Cyclophilin-CD147 interactions: a new target for anti-inflammatory therapeutics

CD147 is a widely expressed plasma membrane protein that has been implicated in a variety of physiological and pathological activities. It is best known for its ability to function as extracellular matrix metalloproteinase inducer (hence the other name for this protein, EMMPRIN), but has also been shown to regulate lymphocyte responsiveness, monocarboxylate transporter expression and spermatogenesis. These functions reflect multiple interacting partners of CD147. Among these CD147-interacting proteins cyclophilins represent a particularly interesting class, both in terms of structural considerations and potential medical implications. CD147 has been shown to function as a signalling receptor for extracellular cyclophilins A and B and to mediate chemotactic activity of cyclophilins towards a variety of immune cells. Recent studies using in vitro and in vivo models have demonstrated a role for cyclophilin-CD147 interactions in the regulation of inflammatory responses in a number of diseases, including acute lung inflammation, rheumatoid arthritis and cardiovascular disease. Agents targeting either CD147 or cyclophilin activity showed significant anti-inflammatory effects in experimental models, suggesting CD147-cyclophilin interactions may be a good target for new anti-inflammatory therapeutics. Here, we review the recent literature on different aspects of cyclophilin-CD147 interactions and their role in inflammatory diseases.

Lipopolysaccharide stimulates HIV-1 entry and degradation in human macrophages

The bacterial endotoxin LPS is a potent stimulator of monocyte and macrophage activation and has been shown to protect differentiated macrophages from de novo infection by HIV-1. However, the mechanisms of this inhibitory activity of LPS are not fully understood. We investigated the effect of LPS on the early post-binding steps of HIV-1 replication in primary macrophages. Paradoxically, when applied together with the virus, LPS stimulated entry of HIV-1 into macrophages, as judged by the amount of internalized HIV-1 RNA and p24. This stimulatory activity did not depend on receptors used for entry and did not require new protein synthesis. However, internalized viral RNA and p24 were rapidly degraded in LPS-stimulated macrophages. Surprisingly, while degradation of HIV-1 p24 in LPS-treated cells was inhibited by bafilomycin A1, HIV-1 RNA was not protected by this agent, suggesting that viral RNA is degraded by a pH-independent mechanism. These results indicate that LPS stimulates both virus uptake and virus degradation in macrophages.

CD147 is a signaling receptor for cyclophilin B

Cyclophilins A and B (CyPA and CyPB) are cyclosporin A binding proteins that can be secreted in response to inflammatory stimuli. We recently identified CD147 as a cell-surface receptor for CyPA and demonstrated that CD147 is an essential component in the CyPA-initiated signaling cascade that culminates in ERK activation and chemotaxis. Here we demonstrate that CD147 also serves as a receptor for CyPB. CyPB induced Ca(2+) flux and chemotaxis of CD147-transfected, but not control, CHO cells, and the chemotactic response of primary human neutrophils to CyPB was blocked by antibodies to CD147. These results suggest that CD147 serves as a receptor for extracellular cyclophilins.

CD147 facilitates HIV-1 infection by interacting with virus-associated cyclophilin A

Cyclophilin A (CyPA) is specifically incorporated into the virions of HIV-1 and has been shown to enhance significantly an early step of cellular HIV-1 infection. Our preliminary studies implicated CD147 as a receptor for extracellular CyPA. Here, we demonstrate a role for CyPA-CD147 interaction during the early steps of HIV-1 infection. Expression of human CD147 increased infection by HIV-1 under one-cycle conditions. However, susceptibility to infection by viruses lacking CyPA (simian immunodeficiency virus or HIV-1 produced in the presence of cyclosporin A) was unaffected by CD147. Virus-associated CyPA coimmunoprecipitated with CD147 from infected cells. Antibody to CD147 inhibited HIV-1 entry as evidenced by the delay in translocation of the HIV-1 core proteins from the membrane and inhibition of viral reverse transcription. Viruses whose replication did not require CyPA (SIV or mutant HIV-1) were resistant to the inhibitory effect of anti-CD147 antibody. These results suggest that HIV-1 entry depends on an interaction between virus-associated CyPA and CD147 on a target cell.

HIV-1 penetrates coronary artery endothelial cells by transcytosis

BACKGROUND

The pathogenesis of HIV-1-related cardiomyopathy is poorly understood, but HIV-1 has been detected in cardiomyocytes. Whether HIV-1 penetrates into the myocardium by infection of coronary artery endothelial cells (CAEC) or using transcellular or paracellular routes across CAEC has not been resolved.

MATERIALS AND METHODS

A model of the CAEC barrier was constructed with primary CAEC (derived from human coronary vessels). Polymerase chain reaction (PCR) assay, infectious assay, and immunofluorescence were employed to show abortive nature of HIV-1 infection of CAEC. Tight junction (TJ) and cell adhesion proteins were visualized by immunofluorescence. The time course of HIV-1 invasion was measured by HIV-1 RNA assay. Inulin permeability assay determined paracellular leakage. Transmission electron microscopy demonstrated virus-induced endothelial vacuolization.

