Cell adhesion through alphaV-containing integrins is required for efficient HIV-1 infection in macrophages

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

The Role of Integrin α4β7 Signaling in Human Immunodeficiency Virus-1 Pathogenesis and Viral Entry in Primary CD4+ T Cells As Revealed by Comparative Phosphoproteomic Signatures

Integrin α₄β_7, a CD4 independent receptor of human immunodeficiency virus-1 (HIV-1) gp120, defines a subset of CD4⁺T cells preferentially targeted by HIV. It is also considered as a promising therapeutic target for HIV-1 infection. Despite its role in HIV acquisition and disease progression, HIV-1-mediated integrin α₄β₇ signaling has not been elucidated so far. In view of this, we determined phosphoproteomic signatures of HIV-1 gp120 signaling as well as signaling mediated by the integrin α₄β₇ ligand, mucosal vascular addressin cell adhesion molecule-1 (MAdCAM-1), in primary CD4⁺ T cells. This is the first comprehensive report on MAdCAM-1 signaling, which is believed to enhance HIV-1 replication. Importantly, we identified proteins associated with both classical and nonclassical integrin functions. We observed that HIV-1 gp120 signaling is associated with proteins that have previously not been associated with HIV-1 pathogenesis and thus, need to be explored further. There was a significant overlap in proteins identified by both MAdCAM-1 and HIV-1 gp120 signaling, which most likely represents cellular processes triggered upon interaction of HIV-1 gp120 with integrin α₄β_7. Pathway analysis revealed enrichment of processes that could facilitate viral replication as well as viral entry through endocytosis. Although these results warrant independent replication and further validation, they suggest the presence of additional potential therapeutic targets. These results also suggest that combinatorial approaches for targeting both HIV-1 gp120 and MAdCAM-1 signaling may be necessary for efficient control of HIV-1 infection as well as novel innovation strategies in HIV therapeutics.

RNA editing by ADAR1 regulates innate and antiviral immune functions in primary macrophages

ADAR1-dependent A-to-I editing has recently been recognized as a key process for marking dsRNA as self, therefore, preventing innate immune activation and affecting the development and resolution of immune-mediated diseases and infections. Here, we have determined the role of ADAR1 as a regulator of innate immune activation and modifier of viral susceptibility in primary myeloid and lymphoid cells. We show that ADAR1 knockdown significantly enhanced interferon, cytokine and chemokine production in primary macrophages that function as antiviral paracrine factors, rendering them resistant to HIV-1 infection. ADAR1 knockdown induced deregulation of the RLRs-MAVS signaling pathway, by increasing MDA5, RIG-I, IRF7 and phospho-STAT1 expression, an effect that was partially rescued by pharmacological blockade of the pathway. In summary, our results demonstrate a role of ADAR1 in regulating innate immune function in primary macrophages, suggesting that macrophages may play an essential role in disease associated to ADAR1 dysfunction. We also show that viral inhibition is exclusively dependent on innate immune activation consequence of ADAR1 knockdown, pointing towards ADAR1 as a potential target to boost antiviral immune response.

Human Immunodeficiency Virus Immune Cell Receptors, Coreceptors, and Cofactors: Implications for Prevention and Treatment

In the last three decades, extensive research on human immunodeficiency virus (HIV) has highlighted its capability to exploit a variety of strategies to enter and infect immune cells. Although CD4(+) T cells are well known as the major HIV target, with infection occurring through the canonical combination of the cluster of differentiation 4 (CD4) receptor and either the C-C chemokine receptor type 5 (CCR5) or C-X-C chemokine receptor type 4 (CXCR4) coreceptors, HIV has also been found to enter other important immune cell types such as macrophages, dendritic cells, Langerhans cells, B cells, and granulocytes. Interestingly, the expression of distinct cellular cofactors partially regulates the rate in which HIV infects each distinct cell type. Furthermore, HIV can benefit from the acquisition of new proteins incorporated into its envelope during budding events. While several publications have investigated details of how HIV manipulates particular cell types or subtypes, an up-to-date comprehensive review on HIV tropism for different immune cells is lacking. Therefore, this review is meant to focus on the different receptors, coreceptors, and cofactors that HIV exploits to enter particular immune cells. Additionally, prophylactic approaches that have targeted particular molecules associated with HIV entry and infection of different immune cells will be discussed. Unveiling the underlying cellular receptors and cofactors that lead to HIV preference for specific immune cell populations is crucial in identifying novel preventative/therapeutic targets for comprehensive strategies to eliminate viral infection.

