Publications by authors named "Daniel Sauter"

95 Publications

International Scientific Collaboration Is Needed to Bridge Science to Society: USERN2020 Consensus Statement.

SN Compr Clin Med 2021 May 11:1-5. Epub 2021 May 11.

http://usern.org.

Scientific collaboration has been a critical aspect of the development of all fields of science, particularly clinical medicine. It is well understood that myriads of benefits can be yielded by interdisciplinary and international collaboration. For instance, our rapidly growing knowledge on COVID-19 and vaccine development could not be attained without expanded collaborative activities. However, achieving fruitful results requires mastering specific tactics in collaborative efforts. These activities can enhance our knowledge, which ultimately benefits society. In addition to tackling the issue of the invisible border between different countries, institutes, and disciplines, the border between the scientific community and society needs to be addressed as well. International and transdisciplinary approaches can potentially be the best solution for bridging science and society. The Universal Scientific Education and Research Network (USERN) is a non-governmental, non-profit organization and network to promote professional, scientific research and education worldwide. The fifth annual congress of USERN was held in Tehran, Iran, in a hybrid manner on November 7-10, 2020, with key aims of bridging science to society and facilitating borderless science. Among speakers of the congress, a group of top scientists unanimously agreed on The USERN 2020 consensus, which is drafted with the goal of connecting society with scientific scholars and facilitating international and interdisciplinary scientific activities in all fields, including clinical medicine.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s42399-021-00896-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8111052PMC
May 2021

Systematic functional analysis of SARS-CoV-2 proteins uncovers viral innate immune antagonists and remaining vulnerabilities.

Cell Rep 2021 05 27;35(7):109126. Epub 2021 Apr 27.

Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany. Electronic address:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evades most innate immune responses but may still be vulnerable to some. Here, we systematically analyze the impact of SARS-CoV-2 proteins on interferon (IFN) responses and autophagy. We show that SARS-CoV-2 proteins synergize to counteract anti-viral immune responses. For example, Nsp14 targets the type I IFN receptor for lysosomal degradation, ORF3a prevents fusion of autophagosomes and lysosomes, and ORF7a interferes with autophagosome acidification. Most activities are evolutionarily conserved. However, SARS-CoV-2 Nsp15 antagonizes IFN signaling less efficiently than the orthologs of closely related RaTG13-CoV and SARS-CoV-1. Overall, SARS-CoV-2 proteins counteract autophagy and type I IFN more efficiently than type II or III IFN signaling, and infection experiments confirm potent inhibition by IFN-γ and -λ1. Our results define the repertoire and selected mechanisms of SARS-CoV-2 innate immune antagonists but also reveal vulnerability to type II and III IFN that may help to develop safe and effective anti-viral approaches.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2021.109126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8078906PMC
May 2021

Switching Sides: How Endogenous Retroviruses Protect Us from Viral Infections.

J Virol 2021 05 24;95(12). Epub 2021 May 24.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

Long disregarded as junk DNA or genomic dark matter, endogenous retroviruses (ERVs) have turned out to represent important components of the antiviral immune response. These remnants of once-infectious retroviruses not only regulate cellular immune activation, but may even directly target invading viral pathogens. In this Gem, we summarize mechanisms by which retroviral fossils protect us from viral infections. One focus will be on recent advances in the role of ERVs as regulators of antiviral gene expression.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/JVI.02299-20DOI Listing
May 2021

Structural basis for GTP-induced dimerization and antiviral function of guanylate-binding proteins.

Proc Natl Acad Sci U S A 2021 Apr;118(15)

School of Life Sciences, Tianjin University, Tianjin, 300072, China;

Guanylate-binding proteins (GBPs) form a family of dynamin-related large GTPases which mediate important innate immune functions. They were proposed to form oligomers upon GTP binding/hydrolysis, but the molecular mechanisms remain elusive. Here, we present crystal structures of C-terminally truncated human GBP5 (hGBP5), comprising the large GTPase (LG) and middle (MD) domains, in both its nucleotide-free monomeric and nucleotide-bound dimeric states, together with nucleotide-free full-length human GBP2. Upon GTP-loading, hGBP5 forms a closed face-to-face dimer. The MD of hGBP5 undergoes a drastic movement relative to its LG domain and forms extensive interactions with the LG domain and MD of the pairing molecule. Disrupting the MD interface (for hGBP5) or mutating the hinge region (for hGBP2/5) impairs their ability to inhibit HIV-1. Our results point to a GTP-induced dimerization mode that is likely conserved among all GBP members and provide insights into the molecular determinants of their antiviral function.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2022269118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8054025PMC
April 2021

Sarbecovirus ORF6 proteins hamper induction of interferon signaling.

Cell Rep 2021 03 12;34(13):108916. Epub 2021 Mar 12.

Division of Systems Virology, Department of Infectious Disease Control, International Research Center for Infectious Diseases, Institute of Medical Science, The University of Tokyo, Tokyo 1088639, Japan; CREST, Japan Science and Technology Agency, Saitama 3220012, Japan. Electronic address:

The presence of an ORF6 gene distinguishes sarbecoviruses such as severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 from other betacoronaviruses. Here we show that ORF6 inhibits induction of innate immune signaling, including upregulation of type I interferon (IFN) upon viral infection as well as type I and III IFN signaling. Intriguingly, ORF6 proteins from SARS-CoV-2 lineages are more efficient antagonists of innate immunity than their orthologs from SARS-CoV lineages. Mutational analyses identified residues E46 and Q56 as important determinants of the antagonistic activity of SARS-CoV-2 ORF6. Moreover, we show that the anti-innate immune activity of ORF6 depends on its C-terminal region and that ORF6 inhibits nuclear translocation of IRF3. Finally, we identify naturally occurring frameshift/nonsense mutations that result in an inactivating truncation of ORF6 in approximately 0.2% of SARS-CoV-2 isolates. Our findings suggest that ORF6 contributes to the poor IFN activation observed in individuals with coronavirus disease 2019 (COVID-19).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2021.108916DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7953434PMC
March 2021

Ozonation products from trace organic chemicals in municipal wastewater and from metformin: peering through the keyhole with supercritical fluid chromatography-mass spectrometry.

Water Res 2021 May 9;196:117024. Epub 2021 Mar 9.

