| Viruses must be able to traffic from initial sites of infection to secondary sites to cause disease. Mammalian orthoreovirus (reovirus) requires non-structural protein sigma1s to disseminate via the blood. However, it is unknown how sigma1s facilitates hematogenous dissemination. We have found that sigma1s supports effective T1L reovirus replication in multiple cell types, including SV-40 immortalized endothelial cells (SVECs). In SVECs, sigma1s is dispensable for viral RNA synthesis and protein stability but functions to support optimal viral protein expression, suggesting that sigma1s functions at the level of viral protein synthesis. In contrast, T3D reovirus is less dependent on sigma1s. While both T3D and T1L sigma1s promote viral protein expression and replication in the T1L genetic background, reoviruses with the T3D genetic background do not need sigma1s for initial rounds of replication and protein expression in SVECs. Although sigma1s does not function as a type-I interferon (IFN-I) antagonist, removal of IFN-I signaling rescues sigma1s-null reovirus replication, but only partially rescues viral protein expression. This indicates that sigma1s contributes to reovirus resistance of IFN-I responses, but there is an IFN-I-independent mechanism by which sigma1s supports viral protein expression. In C57BL/6 mice, sigma1s is required for T1L dissemination after oral inoculation as only the WT virus can be recovered at high titers. However, in IFN-I ?/? receptor subunit 1 knockout mice ( IFNAR1-/-) sigma1s-null titers in secondary organs are comparable to the WT virus, suggesting that IFN-I responses act as a barrier to sigma1s-null reovirus dissemination. Finally, we used the IFN-I sensitivity of the sigma1s-null reovirus to dissect pathways of reovirus dissemination using Cre-lox technology to delete IFNAR1 in lymphatic endothelial cells (LEC). In parental mouse strains and littermate controls, sigma1s is required for reovirus dissemination after oral inoculation. However, in LEC-specific IFNAR1 knockout mice, comparable titers of sigma1s-null and WT reovirus are recovered in secondary organs. This suggests that LECs are a major cell type that mediate reovirus dissemination. These studies provide new insights into the function of sigma1s during reovirus replication and dissemination and highlight new avenues for studies of mechanisms by which reoviruses spread in the host. |
