15th December : Respiratory Viruses/Host Cell Interactions

Host Laboratory : Ali Amara ( Biology of Emerging Viruses, Institut de recherche Saint Louis, Paris)
Goujon Caroline, IRIM, Montpellier :  Intrinsic and innate immune defenses against respiratory viruses
Caroline will present some recent work from her team, using genome-wide and secondary screens in multiple model cell lines to identify novel genes regulating coronavirus replication.
Nell Saunders, Institut Pasteur, Paris : Unlocking the secrets of seasonal coronavirus HKU1 entry
Four endemic seasonal human coronaviruses causing common colds, HKU1, 229E, NL63 and OC43 circulate worldwide. After binding to cellular receptors, coronavirus spike proteins are primed for fusion by transmembrane-serine protease 2 (TMPRSS2) or endosomal cathepsins. NL63 uses angiotensin-converting enzyme 2 (ACE2) as a receptor, whereas 229E uses human aminopeptidase-N. HKU1 and OC43 spikes bind cells through 9-O40 acelytated sialic acid but their protein receptors remain unknown. Here, we show that TMPRSS2 is a functional receptor for HKU1. TMPRSS2 triggers HKU1 spike-mediated cell42 cell fusion and pseudovirus infection. Catalytically inactive TMPRSS2 mutants do not cleave HKU1 spike but allow pseudovirus infection. Furthermore, TMPRSS2 binds with high affinity to the HKU1 receptor binding domain (RBD) (Kd 334 and 137 nM for HKU1A and HKU1B genotypes) but not to SARS-CoV-2. Conserved amino acids within HKU1 RBD are essential for binding to TMPRSS2 and pseudovirus infection. Newly designed anti-TMPRSS2 nanobodies potently inhibit HKU1 spike attachment to TMPRSS2, fusion and pseudovirus infection. The nanobodies also reduce infection of primary human bronchial cells by an authentic HKU-1 virus. Our findings illustrate the various evolution strategies of coronaviruses, which use TMPRSS2 to either directly bind to target cells or to prime their spike for membrane fusion and entry.

Tim Krischuns, Institut Pasteur, Paris : The influenza polymerase and the host RNA polymerase II
The current model is that the influenza virus RNA-dependent RNA polymerase (FluPol) binds either to host RNA polymerase II (RNAP II) or to the acidic nuclear phosphoprotein 32 (ANP32), which drives its conformation and activity towards transcription or replication of the viral genome, respectively. Here, we provide evidence that the FluPol-RNAP II binding interface, beyond its well-acknowledged function in cap-snatching during transcription initiation, has also a pivotal role in replication of the viral genome. Using a combination of cell-based and in vitro approaches, we show that the RNAP II C-terminal-domain, jointly with ANP32, enhances FluPol replication activity. We observe successive conformational changes to switch from a transcriptase to a replicase conformation in the presence of the bound RNPAII C-terminal domain and propose a model in which the host RNAP II is the anchor for transcription and replication of the viral genome. Our data open new perspectives on the spatial coupling of viral transcription and replication and the coordinated balance between these two activities

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