucleus in quiescent lymphocytes and overcoming a block in reverse transcription in macrophages. Vpx interacts with the DDB1-CUL4-DCAF1 E3 ligase complex, which may or may not be required for the ascribed functions. The goal of the current study was to determine whether these activities of Vpx are important in vivo.

RESULTS

An infectious, pathogenic clone of SIVmne was used to examine correlations between Vpx functions in vitro and in vivo. Three previously described HIV-2 Vpx mutants that were shown to be important for nuclear import of the preintegration complex in quiescent lymphocytes were constructed in SIVmne: A vpx-deleted virus, a truncation of Vpx at amino acid 102 that deletes the C-terminal proline-rich domain (X(102)), and a mutant with tyrosines 66, 69, and 71 changed to alanine (X(y-a)). All mutant viruses replicated similarly to wild type SIVmne027 in primary pigtail macaque PBMCs, and were only slightly retarded in CEMx174 cells. However, all the vpx mutant viruses were defective for replication in both human and pigtail monocyte-derived macrophages. PCR assays demonstrated that the efficiency of reverse transcription and the levels of viral integration in macrophages were substantially reduced for the vpx mutant viruses. In vitro, the X(y-a) mutant, but not the X(102) mutant lost interaction with DCAF1. The wild type SIVmne027 and the three vpx mutant SIVs were inoculated by the intra-rectal route into pigtail macaques. Peak levels of plasma viremia of the vpx mutant SIVs were variable, but consistently lower than that observed in macaques infected with wild type SIVmne. In situ hybridization for SIV demonstrated that compared to wild type SIVmne infected macaques five of the six animals inoculated with the vpx mutant SIVs had only low levels of SIV-expressing cells in the rectum, most intestinal epithelial tissues, spleen, and mesenteric and peripheral nodes.

CONCLUSIONS

This work demonstrates that the activities of Vpx to overcome restrictions in culture in vitro are also likely to be important for establishment of infection in vivo and suggest that both the nuclear localization and DCAF1-interaction functions of Vpx are critical in vivo.

HIV-1 envelope subregion length variation during disease progression

The V3 loop of the HIV-1 Env protein is the primary determinant of viral coreceptor usage, whereas the V1V2 loop region is thought to influence coreceptor binding and participate in shielding of neutralization-sensitive regions of the Env glycoprotein gp120 from antibody responses. The functional properties and antigenicity of V1V2 are influenced by changes in amino acid sequence, sequence length and patterns of N-linked glycosylation. However, how these polymorphisms relate to HIV pathogenesis is not fully understood. We examined 5185 HIV-1 gp120 nucleotide sequence fragments and clinical data from 154 individuals (152 were infected with HIV-1 Subtype B). Sequences were aligned, translated, manually edited and separated into V1V2, C2, V3, C3, V4, C4 and V5 subregions. V1-V5 and subregion lengths were calculated, and potential N-linked glycosylation sites (PNLGS) counted. Loop lengths and PNLGS were examined as a function of time since infection, CD4 count, viral load, and calendar year in cross-sectional and longitudinal analyses. V1V2 length and PNLGS increased significantly through chronic infection before declining in late-stage infection. In cross-sectional analyses, V1V2 length also increased by calendar year between 1984 and 2004 in subjects with early and mid-stage illness. Our observations suggest that there is little selection for loop length at the time of transmission; following infection, HIV-1 adapts to host immune responses through increased V1V2 length and/or addition of carbohydrate moieties at N-linked glycosylation sites. V1V2 shortening during early and late-stage infection may reflect ineffective host immunity. Transmission from donors with chronic illness may have caused the modest increase in V1V2 length observed during the course of the pandemic.

The HIV envelope gene (env) encodes viral surface proteins (Env) that are vital to the basic processes used by the virus to infect and cause disease in humans. Adaptations in env determine which cells the virus can infect, and permit the virus to avoid elimination by the immune system. Env is one of the most variable genes known, and it can change dramatically over time in a single individual. However, Env-host cell interactions are complex and incompletely understood, and changes in this viral protein during infection have not yet been systematically described. We examined a large number of env sequences from 154 individuals at various stages of HIV infection but who had never received antiretroviral treatment. We found that the env V1V2 region lengthens during chronic infection and becomes more heavily glycosylated. However, these changes partially reverse during late-stage illness, possibly in response to a weakening host immune system. V1V2 lengths are also increasing over time in the epidemic at large, possibly related to the epidemiology of HIV transmission within the subtype B epidemic. These results provide fundamental insights into the biology of HIV.

Ribonucleoside triphosphates as substrate of human immunodeficiency virus type 1 reverse transcriptase in human macrophages

We biochemically simulated HIV-1 DNA polymerization in physiological nucleotide pools found in two HIV-1 target cell types: terminally differentiated/non-dividing macrophages and activated/dividing CD4(+) T cells. Quantitative tandem mass spectrometry shows that macrophages harbor 22-320-fold lower dNTP concentrations and a greater disparity between ribonucleoside triphosphate (rNTP) and dNTP concentrations than dividing target cells. A biochemical simulation of HIV-1 reverse transcription revealed that rNTPs are efficiently incorporated into DNA in the macrophage but not in the T cell environment. This implies that HIV-1 incorporates rNTPs during viral replication in macrophages and also predicts that rNTP chain terminators lacking a 3'-OH should inhibit HIV-1 reverse transcription in macrophages. Indeed, 3'-deoxyadenosine inhibits HIV-1 proviral DNA synthesis in human macrophages more efficiently than in CD4(+) T cells. This study reveals that the biochemical landscape of HIV-1 replication in macrophages is unique and that ribonucleoside chain terminators may be a new class of anti-HIV-1 agents specifically targeting viral macrophage infection.

Mutational pathways and genetic barriers to CXCR4-mediated entry by human immunodeficiency virus type 1

To examine mutational pathways that lead to CXCR4 use of HIV-1, we analyzed the genotypic and phenotypic characteristics of envelope sequences from a large panel of patient virus populations and individual clones containing different V3 mutations. Basic amino acid substitutions at position 11 were strong determinants of CXCR4-mediated entry but required multiple compensatory mutations to overcome associated reductions in infectivity. In contrast, basic amino acid substitutions at position 25, or substitutions at positions 6-8 resulting in the loss of a potential N-linked glycosylation site, contributed to CXCR4-mediated entry but required additional substitutions acting cooperatively to confer efficient CXCR4 use. Our assumptions, based upon examination of patient viruses, were largely confirmed by characterizing the coreceptor utilization of five distinct panels of isogenic envelope sequences containing V3 amino acid substitutions introduced by site-directed mutagenesis. These results further define the mutational pathways leading to CXCR4 use and their associated genetic barriers.

