Identification for the Genetic Determinant in the env Gene of PVC-211 Murine Leukemia Virus Responsible for Its Brain Capillary Endothelial Cell Tropism

Abstract

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic variant of the nonneuropathogenic Friend MuLV (F-MuLV). Although both -viruses belong to the host range group designated ecotropic, PVC-211 MuLV, but not F-MuLV can infect rat brain capillary endothelial cells (BCEC) efficiently, and it has been reported that there is a clear correlation between BCEC tropism of the virus and its neuropathgenicity. A previous study using chimeric viruses constructed between PVC-211 MuLV and F-MuLV showed that the 916-base-pair (bp) long Xbal-BamHI region of the PVC-211 MuLV genome, which roughly corresponds to the 5' half of the SU protein-coding region of the env gene, contained a major determinant for the BCEC tropism of the virus. This thesis work represents an attempt to pinpoint the actual genetic element responsible for the BCEC tropism of PVC-211 MuLV by the construction of additional recombinant viruses and examination of their infectivity on a cell line, RTEC-6, derived from a primary culture of rat BCEC. The results indicate that the 138-bp long 4/711-A gel fragment of the PVC-211 MuLV env gene in the context of the F-MuLV env gene was sufficient for conferring BCEC tropism on the virus. Interestingly, PVC-211 MuLV was also highly infectious on Chinese hamster ovary (CHO) cells, which are normally resistant to infection by ecotropic MuLVs. The 41111-Agel region of the PVC-211 MuLV env gene was also able to confer CHO cell tropism on the virus in the context of the F-MuLV env gene. Comparison of the nucleotide sequences of the Af/IAge1 region of these two viruses revealed five point mutations, two of which result in two amino acid substitutions (Glun6 and Glu129 in the F-MuLV SU protein to Gly and Lys in PVC-211 MuLV, respectively), suggesting a significant role for these residues in controlling the cellular tropism of the virus. Since subtle changes in the structure of the SU protein can significantly affect the tropism, it is suggested that the characteristic cellular tropism of PVC-211 MuLV is determined at least in part by a unique interaction between the viral SU protein and the receptor expressed on the host cells, such as BCEC and CHO cells. Interference studies of the recombinant viruses on Rat-1 fibroblastic cells indicated that BCEC- and CHO cell-tropic viruses generally have a higher affinity for virus receptors than non- BCEC- and CHO cell- tropic viruses, supporting the possibility that the SU proteinreceptor interaction determines the characteristic cellular tropism of PVC-211 MuLV.