gp120-induced alterations of human astrocyte function: Na(+)/H(+) exchange, K(+) conductance, and glutamate flux

Many human immunodeficiency virus (HIV)-infected patients suffer from impaired neurological function and dementia. This facet of the disease has been termed acquired immunodeficiency syndrome (AIDS)-associated dementia complex (ADC). Several cell types, including astrocytes and neurons, are not productively infected by virus but are involved in ADC pathophysiology. Previous studies of rat astrocytes showed that an HIV coat protein (gp120) accelerated astrocyte Na(+)/H(+) exchange and that the resultant intracellular alkalinization activated a pH-sensitive K(+) conductance. The present experiments were conducted to determine whether gp120 affected human astrocytes in the same fashion. It was found that primary human astrocytes express a pH-sensitive K(+) conductance that was activated on intracellular alkalinization. Also, gp120 treatment of whole cell clamped human astrocytes activated this conductance specifically. Furthermore, gp120 inhibited glutamate uptake by primary human astrocytes. These altered physiological processes could contribute to pathophysiological changes in HIV-infected brains. Because the gp120-induced cell physiological changes were partially inhibited by dimethylamiloride (an inhibitor of Na(+)/H(+) exchange), our findings suggest that modification of human astrocyte Na(+)/H(+) exchange activity may provide a means of addressing some of the neurological complications of HIV infection.

Beta-chemokines and human immunodeficiency virus type-1 proteins evoke intracellular calcium increases in human microglia

Activation of beta-chemokine receptors, co-receptors for human immunodeficiency virus type-1 (HIV-1), stimulates movement and secretion in microglia, possibly through a Ca(2+)-dependent mechanism. We studied chemokine activation of Ca(2+) signaling processes in microglia. Human fetal microglia were grown in primary culture and chemokine-induced increases in intracellular calcium concentration ([Ca(2+)](i)) were measured in single cells using indo-1-based microfluorimetry. Application of 50 ng/ml regulated on activation, normal T expressed and secreted (RANTES; 120 s) evoked responses in 26% of the microglia (187/719 cells). [Ca(2+)](i) increased from a basal level of 66+/-6 nM to peak at 268+/-23 nM (n=187). Chemokine-evoked responses rapidly desensitized as indicated by the rapid return to basal [Ca(2+)](i) levels in the maintained presence of RANTES. The removal of extracellular Ca(2+) or stimulation in the presence of Ni(2+) (2mM) or La(3+) (100 microM) blocked the RANTES-elicited [Ca(2+)](i) increase. The L-type calcium channel antagonist nimodipine (10 microM) inhibited the RANTES-mediated increase in [Ca(2+)](i) by 80+/-16%. Thus, the RANTES-evoked calcium transient appears to result from Ca(2+) influx with little if any release from intracellular stores. Application of gp120(clade) (E) and gp120(CM235) (50 ng/ml) neither mimicked nor antagonized the RANTES-evoked response. Application of 50 ng/ml eotaxin (120 s) evoked an increase in [Ca(2+)](i) in 13% of the human microglia in culture (61/469 cells). The HIV-1 regulatory protein Tat (50 ng/ml) increased the [Ca(2+)](i) in a subset of eotaxin-responsive cells (16/30). The L-type calcium channel antagonist nimodipine (3 microM) inhibited eotaxin- and Tat-mediated increases in [Ca(2+)](i) by 88+/-6% and 93+/-6%, respectively. Thus, activation of CCR3 appears to evoke Ca(2+) influx through L-type Ca(2+) channels.These results indicate that beta-chemokines, RANTES and eotaxin, activate a nimodipine sensitive Ca(2+) influx pathway in human fetal microglia. HIV-1 Tat protein mimicked chemokine-mediated Ca(2+) signaling and may modulate the migratory and secretory responses of microglia.