iRGD peptide as effective transporter of CuInZnxS2+x quantum dots into human cancer cells

In this paper, iRGD peptide-mediated quantum dots (QDs) delivery was studied. In the first step, dodecanethiol-capped CuInZnxS2+x (ZCIS) QDs were prepared and subsequently transferred into water using a standard and facile ligand exchange approach involving 3-mercaptopropionic acid (MPA). ZCIS@MPA nanocrystals possess a photoluminescence quantum yield (PL QY) of 25%, a PL emission centered at ca. 640nm and low distributions in size and shape. Next, the iRGD peptide was electrostatically associated to ZCIS@MPA QDs. After cytotoxicity evaluation, the tumor-targeting and penetrating activities of the iRGD/QD assembly were investigated by confocal microscopy. The experiments performed on various cancer cell lines revealed a high penetration ability of the assembly, while the bare QDs were not internalized. Additionally, imaging experiments were conducted on three-dimensional multicellular tumor spheroids in order to mimic the tumor microenvironment in vivo. iRGD/QD assemblies were found to be evenly distributed throughout the whole HeLa spheroid contrary to normal cells where they were not present. Therefore, iRGD/QD assemblies have a great potential to be used as targeted imaging agents and/or nanocarriers specific to cancer cells.

Characterization of the influence of mediator complex in HIV-1 transcription

HIV-1 exploits multiple host proteins during infection. siRNA-based screenings have identified new proteins implicated in different pathways of the viral cycle that participate in a broad range of cellular functions. The human Mediator complex (MED) is composed of 28 elements and represents a fundamental component of the transcription machinery, interacting with the RNA polymerase II enzyme and regulating its ability to express genes. Here, we provide an evaluation of the MED activity on HIV replication. Knockdown of 9 out of 28 human MED proteins significantly impaired viral replication without affecting cell viability, including MED6, MED7, MED11, MED14, MED21, MED26, MED27, MED28, and MED30. Impairment of viral replication by MED subunits was at a post-integration step. Inhibition of early HIV transcripts was observed by siRNA-mediated knockdown of MED6, MED7, MED11, MED14, and MED28, specifically affecting the transcription of the nascent viral mRNA transactivation-responsive element. In addition, MED14 and MED30 were shown to have special relevance during the formation of unspliced viral transcripts (p < 0.0005). Knockdown of the selected MED factors compromised HIV transcription induced by Tat, with the strongest inhibitory effect shown by siMED6 and siMED14 cells. Co-immunoprecipitation experiments suggested physical interaction between MED14 and HIV-1 Tat protein. A better understanding of the mechanisms and factors controlling HIV-1 transcription is key to addressing the development of new strategies required to inhibit HIV replication or reactivate HIV-1 from the latent reservoirs.

Cell cycle control and HIV-1 susceptibility are linked by CDK6-dependent CDK2 phosphorylation of SAMHD1 in myeloid and lymphoid cells

Proliferating cells are preferentially susceptible to infection by retroviruses. Sterile α motif and HD domain-containing protein-1 (SAMHD1) is a recently described deoxynucleotide phosphohydrolase controlling the size of the intracellular deoxynucleotide triphosphate (dNTP) pool, a limiting factor for retroviral reverse transcription in noncycling cells. Proliferating (Ki67(+)) primary CD4(+) T cells or macrophages express a phosphorylated form of SAMHD1 that corresponds with susceptibility to infection in cell culture. We identified cyclin-dependent kinase (CDK) 6 as an upstream regulator of CDK2 controlling SAMHD1 phosphorylation in primary T cells and macrophages susceptible to infection by HIV-1. In turn, CDK2 was strongly linked to cell cycle progression and coordinated SAMHD1 phosphorylation and inactivation. CDK inhibitors specifically blocked HIV-1 infection at the reverse transcription step in a SAMHD1-dependent manner, reducing the intracellular dNTP pool. Our findings identify a direct relationship between control of the cell cycle by CDK6 and SAMHD1 activity, which is important for replication of lentiviruses, as well as other viruses whose replication may be regulated by intracellular dNTP availability.

