Originally published online as doi:10.1189/jlb.0503220 on July 22, 2003
Published online before print July 22, 2003
(Journal of Leukocyte Biology. 2003;74:726-735.)
© 2003
by Society for Leukocyte Biology
Viral and host cofactors facilitate HIV-1 replication in macrophages
Sharon M. Wahl*,1,
Teresa Greenwell-Wild*,
Gang Peng*,
Ge Ma*,
Jan M. Orenstein
and
Nancy Vázquez*
* Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland; and
Department of Pathology, George Washington University School of Medicine, Washington, D.C.
1Correspondence: Building 30, Rm. 320, 30 Convent Drive, MSC4352, NIDCR, NIH, Bethesda, MD 20892-4352. E-mail: smwahl{at}dir.nidcr.nih.gov
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ABSTRACT
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Human immunodeficiency virus type 1 (HIV-1) infection of CD4+ T lymphocytes leads to their progressive loss, whereas HIV-1-infected macrophages appear to resist HIV-1-mediated apoptotic death. The differential response of these two host-cell populations may be critical in the development of immunodeficiency and long-term persistence of the virus. Multiple contributing factors may favor the macrophage as a resilient host, not only supporting infection by HIV-1 but also promoting replication and persistence of this member of the lentivirus subfamily of primate retroviruses. An encounter between macrophages and R5 virus engages a signal cascade eventuating in transcriptional regulation of multiple genes including those associated with host defense, cell cycle, nuclear factor-
B regulation, and apoptosis. It is important that enhanced gene expression is transient, declining to near control levels, and during this quiescent state, the virus continues its life cycle unimpeded. However, when viral replication becomes prominent, an increase in host genes again occurs under the orchestration of viral gene products. This biphasic host response must fulfill the needs of the parasitic virus as viral replication activity occurs and leads to intracellular and cell surface-associated viral budding. Inroads into understanding how HIV-1 co-opts host factors to generate a permissive environment for viral replication and transmission to new viral hosts may provide opportunities for targeted interruption of this lethal process.
Key Words: opportunistic infections • cDNA expression array • p21 • SLPI • Vpr
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INTRODUCTION
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Shortly after the recognition of a new immunodeficiency disease among drug users and homosexuals [1
], peripheral blood monocytes from such patients were shown to be functionally compromised [2
]. Once a retrovirus [human immunodeficiency virus type 1 (HIV-1)] was identified as the causative agent [3
], the virus could be found in and isolated from tissue macrophages in lung and brain, where devastating sequelae result from infection [4
5
6
]. Although CD4+ T lymphocytes have received the bulk of attention as the key targets for and depletion by the virus, macrophages, which also coexpress CD4 and chemokine receptors, are vulnerable targets for HIV-1. Infected macrophages may transfer HIV-1 to T cells, permit replication of the virus, and/or function as viral reservoirs. Infection with HIV-1 almost inevitably leads to acquired immunodeficiency syndrome (AIDS), a multisystem disorder characterized by immune insufficiency, opportunistic infections, cachexia, and metabolic disturbances. As evidence continues to document the persistence of HIV-1 during highly active antiviral therapy [7
] and the poor susceptibility of macrophages to antiviral therapy [8
], interest in characterizing the mechanisms underlying infection and replication in this population intensifies.
Macrophages can produce copious amounts of HIV-1 in vitro and in vivo (Fig. 1
) [6
, 8
9
10
]. In these cells, HIV-1 is produced on the complex surfaces between cells, on the free surfaces, and in cytoplasmic vacuoles of the Golgi apparatus. Virus budding from macrophage intracellular membranes (Fig. 1B
and 1C)
[6
, 9
] may escape immune surveillance. In contrast to T cell infection, which may be lethal, macrophages and HIV-1 may coexist on a long-term basis. A complete understanding of HIV-1 pathogenesis must incorporate an elucidation of genetic/molecular events induced by the virus in macrophages and how such transcriptome changes modify the outcome of viral infection.
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Figure 1. Infection of macrophages in vitro and in vivo by HIV-1. (A) Adherent monocyte-derived macrophages were infected with R5 HIV-1 BaL and p24 levels monitored by enzyme-linked immunosorbent assay (ELISA) from day 2 post-infection through day 14 when p24 levels peak. (Inset) Macrophage infected with green fluorescent protein-labeled R5 HIV-1 (JR-CSF-GFP HIV-1 was generously provided by Drs. Antonio Valentin and George Pavlakis, National Cancer Institute, National Institutes of Health, Frederick, MD) and stained with a rabbit polyclonal antibody against p21 followed by a secondary antibody conjugated to Texas Red shows staining, which is primarily but not exclusively nuclear. (B) Large numbers of virions are evident by transmission electron microscopy in intracellular vacuoles and budding from macrophage membranes in culture. (C) In tissues, such as brain of HIV-1-infected patients, a similar intracellular and membrane distribution of virions is evident in macrophages. Original magnification, x13,000.
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MACROPHAGES POSSESS ESSENTIAL REQUIREMENTS FOR HIV-1 ENTRY
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HIV-1 infects T lymphocytes and macrophages by targeting CD4 and the seven transmembrane-spanning G protein-coupled coreceptors, CCR5 and CXCR4, via the V3 loop of gp120, which catalyzes membrane fusion [11
]. Freshly isolated blood monocytes constitutively express CD4 and CCR5 with variable levels of CXCR4 [12
], and differentiation into macrophages is associated with increased coreceptors and viral susceptibility. Infection with HIV-1 augments CCR5 mRNA and receptor expression in macrophage cultures (Fig. 2
), likely a viral strategy for cell–cell transmission. Although macrophages express the requisite CD4 and chemokine coreceptors, making them susceptible targets, and macrophage tropic (M-tropic) viral variants (R5 isolates) are preferentially transmitted, it remains challenging to identify HIV-1-positive macrophages early after viral exposure in mucosal tissues [13
] or in the absence of co-pathogens [10
, 14
]. The delayed identification of productively infected macrophages in tissues may reflect the typical protracted evidence of infection in cultured, nonreplicating macrophages (Figs. 1
and 2)
and/or additional signals or cofactors. In mucosal sites, the primary route of transmission, HIV-1 may first encounter myeloid-derived dendritic cells (DC), which are recognized as pivotal facilitators [15
, 16
] of infection largely via expression of DC-specific intercellular adhesion molecule-3-grabbing nonintegrin (SIGN) [17
, 18
], albeit DC-SIGN is not essential for this function [19
]. These cells are often the conduit of infection to the ultimate targets, T cells and macrophages [15
16
17
18
, 20
]. Recent evidence demonstrates that DC-SIGN is expressed on additional cell populations, including macrophages [21
], and new classes of antiretroviral drugs include entry inhibitors targeting DC-SIGN, CCR5, and the other host-cell molecules that mediate binding, entry, and/or fusion [22
, 23
].
