HIV-1 matrix protein p17 enhances the proliferative activity of natural killer cells and increases their ability to secrete proinflammatory cytokines

Detection of HIV-1 matrix protein p17 in sera of viremic and aviremic patients

People living with human immunodeficiency virus type 1 (HIV-1), even if successfully treated with a combined antiretroviral therapy, display a persistent inflammation and chronic immune activation, and an increasing risk of developing cardiovascular and thrombotic events, cancers, and neurologic disorders. Accumulating evidence reveals that biologically active HIV-1 proteins may play a role in the development of these HIV-1-associated conditions. The HIV-1 matrix protein p17 (p17) is released and accumulates in different organs and tissue where it may exert multiple biological activities on different target cells. To assess a role of p17 in different HIV-1-related pathological processes, it is central to definitively ascertain and quantitate its expression in a large number of sera obtained from HIV-1-infected (HIV-1+) patients. To this aim, we developed a specific and highly sensitive p17 capture immunoenzymatic assay. Data obtained highlight a heterogeneous expression of p17 in blood of tested patients, with patients who were negative or displayed from low to relatively high p17 blood concentrations (range from 0.05 to 7.29 nM). Moreover, we found that blood p17 concentration was totally independent from the viremic status of the patient. This finding calls for monitoring HIV-1+ patients in order to evaluate a possible correlation between p17 amount in blood and the likelihood of developing HIV-1-related pathological conditions.

Binding to PI(4,5)P2 is indispensable for secretion of B-cell clonogenic HIV-1 matrix protein p17 variants

HIV-1 matrix protein p17 variants (vp17s) derived from non-Hodgkin's lymphoma (NHL) tissues of HIV-1-seropositive (HIV+) patients promote B-cell growth by activating the Akt signaling pathway. It is fundamental to understand the role played by vp17s in producing a microenvironment that fosters lymphoma development and progression. Therefore, we asked whether vp17s could be secreted from infected cells in their biologically active form. In this study, we show that two B-cell growth-promoting vp17s, NHL-a101 and NHL-a102, characterized by amino acid insertions at position 117 to 118 (Ala-Ala) or 125 to 126 (Gly-Asn), respectively, are secreted from HIV-1-infected Jurkat T cells during the active phase of viral replication. Secretion of biologically active vp17s also occurred in HeLa cells nucleofected with a plasmid expressing the entire Gag gene, following proteolytic cleavage of the Gag precursor polyprotein (Pr55Gag) by cellular aspartyl proteases. Binding of Pr55Gag to phosphatidylinositol-(4,5)-bisphosphate was indispensable for allowing the unconventional secretion of both wildtype p17 and vp17s. Indeed, here we demonstrate that inhibition of Pr55Gag binding to phosphatidylinositol-(4,5)-bisphosphate by using neomycin, or its enzymatic depletion achieved by overexpression of 5ptaseIV, significantly impair the secretion of p17s. We also demonstrated that heparan sulfate proteoglycans were involved in tethering p17s at the cell surface. This finding opens up an interesting way for investigating whether tethered p17s on the surface of HIV-1 reservoirs may represent a likely target for immune-mediated killing.

Evolution toward beta common chain receptor usage links the matrix proteins of HIV-1 and its ancestors to human erythropoietin

The HIV-1 matrix protein p17 (p17) is a pleiotropic molecule impacting on different cell types. Its interaction with many cellular proteins underlines the importance of the viral protein as a major determinant of human specific adaptation. We previously showed the proangiogenic capability of p17. Here, by integrating functional analysis and receptor binding, we identify a functional epitope that displays molecular mimicry with human erythropoietin (EPO) and promotes angiogenesis through common beta chain receptor (βCR) activation. The functional EPO-like epitope was found to be present in the matrix protein of HIV-1 ancestors SIV originated in chimpanzees (SIVcpz) and gorillas (SIVgor) but not in that of HIV-2 and its ancestor SIVsmm from sooty mangabeys. According to biological data, evolution of the EPO-like epitope showed a clear differentiation between HIV-1/SIVcpz-gor and HIV-2/SIVsmm branches, thus highlighting this epitope on p17 as a divergent signature discriminating HIV-1 and HIV-2 ancestors. P17 is known to enhance HIV-1 replication. Similarly to other βCR ligands, p17 is capable of attracting and activating HIV-1 target cells and promoting a proinflammatory microenvironment. Thus, it is tempting to speculate that acquisition of an epitope on the matrix proteins of HIV-1 ancestors capable of triggering βCR may have represented a critical step to enhance viral aggressiveness and early human-to-human SIVcpz/gor dissemination. The hypothesis that the p17/βCR interaction and βCR abnormal stimulation may also play a role in sustaining chronic activation and inflammation, thus marking the difference between HIV-1 and HIV-2 in term of pathogenicity, needs further investigation.