Zinc finger endonuclease targeting PSIP1 inhibits HIV-1 integration

Genome editing using zinc finger nucleases (ZFNs) has been successfully applied to disrupt CCR5 or CXCR4 host factors and inhibit viral entry and infection. Gene therapy using ZFNs to modify the PSIP1 gene, which encodes the lens epithelium-derived growth factor (LEDGF) protein, might restrain an early step of the viral replication cycle at the integration level. ZFNs targeting the PSIP1 gene (ZFNLEDGF) were designed to specifically recognize the sequence after the integrase binding domain (IBD) of the LEDGF/p75 protein. ZFNLEDGF successfully recognized the target region of the PSIP1 gene in TZM-bl cells by heteroduplex formation and DNA sequence analysis. Gene editing induced a frameshift of the coding region and resulted in the abolishment of LEDGF expression at the mRNA and protein levels. Functional assays revealed that infection with the HIV-1 R5 BaL or X4 NL4-3 viral strains was impaired in LEDGF/p75 knockout cells regardless of entry tropism due to a blockade in HIV-1 proviral integration into the host genome. However, residual infection was detected in the LEDGF knockout cells. Indeed, LEDGF knockout restriction was overcome at a high multiplicity of infection, suggesting alternative mechanisms for HIV-1 genome integration rather than through LEDGF/p75. However, the observed residual integration was sensitive to the integrase inhibitor raltegravir. These results demonstrate that the described ZFNLEDGF effectively targets the PSIP1 gene, which is involved in the early steps of the viral replication cycle; thus, ZFNLEDGF may become a potential antiviral agent for restricting HIV-1 integration. Moreover, LEDGF knockout cells represent a potent tool for elucidating the role of HIV integration cofactors in virus replication.

Identification of Hck inhibitors as hits for the development of antileukemia and anti-HIV agents

Hematopoietic cell kinase (Hck) is a member of the Src family of non-receptor protein tyrosine kinases. High levels of Hck are associated with drug resistance in chronic myeloid leukemia. Furthermore, Hck activity has been connected with HIV-1. Herein, structure-based drug design efforts were aimed at identifying novel Hck inhibitors. First, an in-house library of pyrazolo[3,4-d]pyrimidine derivatives, which were previously shown to be dual Abl and c-Src inhibitors, was analyzed by docking studies within the ATP binding site of Hck to select the best candidates to be tested in a cell-free assay. Next, the same computational protocol was applied to screen a database of commercially available compounds. As a result, most of the selected compounds were found active against Hck, with Ki values ranging from 0.14 to 18.4 μM, confirming the suitability of the computational approach adopted. Furthermore, selected compounds showed an interesting antiproliferative activity profile against the human leukemia cell line KU-812, and one compound was found to block HIV-1 replication at sub-toxic concentrations.

Αvβ3-integrin-mediated adhesion is regulated through an AAK1L- and EHD3-dependent rapid-recycling pathway

Protein transport through the endosome is critical for maintaining proper integrin cell surface integrin distribution to support cell adhesion, motility and viability. Here we employ a live-cell imaging approach to evaluate the relationship between integrin function and transport through the early endosome. We discovered that two early endosome factors, AAK1L and EHD3, are critical for αvβ3-integrin-mediated cell adhesion in HeLa cells. siRNA-mediated depletion of either factor delays short-loop β3 integrin recycling from the early endosome back to the cell surface. Total internal reflection fluorescence-based colocalization analysis reveals that β3 integrin transits AAK1L- and EHD3-positive endosomes near the cell surface, a subcellular location consistent with a rapid-recycling role for both factors. Moreover, structure-function analysis reveals that AAK1L kinase activity, as well as its C-terminal domain, is essential for cell adhesion maintenance. Taken together, these data reveal an important role for AAK1L and EHD3 in maintaining cell viability and adhesion by promoting αvβ3 integrin rapid recycling from the early endosome.

