The Neuroinvasiveness of a Murine Retrovirus Is Influenced by a Dileucine-Containing Sequence in the Cytoplasmic Tail of Glycosylated Gag

Abstract

The tempo and intensity of retroviral neuropathogenesis are dependent on the capacity of the virus to invade the central nervous system. For murine leukemia viruses, an important determinant of neuroinvasiveness is the virus-encoded protein glycosylated Gag, the function of which in the virus life cycle is not known. While this protein is dispensable for virus replication, mutations which prevent its expression slow the spread of virus in vivo and restrict virus dissemination to the brain. To further explore the function of this protein, we compared two viruses, CasFrKP (KP) and CasFrKP41 (KP41), which differ dramatically in neurovirulence. KP expresses high early viremia titers, is neuroinvasive, and induces clinical neurologic disease in 100% of neonatally inoculated mice, with an incubation period of 18 to 23 days. In contrast, KP41 expresses early viremia titers 100- fold lower than those of KP, exhibits attenuated neuroinvasiveness, and induces clinical neurologic disease infrequently, with a relatively long incubation period. The genomes of these two viruses differ by only 10 nucleotides, resulting in differences at five residues, all located within the N-terminal cytoplasmic tail of glycosylated Gag. In this study, using KP as the parental virus, we systematically mutated each of the five amino acid residues to those of KP41 and found that substitution mutation of two membrane-proximal residues, E53 and L56, to K and P, respectively produced the greatest effect on early viremia kinetics and neurovirulence. These mutations disrupted the KP sequence E53FLL56, the leucine dipeptide of which suggests the possibility that it may represent a sorting signal for glycosylated Gag. Supporting this idea was the finding that alteration of this sequence motif increased the level of cell surface expression of the protein, which suggests that analysis of the intracellular trafficking of glycosylated Gag may provide further clues to its function.

Correction: Identification of a Novel Gammaretrovirus in Prostate Tumors of Patients Homozygous for R462Q RNASEL Variant

“…However, lesions in this region have been associated with interesting variations in pathogenetic properties in vivo [57][58][59][60][61]. For example, an alteration in ten nt affecting five residues in the N-terminal peptide of glyco-Gag was found to be responsible for a 100-fold difference in the frequency of neuroinvasion observed between CasFrKP and CasFrKP41 MuLV strains [62]. In addition, insertion of an octanucleotide resulting in a stop codon downstream of the CUG start codon prevented severe early hemolytic anemia and prolonged latency of erythroleukemia in mice infected with Friend MuLV [58].…”