NK cells: A double edge sword against SARS-CoV-2

Natural killer (NK) cells are pivotal effectors of the innate immunity protecting an individual from microbes. They are the first line of defense against invading viruses, given their substantial ability to directly target infected cells without the need for specific antigen presentation. By establishing cellular networks with a variety of cell types such as dendritic cells, NK cells can also amplify and modulate antiviral adaptive immune responses. In this review, we will examine the role of NK cells in SARS-COV2 infections causing the ongoing COVID19 pandemic, keeping in mind the controversial role of NK cells specifically in viral respiratory infections and in inflammatory-driven lung damage. We discuss lessons learnt from previous coronavirus outbreaks in humans (caused by SARS-CoV-1 and MERS-COV).

Role of Autophagy in Von Willebrand Factor Secretion by Endothelial Cells and in the In Vivo Thrombin-Antithrombin Complex Formation Promoted by the HIV-1 Matrix Protein p17

Although the advent of combined antiretroviral therapy has substantially improved the survival of HIV-1-infected individuals, non-AIDS-related diseases are becoming increasingly prevalent in HIV-1-infected patients. Persistent abnormalities in coagulation appear to contribute to excess risk for a broad spectrum of non-AIDS defining complications. Alterations in coagulation biology in the context of HIV infection seem to be largely a consequence of a chronically inflammatory microenvironment leading to endothelial cell (EC) dysfunction. A possible direct role of HIV-1 proteins in sustaining EC dysfunction has been postulated but not yet investigated. The HIV-1 matrix protein p17 (p17) is secreted from HIV-1-infected cells and is known to sustain inflammatory processes by activating ECs. The aim of this study was to investigate the possibility that p17-driven stimulation of human ECs is associated with increased production of critical coagulation factors. Here we show the involvement of autophagy in the p17-induced accumulation and secretion of von Willebrand factor (vWF) by ECs. In vivo experiments confirmed the capability of p17 to exert a potent pro-coagulant activity soon after its intravenous administration.

p17 from HIV induces brain endothelial cell angiogenesis through EGFR-1-mediated cell signalling activation

HIV-associated neurocognitive disorder in HIV patients substantially reduces their quality of life. We previously showed that the HIV matrix protein, p17 could stimulate lymph-angiogenesis in vitro potentially contributing to lymphoma tumour growth and in addition is associated with vascular activation in neuro-degenerating brain tissue; here, therefore, we have investigated the detailed molecular mechanisms of this action. We performed in vitro cell culture, angiogenesis experiments, phospho-protein microarrays and Western blotting to identify cellular signalling induced by p17 within human brain endothelial cells (HbMEC), and inhibitor studies to block p17-induced vascular growth. We also characterised the effects of hippocampal CA1 injection of p17 on epidermal growth factor receptor-1 (EGFR1) expression linked to our murine model of dementia. p17 strongly induced angiogenesis of HbMEC (migration, tube formation and spheroid growth). p17 concomitantly increased phosphorylation of EGFR1 as well as down-stream intermediates ERK1/2, FAK, PLC-γ and PKC-β whilst an inhibitor peptide of EGFR, blocked cell signalling and angiogenesis. Finally, Mice that showed reduced cognitive function and behavioural deficiencies after p17 injection, demonstrated that p17 localised in cortical microvessels and also neurones many of which stained positive for p-EGFR1 by histology/IHC. This work provides strong support that p17 may be involved in initiating and/or perpetuating vascular tissue pathophysiology associated with comorbidity in HIV patients.

HIV-1 matrix protein p17 and its variants promote human triple negative breast cancer cell aggressiveness

Background

The introduction of cART has changed the morbidity and mortality patterns affecting HIV-infected (HIV⁺) individuals. The risk of breast cancer in HIV⁺ patients has now approached the general population risk. However, breast cancer has a more aggressive clinical course and poorer outcome in HIV⁺ patients than in general population, without correlation with the CD4 or virus particles count. These findings suggest a likely influence of HIV-1 proteins on breast cancer aggressiveness and progression. The HIV-1 matrix protein (p17) is expressed in different tissues and organs of successfully cART-treated patients and promotes migration of different cells. Variants of p17 (vp17s), characterized by mutations and amino acid insertions, differently from the prototype p17 (refp17), also promote B-cell proliferation and transformation.

