A Highly Attenuated Measles Virus Vaccine Strain Encodes a Fully Functional C Protein

Abstract

The P, V, and C proteins of measles virus are encoded in overlapping reading frames of the P gene, which makes it difficult to analyze the functions of the individual proteins in the context of virus infection. We established a system to analyze the C protein independently from the P and V proteins by placing its gene in an additional transcription unit between the H and L genes. Analyses with this system indicated that a highly attenuated Edmonston lineage vaccine strain encodes a fully functional C protein, and the P and/or V protein is involved in the attenuated phenotype.Measles is a highly contagious disease characterized by high fever and a maculopapular rash. About 4% of deaths in children aged under 5 years are caused by measles worldwide (9). The causative agent, measles virus (MV), belongs to the genus Morbillivirus in the family Paramyxoviridae. The genome of MV is a nonsegmented negative-strand RNA of ϳ16 kb in length and contains six genes. Each gene encodes a single structural protein, namely the nucleocapsid (N), phospho (P), matrix (M), fusion (F), hemagglutinin (H), and large (L) proteins (17). The genome forms a helical ribonucleoprotein complex with the N protein and viral RNAdependent RNA polymerase composed of the P and L proteins. The P protein acts as an essential cofactor of RNA-dependent RNA polymerase and tethers the L protein onto the nucleocapsid template (20). The P gene encodes additional gene products, the V and C proteins, by the processes of RNA editing and alternative translational initiation in a different reading frame, respectively (17). Although the V and C proteins are nonessential for MV replication (29, 35), they act as important virulence factors in vivo (11,28,(44)(45)(46). Many lines of evidence have indicated that the C and V proteins of MV antagonize the host interferon (IFN) responses (10,16,22,23,25,26,37,42,47). The V protein directly interferes with pathways of IFN induction (1) and IFN signaling (25,26,42), while the C protein contributes to circumvention of IFN induction by controlling the levels of viral RNA synthesis (22,23,31). Direct interference with IFN signaling by the C protein has also been reported, although its effects are weaker than those of the V protein (16,37).In a recent study, we showed that a recombinant IC-B strain possessing the P gene of the attenuated Edmonston tag strain (IC/EdP) replicates less efficiently than the parental IC-B strain (a virulent strain) (40). The Edmonston tag strain is a recombinant MV derived from the Edmonston B vaccine strain, which has been passaged numerous times in various cultured cells (30). There are many amino acid differences between the P gene products of the IC-B and Edmonston tag strains ( Fig. 1) (27,30,43). Most of the changes found in the Edmonston tag strain are common to the Edmonston lineage MV strains (27). However, owing to two amino acid substitutions at positions 110 and 272, which are not conserved among the Edmonston lineage MV strains (25-27), the V protein of the Edmonston tag strain is de...

Differential cellular immune responses to wild‐type and attenuated edmonston tag measles virus strains are primarily defined by the viral phosphoprotein gene

“…There are 18 known amino acid differences between the P proteins of the Edmonston tag strain (MVEdmtag) and the IC‐B strain (MVwt). The V proteins of those two strains are known to differ by 16 amino acids, and the C proteins by 4 amino acids [Nakatsu et al, 2009] (Fig. 1).…”

“…The global effect of these key immune evasion factors on cellular immune responses and the cytokine milieu has not been studied comprehensively in humans. There are four known amino acid differences between the C proteins of the wild‐type IC‐B MV strain and the highly attenuated Edmonston tag strain, and 18/16 amino acid differences between the P and V proteins of these two strains, respectively [Nakatsu et al, 2009]. Most of the changes in the Edmonston tag strain are common to Edmonston lineage measles virus strains, however due to tyrosine‐to‐histidine (Y110H) and cysteine‐to‐arginine (C272R) substitutions at amino acid positions 110 and 272 (which are not conserved among the Edmonston lineage strains), the V protein of the Edmonston tag strain is considered defective in countering IFN induction and signaling [Ohno et al, 2004; Devaux et al, 2007; Fontana et al, 2008; Gerlier and Valentin, 2009].…”

Measles Vaccine

“…Moraten and Schwarz are identical in sequence and EZ differs from Moraten/Schwarz at 21 amino acids (8,127,128). Sequences of vaccine strains compared with current WT strains reveal differences in most viral proteins, any of which may contribute to attenuation and no one change or combination of changes has been identified as responsible for attenuation (6,8,36,63,105,127,128,(173)(174)(175).…”

Measles virus‐induced suppression of immune responses

“…Strain dependence may be due in part to sequence differences in the C and V proteins, the MV proteins that regulate IFN responses, but this has not been clearly defined (90,91). C inhibits IFN induction and signaling, in part by decreasing viral RNA synthesis, and has been implicated in prevention of cell death (92)(93)(94)(95)(96).…”