Subtype-associated differences in HIV-1 reverse transcription affect the viral replication

Background

The impact of the products of the pol gene, specifically, reverse transcriptase (RT) on HIV-1 replication, evolution, and acquisition of drug resistance has been thoroughly characterized for subtype B. For subtype C, which accounts of almost 60% of HIV cases worldwide, much less is known. It has been reported that subtype C HIV-1 isolates have a lower replication capacity than B; however, the basis of these differences remains unclear.

Results

We analyzed the impact of the pol gene products from HIV-1 B and C subtypes on the maturation of HIV virions, accumulation of reverse transcription products, integration of viral DNA, frequency of point mutations in provirus and overall viral replication. Recombinant HIV-1 viruses of B and C subtypes comprising the pol fragments encoding protease, integrase and either the whole RT or a chimeric RT from different isolates of the C and B subtypes, were used for infection of cells expressing CXCR4 or CCR5 co-receptors. The viruses carrying different fragments of pol from the isolates of B and C subtypes did not reveal differences in Gag and GagPol processing and viral RNA incorporation into the virions. However, the presence of the whole RT from subtype C, or the chimeric RT containing either the polymerase or the connection and RNase H domains from C isolates, caused significantly slower viral replication regardless of B or C viral backbone. Subtype C RT carrying viruses displayed lower levels of accumulation of strong-stop cDNA in permeabilized virions during endogenous reverse transcription, and decreased accumulation of both strong-stop and positive strand reverse transcription products in infected cells and in isolated reverse transcription complexes. This decreased accumulation correlated with lower levels of viral DNA integration in cells infected with viruses carrying the whole RT or RT domains from subtype C isolates. The single viral genome assay analysis did not reveal significant differences in the frequency of point mutations between the RT from B or C subtypes.

Conclusions

These data suggest that the whole RT as well as distinct polymerase and connection-RNase H domains from subtype C HIV-1 confer a lower level of accumulation of reverse transcripts in the virions and reverse transcription complexes as compared to subtype B, resulting in a lower overall level of virus replication.

Molecular determinants of HIV-1 subtype C coreceptor transition from R5 to R5X4

The molecular mechanism(s) underlying transition from CCR5 to CXCR4 usage of subtype C viruses remain largely unknown. We previously identified a subtype C HIV-1 infected child whose virus demonstrated CXCR4 usage along with CCR5 upon longitudinal follow-up. Here we delineated the molecular determinants of Env involved in expanded coreceptor usage. Residue changes in three positions of Env V3 domain are critical for the dual tropic phenotype. These include: substitution of arginine at position 11, MG or LG insertion between positions 13 and 14, and substitution of threonine at the position immediately downstream of the GPGQ crown. Introducing these mutations into V3 region of a heterologous R5 virus also conferred dual tropism. Molecular modeling of V3 revealed a possible structural basis for the dual tropic phenotype. Determining what defines a subtype C X4 virus will lead to a better understanding of subtype C HIV-1 pathogenesis, and will provide important information relevant to anti-retroviral therapy.

Role of placenta in the vertical transmission of human immunodeficiency virus

OBJECTIVE

Review the role and mechanism of in utero placental transmission of HIV-1.

STUDY DESIGN

A thorough review based on a literature search for publications relevant to this subject was performed using relevant search terms. Articles that describe the genetic and pathophysiology of vertical transmission have been acknowledged. The articles pertinent to the topic were selected to support the discussion.

RESULTS

Vertical transmission may occur through CD4+ endothelial tissues or CD4+ Hofbauer cells. Trophoblasts and villi have CD4 receptors, which make them potential candidates for HIV infection. Placental cytokines and chemokines influence HIV replication in trophoblasts. Genetic analysis of HIV-1 sequences verify the interaction of HIV-1 and placental tissue. The vertical transmission of HIV-1 characterized by selection of genotype variant that escape the mother's immune system.

CONCLUSION

Placental transmission of HIV-1 is a complex incompletely understood process which requires advanced studies. The available literature provides information with regards to the interactions of placental cells with HIV.

[Role of the HIV-1 gp120 V1/V2 domains in the induction of neutralizing antibodies]

The development of a preventive vaccine against human immunodeficiency virus type-1 (HIV-1) provides hope for control of the pandemic over the coming years. Nevertheless, it is clear that one of the greatest difficulties in achieving this vaccine is the high mutation rate of the virus, which enables it to evade the host's immune response. The production of neutralizing antibodies (NAb) against the HIV-1 envelope proteins is believed to play an important role in controlling the infection and in providing effective protection following vaccination. Several studies have shown that the V1/V2 domain of the HIV-1 gp120 envelope protein is involved in viral tropism during infection, in masking conserved neutralizing epitopes, in the conformational changes occurring after coreceptor binding, and in NAb induction. Nonetheless, this domain has been poorly investigated. However, because the V1/V2 domain is highly glycosylated, numerous studies have determined the influence of carbohydrates on NAb production. The present review focuses on the importance of NAb directed against epitopes of the variable regions, mainly V1/V2, their importance in protecting against HIV-1 infection, and the role these regions play in evading the immune response. Lastly, we will discuss the importance of NAb in the search for an effective vaccine against HIV-1.