Complement opsonization of HIV-1 results in a different intracellular processing pattern and enhanced MHC class I presentation by dendritic cells

Induction of optimal HIV-1-specific T-cell responses, which can contribute to controlling viral infection in vivo, depends on antigen processing and presentation processes occurring in DCs. Opsonization can influence the routing of antigen processing and pathways used for presentation. We studied antigen proteolysis and the role of endocytic receptors in MHC class I (MHCI) and II (MHCII) presentation of antigens derived from HIV-1 in human monocyte-derived immature DCs (IDCs) and mature DCs, comparing free and complement opsonized HIV-1 particles. Opsonization of virions promoted MHCI presentation by DCs, indicating that complement opsonization routes more virions toward the MHCI presentation pathway. Blockade of macrophage mannose receptor (MMR) and β7-integrin enhanced MHCI and MHCII presentation by IDCs and mature DCs, whereas the block of complement receptor 3 decreased MHCI and MHCII presentation. In addition, we found that IDC and MDC proteolytic activities were modulated by HIV-1 exposure; complement-opsonized HIV-1 induced an increased proteasome activity in IDCs. Taken together, these findings indicate that endocytic receptors such as MMR, complement receptor 3, and β7-integrin can promote or disfavor antigen presentation probably by routing HIV-1 into different endosomal compartments with distinct efficiencies for degradation of viral antigens and MHCI and MHCII presentation, and that HIV-1 affects the antigen-processing machinery.

Restriction of HIV-1 replication in primary macrophages by IL-12 and IL-18 through the upregulation of SAMHD1

Monocyte-derived macrophages (MDM) can polarize into different subsets depending on the environment and the activation signal to which they are submitted. Differentiation into macrophages allows HIV-1 strains to infect cells of the monocytic lineage. In this study, we show that culture of monocytes with a combination of IL-12 and IL-18 led to macrophage differentiation that was resistant to HIV-1 infection. In contrast, M-CSF-derived MDM were readily infected by HIV-1. When monocytes were differentiated in the presence of M-CSF and then further treated with IL-12/IL-18, cells became resistant to infection. The restriction on HIV-1 replication was not dependent on virus entry or coreceptor expression, as vesicular stomatitis virus-pseudotyped HIV-1 replication was also blocked by IL-12/IL-18. The HIV-1 restriction factor sterile α motif and HD domain-containing protein-1 (SAMHD1) was significantly overexpressed in IL-12/IL-18 MDM compared with M-CSF MDM, and degradation of SAMHD1 by RNA interference or viral-like particles carrying the lentiviral protein Vpx restored HIV-1 infectivity of IL-12/IL-18 MDM. SAMHD1 overexpression induced by IL-12/IL-18 was not dependent on IFN-γ. Thus, we conclude that IL-12 and IL-18 may contribute to the response against HIV-1 infection through the induction of restriction factors such as SAMHD1.

A genetic polymorphism of FREM1 is associated with resistance against HIV infection in the Pumwani sex worker cohort

A subgroup of women enrolled in the Pumwani sex worker cohort remain seronegative and PCR negative for human immunodeficiency virus type 1 despite repeated exposure through high-risk sex work. Studies have shown that polymorphisms of genes involved in antigen presentation and viral restriction factors are associated with resistance to HIV infection. To discover other possible genetic factors underlying this HIV-resistant phenotype, we conducted an exploratory nonbiased, low-resolution, genome-wide single-nucleotide polymorphism (SNP) analysis comparing 60 HIV-resistant women to 48 HIV-infected controls. The SNP minor allele rs1552896, in an intron of FREM1, was significantly associated with the resistant phenotype (P = 1.68 × 10(-5); adjusted P = 2.37 × 10(-4); odds ratio [OR], 9.51; 95% confidence interval [CI], 2.82 to 32.05). We expanded the sample size by genotyping rs1552896 in the Pumwani cohort and comparing 114 HIV-resistant women to 609 HIV-infected controls and confirmed the association (P = 1.7 × 10(-4); OR, 2.67; 95% CI, 1.47 to 4.84). To validate the association in a second cohort, we genotyped 783 women enrolled in a mother-child health study and observed the minor allele of rs1552896 enriched in HIV-uninfected women (n = 488) compared to HIV-infected enrollees (n = 295) (P = 0.036; OR, 1.69; 95% CI, 0.98 to 2.93). Quantitative reverse transcription-PCR showed that FREM1 mRNA was highly expressed in tissues relevant for HIV-1 infection, and immunohistochemical analysis revealed that FREM1 protein is expressed in the ectocervical mucosa of HIV-resistant women. The significant association of rs1552896 with an HIV-resistant phenotype, together with the expression profile of FREM1 in tissues relevant to HIV infection, suggests that FREM1 is a potentially novel candidate gene for resistance to HIV infection.