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Figure 2. Increased CCR5 expression in HIV-1-infected macrophages. Seven-day adherent macrophages were not infected (A) or infected with HIV-1 (B), and fluorescent labeling monitored CCR5 expression using a rabbit polyclonal CCR5 antibody [12
] and a goat anti-rabbit immunoglobulin G conjugated with phycoerythrin. (C) Negative control of infected macrophages stained with secondary antibody alone. (D) Macrophage mRNA was analyzed by Northern blot for CCR5 expression, which was found to increase during the course of infection as shown at days 5 and 14 post-infection (+), but not in uninfected cells (–). Infection was monitored by p24 ELISA. GAPDH, Glyceraldehyde 3-phosphate dehydrogenase.
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SIGNAL TRANSDUCTION ENGAGED BY HIV-1–MACROPHAGE RECEPTOR INTERACTION
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Membrane fusion between virus envelope and the macrophage plasma membrane enables the viral core to gain access to the cytoplasm, an event essential to the infection process. To characterize the early signal-transduction events that precede replication and release of virions in this cell population, we infected human monocyte-derived macrophages with an R5 strain of HIV-1 BaL. Analysis of primary macrophages at high multiplicity of infection to detectably engage signaling pathways revealed evidence of signaling cascades leading to up-regulation of specific inflammation-related genes (N. Vázquez et al., submitted). These early response studies are crucial in characterizing entry and post-entry events in macrophages, and the caveat is that viral proteins that may initially signal but not lead to productive infection represent much of the viral inoculum. One of the first measurable events in the complex interaction between virus and host was activation of Pyk2, a member of the focal adhesion kinase family. As Pyk2 may link G protein-coupled signaling with the mitogen-activated protein kinase (MAPK) pathway, it was significant that phosphorylated p38 MAPK was detected as early as 5 min after HIV-1 exposure [24
]. These data are consistent with recent reports that isolated gp120 induces phosphorylation of MAPK and Pyk2 in monocyte-derived macrophages [25
]. Nonetheless, the transient cell-surface coreceptor activation consequent to the initial HIV-1–macrophage interaction appears not to be of sufficient duration or intensity to fend off the virus but rather, may reprogram the cells to support susceptibility to HIV-1 and maintain cell viability.
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EARLY GENE EXPRESSION ASSOCIATED WITH HIV-1 INFECTION IN PRIMARY MACROPHAGES
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HIV-1 infection of monocyte-derived macrophages in culture and presumably, in vivo follows a pattern in which the virus interacts with the macrophage to initiate signal-transduction events leading to transcription of genes. The response is transient, however, as the cells revert to a "resting" phenotype within 24–48 h, and the virus commences its life cycle within, and then, as the virus initiates active and evident replication, a new profile of gene expression emerges. To define the temporal events associated with the virus–macrophage encounter leading to viral replication, downstream transcriptional effects in HIV-1-exposed macrophage populations were compared over 14 days with uninfected cells in vitro. When adherent macrophages were exposed to HIV-1 BaL for 2 h, washed, and cultured, detectable evidence of viral expression was typically seen after 7 days by RNA, p24, and ultrastructural analysis (Figs. 1
and 2)
.
The transcriptional pathways activated downstream of the CD4–HIV-1 coreceptor binding/signaling event were compared in cDNA microarrays from macrophages exposed to HIV-1 and mock-infected, parallel macrophages from the same donor [26
]. Within the first 3–6 h following HIV-1, genes involved in signal transduction were prominent (Fig. 3A
and B
). As initial receptor engagement by virions on these primary cell cultures is limited, variable, and not synchronized, the large number of up-regulated genes (
150; Fig. 3B
, only 20 genes shown; n=2 donors), albeit at modest levels, was intriguing. Several of the immediate early genes induced by HIV-1 represent engagement of host-defense pathways (chemokines, proteases, cytokines). During ongoing viral infection, innate- and subsequent adaptive-immune factors may contribute to cell and tissue damage, directly or via indirect activation of additional pathways. Molecules produced by infected macrophages may also be beneficial, protecting the host from viral pathogenesis and/or engaging or amplifying the immune response and blocking apoptotic pathways. Persistence of these cells in vitro (and in vivo) may be related to regulation of genes with potential antiapoptotic functions (N. Vázquez et al., submitted). This transcriptional profile of genes, which is distinct from that recently observed in T cells and proliferating T cell lines [27
28
29
], provides important insight into pathogenic mechanisms and potential regulatory and interventional targets.
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Figure 3. Changes in macrophage transcriptome associated with initial HIV-1–macrophage interaction. Monocytes, isolated by elutriation, were plated at 5 x 106/ml in T75 flasks for 7 days. Cells were then infected with HIV-1 BaL. Total cellular RNA was extracted from cells (RNeasy kits, Qiagen, Valencia, CA), and after DNase digestion to remove genomic DNA, 5 µg total RNA was reverse-transcribed in the presence of 32P-adenosine 5'-triphosphate. 32P-labeled probes were hybridized with gene array blots (Atlas Nylon Array, Clontech, Palo Alto, CA) overnight at 68°C. Blots were washed and exposed to a phosphor screen for 24 h, and arrays were analyzed using AtlasImage 1.01a software. By cDNA array, macrophages exposed to HIV-1 for 3–6 h exhibited increased, immediate early gene expression as represented by the functional categories in A ([26
]; N. Vázquez et al., submitted). Twenty of the genes altered during this first 3–6 h after HIV-1 infection are shown in B for two donors. IL, Interleukin; GNB1, Gß1 gene; MCP1, monocyte chemoattractant protein-1; TNF, tumor necrosis factor.
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KINETICS OF HIV-1-INDUCED MACROPHAGE GENE EXPRESSION
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Following the initial viral-induced signal transduction leading to early transcription of host-cell genes, the transcriptional repertoire is not sustained. The ensuing quiescent phase may facilitate the cells escape from immunosurveillance, and the virus is preparing for its regeneration, although associations among the initial signaling cascades, gene transcription, and the macrophage-specific viral dynamics are only now being deciphered. Of the multiple genes up-regulated by initial virus-macrophage interaction, few remained elevated 
twofold above control by 24 h, and the evidence indicates that within 3 days after macrophages are infected with HIV-1, they appear to revert to a nearly resting phenotype comparable with mock-infected controls. Failure to maintain elevated expression of genes associated with macrophage activation leading to antimicrobial activity may favor escape of virus from destruction.
Between 5 and 10 days following exposure to HIV-1, when macrophages typically begin to exhibit detectable evidence of HIV-1 replication, a resurgence of gene expression begins to manifest. By 5 days, evidence that a change was occurring was represented by increases in a few genes, including MCP-1, suggesting that as the virus commences replication, it begins recruiting new hosts for any released virions. Additional genes become evident at 7–10 days, some mimicking the early events (3–6 h) after initial viral-induced macrophage signaling, potentially the consequence of an interaction of newly produced and/or released virions with cell-surface receptors. Nonetheless, even as the majority of cells are maximally producing HIV-1 by day 14, only a limited repertoire of genes appears to be up-regulated (N. Vázquez et al., submitted).