RESULTS

Despite a strong display on CAEC of CXCR4 and a lesser expression of CCR3 and CCR5, HIV-1 did not productively replicate in CAEC, as shown by infectious assay, immunofluorescence, and electron microscopy. HIV-1 infection of CAEC was abortive with minimal reverse transcription of strong stop DNA and pol but not full-length or two LTR DNA circles. Upon infection of the model with 1 million RNA copies of HIV-1JR-FL, virus penetration 2 hr postinfection (PI) was negligible but increased by 1,750% 24 hr PI. The paracellular permeability increased during this period by only 25%. Neither AOP-RANTES nor v-MIPII significantly reduced HIV-1JR-FL invasion. Virus infection did not alter the integral TJ protein occludin and the TJ-associated protein ZO-1. HIV-1 exposed CAEC and brain microvascular endothelial cells (BMVEC) developed extensive cytoplasmic vacuolization with retroviral-like particles in the vacuoles.

CONCLUSIONS

The endothelium is not an impenetrable barrier to HIV-1. The virus opens a transcellular route across coronary and brain endothelia in cytoplasmic vacuoles.

The binding subunit of pertussis toxin inhibits HIV replication in human macrophages and virus expression in chronically infected promonocytic U1 cells

We have recently shown that the binding subunit of pertussis toxin (PTX-B) inhibits the entry and replication of macrophage-tropic (R5) HIV-1 strains in activated primary T lymphocytes. Furthermore, PTX-B suppressed the replication of T cell-tropic (X4) viruses at a postentry level in the same cells. In this study we demonstrate that PTX-B profoundly impairs entry and replication of the HIV-1(ADA) (R5), as well as of HIV pseudotyped with either murine leukemia virus or vesicular stomatitis virus envelopes, in primary monocyte-derived macrophages. In addition, PTX-B strongly inhibited X4 HIV-1 replication in U937 promonocytic cells and virus expression in the U937-derived chronically infected U1 cell line stimulated with cytokines such as TNF-alpha and IL-6. Of interest, TNF-alpha-mediated activation of the cellular transcription factor NF-kappaB was unaffected by PTX-B. Therefore, PTX-B may represent a novel and potent inhibitor of HIV-1 replication to be tested for efficacy in infected individuals. In support of this proposition, a genetically modified mutant of PTX (PT-9K/129G), which is safely administered for prevention of Bordetella pertussis infection, showed an in vitro anti-HIV profile superimposable to that of PTX-B.

Heat-shock protein 70 can replace viral protein R of HIV-1 during nuclear import of the viral preintegration complex

Heat-shock proteins (Hsp's) are a family of molecular chaperones that contribute to protection from environmental stress. In this report, we demonstrate that a member of this family, Hsp70, facilitates nuclear import of HIV-1 preintegration complexes (PICs). The mechanism of this activity appears to be similar to the one used by Vpr, an HIV-1 protein regulating viral nuclear import and replication in macrophages. Indeed Hsp70 stimulated binding of HIV-1 matrix antigen to GST-karyopherin alpha fusion protein and rescued nuclear import of a Vpr-defective HIV-1 strain in vitro. Binding studies with truncated forms of GST-karyopherin alpha demonstrated that both Vpr and Hsp70 bind to a region in the amino-terminal part of the karyopherin alpha molecule. This region appears to be distinct from the binding sites for two other karyopherin alpha cargoes, basic-type NLS-containing proteins and transcription factor STAT-1. Vpr competed with Hsp70 for binding to karyopherin alpha. These results suggest the presence of a novel regulatory site on karyopherin alpha which is used by Hsp70 and Vpr to stimulate interaction between the HIV-1 PIC and karyopherin alpha and thus promote viral nuclear import.

The B-oligomer of pertussis toxin inhibits human immunodeficiency virus type 1 replication at multiple stages

We have recently demonstrated that the binding subunit (B-oligomer) of pertussis toxin (PTX-B) deactivates CCR5 and inhibits entry of R5 human immunodeficiency virus type 1 (HIV-1) strains in activated primary T lymphocytes (M. Alfano et al., J. Exp. Med. 190:597-605, 1999). We now present evidence that PTX-B also affects a post-entry step of HIV-1 replication. While PTX-B inhibited fusion induced by R5 but not that induced by X4 envelopes, it blocked infection of T cells with recombinant HIV-1 particles pseudotyped with R5, X4, and even murine leukemia virus or vesicular stomatitis virus envelopes. It also suppressed HIV-1 RNA synthesis in cultures of infected peripheral blood mononuclear cells when new infections had been inhibited by zidovudine, and it reduced Tat-dependent expression of the luciferase reporter gene controlled by the HIV-1 long terminal repeat (LTR). Surprisingly, PTX-B did not affect expression from the cytomegalovirus promoter, nor did it reduce the basal (Tat-independent) expression from the LTR promoter. These results indicate that PTX-B inhibits HIV-1 infection at both the entry and the post-entry stages of viral replication, with the post-entry activity specifically affecting transcription or stability of Tat-stimulated HIV-1 mRNAs.