Antiretroviral agents effectively block HIV replication after cell-to-cell transfer

Cell-to-cell transmission of HIV has been proposed as a mechanism contributing to virus escape to the action of antiretrovirals and a mode of HIV persistence during antiretroviral therapy. Here, cocultures of infected HIV-1 cells with primary CD4(+) T cells or lymphoid cells were used to evaluate virus transmission and the effect of known antiretrovirals. Transfer of HIV antigen from infected to uninfected cells was resistant to the reverse transcriptase inhibitors (RTIs) zidovudine (AZT) and tenofovir, but was blocked by the attachment inhibitor IgGb12. However, quantitative measurement of viral DNA production demonstrated that all anti-HIV agents blocked virus replication with similar potency to cell-free virus infections. Cell-free and cell-associated infections were equally sensitive to inhibition of viral replication when HIV-1 long terminal repeat (LTR)-driven green fluorescent protein (GFP) expression in target cells was measured. However, detection of GFP by flow cytometry may incorrectly estimate the efficacy of antiretrovirals in cell-associated virus transmission, due to replication-independent Tat-mediated LTR transactivation as a consequence of cell-to-cell events that did not occur in short-term (48-h) cell-free virus infections. In conclusion, common markers of virus replication may not accurately correlate and measure infectivity or drug efficacy in cell-to-cell virus transmission. When accurately quantified, active drugs blocked proviral DNA and virus replication in cell-to-cell transmission, recapitulating the efficacy of antiretrovirals in cell-free virus infections and in vivo.

Trans-infection but not infection from within endosomal compartments after cell-to-cell HIV-1 transfer to CD4+ T cells

Cellular contacts between HIV-1-infected donor cells and uninfected primary CD4(+) T lymphocytes lead to virus transfer into endosomes. Recent evidence suggests that HIV particles may fuse with endosomal membranes to initiate a productive infection. To explore the role of endocytosis in the entry and replication of HIV, we evaluated the infectivity of transferred HIV particles in a cell-to-cell culture model of virus transmission. Endocytosed virus led to productive infection of cells, except when cells were cultured in the presence of the anti-gp120 mAb IgGb12, an agent that blocks virus attachment to CD4, suggesting that endocytosed virus was recycled to the outer cell surface. Confocal microscopy confirmed the colocalization of internalized virus antigen and the endosomal marker dynamin. Additionally, virus transfer, fusion, or productive infection was not blocked by dynasore, dynamin-dependent endosome-scission inhibitor, at subtoxic concentrations, suggesting that the early capture of virus into intracellular compartments did not depend on endosomal maturation. Our results suggest that endocytosis is not a mechanism of infection of primary CD4 T cells, but may serve as a reservoir capable of inducing trans-infection of cells after the release of HIV particles to the extracellular environment.

Inhibition of integrin α6 expression by cell-free varicella-zoster virus

Varicella-zoster virus (VZV) causes chickenpox and shingles. VZV is released from infected cells during natural infection, but remains highly cell-associated during experimental infection, and so most studies have utilized cell-associated infection models. We examined the impact of cell-free VZV infection of primary human foreskin fibroblasts (HFFs) on the receptor integrin α6 (ITGA6). qPCR and flow cytometry demonstrated that both cell-free VZV and cell-free UV-inactivated VZV downregulated transcription and cell-surface protein expression of ITGA6. To establish whether ITGA6 altered VZV infection, VZV transcripts and nuclear DNA levels were measured in HFFs treated with ITGA6 blocking antibody before infection. ITGA6 blocking did not impair virus entry but did negatively impact VZV transcription, and this effect was virus specific as transcription of the related herpes simplex virus type 1 was not similarly inhibited. This study identifies modulation of ITGA6 during cell-free VZV infection, and provides the first evidence linking ITGA6 with post-entry productive VZV gene expression.