Methods

Wound-healing assay, matrigel-based invasion assay, and anchorage-independent proliferation assay were employed to compare the biological activity exerted by refp17 and three different vp17s on the triple-negative human breast cancer cell line MDA-MB 231. Intracellular signaling was investigated by western blot analysis.

Results

Motility and invasiveness increased in cells treated with both refp17 and vp17s compared to untreated cells. The effects of the viral proteins were mediated by binding to the chemokine receptor CXCR2 and activation of the ERK1/2 signaling pathway. However, vp17s promoted MDA-MB 231 cell growth and proliferation in contrast to refp17-treated or not treated cells.

Conclusions

In the context of the emerging role of the microenvironment in promoting and supporting cancer cell growth and metastatic spreading, here we provide the first evidence that exogenous p17 may play a crucial role in sustaining breast cancer cell migration and invasiveness, whereas some p17 variants may also be involved in cancer cell growth and proliferation.

HIV-1 matrix protein p17 misfolding forms toxic amyloidogenic assemblies that induce neurocognitive disorders

Human immunodeficiency virus type-1 (HIV-1)-associated neurocognitive disorder (HAND) remains an important neurological manifestation that adversely affects a patient’s quality of life. HIV-1 matrix protein p17 (p17) has been detected in autoptic brain tissue of HAND individuals who presented early with severe AIDS encephalopathy. We hypothesised that the ability of p17 to misfold may result in the generation of toxic assemblies in the brain and may be relevant for HAND pathogenesis. A multidisciplinary integrated approach has been applied to determine the ability of p17 to form soluble amyloidogenic assemblies in vitro. To provide new information into the potential pathogenic role of soluble p17 species in HAND, their toxicological capability was evaluated in vivo. In C. elegans, capable of recognising toxic assemblies of amyloidogenic proteins, p17 induces a specific toxic effect which can be counteracted by tetracyclines, drugs able to hinder the formation of large oligomers and consequently amyloid fibrils. The intrahippocampal injection of p17 in mice reduces their cognitive function and induces behavioral deficiencies. These findings offer a new way of thinking about the possible cause of neurodegeneration in HIV-1-seropositive patients, which engages the ability of p17 to form soluble toxic assemblies.

Cellular aspartyl proteases promote the unconventional secretion of biologically active HIV-1 matrix protein p17

The human immune deficiency virus type 1 (HIV-1) matrix protein p17 (p17), although devoid of a signal sequence, is released by infected cells and detected in blood and in different organs and tissues even in HIV-1-infected patients undergoing successful combined antiretroviral therapy (cART). Extracellularly, p17 deregulates the function of different cells involved in AIDS pathogenesis. The mechanism of p17 secretion, particularly during HIV-1 latency, still remains to be elucidated. A recent study showed that HIV-1-infected cells can produce Gag without spreading infection in a model of viral latency. Here we show that in Gag-expressing cells, secretion of biologically active p17 takes place at the plasma membrane and occurs following its interaction with phosphatidylinositol-(4,5)-bisphosphate and its subsequent cleavage from the precursor Gag (Pr55^Gag) operated by cellular aspartyl proteases. These enzymes operate a more complex Gag polypeptide proteolysis than the HIV-1 protease, thus hypothetically generating slightly truncated or elongated p17s in their C-terminus. A 17 C-terminal residues excised p17 was found to be structurally and functionally identical to the full-length p17 demonstrating that the final C-terminal region of p17 is irrelevant for the protein’s biological activity. These findings offer new opportunities to identify treatment strategies for inhibiting p17 release in the extracellular microenvironment.

Detection of HIV-1 matrix protein p17 quasispecies variants in plasma of chronic HIV-1-infected patients by ultra-deep pyrosequencing

BACKGROUND

The HIV-1 matrix protein p17 (p17MA) is a pleiotropic protein that plays a key role in the HIV-1 life cycle. It has been long believed to have a highly conserved primary amino acid sequence and a well-preserved structural integrity to avoid severe fitness consequences. However, recent data revealed that the carboxy (COOH)-terminus of p17MA possesses high levels of predicted intrinsic disorder, which would subtend to at least partially unfolded status of this region. This finding pointed to the need of investigating p17MA heterogeneity.

METHODS

The degree of intrapatient variations in the p17MA primary sequence was assessed on plasma viral RNA by using ultra-deep pyrosequencing.

RESULTS

Data obtained support a complex nature of p17MA quasispecies, with variants present at variable frequency virtually in all patients. Clusters of mutations were scattered along the entire sequence of the viral protein, but they were more frequently detected within the COOH-terminal region of p17MA. Moreover, deletions and insertions also occurred in a restricted area of the COOH-terminal region.