Helmholtz Centre for Environmental Research - UFZ, Department of Analytical Chemistry, Permoserstrasse 15, 04318 Leipzig, Germany; University of Leipzig, Institute for Analytical Chemistry, Linnéstrasse 3, 04103 Leipzig, Germany. Electronic address:

Ozonation is an important process to further reduce the trace organic chemicals (TrOCs) in treated municipal wastewater before discharge into surface waters, and is expected to form products that are more oxidized and more polar than their parent compounds. Many of these ozonation products (OPs) are biodegradable and thus removed by post-treatment (e.g., aldehydes). Most studies on OPs of TrOCs in wastewater rely on reversed-phase liquid chromatography- mass spectrometry (RPLC-MS), which is not suited for highly polar analytes. In this study, supercritical fluid chromatography combined with high resolution MS (SFC-HRMS) was applied in comparison to the generic RPLC-HRMS to search for OPs in ozonated wastewater treatment plant effluent at pilot-scale. While comparable results were obtained from these two techniques during suspect screenings for known OPs, a total of 23 OPs were only observed by SFC-HRMS via non-targeted screening. Several SFC-only OPs were proposed as the derivatives of methoxymethylmelamines, phenolic sulfates/sulfonates, and metformin; the latter was confirmed by laboratory-scale ozonation experiments. A complete ozonation pathway of metformin, a widespread and extremely hydrophilic TrOC in aquatic environment, was elaborated based on SFC-HRMS analysis. Five of the 10 metformin OPs are reported for the first time in this study. Three different dual-media filters were compared as post-treatments, and a combination of sand/anthracite and fresh post-granular activated carbon proved most effective in OPs removal due to the additional adsorption capacity. However, six SFC-only OPs, two of which originating from metformin, appeared to be persistent during all post-treatments, raising concerns on their occurrence in drinking water sources impacted by wastewater.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.watres.2021.117024DOI Listing
May 2021

Targeting of CXCR4 by the Naturally Occurring CXCR4 Antagonist EPI-X4 in Waldenström's Macroglobulinemia.

Cancers (Basel) 2021 Feb 16;13(4). Epub 2021 Feb 16.

Comprehensive Cancer Center Ulm, Institute of Experimental Cancer Research, University Hospital Ulm, 89081 Ulm, Germany.

CXCR4 expression and downstream signaling have been identified as key factors in malignant hematopoiesis. Thus, up to 40% of all patients with Waldenström's macroglobulinemia (WM) carry an activating mutation of CXCR4 that leads to a more aggressive clinical course and inferior outcome upon treatment with the Bruton's tyrosine kinase inhibitor ibrutinib. Nevertheless, little is known about physiological mechanisms counteracting CXCR4 signaling in hematopoietic neoplasms. Recently, the endogenous human peptide EPI-X4 was identified as a natural CXCR4 antagonist that effectively blocks CXCL12-mediated receptor internalization and suppresses the migration and invasion of cancer cells towards a CXCL12 gradient. Here, we demonstrate that EPI-X4 efficiently binds to CXCR4 of WM cells and decreases their migration towards CXCL12. The CXCR4 inhibitory activity of EPI-X4 is accompanied by reduced expression of genes involved in MAPK signaling and energy metabolism. Notably, the anti-WM activity of EPI-X4 could be further augmented by the rational design of EPI-X4 derivatives showing higher binding affinity to CXCR4. In summary, these data demonstrate that a naturally occurring anti-CXCR4 peptide is able to interfere with WM cell behaviour, and that optimized derivatives of EPI-X4 may represent a promising approach in suppressing growth promoting CXCR4 signaling in WM.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/cancers13040826DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7920274PMC
February 2021

Evolutionary conflicts and adverse effects of antiviral factors.

Elife 2021 Jan 15;10. Epub 2021 Jan 15.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

Human cells are equipped with a plethora of antiviral proteins protecting them against invading viral pathogens. In contrast to apoptotic or pyroptotic cell death, which serves as ultima ratio to combat viral infections, these cell-intrinsic restriction factors may prevent or at least slow down viral spread while allowing the host cell to survive. Nevertheless, their antiviral activity may also have detrimental effects on the host. While the molecular mechanisms underlying the antiviral activity of restriction factors are frequently well investigated, potential undesired effects of their antiviral functions on the host cell are hardly explored. With a focus on antiretroviral proteins, we summarize in this review how individual restriction factors may exert adverse effects as trade-off for efficient defense against attacking pathogens.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7554/eLife.65243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7811402PMC
January 2021

SARS-CoV-2 Is Restricted by Zinc Finger Antiviral Protein despite Preadaptation to the Low-CpG Environment in Humans.

mBio 2020 10 16;11(5). Epub 2020 Oct 16.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

Recent evidence shows that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is sensitive to interferons (IFNs). However, the most effective types of IFNs and the underlying antiviral effectors remain to be defined. Here, we show that zinc finger antiviral protein (ZAP), which preferentially targets CpG dinucleotides in viral RNA sequences, restricts SARS-CoV-2. We further demonstrate that ZAP and its cofactors KHNYN and TRIM25 are expressed in human lung cells. Type I, II, and III IFNs all strongly inhibited SARS-CoV-2 and further induced ZAP expression. Comprehensive sequence analyses revealed that SARS-CoV-2 and its closest relatives from horseshoe bats showed the strongest CpG suppression among all known human and bat coronaviruses, respectively. Nevertheless, endogenous ZAP expression restricted SARS-CoV-2 replication in human lung cells, particularly upon treatment with IFN-α or IFN-γ. Both the long and the short isoforms of human ZAP reduced SARS-CoV-2 RNA expression levels, but the former did so with greater efficiency. Finally, we show that the ability to restrict SARS-CoV-2 is conserved in ZAP orthologues of the reservoir bat and potential intermediate pangolin hosts of human coronaviruses. Altogether, our results show that ZAP is an important effector of the innate response against SARS-CoV-2, although this pandemic pathogen emerged from zoonosis of a coronavirus that was preadapted to the low-CpG environment in humans. Although interferons inhibit SARS-CoV-2 and have been evaluated for treatment of coronavirus disease 2019 (COVID-19), the most effective types and antiviral effectors remain to be defined. Here, we show that IFN-γ is particularly potent in restricting SARS-CoV-2 and in inducing expression of the antiviral factor ZAP in human lung cells. Knockdown experiments revealed that endogenous ZAP significantly restricts SARS-CoV-2. We further show that CpG dinucleotides which are specifically targeted by ZAP are strongly suppressed in the SARS-CoV-2 genome and that the two closest horseshoe bat relatives of SARS-CoV-2 show the lowest genomic CpG content of all coronavirus sequences available from this reservoir host. Nonetheless, both the short and long isoforms of human ZAP reduced SARS-CoV-2 RNA levels, and this activity was conserved in horseshoe bat and pangolin ZAP orthologues. Our findings indicating that type II interferon is particularly efficient against SARS-CoV-2 and that ZAP restricts this pandemic viral pathogen might promote the development of effective immune therapies against COVID-19.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mBio.01930-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7569149PMC
October 2020

HIV-1 infection activates endogenous retroviral promoters regulating antiviral gene expression.