Small molecule inhibitor of HIV-1 nuclear import suppresses HIV-1 replication in human lymphoid tissue ex vivo: a potential addition to current anti-HIV drug repertoire

Despite recent progress in anti-HIV therapy, which has to do mainly with introduction of protease inhibitors into clinical practice, drug toxicity and emergence of drug-resistant isolates during the long-term treatment of the patients necessitates search for new drugs that can be added to currently used components of a multi-drug cocktail in highly active anti-retroviral therapy (HAART). Recently, we described a class of arylene bis(methylketone) compounds that inhibit nuclear import of HIV-1 pre-integration complexes and suppress viral replication in macrophages and PBMC in vitro. In this report, we demonstrate that one of these compounds, CNI-H1194, inhibited HIV-1 replication in primary lymphoid tissue ex vivo. The compound did not antagonize the activity of currently used anti-HIV drugs that inhibit viral reverse transcriptase or protease. These results suggest that arylene bis(methylketone) compounds might be a valuable addition to HAART.

Two nuclear localization signals in the HIV-1 matrix protein regulate nuclear import of the HIV-1 pre-integration complex

Replication of HIV-1 in non-dividing and slowly proliferating cell populations depends on active import of the viral pre-integration complex (PIC) into the cell nucleus. While it is commonly accepted that this process is mediated by an interaction between the HIV-1 PIC and the cellular nuclear import machinery, controversial results have been reported concerning the mechanisms of this interaction. Here, we demonstrate that a recently identified nuclear localization signal within the HIV-1 matrix protein (MA), MA NLS-2, together with previously described MA NLS-1, mediates nuclear import of the HIV-1 PIC. Inactivation of both MA NLSs precluded nuclear translocation of MA and rendered the virus defective in nuclear import and replication in non-dividing macrophage cultures, even when functional Vpr and integrase (IN), two more viral proteins implicated in HIV-1 nuclear import, were present. Taken together, these results indicate that Vpr does not function as an independent nuclear import factor and demonstrate that HIV-1 MA, by virtue of its two nuclear localization signals, regulates HIV-1 nuclear import.

Nitric oxide regulates MIP-1alpha expression in primary macrophages and T lymphocytes: implications for anti-HIV-1 response

BACKGROUND

Chemokines and chemokine receptors have been shown to play a critical role in HIV infection. Chemokine receptors have been identified as coreceptors for viral entry into susceptible target cells, and several members of the beta chemokine subfamily of cytokines, MIP-1alpha, MIP-1beta, and RANTES, have been identified as the major human immunodeficiency virus (HIV)-suppressive factors produced by activated CD8+ T lymphocytes. In macrophages, HIV-1 infection itself was shown to upregulate the production of MIP-1alpha and MIP-1beta. In the present study, we address the mechanisms by which HIV-1 infection regulates beta chemokine responses in macrophages and lymphocytes.

MATERIAL AND METHODS

To address whether nitric oxide (NO), generated as a consequence of HIV-1 infection, regulates beta chemokine responses in monocyte/macrophages and/or macrophage-depleted peripheral blood mononuclear cells (PBMCs) these two cell populations were isolated from HIV seronegative donors, placed in culture, and infected with HIV-1 in either the presence or absence of exogenous activators (e.g. lipopolysaccharide, phytohemagglutinin), inhibitors of nitric oxide synthase (NOS), or chemical donors of NO. Cultures were analyzed for beta chemokine responses by ELISA and RNase protection.

RESULTS

LPS-induced MIP-1alpha release is enhanced in HIV-1-infected, as compared to uninfected, monocyte/macrophage cultures, and this enhancing effect is partially blocked by the addition of inhibitors of NOS, and can be reproduced by chemical generators of NO even in the absence of HIV-1 infection. A similar strategy was used to demonstrate a role for NO in HIV-1-mediated induction of MIP-1alpha in unstimulated macrophage cultures. NOS inhibitors also decreased MIP-1alpha and MIP-1beta production by phytohemagglutinin-stimulated monocyte-depleted PBMC cultures.

CONCLUSIONS

These results indicate that NO amplifies MIP-1alpha responses in activated macrophages and lymphocytes, and suggests that this pleiotropic molecule might function as an enhancing signal that regulates secretion of beta chemokines during HIV-1 infection. These findings reveal a novel mechanism by which NO might regulate the anti-HIV activity of immune cells.

