Biology subjects

Bircher, C.

Publications and source records attributed to Bircher, C..

3 recordsLinked to original sources

bioRxiv2024

Globoside is an essential intracellular factor required for parvovirus B19 endosomal escape in erythroid progenitor cells

Human parvovirus B19 (B19V), like most parvoviruses, possesses phospholipase A2 (PLA2) activity, which is thought to mediate endosomal escape by membrane disruption. Here, we challenge this model and find evidence for a mechanism of B19V entry mediated by the glycosphingolipid globoside without endosome disruption and retrograde transport to the Golgi. We show that B19V PLA2 activity requires specific calcium levels and pH conditions that are not optimal in endosomes. Accordingly, endosomal membrane integrity was maintained during B19V entry. Furthermore, endosomes remained intact when loaded with MS2 bacteriophage particles pseudotyped with multiple B19V PLA2 subunits, providing superior enzymatic potential compared to native B19V. In globoside knockout cells, incoming viruses are arrested in the endosomal compartment and the infection is blocked. Infection can be rescued by promoting endosomal leakage with polyethyleneimine (PEI), demonstrating the essential role of globoside in facilitating endosomal escape. Incoming virus colocalizes with Golgi markers and interfering with Golgi function blocks infection, suggesting that globoside-mediated entry involves the Golgi compartment, which provides conditions favorable for the lipolytic PLA2. Our study challenges the current model of B19V entry and identifies globoside as an essential intracellular receptor required for endosomal escape.

microbiology↗

bioRxiv2022

Methylene blue, Mycophenolic acid, Posaconazole, and Niclosamide inhibit SARS-CoV-2Omicron variant BA.1 infection of human airway epithelial explant cultures

Sublineages of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) Omicron variants continue to amass mutations in the spike (S) glycoprotein, which leads to immune evasion and rapid spread of the virus across the human population. Here we demonstrate the susceptibility of the Omicron variant BA.1 (B.1.1.529.1) to four repurposable drugs, Methylene blue (MB), Mycophenolic acid (MPA), Posaconazole (POS), and Niclosamide (Niclo) in post-exposure treatments of primary human airway cell cultures. MB, MPA, POS, and Niclo are known to block infection of human nasal and bronchial airway epithelial explant cultures (HAEEC) with the Wuhan strain, and four variants of concern (VoC), Alpha (B.1.1.7), Beta (B.1.351), Gamma (B.1.1.28), Delta (B.1.617.2) (1, 2). Our results not only show broad anti-coronavirus effects of MB, MPA, POS and Niclo, but also demonstrate that the Omicron variant BA.1 (B.1.1.529.1) sheds infectious virus from HAEEC over at least 15 days, and maintains both intracellular and extracellular viral genomic RNA without overt toxicity, suggesting viral persistence. The data underscore the broad effects of MB, MPA, POS, and Niclo against SARS-CoV-2 and the currently circulating VoC, and reinforce the concept of repurposing drugs in clinical trials against COVID-19.

microbiology↗

bioRxiv2021

Human parvovirus B19 interacts with globoside under acidic conditions as an essential step in endocytic trafficking

The glycosphingolipid (GSL) globoside (Gb4) is essential for parvovirus B19 (B19V) infection. Historically considered the cellular receptor of B19V, the role of Gb4 and its interaction with B19V are controversial. In this study, we applied artificial viral particles, genetically modified cells, and specific competitors to address the interplay between the virus and the GSL. Our findings demonstrate that Gb4 is not involved in the binding or internalization process of the virus into permissive erythroid cells, a function that corresponds to the VP1u cognate receptor. However, Gb4 is essential at a post-internalization step before the delivery of the single-stranded viral DNA into the nucleus. In susceptible erythroid Gb4 knockout cells, incoming viruses were arrested in the endosomal compartment, showing no cytoplasmic spreading of capsids as observed in Gb4-expressing cells. Hemagglutination and binding assays revealed that pH acts as a switch to modulate the affinity between the virus and the GSL. Capsids interact with Gb4 exclusively under acidic conditions and dissociate at neutral pH. Inducing a specific Gb4-mediated attachment to permissive erythroid cells by acidification of the extracellular environment led to a non-infectious uptake of the virus, indicating that low pH-mediated binding to the GSL initiates active membrane processes resulting in vesicle formation. In summary, this study provides mechanistic insight into the interaction of B19V with Gb4. The strict pH-dependent binding to the ubiquitously expressed GSL prevents the redirection of the virus to nonpermissive tissues while promoting the interaction in acidic intracellular compartments as an essential step in infectious endocytic trafficking. Author summaryThe neutral glycosphingolipid globoside (Gb4) has been historically considered the cellular receptor of B19V, however, its wide expression profile does not correlate well with the restricted tropism of the virus. Here, we show that Gb4 is essential for the infection at a step following virus uptake and before the delivery of the viral ssDNA into the nucleus. B19V interacts with Gb4 exclusively under acidic conditions, prohibiting the interaction on the plasma membrane and promoting it inside the acidic endosomal compartments, which are engaged by the virus and the GSL after internalization. In the absence of Gb4, incoming viruses are retained in the endocytic compartment and the infection is aborted. This study reveals the mechanism of the interaction between the virus and the glycosphingolipid and redefines the role of Gb4 as an essential intracellular partner required for infectious entry.

microbiology↗