Nucleic Acids Res 2020 11;48(19):10890-10908

Institute of Molecular Virology, Ulm University Medical Center, Ulm 89081, Germany.

Although endogenous retroviruses (ERVs) are known to harbor cis-regulatory elements, their role in modulating cellular immune responses remains poorly understood. Using an RNA-seq approach, we show that several members of the ERV9 lineage, particularly LTR12C elements, are activated upon HIV-1 infection of primary CD4+ T cells. Intriguingly, HIV-1-induced ERVs harboring transcription start sites are primarily found in the vicinity of immunity genes. For example, HIV-1 infection activates LTR12C elements upstream of the interferon-inducible genes GBP2 and GBP5 that encode for broad-spectrum antiviral factors. Reporter assays demonstrated that these LTR12C elements drive gene expression in primary CD4+ T cells. In line with this, HIV-1 infection triggered the expression of a unique GBP2 transcript variant by activating a cryptic transcription start site within LTR12C. Furthermore, stimulation with HIV-1-induced cytokines increased GBP2 and GBP5 expression in human cells, but not in macaque cells that naturally lack the GBP5 gene and the LTR12C element upstream of GBP2. Finally, our findings suggest that GBP2 and GBP5 have already been active against ancient viral pathogens as they suppress the maturation of the extinct retrovirus HERV-K (HML-2). In summary, our findings uncover how human cells can exploit remnants of once-infectious retroviruses to regulate antiviral gene expression.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gkaa832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7641743PMC
November 2020

SARS-CoV-2 ORF3b Is a Potent Interferon Antagonist Whose Activity Is Increased by a Naturally Occurring Elongation Variant.

Cell Rep 2020 09 4;32(12):108185. Epub 2020 Sep 4.

Division of Systems Virology, Department of Infectious Disease Control, International Research Center for Infectious Diseases, Institute of Medical Science, the University of Tokyo, Tokyo 1088639, Japan. Electronic address:

One of the features distinguishing SARS-CoV-2 from its more pathogenic counterpart SARS-CoV is the presence of premature stop codons in its ORF3b gene. Here, we show that SARS-CoV-2 ORF3b is a potent interferon antagonist, suppressing the induction of type I interferon more efficiently than its SARS-CoV ortholog. Phylogenetic analyses and functional assays reveal that SARS-CoV-2-related viruses from bats and pangolins also encode truncated ORF3b gene products with strong anti-interferon activity. Furthermore, analyses of approximately 17,000 SARS-CoV-2 sequences identify a natural variant in which a longer ORF3b reading frame was reconstituted. This variant was isolated from two patients with severe disease and further increased the ability of ORF3b to suppress interferon induction. Thus, our findings not only help to explain the poor interferon response in COVID-19 patients but also describe the emergence of natural SARS-CoV-2 quasispecies with an extended ORF3b gene that may potentially affect COVID-19 pathogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2020.108185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7473339PMC
September 2020

Nuclear PYHIN proteins target the host transcription factor Sp1 thereby restricting HIV-1 in human macrophages and CD4+ T cells.

PLoS Pathog 2020 08 6;16(8):e1008752. Epub 2020 Aug 6.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

Members of the family of pyrin and HIN domain containing (PYHIN) proteins play an emerging role in innate immunity. While absent in melanoma 2 (AIM2) acts a cytosolic sensor of non-self DNA and plays a key role in inflammasome assembly, the γ-interferon-inducible protein 16 (IFI16) restricts retroviral gene expression by sequestering the transcription factor Sp1. Here, we show that the remaining two human PYHIN proteins, i.e. myeloid cell nuclear differentiation antigen (MNDA) and pyrin and HIN domain family member 1 (PYHIN1 or IFIX) share this antiretroviral function of IFI16. On average, knock-down of each of these three nuclear PYHIN proteins increased infectious HIV-1 yield from human macrophages by more than an order of magnitude. Similarly, knock-down of IFI16 strongly increased virus transcription and production in primary CD4+ T cells. The N-terminal pyrin domain (PYD) plus linker region containing a nuclear localization signal (NLS) were generally required and sufficient for Sp1 sequestration and anti-HIV-1 activity of IFI16, MNDA and PYHIN1. Replacement of the linker region of AIM2 by the NLS-containing linker of IFI16 resulted in a predominantly nuclear localization and conferred direct antiviral activity to AIM2 while attenuating its ability to form inflammasomes. The reverse change caused nuclear-to-cytoplasmic relocalization of IFI16 and impaired its antiretroviral activity but did not result in inflammasome assembly. We further show that the Zn-finger domain of Sp1 is critical for the interaction with IFI16 supporting that pyrin domains compete with DNA for Sp1 binding. Finally, we found that human PYHIN proteins also inhibit Hepatitis B virus and simian vacuolating virus 40 as well as the LINE-1 retrotransposon. Altogether, our data show that IFI16, PYHIN1 and MNDA restrict HIV-1 and other viral pathogens by interfering with Sp1-dependent gene expression and support an important role of nuclear PYHIN proteins in innate antiviral immunity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.ppat.1008752DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7433898PMC
August 2020

Vpu modulates DNA repair to suppress innate sensing and hyper-integration of HIV-1.