THE VERTICAL TRANSMISSION OF HUMAN IMMUNODEFICIENCY VIRUS TYPE 1: Molecular and Biological Properties of the Virus

The vertical (mother-to-infant) transmission of human immunodeficiency virus type 1 (HIV-1 ) occurs at an estimated rate of more than 30% and is the major cause of AIDS in children. Numerous maternal parameters, including advanced dinical stages, low CD4+ lymphocte counts, high viral load, immune response, and disease progression have been implicated in an increased risk of vertical transmission. While the use of antiretroviral therapy (ART) during pregnancy has been shown to reduce the risk of vertical transmission, selective transmission of ART-resistant mutants has also been documented. Elucidation of the molecular mechanisms of vertical transmission might provide relevant information for the development of effective strategies for prevention and treatment. By using HIV-1 infected mother-infant pairs as a transmitter-recipient model, the minor genotypes of HIV-1 with macrophage-tropic and non-syncytium-inducing phenotypes (R5 viruses) in infected mothers were found to be transmitted to their infants and were initially maintained in the infants with the same properties. In addition, the transmission of major and multiple genotypes has been suggested. Furthermore, HIV-1 sequences found in non-transmitting mothers (mothers who failed to transmit HIV-1 to their infants in the absence of ART) were less heterogeneous than those from transmitting mothers, suggesting that viral heterogeneity may play an important role in vertical transmission. In the analysis of other regions of the HIV-1 genome, we have shown a high conservation of intact and functional gag p17, vif, vpr, vpu, tat, and nef open reading frames following mother-to-infant transmission. Moreover the accessory genes, vif and vpr, were less functionally conserved in the isolates of non-transmitting mothers than transmitting mothers and their infants. We, therefore, should target the properties of transmitted viruses to develop new and more effective strategies for the prevention and treatment of HIV-1 infection.

The V1-V3 region of a brain-derived HIV-1 envelope glycoprotein determines macrophage tropism, low CD4 dependence, increased fusogenicity and altered sensitivity to entry inhibitors

Background

HIV-1 infects macrophages and microglia in the brain and can cause neurological disorders in infected patients. We and others have shown that brain-derived envelope glycoproteins (Env) have lower CD4 dependence and higher avidity for CD4 than those from peripheral isolates, and we have also observed increased fusogenicity and reduced sensitivity to the fusion inhibitor T-1249. Due to the genetic differences between brain and spleen env from one individual throughout gp120 and in gp41's heptad repeat 2 (HR2), we investigated the viral determinants for the phenotypic differences by performing functional studies with chimeric and mutant Env.

Results

Chimeric Env showed that the V1/V2-C2-V3 region in brain's gp120 determines the low CD4 dependence and high avidity for CD4, as well as macrophage tropism and reduced sensitivity to the small molecule BMS-378806. Changes in brain gp41's HR2 region did not contribute to the increased fusogenicity or to the reduced sensitivity to T-1249, since a T-1249-based peptide containing residues found in brain's but not in spleen's HR2 had similar potency than T-1249 and interacted similarly with an immobilized heptad repeat 1-derived peptide in surface plasmon resonance analysis. However, the increased fusogenicity and reduced T-1249 sensitivity of brain and certain chimeric Env mostly correlated with the low CD4 dependence and high avidity for CD4 determined by brain's V1-V3 region. Remarkably, most but not all of these low CD4-dependent, macrophage tropic envelopes glycoproteins also had increased sensitivity to the novel allosteric entry inhibitor HNG-105. The gp120's C2 region asparagine 283 (N283) has been previously associated with macrophage tropism, brain infection, lower CD4 dependence and higher CD4 affinity. Therefore, we introduced the N283T mutation into an env clone from a brain-derived isolate and into a brain tissue-derived env clone, and the T283N change into a spleen-derived env from the same individual; however, we found that their phenotypes were not affected.

Conclusion

We have identified that the V1-V3 region of a brain-derived envelope glycoprotein seems to play a crucial role in determining not only the low CD4 dependence and increased macrophage tropism, but also the augmented fusogenicity and reduced sensitivity to T-1249 and BMS-378806. By contrast, increased sensitivity to HNG-105 mostly correlated with low CD4 dependence and macrophage tropism but was not determined by the presence of the brain's V1-V3 region, confirming that viral determinants of phenotypic changes in brain-derived envelope glycoproteins are likely complex and context-dependent.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4(+) T cell population, despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics with different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

Coreceptor tropism can be influenced by amino acid substitutions in the gp41 transmembrane subunit of human immunodeficiency virus type 1 envelope protein

Many studies have demonstrated that the third variable region (V3) of the human immunodeficiency virus type 1 (HIV-1) envelope protein (Env) is a major determinant of coreceptor tropism. Other regions in the surface gp120 subunit of Env can modulate coreceptor tropism in a manner that is not fully understood. In this study, we evaluated the effect of env determinants outside of V3 on coreceptor usage through the analysis of (i) patient-derived env clones that differ in coreceptor tropism, (ii) chimeric env sequences, and (iii) site-directed mutants. The introduction of distinct V3 sequences from CXCR4-using clones into an R5-tropic env backbone conferred the inefficient use of CXCR4 in some but not all cases. Conversely, in many cases, X4- and dual-tropic env backbones containing the V3 sequences of R5-tropic clones retained the ability to use CXCR4, suggesting that sequences outside of the V3 regions of these CXCR4-using clones were responsible for CXCR4 use. The determinants of CXCR4 use in a set of dual-tropic env sequences with V3 sequences identical to those of R5-tropic clones mapped to the gp41 transmembrane (TM) subunit. In one case, a single-amino-acid substitution in the fusion peptide of TM was able to confer CXCR4 use; however, TM substitutions associated with CXCR4 use varied among different env sequences. These results demonstrate that sequences in TM can modulate coreceptor specificity and that env sequences other than that of V3 may facilitate efficient CXCR4-mediated entry. We hypothesize that the latter plays an important role in the transition from CCR5 to CXCR4 coreceptor use.

Opposite immune reactivity of serum IgG and secretory IgA to conformational recombinant proteins mimicking V1/V2 domains of three different HIV type 1 subtypes depending on glycosylation

The V1/V2 domain of the HIV-1 gp120 envelope protein has been shown to contribute to viral cell tropism during infection and also to viral recognition by neutralizing monoclonal antibodies. However, this domain has been poorly investigated. Carbohydrates have been demonstrated to dramatically influence immune reactivity of antisera to viral glycoprotein antigens. In this study, DNA sequences coding for V1/V2 domains from HIV-1 primary isolates of three subtypes (A, B, and C) were subcloned into a secretion vector and used to transfect CHO cells that are able to achieve the glycosylation of proteins. The structure of purified recombinant V1/V2 proteins was tested using two anti-V1/V2 monoclonal antibodies directed against either a linear or a conformational and glycosylation-dependent epitope (8.22.2 and 697-D). Serum or saliva of 14/82 seropositive patients with anti-V1/V2 reactivity demonstrated good recognition of the recombinant proteins. Deglycosylation of the recombinant proteins was found to increase the reactivity of the serum IgG to the clade A and C but not to clade B V1/V2 domain demonstrating that the recognition of glycosylation sites by serum IgG is clade dependent. When considering SIgA from parotid saliva, deglycosylation of all recombinant proteins tested decreased the reactivity, suggesting that glycosylation plays an important role in the recognition of V1/V2 domain target epitopes by this class of antibodies. In conclusion, these results suggest the influence of carbohydrate moieties on the specificity of the antibodies to the V1/V2 domain produced during HIV infection and the potential importance of viral glycans in vaccine responses after mucosal administration.

