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Functional Interplay Between Murine Leukemia Virus Glycogag, Serinc5, and Surface Glycoprotein Governs Virus Entry, with Opposite Effects on Gammaretroviral and Ebolavirus Glycoproteins

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ABSTRACT

Gammaretroviruses, such as murine leukemia viruses (MLVs), encode, in addition to the canonical Gag, Pol, and Env proteins that will form progeny virus particles, a protein called “glycogag” (glycosylated Gag). MLV glycogag contains the entire Gag sequence plus an 88-residue N-terminal extension. It has recently been reported that glycogag, like the Nef protein of HIV-1, counteracts the antiviral effects of the cellular protein Serinc5. We have found, in agreement with prior work, that glycogag strongly enhances the infectivity of MLVs with some Env proteins but not those with others. In contrast, however, glycogag was detrimental to MLVs carrying Ebolavirus glycoprotein. Glycogag could be replaced, with respect to viral infectivity, by the unrelated S2 protein of equine infectious anemia virus. We devised an assay for viral entry in which virus particles deliver the Cre recombinase into cells, leading to the expression of a reporter. Data from this assay showed that both the positive and the negative effects of glycogag and S2 upon MLV infectivity are exerted at the level of virus entry. Moreover, transfection of the virus-producing cells with a Serinc5 expression plasmid reduced the infectivity and entry capability of MLV carrying xenotropic MLV Env, particularly in the absence of glycogag. Conversely, Serinc5 expression abrogated the negative effects of glycogag upon the infectivity and entry capability of MLV carrying Ebolavirus glycoprotein. As Serinc5 may influence cellular phospholipid metabolism, it seems possible that all of these effects on virus entry derive from changes in the lipid composition of viral membranes.

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Antagonism between Serinc5 and glycogag with respect to MLV(Xeno) and MLV(Ebola) infectivity. Specific infectivities of MLV with wild-type Gag-Pol (blue bars) or mutant Gag-Pol lacking gGag (red bars) produced in the absence or presence of increasing amounts of Serinc5 expression plasmid and with Xeno (A) or Eb-FL (B) glycoprotein are shown. The Serinc5/Gag-Pol plasmid ratios used were increased by threefold increments from 1:81 to 1:3. The infectivity measurements were performed on the HT1080/mCAT1 cell line.
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fig8: Antagonism between Serinc5 and glycogag with respect to MLV(Xeno) and MLV(Ebola) infectivity. Specific infectivities of MLV with wild-type Gag-Pol (blue bars) or mutant Gag-Pol lacking gGag (red bars) produced in the absence or presence of increasing amounts of Serinc5 expression plasmid and with Xeno (A) or Eb-FL (B) glycoprotein are shown. The Serinc5/Gag-Pol plasmid ratios used were increased by threefold increments from 1:81 to 1:3. The infectivity measurements were performed on the HT1080/mCAT1 cell line.

Mentions: As glycogag has been shown to antagonize Serinc5 (25, 26), it was of interest to determine the effect of Serinc5 expression upon the infectivities of MLV(Xeno) and MLV(Ebola) virions. Viruses were produced by transfection of 293T cells with graded doses of a Serinc5 expression plasmid, in addition to the plasmids encoding the viral constituents and pBabeLuc. As shown by the results in Fig. 8A, the stepwise addition of Serinc5 plasmid drastically reduced the specific infectivity of MLV(Xeno) in the absence of glycogag (Fig. 8A, red bars), as previously reported by Rosa et al. (25). At the lowest Serinc5 dose tested, the specific infectivity of the virus without glycogag decreased by ~20-fold, whereas that of the virus with glycogag (Fig. 8A, blue bars) decreased by less than twofold. The highest dose of Serinc5 resulted in an ~100-fold loss of specific infectivity of glycogag-negative virus relative to the amount of virus produced with no added Serinc5. In contrast, glycogag-positive virus, whose initial specific infectivity was ~10-fold higher than that of the virus without glycogag, only suffered a ~20-fold loss of specific infectivity at the highest Serinc5 dose. Thus, glycogag mitigates the adverse effects of Serinc5 expression upon MLV(Xeno) infectivity.