Nat Microbiol 2020 10 20;5(10):1247-1261. Epub 2020 Jul 20.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

To avoid innate sensing and immune control, human immunodeficiency virus type 1 (HIV-1) has to prevent the accumulation of viral complementary DNA species. Here, we show that the late HIV-1 accessory protein Vpu hijacks DNA repair mechanisms to promote degradation of nuclear viral cDNA in cells that are already productively infected. Vpu achieves this by interacting with RanBP2-RanGAP1*SUMO1-Ubc9 SUMO E3-ligase complexes at the nuclear pore to reprogramme promyelocytic leukaemia protein nuclear bodies and reduce SUMOylation of Bloom syndrome protein, unleashing end degradation of viral cDNA. Concomitantly, Vpu inhibits RAD52-mediated homologous repair of viral cDNA, preventing the generation of dead-end circular forms of single copies of the long terminal repeat and permitting sustained nucleolytic attack. Our results identify Vpu as a key modulator of the DNA repair machinery. We show that Bloom syndrome protein eliminates nuclear HIV-1 cDNA and thereby suppresses immune sensing and proviral hyper-integration. Therapeutic targeting of DNA repair may facilitate the induction of antiviral immunity and suppress proviral integration replenishing latent HIV reservoirs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41564-020-0753-6DOI Listing
October 2020

Convergent Evolution of HLA-C Downmodulation in HIV-1 and HIV-2.

mBio 2020 07 14;11(4). Epub 2020 Jul 14.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

HLA-C-mediated antigen presentation induces the killing of human immunodeficiency virus (HIV)-infected CD4 T cells by cytotoxic T lymphocytes (CTLs). To evade killing, many HIV-1 group M strains decrease HLA-C surface levels using their accessory protein Vpu. However, some HIV-1 group M isolates lack this activity, possibly to prevent the activation of natural killer (NK) cells. Analyzing diverse primate lentiviruses, we found that Vpu-mediated HLA-C downregulation is not limited to pandemic group M but is also found in HIV-1 groups O and P as well as several simian immunodeficiency viruses (SIVs). We show that Vpu targets HLA-C primarily at the protein level, independently of its ability to suppress NF-κB-driven gene expression, and that in some viral lineages, HLA-C downregulation may come at the cost of efficient counteraction of the restriction factor tetherin. Remarkably, HIV-2, which does not carry a gene, uses its accessory protein Vif to decrease HLA-C surface expression. This Vif activity requires intact binding sites for the Cullin5/Elongin ubiquitin ligase complex but is separable from its ability to counteract APOBEC3G. Similar to HIV-1 Vpu, the degree of HIV-2 Vif-mediated HLA-C downregulation varies considerably among different virus isolates. In agreement with opposing selection pressures , we show that the reduction of HLA-C surface levels by HIV-2 Vif is accompanied by increased NK cell-mediated killing. In summary, our results highlight the complex role of HLA-C in lentiviral infections and demonstrate that HIV-1 and HIV-2 have evolved at least two independent mechanisms to decrease HLA-C levels on infected cells. Genome-wide association studies suggest that HLA-C expression is a major determinant of viral load set points and CD4 T cell counts in HIV-infected individuals. On the one hand, efficient HLA-C expression enables the killing of infected cells by cytotoxic T lymphocytes (CTLs). On the other hand, HLA-C sends inhibitory signals to natural killer (NK) cells and enhances the infectivity of newly produced HIV particles. HIV-1 group M viruses modulate HLA-C expression using the accessory protein Vpu, possibly to balance CTL- and NK cell-mediated immune responses. Here, we show that the second human immunodeficiency virus, HIV-2, can use its accessory protein Vif to evade HLA-C-mediated restriction. Furthermore, our mutational analyses provide insights into the underlying molecular mechanisms. In summary, our results reveal how the two human AIDS viruses modulate HLA-C, a key component of the antiviral immune response.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mBio.00782-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7360927PMC
July 2020

Decreased, Deformed, Defective-How HIV-1 Vpu Targets Peroxisomes.

mBio 2020 05 26;11(3). Epub 2020 May 26.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

Peroxisomes are found in essentially all eukaryotic cells and have been described as important hubs in innate sensing and the induction of type III interferons upon viral infection. Nevertheless, it remains poorly investigated how viral pathogens modulate biogenesis or function of peroxisomes to evade innate sensing and restriction. In a recent study, Hobman and colleagues found that the accessory viral protein u (Vpu) of HIV-1 inhibits peroxisome activity by depleting cellular peroxisome pools. This depletion could be ascribed to a Vpu-dependent induction of four microRNAs (miRNAs) that suppress the expression of peroxisomal biogenesis factors PEX2, PEX7, PEX11B, and PEX13. Although the downstream effects on antiretroviral gene expression and HIV-1 replication remain to be determined, these findings provide important insights into peroxisome biogenesis and the modulation of cell organelles by HIV-1 Vpu.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mBio.00967-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7251213PMC
May 2020

A Placenta Derived C-Terminal Fragment of β-Hemoglobin With Combined Antibacterial and Antiviral Activity.

Front Microbiol 2020 6;11:508. Epub 2020 Apr 6.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

The placenta acts as physical and immunological barrier against the transmission of viruses and bacteria from mother to fetus. However, the specific mechanisms by which the placenta protects the developing fetus from viral and bacterial pathogens are poorly understood. To identify placental peptides and small proteins protecting from viral and bacterial infections, we generated a peptide library from 10 kg placenta by chromatographic means. Screening the resulting 250 fractions against Herpes-Simplex-Virus 2 (HSV-2), which is rarely transmitted through the placenta, in a cell-based system identified two adjacent fractions with significant antiviral activity. Further rounds of chromatographic purification and anti-HSV-2 testing allowed to purify the bioactive peptide. Mass spectrometry revealed the presence of a 36-mer derived from the C-terminal region of the hemoglobin β subunit. The purified and corresponding chemically synthesized peptide, termed HBB(112-147), inhibited HSV-2 infection in a dose-dependent manner, with a mean IC in the median μg/ml range. Full-length hemoglobin tetramer had no antiviral activity. HBB(112-147) did not impair infectivity by direct targeting of the virions but prevented HSV-2 infection at the cell entry level. The peptide was inactive against Human Immunodeficiency Virus Type 1, Rubella and Zika virus infection, suggesting a specific anti-HSV-2 mechanism. Notably, HBB(112-147) has previously been identified as broad-spectrum antibacterial agent. It is abundant in placenta, reaching concentrations between 280 and 740 μg/ml, that are well sufficient to inhibit HSV-2 and prototype Gram-positive and -negative bacteria. We here additionally show, that HBB(112-147) also acts potently against strains (including a multi-drug resistant strain) in a dose dependent manner, while full-length hemoglobin is inactive. Interestingly, the antibacterial activity of HBB(112-147) was increased under acidic conditions, a hallmark of infection and inflammatory conditions. Indeed, we found that HBB(112-147) is released from the hemoglobin precursor by Cathepsin D and Napsin A, acidic proteases highly expressed in placental and other tissues. We propose that upon viral or bacterial infection, the abundant hemoglobin precursor is proteolytically processed to release HBB(112-147), a broadly active antimicrobial innate immune defense peptide.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fmicb.2020.00508DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7153485PMC
April 2020

Nef-Mediated CD3-TCR Downmodulation Dampens Acute Inflammation and Promotes SIV Immune Evasion.