Role of HIV-1 subtype C envelope V3 to V5 regions in viral entry, coreceptor utilization and replication efficiency in primary T-lymphocytes and monocyte-derived macrophages

Background

Several subtypes of HIV-1 circulate in infected people worldwide, including subtype B in the United States and subtype C in Africa and India. To understand the biological properties of HIV-1 subtype C, including cellular tropism, virus entry, replication efficiency and cytopathic effects, we reciprocally inserted our previously characterized envelope V3–V5 regions derived from 9 subtype C infected patients from India into a subtype B molecular clone, pNL4-3. Equal amounts of the chimeric viruses were used to infect T-lymphocyte cell lines (A3.01 and MT-2), coreceptor cell lines (U373-MAGI-CCR5/CXCR4), primary blood T-lymphocytes (PBL) and monocyte-derived macrophages (MDM).

Results

We found that subtype C envelope V3–V5 region chimeras failed to replicate in T-lymphocyte cell lines but replicated in PBL and MDM. In addition, these chimeras were able to infect U373MAGI-CD4⁺-CCR5⁺ but not U373MAGI-CD4⁺-CXCR4⁺ cell line, suggesting CCR5 coreceptor utilization and R5 phenotypes. These subtype C chimeras were unable to induce syncytia in MT-2 cells, indicative of non-syncytium inducing (NSI) phenotypes. More importantly, the subtype C envelope chimeras replicated at higher levels in PBL and MDM compared with subtype B chimeras and isolates. Furthermore, the higher levels subtype C chimeras replication in PBL and MDM correlated with increased virus entry in U373MAGI-CD4⁺-CCR5⁺.

Conclusion

Taken together, these results suggest that the envelope V3 to V5 regions of subtype C contributed to higher levels of HIV-1 replication compared with subtype B chimeras, which may contribute to higher viral loads and faster disease progression in subtype C infected individuals than other subtypes as well as rapid HIV-1 subtype C spread in India.

An evolutionary-network model reveals stratified interactions in the V3 loop of the HIV-1 envelope

The third variable loop (V3) of the human immunodeficiency virus type 1 (HIV-1) envelope is a principal determinant of antibody neutralization and progression to AIDS. Although it is undoubtedly an important target for vaccine research, extensive genetic variation in V3 remains an obstacle to the development of an effective vaccine. Comparative methods that exploit the abundance of sequence data can detect interactions between residues of rapidly evolving proteins such as the HIV-1 envelope, revealing biological constraints on their variability. However, previous studies have relied implicitly on two biologically unrealistic assumptions: (1) that founder effects in the evolutionary history of the sequences can be ignored, and; (2) that statistical associations between residues occur exclusively in pairs. We show that comparative methods that neglect the evolutionary history of extant sequences are susceptible to a high rate of false positives (20%-40%). Therefore, we propose a new method to detect interactions that relaxes both of these assumptions. First, we reconstruct the evolutionary history of extant sequences by maximum likelihood, shifting focus from extant sequence variation to the underlying substitution events. Second, we analyze the joint distribution of substitution events among positions in the sequence as a Bayesian graphical model, in which each branch in the phylogeny is a unit of observation. We perform extensive validation of our models using both simulations and a control case of known interactions in HIV-1 protease, and apply this method to detect interactions within V3 from a sample of 1,154 HIV-1 envelope sequences. Our method greatly reduces the number of false positives due to founder effects, while capturing several higher-order interactions among V3 residues. By mapping these interactions to a structural model of the V3 loop, we find that the loop is stratified into distinct evolutionary clusters. We extend our model to detect interactions between the V3 and C4 domains of the HIV-1 envelope, and account for the uncertainty in mapping substitutions to the tree with a parametric bootstrap.

Effects of vpu start-codon mutations on human immunodeficiency virus type 1 replication in macrophages

The human immunodeficiency virus type 1 (HIV-1) vpu protein increases the release of virus particles from infected cells. Mutations that abrogate vpu function have a profound effect on HIV-1 replication in primary macrophage cultures. About 1.24 % of primary isolates in the HIV databases have vpu start-codon mutations. In addition, the envelope of the AD8 isolate was reported to compensate for the lack of vpu, whilst the YU-2 virus (cloned directly from the brain tissue of an infected individual) is macrophage-tropic, despite having a vpu start-codon mutation. These observations raise the possibility that envelopes evolve to compensate for the loss of vpu function in vivo. Chimeric vpu+ and vpu- replication-competent clones were constructed that contained the envelopes of SF162, AD8 or YU-2. Macrophages were infected with these chimeras and virus release was measured over time by a reverse transcriptase ELISA. It was found that vpu-deficient chimeras carrying AD8 and YU-2 envelopes were consistently released at lower levels than their wild-type (wt) vpu counterparts, indicating that these envelopes did not compensate for the lack of vpu. Non-chimeric vpu+ and vpu- AD8 and YU-2 followed similar patterns, although replication by vpu-deficient AD8 was variable, with virion release reaching 60 % of that recorded for AD8 with a wt vpu. In summary, no evidence was found that the AD8 or YU-2 envelopes can compensate for the lack of vpu for replication in macrophages.

Anti-vpr activities of heat shock protein 27

HIV-1 Vpr plays a pivotal role in viral pathogenesis and is preferentially targeted by the host immune system. In this report, we demonstrate that a small heat shock protein, HSP27, exhibits Vpr-specific antiviral activity, as its expression is specifically responsive to vpr gene expression and increased levels of HSP27 inhibit Vpr-induced cell cycle G2 arrest and cell killing. We further show that overexpression of HSP27 reduces viral replication in T-lymphocytes in a Vpr-dependent manner. Mechanistically, Vpr triggers HSP27 expression through heat shock factor (HSF) 1, but inhibits prolonged expression of HSP27 under heat-shock conditions. Together, these data suggest a potential dynamic and antagonistic interaction between HIV-1 Vpr and a host cell HSP27, suggesting that HSP27 may contribute to cellular intrinsic immunity against HIV infection.

