Protruding Domain of Capsid Protein Is Necessary and Sufficient To Determine Murine Norovirus Replication and Pathogenesis In Vivo

Abstract

bHuman noroviruses (HuNoVs) are the major cause of epidemic, nonbacterial gastroenteritis worldwide. Due to the lack of a tractable model system and the inability to grow HuNoVs in cell culture, factors required for the norovirus (NoV) life cycle and pathogenesis in the host remain largely unknown. The discovery of murine norovirus (MNV) and the development of reversegenetics systems for this virus provide an opportunity to study these aspects of NoV infection in vitro and in vivo. Previous studies identified a single amino acid at residue 296 in the protruding (P) domain of the capsid protein that is responsible for determining the virulence of the MNV clone MNV1.CW1 in 12956/SvEv background STAT1-deficient (STAT1 ؊/؊ ) mice. In this report, we identified and characterized another determinant of lethality in the P domain that is necessary and sufficient to determine the replication and pathogenesis of the MNV clones MNV1.CW3 and CR6.STL1 in C57BL/6 background STAT1 ؊/؊ mice. Furthermore, we describe how the role of residue 296 in MNV virulence differs between STAT1 ؊/؊ mouse strains. We also describe potential interactions between subdomains of the P domain, as well as between other virus elements, which facilitate recovery of MNV using a reverse-genetics system.

A Single-Amino-Acid Change in Murine Norovirus NS1/2 Is Sufficient for Colonic Tropism and Persistence

“…In contrast to virulence in STAT1 knockout mice (31), reciprocal replacement of the capsid gene did not alter persistence. Instead, the NS1/2 gene of CR6 enabled persistence of CW3.…”

“…Subsequently, many closely related strains of MNV isolated from stool samples were shown to persist in immune-sufficient mice (15,28). One of these persistent stool isolates, CR6, has been shown to be avirulent in STAT1 knockout mice, demonstrating a second phenotypic distinction from MNV1 (31). A reverse genetics system for MNV exists (32), making phenotypic analyses of MNV1 and persistent strains possible (14,31,33,34).…”

“…A reverse genetics system for MNV exists (32), making phenotypic analyses of MNV1 and persistent strains possible (14,31,33,34). The increased virulence of MNV1 has been linked to the protruding domain of the capsid gene (31,33), but the gene responsible for MNV persistence has not been identified.…”

“…MNV1 was identified as a cause of lethality in RAG/STAT1 knockout mice (29), and it was passaged intracranially in these mice until a culture system was established (30). While MNV1 rapidly kills STAT1 knockout mice, it persists avirulently in RAG knockout mice and is cleared from immune-sufficient mice (29,31). Subsequently, many closely related strains of MNV isolated from stool samples were shown to persist in immune-sufficient mice (15,28).…”

High-Resolution Functional Profiling of the Norovirus Genome

“…MNV has also been isolated from wild mice, confirming its widespread distribution (59). Studies with MNV have begun to probe various aspects of the norovirus replication cycle, including entry mechanisms and attachment factors (24,48,49,67), viral protein function (8,19,30,43,64,66), determinants of virulence (7), and host immune responses (14, 15, 42); however, our understanding of the molecular mechanisms of norovirus genome translation and replication lags far behind that for other RNA viruses.MNV is a positive-sense single-stranded RNA virus with a genome of approximately 7.4 kb covalently attached to a viral genome-linked protein (VPg) at the 5= end and polyadenylated at the 3= end (33). The 5= and 3= untranslated regions (UTRs) are extremely short, 5 and 78 nucleotides (nt), respectively, for MNV-1 (33).…”