Differential prevalence of the HLA-C -- 35 CC genotype among viremic long term non-progressor and elite controller HIV+ individuals

Susceptibility to HIV infection and disease progression are complex traits modulated by environmental and genetic factors, affecting innate and adaptive immune responses, among other cellular processes. A single nucleotide polymorphism (SNP) 35 kb upstream of the HLA-C gene locus (-35C/T) was previously shown to correlate with increased HLA-C expression and improved control of HIV-1. Here, we genotyped the -35C/T SNP in 639 subjects (180 uninfected patients, 304 HIV progressors and 155 LTNP) and confirmed the association of the -35C/T variant with the LTNP phenotype. The genotype frequencies in the general population subjects did not differ significantly from those seen in HIV progressors (p-value=0.472). However, a significant higher frequency of the protective CC genotype was identified when LTNP were compared either with HIV progressors alone (p-value<0.0001) or progressors and uninfected subjects together (p-value<0.0001). When considering aviremic LTNP alone (elite controllers; viral load below 50 copies/ml), the -35 CC genotype was not overrepresented compared to HIV progressors. Conversely, a significant association was found with the viremic LTNP groups (viral loads below 10,000 copies/ml). These results suggest that other factors alone or in combination with the -35 CC genotype may play an important role in differentiating the elite controller status from LTNP. Combination of different genetic variants may have additive or epistatic effects determining the HIV course of infection.

Viral determinants of HIV-1 macrophage tropism

Macrophages are important target cells for HIV-1 infection that play significant roles in the maintenance of viral reservoirs and other aspects of pathogenesis. Understanding the determinants of HIV-1 tropism for macrophages will inform HIV-1 control and eradication strategies. Tropism for macrophages is both qualitative (infection or not) and quantitative (replication capacity). For example many R5 HIV-1 isolates cannot infect macrophages, but for those that can the macrophage replication capacity can vary by up to 1000-fold. Some X4 viruses are also capable of replication in macrophages, indicating that cellular tropism is partially independent of co-receptor preference. Preliminary data obtained with a small number of transmitted/founder viruses indicate inefficient macrophage infection, whereas isolates from later in disease are more frequently tropic for macrophages. Thus tropism may evolve over time, and more macrophage tropic viruses may be implicated in the pathogenesis of advanced HIV-1 infection. Compartmentalization of macrophage-tropic brain-derived envelope glycoproteins (Envs), and non-macrophage tropic non-neural tissue-derived Envs points to adaptation of HIV-1 quasi-species in distinct tissue microenvironments. Mutations within and adjacent to the Env-CD4 binding site have been identified that determine macrophage tropism at the entry level, but post-entry molecular determinants of macrophage replication capacity involving HIV-1 accessory proteins need further definition.

Development of resistance to VIR-353 with cross-resistance to the natural HIV-1 entry virus inhibitory peptide (VIRIP)

OBJECTIVE

Virus-inhibitory peptide (VIRIP) has been identified as a component of human hemofiltrate that blocks HIV-1 gp41-dependent fusion by interacting with the fusion peptide. A VIRIP analogue (VIR-576) has been shown to be effective in a phase I/II clinical trial. We have evaluated the activity and mechanism of HIV-1 resistance to VIRIP and its analogue, VIR-353.

METHODS

Anti-HIV activity and passage of HIV-1 strains in cell culture were used to generate and identify mutations that confer resistance to VIRIP and VIR-353. Recombinant viruses harboring the most relevant mutations were generated and characterized.