Functional Interplay Between Murine Leukemia Virus Glycogag, Serinc5, and Surface Glycoprotein Governs Virus Entry, with Opposite Effects on Gammaretroviral and Ebolavirus Glycoproteins
Antagonism between Serinc5 and glycogag with respect to MLV(Xeno) and MLV(Ebola) infectivity. Specific infectivities of MLV with wild-type Gag-Pol (blue bars) or mutant Gag-Pol lacking gGag (red bars) produced in the absence or presence of increasing amounts of Serinc5 expression plasmid and with Xeno (A) or Eb-FL (B) glycoprotein are shown. The Serinc5/Gag-Pol plasmid ratios used were increased by threefold increments from 1:81 to 1:3. The infectivity measurements were performed on the HT1080/mCAT1 cell line.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig8: Antagonism between Serinc5 and glycogag with respect to MLV(Xeno) and MLV(Ebola) infectivity. Specific infectivities of MLV with wild-type Gag-Pol (blue bars) or mutant Gag-Pol lacking gGag (red bars) produced in the absence or presence of increasing amounts of Serinc5 expression plasmid and with Xeno (A) or Eb-FL (B) glycoprotein are shown. The Serinc5/Gag-Pol plasmid ratios used were increased by threefold increments from 1:81 to 1:3. The infectivity measurements were performed on the HT1080/mCAT1 cell line.
Mentions: As glycogag has been shown to antagonize Serinc5 (25, 26), it was of interest to determine the effect of Serinc5 expression upon the infectivities of MLV(Xeno) and MLV(Ebola) virions. Viruses were produced by transfection of 293T cells with graded doses of a Serinc5 expression plasmid, in addition to the plasmids encoding the viral constituents and pBabeLuc. As shown by the results in Fig. 8A, the stepwise addition of Serinc5 plasmid drastically reduced the specific infectivity of MLV(Xeno) in the absence of glycogag (Fig. 8A, red bars), as previously reported by Rosa et al. (25). At the lowest Serinc5 dose tested, the specific infectivity of the virus without glycogag decreased by ~20-fold, whereas that of the virus with glycogag (Fig. 8A, blue bars) decreased by less than twofold. The highest dose of Serinc5 resulted in an ~100-fold loss of specific infectivity of glycogag-negative virus relative to the amount of virus produced with no added Serinc5. In contrast, glycogag-positive virus, whose initial specific infectivity was ~10-fold higher than that of the virus without glycogag, only suffered a ~20-fold loss of specific infectivity at the highest Serinc5 dose. Thus, glycogag mitigates the adverse effects of Serinc5 expression upon MLV(Xeno) infectivity.

View Article: PubMed Central - PubMed

ABSTRACT

Gammaretroviruses, such as murine leukemia viruses (MLVs), encode, in addition to the canonical Gag, Pol, and Env proteins that will form progeny virus particles, a protein called “glycogag” (glycosylated Gag). MLV glycogag contains the entire Gag sequence plus an 88-residue N-terminal extension. It has recently been reported that glycogag, like the Nef protein of HIV-1, counteracts the antiviral effects of the cellular protein Serinc5. We have found, in agreement with prior work, that glycogag strongly enhances the infectivity of MLVs with some Env proteins but not those with others. In contrast, however, glycogag was detrimental to MLVs carrying Ebolavirus glycoprotein. Glycogag could be replaced, with respect to viral infectivity, by the unrelated S2 protein of equine infectious anemia virus. We devised an assay for viral entry in which virus particles deliver the Cre recombinase into cells, leading to the expression of a reporter. Data from this assay showed that both the positive and the negative effects of glycogag and S2 upon MLV infectivity are exerted at the level of virus entry. Moreover, transfection of the virus-producing cells with a Serinc5 expression plasmid reduced the infectivity and entry capability of MLV carrying xenotropic MLV Env, particularly in the absence of glycogag. Conversely, Serinc5 expression abrogated the negative effects of glycogag upon the infectivity and entry capability of MLV carrying Ebolavirus glycoprotein. As Serinc5 may influence cellular phospholipid metabolism, it seems possible that all of these effects on virus entry derive from changes in the lipid composition of viral membranes.

No MeSH data available.


Related in: MedlinePlus