HIV-1 gp120- and gp160-induced apoptosis in cultured endothelial cells is mediated by caspases

The immune dysfunction and cell destruction that occur in the human immunodeficiency virus (HIV)-infected host appear to result from the direct cytopathic effects of viral infection and the effects of viral proteins on uninfected bystander cells. Recently, the alpha-chemokine receptor CXCR4 has been reported to mediate apoptosis in neuronal cells and in CD4(+) and CD8(+) T cells after its binding to HIV-1 envelope proteins. In the current study, it was observed that human umbilical vein endothelial cells (HUVEC) undergo apoptosis after their treatment with the HIV-1 envelope proteins gp120/160. Anti-CXCR4 monoclonal antibody decreased HIV-1 gp120/160-induced apoptosis, suggesting that the CXCR4 chemokine receptor mediates the apoptotic effects of these HIV envelope glycoproteins. Further studies revealed that caspases play an important role in this process because the pretreatment of cells with a general caspase enzyme inhibitor decreased the extent of HUVEC apoptosis induced by gp120/160. In addition, it was found that caspase-3 was activated on HIV-1 gp120/160 treatment of these cells. It was also observed that gp120/160 treatment slightly increased the expression of the pro-apoptotic molecule Bax. These results suggest that HIV-1 envelope glycoproteins can disrupt endothelial integrity through the interaction with CXCR4, thereby facilitating virus transit out of the bloodstream and contributing to the vascular injury syndromes seen in acquired immunodeficiency syndrome. (Blood. 2000;96:1438-1442)

Apoptosis induced by gp120 in the neocortex of rat involves enhanced expression of cyclooxygenase type 2 and is prevented by NMDA receptor antagonists and by the 21-aminosteroid U-74389G

The effects of a single dose of the HIV-1 coat protein gp120 given into one lateral cerebral ventricle (i.c.v.) on the expression of cyclooxygenase type 2 (COX-2) and PGE(2) levels have been studied using Western blotting and ELISA techniques applied to brain tissue extracts obtained from the neocortex of individual rats, one of the regions of the central nervous system where the viral protein causes apoptosis. The results demonstrate that COX-2 expression is almost doubled 6 h after a single dose (100 ng) of gp120 and this is paralleled by a statistically significant elevation of PGE(2). Enhanced COX-2 expression is implicated in the mechanisms of apoptosis evoked by gp120 because the latter is prevented by NS398 (10 mg/kg i.p.), a selective inhibitor of COX-2 activity. Protection is also afforded by NMDA receptor antagonists, such as MK801 (0.3 mg/kg i.p.) and CGP040116 (10 mg/kg i.p.), and by the free radical scavenger, U-74389G (10 mg/kg i.p.), supporting a glutamate-mediated, excitotoxic, mechanism of apoptotic death induced by gp120. These data together with the observation that MK801 failed to prevent gp120-enhanced COX-2 expression indicate that products of the arachidonic cascade may be responsible for elevation of synaptic glutamate leading neocortical cells to oxidative stress and excitotoxic apoptosis.

HIV- and FIV-derived gp120 alter spatial memory, LTP, and sleep in rats

Human immunodeficiency virus (HIV)-associated dementia (HAD) has been detected in 20-30% of patients suffering AIDS. The envelope glycoprotein 120 (gp120) derived from HIV seems to play a critical role in the pathophysiology of this dementia. Likewise, the feline immunodeficiency virus (FIV)-derived gp120 causes neurological and electrophysiological abnormalitites in cats. We have studied the effects of gp120 derived from HIV or FIV on learning and memory processing, hippocampal long-term potentiation (LTP), hippocampal neuronal cAMP production, the sleep-waking cycle, and locomotor activity and equilibrium in rats. Results showed that while both HIV- and FIV-gp120 impaired the rat's performance in the Barnes maze task, only HIVgp120 impaired the induction and maintenance of LTP. However, both glycoproteins induced a significant decrease in the posttetanic potentiation. HIVgp120 also caused a significant reduction in cAMP production in the hippocampus. Regarding the sleep-waking cycle, HIV- and FIV-gp120 increased the waking state and slow-wave sleep 1 (SWS1), while decreasing both SWS2 and REM sleep. Locomotor activity and equilibrium were significantly altered by these glycoproteins. These results suggest that HIVgp120 causes neurophysiological abnormalities and therefore may facilitate HAD development in AIDS patients.

Immediate and neurotoxic effects of HIV protein gp120 act through CXCR4 receptor

Primary rat hippocampal neurones show pronounced elevations of intracellular calcium within minutes of exposure to the HIV coat protein gp120. Culture of hippocampal neurones with gp120 causes significant neurotoxicity. We find that the peptide VSLSYRCPCRFF, a competitive inhibitor of the CXCR4 chemokine receptor, markedly inhibits toxicity and eliminates the acute calcium elevation. CXCR4 receptors are thought to signal to the Gi/Go family of trimeric GTP binding proteins. Pretreatment of hippocampal neurones with pertussis toxin to inactivate Gi/Go proteins markedly reduced gp120 neurotoxicity. These results indicate that both short and long term effects of gp120 are the result of activation of the CXCR4 receptor.

