CD300LF Polymorphisms of Inbred Mouse Strains Confer Resistance to Murine Norovirus Infection in a Cell Type-Dependent Manner

Abstract

Human norovirus is the leading cause of gastroenteritis worldwide, yet basic questions about its life cycle remain unanswered due to an historical lack of robust experimental systems. Recent studies on the closely related murine norovirus (MNV) have identified CD300LF as an indispensable entry factor for MNV. We compared MNV susceptibility of cells from different mouse strains and identified polymorphisms in murine CD300LF, which are critical for its function as an MNV receptor. Bone marrow-derived macrophages (BMDMs) from I/LnJ mice were resistant to infection from multiple MNV strains, which readily infect BMDMs from C57BL/6J mice. The resistance of I/LnJ BMDMs was specific to MNV, since the cells supported infection of other viruses comparably to C57BL/6J BMDMs. Transduction of I/LnJ BMDMs with C57BL/6J CD300LF made the cells permissible to MNV infection, suggesting that the cause of resistance lies in the entry step of MNV infection. In fact, we mapped this phenotype to a 4 amino acid difference at the CC' loop of CD300LF; swapping of these amino acids between C57BL/6J and I/LnJ CD300LF proteins made the mutant C57BL/6J CD300LF functionally impaired and the corresponding mutant of I/LnJ CD300LF functional as an MNV entry factor. Surprisingly, expression of the I/LnJ CD300LF in other cell types made the cells infectible by MNV, even though the I/LnJ allele did not function as an MNV receptor in macrophage-like cells. Correspondingly, I/LnJ CD300LF bound MNV virions in permissive cells but not in non-permissive cells. Collectively, our data suggest the existence of a cell-type-specific modifier of MNV entry. IMPORTANCE MNV is a prevalent model system for studying human norovirus–the leading cause of gastroenteritis worldwide and thus a sizeable public health burden. Elucidating mechanisms underlying susceptibility of host cells to MNV infection can lead to insights on the roles that specific cell types play during norovirus pathogenesis. Here, we show that different alleles of the proteinaceous receptor for MNV, CD300LF, function in a cell type-dependent manner. In contrast to the C57BL/6J allele that functions as an MNV entry factor in all tested cell types, including human cells, I/LnJ CD300LF does not function as an MNV entry factor in macrophage-like cells but does allow MNV entry in other cell types. Together, these observations indicate the existence of cell-type specific modifiers of CD300LF-dependent MNV entry.

Amino acid substitutions in norovirus VP1 dictate cell tropism via an attachment process dependent on membrane mobility

“…To address potential differences in CD300lf expression between the cell types, we compared the expression levels of CD300lf receptor in BV-2 and BV-2S cells by western blot (Supplemental Figure 2B). The western blot indicated the presence of multiple CD300lf glycosylation states (75 kDa main isoform), as has been previously described (37, 38), however there was no clear difference in relative expression of these different forms between BV-2 and BV-2S cells. BHK-21 cells were used as a negative control, and L-cells and RAW 264.7 cells were used as positive controls for CD300lf expression.…”

Noroviruses—The State of the Art, Nearly Fifty Years after Their Initial Discovery

“…Recent advances in the field comprise an updated classification system [ 10 ], the description of alternative virus-like protein (VLP) morphologies [ 48 ], and the further elucidation of the functions of both structural and nonstructural viral proteins and their roles in the norovirus replicative cycle [ 36 , 52 , 92 , 101 ]. Important milestones include new insights into cell tropism [ 40 , 44 ], host- and microbial attachment factors and receptors [ 43 , 59 , 60 , 61 , 71 , 72 , 73 , 79 , 360 ], interactions with the cellular translational apparatus [ 80 , 83 , 84 ], and viral egress from cells [ 110 ]. Noroviruses have been detected in previously unrecognised host species [ 18 , 19 ]; detection itself is facilitated by the novel analytical techniques that increasingly supplement established molecular methods [ 259 , 261 , 262 , 263 , 265 ].…”

Glycan Recognition in Human Norovirus Infections

“…Bone marrow-derived macrophages (BMDMs) from C57BL/6J mice are susceptible to MNV infection but BMDMs from I/LnJ mice are not. The CD300lf has altered amino-acid sequences between these two different mouse strains and is responsible for resistance to MNV infection of BMDMs from the I/LnJ mice [108]. In the susceptible C57BL/6J mouse, those amino contain two potential O-glycosylation sites lost in the resistant mouse.…”