CONCLUSIONS

On the whole, our data show that the intrapatient level of sequence diversity in the p17MA is much higher than predicted before. Our results pave the way for further studies aimed at unraveling possible correlations between the presence of distinct p17MA variants and peculiar clinical evolutions of HIV-1 disease. The presence of p17MA quasispecies diversity may offer new tools to improve our understanding of the viral adaptation during the natural history of HIV-1 infection.

Simian immunodeficiency virus and human immunodeficiency virus type 1 matrix proteins specify different capabilities to modulate B cell growth

Exogenous HIV-1 matrix protein p17 (p17) deregulates the function of different cells after its N-terminal loop (AT20) binding to the chemokine receptors CXCR1 and CXCR2. One site within AT20 has been recently found to be the major determinant of viral fitness following transmission of simian immunodeficiency virus (SIV) to the human host. Therefore, we sought to determine whether SIV matrix protein (MA) was already capable of interacting with CXCR1 and CXCR2 and mimic p17 biological activities rather than this being a newly acquired function during host adaptation. We show here that SIV MA binds with the same affinity of p17 to CXCR1 and CXCR2 and displays both p17 proangiogenic on human primary endothelial cells and chemotactic activity on human primary monocytes and B cells. However, SIV MA exhibited a higher degree of plasticity than p17 in the C terminus, a region known to play a role in modulating B cell growth. Indeed, in contrast to p17, SIV MA was found to activate the phosphatidylinositol 3-kinase/Akt signaling pathway and strongly promote B cell proliferation and clonogenic activity. Interestingly, we have recently highlighted the existence of a Ugandan HIV-1 strain-derived p17 variant (S75X) with the same B cell growth-promoting activity of SIV MA. Computational modeling allowed us to hypothesize an altered C terminus/core region interaction behind SIV MA and S75X activity. Our findings suggest the appearance of a structural constraint in the p17 C terminus that controls B cell growth, which may help to elucidate the evolutionary trajectory of HIV-1.

IMPORTANCE

The HIV-1 matrix protein p17 (p17) deregulates the biological activities of different cells after binding to the chemokine receptors CXCR1 and CXCR2. The p17 functional domain responsible for receptors interaction includes an amino acid which is considered the major determinant of SIV replication in humans. Therefore, we sought to determine whether SIV matrix protein (SIV MA) already had the ability to bind to both chemokine receptors rather than being a function newly acquired during host adaptation. We show here that SIV MA binds to CXCR1 and CXCR2 and fully mimics the p17 proangiogenic and chemokine activity. However, it differs from p17 in its ability to signal into B cells and promote B cell growth and clonogenicity. Computational analysis suggests that the accumulation of mutations in the C-terminal region may have led to a further SIV MA adaptation to the human host. This finding in turn sheds light on the evolutionary trajectory of HIV-1.

HIV-1 matrix protein p17 promotes lymphangiogenesis and activates the endothelin-1/endothelin B receptor axis

OBJECTIVE

AIDS-related lymphomas are high grade and aggressively metastatic with poor prognosis. Lymphangiogenesis is essential in supporting proliferation and survival of lymphoma, as well as tumor dissemination. Data suggest that aberrant lymphangiogenesis relies on action of HIV-1 proteins rather than on a direct effect of the virus itself. HIV-1 matrix protein p17 was found to accumulate and persist in lymph nodes of patients even under highly active antiretroviral therapy. Because p17 was recently found to exert a potent proangiogenic activity by interacting with chemokine (C-X-C motif) receptors 1 and 2, we tested the prolymphangiogenic activity of the viral protein.

APPROACH AND RESULTS

Human primary lymph node-derived lymphatic endothelial cells were used to perform capillary-like structure formation, wound healing, spheroids, and Western blot assays after stimulation with or without p17. Here, we show that p17 promotes lymphangiogenesis by binding to chemokine (C-X-C motif) receptor-1 and chemokine (C-X-C motif) receptor-2 expressed on lymph node-derived lymphatic endothelial cells and activating the Akt/extracellular signal-regulated kinase signaling pathway. In particular, it was found to induce capillary-like structure formation, sprout formation from spheroids, and increase lymph node-derived lymphatic endothelial cells motility. The p17 lymphangiogenic activity was, in part, sustained by activation of the endothelin-1/endothelin receptor B axis. A Matrigel plug assay showed that p17 was able to promote the outgrowth of lymphatic vessels in vivo, demonstrating that p17 directly regulates lymphatic vessel formation.