Cell Rep 2020 02;30(7):2261-2274.e7

Institute of Molecular Virology - Ulm University Medical Center, Meyerhofstraße 1, 89081 Ulm, Germany. Electronic address:

The inability of Nef to downmodulate the CD3-T cell receptor (TCR) complex distinguishes HIV-1 from other primate lentiviruses and may contribute to its high virulence. However, the role of this Nef function in virus-mediated immune activation and pathogenicity remains speculative. Here, we selectively disrupted this Nef activity in SIV and analyzed the consequences for the virological, immunological, and clinical outcome of infection in rhesus macaques. The inability to downmodulate CD3-TCR does not impair viral replication during acute infection but is associated with increased immune activation and antiviral gene expression. Subsequent early reversion in three of six animals suggests strong selective pressure for this Nef function and is associated with high viral loads and progression to simian AIDS. In the absence of reversions, however, viral replication and the clinical course of infection are attenuated. Thus, Nef-mediated downmodulation of CD3 dampens the inflammatory response to simian immunodeficiency virus (SIV) infection and seems critical for efficient viral immune evasion.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2020.01.069DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7052273PMC
February 2020

CpG Frequency in the 5' Third of the Gene Determines Sensitivity of Primary HIV-1 Strains to the Zinc-Finger Antiviral Protein.

mBio 2020 01 14;11(1). Epub 2020 Jan 14.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

CpG dinucleotide suppression has been reported to allow HIV-1 to evade inhibition by the zinc-finger antiviral protein (ZAP). Here, we show that primate lentiviruses display marked differences in CpG frequencies across their genome, ranging from 0.44% in simian immunodeficiency virus SIVwrc from Western red colobus to 2.3% in SIVmon infecting mona monkeys. Moreover, functional analyses of a large panel of human and simian immunodeficiency viruses revealed that the magnitude of CpG suppression does not correlate with their susceptibility to ZAP. However, we found that the number of CpG dinucleotides within a region of ∼700 bases at the 5' end of the gene determines ZAP sensitivity of primary HIV-1 strains but not of HIV-2. Increased numbers of CpGs in this region were associated with reduced mRNA expression and viral protein production. ZAP sensitivity profiles of chimeric simian-human immunodeficiency viruses (SHIVs) expressing different HIV-1 genes were highly similar to those of the corresponding HIV-1 strains. The frequency of CpGs in the identified region correlated with differences in clinical progression rates. Thus, the CpG frequency in a specific part of , rather than the overall genomic CpG content, governs the susceptibility of HIV-1 to ZAP and might affect viral pathogenicity Evasion of the zinc-finger antiviral protein (ZAP) may drive CpG dinucleotide suppression in HIV-1 and many other viral pathogens but the viral determinants of ZAP sensitivity are poorly defined. Here, we examined CpG suppression and ZAP sensitivity in a large number of primate lentiviruses and demonstrate that their genomic frequency of CpGs varies substantially and does not correlate with ZAP sensitivity. We further show that the number of CpG residues in a defined region at the 5' end of the gene together with structural features plays a key role in HIV-1 susceptibility to ZAP and correlates with differences in clinical progression rates in HIV-1-infected individuals. Our identification of a specific part of as a major determinant of HIV-1 susceptibility to ZAP restriction provides a basis for future studies of the underlying inhibitory mechanisms and their potential relevance in the pathogenesis of AIDS.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mBio.02903-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6960287PMC
January 2020

Furin-mediated protein processing in infectious diseases and cancer.

Clin Transl Immunology 2019 5;8(8):e1073. Epub 2019 Aug 5.

Institute of Molecular Virology Ulm University Medical Center Ulm Germany.

Proteolytic cleavage regulates numerous processes in health and disease. One key player is the ubiquitously expressed serine protease furin, which cleaves a plethora of proteins at polybasic recognition motifs. Mammalian substrates of furin include cytokines, hormones, growth factors and receptors. Thus, it is not surprising that aberrant furin activity is associated with a variety of disorders including cancer. Furthermore, the enzymatic activity of furin is exploited by numerous viral and bacterial pathogens, thereby enhancing their virulence and spread. In this review, we describe the physiological and pathophysiological substrates of furin and discuss how dysregulation of a simple proteolytic cleavage event may promote infectious diseases and cancer. One major focus is the role of furin in viral glycoprotein maturation and pathogenicity. We also outline cellular mechanisms regulating the expression and activation of furin and summarise current approaches that target this protease for therapeutic intervention.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/cti2.1073DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6682551PMC
August 2019

Primary HIV-1 Strains Use Nef To Downmodulate HLA-E Surface Expression.

J Virol 2019 10 30;93(20). Epub 2019 Sep 30.

Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany

Human immunodeficiency virus type 1 (HIV-1) has evolved elaborate ways to evade immune cell recognition, including downregulation of classical HLA class I (HLA-I) from the surfaces of infected cells. Recent evidence identified HLA-E, a nonclassical HLA-I, as an important part of the antiviral immune response to HIV-1. Changes in HLA-E surface levels and peptide presentation can prompt both CD8 T-cell and natural killer (NK) cell responses to viral infections. Previous studies reported unchanged or increased HLA-E levels on HIV-1-infected cells. Here, we examined HLA-E surface levels following infection of CD4 T cells with primary HIV-1 strains and observed that a subset downregulated HLA-E. Two primary strains of HIV-1 that induced the strongest reduction in surface HLA-E expression were chosen for further testing. Expression of single Nef or Vpu proteins in a T-cell line, as well as tail swap experiments exchanging the cytoplasmic tail of HLA-A2 with that of HLA-E, demonstrated that Nef modulated HLA-E surface levels and targeted the cytoplasmic tail of HLA-E. Furthermore, infection of primary CD4 T cells with HIV-1 mutants showed that a lack of functional Nef (and Vpu to some extent) impaired HLA-E downmodulation. Taken together, the results of this study demonstrate for the first time that HIV-1 can downregulate HLA-E surface levels on infected primary CD4 T cells, potentially rendering them less vulnerable to CD8 T-cell recognition but at increased risk of NKG2A NK cell killing. For almost two decades, it was thought that HIV-1 selectively downregulated the highly expressed HLA-I molecules HLA-A and HLA-B from the cell surface in order to evade cytotoxic-T-cell recognition, while leaving HLA-C and HLA-E molecules unaltered. It was stipulated that HIV-1 infection thereby maintained inhibition of NK cells via inhibitory receptors that bind HLA-C and HLA-E. This concept was recently revised when a study showed that primary HIV-1 strains reduce HLA-C surface levels, whereas the cell line-adapted HIV-1 strain NL4-3 lacks this ability. Here, we demonstrate that infection with distinct primary HIV-1 strains results in significant downregulation of surface HLA-E levels. Given the increasing evidence for HLA-E as an important modulator of CD8 T-cell and NKG2A NK cell functions, this finding has substantial implications for future immunomodulatory approaches aimed at harnessing cytotoxic cellular immunity against HIV.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/JVI.00719-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6798123PMC
October 2019

[Postoperative mobilization after total hip arthroplasty : Measured by Fitbit activity trackers].