An anti-human immunodeficiency virus multiple antigen peptide encompassing the cleavage region of the env precursor interferes with membrane fusion at a post-CD4 binding step

CLIV is a multiple antigen peptide ([PTKAKRRVVQREKR](4)-K(2)-K-betaA) that encompasses the cleavage region of the human immunodeficiency virus type 1 (HIV-1) envelope precursor. It displays an antiviral activity against HIV-1 and HIV-2 and inhibits HIV-1 Env-mediated cell-to-cell fusion. This effect has previously been attributed to interference with Env processing, resulting in the expression of a nonfusogenic envelope [Virology (1998) 247, 137]. However, we show here that CLIV does not alter the status of Env cleavage at steady state. Using various aggregation/syncytium assays that allow us to discriminate between gp120/CD4 binding and binding followed by gp41-mediated fusion, we demonstrate that CLIV inhibits a step of the cell-to-cell fusion process after CD4 binding. We demonstrate also that CLIV binds at 37 degrees C to a single class of protein present at the CD4(+) cell surface (Scatchard analysis: K(d) = 8 nM; B(max) = 10(4) sites/cell) and that the fusion inhibition activity seems to correlate with binding to this proteic component. In contrast, CLIV interacts with neither membrane-inserted nor CD4-associated Env. We therefore propose that CLIV interferes after Env/CD4 binding with a step of the membrane fusion process that may involve the C-terminal domain of gp120.

Inhibition of natural killer cell cytotoxicity and interferon gamma production by the envelope protein of HIV and prevention by vasoactive intestinal peptide

Natural killer (NK) cell dysfunction is common in human immunodeficiency virus (HIV)-infected subjects, although its mechanisms are poorly understood. A direct effect of HIV envelope glycoprotein gp120 may be involved. We investigated the in vitro effects of gp120 on the major NK cell effector functions, natural cytotoxicity and cytokine production. In addition, the ability of the vasoactive intestinal peptide (VIP) to modulate these effects was investigated. Our results indicated that gp120 inhibits NK natural cytotoxicity and showed, for the first time, that the inhibition affects also the production of the proinflammatory cytokine interferon-gamma (IFN-gamma). Interestingly, the inhibitory effect on NK cell functions was obtained with gp120 at concentrations within the range measured in the serum of HIV-infected subjects. Furthermore, we showed that the inhibitory activity of gp120 can be prevented by coincubation with VIP, even if VIP has no stimulatory activity by itself. Taken together these data suggest that (1) an inhibitory effect of gp120 may account for the NK cell dysfunction in HIV-infected subjects; (2) the gp120-mediated decrease in IFN-gamma production by NK cells may contribute to the cytokine imbalance observed in HIV infection; and (3) VIP counteracts the inhibitory effect of gp120 on NK cell functions.

HIV-1 coat glycoprotein gp120 induces apoptosis in rat brain neocortex by deranging the arachidonate cascade in favor of prostanoids

Human immunodeficiency virus type-1 coat glycoprotein gp 120 causes delayed programmed cell death (apoptosis) in rat brain neocortex. Here, we investigated the possible role of the arachidonate cascade and membrane peroxidation in this process. It is shown that gp 120 causes a rapid increase in the activity and expression of the arachidonate-metabolizing enzyme prostaglandin H synthase, paralleled by increased prostaglandin E(2) levels. The selective inhibitor of prostaglandin H synthase indomethacin inhibited enzyme activity, reduced prostaglandin E(2) content, and partially protected neocortex against gp 120-induced apoptosis. Conversely, the activity and expression of the arachidonate-metabolizing enzyme 5-lipoxygenase decreased upon gp 120 treatment, as well as the level of its product, leukotriene B(4). Treatment with gp 120 also reduced membrane lipid peroxidation, and this may be implicated in the execution of programmed cell death. These results suggest that early derangement of the arachidonate cascade in favor of prostanoids may be instrumental in the execution of delayed apoptosis in the brain neocortex of rats.

gp120- and TNF-alpha-induced modulation of human B cell function: proliferation, cyclic AMP generation, Ig production, and B-cell receptor expression

BACKGROUND

It is well known that HIV-1 infection induces profound alterations in the immune system, including hyperactivation of B cells. TNF-alpha induces HIV-1 replication and immunodysregulation, including polyclonal B-cell activation.

