Multiple basic amino acids in the cleavage site of H7N9 hemagglutinin contribute to high virulence in mice

Abstract

Background: Avian influenza A (H7N9) virus has caused more than 1,500 cases of human infection since its emergence in early 2013. Displaying little or no pathogenicity in poultry, but a 40% case-fatality rate in humans, five waves of H7N9 human infections occurred in China during 2013-2017, caused solely by a low pathogenicity strain. However, avian isolates possessing a polybasic connecting peptide in the hemagglutinin (HA) protein were detected in mid-2016, indicating that a highly pathogenic virus had emerged and was cocirculating with the low pathogenicity strains.Methods: Here we characterize the pathogenicity of a newly emerged human H7N9 variant with a PEVPKRKRTAR/GLF insertion motif at the cleavage site of the HA protein in vitro and in vivo.Results: This variant replicates in MDCK cells independently of TPCK-trypsin, which is indicative of high pathogenicity in chickens. The 50% mouse lethal dose (MLD 50 ) of this novel isolate was less than 10 plaque forming units (PFU), compared with 3.16×10 4 for an identical virus lacking the polybasic insertion, indicating a high virulence phenotype.Conclusions: Our results demonstrate that the multiple basic amino acid insertion in the HA protein of the H7N9 variant confers high virulence in mammals, highlighting a potential risk to humans. Continuous viral surveillance is therefore necessary in the China region to improve pandemic preparedness.

Roles of host proteases in the entry of SARS-CoV-2

“…The polybasic site was reported to be associated with virulence and tropism of various viruses, most notably Yadati et al 2020;Bollavaram et al 2021;Choe et al 2006 in the hemagglutinin protein of avian influenza (Garten et al 1994;Stieneke-Gröber et al 1992;Decha et al 2008;Horimoto and Kawaoka 1995). The polybasic cleavage site has been directly linked to severe and systemic pathogenesis (Acland et al 1984;Schrauwen et al 2012) in bird populations, whereas influenza strains lacking the polybasic cleavage site are typically limited to the respiratory and gastrointestinal tracts (Bertram et al 2010;Song et al 2021). The S1/S2 cleavage facilitates more assessable RBD to the receptor ACE2 (Berger and Schaffitzel 2020), and receptor binding causes a conformational change of the S, resulting in exposure of the S2' site, and the proteolytic cleavage leads to expose the fusion peptide to cell membrane (Perlman et al 2020;Gallagher and Buchmeier 2001;Millet and Whittaker 2014;Bestle et al 2020;Papa et al 2021).…”

Generation of a pdmH1N1 2018 Influenza A Reporter Virus Carrying a mCherry Fluorescent Protein in the PA Segment

“…To date, pandemic H1N1 (pdmH1N1/2009) and H3N2 subtypes co-circulate with type B viruses worldwide ( Phipps et al., 2017 ). However, outbreaks of avian influenza viruses (i.e., H5N1, H7N9, and H9N2) in humans, although not resulting in a pandemic, show that exposure to infected poultry is the main risk factor for infection ( Centers for Disease, C. and Prevention, 1997 ; Song and Qin, 2020 ; Song et al., 2021 ). Moreover, the IAV-segmented genome structure easily undergoes reassortment among hosts and among various subtypes, which may result in novel pandemic strains that threaten human health ( Steel and Lowen, 2014 ).…”