Publications by authors named "Benoit Fischer"

8 Publications

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Phospholipidosis is a shared mechanism underlying the antiviral activity of many repurposed drugs against SARS-CoV-2.

bioRxiv 2021 Mar 24. Epub 2021 Mar 24.

Repurposing drugs as treatments for COVID-19 has drawn much attention. A common strategy has been to screen for established drugs, typically developed for other indications, that are antiviral in cells or organisms. Intriguingly, most of the drugs that have emerged from these campaigns, though diverse in structure, share a common physical property: cationic amphiphilicity. Provoked by the similarity of these repurposed drugs to those inducing phospholipidosis, a well-known drug side effect, we investigated phospholipidosis as a mechanism for antiviral activity. We tested 23 cationic amphiphilic drugs-including those from phenotypic screens and others that we ourselves had found-for induction of phospholipidosis in cell culture. We found that most of the repurposed drugs, which included hydroxychloroquine, azithromycin, amiodarone, and four others that have already progressed to clinical trials, induced phospholipidosis in the same concentration range as their antiviral activity; indeed, there was a strong monotonic correlation between antiviral efficacy and the magnitude of the phospholipidosis. Conversely, drugs active against the same targets that did not induce phospholipidosis were not antiviral. Phospholipidosis depends on the gross physical properties of drugs, and does not reflect specific target-based activities, rather it may be considered a confound in early drug discovery. Understanding its role in infection, and detecting its effects rapidly, will allow the community to better distinguish between drugs and lead compounds that more directly impact COVID-19 from the large proportion of molecules that manifest this confounding effect, saving much time, effort and cost.

One Sentence Summary: Drug-induced phospholipidosis is a single mechanism that may explain the efficacy of a wide-variety of therapeutics repurposed for COVID-19.
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http://dx.doi.org/10.1101/2021.03.23.436648DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8010720PMC
March 2021

Tankyrases Promote Homologous Recombination and Check Point Activation in Response to DSBs.

PLoS Genet 2016 Feb 4;12(2):e1005791. Epub 2016 Feb 4.

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.

DNA lesions are sensed by a network of proteins that trigger the DNA damage response (DDR), a signaling cascade that acts to delay cell cycle progression and initiate DNA repair. The Mediator of DNA damage Checkpoint protein 1 (MDC1) is essential for spreading of the DDR signaling on chromatin surrounding Double Strand Breaks (DSBs) by acting as a scaffold for PI3K kinases and for ubiquitin ligases. MDC1 also plays a role both in Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR) repair pathways. Here we identify two novel binding partners of MDC1, the poly (ADP-ribose) Polymerases (PARPs) TNKS1 and 2. We find that TNKSs are recruited to DNA lesions by MDC1 and regulate DNA end resection and BRCA1A complex stabilization at lesions leading to efficient DSB repair by HR and proper checkpoint activation.
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http://dx.doi.org/10.1371/journal.pgen.1005791DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4741384PMC
February 2016

Ubiquitin Receptor Protein UBASH3B Drives Aurora B Recruitment to Mitotic Microtubules.

Dev Cell 2016 Jan;36(1):63-78

Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Centre National de la Recherche Scientifique UMR 7104, Institut National de la Santé et de la Recherche Médicale U964, Université de Strasbourg, 67404 Illkirch, France. Electronic address:

Mitosis ensures equal segregation of the genome and is controlled by a variety of ubiquitylation signals on substrate proteins. However, it remains unexplored how the versatile ubiquitin code is read out during mitotic progression. Here, we identify the ubiquitin receptor protein UBASH3B as an important regulator of mitosis. UBASH3B interacts with ubiquitylated Aurora B, one of the main kinases regulating chromosome segregation, and controls its subcellular localization but not protein levels. UBASH3B is a limiting factor in this pathway and is sufficient to localize Aurora B to microtubules prior to anaphase. Importantly, targeting Aurora B to microtubules by UBASH3B is necessary for the timing and fidelity of chromosome segregation in human cells. Our findings uncover an important mechanism defining how ubiquitin attachment to a substrate protein is decoded during mitosis.
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http://dx.doi.org/10.1016/j.devcel.2015.12.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5400057PMC
January 2016

PI4K-beta and MKNK1 are regulators of hepatitis C virus IRES-dependent translation.

Sci Rep 2015 Sep 1;5:13344. Epub 2015 Sep 1.

Department of Medicine II, University of Freiburg, Freiburg, Germany.

Cellular translation is down-regulated by host antiviral responses. Picornaviridae and Flaviviridae including hepatitis C virus (HCV) evade this process using internal ribosomal entry sequences (IRESs). Although HCV IRES translation is a prerequisite for HCV replication, only few host factors critical for IRES activity are known and the global regulator network remains largely unknown. Since signal transduction is an import regulator of viral infections and the host antiviral response we combined a functional RNAi screen targeting the human signaling network with a HCV IRES-specific reporter mRNA assay. We demonstrate that the HCV host cell cofactors PI4K and MKNK1 are positive regulators of HCV IRES translation representing a novel pathway with a functional relevance for the HCV life cycle and IRES-mediated translation of viral RNA.
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http://dx.doi.org/10.1038/srep13344DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4555030PMC
September 2015

The human TREX-2 complex is stably associated with the nuclear pore basket.

J Cell Sci 2013 Jun 16;126(Pt 12):2656-67. Epub 2013 Apr 16.

Cellular Signaling and Nuclear Dynamics Program, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), CNRS UMR 7104, INSERM U964, Université de Strasbourg, BP 10142 - 67404 ILLKIRCH Cedex, CU de Strasbourg, France.

