Fitness selection of hyperfusogenic measles virus F proteins associated with neuropathogenic phenotypes

Abstract

Measles virus (MeV) is resurgent and caused >200,000 deaths in 2019. MeV infection can establish a chronic latent infection of the brain that can recrudesce months to years after recovery from the primary infection. Recrudescent MeV leads to fatal subacute sclerosing panencephalitis (SSPE) or measles inclusion body encephalitis (MIBE) as the virus spreads across multiple brain regions. Most clinical isolates of SSPE/MIBE strains show mutations in the fusion (F) gene that result in a hyperfusogenic phenotype in vitro and allow for efficient spread in primary human neurons. Wild-type MeV receptor binding protein (RBP) is indispensable for manifesting these mutant F phenotypes, even though neurons lack canonical MeV receptors (CD150/SLAMF1 or Nectin-4). How such hyperfusogenic F mutants are selected for, and whether they confer a fitness advantage for efficient neuronal spread is unresolved. To better understand the fitness landscape that allows for the selection of such hyperfusogenic F mutants, we conducted a screen of ≥3.1x105 MeV-F point mutants in their genomic context. We rescued and amplified our genomic MeV-F mutant libraries in BSR-T7 cells under conditions where MeV-F-T461I (a known SSPE mutant), but not wild-type MeV can spread. We recovered known SSPE mutants but also characterized at least 15 novel hyperfusogenic F mutations with a SSPE phenotype. Structural mapping of these mutants onto the pre-fusion MeV-F trimer confirm and extend our understanding of the fusion regulatory domains in MeV-F. Our list of hyperfusogenic F mutants is a valuable resource for future studies into MeV neuropathogenesis and the regulation of paramyxovirus fusion.

SARS-CoV-2 spike P681R mutation, a hallmark of the Delta variant, enhances viral fusogenicity and pathogenicity

“…Regarding this, the HIV-1 variants with higher fusogenicity have been isolated from AIDS patients, but the enhanced fusogenicity does not promote viral replication in in vitro cell cultures (Sterjovski et al, 2007). Similarly, the measles virus (Paramyxoviridae) harboring the deficient mutation in viral matrix protein (Cathomen et al, 1998) and substitution mutations in viral fusion protein (Ikegame et al, 2021;Watanabe et al, 2013) are highly fusogenic and efficiently expands via cell-cell fusion. However, the growth kinetics of the mutated measles virus with higher fusogenicity in in vitro cell cultures is less efficient than the parental virus (Cathomen et al, 1998).…”

“…Therefore, the discrepancy between the efficacy of viral growth in in vitro cell cultures and viral fusogenicity is not specific for SARS-CoV-2. Rather, the higher fusogenicity is associated with the severity of viral pathogenicity such as HIV-1 encephalitis (Rossi et al, 2008) and fatal subacute sclerosing panencephalitis, which is caused by measles virus infection in brain (Ikegame et al, 2021;Watanabe et al, 2013). Although the association between the COVID-19 severity and/or unusual symptoms caused by SARS-CoV-2 infection and the P681R mutation remains unclear, an early report from the PRE suggests the B.1.617.2 variant, which bears the P681R mutation, may be more pathogenic than the B.1.1.7 lineage (PHE, 2021).…”

Zoonotic potential of a novel bat morbillivirus

“…1a, bottom row), suggesting a degree of promiscuity. We quanti ed these differential syncytia formation results on an image cytometer as described 15 (Fig. 1b).…”

“…Genome coding plasmids for MeV; (p(+) MV323-AcGFP) and CDV; pCDV-5804P were kindly gifted from Dr. Makoto Takeda 42 and Dr. Veronica von Messling respectively 43 . We transferred the MeV genome sequence into pEMC vector, adding an optimal T7 promotor, a hammer head ribozyme, and we introduced an eGFP transcriptional unit at the head of the genome (pEMC-IC323-eGFP), which is reported in the previous study 15 .…”

Molecular signatures in cetacean morbillivirus and host species proteomes: Unveiling the evolutionary dynamics of an enigmatic pathogen?

“…Moreover, while human neurons do not express SLAM and nectin‐4, the latter is expressed by cells of the canine central nervous system and is involved in CDV neurovirulence 28,29 . Furthermore, mutations at the phosphoprotein (P) and the matrix (M) genes resulting in defective M protein, or at the fusion (F) gene producing hyperfusogenic F protein 30–32 have been reported to promote cell‐to‐cell spread of MeV nucleocapsid (NC) in infected human brains and to correlate with the aforementioned neuropathogenic phenotype. In addition, a novel molecular mechanism was described recently, where host cell adhesion molecules 1 (CADM1) and 2 (CADM2) interact in cis with MeV H in neurons as well as in other cells lacking SLAM and nectin‐4, thereby allowing membrane fusion and cell‐to‐cell trans‐synaptic spread 33 .…”