Lipopolysaccharide inhibits HIV-1 infection of monocyte- derived macrophages through direct and sustained down-regulation of CC chemokine receptor 5

It is now well established that HIV-1 requires interactions with both CD4 and a chemokine receptor on the host cell surface for efficient infection. The expression of the CCR5 chemokine receptor in human macrophages facilitates HIV-1 entry into these cells, which are considered important in HIV pathogenesis not only as viral reservoirs but also as modulators of altered inflammatory function in HIV disease and AIDS. LPS, a principal constituent of Gram-negative bacterial cell walls, is a potent stimulator of macrophages and has been shown to inhibit HIV infection in this population. We now present evidence that one mechanism by which LPS mediates its inhibitory effect on HIV-1 infection is through a direct and unusually sustained down-regulation of cell-surface CCR5 expression. This LPS-mediated down-regulation of CCR5 expression was independent of de novo protein synthesis and differed from the rapid turnover of these chemokine receptors observed in response to two natural ligands, macrophage-inflammatory protein-1alpha and -1beta. LPS did not act by down-regulating CCR5 mRNA (mRNA levels actually increased slightly after LPS treatment) or by enhancing the degradation of internalized receptor. Rather, the observed failure of LPS-treated macrophages to rapidly restore CCR5 expression at the cell-surface appeared to result from altered recycling of chemokine receptors. Taken together, our results suggest a novel pathway of CCR5 recycling in LPS-stimulated human macrophages that might be targeted to control HIV-1 infection.

Activation-induced resistance of human macrophages to HIV-1 infection in vitro

Cells of the monocyte/macrophage lineage are the first targets of HIV-1 in patients and also serve as reservoirs for the virus during the course of infection. We investigated the effects of cell activation on early events of HIV-1 infection of monocyte-derived macrophages. Addition of LPS, a potent stimulator of macrophages, at the time of infection stimulated entry of HIV-1 into monocyte-derived macrophages, as judged by accumulation of early products of RT, but inhibited the synthesis of late RT products and strongly repressed nuclear import of the viral DNA, resulting in protection from infection. This effect was mediated by the CD14 receptor and involved activation of the p38 mitogen-activated protein kinase pathway. Disruption of this signaling pathway using a specific inhibitor of the p38 mitogen-activated protein kinase (SB203580) restored HIV-1 infection in the presence of LPS. These results suggest a novel view of the role of macrophage activation in anti-HIV responses of the immune system.

Viral protein R of HIV-1

Viral protein R (Vpr) of HIV-1 belongs to a class of so called 'accessory' proteins, originally thought to be dispensable for virus replication, at least in vitro. Indeed, viruses with mutated or deleted Vpr replicate well in transformed T cell lines. However, recently published results reveal several important functions performed by Vpr, which are critical for HIV-1 replication in vivo. Vpr plays an important role in regulating nuclear import of the HIV-1 pre-integration complex, and is required for virus replication in non-dividing cells. Vpr also induces cell cycle arrest in proliferating cells, stimulates virus transcription, and regulates activation and apoptosis of infected cells. These diverse functions are mediated by the interaction of Vpr with different cellular proteins, many of which carry the WxxF amino acid motif. The molecular events underlying the activity of Vpr are reviewed in this article.

Human immunodeficiency virus type 1 T-lymphotropic strains enter macrophages via a CD4- and CXCR4-mediated pathway: replication is restricted at a postentry level

The human immunodeficiency virus type 1 (HIV-1) laboratory strains adapted to T-cell lines, as well as most syncytium-inducing primary isolates, replicate poorly in macrophages, which, beside CD4(+) T lymphocytes, are major targets of HIV-1. In the present work, we used a semiquantitative PCR-based technique to study viral entry into cells, kinetics of reverse transcription, and translocation of the viral DNA into the nucleus of macrophages infected with different HIV-1 strains. Our results demonstrate that T-lymphotropic strains efficiently enter macrophages. Entry was inhibited by a monoclonal antibody against CD4 and by stromal cell-derived factor 1alpha, a natural ligand of CXCR4, suggesting that both CD4 and CXCR4 act as receptors on macrophages for HIV-1 T-lymphotropic strains. Analysis of the kinetics of reverse transcription and nuclear import revealed that the most pronounced differences between T-lymphotropic and macrophagetropic strains occurred at the level of nuclear translocation of viral DNA, although a delay in reverse transcription was also observed. These results suggest that postentry steps are critical for restricted replication of T-lymphotropic HIV-1 strains in macrophages.

Viral protein R regulates docking of the HIV-1 preintegration complex to the nuclear pore complex

Replication of human immunodeficiency virus type 1 (HIV-1) in non-dividing cells depends critically on import of the viral preintegration complex into the nucleus. Recent evidence suggests that viral protein R (Vpr) plays a key regulatory role in this process by binding to karyopherin alpha, a cellular receptor for nuclear localization signals, and increasing its affinity for the nuclear localization signals. An in vitro binding assay was used to investigate the role of Vpr in docking of the HIV-1 preintegration complex (PIC) to the nuclear pore complex. Mutant HIV-1 PICs that lack Vpr were impaired in the ability to dock to isolated nuclei and recombinant nucleoporins. Although Vpr by itself associated with nucleoporins, the docking of Vpr+ PICs was dependent on karyopherin beta and was blocked by antibodies to beta. Vpr stabilized docking by preventing nucleoporin-stimulated dissociation of the import complex. These results suggest a biochemical mechanism for Vpr function in transport of the HIV-1 genome across the nuclear pore complex.

