Gene-Specific Contributions to Mumps Virus Neurovirulence and Neuroattenuation

Abstract

Mumps virus (MuV) is highly neurotropic and was the leading cause of aseptic meningitis in the WesternHemisphere prior to widespread use of live attenuated MuV vaccines. Due to the absence of markers of virus neuroattenuation and neurovirulence, ensuring mumps vaccine safety has proven problematic, as demonstrated by the occurrence of aseptic meningitis in recipients of certain vaccine strains. Here we examined the genetic basis of MuV neuroattenuation and neurovirulence by generating a series of recombinant viruses consisting of combinations of genes derived from a cDNA clone of the neurovirulent wild-type 88-1961 strain (r88) and from a cDNA clone of the highly attenuated Jeryl Lynn vaccine strain (rJL). Testing of these viruses in rats demonstrated the ability of several individual rJL genes and gene combinations to significantly neuroattenuate r88, with the greatest effect imparted by the rJL nucleoprotein/matrix protein combination. Interestingly, no tested combination of r88 genes, including the nucleoprotein/matrix protein combination, was able to convert rJL into a highly neurovirulent virus, highlighting mechanistic differences between processes involved in neuroattenuation and neurovirulence.Mumps virus (MuV) is a paramyxovirus belonging to the Rubulavirus genus. The nonsegmented negative-sense genome of 15,384 nucleotides contains the following seven transcription units: the nucleoprotein (N), the V/phosphoprotein (V/P/ I), the matrix protein (M), the fusion protein (F), the small hydrophobic protein (SH), the hemagglutinin-neuraminidase protein (HN), and the large protein (L) genes. Each gene encodes a single protein, with the exception of the V/P/I gene (conventionally referred to as the P gene), which gives rise to additional mRNA species as a result of the cotranscriptional insertion of nontemplated G nucleotides between positions 461 and 466, the so-called editing site. Faithful transcription of the gene produces the V protein, whereas insertion of two G residues within the editing site produces an mRNA encoding the P protein, and insertion of four G residues produces an mRNA encoding the I protein, analogous to the W protein identified in other paramyxoviruses (9,20,28). The roles of the viral proteins in the life cycle of paramyxoviruses have been well described in the literature (9,12,20). Briefly, the N protein encapsidates the nascent viral RNA as it is being synthesized, forming a ribonucleoprotein (RNP) complex, which serves as the substrate for the viral RNA-dependent RNA polymerase (RdRp), formed by the P and L proteins. The HN glycoprotein mediates attachment of the virus to its cellular receptor (sialic acid) and, together with the F glycoprotein, mediates fusion of the virion membrane with the target cell membrane. Based on studies of related paramyxoviruses, the M protein is involved in assembling the RNP at the plasma membrane in regions containing the HN and F glycoproteins, presumably via interacting with the carboxy-terminal tail portion of the RNP-associated N protein and the cy...

Deep sequencing reveals persistence of cell-associated mumps vaccine virus in chronic encephalitis

“…MuV JL5 -London was characterised by the expansion of variants present at low frequency in the original vaccine, two of which have previously been described [8], as well as fixed de novo mutations in the M, N, P, L and F genes, a finding which again references those described for MV in SSPE. While most amino acid substitutions occurred in the M gene, in vitro data using the rat model implicates the F protein [3,16] as key for mumps virus neurovirulence in acute encephalitis [16,24] as well as for measles neurovirulence in SSPE [3]. The absence of within-host sequence diversity in the M and F ORFs ( Figure S5, Table S7) further suggests functional constraints on these genes and supports directional selection acting on one or more of the amino acid changes in these proteins favouring spread and replication of MuV JL5 in the brain.…”

Wild and attenuated vaccine RS-12 strains of mumps virus exhibit differences in amino acid sequences of their proteins

“…There is currently limited data available on sequencing of the full-length genomes of attenuated MuV vaccine strains. Although it was recently indicated that N/M proteins are involved in viral pathogenicity/attenuation of MuV (Sauder et al, 2011), these patterns have not been observed in all strains (Lemon et al, 2007;Malik et al, 2009;Liang et al, 2010;Xu et al, 2012). As a result, no unique differentiation marker has been found between parental wild and attenuated passages of different vaccine strains.…”

Genetic Variation in the HN and SH Genes of Mumps Viruses: A Comparison of Strains from Mumps Cases with and without Neurological Symptoms

“…The major genetic determinant of neurovirulence of the rodent-adapted Kilham strain appears to be the F gene [42]. While the neurovirulence of the wild-type MuV isolate 88-1961 seems to be a multigenic trait [43]. Such a scenario was described with the 88-1961 strain, where an additive effect on neuroattenuation of the two mutations – one in the HN protein and one in the L polymerase protein – was demonstrated [37].…”