Anti-vpr activities of heat shock protein 27

HIV-1 Vpr plays a pivotal role in viral pathogenesis and is preferentially targeted by the host immune system. In this report, we demonstrate that a small heat shock protein, HSP27, exhibits Vpr-specific antiviral activity, as its expression is specifically responsive to vpr gene expression and increased levels of HSP27 inhibit Vpr-induced cell cycle G2 arrest and cell killing. We further show that overexpression of HSP27 reduces viral replication in T-lymphocytes in a Vpr-dependent manner. Mechanistically, Vpr triggers HSP27 expression through heat shock factor (HSF) 1, but inhibits prolonged expression of HSP27 under heat-shock conditions. Together, these data suggest a potential dynamic and antagonistic interaction between HIV-1 Vpr and a host cell HSP27, suggesting that HSP27 may contribute to cellular intrinsic immunity against HIV infection.

HIV-1 buds predominantly at the plasma membrane of primary human macrophages

HIV-1 assembly and release are believed to occur at the plasma membrane in most host cells with the exception of primary macrophages, for which exclusive budding at late endosomes has been reported. Here, we applied a novel ultrastructural approach to assess HIV-1 budding in primary macrophages in an immunomarker-independent manner. Infected macrophages were fed with BSA-gold and stained with the membrane-impermeant dye ruthenium red to identify endosomes and the plasma membrane, respectively. Virus-filled vacuolar structures with a seemingly intracellular localization displayed intense staining with ruthenium red, but lacked endocytosed BSA-gold, defining them as plasma membrane. Moreover, HIV budding profiles were virtually excluded from gold-filled endosomes while frequently being detected on ruthenium red-positive membranes. The composition of cellular marker proteins incorporated into HIV-1 supported a plasma membrane-derived origin of the viral envelope. Thus, contrary to current opinion, the plasma membrane is the primary site of HIV-1 budding also in infected macrophages.

Persistent resistance to HIV-1 infection in CD4 T cells from exposed uninfected Vietnamese individuals is mediated by entry and post-entry blocks

BACKGROUND

We have previously reported that CD4 T cells from some exposed uninfected (EU) Vietnamese intravenous drug users are relatively resistant to HIV infection in vitro. Here, we further characterized the restriction of viral replication in CD4 T cells from five EUs and assessed its persistence in serial samples.

RESULTS

CD4 T cells and/or PBMC sampled during a period of between 2 and 6 years were challenged with replication-competent HIV-1 and other retroviral particles pseudotyped with envelope proteins of various tropisms. CCR5 expression and function in resistant CD4 T cells was evaluated. The step at which HIV-1 replication is restricted was investigated by real-time PCR quantification of HIV-1 reverse transcripts. We identified three patterns of durable HIV-1 restriction in EU CD4 T cells. CD4 T cells from four of the five EU subjects were resistant to HIV-1 R5 infection. In two cases this resistance was associated with low CCR5 surface expression, which was itself associated with heterozygous CCR5 mutations. In the other two cases, CD4 T cells were resistant to HIV-1 R5 infection despite normal CCR5 expression and signaling function, and normal beta-chemokine secretion upon CD4 T cell activation. Instead, restriction appeared to be due to enhanced CD4 T cell sensitivity to beta-chemokines in these two subjects. In the fifth EU subject the restriction involved post-entry steps of viral replication and affected not only HIV-1 but also other lentiviruses. The restriction was not overcome by a high viral inoculum, suggesting that it was not mediated by a saturable inhibitory factor.

CONCLUSION

Various constitutive mechanisms of CD4 T cell resistance to HIV-1 infection, affecting entry or post-entry steps of viral replication, are associated with resistance to HIV-1 in subjects who remain uninfected despite long-term high-risk behavior.

Ultrastructural analysis of ESCRT proteins suggests a role for endosome-associated tubular-vesicular membranes in ESCRT function

The endosomal sorting complex required for transport (ESCRT) is thought to support the formation of intralumenal vesicles of multivesicular bodies (MVBs). The ESCRT is also required for the budding of HIV and has been proposed to be recruited to the HIV-budding site, the plasma membrane of T cells and MVBs in macrophages. Despite increasing data on the function of ESCRT, the ultrastructural localization of its components has not been determined. We therefore localized four proteins of the ESCRT machinery in human T cells and macrophages by quantitative electron microscopy. All the proteins were found throughout the endocytic pathway, including the plasma membrane, with only around 10 and 3% of the total labeling in the cytoplasm and on the MVBs, respectively. The majority of the labeling (45%) was unexpectedly found on tubular-vesicular endosomal membranes rather than on endosomes themselves. The ESCRT labeling was twice as concentrated on early and late endosomes/lysosomes in macrophages compared with that in T cells, where it was twice more abundant at the plasma membrane. The ESCRT proteins were not redistributed on HIV infection, suggesting that the amount of ESCRT proteins located at the budding site suffices for HIV release. These results represent the first systematic ultrastructural localization of ESCRT and provide insights into its role in uninfected and HIV-infected cells.

Human immunodeficiency virus type 1 coreceptor switching: V1/V2 gain-of-fitness mutations compensate for V3 loss-of-fitness mutations

Human immunodeficiency virus type 1 (HIV-1) entry into target cells is mediated by the virus envelope binding to CD4 and the conformationally altered envelope subsequently binding to one of two chemokine receptors. HIV-1 envelope glycoprotein (gp120) has five variable loops, of which three (V1/V2 and V3) influence the binding of either CCR5 or CXCR4, the two primary coreceptors for virus entry. Minimal sequence changes in V3 are sufficient for changing coreceptor use from CCR5 to CXCR4 in some HIV-1 isolates, but more commonly additional mutations in V1/V2 are observed during coreceptor switching. We have modeled coreceptor switching by introducing most possible combinations of mutations in the variable loops that distinguish a previously identified group of CCR5- and CXCR4-using viruses. We found that V3 mutations entail high risk, ranging from major loss of entry fitness to lethality. Mutations in or near V1/V2 were able to compensate for the deleterious V3 mutations and may need to precede V3 mutations to permit virus survival. V1/V2 mutations in the absence of V3 mutations often increased the capacity of virus to utilize CCR5 but were unable to confer CXCR4 use. V3 mutations were thus necessary but not sufficient for coreceptor switching, and V1/V2 mutations were necessary for virus survival. HIV-1 envelope sequence evolution from CCR5 to CXCR4 use is constrained by relatively frequent lethal mutations, deep fitness valleys, and requirements to make the right amino acid substitution in the right place at the right time.