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HOST-CELL FACTORS THAT INFLUENCE VIRAL REPLICATION
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One of the genes consistently up-regulated immediately after HIV-1 infection and then again during the emergence of viral replication is the cyclin-dependent kinase (CDK) inhibitor p21, which is a classical G1-phase cell-cycle inhibitor that binds to several cyclin/CDK complexes preventing Rb phosphorylation [30
]. Progressive up-regulation of p21 message and protein reportedly occurs during maturation of hematopoietic progenitor cells [31
], and p21 has also been shown to be play a role in survival and differentiation of U937 cells [32
]. Our studies provide evidence for a novel association between this cell cycle-dependent kinase inhibitor and HIV-1 replication in macrophages. How p21 facilitates viral infection in fully differentiated macrophages is unclear, but studies with 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), a synthetic oleanane triterpenoid reported to have potent differentiating, antiproliferative, and anti-inflammatory activities and identified as a ligand of the peroxisome proliferator-activated receptor 
(PPAR) [33
], hint at a possible mode of action. Our data suggest that CDDO, as a ligand for PPAR, may down-modulate HIV-1 infection via its connection with virus-induced p21 (N. Vázquez et al., submitted).
Another cellular component necessary in the assembly of new virions is the host-cell proteasome [34
]. Associated with establishment of viral infection in macrophage hosts, the cells alter their expression of genes for several proteasome components (N. Vázquez et al., submitted). Proteasome inhibitors, such as MG132, as well as secretory leukocyte protease inhibitor (SLPI; G. Peng et al., submitted) markedly inhibit viral production in macrophages [34
, 35
]. Epithelial cells produce SLPI, a 12-kDa cationic, nonglycosylated, endogenous protein found in large quantities in mucosal fluids [36
] and lesser concentrations in blood [37
]. Although originally identified as a serine-protease inhibitor [38
], SLPI has recently been associated with multiple functions, some of which may be independent of its antiprotease activity including inhibition of NF-B, anti-inflammatory, antibacterial, and antiretroviral activity [35
, 39
40
41
42
43
]. The antiviral activity of SLPI appears a result of interaction with host-cell molecules rather than the virus, as SLPI does not bind directly to the virus envelope proteins gp120, gp160, or aspartyl protease or reverse transcriptase [35
, 39
]. Its activity appears independent of the HIV-1 cellular receptor CD4, as SLPI failed to down-regulate CD4 expression, did not bind to a recombinant form of the cell-surface protein, and did not prevent virus binding to monocytes [35
, 39
]. The unique antiviral activity of SLPI appears to reside in disruption of the viral infection process soon after virus binding but may also block NF-B as well as proteasome-proteolytic activity, essential for viral assembly, and consequently, may be considered an endogenous target for amplification or for exogenous delivery.
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HIV-1-ENCODED PROTEIN INTERACTIONS WITH HOST-CELL FACTORS
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In its parasitic relationship with macrophages, HIV-1 encodes a number of genes that are essential, not only to its ability to replicate but which also have substantial effects on host-cell molecular and cellular functions. In addition to the main viral, structural component genes gag, pol, and env, which mediate replication, HIV-1 encodes regulatory and accessory proteins (Fig. 4
). Regulatory gene Tat and Rev products control intracellular transcriptional and post-transcriptional events in viral gene expression [44
]. The regulator of expression of viral proteins (Rev), a novel viral phosphoprotein, is essential for efficient nuclear transport of RNA, based on recognition of the Rev-responsive element in the viral unspliced or partially spliced RNA [45
]. Besides its high affinity for RNA, this 13-kDa protein depolymerizes and/or inhibits polymerization of microtubules [46
], influencing intracellular viral trafficking. Beyond its support of viral RNA transport, limited evidence exists for a regulatory influence of Rev on macrophage proteins.
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Figure 4. HIV accessory proteins regulate macrophage host factors. Macrophage accessory proteins Vpr, Vpu, Vif, and Nef, in addition to Tat-regulatory protein, influence signal transduction, gene expression, and protein production in macrophages, as shown, in parallel or distinctly from their functional activity in T lymphocyte targets. Sp1, Specificity protein-1; GR, glucocorticoid receptor; QA, quinolinic acid; TRAIL, TNF-related apoptosis-inducing ligand; iNOS, inducible nitric oxide synthase; MR, mannose receptor; STAT, signal transducer and activator of transcription; AP-1, activated protein-1; HCK, hematopoietic cell kinase; FcR, Fc receptor.
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The transcriptional transactivator, Tat, one of the earliest genes expressed during HIV-1 infection [47
], transactivates long-terminal repeat (LTR)-driven gene expression, exploiting the host transcriptional machinery to orchestrate new HIV-1 gene expression. However, its activities are not restricted to this pathway, and HIV-1-associated or exogenous-free Tat also interacts with protein kinase R (PKR) and the transcriptional coactivators p300 and cyclic AMP response element-binding protein [48
, 49
] to modulate cellular functions, including cell-cycle and apoptotic pathways. In this regard, Tat increases expression of antiapoptotic Bcl-2 in human macrophages [50
], consistent with induction of other antiapoptotic genes by intact virus (N. Vázquez et al., submitted). Although macrophages exposed to Tat may be protected from apoptosis, Tat up-regulates macrophage production of TNF-
[51
] and TRAIL (Fig. 4)
with the potential to induce apoptosis in bystander T cells [52
]. Tat also drives production of macrophage IL-lß [53
] and the neurotoxin, quinolinic acid [54
]. Further contributing to neuropathogenesis, Tat augments chemokine and cytokine production by microglia [55
]. Moreover, Tat transcriptionally decreases MR expression to dampen antigen or pathogen capture [56
] and suppresses interferon- (IFN-)-induced iNOS microbicidal activity [57
].
In a recent study, intact HIV-1 and Tat, which can be secreted by infected cells to affect proximal, uninfected cells, have been shown to coordinately modulate immature DC transcription of 33 genes, including CC and CXC chemokines [58
]. Tat drives chemokine expression in macrophage cultures as well, including macrophage-inflammatory protein-1 (MIP-1) and MCP-1 [59
, 60
], and may represent a dominant viral protein underlying HIV-1-induced chemokine expression, as detected in our cDNA expression arrays [26
] (Figs. 3
and 4)
. In another clever maneuver, HIV-1-released Tat is itself chemotactic, mimicking ß chemokines and sharing their receptors [61
]. Not only does Tat induce chemotaxis, but Tat protein augments expression of viral coreceptors CCR5 and CXCR4 [62
]. It is interesting that Tat mRNA decreases during the course of macrophage infection with a concomitant decline in Tat activity and virus production, suggesting that selective reduction of Tat protein is associated with a persistent, less-productive phase of infection [63
].
