Effects of Subtle Changes in the SU Protein of Ecotropic Murine Leukemia Virus on Its Brain Capillary Endothelial Cell Tropism and Interference Properties

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic variant of Friend MuLV (F-MuLV) that causes a rapidly progressive neurodegenerative disease in susceptible rodents. PVC-211 MuLV, but not the parental F-MuLV, can infect rat brain capillary endothelial cells (BCEC) efficiently, and the major determinant for BCEC tropism of PVC-211 MuLV is localized within theXbaI–BamHI fragment of the viral genome containing the 5′ half of theenvgene. To further dissect theXbaI–BamHI region for its effects on BCEC tropism, we constructed recombinant viruses between PVC-211 MuLV and F-MuLV and tested their infectivity on a cell line established from rat BCEC. Our results indicated that Glu116-to-Gly and Glu129-to-Lys substitutions in the background of the F-MuLV envelope SU protein were sufficient for conferring BCEC tropism on the virus. Interference studies of these viruses on Rat-1 fibroblastic cells showed that the structure of the SU protein encoded by theXbaI–BamHI region also has significant effects on their affinity for the rat ecotropic MuLV receptor. These results support the possibility that structural elements I and II of the SU protein are important determinants for virus–receptor interaction.