Covariability of selected amino acid positions for HIV type 1 subtypes C and B

We studied covariability of selected amino acid positions in globally dominant HIV-1 subtype C viruses. The analyzed sequences spanned the V3 loop, Gag p17, Gag p24, and five CTL epitope-rich regions in Gag, Nef, and Tat. The corresponding regions in HIV-1 subtype B were also evaluated. The analyses identified a great number of covarying pairs and triples of sites in the HIV-1B V3 loop (173 site pairs, 242 site triples). Several of these interactions were found in the earlier studies [e.g., the V3 loop covariability analyses by Korber et al. (Proc Natl Acad Sci USA 1993;90:7176-7180) and Bickel et al. (AIDS Res Hum Retroviruses 1996;12:1401-1411)] and have known biological significance. However, generally these key covarying sites did not covary in the HIV-1C V3 loop (total 17 covarying site pairs), suggesting that the V3 loop may have subtype differences in functional or structural operating characteristics. Covariability of positions 309 and 312 was observed in the immunodominant region HIV-1C Gag 291-320 but no covariability was found in the corresponding region of HIV-1B, and vice versa for Nef 122-141; these findings may reflect subtype-specific covariability within immunologically relevant regions. Gag p17 exhibited greater covariability and less diversity for HIV-1B than HIV-1C, raising the hypothesis that Gag p17 is highly immunodominant in HIV-1B and is especially important for HIV-1B vaccines. Information on covariability should be better exploited in assessments of HIV-1 diversity and how to surmount it with vaccine design.

Oxadiazols: a new class of rationally designed anti-human immunodeficiency virus compounds targeting the nuclear localization signal of the viral matrix protein

Despite recent progress in anti-human immunodeficiency virus (HIV) therapy, drug toxicity and emergence of drug-resistant isolates during long-term treatment of HIV-infected patients necessitate the search for new targets that can be used to develop novel antiviral agents. One such target is the process of nuclear translocation of the HIV preintegration complex. Previously we described a class of arylene bis(methylketone) compounds that inhibit HIV-1 nuclear import by targeting the nuclear localization signal (NLS) in the matrix protein (MA). Here we report a different class of MA NLS-targeting compounds that was selected using computer-assisted drug design. The leading compound from this group, ITI-367, showed potent anti-HIV activity in cultures of T lymphocytes and macrophages and also inhibited HIV-1 replication in ex vivo cultured lymphoid tissue. The virus carrying inactivating mutations in MA NLS was resistant to ITI-367. Analysis by real-time PCR demonstrated that the compound specifically inhibited nuclear import of viral DNA, measured by two-long terminal repeat circle formation. Evidence of the existence of this mechanism was provided by immunofluorescent microscopy, using fluorescently labeled HIV-1, which demonstrated retention of the viral DNA in the cytoplasm of drug-treated macrophages. Compounds inhibiting HIV-1 nuclear import may be attractive candidates for further development.

Analysis of the env V3 sequences obtained from patients with HIV type 1 infection treated with the immune modulant agent tucaresol

Tucaresol, a Schiff base-forming compound that is shown to enhance cytotoxic T cell responses and the production of type 1 cytokines, represents a potentially useful adjuvant factor for treating HIV-1 infection. We studied the effect of tucaresol on V3 sequences within the HIV-1 env region derived from patients with different virologic and immunologic features who were enrolled in a phase I/II randomized clinical trial. The sequence analysis of the env V3 region of the viruses at baseline has confirmed a genotypic pattern similar to a macrophagotropic virus model; we analyzed the follow-up sequences at week 16 of the protocol and did not observe any difference in the tropism determinants within the third variable fragment of the env region. The administration of tucaresol did not accelerate env V3 evolution thus preventing modifications of HIV-1 tropism over time.

Role of low CD4 levels in the influence of human immunodeficiency virus type 1 envelope V1 and V2 regions on entry and spread in macrophages

Human immunodeficiency virus type 1 (HIV-1) isolates vary in their ability to infect macrophages. Previous experiments have mapped viral determinants of macrophage infectivity to the V3 hypervariable region of the HIV-1 envelope glycoprotein. In our earlier studies, V1 and V2 sequences of HIV-1 were also shown to alter the ability of virus to spread in macrophage cultures, whereas no effect was seen in lymphocyte cultures. In the present study, determinants that allowed certain HIV-1 clones to infect and spread in macrophages were primarily mapped to the V2 region and were found to act by influencing early events of viral infection. By an assay of viral entry into macrophages, it was shown that viruses with the V2 region from the Ba-L strain of HIV-1 had >10-fold-higher entry efficiency than viruses with the V2 region derived from the NL4-3 strain. V1 region differences between these groups caused a twofold difference in entry. The known low expression of CD4 on macrophages appeared to be important in this process. In entry assays conducted with HeLa cell lines expressing various levels of CD4 and CCR5, low levels of CD4 influenced the efficiency of entry and fusion which were dependent on viral V1 and V2 envelope sequences. In contrast, no effect of V1 or V2 was seen in HeLa cells expressing high levels of CD4. Thus, the limited expression of CD4 on macrophages or other cell types could serve as a selective factor for V1 and V2 envelope sequences, and this selection could in turn influence many aspects of AIDS pathogenesis in vivo.

Anti-Vpr activity of a yeast chaperone protein

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) exerts multiple effects on viral and host cellular activities during viral infection, including nuclear transport of the proviral integration complex, induction of cell cycle G(2) arrest, and cell death. In this report, we show that a fission yeast chaperone protein Hsp16 inhibits HIV-1 by suppressing these Vpr activities. This protein was identified through three independent genome-wide screens for multicopy suppressors of each of the three Vpr activities. Consistent with the properties of a heat shock protein, heat shock-induced elevation or overproduction of Hsp16 suppressed Vpr activities through direct protein-protein interaction. Even though Hsp16 shows a stronger suppressive effect on Vpr in fission yeast than in mammalian cells, similar effects were also observed in human cells when fission yeast hsp16 was expressed either in vpr-expressing cells or during HIV-1 infection, indicating a possible highly conserved Vpr suppressing activity. Furthermore, stable expression of hsp16 prior to HIV-1 infection inhibits viral replication in a Vpr-dependent manner. Together, these data suggest that Hsp16 inhibits HIV-1 by suppressing Vpr-specific activities. This finding could potentially provide a new approach to studying the contribution of Vpr to viral pathogenesis and to reducing Vpr-mediated detrimental effects in HIV-infected patients.