CONCLUSIONS

Our results suggest that p17 may generate a prolymphangiogenic microenvironment and plays a role in predisposing the lymph node to lymphoma growth and metastasis. This finding offers new opportunities to identify treatment strategies in combating AIDS-related lymphomas.

Synthetic HIV-1 matrix protein p17-based AT20-KLH therapeutic immunization in HIV-1-infected patients receiving antiretroviral treatment: A phase I safety and immunogenicity study

BACKGROUND

Therapeutic vaccination is a promising novel approach to treat HIV-1 infected people by boosting or redirecting immune system to neutralize critical HIV-1 antigens whose biological effects are relevant in the context of viral pathogenesis. With the aim to induce neutralizing antibodies to the matrix protein p17 we have developed a peptide-based immunogen (AT20-KLH) and evaluated its safety and immunogenicity.

METHODOLOGY

Twenty four asymptomatic HAART-treated HIV-1+ patients were enrolled in a phase I clinical study and were randomized to three groups: 2 groups were treated with five IM injection (Arm A: 25μg/inoculation; Arm B: 100μg/inoculation) at day (D) D0, D28, D56, D84 and D112; the control group (Arm C) were not injected. Safety was assessed by monitoring local and systemic adverse events (AEs), recorded till D168. Evaluation of immunogenicity was by titering antibodies at D0, D35, D56, D63, D84, D91, D112, D140 and D168 using ELISA.

RESULTS

In all, 105 local and systemic AEs were reported across the three groups. Most were mild and resolved without sequelae. Also the few unsolicited events, deemed unrelated to the study vaccines, caused no problems. No significant changes in the routine laboratory parameters, CD4 T-cell count or HIV-1 viremia were found. At the time of enrollment 23 out of 24 patients had no anti-AT20 antibodies, whereas 11 exhibited anti-p17 antibodies. Irrespective of the presence of preimmunization antibodies, all subjects developed high titers of anti-AT20 antibodies (GM 9775) in response to both AT20-KLH doses. These antibodies were also capable of recognizing AT20 within the p17 framework.

CONCLUSIONS

The AT20 peptide-based approach has allowed to redirect HAART-treated patients' humoral responses toward a previously untargeted hotspot of functional activity. Overall, the tested AT20-KLH doses were safe and well tolerated, supporting further exploration of AT20-KLH as an HIV-1 therapeutic vaccine candidate.

Molecular interaction studies of HIV-1 matrix protein p17 and heparin: identification of the heparin-binding motif of p17 as a target for the development of multitarget antagonists

Once released by HIV(+) cells, p17 binds heparan sulfate proteoglycans (HSPGs) and CXCR1 on leukocytes causing their dysfunction. By exploiting an approach integrating computational modeling, site-directed mutagenesis of p17, chemical desulfation of heparin, and surface plasmon resonance, we characterized the interaction of p17 with heparin, a HSPG structural analog, and CXCR1. p17 binds to heparin with an affinity (K(d) = 190 nm) that is similar to those of other heparin-binding viral proteins. Two stretches of basic amino acids (basic motifs) are present in p17 N and C termini. Neutralization (Arg→Ala substitution) of the N-terminal, but not of the C-terminal basic motif, causes the loss of p17 heparin-binding capacity. The N-terminal heparin-binding motif of p17 partially overlaps the CXCR1-binding domain. Accordingly, its neutralization prevents also p17 binding to the chemochine receptor. Competition experiments demonstrated that free heparin and heparan sulfate (HS), but not selectively 2-O-, 6-O-, and N-O desulfated heparins, prevent p17 binding to substrate-immobilized heparin, indicating that the sulfate groups of the glycosaminoglycan mediate p17 interaction. Evaluation of the p17 antagonist activity of a panel of biotechnological heparins derived by chemical sulfation of the Escherichia coli K5 polysaccharide revealed that the highly N,O-sulfated derivative prevents the binding of p17 to both heparin and CXCR1, thus inhibiting p17-driven chemotactic migration of human monocytes with an efficiency that is higher than those of heparin and HS. Here, we characterized at a molecular level the interaction of p17 with its cellular receptors, laying the basis for the development of heparin-mimicking p17 antagonists.