OBJECTIVE

We sought to determine the effects of surface-binding HIV-1 envelope glycoprotein (gp120) and TNF-alpha on human B-cell function.

METHODS

HIV-1 seronegative peripheral blood human B cells were purified and activated by CD40 mAb and IL-4. In vitro studies of B-cell proliferation, cyclic AMP (cAMP) generation, receptor expression, and Ig production were performed.

RESULTS

gp120, an Ig superantigen, stimulated HIV-1 seronegative and HIV-1 seropositive human B-cell cAMP generation, proliferation, and Ig production. These gp120-induced B-cell responses were demonstrated to be specific as evidenced by the abrogation of the stimulatory response in the presence of anti-gp120 mAb, blocking of CD4 resulting in no change on gp120-induced B-cell responses, and the binding of gp120 in these B cells. TNF-alpha also stimulated cAMP generation, proliferation, and Ig production in B cells, and the binding of gp120 to these B cells stimulated by TNF-alpha further enhanced cell proliferation, cAMP generation, and Ig production. Antigenic expression of the B-cell receptor CD79b was down-regulated by gp120 but was not altered by the addition of TNF-alpha.

CONCLUSION

gp120 modulation of TNF-alpha-induced B-cell receptor- and cAMP-mediated signal transduction events may be involved in the B-cell abnormalities observed in HIV-1 infection.

Nitric oxide production and apoptosis by GP120

Nitric oxide (NO) is increased by gp120 in astrocytes and in monocyte-derived macrophages. Of the gp120 fragments (F1: amino acid 254-274, F2: amino acid 315-329, F3: amino acid 421-438), F1 has been shown to increase NO in astrocytes and gp120 also primes CD4+ T cells for apoptosis. Peripheral blood mononuclear cells (PBMCs) at 10(6)/ml (N = 10) were incubated at 24 and 72 hours in RPMI, 10% CO2 with low doses (100 nM) gp120 and high doses (400 nM) of the smaller fragments. Supernatants were collected and assayed for the relative contribution of gp120 and its fragments on NO production at both time points. Apoptosis was detected by in situ hybridization with and without 1 microgram/ml LPS as superantigen at 72 hours. The major contribution to apoptosis and NO production was from F1. At 24 hours F1 had a 1.9-fold increase from control, whereas F2 and F3 had 1.25- and 1.35-fold increases. At 72 hours both F1 and F2 had a 1.5-fold increase and F3 had a 1.33 increase. Thus, F1 contributed significantly to NO production at 24 hours. Both F1 and F2 had significant contributions to NO production at 72 hours. F1 had the most contribution to apoptosis both with and without lipopolysaccharide (LPS). These findings may contribute to further understanding the mechanism of HIV-induced apoptosis.

HIV-derived protein gp120 suppresses P3 potential in rats: potential implications in HIV-associated dementia

Between 20 and 30% of AIDS patients have neurological symptoms characterized by motor impairment, memory loss and progressive dementia. Previous studies have implicated the HIV derived gp120, which produces behavioral deficits and electrophysiological alterations in rats. The goal of the present study was to describe the effect of this protein on the P3 event-related potential (ERP), evoked by a passive discrimination task in rats. We used II rats divided into two groups: HIV gp120 (n = 6) and control (n = 5). We recorded the P3 wave before any treatment (baseline), during the i.c.v. administration of either HIVgp 120 (700 ng/5 days) or saline (pH 7.2), and 24 h, 7, 14 and 21 days after the last injection. There were no changes between groups in the amplitude or latencies of the observed components (N1, P2, N2 and P3) evoked by target stimuli, during baseline or during the injection period. However, the HIV gp120 group showed a significant amplitude reduction in P3 wave 24 h after the last injection, while the N1, P2 and N2 waves remained unchanged. However, from the 7th day through the 21st day, P2 and N2 components also disappeared and only the N1 component could be observed in the HIV gp 20-treated group. These changes in the N2, P2 and P3 potentials, suggesting an alteration in cognitive processes, further support the neurotoxic activity of HIV gp120 and its role in AIDS dementia.