Role of cyclophilin A in the uptake of HIV-1 by macrophages and T lymphocytes

Cyclophilins are a family of proteins that bind cyclosporin A (CsA) and possess peptidyl-prolyl cis-trans isomerase activity. In addition, they are secreted by activated cells and act in a cytokine-like manner, presumably via signaling through a cell surface cyclophilin receptor. More recently, host-derived cyclophilin A (CyPA) has been shown to be incorporated into HIV-1 virions and its incorporation essential for viral infectivity. Here we present evidence supporting a role for viral-associated CyPA in the early events of HIV-1 infection. We report that HIV-1 infection of primary peripheral blood mononuclear cells can be inhibited by: (i) an excess of exogenously added CyPA; (ii) a CsA analogue unable to enter the cells; (iii) neutralizing antibodies to CyPA. Taken together with our observations that recombinant CyPA-induced mobilization of calcium in immortalized, as well as primary, CD4+ T lymphocytes, and that incubation of T cells with iodinated CyPA, followed by chemical cross-linking, resulted in the formation of a high molecular mass complex on the cell surface, these results suggest that HIV-1-associated CyPA mediates an early event in viral infection via interaction with a cellular receptor. This interaction may present a target for anti-HIV therapies and vaccines.

Viral protein R regulates nuclear import of the HIV-1 pre-integration complex

Replication of human immunodeficiency virus type 1 (HIV-1) in non-dividing cells critically depends on import of the viral pre-integration complex into the nucleus. Genetic evidence suggests that viral protein R (Vpr) and matrix antigen (MA) are directly involved in the import process. An in vitro assay that reconstitutes nuclear import of HIV-1 pre-integration complexes in digitonin-permeabilized cells was used to demonstrate that Vpr is the key regulator of the viral nuclear import process. Mutant HIV-1 pre-integration complexes that lack Vpr failed to be imported in vitro, whereas mutants that lack a functional MA nuclear localization sequence (NLS) were only partially defective. Strikingly, the import defect of the Vpr- mutant was rescued when recombinant Vpr was re-added. In addition, import of Vpr- virus was rescued by adding the cytosol of HeLa cells, where HIV-1 replication had been shown to be Vpr-independent. In a solution binding assay, Vpr associated with karyopherin alpha, a cellular receptor for NLSs. This association increased the affinity of karyopherin alpha for basic-type NLSs, including that of MA, thus explaining the positive effect of Vpr on nuclear import of the HIV-1 pre-integration complex and BSA-NLS conjugates. These results identify the biochemical mechanism of Vpr function in transport of the viral pre-integration complex to, and across, the nuclear membrane.

Relative contribution of transcription and translation to the induction of tumor necrosis factor-alpha by lipopolysaccharide

The synthesis of tumor necrosis factor-alpha has been suggested to be regulated at both the transcriptional and translational levels in response to stimulation by bacterial lipopolysaccharide, although the relative contribution of these two mechanisms has not been quantitatively evaluated. Here, using the murine monocytic cell line RAW 264.7 as a model system, we show that steady-state TNF-alpha mRNA levels increase approximately 77-fold following treatment with lipopolysaccharide for 2 h and to a maximum of 164-fold after 8 h as measured by an RNase protection assay. The TNF-alpha gene transcription rate increases approximately 5-fold following exposure to lipopolysaccharide for 2 h as measured by a nuclear run-on assay. TNF-alpha mRNA stability did not change in the presence of lipopolysaccharide. A ribosomal sedimentation assay and an RNA transfection assay revealed that the translation rate of endogenous as well as transiently transfected TNF-alpha mRNAs increases only approximately 2-3-fold after stimulation with lipopolysaccharide for 2 h. Taken together, these results suggest that the large increase in the level of secreted TNF-alpha protein in RAW 264.7 cells is due primarily to activation of TNF-alpha gene transcription.

Cell proliferation is not required for productive HIV-1 infection of macrophages

Lentiviruses, including HIV-1, are considered a rare example of retroviruses which do not require cell proliferation for their replication. However, this notion was questioned in several publications where productive HIV-1 infection was found to be restricted to a small fraction of macrophages with proliferative capacity. Since the mode of HIV-1 replication in macrophages is of great clinical relevance, we performed a single-cell analysis of HIV-1 replication and [3H]thymidine incorporation. Our results indicate that while 17% macrophages were detected as HIV-1 DNA-positive 12 hr after infection, only 2% of those cells had incorporated tritium, about the same percentage as in the uninfected cell population. Forty-eight hours after infection, 38% macrophages were HIV-1 DNA-positive and 47% of those had incorporated tritium, while the percentage of tritium-positive uninfected cells did not change (1%). These results demonstrate directly that HIV-1 DNA does not colocalize with [3H]thymidine and support the notion that cell proliferation is not required for HIV-1 infection of macrophages.

