Inhibition of HIV-1 replication by balsamin, a ribosome inactivating protein of Momordica balsamina

Ribosome-inactivating proteins (RIPs) are endowed with several medicinal properties, including antiviral activity. We demonstrate here that the recently identified type I RIP from Momordica balsamina also possesses antiviral activity, as determined by viral growth curve assays and single-round infection experiments. Importantly, this activity is at play even as doses where the RIP has no cytotoxic effect. In addition, balsamin inhibits HIV-1 replication not only in T cell lines but also in human primary CD4(+) T cells. This antiviral compound exerts its activity at a viral replicative step occurring later than reverse-transcription, most likely on viral protein translation, prior to viral budding and release. Finally, we demonstrate that balsamin antiviral activity is broad since it also impedes influenza virus replication. Altogether our results demonstrate that type I RIP can exert a potent anti-HIV-1 activity which paves the way for new therapeutic avenues for the treatment of viral infections

Langerin (CD207) represents a novel interferon-stimulated gene in Langerhans cells

Interferons (IFNs) are “warning signal” cytokines released upon pathogen sensing. IFNs control the expression of interferon-stimulated genes (ISGs), which are often crucial to restrict viral infections and establish a cellular antiviral state.1,2 Langerin (CD207), a well-known surface receptor on Langerhans cells (LC), belongs to the C-type lectin receptor (CLR) family and constitutes a major pathogen binding receptor able to regulate both innate and adaptive immune responses.3,4 Importantly, this CLR was reported as an antiviral receptor, notably able to bind and internalize incoming human immunodeficiency virus (HIV) virions in Birbeck granules for degradation.5,6 However, langerin was never viewed as a contributor to the interferon-mediated antiviral immune response. We now provide evidence that langerin is an ISG showing upregulated expression upon IFN treatment in monocyte-derived and ex vivo human skin-isolated LCs

TGFβ induces a SAMHD1-independent post-entry restriction to HIV-1 infection of human epithelial Langerhans cells

Sterile alpha motif (SAM) and histidine-aspartic (HD) domains protein 1 (SAMHD1) was previously identified as a critical post-entry restriction factor to HIV-1 infection in myeloid dendritic cells. Here we show that SAMHD1 is also expressed in epidermis-isolated Langerhans cells (LC), but degradation of SAMHD1 does not rescue HIV-1 or vesicular stomatitis virus G-pseudotyped lentivectors infection in LC. Strikingly, using Langerhans cells model systems (mutz-3-derived LC, monocyte-derived LC [MDLC], and freshly isolated epidermal LC), we characterize previously unreported post-entry restriction activity to HIV-1 in these cells, which acts at HIV-1 reverse transcription, but remains independent of restriction factors SAMHD1 and myxovirus resistance 2 (MX2). We demonstrate that transforming growth factor-β signaling confers this potent HIV-1 restriction in MDLC during their differentiation and blocking of mothers against decapentaplegic homolog 2 (SMAD2) signaling in MDLC restores cells’ infectivity. Interestingly, maturation of MDLC with a toll-like receptor 2 agonist or transforming growth factor-α significantly increases cells’ susceptibility to HIV-1 infection, which may explain why HIV-1 acquisition is increased during coinfection with sexually transmitted infections. In conclusion, we report a SAMHD1-independent post-entry restriction in MDLC and LC isolated from epidermis, which inhibits HIV-1 replication. A better understanding of HIV-1 restriction and propagation from LC to CD4+ T cells may help in the development of new microbicides or vaccines to curb HIV-1 infection at its earliest stages during mucosal transmission

Two novel human cytomegalovirus NK cell evasion functions target MICA for lysosomal degradation

NKG2D plays a major role in controlling immune responses through the regulation of natural killer (NK) cells, αβ and γδ T-cell function. This activating receptor recognizes eight distinct ligands (the MHC Class I polypeptide-related sequences (MIC) A andB, and UL16-binding proteins (ULBP)1–6) induced by cellular stress to promote recognition cells perturbed by malignant transformation or microbial infection. Studies into human cytomegalovirus (HCMV) have aided both the identification and characterization of NKG2D ligands (NKG2DLs). HCMV immediate early (IE) gene up regulates NKGDLs, and we now describe the differential activation of ULBP2 and MICA/B by IE1 and IE2 respectively. Despite activation by IE functions, HCMV effectively suppressed cell surface expression of NKGDLs through both the early and late phases of infection. The immune evasion functions UL16, UL142, and microRNA(miR)-UL112 are known to target NKG2DLs. While infection with a UL16 deletion mutant caused the expected increase in MICB and ULBP2 cell surface expression, deletion of UL142 did not have a similar impact on its target, MICA. We therefore performed a systematic screen of the viral genome to search of addition functions that targeted MICA. US18 and US20 were identified as novel NK cell evasion functions capable of acting independently to promote MICA degradation by lysosomal degradation. The most dramatic effect on MICA expression was achieved when US18 and US20 acted in concert. US18 and US20 are the first members of the US12 gene family to have been assigned a function. The US12 family has 10 members encoded sequentially through US12–US21; a genetic arrangement, which is suggestive of an ‘accordion’ expansion of an ancestral gene in response to a selective pressure. This expansion must have be an ancient event as the whole family is conserved across simian cytomegaloviruses from old world monkeys. The evolutionary benefit bestowed by the combinatorial effect of US18 and US20 on MICA may have contributed to sustaining the US12 gene family

