A single amino acid change in the E2 spike protein of a virulent strain of Semliki Forest virus attenuates pathogenicity

Abstract

The virulent strain SFV4 of Semliki Forest virus (SFV), produced from the infectious clone pSP6-SFV4, is lethal after intranasal (i.n.) infection of adult mice and for pregnant mice after intraperitoneal (i.p.) infection. In contrast, the A7 strain of SFV is avirulent when given i.n. to adult mice, but induces fetal death in pregnant mice after i.p. infection. The nucleotide and deduced amino acid sequences of part of the core and all of the envelope region of A7-SFV were determined and compared to those of SFV4. A7 differed from SFV4 at 80 nucleotides (nt) in the coding sequence, 15 of which were associated with amino acid differences and seven of which (two in the E2 protein and five in El) were nonconservative. The 3' non-coding sequence of A7 was longer (415 nt) than that of SFV4 (263 nt) and a divergent sequence of 181 nt was present adjacent to the end of the E1 coding region. The effects on virulence of two mutations in the E2 gene of SFV4, resulting in the non-conservative amino acid substitutions present in A7, were analysed. One mutation (mut 8729 a/c) resulted in only slight attenuation, whereas the other (mut 8902 a/g) resulted in avirulence for pregnant mice. However, mut 8902 a/g was lethal for the majority of developing fetuses after i.p. infection of the mother.

Apoptosis induced by Semliki Forest virus is RNA replication dependent and mediated via Bak

“…The involvement of the capsid serine protease in caspase processing/activation can be excluded because rSFV lacking its expression kills as efficiently as native viruses. Similarly, although Glasgow et al 36 reported that a single mutation in E2 decreased the cytotoxicity and virulence of SFV in mice, we do not think that envelope proteins contribute greatly to the initiation of SFV-induced apoptosis. By contrast, the involvement of the non-structural cysteine protease nsP2 is more difficult to disentangle.…”

Sequence analysis of the avirulent, demyelinating A7 strain of Semliki Forest virus.

“…In order to identify pathogenicity determinants of the A7 strain of SFV, we sequenced the envelope protein region and showed that A7 differed from SFV4 in amino acid sequence. The 3h non-translated region was longer than that of SFV4 and contained repeated elements (Glasgow et al, 1994). Similar results were obtained by Santagati et al (1994), who also showed that a chimera containing most of the E2 region from A7 and the remainder of the genome from SFV4 was attenuated (Santagati et al, 1995).…”

“…SFV differs from Sindbis virus in having a greater range of pathogenicity for the central nervous system (CNS) and foetus (Atkins et al, 1985(Atkins et al, , 1994(Atkins et al, , 1995. Virulent strains such as the prototype strain or the L10 strain cause a lethal threshold of damage to neurons in the CNS (Atkins & Sheahan, 1982 ;Atkins et al, 1990 ;Smyth et al, 1990 ;Glasgow et al, 1991 ;Balluz et al, 1993).…”

“…Virulent strains such as the prototype strain or the L10 strain cause a lethal threshold of damage to neurons in the CNS (Atkins & Sheahan, 1982 ;Atkins et al, 1990 ;Smyth et al, 1990 ;Glasgow et al, 1991 ;Balluz et al, 1993). Avirulent strains or mutants such as A7 and M9 are less cytopathic for neurons (Atkins et al, 1985(Atkins et al, , 1995Fazakerley et al, 1993) and induce demyelination which is triggered by infection of oligodendrocytes (Atkins et al, 1985(Atkins et al, , 1994 and is partially immune-mediated (Gates et al, 1984 ;Fazakerley & Webb, 1987 ;Subak-Sharpe et al, 1993).…”

“…1 ; Liljestro$ m et al, 1991 ;Glasgow et al, 1991Glasgow et al, , 1994Santagati et al, 1995). This clone was constructed from the prototype strain of SFV of known sequence (Garoff et al, 1980 a, b ;Takkinen, 1986).…”