The critical role of p38 MAP kinase in T cell HIV-1 replication

BACKGROUND

Replication of HIV-1 in human T lymphocytes requires the activation of host cellular proteins. This study identifies p38 mitogen-activated protein kinase (MAPK) as one such kinase necessary for HIV-1 replication in T cells.

MATERIALS AND METHODS

Primary human T lymphocytes were infected with the LAI strain of HIV-1 and Jurkat cells were infected with the RF strain of HIV-1. HIV replication was measured by reverse transcriptase activity. Cellular expression of endogenous p38 MAPK protein was analyzed using immunoprecipitation. Blockade of p38 MAPK expression was achieved using antisense oligonucleotides to p38 MAPK and the guanylhydrazone compound CNI-1493, an inhibitor of p38 MAPK activation.

RESULTS

HIV-1 infection of both primary human T lymphocytes and a T cell line rapidly activated the cellular p38 MAPK pathway, which remained activated for the duration of the culture. Addition of phosphothioated antisense oligonucleotides to p38 MAPK specifically inhibited viral replication. Blockade of p38 MAPK activation by addition of CNI-1493 also inhibited HIV-1 viral replication of primary T lymphocytes in a dose- and time-dependent manner. Stimulation of p38 MAPK activation did not occur with the addition of heat-inactivated virus, suggesting that viral internalization, and not just membrane binding, is necessary for p38 MAPK activation.

CONCLUSIONS

These results indicate that activation of the p38 MAPK cascade is critical for HIV-1 replication in primary T lymphocytes, and that blockade of this signal transduction pathway may be a novel therapeutic approach to the treatment of HIV-1 infection.

Critical role of reverse transcriptase in the inhibitory mechanism of CNI-H0294 on HIV-1 nuclear translocation

HIV-1 replication requires the translocation of viral genome into the nucleus of a target cell. We recently reported the synthesis of an arylene bis(methyl ketone) compound (CNI-H0294) that inhibits nuclear targeting of the HIV-1 genome and thus HIV-1 replication in monocyte cultures. Here we demonstrate that CNI-H0294 inhibits nuclear targeting of HIV-1-derived preintegration complexes by inactivating the nuclear localization sequence of the HIV-1 matrix antigen in a reaction that absolutely requires reverse transcriptase. This drug/reverse transcriptase interaction defines the specificity of its antiviral effect and is most likely mediated by the pyrimidine side-chain of CNI-H0294. After binding to reverse transcriptase, the carbonyl groups of CNI-H0294 react with the nuclear localization sequence of matrix antigen and prevent its binding to karyopherin alpha, the cellular receptor for nuclear localization sequences that carries proteins into the nucleus. Our results provide a basis for the development of a novel class of compounds that inhibit nuclear translocation and that can, in principle, be modified to target specific infectious agents.

A critical role of nitric oxide in human immunodeficiency virus type 1-induced hyperresponsiveness of cultured monocytes

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) infection leads to a general exhaustion of the immune system. Prior to this widespread decline of immune functions, however, there is an evident hyperactivation of the monocyte/macrophage arm. Increased levels of cytokines and other biologically active molecules produced by activated monocytes may contribute to the pathogenesis of HIV disease both by activating expression of HIV-1 provirus and by direct effects on cytokine-sensitive tissues, such as lung or brain. In this article, we investigate mechanisms of hyperresponsiveness of HIV-infected monocytes.

MATERIALS AND METHODS

The study was performed on monocyte cultures infected in vitro with a monocytetropic strain HIV-1ADA. Cytokine production was induced by stimulation of cultures with lipopolysaccharides (LPS) and measured by ELISA. To study involvement of nitric oxide (NO) in the regulation of cytokine expression, inhibitors of nitric oxide synthase (NOS) or chemical donors of NO were used.

RESULTS

We demonstrate that infection with HIV-1 in vitro primes human monocytes for subsequent activation with LPS, resulting in increased production of pro-inflammatory cytokines tumor necrosis factor (TNF) and interleukin 6 (IL-6). This priming effect can be blocked by Ca(2+)-chelating agents and by the NOS inhibitor L-NMMA, but not by hemoglobin. It could be reproduced on uninfected monocyte cultures by using donors of NO, but not cGMP, together with LPS.

CONCLUSIONS

NO, which is expressed in HIV-1-infected monocyte cultures, induces hyperresponsiveness of monocytes by synergizing with calcium signals activated in response to LPS stimulation. This activation is cGMP independent. Our findings demonstrate the critical role of NO in HIV-1-specific hyperactivation of monocytes.