In contrast to structural and regulatory molecules, HIV-1 accessory genes, viral infectivity factor (Vif), viral protein R (Vpr), viral protein u (Vpu), and 27-kDa negative factor (Nef), unique to lentiviruses, are not uniformly required for HIV-1 replication but make life easier for the virus as well as contribute to viral pathogenesis. Most likely, the accessory proteins operate in conjunction with specific host molecules, linking viral and cellular factors to pre-existing pathways (Fig. 4)
. For example, Vpr is a 96 amino acid protein encoded by the virus, which is imported into the nucleus in the early phases of infection and then packaged into viral particles during assembly [64
]. Successful HIV-1 infection of nondividing target cells requires the translocation of the viral preintegration complex across the nuclear envelope in the absence of mitosis, a feature that distinguishes lentiviruses from other genus of retroviruses [65
, 66
]. Phosphorylation by an unidentified kinase seems to be important in the regulation of Vpr function during macrophage HIV-1 infection [67
], with poor viral replication when Vpr is mutated [68
, 69
] or in the presence of oligodeoxynucleotides against Vpr [70
]. It has been reported that Vpr binds to p300, mimics the function of p160 nuclear receptor coactivators, and enhances the HIV-1 LTR promoter, in addition to glucocorticoid-responsive promoters [71
, 72
]. Vpr also potentiates the suppressive actions of ligand-activated GR by suppressing IL-12 p35 subunit in stimulated monocytes [73
] and induces latently infected, promonocytic cell lines into productive viral expression, compatible with a role post-viral integration [74
]. These actions of Vpr result in host-cell function dysregulation, affecting cell cycle and transcription, with increased virus production and consequently, disease progression [65
]. In vitro, Vpr has been shown to interfere with chemokine (MIP-1 and -ß, regulated on activation, normal T expressed and secreted) production [75
] but also to induce IL-8 by activation of NF-B and NF–IL-6 [76
], consistent with enhanced gene expression for this chemokine in infected cells (Fig. 3B)
and elevated levels of IL-8 in HIV-1-infected patients [77
].
Detectable levels of Vpr in plasma and cerebral spinal fluid of HIV-1-infected patients suggest that cell- or virus-free Vpr can affect proximal and distal sites that may not be infected [78
, 79
]. Furthermore, synthetic Vpr is taken up by macrophages and imported into the nucleus, independent of cellular receptors [79
]. Preliminary studies in our laboratory indicate that Vpr may be responsible, at least in part, for the enhanced expression of macrophage p21 (N. Vázquez et al., unpublished observations), as recently suggested in T lymphoid and myeloid cell lines [80
]. The potential consequences and/or differential roles of Vpr in replicating and nonreplicating cell populations are still not completely understood, but these findings guarantee further investigation to advance our understanding of HIV-1 pathogenesis.
Vpu, a unique, integral membrane phosphoprotein, enhances release of viral particles in macrophages and lymphocytes [81
], although one study suggested differential susceptibility, in that loss of Vpu reduced virus production in macrophages by up to 1000-fold with only marginal inhibition in lymphocytes [68
]. Enhanced virus release rate has been associated with expression of an ion channel activity that is confined to the transmembrane helix, promoting oligomerization of Vpu in the membrane and stabilizing the conductive state of the channel [82
]. Vpu promotes degradation of CD4 in the endoplasmic reticulum through a ubiquitin/proteasome pathway [83
, 84
], although CD4 degradation may also be Nef-dependent or involve intracellular trapping of CD4 by Env glycoproteins. In vivo, the loss of macrophage tropism by one viral variant was a result of a single mutation in the start codon of Vpu [85
]. In T cells [84
], Vpu inhibits NF-B by interacting as a competitive inhibitor with TrCP, a cellular factor involved in the degradation of IB, which may facilitate T cell apoptosis [86
] but may not be a relevant scenario in macrophages, which can persist long-term once infected. Vpu is reportedly involved in virus release in primary macrophages [87
], but the mechanisms remain unclear.
Vif-deficient virions can enter target cells but are unable to proceed through integration of the cDNA into the host genome. In macrophages, Vif binds to Src family tyrosine kinase Hck and suppresses this kinase that otherwise negatively controls HIV-1 replication [88
]. MAPK phosphorylates Vif, which loses its activity if this phosphorylation site is mutated, further linking MAPK to regulation of HIV-1 replication [89
]. Whether packaging of Vif into virions via its interaction with viral RNA underlies its ability to regulate viral infectivity is under study.
The Nef protein, originally thought to suppress gene expression from the HIV LTR, actually promotes efficient viral replication through its interactions with endocytic and lysosomal targeting pathways [90
, 91
]. Nef is the most abundant, early viral transcript and is post-translationally modified by myristolation [92
]. Molecular epidemiology studies have identified Nef as a critical contributor to AIDS pathogenesis and in maintaining high viral loads, and Nef-defective HIV has been associated with long-term nonprogressors [93
]. Nef promotes infection, replication, and survival of the virus in primary macrophages as well as lymphocytes [94
, 95
] (Fig. 4)
. As a membrane-associated phosphoprotein, Nef reportedly down-regulates not only CD4 but also major histocompatibility complex type I from the cell surface by linking CD4 with adaptor protein complexes in clathrin-coated pits [96
]. To direct its regulatory activity on macrophage phenotype and function, Nef interacts with the Nef-associated kinase, a p21-activated kinase, which mediates its pathogenic effects [97
]. Nef also modulates cellular activation pathways, possibly via its interaction with Src-like kinases, such as HcK, and by activating MAPK, STAT1, and STAT3 [98
99
100
]. Hck, which is expressed primarily in macrophages and polymorphonuclear neutrophils [101
], is rapidly induced following macrophage activation and controls phagocytosis, FcR, integrin signaling, and TNF- [102
, 103
]. Nef also triggers IL-lß and IL-6, correlating with de novo synthesis and activation of NF-B [104
], and chemokine production in macrophages has been shown for soluble and viral-encoded Nef [105
]. Collectively, these HIV-1 structural, regulatory, and accessory gene products commandeer macrophage-genetic machinery to their benefit, facilitating infection, replication, and assembly of new virions to assure HIV-1 survival and dissemination.
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CONTRIBUTION OF MACROPHAGE COINFECTION TO HIV-1 REPLICATION
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One of the early findings in HIV-1 immunocompromised hosts was the striking susceptibility to opportunistic infections (OI) [1
]. In our analysis of tissue specimens from HIV-1-positive individuals with OI, we observed a striking increase in HIV-1 within macrophages, which were coinfected with one of several pathogens [10
], suggesting that not only does HIV-1 immunodeficiency increase susceptibility to OI but that the opportunistic pathogens promote HIV-1 in a reciprocal relationship. It is clear that immune activation at sites of inflammation [106
] or in coinfection sites [10
, 14
] provides key signals that not only promote permissiveness for macrophage HIV-1 infection but also enhance viral replication. We have focused on dissecting the macrophage response to one of these pathogens, Mycobacterium avium, to understand how it impacts on macrophage phenotype and function to augment permissiveness to HIV-1. M. avium infects human hosts following mucosal entry and in the absence of appropriate T cell function, particularly IFN-, and takes up residence in macrophages, where it replicates and persists.