In eukaryotes, mRNA export involves many evolutionarily conserved factors that carry the nascent transcript to the nuclear pore complex (NPC). The THO/TREX complex couples transcription to mRNA export and recruits the mRNA export receptor NXF1 for the transport of messenger ribonucleoprotein particles (mRNP) to the NPC. The transcription and export complex 2 (TREX-2) was suggested to interact with NXF1 and to shuttle between transcription sites and the NPC. Here, we characterize the dynamics of human TREX-2 and show that it stably associates with the NPC basket. Moreover, the association of TREX-2 with the NPC requires the basket nucleoporins NUP153 and TPR, but is independent of transcription. Differential profiles of mRNA nuclear accumulation reveal that TREX-2 functions similarly to basket nucleoporins, but differently from NXF1. Thus, our results show that TREX-2 is an NPC-associated complex in mammalian cells and suggest that it is involved in putative NPC basket-related functions.
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http://dx.doi.org/10.1242/jcs.118000DOI Listing
June 2013

Cullin 3 mediates SRC-3 ubiquitination and degradation to control the retinoic acid response.

Proc Natl Acad Sci U S A 2011 Dec 6;108(51):20603-8. Epub 2011 Dec 6.

Department of Functional Genomics and Cancer, Institut National de la Santé et de la Recherche Médicale U964, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, Université de Strasbourg, BP 10142, 67404 Illkirch Cedex, France.

SRC-3 is an important coactivator of nuclear receptors including the retinoic acid (RA) receptor α. Most of SRC-3 functions are facilitated by changes in the posttranslational code of the protein that involves mainly phosphorylation and ubiquitination. We recently reported that SRC-3 is degraded by the proteasome in response to RA. Here, by using an RNAi E3-ubiquitin ligase entry screen, we identified CUL-3 and RBX1 as components of the E3 ubiquitin ligase involved in the RA-induced ubiquitination and subsequent degradation of SRC-3. We also show that the RA-induced ubiquitination of SRC-3 depends on its prior phosphorylation at serine 860 that promotes binding of the CUL-3-based E3 ligase in the nucleus. Finally, phosphorylation, ubiquitination, and degradation of SRC-3 cooperate to control the dynamics of transcription. In all, this process participates to the antiproliferative effect of RA.
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http://dx.doi.org/10.1073/pnas.1102572108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3251120PMC
December 2011

EGFR and EphA2 are host factors for hepatitis C virus entry and possible targets for antiviral therapy.

Nat Med 2011 May 24;17(5):589-95. Epub 2011 Apr 24.

Institut National de la Santé et de la Recherche Médicale, U748, Strasbourg, France.

Hepatitis C virus (HCV) is a major cause of liver disease, but therapeutic options are limited and there are no prevention strategies. Viral entry is the first step of infection and requires the cooperative interaction of several host cell factors. Using a functional RNAi kinase screen, we identified epidermal growth factor receptor and ephrin receptor A2 as host cofactors for HCV entry. Blocking receptor kinase activity by approved inhibitors broadly impaired infection by all major HCV genotypes and viral escape variants in cell culture and in a human liver chimeric mouse model in vivo. The identified receptor tyrosine kinases (RTKs) mediate HCV entry by regulating CD81-claudin-1 co-receptor associations and viral glycoprotein-dependent membrane fusion. These results identify RTKs as previously unknown HCV entry cofactors and show that tyrosine kinase inhibitors have substantial antiviral activity. Inhibition of RTK function may constitute a new approach for prevention and treatment of HCV infection.
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http://dx.doi.org/10.1038/nm.2341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938446PMC
May 2011

E6 proteins from diverse papillomaviruses self-associate both in vitro and in vivo.

J Mol Biol 2010 Feb 13;396(1):90-104. Epub 2009 Nov 13.

Ecole Supérieure de Biotechnologie de Strasbourg (IREBS, FRE 3211), Boulevard Sébastien Brant, BP 10413, 67412 Illkirch Cedex, France.

Papillomavirus E6 oncoproteins bind and often provoke the degradation of many cellular proteins important for the control of cell proliferation and/or cell death. Structural studies on E6 proteins have long been hindered by the difficulties of obtaining highly concentrated samples of recombinant E6. Here, we show that recombinant E6 proteins from eight human papillomavirus strains and one bovine papillomavirus strain exist as oligomeric and multimeric species. These species were characterized using a variety of biochemical and biophysical techniques, including analytical gel filtration, activity assays, surface plasmon resonance, electron microscopy and Fourier transform infrared spectroscopy. The characterization of E6 oligomers is facilitated by the fusion to the maltose binding protein, which slows the formation of higher-order multimeric species. The proportion of each oligomeric form varies depending on the viral strain considered. Oligomers appear to consist of folded units, which, in the case of high-risk mucosal human papillomavirus E6, retain binding to the ubiquitin ligase E6-associated protein and the capacity to degrade the proapoptotic protein p53. In addition to the small-size oligomers, E6 proteins spontaneously assemble into large organized multimeric structures, a process that is accompanied by a significant increase in the beta-sheet secondary structure content. Finally, co-localisation experiments using E6 equipped with different tags further demonstrate the occurrence of E6 self-association in eukaryotic cells. The ensemble of these data suggests that self-association is a general property of E6 proteins that occurs both in vitro and in vivo and might therefore be functionally relevant.
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http://dx.doi.org/10.1016/j.jmb.2009.11.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3900769PMC
February 2010
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