Opposite effects of HIV-1 p17 variants on PTEN activation and cell growth in B cells

The HIV-1 matrix protein p17 is a structural protein that can act in the extracellular environment to deregulate several functions of immune cells, through the interaction of its NH(2)-terminal region with a cellular surface receptor (p17R). The intracellular events triggered by p17/p17R interaction have been not completely characterized yet. In this study we analyze the signal transduction pathways induced by p17/p17R interaction and show that in Raji cells, a human B cell line stably expressing p17R on its surface, p17 induces a transient activation of the transcriptional factor AP-1. Moreover, it was found to upregulate pERK1/2 and downregulate pAkt, which are the major intracellular signalling components involved in AP-1 activation. These effects are mediated by the COOH-terminal region of p17, which displays the capability of keeping PTEN, a phosphatase that regulates the PI3K/Akt pathway, in an active state through the serine/threonine (Ser/Thr) kinase ROCK. Indeed, the COOH-terminal truncated form of p17 (p17Δ36) induced activation of the PI3K/Akt pathway by maintaining PTEN in an inactive phosphorylated form. Interestingly, we show that among different p17s, a variant derived from a Ugandan HIV-1 strain, named S75X, triggers an activation of PI3K/Akt signalling pathway, and leads to an increased B cell proliferation and malignant transformation. In summary, this study shows the role of the COOH-terminal region in modulating the p17 signalling pathways so highlighting the complexity of p17 binding to and signalling through its receptor(s). Moreover, it provides the first evidence on the presence of a p17 natural variant mimicking the p17Δ36-induced signalling in B cells and displaying the capacity of promoting B cell growth and tumorigenesis.

HIV-1 matrix protein p17: a candidate antigen for therapeutic vaccines against AIDS

The success in the development of anti-retroviral therapies (HAART) that contain human immunodeficiency virus type 1 (HIV-1) infection is challenged by the cost of this lifelong therapy and by its toxicity. Immune-based therapeutic strategies that boost the immune response against HIV-1 proteins or protein subunits have been recently proposed to control virus replication in order to provide protection from disease development, reduce virus transmission, and help limit the use of anti-retroviral treatments. HIV-1 matrix protein p17 is a structural protein that is critically involved in most stages of the life cycle of the retrovirus. Besides its well established role in the virus life cycle, increasing evidence suggests that p17 may also be active extracellularly in deregulating biological activities of many different immune cells that are directly or indirectly involved in AIDS pathogenesis. Thus, p17 might represent a promising target for developing a therapeutic vaccine as a contribution to combating AIDS. In this article we review the biological characteristics of HIV-1 matrix protein p17 and we describe why a synthetic peptide representative of the p17 functional epitope may work as a vaccine molecule capable of inducing anti-p17 neutralizing response against p17 derived from divergent HIV-1 strains.

Specific phenotypic and functional features of natural killer cells from HIV-infected long-term nonprogressors and HIV controllers

BACKGROUND

Recent evidence suggests that natural killer (NK) cells play a crucial role in the HIV pathogenesis. Long-term nonprogressor (LTNP) and HIV controllers are rare HIV-infected patients who control viral replication and show delayed disease progression. They represent fascinating models of natural protection against disease progression and for studying the immunological response to the virus.

METHODS

We have conducted an extensive analysis of the phenotypic and functional properties of CD56, CD56 and CD56/CD16 NK cell subsets from LTNP and HIV-controllers, and compared them with HIV progressors and healthy donors.

RESULTS

Hierarchical clustering analysis of NK phenotypic markers revealed that LTNP and HIV controllers, exhibit peculiar phenotypic features, associated with high levels of interferon-g, activation markers, and cytolytic activity in CD3CD56 NK cells against K562 target cells. More importantly, cytolytic activity against autologous CD4 T cells is abrogated after treatment with anti-NKp44L mAb, in LTNP and HIV progressors, suggesting a key role of NKp44L. In contrast, in HIV controllers and healthy donors, NKp44L expression on CD4 T cells and autologous NK lysis were both poorly detected.

CONCLUSIONS

These results show that NK cells from LTNP and HIV controllers display phenotypic and functional features and suggest a consistent continuous involvement of the innate immune response in the failure to control viral replication. Collectively, these data may have important implication in the design of new anti-HIV therapeutical strategies based on the particular functional activity of NK cells.

Synthetic peptide AT20 coupled to KLH elicits antibodies against a conserved conformational epitope from a major functional area of the HIV-1 matrix protein p17

The major challenge for the development of a highly effective peptide-based vaccine is represented by the diversity of HIV-1 strains among human population. HIV-1 matrix protein p17 is a candidate antigen for therapeutic vaccines against AIDS. Here we show that antibodies elicited in animals by immunizing them with a synthetic peptide representative of the p17 functional epitope (AT20) derived from HIV-1 BH10 (clade B), neutralize the biological activity of p17 derived from divergent strains displaying critical mutations within AT20, by recognizing a highly conserved conformational epitope. This finding shows that AT20, as an immunogenic molecule, elicits broadly neutralizing anti-p17 antibodies.