HIV-1 gp120 and chemokines activate ion channels in primary macrophages through CCR5 and CXCR4 stimulation

HIV type 1 (HIV-1) uses the chemokine receptors CCR5 and CXCR4 as coreceptors for entry into target cells. Here we show that the HIV-1 envelope gp120 (Env) activates multiple ionic signaling responses in primary human macrophages, which are important targets for HIV-1 in vivo. Env from both CCR5-dependent JRFL (R5) and CXCR4-dependent IIIB (X4) HIV-1 opened calcium-activated potassium (K(Ca)), chloride, and calcium-permeant nonselective cation channels in macrophages. These signals were mediated by CCR5 and CXCR4 because macrophages lacking CCR5 failed to respond to JRFL and an inhibitor of CXCR4 blocked ion current activation by IIIB. MIP-1beta and SDF-1alpha, chemokine ligands for CCR5 and CXCR4, respectively, also activated K(Ca) and Cl(-) currents in macrophages, but nonselective cation channel activation was unique to gp120. Intracellular Ca(2+) levels were also elevated by gp120. The patterns of activation mediated by CCR5 and CXCR4 were qualitatively similar but quantitatively distinct, as R5 Env activated the K(Ca) current more frequently, elicited Cl(-) currents that were approximately 2-fold greater in amplitude, and elevated intracellular Ca(+2) to higher peak and steady-state levels. Env from R5 and X4 primary isolates evoked similar current responses as the corresponding prototype strains. Thus, the interaction of HIV-1 gp120 with CCR5 or CXCR4 evokes complex and distinct signaling responses in primary macrophages, and gp120-evoked signals differ from those activated by the coreceptors' chemokine ligands. Intracellular signaling responses of macrophages to HIV-1 may modulate postentry steps of infection and cell functions apart from infection.

Expression of the novel T cell activation molecule hpH4 in HIV-infected patients: correlation with disease status

We have described hpH4, a surface glycoprotein selectively expressed by activated T cells and mature thymocytes and displaying weak lateral association with CD4. The hpH4 expression pattern and biochemical features, together with analysis of its tryptic digest by peptide mass searching using MALDI-MS, suggested that it is a novel molecule. The aim of this work was to evaluate the peripheral blood T cell expression of hpH4 in HIV-infected patients and the interplay between HIV gp120 and hpH4, since both molecules interact with CD4. hpH4 expression during HIV-1 infection was evaluated by assessing 55 patients at various disease stages and following up 3 patients with primary infection and 3 patients with AIDS. hpH4 expression displayed a peak in the early phase of primary infection, dropped to control levels in the asymptomatic phase, and was newly expressed, at low levels, as AIDS developed. The expression kinetics were different than those shown by HLA-DR, CD25, and CD38. The most striking findings were the transient hpH4 expression peak displayed in the earliest stage, which was unique for hpH4. Incubation of T cells from normal donors with HIV gp120 induced transient hpH4 expression in resting CD4+ T cells and potentiated the hpH4 lateral association with CD4 in activated T cells. Moreover, hpH4 triggering inhibited gp120-induced death of CD4+ cells. Therefore, H4 expression may be a response to avoid apoptosis induced by HIV products.

Human immunodeficiency virus-1 coat protein gp120 impairs contextual fear conditioning: a potential role in AIDS related learning and memory impairments

Many AIDS patients suffer from cognitive impairments including deficits in learning and memory. The Human Immunodeficiency Virus-1 (HIV-1) envelope glycoprotein gp120 is one possible mediator of these impairments. This is because gp120 activates brain microglial cells and astrocytes, and in vivo activation of glia leads to the release of the proinflammatory cytokine interleukin-1 beta (IL-1beta). gp120 induced IL-1beta release could be involved in producing memory impairments associated with AIDS because central IL-1beta activity adversely affects cognitive function. The reported experiments evaluated the effects of i.c.v. gp120 administration and subsequent IL-1beta activity on learning and memory processes in the rat. Intracerebroventricular gp120 produced memory impairments on hippocampally dependent contextual fear conditioning, but not hippocampally independent auditory-cue fear conditioning following post-conditioning gp120 administration. Central gp120 administration also caused increases in IL-1beta protein levels in the hippocampus and frontal cortex but not in the hypothalamus. gp120 induced memory impairments were blocked by 2 different IL-1 antagonists, alpha melanocyte stimulating hormone (alphaMSH) and interleukin-1 receptor antagonist (IL-1ra). Finally, heat denaturation of the tertiary structure of gp120 abolished its effects on fear conditioning, suggesting that gp120 impairs contextual fear conditioning by binding to its receptors on glia.