To mimic the T cell-insufficient paradigm of AIDS, we infected purified macrophages in culture and monitored the influence of the bacteria on the host cells with reference to augmented susceptibility to HIV-1 [14
] and the inability to clear the organisms in the absence of T cell cytokines. M. avium drives activation of the major transcriptional activator of inflammatory cytokines, NF-B, and increases CCR5 expression and cytokines, which promote HIV-1 replication [10
, 12
, 14
] in addition to manipulating macrophages for their own intracellular growth and survival. Based on the dramatic increase in macrophage accumulation in sites of mycobacterial infection in vivo, augmented production of chemotactic factors was demonstrated [107
, 108
]. As evident at the molecular and protein levels, M. avium-infected macrophages secreted the chemokines MCP-1 and MIP-1 rapidly after infection [107
], consistent with the ability of M. avium to instruct infected macrophages to recruit new hosts to perpetuate and disseminate the mycobacterial infection while also providing vulnerable new targets for HIV-1. Furthermore, induction of proinflammatory cytokines, which appear to maintain HIV-1 in a state of active replication rather than latency, may provide a mechanism through which opportunistic infections function as cofactors to enhance expression of the virus and exacerbate HIV-1 disease.
One of the earliest consequences of the interaction of M. avium with Toll-like receptor 2 was an increase in the phosphorylation state of p38 MAPK and activation of a series of transcription factors leading to changes in gene expression [108
]. By transcriptome analysis, M. avium was shown to up-regulate p21, which may facilitate HIV-1 infection. Furthermore, a rapid and profound increase in gene expression for the cytokines TNF- and IL-lß occurred in macrophages infected with M. avium [108
]. Paradoxically, a corresponding increase in TNF- protein was not matched by secretion of IL-lß. In pursuing an explanation for this dichotomy, we uncovered a novel pathway by which M. avium suppresses IL-lß to dampen host defense involving decreased activity of the IL-lß-converting enzyme (caspase 1); (S. M. Wahl et al., submitted). By suppressing caspase 1-dependent proteolysis of the inactive IL-lß precursor into its active, proinflammatory form, M. avium may not only facilitate its own survival within macrophage intracellular vacuoles but also abort the evolution of the adaptive-immune response and coincidentally, dampen the host response to HIV-1. Downstream, transcriptional events also revealed an increase in gene expression of IL-10 and other immunosuppressive molecules, which may serve to suppress the host response, which would otherwise be detrimental to the bacteria [108
] and to HIV-1. Thus, although HIV-1 infection and its consequences underlie the susceptibility to opportunistic pathogens, it is becoming clear that there is a reciprocal pathway by which the OI influences HIV-1.
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CONCLUSIONS
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More than 40 million people are infected with HIV-1 worldwide, and efforts continue in dissecting its pattern of infection and routes of escape from immune detection and clearance. Continued mutation of the virus makes it a moving, therapeutic target, prompting enhanced emphasis on identification of host-cell factors that may represent strategic targets for pharmacologic intervention. T lymphocytes and macrophages expressing CD4 and the seven transmembrane chemokine coreceptors CXCR4 and CCR5 are susceptible to HIV-1 infection. Infected macrophages not only allow viral replication intracellularly and at the cell surface, supporting a heavy viral burden, but can also transfer virus to T lymphocytes. Macrophage contributions to HIV-1 pathogenesis are compounded by their involvement in the complications consequent to infection with opportunistic pathogens.
By transcriptome analysis, multiple host-cell genes have been identified that are influenced during the viral life cycle and warrant further study as infection- or rate-limiting factors in viral replication in the continuing quest for development of new therapeutics. The complex replication of HIV-1 appears to involve numerous interactions with host-cell factors, not unusual in that viruses must rely on and usurp cellular proteins. Inactivation of host-cell susceptibility genes and/or their products that determine the kinetics of infection, as exemplified by CCR5 and also p21, may result in viral resistance. It is conceivable that even a partial down-modulation of such rate-limiting host genes may be detrimental to the virus. With the completion of the human genome, attention can now focus on imparting function to recently identified genes controlled by HIV-1, with emphasis on those involved in virulence and pathogenesis.
Received May 14, 2003;
accepted June 24, 2003.
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REFERENCES
|
|---|
- Masur, H., Michelis, M. A., Greene, J. B., Onorato, I., Stouwe, R. A., Holzman, R. S., Wormser, G., Brettman, L., Lange, M., Murray, H. W., Cunningham-Rundles, S. (1981) An outbreak of community-acquired Pneumocystis carinii pneumonia: initial manifestation of cellular immune dysfunction N. Engl. J. Med. 305,1431-1438[Abstract]
- Smith, P. D., Ohura, K., Masur, H., Lane, H. C., Fauci, A. S., Wahl, S. M. (1984) Monocyte function in the acquired immune deficiency syndrome. Defective chemotaxis J. Clin. Invest. 74,2121-2128
- Kulstad, R.E. (1986) AIDS: Papers from Science, 1982–1985 American Association for the Advancement of Science Washington, DC.
- Gartner, S., Markovits, P., Markovitz, D. M., Kaplan, M. H., Gallo, R. C., Popovic, M. (1986) The role of mononuclear phagocytes in HTLV-III/LAV infection Science 233,215-219[Abstract/Free Full Text]
- Koenig, S., Gendelman, H. E., Orenstein, J. M., Dal Canto, M. C., Pezeshkpour, G. H., Yungbluth, M., Janotta, F., Aksamit, A., Martin, M. A., Fauci, A. S. (1986) Detection of AIDS virus in macrophages in brain tissue from AIDS patients with encephalopathy Science 233,1089-1093[Abstract/Free Full Text]
- Wahl, S. M., Orenstein, J. M., Smith, P. D. (1996) Macrophage function in HIV infection Immunology of HIV Infection ,303-336 Plenum New York, NY.