HIV-1 matrix protein p17 induces human plasmacytoid dendritic cells to acquire a migratory immature cell phenotype

Numerical and functional defects in plasmacytoid dendritic cells (pDCs) are an important hallmark of progressive HIV-1 infection, yet its etiology remains obscure. HIV-1 p17 matrix protein (p17) modulates a variety of cellular responses, and its biological activity depends on the expression of p17 receptors (p17Rs) on the surface of target cells. In this study, we show that peripheral blood pDCs express p17Rs on their surface and that freshly isolated pDCs are sensitive to p17 stimulation. Upon p17 treatment, pDCs undergo phenotypic differentiation with up-regulation of CCR7. A chemotaxis assay reveals that p17-treated pDCs migrate in response to CCL19, suggesting that these cells may acquire the ability to migrate to secondary lymphoid organs. In contrast, p17 does not induce release of type I IFN nor does it enhance pDC expression of CD80, CD86, CD83, or MHC class II. Microarray gene expression analysis indicated that p17-stimulated pDCs down-regulate the expression of molecules whose functions are crucial for efficient protein synthesis, protection from apoptosis, and cell proliferation induction. Based on these results, we propose a model where p17 induces immature circulating pDCs to home in lymph nodes devoid of their ability to serve as a link between innate and adaptative immune systems.

HIV-1 matrix protein p17 binds to monocytes and selectively stimulates MCP-1 secretion: role of transcriptional factor AP-1

HIV‐1 matrix protein p17 activates a variety of cell responses which play a critical role in viral replication and infection. Its activity depends on the expression of p17 receptors (p17R) on the surface of target cells. Whether p17 also plays a role in stimulating human monocytes, a major HIV‐1 reservoir, is not known. Here we show that human monocytes constitutively express p17Rs and that p17 selectively triggers these cells to produce MCP‐1. The effect of p17 on MCP‐1 expression was observed at the transcriptional level and was primarily dependent on the activation of the transcription factor AP‐1. p17 increased the binding activity of AP‐1 complexes in a time‐ and dose‐dependent manner. Deletion of the AP‐1 binding sites in the MCP‐1 promoter resulted in the lack of p17‐induced MCP‐1 transcription. In particular, the P3 binding site located between −69 and −63 position seems to be essential to MCP‐1 mRNA induction in p17‐treated monocytes. An ever increasing amount of evidences shows a tight link between biologically dysregulated monocytes, AP‐1 activation, MCP‐1 release and HIV‐1 pathogenesis. Overall our results suggest that p17 may play a critical role in the monocyte‐mediated inflammatory processes, which are suspected to be major precipitating events in AIDS‐defining diseases.

HIV-1 p17 binds heparan sulfate proteoglycans to activated CD4(+) T cells

We have previously shown that HIV-1 p17 binds to activated peripheral blood mononuclear cells and enhances secretion of pro-inflammatory cytokines, but we were unable to define a ligand on activated cells. In this work we evaluate the hypothesis that HIV-1 p17 may be a heparin/heparan sulfate-binding protein. HIV-1 p17 contains C- and N-terminal sequences with positively charged residues and a consensus cluster for heparin binding. We demonstrated by affinity chromatography that HIV-1 p17 binds strongly to heparin-agarose at physiological pH. Soluble heparins and heparan sulfate but not chondroitin 4-sulfate and dextran sulfate inhibit binding of HIV-1 p17 to heparin solid phase and to activated CD4(+) T cells. Furthermore the inhibition of cell sulfatation by chlorate treatment completely counteracts HIV-1 p17 binding to activated cells. These results indicate for the first time that HIV-1 p17 can be ascribed to the heparin binding protein family and suggest that this interaction might play a key role in the ability of the protein to induce an inflammatory effect on activated cells.