Glucocorticoids exacerbate the deleterious effects of gp120 in hippocampal and cortical explants

Glucocorticoids (GCs), the adrenal steroids secreted during stress, can compromise the ability of hippocampal neurons to survive numerous necrotic insults. We have previously observed that GCs worsen the deleterious effects of gp120, the glycoprotein of the acquired immune deficiency syndrome virus, which can indirectly damage neurons and which is thought to play a role in the neuropathological features of human immunodeficiency virus infection. Specifically, GCs augment gp120-induced calcium mobilization, ATP depletion, decline in mitochondrial potential, and neurotoxicity in fetal monolayer cultures from a number of brain regions. In the present report, we demonstrate a similar gp120/GC synergy in adult hippocampal and cortical explants. We generated explants from rats that were either adrenalectomized, adrenally intact, or intact and treated with corticosterone to produce levels seen in response to major stressors. Metabolic rates in explants were then indirectly assessed with silicon microphysiometry, and cytosolic calcium concentrations were assessed with fura-2 fluorescent microscopy. We observed that basal levels of GCs tonically augment the disruptive effects of gp120 on metabolism in the CA1 cell field of the hippocampus and in the cortex. Moreover, raising GC concentrations into the stress range exacerbated the ability of gp120 to mobilize cytosolic calcium in a number of hippocampal cell fields. Finally, we observed that the synthetic GC prednisone had similarly exacerbating effects on gp120. Thus, GCs can worsen the deleterious effects of gp120 in a system that is more physiologically relevant than the fetal monolayer culture and in a region-specific manner.

Fibroblast growth factor modulates HIV coreceptor CXCR4 expression by neural cells. HNRC Group

Recent studies suggest that the chemokine receptor CXCR4 may be involved in mediating the neurodegenerative process in the brains of patients with acquired immunodeficiency disease (AIDS). In this context, we hypothesize that neurotrophic factors, such as fibroblast growth factor (FGF), might protect against human immunodeficiency virus (HIV)-mediated neurotoxicity via regulating the expression of CXCR4 in neural cells. For this purpose, levels of CXCR4 were determined in neuronal and glial cell lines after FGF1 and 2 treatment. In addition, levels of CXCR4 immunoreactivity were associated with levels of FGF1 immunoreactivity in the brains of HIV-positive patients. These studies showed that neuronal CXCR4 levels decreased in a dose-dependent manner after exposure to FGF. Conversely, glial CXCR4 was increased in a dose-dependent manner after FGF2 treatment. These effects were dependent on the FGF receptor tyrosine kinase signaling pathway, because FGF-induced effects on CXCR4 were blocked by the tyrosine kinase inhibitor, 5'-deoxy-5'methylthioadenosine, or by anti-FGF receptor antibody. Stromal cell-derived factor-1, the ligand for CXCR4, and HIV gp120 neurotoxicity was attenuated by FGF1 in a dose-dependent manner in vitro, further supporting physiological relevance. In the brains of AIDS patients, the levels of neural CXCR4 immunoreactivity were inversely associated with FGF levels. Taken together, these results support the possibility that the neuroactive effects of FGF in HIV encephalitis might be mediated through regulation of the expression of CXCR4.

Subunit-dependent inhibition of recombinant rodent N-methyl-D-aspartate receptors by a HIV-1 glycoprotein 120 derived peptide

Considerable evidence suggests that low (picomolar) concentrations of the HIV-1 envelope glycoprotein gp120 induce neuronal cell death by stimulating the release of microglial toxins, which in turn activate N-methyl-D-aspartate (NMDA) receptors. Conversely, high (micromolar) concentrations of gp120 have been reported to directly inhibit NMDA receptor-mediated currents and do not induce neurotoxicity. Here we show that micromolar concentrations of a synthetic peptide corresponding to the V3-loop of gp120 (V3-pep) inhibited agonist responses of recombinant heteromeric rodent NMDA receptors expressed in Xenopus laevis oocytes by decreasing their apparent glycine affinity. Different combinations of NMDA receptor subunits displayed differential sensitivities to inhibition by V3-pep, with a potency rank order of NR1/2B > NR1/2D > NR1/2C > or = NR1/2A. Our observations may provide an explanation for the reduced neurotoxicity of high doses of gp120 in cell cultures and may be useful for the pharmacological discrimination of NMDA receptor subtypes.