Orthopade 2020 Mar;49(3):230-237

Orthopädie und Traumatologie, Kantonsspital Münsterlingen, Münsterlingen, Schweiz.

Background: Patients are becoming increasingly more independent and self-determined, in addition to having shorter post-operative hospitalization. This is why it is more important than ever to actively involve patients in the follow-up treatment. The question arises as to whether post-operative rehabilitation can be improved with modern devices.

Methods: As part of a prospective study, the post-operative mobilization was recorded and analyzed by Fitbit®-activity-trackers between 05/2016 and 08/2017 in 100 patients who received a THA. 50 men (Ø 70.6y) and 50 women (Ø 71.1y) were included. Furthermore, the patients were interviewed about their acceptance of the Fitbit®-wristband.

Results: The average hospital stay was 7.98 days (SD ± 1.76). The number of steps on the first post-operative day was 712 (SD ± 617). On average (during total hospitalization), 1528 (SD ± 1076) steps were completed daily. One day before discharge, the average number of steps was 2165 (SD ± 1570) on that particular day. There were no gender differences in age and pre-operative Harris hip scores (♂55.3 vs. ♀53.9). Also, there were no statistically significant differences in the number of steps on the first postoperative day (♂745 vs. ♀678). A statistically significant result can be found in the number of steps prior to discharge: on this day, the men took 2483 and the women 1846 steps (p = 0.04). 42% of our patients own a modern smartphone and are able to operate software applications. 52% of the patients found the activity tracker to be motivating, 65% were open to new technologies (e.g. activity trackers) in the hospital. 14% did not check at all or only queried their wristband data once a day, 65% queried 2-4 times/day, and 21% retrieved the data >5 times/day.

Discussion: On average, 1528 steps were completed daily. In a comparison of the men and women, the men were only able to demonstrate significantly more steps than the women on the day prior to discharge. The men had significantly shorter hospital stays than the women. The younger the patients, the more mobile they were. A majority of patients are familiar with and/or interested in new technologies. This interest and curiosity should be consciously used for integration in the post-operative treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00132-019-03768-9DOI Listing
March 2020

Upregulation of BST-2 by Type I Interferons Reduces the Capacity of Vpu To Protect HIV-1-Infected Cells from NK Cell Responses.

mBio 2019 06 18;10(3). Epub 2019 Jun 18.

Centre de Recherche du CHUM, Montreal, Quebec, Canada

The HIV-1 accessory protein Vpu enhances viral release by counteracting the restriction factor BST-2. Furthermore, Vpu promotes NK cell evasion by downmodulating cell surface NTB-A and PVR, known ligands of the NK cell receptors NTB-A and DNAM-1, respectively. While it has been established that Vpu's transmembrane domain (TMD) is required for the interaction and intracellular sequestration of BST-2, NTB-A, and PVR, it remains unclear how Vpu manages to target these proteins simultaneously. In this study, we show that upon upregulation, BST-2 is preferentially downregulated by Vpu over its other TMD substrates. We found that type I interferon (IFN)-mediated BST-2 upregulation greatly impairs the ability of Vpu to downregulate NTB-A and PVR. Our results suggest that occupation of Vpu by BST-2 affects its ability to downregulate other TMD substrates. Accordingly, knockdown of BST-2 increases Vpu's potency to downmodulate NTB-A and PVR in the presence of type I IFN treatment. Moreover, we show that expression of human BST-2, but not that of the macaque orthologue, decreases Vpu's capacity to downregulate NTB-A. Importantly, we show that type I IFNs efficiently sensitize HIV-1-infected cells to NTB-A- and DNAM-1-mediated direct and antibody-dependent NK cell responses. Altogether, our results reveal that type I IFNs decrease Vpu's polyfunctionality, thus reducing its capacity to protect HIV-1-infected cells from NK cell responses. The restriction factor BST-2 and the NK cell ligands NTB-A and PVR are among a growing list of membrane proteins found to be downregulated by HIV-1 Vpu. BST-2 antagonism enhances viral release, while NTB-A and PVR downmodulation contributes to NK cell evasion. However, it remains unclear how Vpu can target multiple cellular factors simultaneously. Here we provide evidence that under physiological conditions, BST-2 is preferentially targeted by Vpu over NTB-A and PVR. Specifically, we show that type I IFNs decrease Vpu's polyfunctionality by upregulating BST-2, thus reducing its capacity to protect HIV-1-infected cells from NK cell responses. This indicates that there is a hierarchy of Vpu substrates upon IFN treatment, revealing that for the virus, targeting BST-2 as part of its resistance to IFN takes precedence over evading NK cell responses. This reveals a potential weakness in HIV-1's immunoevasion mechanisms that may be exploited therapeutically to harness NK cell responses against HIV-1.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mBio.01113-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6581860PMC
June 2019

IFI16 Targets the Transcription Factor Sp1 to Suppress HIV-1 Transcription and Latency Reactivation.

Cell Host Microbe 2019 06 4;25(6):858-872.e13. Epub 2019 Jun 4.

