The Transdominant Endogenous Retrovirus enJS56A1 Associates with and Blocks Intracellular Trafficking of Jaagsiekte Sheep Retrovirus Gag

Abstract

The sheep genome harbors approximately 20 endogenous retroviruses (enJSRVs) highly related to the exogenous Jaagsiekte sheep retrovirus (JSRV). One of the enJSRV loci, enJS56A1, acts as a unique restriction factor by blocking JSRV in a transdominant fashion at a late stage of the retroviral cycle. To better understand the molecular basis of this restriction (termed JLR, for JSRV late restriction), we functionally characterized JSRV and enJS56A1 Gag proteins. We identified the putative JSRV Gag membrane binding and late domains and determined their lack of involvement in JLR. In addition, by using enJS56A1 truncation mutants, we established that the entire Gag protein is necessary to restrict JSRV exit. By using differentially tagged viruses, we observed, by confocal microscopy, colocalization between JSRV and enJS56A1 Gag proteins. By coimmunoprecipitation and molecular complementation analyses, we also revealed intracellular association and likely coassembly between JSRV and enJS56A1 Gag proteins. Interestingly, JSRV and enJS56A1 Gag proteins showed distinct intracellular targeting: JSRV exhibited pericentrosomal accumulation of Gag staining, while enJS56A1 Gag did not accumulate in this region. Furthermore, the number of cells displaying pericentrosomal JSRV Gag was drastically reduced in the presence of enJS56A1. We identified amino acid residue R21 in JSRV Gag as the primary determinant of centrosome targeting. We concluded that JLR is dependent on a Gag-Gag interaction between enJS56A1 and JSRV leading to altered cellular localization of the latter.

Comprehensive analysis of endogenous bornavirus-like elements in eukaryote genomes

“…Therefore, expression of EBLNs may have inhibited the BDV polymerase by changing the N : P ratio. Second, EBLNs may have functioned as dominant negative proteins against the bornavirus N protein, like the ERV Gag protein that can block exogenous retroviruses in sheep at late stages of viral replication [89]. Finally, EBLNs may have been involved in immunity mediated by small RNAs as described above.…”

Evolutionary dynamics of endogenous Jaagsiekte sheep retroviruses proliferation in the domestic sheep, mouflon and Pyrenean chamois

“…Moreover, some newly inserted proviruses acquired a defective Gag polyprotein resulting in a transdominant phenotype able to block late replication steps of related exogenous retroviruses (Mura et al, 2004;Arnaud et al, 2007;Murcia et al, 2007;Armezzani et al, 2011).…”

Endogenous Retroviruses of Sheep: A Model System for Understanding Physiological Adaptation to an Evolving Ruminant Genome

“…JSRV late restriction likely occurs via the production of defective Gag protein by the transdominant proviruses that form viral particles and/or multimers with the functional Gag proteins, which then accumulate in the cytoplasm as pre-aggresome structures that are subsequently degraded by the proteasome. Therefore, the transdominant proviruses prevent Gag proteins of the competent virus to interact with the trafficking cellular machinery and ultimately the release of viral particles [25,26]. Available evidence strongly supports the hypothesis that selection of transdominant enJSRV loci protected sheep against infection with related exogenous retroviruses, including JSRV and perhaps enzootic nasal tumor virus or ENTV.…”

“…As described for other viruses, enJSRVs Env can prevent JSRV entry by a classic mechanism of receptor interference [23]. In addition, two enJSRV loci (enJS56A1 and enJSRV-20) can block JSRV replication at a late stage of the retroviral replication cycle by a block referred to as JSRV late restriction [11,24,25]. These two transdominant proviruses entered the host genome 3 million years ago before and during speciation within the genus Ovis [11].…”