Relationships between the anti-HIV V(3)-derived peptide SPC(3) and lymphocyte membrane properties involved in virus entry: SPC(3) interferes with CXCR(4)

SPC(3) is a multiple antigen peptide derived from the V(3) loop of human immunodeficiency virus (HIV) envelope (Env). It exerts a potent anti-HIV activity whereas it alters neither Env expression nor binding to CD(4). Here, SPC(3) binding characteristics, its subsequent intracellular fate and the fact that it inhibited SDF(1)alpha binding to the lymphocyte surface provided strong arguments to conclude that it exerts its anti-HIV activity through interference with the CXCR(4) coreceptor. In contrast, it interferes with none of the other major surface proteins and mechanisms involving V(3) and implicated in infection, as shown here. This work identifies the target mechanism of SPC(3).

Role of nitric oxide in the promoting effect of HIV type 1 infection and of gp120 envelope glycoprotein on interleukin 4-induced IgE production by normal human mononuclear cells

Increased levels of serum IgE have been described in HIV-1 infection; however, mechanisms implicated in this immunoglobulin production remain unknown. In this study, we demonstrate that in vitro infection of human peripheral blood mononuclear cells (PBMCs) by HIV-1 monocytotropic (Ba-L) or lymphocytotropic (LAI) strains promotes IL-4-induced IgE production, indicating that the HIV-1 infectious process may participate in the IgE production observed in vivo. The effect of membrane glycoproteins (gp160, gp120, and gp41) was also evaluated. It was found that gp120 specifically potentiates in a dose-dependent manner IL-4-induced IgE production and does not affect IL-4-induced IgG, IgA, or IgM production. In these experiments, gp160 was also found to upregulate IL-4-induced IgE production, whereas gp41 was ineffective. This effect of gp120, gp160, and HIV-1 infection on IgE synthesis was not observed in the absence of IL-4. In the presence of IL-4, the inducing effect of gp120 appeared to be indirect because gp120 did not modify purified B lymphocyte IgE production after IL-4 and anti-CD40 monoclonal antibody stimulation. As HIV-1 infection is associated with alterations of PBMC redox metabolism, the role of nitric oxide (NO) in this IgE production by human PBMCs was evaluated. In the presence of a specific inhibitor of NO synthase pathways (L-NAME), IgE production induced by IL-4 and gp120 was abolished. Taken together, these data indicate that HIV-1 envelope glycoprotein gp120 (and gp160) specifically enhances IL-4-induced IgE production by normal human PBMCs, probably through the regulation of the nitric oxide pathway.

Modulation of CD4, CXCR-4, and CCR-5 makes human hematopoietic progenitor cell lines infected with human herpesvirus-6 susceptible to human immunodeficiency virus type 1

Two CD34+ human hematopoietic progenitor cell (HPC) lines, KG-1 and TF-1, became susceptible to human immunodeficiency virus type 1 (HIV-1) infection in the presence of a concurrent infection by human herpesvirus-6 (HHV-6). We have analyzed the possible mechanism(s) underlying this phenomenon in light of the recent demonstration that at least two members of the chemokine receptor family, CXCR4 (LESTR/fusin) and CCR5 molecules, are the HIV-1-specific coreceptors necessary, together with the high-affinity receptor CD4, for entry into target cells of T-tropic and M-tropic HIV-1 isolates, respectively. KG-1 cells show CXCR4 and CCR5 surface molecules in a large proportion of the cell population. Therefore, their susceptibility to both T-tropic and M-tropic HIV-1 strains, caused by HHV-6 infection, can be explained by the HHV-6-induced appearance of CD4 molecules in about 40% of the cell population. In TF-1 cells, 10%-15% of which are CD4+ and exhibit a consistent CCR5 presence in a large proportion of the cell population and a hardly detectable amount of CXCR4 in a very limited number of cells, HHV-6 infection does not modify the cell surface availability of HIV-1-specific high-affinity receptor or coreceptors.