- Persaud, D., Zhou, Y., Siliciano, J. M., Siliciano, R. F. (2003) Latency in human immunodeficiency virus type 1 infection: no easy answers J. Virol. 77,1659-1665[Free Full Text]
- Igarashi, T., Brown, C. R., Endo, Y., Buckler-White, A., Plishka, R., Bischofberger, N., Hirsch, V., Martin, M. A. (2001) Macrophage are the principal reservoir and sustain high virus loads in rhesus macaques after the depletion of CD4+ T cells by a highly pathogenic simian immunodeficiency virus/HIV type 1 chimera (SHIV): implications for HIV-1 infections of humans Proc. Natl. Acad. Sci. USA 98,658-663[Abstract/Free Full Text]
- Orenstein, J. M., Meltzer, M. S., Phipps, T., Gendelman, H. E. (1988) Cytoplasmic assembly and accumulation of human immunodeficiency virus types 1 and 2 in recombinant human colony-stimulating factor-1-treated human monocytes: an ultrastructural study J. Virol. 62,2578-2586[Abstract/Free Full Text]
- Orenstein, J. M., Fox, C., Wahl, S. M. (1997) Macrophages as a source of HIV during opportunistic infections Science 276,1857-1861[Abstract/Free Full Text]
- Berger, E. A., Murphy, P. M., Farber, J. M. (1999) Chemokine receptors as HIV-1 coreceptors: roles in viral entry, tropism, and disease Annu. Rev. Immunol. 17,657-700[CrossRef][Medline]
- Wahl, S. M., Greenwell-Wild, T., Peng, G., Hale-Donze, H., Orenstein, J. M. (1999) Co-infection with opportunistic pathogens promotes human immunodeficiency virus type 1 infection in macrophages J. Infect. Dis. 179,S457-S460
- Schacker, T., Little, S., Connick, E., Gebhard, K., Zhang, Z. Q., Krieger, J., Pryor, J., Havlir, D., Wong, J. K., Schooley, R. T., Richman, D., Corey, L., Haase, A. T. (2001) Productive infection of T cells in lymphoid tissues during primary and early human immunodeficiency virus infection J. Infect. Dis. 183,555-562[CrossRef][Medline]
- Wahl, S. M., Greenwell-Wild, T., Peng, G., Hale-Donze, H., Doherty, T. M., Mizel, D., Orenstein, J. M. (1998) Mycobacterium avium complex augments macrophage HIV-1 production and increases CCR5 expression Proc. Natl. Acad. Sci. USA 95,12574-12579[Abstract/Free Full Text]
- Granelli-Piperno, A., Delgado, E., Finkel, V., Paxton, W., Steinman, R. M. (1998) Immature dendritic cells selectively replicate macrophagetropic (M-tropic) human immunodeficiency virus type 1, while mature cells efficiently transmit both M- and T-tropic virus to T cells J. Virol. 72,2733-2737[Abstract/Free Full Text]
- Frankel, S. S., Steinman, R. M., Michael, N. L., Kim, S. R., Bhardwaj, N., Pope, M., Louder, M. K., Ehrenberg, P. K., Parren, P. W., Burton, D. R., Katinger, H., VanCott, T. C., Robb, M. L., Birx, D. L., Mascola, J. R. (1998) Neutralizing monoclonal antibodies block human immunodeficiency virus type 1 infection of dendritic cells and transmission to T cells J. Virol. 72,9788-9794[Abstract/Free Full Text]
- Geijtenbeek, T. B., Kwon, D. S., Torensma, R., van Vliet, S. J., van Duijnhoven, G. C., Middel, J., Cornelissen, I. L., Nottet, H. S., KewalRamani, V. N., Littman, D. R., Figdor, C. G., van Kooyk, Y. (2000) DC-SIGN, a dendritic cell-specific HIV-1-binding protein that enhances trans-infection of T cells Cell 100,587-597[CrossRef][Medline]
- Baribaud, F., Pohlmann, S., Doms, R. W. (2001) The role of DC-SIGN and DC-SIGNR in HIV and SIV attachment, infection, and transmission Virology 286,1-6[CrossRef][Medline]
- Wu, L., Bashirova, A. A., Martin, T. D., Villamide, L., Mehlhop, E., Chertov, A. O., Unutmaz, D., Pope, M., Carrington, M., KewalRamani, V. N. (2002) Rhesus macaque dendritic cells efficiently transmit primate lentiviruses independently of DC-SIGN Proc. Natl. Acad. Sci. USA 99,1568-1573[Abstract/Free Full Text]
- Kacani, L., Frank, I., Spruth, M., Schwendinger, M. G., Mullauer, B., Sprinzl, G. M., Steindl, F., Dierich, M. P. (1998) Dendritic cells transmit human immunodeficiency virus type 1 to monocytes and monocyte-derived macrophages J. Virol. 72,6671-6677[Abstract/Free Full Text]
- Mummidi, S., Catano, G., Lam, L., Hoefle, A., Telles, V., Begum, K., Jimenez, F., Ahuja, S. S., Ahuja, S. K. (2001) Extensive repertoire of membrane-bound and soluble dendritic cell-specific ICAM-3-grabbing nonintegrin 1 (DC-SIGN1) and DC-SIGN2 isoforms. Inter-individual variation in expression of DC-SIGN transcripts J. Biol. Chem. 276,33196-33212[Abstract/Free Full Text]
- Starr-Spires, L. D., Collman, R. G. (2002) HIV-1 entry and entry inhibitors as therapeutic agents Clin. Lab. Med. 22,681-701[CrossRef][Medline]
- De Clercq, E. (2002) New anti-HIV agents and targets Med. Res. Rev. 22,531-565[CrossRef][Medline]
- Vazquez, N., Greenwell-Wild, T., Wahl, S. M. (2001) HIV-1 infection and signaling pathways in human macrophages FASEB J. 15,A1011
- Del Corno, M., Liu, Q. H., Schols, D., de Clercq, E., Gessani, S., Freedman, B. D., Collman, R. G. (2001) HIV-1 gp120 and chemokine activation of Pyk2 and mitogen-activated protein kinases in primary macrophages mediated by calcium-dependent, pertussis toxin-insensitive chemokine receptor signaling Blood 98,2909-2916[Abstract/Free Full Text]
- Greenwell-Wild, T., Orenstein, J. M., Wahl, S. M. (2000) Differential cellular gene expression during HIV-1 infection of macrophages FASEB J. 14,A1033
- Corbeil, J., Sheeter, D., Genini, D., Rought, S., Leoni, L., Du, P., Ferguson, M., Masys, D. R., Welsh, J. B., Fink, J. L., Sasik, R., Huang, D., Drenkow, J., Richman, D. D., Gingeras, T. (2001) Temporal gene regulation during HIV-1 infection of human CD4+ T cells Genome Res. 11,1198-1204[Abstract/Free Full Text]
- Ryo, A., Suzuki, Y., Arai, M., Kondoh, N., Wakatsuki, T., Hada, A., Shuda, M., Tanaka, K., Sato, C., Yamamoto, M., Yamamoto, N. (2000) Identification and characterization of differentially expressed mRNAs in HIV type 1-infected human T cells AIDS Res. Hum. Retroviruses 16,995-1005[CrossRef][Medline]