Punica granatum (Pomegranate) juice provides an HIV-1 entry inhibitor and candidate topical microbicide

Background

For ≈ 24 years the AIDS pandemic has claimed ≈ 30 million lives, causing ≈ 14,000 new HIV-1 infections daily worldwide in 2003. About 80% of infections occur by heterosexual transmission. In the absence of vaccines, topical microbicides, expected to block virus transmission, offer hope for controlling the pandemic. Antiretroviral chemotherapeutics have decreased AIDS mortality in industrialized countries, but only minimally in developing countries. To prevent an analogous dichotomy, microbicides should be: acceptable; accessible; affordable; and accelerative in transition from development to marketing. Already marketed pharmaceutical excipients or foods, with established safety records and adequate anti-HIV-1 activity, may provide this option.

Methods

Fruit juices were screened for inhibitory activity against HIV-1 IIIB using CD4 and CXCR4 as cell receptors. The best juice was tested for inhibition of: (1) infection by HIV-1 BaL, utilizing CCR5 as the cellular coreceptor; and (2) binding of gp120 IIIB and gp120 BaL, respectively, to CXCR4 and CCR5. To remove most colored juice components, the adsorption of the effective ingredient(s) to dispersible excipients and other foods was investigated. A selected complex was assayed for inhibition of infection by primary HIV-1 isolates.

Results

HIV-1 entry inhibitors from pomegranate juice adsorb onto corn starch. The resulting complex blocks virus binding to CD4 and CXCR4/CCR5 and inhibits infection by primary virus clades A to G and group O.

Conclusion

These results suggest the possibility of producing an anti-HIV-1 microbicide from inexpensive, widely available sources, whose safety has been established throughout centuries, provided that its quality is adequately standardized and monitored.

Heat-shock protein 70 exerts opposing effects on Vpr-dependent and Vpr-independent HIV-1 replication in macrophages

HIV-1 viral protein R (Vpr) shuttles between the nucleus and the cytoplasm and is believed to contribute to the process of nuclear translocation of the viral preintegration complex, thus facilitating HIV-1 replication in macrophages. In this report, we demonstrate that Hsp70, a heat-shock protein contributing to cellular stress responses, inhibits nuclear translocation of HIV-1 Vpr. In macrophages, Hsp70 is induced shortly after HIV-1 infection. Recombinant Hsp70 or a mild heat shock diminished replication of the wild-type HIV-1, suggesting that Hsp70 might function as an innate antiviral factor. Surprisingly, Hsp70 stimulated nuclear import and replication in macrophages of the Vpr-deficient HIV-1 construct. This finding suggests that Hsp70 and Vpr may function in a similar manner when expressed separately, but they neutralize each other's activity when present together. Consistent with this interpretation, Hsp70 coprecipitated with Vpr from HIV-1–infected cells.

HIV-1 fitness and macrophages

HIV-1 comprises a collection of closely related, but not identical, viruses or quasispecies. Fitness represents a selective advantage for propagation among populations of organisms competing in a particular environment and is an important characteristic of viruses because of a link between fitness and pathogenesis. Environmental differences based on the type of cell that is targeted for infection or the cell type that produces virus, impact fitness. CD4-expressing cells of lymphocyte or macrophage lineage are the principal host cells for HIV-1, although the milieu in lymphocytes is distinct from the macrophage environment from the perspective of cell half-life and activation, signal transduction and expression of coreceptors, and bioavailability of antiretroviral drugs. Multiple viral determinants, including entry via envelope glycoproteins, replication by reverse transcriptase, and virion maturation by protease activity, contribute to fitness in different cells and provide targets for current antiretroviral therapies. This review focuses on fitness of HIV-1 in macrophages and examines the impact of protease inhibitors on fitness of quasispecies and an unexplained discordance between fitness and pathogenesis.

Human immunodeficiency virus type 1 envelope-mediated neuronal death: uncoupling of viral replication and neurotoxicity

Although brain tissue from patients with human immunodeficiency virus (HIV) and/or AIDS is consistently infected by HIV type 1 (HIV-1), only 20 to 30% of patients exhibit clinical or neuropathological evidence of brain injury. Extensive HIV-1 sequence diversity is present in the brain, which may account in part for the variability in the occurrence of HIV-induced brain disease. Neurological injury caused by HIV-1 is mediated directly by neurotoxic viral proteins or indirectly through excess production of host molecules by infected or activated glial cells. To elucidate the relationship between HIV-1 infection and neuronal death, we examined the neurotoxic effects of supernatants from human 293T cells or macrophages expressing recombinant HIV-1 virions or gp120 proteins containing the V1V3 or C2V3 envelope region from non-clade B, brain-derived HIV-1 sequences. Neurotoxicity was measured separately as apoptosis or total neuronal death, with apoptosis representing 30 to 80% of the total neuron death observed, depending on the individual virus. In addition, neurotoxicity was dependent on expression of HIV-1 gp120 and could be blocked by anti-gp120 antibodies, as well as by antibodies to the human CCR5 and CXCR4 chemokine receptors. Despite extensive sequence diversity in the recombinant envelope region (V1V3 or C2V3), there was limited variation in the neurotoxicity induced by supernatants from transfected 293T cells. Conversely, supernatants from infected macrophages caused a broader range of neurotoxicity levels that depended on each virus and was independent of the replicative ability of the virus. These findings underscore the importance of HIV-1 envelope protein expression in neurotoxic pathways associated with HIV-induced brain disease and highlight the envelope as a target for neuroprotective therapeutic interventions.