RESULTS

VIRIP and VIR-353 showed anti-HIV-1 activity with EC(50) of 28 and 0.3 μmol/l, respectively, and were active against virus resistant to BMS-155, AMD3100, T20, TAK-779 or nevirapine. Time of addition experiments showed that VIR-353 targets a time/site of action corresponding to gp41-dependent fusion. VIR-353-resistant virus was generated after 450 days in cell culture, suggesting a high genetic barrier for resistance. The VIR-353-resistant virus was cross-resistant to VIRIP but remained sensitive to T20, AMD3100 or zidovudine. Recombination of gp41 into a wild-type backbone partially recovered the resistant phenotype, but both gp120 and gp41 from the resistant virus were necessary to restore resistance to VIRIP or VIR-353. Site-directed mutagenesis confirmed the role of specific mutations and identified a combination of three mutations (A433T/V489I/V570I) as the most relevant to VIRIP resistance.

CONCLUSION

VIRIP may interact with a region of gp41 that is essential for fusion but not the fusion peptide. Our results highlight interactions between gp41 and gp120 that may be required during the fusion process.

Complement opsonization of HIV-1 enhances the uptake by dendritic cells and involves the endocytic lectin and integrin receptor families

Interaction with the complement system is an underappreciated aspect of HIV-1 infection; even in primary infection, complement fragments are found on virions with potential to affect the interplay between the virus and dendritic cells (DC). Since opsonization may affect the efficiency of uptake and the type of receptors utilized, we compared the interactions of DC with free HIV-1 (F-HIV) and complement opsonized HIV-1 (C-HIV). We demonstrate that C-HIV significantly enhanced the uptake by immature DC (IDC) and mature DC (MDC) and that the internalization rate was dependent on both opsonization of the virus and DC maturation state. Increased DC uptake of C-HIV was not due to opsonization related increased binding of virus to the surface of DC but rather increased internalization of C-HIV despite utilizing a similar repertoire of receptors as F-HIV. Both F-HIV and C-HIV interacted with C-type lectins, integrins, and CD4 and blocking these receptor families prevented HIV-1 from binding to DC at 4°C. Blocking integrins significantly reduced the binding and uptake of F-HIV and C-HIV implicating the involvement of several integrins such as β1-integrin, CR3, LFA-1, and α4β7. Distinctive for C-HIV was usage of β1-integrin and for F-HIV, usage of β7-integrin, whereas both F-HIV and C-HIV utilized both integrin chains of CR3. We have in this study identified the receptor types used by both F-HIV and C-HIV to bind to DC. Noteworthy, C-HIV was internalized more efficiently by DC than F-HIV, probably via receptor mediated endocytosis, which may entail different intracellular processing of the virus leading to both elevated infection and altered activation of HIV specific immune responses.

Chemotactic antiviral cytokines promote infectious apical entry of human adenovirus into polarized epithelial cells

Mucosal epithelia provide strong barriers against pathogens. For instance, the outward facing apical membrane of polarized epithelial cells lacks receptors for agents, such as hepatitis C virus, herpesvirus, reovirus, poliovirus or adenovirus. In addition, macrophages eliminate pathogens from the luminal space. Here we show that human adenovirus type 5 engages an antiviral immune response to enter polarized epithelial cells. Blood-derived macrophages co-cultured apically on polarized epithelial cells facilitate epithelial infection. Infection also occurs in the absence of macrophages, if virus-conditioned macrophage-medium containing the chemotactic cytokine CXCL8 (interleukin-8), or recombinant CXCL8 are present. In polarized cells, CXCL8 activates a Src-family tyrosine kinase via the apical CXCR1 and CXCR2 receptors. This activation process relocates the viral co-receptor ανβ3 integrin to the apical surface, and enables apical binding and infection with adenovirus depending on the primary adenovirus receptor CAR. This paradigm may explain how other mucosal pathogens enter epithelial cells.

Studying how pathogens enter polarized epithelial cells is important for understanding infection. Here, activation of chemokine receptors on the apical membrane of epithelial cells, is shown to engage Src family tyrosine signalling, resulting in relocation of the viral co-receptor αvβ3 to the apical membrane and adenovirus entry.