- Geiss, G. K., Bumgarner, R. E., An, M. C., Agy, M. B., van’t Wout, A. B., Hammersmark, E., Carter, V. S., Upchurch, D., Mullins, J. I., Katze, M. G. (2000) Large-scale monitoring of host cell gene expression during HIV-1 infection using cDNA microarrays Virology 266,8-16[CrossRef][Medline]
- Morgan, D. O. (1995) Principles of CDK regulation Nature 374,131-134[CrossRef][Medline]
- Steinman, R. A., Huang, J., Yaroslavskiy, B., Goff, J. P., Ball, E. D., Nguyen, A. (1998) Regulation of p21(WAF1) expression during normal myeloid differentiation Blood 91,4531-4542[Abstract/Free Full Text]
- Asada, M., Yamada, T., Fukumuro, K., Mizutani, S. (1998) p21Cip1/WAF1 is important for differentiation and survival of U937 cells Leukemia 12,1944-1950[CrossRef][Medline]
- Wang, Y., Porter, W. W., Suh, N., Honda, T., Gribble, G. W., Leesnitzer, L. M., Plunket, K. D., Mangelsdorf, D. J., Blanchard, S. G., Willson, T. M., Sporn, M. B. (2000) A synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), is a ligand for the peroxisome proliferator-activated receptor gamma Mol. Endocrinol. 14,1550-1556[Abstract/Free Full Text]
- Schubert, U., Ott, D. E., Chertova, E. N., Welker, R., Tessmer, U., Princiotta, M. F., Bennink, J. R., Krausslich, H. G., Yewdell, J. W. (2000) Proteasome inhibition interferes with gag polyprotein processing, release, and maturation of HIV-1 and HIV-2 Proc. Natl. Acad. Sci. USA 97,13057-13062[Abstract/Free Full Text]
- McNeely, T. B., Dealy, M., Dripps, D. J., Orenstein, J. M., Eisenberg, S. P., Wahl, S. M. (1995) Secretory leukocyte protease inhibitor: a human saliva protein exhibiting anti-human immunodeficiency virus 1 activity in vitro J. Clin. Invest. 96,456-464
- Shugars, D. C., Wahl, S. M. (1998) The role of the oral environment in HIV-1 transmission J. Am. Dent. Assoc. 129,851-858[Abstract/Free Full Text]
- Grobmyer, S. R., Barie, P. S., Nathan, C. F., Fuortes, M., Lin, E., Lowry, S. F., Wright, C. D., Weyant, M. J., Hydo, L., Reeves, F., Shiloh, M. U., Ding, A. (2000) Secretory leukocyte protease inhibitor, an inhibitor of neutrophil activation, is elevated in serum in human sepsis and experimental endotoxemia Crit. Care Med. 28,1276-1282[CrossRef][Medline]
- Thompson, R. C., Ohlsson, K. (1986) Isolation, properties, and complete amino acid sequence of human secretory leukocyte protease inhibitor, a potent inhibitor of leukocyte elastase Proc. Natl. Acad. Sci. USA 83,6692-6696[Abstract/Free Full Text]
- McNeely, T. B., Shugars, D. C., Rosendahl, M., Tucker, C., Eisenberg, S. P., Wahl, S. M. (1997) Inhibition of human immunodeficiency virus type 1 infectivity by secretory leukocyte protease inhibitor occurs prior to viral reverse transcription Blood 90,1141-1149[Abstract/Free Full Text]
- Zhang, Y., DeWitt, D. L., McNeely, T. B., Wahl, S. M., Wahl, L. M. (1997) Secretory leukocyte protease inhibitor suppresses the production of monocyte prostaglandin H synthase-2, prostaglandin E2, and matrix metalloproteinases J. Clin. Invest. 99,894-900[Medline]
- Song, X., Zeng, L., Jin, W., Thompson, J., Mizel, D. E., Lei, K., Billinghurst, R. C., Poole, A. R., Wahl, S. M. (1999) Secretory leukocyte protease inhibitor suppresses the inflammation and joint damage of bacterial cell wall-induced arthritis J. Exp. Med. 190,535-542[Abstract/Free Full Text]
- Hiemstra, P. S., van Wetering, S., Stolk, J. (1998) Neutrophil serine proteinases and defensins in chronic obstructive pulmonary disease: effects on pulmonary epithelium Eur. Respir. J. 12,1200-1208[Abstract]
- Ashcroft, G. S., Lei, K., Jin, W., Longenecker, G., Kulkarni, A. B., Greenwell-Wild, T., Hale-Donze, H., McGrady, G., Song, X. Y., Wahl, S. M. (2000) Secretory leukocyte protease inhibitor mediates non-redundant functions necessary for normal wound healing Nat. Med. 6,1147-1153[CrossRef][Medline]
- Freed, E. O. (2001) HIV-1 replication Somat. Cell Mol. Genet. 26,13-33[CrossRef][Medline]
- Pollard, V. W., Malim, M. H. (1998) The HIV-1 Rev protein Annu. Rev. Microbiol. 52,491-532[CrossRef][Medline]
- Watts, N. R., Sackett, D. L., Ward, R. D., Miller, M. W., Wingfield, P. T., Stahl, S. S., Steven, A. C. (2000) HIV-1 rev depolymerizes microtubules to form stable bilayered rings J. Cell Biol. 150,349-360[Abstract/Free Full Text]
- Wu, Y., Marsh, J. W. (2001) Selective transcription and modulation of resting T cell activity by preintegrated HIV DNA Science 293,1503-1506[Abstract/Free Full Text]
- Demarchi, F., Gutierrez, M. I., Giacca, M. (1999) Human immunodeficiency virus type 1 tat protein activates transcription factor NF-kappaB through the cellular interferon-inducible, double-stranded RNA-dependent protein kinase, PKR J. Virol. 73,7080-7086[Abstract/Free Full Text]
- Marzio, G., Giacca, M. (1999) Chromatin control of HIV-1 gene expression Genetica 106,125-130[CrossRef][Medline]
- Zhang, M., Li, X., Pang, X., Ding, L., Wood, O., Clouse, K. A., Hewlett, I., Dayton, A. I. (2002) Bcl-2 upregulation by HIV-1 Tat during infection of primary human macrophages in culture J. Biomed. Sci. 9,133-139[CrossRef][Medline]
- Mayne, M., Holden, C. P., Nath, A., Geiger, J. D. (2000) Release of calcium from inositol 1,4,5-trisphosphate receptor-regulated stores by HIV-1 Tat regulates TNF-alpha production in human macrophages J. Immunol. 164,6538-6542[Abstract/Free Full Text]
- Zhang, M., Li, X., Pang, X., Ding, L., Wood, O., Clouse, K., Hewlett, I., Dayton, A. I. (2001) Identification of a potential HIV-induced source of bystander-mediated apoptosis in T cells: upregulation of trail in primary human macrophages by HIV-1 tat J. Biomed. Sci. 8,290-296[CrossRef][Medline]
- Nath, A., Conant, K., Chen, P., Scott, C., Major, E. O. (1999) Transient exposure to HIV-1 Tat protein results in cytokine production in macrophages and astrocytes. A hit and run phenomenon J. Biol. Chem. 274,17098-17102[Abstract/Free Full Text]
- Smith, D. G., Guillemin, G. J., Pemberton, L., Kerr, S., Nath, A., Smythe, G. A., Brew, B. J. (2001) Quinolinic acid is produced by macrophages stimulated by platelet activating factor, Nef and Tat J. Neurovirol. 7,56-60[CrossRef][Medline]