Susceptibility to highly sulphated glycosaminoglycans of human immunodeficiency virus type 1 replication in peripheral blood lymphocytes and monocyte-derived macrophages cell cultures

In the search for new drugs against human immunodeficiency virus type 1 (HIV-1), the replication of III(B) and BaL strains, and of seven primary isolates from AIDS patients, cultured both in peripheral blood lymphocytes (PBLs) and in monocyte-derived macrophages (MACs), was investigated in the presence of two dermatan sulphate and heparin at 10 microg/ml. The three polysaccharides effectively inhibited the replication of III(B) in PBLs and of BaL in MACs, while producing either a slight inhibition or an unexpected large increase in the replication of the seven primary isolates, especially in MAC cultures. In one case, stimulation was found in PBLs and, at lower doses, also with BaL in MACs. Co-receptor use, adaptation to C8166 T cell line, partial sequence of the gp120 V3 loop, variation in positive charge distribution and number of potential glycosylation sites along the V3 loop were assessed for each strain. No explanation could be found for the different susceptibility of the viruses to the polysaccharides. Their presence probably brings about both inhibitory and stimulatory effects, the final outcome depending on the virus, cells and polysaccharide.

Addition of a single gp120 glycan confers increased binding to dendritic cell-specific ICAM-3-grabbing nonintegrin and neutralization escape to human immunodeficiency virus type 1

The potential role of dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) binding in human immunodeficiency virus transmission across the mucosal barrier was investigated by assessing the ability of simian-human immunodeficiency chimeric viruses (SHIVs) showing varying degrees of mucosal transmissibility to bind the DC-SIGN expressed on the surface of transfected cells. We found that gp120 of the highly transmissible, pathogenic CCR5-tropic SHIV(SF162P3) bound human and rhesus DC-SIGN with an efficiency threefold or greater than that of gp120 of the nonpathogenic, poorly transmissible parental SHIV(SF162), and this increase in binding to the DC-SIGN of the SHIV(SF162P3) envelope gp120 translated into an enhancement of T-cell infection in trans. The presence of an additional glycan at the N-terminal base of the V2 loop of SHIV(SF162P3) gp120 compared to that of the parental virus was shown to be responsible for the increase in binding to DC-SIGN. Interestingly, this glycan also conferred escape from autologous neutralization, raising the possibility that the modification occurred as a result of immune selection. Our data suggest that more-efficient binding of envelope gp120 to DC-SIGN could be relevant to the enhanced mucosal transmissibility of SHIV(SF162P3) compared to that of parental SHIV(SF162).

Compartmentalization of HIV-1 between breast milk and blood of HIV-infected mothers

HIV-1 variants in breast milk and peripheral blood have been compared in three HIV-1 infected mothers. Analysis of DNA and RNA env C2-V3 sequences showed a differential distribution of HIV variants between the two compartments. The major provirus variant found in breast milk corresponds to a minor variant in the blood of two mothers. In the third mother, the predominant proviral variant detected in breast milk was not represented in the HIV-1 blood population. The major RNA variant in breast milk was not represented in the blood of two mothers. The predominant RNA variant in breast milk and blood was however the same for the third mother. Unexpectedly, the pattern of free virus variants in breast milk of three mothers did not correspond to that of the proviral form, suggesting that free viruses do not derive from infected cells in breast milk. The observation of a compartmentalization of HIV-1 between peripheral blood and breast milk emphasizes that postnatal transmission of HIV occurs with variants that may not be predicted from the analysis of circulating viral populations.

Role of nucleotide sequences in the V3 region in efficient replication of CCR5-utilizing human immunodeficiency virus type 1 in macrophages

Macrophages express both CXCR4 and CCR5 coreceptors, but restrict X4 HIV-1 replication unless the Env-V3 region, a major determinant of cell tropism, is exchanged with that of R5 HIV-1. As the V3 exchange concomitantly alters the nucleotide sequences, we introduced silent mutations in the V3 or C2 region of macrophage-tropic R5 JRFL without changing the amino acids. Immunoblot analysis confirmed that viral proteins including Env-gp120 were similarly incorporated in wild-type (wt) and mutant virions. The silent mutants infected CCR5-positive MAGIC5 cells but not CCR5-negative MAGI cells, as productively as wt viruses, indicating that the silent mutations did not alter coreceptor utilization. In contrast, two of three silent V3-mutant viruses failed to replicate efficiently in primary macrophages, whereas other V3- or C2-mutants and wt JRFL infected macrophages productively. Furthermore, synthesis of the full-length viral DNA of the aberrant V3-mutant was largely reduced in macrophages. These results suggest that V3 nucleotide sequences may be one of the postentry factors restricting HIV-1 replication in macrophages.

Phosphorylation of Vpr regulates HIV type 1 nuclear import and macrophage infection

Viral protein R (Vpr) of human immunodeficiency virus type 1 (HIV-1) is a small accessory protein that regulates nuclear import of the viral preintegration complex and facilitates infection of nondividing cells, such as macrophages. Studies demonstrated that a fraction of Vpr molecules is phosphorylated in the virions and in HIV-1-infected cells, but the role of phosphorylation in nuclear import activity of Vpr has not been established. We found that Vpr is phosphorylated predominantly on the serine residue in position 79, and mutations affecting Vpr phosphorylation significantly attenuated viral replication in macrophages, but not in activated T lymphocytes or cell lines. The replication defect was mapped by polymerase chain reaction analysis to the step of nuclear import. These results suggest that phosphorylation of Vpr regulates its activity in the nuclear import of the HIV-1 preintegration complex.

Neuroimmune and neurovirological aspects of human immunodeficiency virus infection

Like most lentiviruses, HIV-1 causes both immune suppression and neurological disease. Neurological disease may occur at any stage of HIV infection but is most apparent with severe immune suppression. Cognitive impairment, reflected strikingly by HIV-associated dementia, has attracted intense interest since the outset of the HIV epidemic, and understanding of its pathogenesis has been spurred on by the emergence of several hypotheses outlining potential pathogenic mechanisms. The release of inflammatory molecules by HIV-infected microglia and macrophages and the concurrent neuronal damage play central roles in the conceptualization of HIV neuropathogenesis. Many inflammatory molecules appear to contribute to the pathogenic cascade and their individual roles remain undefined. At the same time, the abundance of virus in the brain and the type or strain of virus found in the brain may also be important codeterminants of neurological disease, as shown for other neurotropic viruses. Coreceptor use by HIV found in the brain appears to closely mirror what has been reported in systemic macrophages. The impact of HAART on viral genotype and phenotype found in the brain, and its relationship to clinical disease, remain uncertain. Several interesting animal models have been developed, using other lentiviruses, transgenic animals, and HIV-infected SCID mice, that may prove useful in future pathogenesis and therapeutic studies. Despite the progress in the understanding of HIV neuropathogenesis, many questions remain unanswered.