Enhanced stability of M1 protein mediated by a phospho-resistant mutation promotes the replication of prevailing avian influenza virus in mammals

Abstract

Avian influenza virus (AIV) can evolve multiple strategies to combat host antiviral defenses and establish efficient infectivity in mammals, including humans. H9N2 AIV and its reassortants (such as H5N6 and H7N9 viruses) pose an increasing threat to human health; however, the mechanisms involved in their increased virulence remain poorly understood. We previously reported that the M1 mutation T37A has become predominant among chicken H9N2 isolates in China. Here, we report that, since 2010, this mutation has also been found in the majority of human isolates of H9N2 AIV and its emerging reassortants. The T37A mutation of M1 protein enhances the replication of H9N2 AIVs in mice and in human cells. Interestingly, having A37 instead of T37 increases the M1 protein stability and resistance to proteasomal degradation. Moreover, T37 of the H9N2 M1 protein is phosphorylated by protein kinase G (PKG), and this phosphorylation induces the rapid degradation of M1 and reduces viral replication. Similar effects are also observed in the novel H5N6 virus. Additionally, ubiquitination at K187 contributes to M1-37T degradation and decreased replication of the virus harboring T37 in the M1 protein. The prevailing AIVs thereby evolve a phospho-resistant mutation in the M1 protein to avoid viral protein degradation by host factors, which is advantageous in terms of replication in mammalian hosts.

Continued Circulation of Highly Pathogenic H5 Influenza Viruses in Vietnamese Live Bird Markets in 2018–2021

“…The viruses characterized here also possessed a few sequence nucleotide polymorphisms in the M1 gene ( Supplemental Table S3 ). Two of these may be associated with biological functions: the M1-T37A substitution increased the infectivity of an H9N2 influenza virus [ 79 ] by increasing M1 stability [ 80 ], and the M1-A227S substitution affected nucleocytoplasmic transport [ 81 ]. We currently do not know whether the M1-37A/T and M1-227A/T polymorphisms detected in this study similarly influence the respective H5N6 viruses.…”

Highly Pathogenic H5 Influenza Viruses Isolated between 2016 and 2017 in Vietnamese Live Bird Markets

“…In addition to the polymerase and NP genes, an M1-A37T polymorphism was detected for 1.6% of A/duck/Vietnam/HN3668/2017 sequence reads ( Supplemental Table S4 ); interestingly, the M1-T37A mutation has been reported to increase M1 stability [ 81 ] and the infectivity of an H9N2 virus [ 62 ]. A/duck/Vietnam/HN3668/2017 also encoded an M2-V27I subpopulation ( Supplemental Table S4 ); this amino acid substitution confers resistance to adamantine [ 82 ].…”

Pathogenicity and virulence of influenza

“…The D30N substitution changes the shape of H5N1 viral particles from filamentous to spherical, although the mechanism by which the virion shape affects viral pathogenicity is unknown [ 115 ]. M1 T37A of the H9N2 virus abolishes the phosphorylation site to stabilize the M1 protein and increases viral replication in mice and human cells [ 116 ].…”