Novel monocyclam derivatives as HIV entry inhibitors: Design, synthesis, anti-HIV evaluation, and their interaction with the CXCR4 co-receptor

The CXCR4 receptor has been shown to interact with the human immunodeficiency virus (HIV) envelope glycoprotein gp120, leading to fusion of viral and cell membranes. Therefore, ligands that can attach to this receptor represent an important class of therapeutic agents against HIV, thus inhibiting the first step in the cycle of viral infection: the virus-cell entry/fusion. Herein we describe the in silico design, synthesis, and biological evaluation of novel monocyclam derivatives as HIV entry inhibitors. In vitro activity testing of these compounds in cell cultures against HIV strains revealed EC(50) values in the low micromolar range without cytotoxicity at the concentrations tested. Docking and molecular dynamics simulations were performed to predict the binding interactions between CXCR4 and the novel monocyclam derivatives. A binding mode of these compounds is proposed which is consistent with the main existing site-directed mutagenesis data on the CXCR4 co-receptor. Moreover, molecular modeling comparisons were performed between these novel monocyclams, previously reported non-cyclam compounds from which the monocyclams are derived, and the well-known AMD3100 bicyclam CXCR4 inhibitors. Our results suggest that these three structurally diverse CXCR4 inhibitors bind to overlapping but not identical amino acid residues in the transmembrane regions of the receptor.

Endocytosis of HIV: anything goes

The major pathway for HIV internalization in CD4+ T cells has been thought to be the direct fusion of virus and cell membranes, because the cell surface is the point of entry of infectious particles. However, the exact contribution of endocytic pathways to the infection of CD4+ T lymphocytes is unknown, and the mechanisms involved in endocytosis of HIV particles are unclear. Recent evidence suggests that endocytosis of cell-free and cell-associated virus particles could lead to effective virus entry and productive infections. Such observations have, in turn, spurred a debate on the relevance of endosomal entry as a mechanism of escape from the immune system and HIV entry inhibitors. In this paper, we review the endocytosis of HIV and discuss its role in HIV infection and pathogenesis.

Profiling of cellular proteins in porcine reproductive and respiratory syndrome virus virions by proteomics analysis

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped virus, bearing severe economic consequences to the swine industry worldwide. Previous studies on enveloped viruses have shown that many incorporated cellular proteins associated with the virion's membranes that might play important roles in viral infectivity. In this study, we sought to proteomically profile the cellular proteins incorporated into or associated with the virions of a highly virulent PRRSV strain GDBY1, and to provide foundation for further investigations on the roles of incorporated/associated cellular proteins on PRRSV's infectivity.

Results

In our experiment, sixty one cellular proteins were identified in highly purified PRRSV virions by two-dimensional gel electrophoresis coupled with mass spectrometric approaches. The identified cellular proteins could be grouped into eight functional categories including cytoskeletal proteins, chaperones, macromolecular biosynthesis proteins, metabolism-associated proteins, calcium-dependent membrane-binding proteins and other functional proteins. Among the identified proteins, four have not yet been reported in other studied envelope viruses, namely, guanine nucleotide-binding proteins, tyrosine 3-monooxygenase/tryptophan 5-monooxygenase, peroxiredoxin 1 and galectin-1 protein. The presence of five selected cellular proteins (i.e., β-actin, Tubulin, Annexin A2, heat shock protein Hsp27, and calcium binding proteins S100) in the highly purified PRRSV virions was validated by Western blot and immunogold labeling assays.

Conclusions

Taken together, the present study has demonstrated the incorporation of cellular proteins in PRRSV virions, which provides valuable information for the further investigations for the effects of individual cellular proteins on the viral replication, assembly, and pathogenesis.

ADS-J1 inhibits HIV-1 entry by interacting with gp120 and does not block fusion-active gp41 core formation

We had shown that virus resistance to ADS-J1 was associated with amino acid changes in the envelope glycoprotein, mostly located in the gp120 coding region. Time-of-addition and endocytic virus transfer assays clearly demonstrated that ADS-J1 behaved as a gp120 inhibitor. ADS-J1-resistant virus was cross-resistant to the polyanion dextran sulfate, and recombination of gp120 recovered only the ADS-J1-resistant phenotype. In summary, ADS-J1 blocks an early step of virus entry that appears to be driven by gp120 alone.