HIV-1 Nef impairs the dynamic of DC/NK crosstalk: different outcome of CD56(dim) and CD56(bright) NK cell subsets

Dendritic cells (DCs) and natural killer (NK) cells are essential components of the innate immunity and play a critical role in the first phase of host defense against infection. Interactions between DCs and NK cells have been demonstrated in a variety of settings, with evidence emerging of complex bidirectional crosstalk between the two cell types. The accessory HIV-1 Nef protein is a crucial determinant for viral replication and pathogenesis. We previously demonstrated that Nef, hijacking DC functional activity, subverts the DC arm of immune response to escape the adaptive immune attack. Here, we monitor the effect of Nef on the outcome of the innate immune response, focusing on the impact of Nef on DC/NK crosstalk. We demonstrate that Nef up-regulates the ability of DCs to stimulate the immunoregulatory NK cells (CD56(bright)) as assessed by the activated phenotype, up-regulation of their proliferative response and INF-gamma release. On the other hand, Nef-pulsed DCs inhibit cytotoxic NK cells (CD56(dim)), as assessed by the reduced HLA-DR surface expression, reduced proliferation and cytotoxic activity. Moreover, in the presence of Nef-pulsed DCs, we found a significant up-regulation of TNF-alpha secretion and a significant reduction of IL-10, GM-CSF, MIP-1alpha and RANTES secretion. Our findings suggest that the Nef-induced dysregulation in the DC/NK cell crosstalk may represent a potential mechanism through which HIV escapes innate immune surveillance.

HIV-1 Matrix Protein p17 Modulatesin VivoPreactivated Murine T-Cell Response and Enhances the Induction of Systemic and Mucosal Immunity Against Intranasally Co-administered Antigens

HIV-1 p17 is a viral cytokine that acts on preactivated, but not on resting, human T cells promoting proliferation, proinflammatory cytokines release and HIV-1 replication, after binding to a cellular receptor (p17R). Here, we demonstrate that p17Rs are expressed on activated murine T cells, which respond to p17 stimulation similarly to their human counterpart. We developed a mouse model of abortive HSV-1 infection to induce T cell activation in vivo. Preactivated cells expressed p17Rs and were highly susceptible to p17 stimulation, which triggered proinflammatory cytokines release and promoted CD4+ T cell survival and expansion. Coculture of in vivo activated splenocytes with macrophages in the presence of p17 further increased their ability to produce IFN-gamma. The presence of macrophages and activated T cells at mucosal sites prompted us to investigate the immunomodulatory activities of p17 in vivo. Intranasal coadministration of p17 with beta-galactosidase (beta-gal) resulted in improved beta-gal specific cellular and humoral immune responses at systemic and mucosal levels. It is well established that HIV-1 replication is driven in an autocrine/paracrine manner by endogenously produced proinflammatory cytokines. Our results highlight the role of p17 in sustaining cellular activation and inflammation, thereby promoting a permissive microenvironment for HIV-1 replication. In addition, p17 is a promising candidate antigen, exhibiting immunomodulatory/adjuvant properties, that need to be exploited in the development of HIV/AIDS vaccines.

HIV p17 reverses the anti-inflammatory activity of IL-4 on IL-15 stimulated monocytes and modulates their ability to secrete MIP-1 alpha

Monocytes play a central role in the immune system by producing and reacting to different soluble factors. Cytokine dysregulation is an hallmark in HIV-infected individuals and it is one of the most significant factors leading to impaired immunity in HIV/AIDS disease. This study investigates the possibility of modulation in the secretion of some inflammatory cytokines and chemokines induced by HIV p17 in monocytes. The results show that p17, while ineffective on resting monocytes, exerts an inflammatory action on IL-4 mediated inhibition of TNF-alpha and IFN-gamma production induced by IL-15 stimulation. In addition, p17 is able to reduce MIP-1alpha secretion, but unable to influence IL-6 production. The ability of HIV p17 to contribute to an altered pattern of secreted soluble factors might imply a key role for this viral protein in the development of AIDS pathogenesis.

Polymorphism of HIV-1 gag (p17) gene from female sex workers in Calcutta, India

HIV-1 subtype C is the major subtype in India as evidenced from the analysis of specific regions within envelope and gag gene. The matrix protein (p17) of HIV-1 which is involved in several functions like the viral RNA transport, nuclear localization, assembly of pre-integration complex into host nucleus has been used to study the strain diversity among female sexworkers in Calcutta. The gene encoding for the HIV-1 matrix protein, p17 was amplified by nested polymerase chain reaction (PCR) from blood samples of HIV-1 seropositive female sex workers (FSW) in Calcutta, India. Genes of twenty-two samples were sequenced and the phylogenetic analysis with different global strains showed that the majority (seventeen) was clustered with Indian type C. A few samples were found to be close to other C subtypes isolated from South Africa, China and Myanmar. The comparison of Calcutta samples with the samples from other regions of India along with other non-asian subtype C sequences clearly revealed a different cluster of Indian sequences. The two samples, cal 242 and cal 709 was found to be the most divergent type and showed close relatedness with African C subtypes.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.