- Sheng, W. S., Hu, S., Hegg, C. C., Thayer, S. A., Peterson, P. K. (2000) Activation of human microglial cells by HIV-1 gp41 and Tat proteins Clin. Immunol. 96,243-251[CrossRef][Medline]
- Caldwell, R. L., Egan, B. S., Shepherd, V. L. (2000) HIV-1 Tat represses transcription from the mannose receptor promoter J. Immunol. 165,7035-7041[Abstract/Free Full Text]
- Barton, C. H., Biggs, T. E., Mee, T. R., Mann, D. A. (1996) The human immunodeficiency virus type 1 regulatory protein Tat inhibits interferon-induced iNos activity in a murine macrophage cell line J. Gen. Virol. 77,1643-1647[Abstract/Free Full Text]
- Izmailova, E., Bertley, F. M., Huang, Q., Makori, N., Miller, C. J., Young, R. A., Aldovini, A. (2003) HIV-1 Tat reprograms immature dendritic cells to express chemoattractants for activated T cells and macrophages Nat. Med. 9,191-197[CrossRef][Medline]
- Bonwetsch, R., Croul, S., Richardson, M. W., Lorenzana, C., Valle, L. D., Sverstiuk, A. E., Amini, S., Morgello, S., Khalili, K., Rappaport, J. (1999) Role of HIV-1 Tat and CC chemokine MIP-1alpha in the pathogenesis of HIV associated central nervous system disorders J. Neurovirol. 5,685-694[Medline]
- Weiss, J. M., Nath, A., Major, E. O., Berman, J. W. (1999) HIV-1 Tat induces monocyte chemoattractant protein-1-mediated monocyte transmigration across a model of the human blood-brain barrier and up-regulates CCR5 expression on human monocytes J. Immunol. 163,2953-2959[Abstract/Free Full Text]
- Albini, A., Ferrini, S., Benelli, R., Sforzini, S., Giunciuglio, D., Aluigi, M. G., Proudfoot, A. E., Alouani, S., Wells, T. N., Mariani, G., Rabin, R. L., Farber, J. M., Noonan, D. M. (1998) HIV-1 Tat protein mimicry of chemokines Proc. Natl. Acad. Sci. USA 95,13153-13158[Abstract/Free Full Text]
- Huang, L., Bosch, I., Hofmann, W., Sodroski, J., Pardee, A. B. (1998) Tat protein induces human immunodeficiency virus type 1 (HIV-1) coreceptors and promotes infection with both macrophage-tropic and T-lymphotropic HIV-1 strains J. Virol. 72,8952-8960[Abstract/Free Full Text]
- Sonza, S., Mutimer, H. P., O’Brien, K., Ellery, P., Howard, J. L., Axelrod, J. H., Deacon, N. J., Crowe, S. M., Purcell, D. F. (2002) Selectively reduced tat mRNA heralds the decline in productive human immunodeficiency virus type 1 infection in monocyte-derived macrophages J. Virol. 76,12611-12621[Abstract/Free Full Text]
- Sherman, M. P., Greene, W. C. (2002) Slipping through the door: HIV entry into the nucleus Microbes Infect 4,67-73[CrossRef][Medline]
- Emerman, M. (1996) HIV-1, Vpr and the cell cycle Curr. Biol. 6,1096-1103[CrossRef][Medline]
- Elder, R. T., Benko, Z., Zhao, Y. (2002) HIV-1 VPR modulates cell cycle G2/M transition through an alternative cellular mechanism other than the classic mitotic checkpoints Front. Biosci. 7,d349-d357[Medline]
- Agostini, I., Popov, S., Hao, T., Li, J. H., Dubrovsky, L., Chaika, O., Chaika, N., Lewis, R., Bukrinsky, M. (2002) Phosphorylation of Vpr regulates HIV type 1 nuclear import and macrophage infection AIDS Res. Hum. Retroviruses 18,283-288[CrossRef][Medline]
- Balliet, J. W., Kolson, D. L., Eiger, G., Kim, F. M., McGann, K. A., Srinivasan, A., Collman, R. (1994) Distinct effects in primary macrophages and lymphocytes of the human immunodeficiency virus type 1 accessory genes vpr, vpu, and nef: mutational analysis of a primary HIV-1 isolate Virology 200,623-631[CrossRef][Medline]
- Connor, R. I., Chen, B. K., Choe, S., Landau, N. R. (1995) Vpr is required for efficient replication of human immunodeficiency virus type-1 in mononuclear phagocytes Virology 206,935-944[CrossRef][Medline]
- Balotta, C., Lusso, P., Crowley, R., Gallo, R. C., Franchini, G. (1993) Antisense phosphorothioate oligodeoxynucleotides targeted to the vpr gene inhibit human immunodeficiency virus type 1 replication in primary human macrophages J. Virol. 67,4409-4414[Abstract/Free Full Text]
- Subbramanian, R. A., Kessous-Elbaz, A., Lodge, R., Forget, J., Yao, X. J., Bergeron, D., Cohen, E. A. (1998) Human immunodeficiency virus type 1 Vpr is a positive regulator of viral transcription and infectivity in primary human macrophages J. Exp. Med. 187,1103-1111[Abstract/Free Full Text]
- Kino, T., Gragerov, A., Slobodskaya, O., Tsopanomichalou, M., Chrousos, G. P., Pavlakis, G. N. (2002) Human immunodeficiency virus type 1 (HIV-1) accessory protein Vpr induces transcription of the HIV-1 and glucocorticoid-responsive promoters by binding directly to p300/CBP coactivators J. Virol. 76,9724-9734[Abstract/Free Full Text]
- Kino, T., Gragerov, A., Kopp, J. B., Stauber, R. H., Pavlakis, G. N., Chrousos, G. P. (1999) The HIV-1 virion-associated protein vpr is a coactivator of the human glucocorticoid receptor J. Exp. Med. 189,51-62[Abstract/Free Full Text]
- Levy, D. N., Refaeli, Y., Weiner, D. B. (1995) Extracellular Vpr protein increases cellular permissiveness to human immunodeficiency virus replication and reactivates virus from latency J. Virol. 69,1243-1252[Abstract]
- Muthumani, K., Kudchodkar, S., Papasavvas, E., Montaner, L. J., Weiner, D. B., Ayyavoo, V. (2000) HIV-1 Vpr regulates expression of beta chemokines in human primary lymphocytes and macrophages J. Leukoc. Biol. 68,366-372[Abstract/Free Full Text]
- Roux, P., Alfieri, C., Hrimech, M., Cohen, E. A., Tanner, J. E. (2000) Activation of transcription factors NF-kappaB and NF-IL-6 by human immunodeficiency virus type 1 protein R (Vpr) induces interleukin-8 expression J. Virol. 74,4658-4665[Abstract/Free Full Text]
- Matsumoto, T., Miike, T., Nelson, R. P., Trudeau, W. L., Lockey, R. F., Yodoi, J. (1993) Elevated serum levels of IL-8 in patients with HIV infection Clin. Exp. Immunol. 93,149-151[Medline]
- Levy, D. N., Refaeli, Y., MacGregor, R. R., Wei
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ABSTRACT
INTRODUCTION