Quantitative Multicolor Super-Resolution Microscopy Reveals Tetherin HIV-1 Interaction

Virus assembly and interaction with host-cell proteins occur at length scales below the diffraction limit of visible light. Novel super-resolution microscopy techniques achieve nanometer resolution of fluorescently labeled molecules. The cellular restriction factor tetherin (also known as CD317, BST-2 or HM1.24) inhibits the release of human immunodeficiency virus 1 (HIV-1) through direct incorporation into viral membranes and is counteracted by the HIV-1 protein Vpu. For super-resolution analysis of HIV-1 and tetherin interactions, we established fluorescence labeling of HIV-1 proteins and tetherin that preserved HIV-1 particle formation and Vpu-dependent restriction, respectively. Multicolor super-resolution microscopy revealed important structural features of individual HIV-1 virions, virus assembly sites and their interaction with tetherin at the plasma membrane. Tetherin localization to micro-domains was dependent on both tetherin membrane anchors. Tetherin clusters containing on average 4 to 7 tetherin dimers were visualized at HIV-1 assembly sites. Combined biochemical and super-resolution analysis revealed that extended tetherin dimers incorporate both N-termini into assembling virus particles and restrict HIV-1 release. Neither tetherin domains nor HIV-1 assembly sites showed enrichment of the raft marker GM1. Together, our super-resolution microscopy analysis of HIV-1 interactions with tetherin provides new insights into the mechanism of tetherin-mediated HIV-1 restriction and paves the way for future studies of virus-host interactions

Immunoamphisomes in dendritic cells amplify TLR signaling and enhance exogenous antigen presentation on MHC-II

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TLR-4 engagement of dendritic cells confers a BST-2/tetherin-mediated restriction of HIV-1 infection to CD4+ T cells across the virological synapse

International audienceBackground : Dendritic cells and their subsets, located at mucosal surfaces, are among the first immune cells toencounter disseminating pathogens. The cellular restriction factor BST-2/tetherin (also known as CD317 or HM1.24)potently restricts HIV-1 release by retaining viral particles at the cell surface in many cell types, including primarycells such as macrophages. However, BST-2/tetherin does not efficiently restrict HIV-1 infection in immaturedendritic cells.Results : We now report that BST-2/tetherin expression in myeloid (myDC) and monocyte-derived dendritic cells (DC)can be significantly up-regulated by IFN-αtreatment and TLR-4 engagement with LPS. In contrast to HeLa or 293Tcells, infectious HIV-1 release in immature DC and IFN-α–matured DC was only modestly affected in the absence ofVpu compared to wild-type viruses. Strikingly, immunofluorescence analysis revealed that BST-2/tetherin was excludedfrom HIV containing tetraspanin-enriched microdomains (TEMs) in both immature DC and IFN-α–matured DC. Incontrast, in LPS-mediated mature DC, BST-2/tetherin exerted a significant restriction in transfer of HIV-1 infection toCD4+T cells. Additionally, LPS, but not IFN-αstimulation of immature DC, leads to a dramatic redistribution of cellularrestriction factors to the TEM as well as at the virological synapse between DC and CD4+Tcells. Conclusions : In conclusion, we demonstrate that TLR-4 engagement in immature DC significantly up-regulates theintrinsic antiviral activity of BST-2/tetherin, during cis-infection of CD4+T cells across the DC/T cell virological synapse.Manipulating the function and potency of cellular restriction factors such as BST-2/tetherin to HIV-1 infection, hasimplications in the design of antiviral therapeutic strategies

Daxx Inhibits HIV-1 Reverse Transcription and Uncoating in a SUMO-Dependent Manner

International audienceDeath domain-associated protein 6 (Daxx) is a multifunctional, ubiquitously expressed and highly conserved chaperone protein involved in numerous cellular processes, including apoptosis, transcriptional repression, and carcinogenesis. In 2015, we identified Daxx as an antiretroviral factor that interfered with HIV-1 replication by inhibiting the reverse transcription step. In the present study, we sought to unravel the molecular mechanism of Daxx-mediated restriction and, in particular, to identify the protein(s) that Daxx targets in order to achieve its antiviral activity. First, we show that the SUMO-interacting motif (SIM) located at the C-terminus of the protein is strictly required for Daxx to inhibit HIV-1 reverse transcription. By performing a quantitative proteomic screen combined with classical biochemical analyses, we found that Daxx associated with incoming HIV-1 cores through a SIM-dependent interaction with cyclophilin A (CypA) and capsid (CA). Daxx was found to reside within a multiprotein complex associated with viral capsids, also containing TNPO3, TRIM5α, and TRIM34. Given the well-known influence of these cellular factors on the stability of HIV-1 cores, we investigated the effect of Daxx on the cytoplasmic fate of incoming cores and found that Daxx prevented HIV-1 uncoating in a SIM-dependent manner. Altogether, our findings suggest that, by recruiting TNPO3, TRIM5α, and TRIM34 and possibly other proteins onto incoming HIV-1 cores through a SIM-dependent interaction with CA-bound CypA, Daxx increases their stability, thus preventing uncoating and reverse transcription. Our study uncovers a previously unknown function of Daxx in the early steps of HIV-1 infection and further illustrates how reverse transcription and uncoating are two tightly interdependent processes