Suppression of proinflammatory cytokines in monocytes by a tetravalent guanylhydrazone

An overproduction of proinflammatory cytokines by activated macrophages/monocytes mediates the injurious sequelae of inflammation, septic shock, tissue injury, and cachexia. We recently synthesized a tetravalent guanylhydrazone compound (CNI-1493) that inhibits cytokine-inducible arginine transport and nitric oxide (NO) production in macrophages, and protects mice against lethal endotoxemia and carrageenan-induced inflammation. During these investigations we noticed that CNI-1493 effectively prevented lipopolysaccharide (LPS)-induced NO production, even when added in concentrations 10-fold less than required to competitively inhibit L-arginine uptake, suggesting that the suppressive effects of this guanylhydrazone compound might extend to other LPS-induced responses. Here, we report that CNI-1493 suppressed the LPS-stimulated production of proinflammatory cytokines (tumor necrosis factor [TNF], interleukins 1beta and 6, macrophage inflammatory proteins 1alpha and 1beta) from human peripheral blood mononuclear cells. Cytokine suppression was specific, in that CNI-1493 did not inhibit either the constitutive synthesis of transforming growth factor beta or the upregulation of major histocompatibility complex class II by interferon gamma (IFN-gamma). In contrast to the macrophage suppressive actions of dexamethasone, which are overridden in the presence of IFN-gamma, CNI-1493 retained its suppressive effects even in the presence of IFN-gamma. The mechanism of cytokine-suppressive action by CNI-1493 was independent of extracellular L-arginine content and NO production and is not restricted to induction by LPS. As a selective inhibitor of macrophage activation that prevents TNF production, this tetravalent guanylhydrazone could be useful in the development of cytokine-suppressive agents for the treatment of diseases mediated by overproduction of cytokines.

Human immunodeficiency virus type 1 infection alters chemokine beta peptide expression in human monocytes: implications for recruitment of leukocytes into brain and lymph nodes

Two chemokine (chemoattractant cytokines) beta peptides, macrophage inflammatory proteins 1 alpha and 1 beta (MIP-1 alpha and MIP-1 beta), were induced in human monocyte cultures following infection with the human immunodeficiency virus type 1 (HIV-1). Induction depended on productive viral infection: not only did the kinetics of MIP-1 peptide induction closely follow those of viral replication, but monocyte cultures inoculated with heat-inactivated virus or infected in the presence of AZT failed to produce these chemokine beta peptides. In addition, HIV infection markedly altered the pattern of beta chemokine expression elicited by tumor necrosis factor (TNF), itself a potent proinflammatory cytokine upregulated during the development of AIDS. Reverse transcription (RT)-PCR and RT-in situ PCR studies on brain tissue from patients with AIDS dementia demonstrated elevated MIP-1 alpha and MIP-1 beta mRNA expression relative to comparable samples from HIV-1-infected patients without dementia. Cells expressing chemokines in HIV-1-infected brains were identified morphologically as microglia and astrocytes. As MIP-1 alpha and MIP-1 beta are potent chemoattractants for both monocytes and specific subpopulations of lymphocytes, this dysregulation of beta chemokine expression may influence the trafficking of leukocytes during HIV infection. These data, taken together, suggest a mechanism by which HIV-1-infected monocytes might recruit uninfected T cells and monocytes to sites of active viral replication or inflammation, notably the brain and lymph nodes.

An inhibitor of macrophage arginine transport and nitric oxide production (CNI-1493) prevents acute inflammation and endotoxin lethality

BACKGROUND

Nitric oxide (NO), a small effector molecule produced enzymatically from L-arginine by nitric oxide synthase (NOS), is a mediator not only of important homeostatic mechanisms (e.g., blood vessel tone and tissue perfusion), but also of key aspects of local and systemic inflammatory responses. Previous efforts to develop inhibitors of NOS to protect against NO-mediated tissue damage in endotoxin shock have been unsuccessful, largely because such competitive NOS antagonists interfere with critical vasoregulatory NO production in blood vessels and decrease survival in endotoxemic animals. Accordingly, we sought to develop a pharmaceutical approach to selectively inhibit NO production in macrophages while sparing NO responses in blood vessels.

MATERIALS AND METHODS

The process of cytokine-inducible L-arginine transport and NO production were studied in the murine macrophage-like cell line (RAW 264.7). A series of multivalent guanylhydrazones were synthesized to inhibit cytokine-inducible L-arginine transport. One such compound (CNI-1493) was studied further in animal models of endothelial-derived relaxing factor (EDRF) activity, carrageenan inflammation, and lethal lipopolysaccharide (LPS) challenge.

RESULTS

Upon activation with cytokines, macrophages increase transport of L-arginine to support the production of NO by NOS. Since endothelial cells do not require this additional arginine transport to produce NO, we reasoned that a competitive inhibitor of cytokine-inducible L-arginine transport would not inhibit EDRF activity in blood vessels, and thus might be effectively employed against endotoxic shock. CNI-1493, a tetravalent guanylhydrazone, proved to be a selective inhibitor of cytokine-inducible arginine transport and NO production, but did not inhibit EDRF activity. In mice, CNI-1493 prevented the development of carrageenan-induced footpad inflammation, and conferred protection against lethal LPS challenge.