Differential signalling of the chemokine receptor CXCR4 by stromal cell-derived factor 1 and the HIV glycoprotein in rat neurons and astrocytes

CXCR4 is the Gi protein-linked seven-transmembrane receptor for the alpha chemokine stromal cell-derived factor 1 (SDF-1), a chemoattractant for lymphocytes. This receptor is highly conserved between human and rodent. CXCR4 is also a coreceptor for entry of human immunodeficiency virus (HIV) in T cells and is expressed in the CNS. To investigate how these CXCR4 ligands influence CNS development and/or function, we have examined the expression and signalling of this chemokine receptor in rat neurons and astrocytes in vitro. CXCR4 transcripts and protein are synthesized by both cell types and in E15 brain neuronal progenitors. In these progenitors, SDF-1, but not gp120 (the HIV glycoprotein), induced activation of extracellular signal regulated kinases (ERKs) 1/2 and a dose-dependent chemotactic response. This chemotaxis was inhibited by Pertussis toxin, which uncouples Gi proteins and the bicyclam AMD3100, a highly selective CXCR4 antagonist, as well as by an inhibitor of the MAP kinase pathway. In differentiated neurons, both SDF-1 and the glycoprotein of HIV, gp120, triggered activation of ERKs with similar kinetics. These effects were significantly inhibited by Pertussis toxin and the CXCR4 antagonist. Rat astrocytes also responded to SDF-1 signalling by phosphorylation of ERKs but, in contrast to cortical neurons, no kinase activation was induced by gp120. Thus neurons and astrocytes can respond differently to signalling by SDF-1 and/or gp120. As SDF-1 triggers directed migration of neuronal progenitors, this alpha chemokine may play a role in cortex development. In differentiated neurons, both natural and viral ligands of CXCR4 activate ERKs and may therefore influence neuronal function.

Reversal of human immunodeficiency virus type 1 protein-induced inhibition of natural killer cell activity by alpha interferon and interleukin-2

A recombinant fusion peptide, Env-Gag, derived from the human immunodeficiency virus type 1 (HIV-1) genome corresponding to a defined portion of the envelope (Env) and internal core (Gag) proteins was examined for immunoregulatory effects on the cytotoxic activity of natural killer (NK) cell-enriched, large granular lymphocytes (LGL) from healthy donors. Percoll-separated, NK cell-enriched LGL precultured for 24 h with Env-Gag at 10- and 50-ng/ml concentrations, which significantly stimulated lymphocyte proliferation, caused significant suppression of NK cell activity. Denatured Env-Gag did not cause any effect on the NK cell activity of LGL. Two other control peptides, one derived from the Escherichia coli vector used to clone the HIV Env-Gag fusion peptide and the other derived from a non-HIV-1 viral antigen (rubeola virus), did not produce any observable effect on the NK cell activity of LGL, demonstrating the specificity of the effect produced by Env-Gag. Subsequent treatment of LGL with alpha interferon (IFN-alpha) or interleukin 2 (IL-2) alone partially reversed the Env-Gag-induced suppression of NK cell activity. However, LGL treated with both IFN-alpha and IL-2 completely reversed the suppression of NK cell cytotoxicity by Env-Gag. The combined effect of IFN-alpha and IL-2 in enhancing NK cell activity may provide a novel therapeutic approach to the restoration of depressed NK cell activity observed in HIV-infected patients.

Glial and neuronal cells express functional chemokine receptor CXCR4 and its natural ligand stromal cell-derived factor 1

Chemokines are a family of proteins that chemoattract and activate cells by interacting with specific receptors on the surface of their targets. The chemokine stromal cell-derived factor 1, (SDF1), binds to the seven-transmembrane G protein-coupled CXCR4 receptor and acts to modulate cell migration, differentiation, and proliferation. CXCR4 and SDF1 are reported to be expressed in various tissues including brain. Here we show that SDF1 and CXCR4 are expressed in cultured cortical type I rat astrocytes, cortical neurons, and cerebellar granule cells. In cortical astrocytes, prolonged treatment with lipopolysaccharide induced an increase of SDF1 expression and a down-regulation of CXCR4, whereas treatment with phorbol esters did not affect SDF1 expression and down-modulated CXCR4 receptor expression. We also demonstrated the ability of human SDF1alpha (hSDF1alpha) to increase the intracellular calcium level in cultured astrocytes and cortical neurons, whereas in the same conditions, cerebellar granule cells did not modify their intracellular calcium concentration. Furthermore, in cortical astrocytes, the simultaneous treatment of hSDF1alpha with the HIV-1 capside glycoprotein gp120 inhibits the cyclic AMP formation induced by forskolin treatment.