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SUMMARY IQGAP1 is a master regulator of many cellular processes, including intracellular vesicle trafficking and endocytosis. We show that depletion of IQGAP1 in a variety of cell types increases the release of HIV-1 infectious virions and that overexpression diminishes virion production, with neither affecting the early stages of infection. IQGAP1 negatively regulates the steady-state levels of HIV-1 Gag at the plasma membrane, the site of assembly. We establish that IQGAP1 interacts with both the nucleocapsid and p6 domains of Gag, and interaction with either domain is sufficient for its regulatory function. Finally, we demonstrate that IQGAP1 regulation is independent of HIV-1 Gag “late-domains” sequences required by the virus to recruit the cellular ESCRT machinery. Thus, we provide evidence that IQGAP1 is a negative regulatory factor inhibiting efficient budding of HIV-1 by reducing Gag accumulation at the plasma membrane., Graphical Abstract, In Brief IQGAP1 is a ubiquitously expressed master regulator of many cellular processes, including intracellular trafficking. Sabo et al. demonstrate that in a variety of cell types, IQGAP1 acts as a negative regulator of HIV-1 viral particle release by reducing accumulation of the Gag viral structural protein at the plasma membrane.

Moloney Murine Leukemia Virus (M-MLV) proviral DNA is transcriptionally silenced in embryonic cells by a large repressor complex tethered to the provirus by two sequence-specific DNA binding proteins, ZFP809 and YY1. A central component of the complex is Trim28, a scaffold protein that regulates many target genes involved in cell cycle progression, DNA damage responses, and viral gene expression. The silencing activity of Trim28, and its interactions with corepressors are often regulated by post-translational modifications such as sumoylation and phosphorylation. We defined the interaction domains of Trim28 and YY1, and investigated the role of sumoylation and phosphorylation of Trim28 in mediating M-MLV silencing. The RBCC domain of Trim28 was sufficient for interaction with YY1, and acidic region 1 and zinc fingers of YY1 were necessary and sufficient for its interaction with Trim28. Additionally, we found that residue K779 was critical for Trim28-mediated silencing of M-MLV in embryonic cells.

While beta-amyloid (Aβ), a classic hallmark of Alzheimer’s disease (AD) and dementia, has long been known to be elevated in the human immunodeficiency virus type 1 (HIV-1)-infected brain, why and how Aβ is produced, along with its contribution to HIV-associated neurocognitive disorder (HAND) remains ill-defined. Here, we reveal that the membrane-associated amyloid precursor protein (APP) is highly expressed in macrophages and microglia, and acts as an innate restriction against HIV-1. APP binds the HIV-1 Gag polyprotein, retains it in lipid rafts and blocks HIV-1 virion production and spread. To escape this restriction, Gag promotes secretase-dependent cleavage of APP, resulting in the overproduction of toxic Aβ isoforms. This Gag-mediated Aβ production results in increased degeneration of primary cortical neurons, and can be prevented by γ-secretase inhibitor treatment. Interfering with HIV-1’s evasion of APP-mediated restriction also suppresses HIV-1 spread, offering a potential strategy to both treat infection and prevent HAND., HIV infection results in elevated beta-amyloid (Aβ) levels in the brain, but the underlying mechanisms are unclear. Here, the authors show that amyloid precursor protein inhibits virion production and that HIV Gag, counteracting this antiviral function, results in secretase-dependent Aβ production and neuron degeneration.

// Oded Danziger 1, * , Ben Shai 1, * , Yosef Sabo 1 , Eran Bacharach 1 , Marcelo Ehrlich 1 1 Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel * These authors contributed equally to this work Correspondence to: Marcelo Ehrlich, email: marceloe@post.tau.ac.il Eran Bacharach, email: eranba@tauex.tau.ac.il Keywords: human metapneumovirus, epizootic hemorrhagic disease virus, epigenetic silencing, interferon, prostate cancer cells Received: March 21, 2016 Accepted: May 13, 2016 Published: June 28, 2016 ABSTRACT Interferons (IFNs) induce anti-viral programs, regulate immune responses, and exert anti-proliferative effects. To escape anti-tumorigenic effects of IFNs, malignant cells attenuate JAK/STAT signaling and expression of IFN stimulated genes (ISGs). Such attenuation may enhance the susceptibility of tumor cells to oncolytic virotherapy. Here we studied genetic and epigenetic mechanisms of interference with JAK/STAT signaling and their contribution to susceptibility of prostate cancer cells to viral infection. Bioinformatics analysis of gene-expression in cohorts of prostate cancer patients revealed genetic and epigenetic interference with the IFN program. To correlate lack of IFN signaling and susceptibility to viral infection and oncolysis; we employed LNCaP prostate cancer cells as cellular model, and the human metapneumovirus and the epizootic hemorrhagic disease virus as infectious agents. In LNCaP cells, JAK1 is silenced by bi-allelic inactivating mutations and epigenetic silencing, which also silences ISGs. Chemical inhibition of epigenetic silencing partially restored IFN-sensitivity, induced low levels of expression of selected ISGs and attenuated, but failed to block, viral infection and oncolysis. Since viral infection was not blocked by epigenetic modifiers, and these compounds may independently-induce anti-tumor effects, we propose that epigenetic modifiers and virotherapy are compatible in treatment of prostate tumors defective in JAK1 expression and IFN signaling.

N-myristoylation is the covalent attachment of myristic acid to the N terminus of proteins in eukaryotic cells. The matrix domain (MA) of HIV-1 Gag protein is N-myristoylated and plays an important role in virus budding. In screening for host factors that interact with HIV-1 MA, we found that heme oxygenase (HO-2) specifically binds the myristate moiety of Gag. HO-2 was also found to bind TRAM, an adaptor protein for Toll-like receptor 4 (TLR4), and thereby impact both virus replication and cellular inflammatory responses. A crystal structure revealed that HO-2 binds myristate via a hydrophobic channel adjacent to the heme-binding pocket. Inhibiting HO-2 expression, or blocking myristate binding with a heme analog, led to marked increases in virus production. HO-2 deficiency caused hyperresponsive TRAM-dependent TLR4 signaling and hypersensitivity to the TLR4 ligand lipopolysaccharide. Thus, HO-2 is a cellular myristate-binding protein that negatively regulates both virus replication and host inflammatory responses.

The original version of this Article contained an error in the Methods section ‘Viruses and drugs’. The timing for drug treatment of CHME3 4 × 4 or 293T cells with γ-secretase inhibitor or BACE1 inhibitor was incorrectly given as ‘1 day prior to infection or transfection’ and should have stated ‘4 or 6 h post transfection or infection, respectively’. This error is now corrected in both the PDF and HTML versions of the Article.