Institute of Molecular Virology, Ulm University Medical Center, 89081 Ulm, Germany. Electronic address:

The interferon γ-inducible protein 16 (IFI16) is known as immune sensor of retroviral DNA intermediates. We show that IFI16 restricts HIV-1 independently of immune sensing by binding and inhibiting the host transcription factor Sp1 that drives viral gene expression. This antiretroviral activity and ability to bind Sp1 require the N-terminal pyrin domain and nuclear localization of IFI16, but not the HIN domains involved in DNA binding. Highly prevalent clade C HIV-1 strains are more resistant to IFI16 and less dependent on Sp1 than other HIV-1 subtypes. Furthermore, inhibition of Sp1 by IFI16 or pharmacologically by Mithramycin A suppresses reactivation of latent HIV-1 in CD4 T cells. Finally, IFI16 also inhibits retrotransposition of LINE-1, known to engage Sp1, and murine IFI16 homologs restrict Friend retrovirus replication in mice. Thus, IFI16 restricts retroviruses and retrotransposons by interfering with Sp1-dependent gene expression, and evasion from this restriction may facilitate spread of HIV-1 subtype C.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chom.2019.05.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6681451PMC
June 2019

N4BP1 restricts HIV-1 and its inactivation by MALT1 promotes viral reactivation.

Nat Microbiol 2019 09 27;4(9):1532-1544. Epub 2019 May 27.

Department of Medical Chemistry, Graduate School of Medicine, Kyoto University, Kyoto, Japan.

RNA-modulating factors not only regulate multiple steps of cellular RNA metabolism, but also emerge as key effectors of the immune response against invading viral pathogens including human immunodeficiency virus type-1 (HIV-1). However, the cellular RNA-binding proteins involved in the establishment and maintenance of latent HIV-1 reservoirs have not been extensively studied. Here, we screened a panel of 62 cellular RNA-binding proteins and identified NEDD4-binding protein 1 (N4BP1) as a potent interferon-inducible inhibitor of HIV-1 in primary T cells and macrophages. N4BP1 harbours a prototypical PilT N terminus-like RNase domain and inhibits HIV-1 replication by interacting with and degrading viral mRNA species. Following activation of CD4 T cells, however, N4BP1 undergoes rapid cleavage at Arg 509 by the paracaspase named mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1). Mutational analyses and knockout studies revealed that MALT1-mediated inactivation of N4BP1 facilitates the reactivation of latent HIV-1 proviruses. Taken together, our findings demonstrate that the RNase N4BP1 is an efficient restriction factor of HIV-1 and suggest that inactivation of N4BP1 by induction of MALT1 activation might facilitate elimination of latent HIV-1 reservoirs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41564-019-0460-3DOI Listing
September 2019

Guanylate-Binding Proteins 2 and 5 Exert Broad Antiviral Activity by Inhibiting Furin-Mediated Processing of Viral Envelope Proteins.

Cell Rep 2019 05;27(7):2092-2104.e10

Institute of Molecular Virology, Ulm University Medical Center, Ulm 89081, Germany. Electronic address:

Guanylate-binding protein (GBP) 5 is an interferon (IFN)-inducible cellular factor reducing HIV-1 infectivity by an incompletely understood mechanism. Here, we show that this activity is shared by GBP2, but not by other members of the human GBP family. GBP2/5 decrease the activity of the cellular proprotein convertase furin, which mediates conversion of the HIV-1 envelope protein (Env) precursor gp160 into mature gp120 and gp41. Because this process primes HIV-1 Env for membrane fusion, viral particles produced in the presence of GBP2/5 are poorly infectious due to increased incorporation of non-functional gp160. Furin activity is critical for the processing of envelope glycoproteins of many viral pathogens. Consistently, GBP2/5 also inhibit Zika, measles, and influenza A virus replication and decrease infectivity of viral particles carrying glycoproteins of Marburg and murine leukemia viruses. Collectively, our results show that GPB2/5 exert broad antiviral activity by suppressing the activity of the virus-dependency factor furin.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.04.063DOI Listing
May 2019

HIV-1 Vpu is a potent transcriptional suppressor of NF-κB-elicited antiviral immune responses.

Elife 2019 02 5;8. Epub 2019 Feb 5.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

Many viral pathogens target innate sensing cascades and/or cellular transcription factors to suppress antiviral immune responses. Here, we show that the accessory viral protein U (Vpu) of HIV-1 exerts broad immunosuppressive effects by inhibiting activation of the transcription factor NF-κB. Global transcriptional profiling of infected CD4 +T cells revealed that -deficient HIV-1 strains induce substantially stronger immune responses than the respective wild type viruses. Gene set enrichment analyses and cytokine arrays showed that Vpu suppresses the expression of NF-κB targets including interferons and restriction factors. Mutational analyses demonstrated that this immunosuppressive activity of Vpu is independent of its ability to counteract the restriction factor and innate sensor tetherin. However, Vpu-mediated inhibition of immune activation required an arginine residue in the cytoplasmic domain that is critical for blocking NF-κB signaling downstream of tetherin. In summary, our findings demonstrate that HIV-1 Vpu potently suppresses NF-κB-elicited antiviral immune responses at the transcriptional level.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7554/eLife.41930DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6372280PMC
February 2019

Key Viral Adaptations Preceding the AIDS Pandemic.

Cell Host Microbe 2019 01;25(1):27-38

Institute of Molecular Virology, Ulm University Medical Centre, Ulm 89081, Germany. Electronic address:

HIV, the causative agent of AIDS, has a complex evolutionary history involving several cross-species transmissions and recombination events as well as changes in the repertoire and function of its accessory genes. Understanding these events and the adaptations to new host species provides key insights into innate defense mechanisms, viral dependencies on cellular factors, and prerequisites for the emergence of the AIDS pandemic. In addition, understanding the factors and adaptations required for the spread of HIV in the human population helps to better assess the risk of future lentiviral zoonoses and provides clues to how improved control of viral replication can be achieved. Here, we summarize our current knowledge on viral features and adaptations preceding the AIDS pandemic. We aim at providing a viral point of view, focusing on known key hurdles of each cross-species transmission and the mechanisms that HIV and its simian precursors evolved to overcome them.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chom.2018.12.002DOI Listing
January 2019

A Mass Spectrometry-Based Profiling of Interactomes of Viral DDB1- and Cullin Ubiquitin Ligase-Binding Proteins Reveals NF-κB Inhibitory Activity of the HIV-2-Encoded Vpx.

Front Immunol 2018 19;9:2978. Epub 2018 Dec 19.

Institute for Virology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.