CONCLUSIONS

A selective inhibitor of cytokine-inducible L-arginine transport that does not inhibit vascular EDRF responses is effective against endotoxin lethality and significantly reduces inflammatory responses.

Nuclear localization signal of HIV-1 as a novel target for therapeutic intervention

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) is a lentivirus and shares with other members of this retroviral subfamily the ability to replicate in nondividing cells, in particular, cells of the monocyte/macrophage lineage. This feature relies on the presence of a specific nuclear localization signal (NLS) within the viral matrix protein (MA p17), which to some degree can be complemented by the activity of the viral vpr gene product. The MA p17 NLS ensures efficient transportation of the viral preintegration complex into the nucleus of an infected macrophage and confers persistence of HIV-1 in quiescent T cells, and therefore presents an attractive target for therapeutic intervention.

MATERIALS AND METHODS

Nuclear localization signals (NLS) in general and the HIV-1 MA p17 NLS in particular are characterized by a stretch of positively charged amino acids including one or more lysine residues. A series of compounds potentially capable of binding and reacting with lysine by forming Schiff base adducts was synthesized. Our special consideration was to make compounds that would preferentially bind to two closely contiguous amino functions, as opposed to isolated single lysine residues. We assumed that this approach might specifically target the compound to NLS while affecting other regions less, thus reducing nonspecific cytotoxicity. Antiviral activity was assessed in primary monocytes and in peripheral blood lymphocytes (PBL) infected with HIV-1ADA strain. Viral replication was monitored by reverse transcriptase (RT) activity in the supernatant. Efficiency of nuclear importation of the viral preintegration complex was estimated by the formation of 2-LTR circle forms of HIV-1 DNA and also by in situ PCR techniques.

RESULTS

Arylene bis(methyl ketone) compounds with a nitrogenous third subsituent, especially a pyrimidinic side-chain, inhibited HIV-1 replication in human monocytes at an IC50 as low as 1 nM. These compounds did not block HIV-1 replication in peripheral blood lymphocyte cultures. The inhibitory effect observed in monocyte cultures appeared in the context of markedly reduced nuclear importation of viral DNA in the presence of the drug. No cytotoxic effects of the compounds was observed in vitro at concentrations as high as 10 microM. An amidinohydrazone derivative of the most active compound was about 100 times less active than the parent, indicating that carbonyl groups were instrumental in the antiviral effect.

CONCLUSIONS

These early results suggest that retroviral replication in nondividing cells is susceptible to pharmaceutical intervention targeted against the NLS activity of HIV-1 proteins in the viral preintegration complex. The compounds described efficiently block translocation of viral DNA to the nuclei of infected primary monocytes, and inhibit viral replication. This inhibition is effective only in nondividing cells and is not seen in proliferating cultures, such as activated PBLs. Thus, drugs that target HIV-1 NLS may be useful to specifically block the macrophage arm of HIV infection and could thereby be of value in treating macrophage-specific manifestations of HIV disease, such as HIV-1 dementia. In combination with other drugs, potential therapeutics exploiting this target may also help to control the progression of HIV-1 infection and disease.

Human immunodeficiency virus type 1 2-LTR circles reside in a nucleoprotein complex which is different from the preintegration complex

The preintegration complex of human immunodeficiency virus type 1 (HIV-1) is a large nucleoprotein complex containing viral nucleic acids in association with products of the viral gag and pol genes. One of these proteins, integrase, is absolutely required for the integration and formation of the provirus. Although HIV-1-specific 2-LTR circles from nuclei of HIV-1-infected cells were found to be associated within a high-molecular-weight nucleoprotein complex, antibodies to HIV-1 integrase failed to precipitate this form of viral DNA. This result indicates that circular forms of HIV-1 DNA are not associated with integrase. These viral DNA forms seem to exist in a context of a nucleoprotein complex that is different from a preintegration complex of HIV-1.

HIV-1 replication and potential targets for intervention

Intense research into fundamental processes of human immunodeficiency syndrome type 1 (HIV-1) replication has yielded knowledge that in many aspects equals or exceeds that of the oncogenic retroviruses. The availability of sensitive virus detection methods has allowed a more thorough characterization of the biology of virus persistence and latency in vivo and removed the dependence on in vitro models. As a clearer picture of the pattern of HIV-1 replication in vivo evolves, it becomes apparent that HIV-1 biology is distinct from that of the prototypic oncogenic retroviruses in several key aspects, particularly with regard to host cell range and determinants of viral permissiveness. In this respect it may be appropriate to examine the lentivirus, rather than the oncovirus model system to better understand the biology and pathogenesis of HIV-1 infection. This synopsis of recent and ongoing research developments in HIV-1 replication and pathogenesis emphasizes the determinants of host cell permissiveness, early events in virus replication, and underlying features in HIV-1 cytopathogenesis. In addition, basic viral replication processes which can be exploited for therapeutic intervention are discussed.