Functional Properties and Genetic Relatedness of the Fusion and Hemagglutinin-Neuraminidase Proteins of a Mumps Virus-Like Bat Virus

Abstract

A bat virus with high phylogenetic relatedness to human mumps virus (MuV) was identified recently at the nucleic acid level. We analyzed the functional activities of the hemagglutinin-neuraminidase (HN) and the fusion (F) proteins of the bat virus (batMuV) and compared them to the respective proteins of a human isolate. Transfected cells expressing the F and HN proteins of batMuV were recognized by antibodies directed against these proteins of human MuV, indicating that both viruses are serologically related. Fusion, hemadsorption, and neuraminidase activities were demonstrated for batMuV, and either bat-derived protein could substitute for its human MuV counterpart in inducing syncytium formation when coexpressed in different mammalian cell lines, including chiropteran cells. Cells expressing batMuV glycoproteins were shown to have lower neuraminidase activity. The syncytia were smaller, and they were present in lower numbers than those observed after coexpression of the corresponding glycoproteins of a clinical isolate of MuV (hMuV). The phenotypic differences in the neuraminidase and fusion activity between the glycoproteins of batMuV and hMuV are explained by differences in the expression level of the HN and F proteins of the two viruses. In the case of the F protein, analysis of chimeric proteins revealed that the signal peptide of the bat MuV fusion protein is responsible for the lower surface expression. These results indicate that the surface glycoproteins of batMuV are serologically and functionally related to those of hMuV, raising the possibility of bats as a reservoir for interspecies transmission. IMPORTANCEThe recently described MuV-like bat virus is unique among other recently identified human-like bat-associated viruses because of its high sequence homology (approximately 90% in most genes) to its human counterpart. Although it is not known if humans can be infected by batMuV, the antigenic relatedness between the bat and human forms of the virus suggests that humans carrying neutralizing antibodies against MuV are protected from infection by batMuV. The close functional relationship between MuV and batMuV is demonstrated by cooperation of the respective HN and F proteins to induce syncytium formation in heterologous expression studies. An interesting feature of the glycoproteins of batMuV is the downregulation of the fusion activity by the signal peptide of F, which has not been reported for other paramyxoviruses. These results are important contributions for risk assessment and for a better understanding of the replication strategy of batMuV.

Calu-3 cells are largely resistant to entry driven by filovirus glycoproteins and the entry defect can be rescued by directed expression of DC-SIGN or cathepsin L

“…Expression plasmids encoding for the envelope glycoproteins of EBOV, BDBV, TAFV, RESTV, SUDV, MARV, LLOV, NiV, MuV, LASV, LCMV, MACV and VSV have been described previously (Hoffmann et al, 2016;Wrensch et al, 2014;Krüger et al, 2015). The plasmids required for the trVLP system (Watt et al, 2014) and VP30-luciferase containing particles have also been described before (Hoffmann et al, 2017).…”

The Hemagglutinin of Bat-Associated Influenza Viruses Is Activated by TMPRSS2 for pH-Dependent Entry into Bat but Not Human Cells

“…We inoculated cell lines from different host species, including those standardly used for FLUAV research, as well as cell lines derived from different bat species (Table 1), as they are the natural reservoir for batFLUAV. We chose bat cell lines known to be susceptible to infection by viruses of different families [28,29,31] and previously used to functionally characterize surface glycoproteins of bat-borne viruses [28,36,38]. It is well established that FLUAV-HA depends on proteolytic cleavage by host cell proteases to transit into an active form [12] and it has been previously reported that batFLUAV can be activated by exogenous trypsin [39][40][41].…”

Entry, Replication, Immune Evasion, and Neurotoxicity of Synthetically Engineered Bat-Borne Mumps Virus

“…Viral RNA of batMuV, a virus closely related to hMuVs, has been detected in an African fruit bat, but no infectious virus has been isolated. To date, studies of batMuV have been limited to either expression of individual batMuV proteins in cell cultures (Kr€ uger et al, 2015) or generation of recombinant chimeric hMuVs modified to encode the batMuV glycoprotein genes (Katoh et al, 2016;Kr€ uger et al, 2016;Beaty et al, 2017). However, in the absence of the use of authentic batMuV, the significance of these observations remains unclear.…”

“…Cells were fixed with 4% paraformaldehyde and permeabilized with 0.2% Triton X-100. Viral proteins were detected by incubation with antibodies directed against MuV N (N 5495, mouse), P (P 2037, mouse), M (M 2124, mouse) (Ö rvell, 1984), the cytoplasmic tail of MuV F (rabbit) (Kr€ uger et al, 2015), the ectodomain of MuV HN (rabbit) (Ö rvell, 1978) or neutralizing antibodies against MuV Kilham strain (rabbit) (Ö rvell et al, 1997) in a humidity chamber for 1 h. HA-labeled V, I and SH proteins were detected by incubation with antibodies directed against the HA epitope (mouse, Sigma-Aldrich). Cellular NF-kB p65 was detected by incubation with polyclonal NF-kB p65 antibodies (rabbit, Thermo Fisher Scientific).…”