Viruses and hosts are situated in a molecular arms race. To avoid morbidity and mortality, hosts evolved antiviral restriction factors. These restriction factors exert selection pressure on the viruses and drive viral evolution toward increasingly efficient immune antagonists. Numerous viruses exploit cellular DNA damage-binding protein 1 (DDB1)-containing Cullin RocA ubiquitin ligases (CRLs) to induce the ubiquitination and subsequent proteasomal degradation of antiviral factors expressed by their hosts. To establish a comprehensive understanding of the underlying protein interaction networks, we performed immuno-affinity precipitations for a panel of DDB1-interacting proteins derived from viruses such as mouse cytomegalovirus (MCMV, Murid herpesvirus [MuHV] 1), rat cytomegalovirus Maastricht MuHV2, rat cytomegalovirus English MuHV8, human cytomegalovirus (HCMV), hepatitis B virus (HBV), and human immunodeficiency virus (HIV). Cellular interaction partners were identified and quantified by mass spectrometry (MS) and validated by classical biochemistry. The comparative approach enabled us to separate unspecific interactions from specific binding partners and revealed remarkable differences in the strength of interaction with DDB1. Our analysis confirmed several previously described interactions like the interaction of the MCMV-encoded interferon antagonist pM27 with STAT2. We extended known interactions to paralogous proteins like the interaction of the HBV-encoded HBx with different Spindlin proteins and documented interactions for the first time, which explain functional data like the interaction of the HIV-2-encoded Vpr with Bax. Additionally, several novel interactions were identified, such as the association of the HIV-2-encoded Vpx with the transcription factor RelA (also called p65). For the latter interaction, we documented a functional relevance in antagonizing NF-κB-driven gene expression. The mutation of the DDB1 binding interface of Vpx significantly impaired NF-κB inhibition, indicating that Vpx counteracts NF-κB signaling by a DDB1- and CRL-dependent mechanism. In summary, our findings improve the understanding of how viral pathogens hijack cellular DDB1 and CRLs to ensure efficient replication despite the expression of host restriction factors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fimmu.2018.02978DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6305766PMC
October 2019

SIVcol Nef counteracts SERINC5 by promoting its proteasomal degradation but does not efficiently enhance HIV-1 replication in human CD4+ T cells and lymphoid tissue.

PLoS Pathog 2018 08 20;14(8):e1007269. Epub 2018 Aug 20.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany.

SERINC5 is a host restriction factor that impairs infectivity of HIV-1 and other primate lentiviruses and is counteracted by the viral accessory protein Nef. However, the importance of SERINC5 antagonism for viral replication and cytopathicity remained unclear. Here, we show that the Nef protein of the highly divergent SIVcol lineage infecting mantled guerezas (Colobus guereza) is a potent antagonist of SERINC5, although it lacks the CD4, CD3 and CD28 down-modulation activities exerted by other primate lentiviral Nefs. In addition, SIVcol Nefs decrease CXCR4 cell surface expression, suppress TCR-induced actin remodeling, and counteract Colobus but not human tetherin. Unlike HIV-1 Nef proteins, SIVcol Nef induces efficient proteasomal degradation of SERINC5 and counteracts orthologs from highly divergent vertebrate species, such as Xenopus frogs and zebrafish. A single Y86F mutation disrupts SERINC5 and tetherin antagonism but not CXCR4 down-modulation by SIVcol Nef, while mutation of a C-proximal di-leucine motif has the opposite effect. Unexpectedly, the Y86F change in SIVcol Nef had little if any effect on viral replication and CD4+ T cell depletion in preactivated human CD4+ T cells and in ex vivo infected lymphoid tissue. However, SIVcol Nef increased virion infectivity up to 10-fold and moderately increased viral replication in resting peripheral blood mononuclear cells (PBMCs) that were first infected with HIV-1 and activated three or six days later. In conclusion, SIVcol Nef lacks several activities that are conserved in other primate lentiviruses and utilizes a distinct proteasome-dependent mechanism to counteract SERINC5. Our finding that evolutionarily distinct SIVcol Nefs show potent anti-SERINC5 activity supports a relevant role of SERINC5 antagonism for viral fitness in vivo. Our results further suggest this Nef function is particularly important for virion infectivity under conditions of limited CD4+ T cell activation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.ppat.1007269DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6117100PMC
August 2018

Preadaptation of Simian Immunodeficiency Virus SIVsmm Facilitated Env-Mediated Counteraction of Human Tetherin by Human Immunodeficiency Virus Type 2.

J Virol 2018 09 29;92(18). Epub 2018 Aug 29.

Institute of Molecular Virology, Ulm University Medical Center, Ulm, Germany

The host restriction factor tetherin inhibits virion release from infected cells and poses a significant barrier to successful zoonotic transmission of primate lentiviruses to humans. While most simian immunodeficiency viruses (SIV), including the direct precursors of human immunodeficiency virus type 1 (HIV-1) and HIV-2, use their Nef protein to counteract tetherin in their natural hosts, they fail to antagonize the human tetherin ortholog. Pandemic HIV-1 group M and epidemic group O strains overcame this hurdle by adapting their Vpu and Nef proteins, respectively, whereas HIV-2 group A uses its envelope (Env) glycoprotein to counteract human tetherin. Whether or how the remaining eight groups of HIV-2 antagonize this antiviral factor has remained unclear. Here, we show that Nef proteins from diverse groups of HIV-2 do not or only modestly antagonize human tetherin, while their ability to downmodulate CD3 and CD4 is highly conserved. Experiments in transfected cell lines and infected primary cells revealed that not only Env proteins of epidemic HIV-2 group A but also those of a circulating recombinant form (CRF01_AB) and rare groups F and I decrease surface expression of human tetherin and significantly enhance progeny virus release. Intriguingly, we found that many SIVsmm Envs also counteract human as well as smm tetherin. Thus, Env-mediated tetherin antagonism in different groups of HIV-2 presumably stems from a preadaptation of their SIVsmm precursors to humans. In summary, we identified a phenotypic trait of SIVsmm that may have facilitated its successful zoonotic transmission to humans and the emergence of HIV-2. HIV-2 groups A to I resulted from nine independent cross-species transmission events of SIVsmm to humans and differ considerably in their prevalence and geographic spread. Thus, detailed characterization of these viruses offers a valuable means to elucidate immune evasion mechanisms and human-specific adaptations determining viral spread. In a systematic comparison of rare and epidemic HIV-2 groups and their simian SIVsmm counterparts, we found that the ability of Nef to downmodulate the primary viral entry receptor CD4 and the T cell receptor CD3 is conserved, while effects on CD28, CD74, and major histocompatibility complex class I surface expression vary considerably. Furthermore, we show that not only the Env proteins of HIV-2 groups A, AB, F, and I but also those of some SIVsmm isolates antagonize human tetherin. This finding helps to explain why SIVsmm has been able to cross the species barrier to humans on at least nine independent occasions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/JVI.00276-18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6146695PMC
September 2018