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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.

No MeSH data available.


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Effect of gGag on MLV infectivity is determined by Env protein. Specific infectivities of MLV with indicated Env glycoproteins produced in the presence or absence of gGag. Viruses were produced with wild-type or gGag-deficient Gag-Pol together with the indicated Env expression clones. The x axis shows the type of Env glycoprotein on the virus. For each Env, the red dots represent the ratios of specific infectivities of virus with gGag to virus without gGag in individual experiments. The plus signs show the geometric means of these values, and the bars at the top and bottom of each vertical line show associated 95% confidence intervals for each Env. Eb-FL, full-length Ebola glycoprotein; EbΔMuc, Ebola glycoprotein with deletion of mucinlike domain. The target cell line used for viruses with VSV(g), Ampho (amphotropic), 10A1, GALV, RD114, Xeno (xenotropic), Eb-FL, and EbΔMuc glycoproteins was HT1080, the target cell line used for viruses with Eco (ecotropic) and BLV glycoprotein was HT1080/mCAT1, and the target cell line used for viruses with RSV Env A was D17 cells expressing subgroup A receptor.
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fig4: Effect of gGag on MLV infectivity is determined by Env protein. Specific infectivities of MLV with indicated Env glycoproteins produced in the presence or absence of gGag. Viruses were produced with wild-type or gGag-deficient Gag-Pol together with the indicated Env expression clones. The x axis shows the type of Env glycoprotein on the virus. For each Env, the red dots represent the ratios of specific infectivities of virus with gGag to virus without gGag in individual experiments. The plus signs show the geometric means of these values, and the bars at the top and bottom of each vertical line show associated 95% confidence intervals for each Env. Eb-FL, full-length Ebola glycoprotein; EbΔMuc, Ebola glycoprotein with deletion of mucinlike domain. The target cell line used for viruses with VSV(g), Ampho (amphotropic), 10A1, GALV, RD114, Xeno (xenotropic), Eb-FL, and EbΔMuc glycoproteins was HT1080, the target cell line used for viruses with Eco (ecotropic) and BLV glycoprotein was HT1080/mCAT1, and the target cell line used for viruses with RSV Env A was D17 cells expressing subgroup A receptor.

Mentions: MLV Envs are polymorphic, and different viral isolates use different cell surface receptors in infection. We tested the glycogag requirement for MLV particles carrying a wide variety of Env proteins. The effects of glycogag on the specific infectivities are presented in Fig. 4 as the ratio of the specific infectivity of the virus produced with glycogag to that produced in the absence of glycogag. We found that there was a strong glycogag requirement for viruses carrying not only amphotropic (Ampho) or xenotropic Env (as reported by Pizzato [11]) but also with Env from 10A1 MLV, a highly leukemogenic recombinant derived from amphotropic MLV that uses both the amphotropic receptor SLC20A2 and a second, related receptor, SLC20A1, for entry into cells (18, 19). In contrast, as shown by Pizzato (11), the specific infectivity of virus with the Moloney MLV ecotropic Env [MLV(Eco) Env] and vesicular stomatitis virus glycoprotein [VSV(g)] is not significantly affected by the presence of glycogag (Fig. 4).


Functional Interplay Between Murine Leukemia Virus Glycogag, Serinc5, and Surface Glycoprotein Governs Virus Entry, with Opposite Effects on Gammaretroviral and Ebolavirus Glycoproteins
Effect of gGag on MLV infectivity is determined by Env protein. Specific infectivities of MLV with indicated Env glycoproteins produced in the presence or absence of gGag. Viruses were produced with wild-type or gGag-deficient Gag-Pol together with the indicated Env expression clones. The x axis shows the type of Env glycoprotein on the virus. For each Env, the red dots represent the ratios of specific infectivities of virus with gGag to virus without gGag in individual experiments. The plus signs show the geometric means of these values, and the bars at the top and bottom of each vertical line show associated 95% confidence intervals for each Env. Eb-FL, full-length Ebola glycoprotein; EbΔMuc, Ebola glycoprotein with deletion of mucinlike domain. The target cell line used for viruses with VSV(g), Ampho (amphotropic), 10A1, GALV, RD114, Xeno (xenotropic), Eb-FL, and EbΔMuc glycoproteins was HT1080, the target cell line used for viruses with Eco (ecotropic) and BLV glycoprotein was HT1080/mCAT1, and the target cell line used for viruses with RSV Env A was D17 cells expressing subgroup A receptor.
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Related In: Results  -  Collection

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fig4: Effect of gGag on MLV infectivity is determined by Env protein. Specific infectivities of MLV with indicated Env glycoproteins produced in the presence or absence of gGag. Viruses were produced with wild-type or gGag-deficient Gag-Pol together with the indicated Env expression clones. The x axis shows the type of Env glycoprotein on the virus. For each Env, the red dots represent the ratios of specific infectivities of virus with gGag to virus without gGag in individual experiments. The plus signs show the geometric means of these values, and the bars at the top and bottom of each vertical line show associated 95% confidence intervals for each Env. Eb-FL, full-length Ebola glycoprotein; EbΔMuc, Ebola glycoprotein with deletion of mucinlike domain. The target cell line used for viruses with VSV(g), Ampho (amphotropic), 10A1, GALV, RD114, Xeno (xenotropic), Eb-FL, and EbΔMuc glycoproteins was HT1080, the target cell line used for viruses with Eco (ecotropic) and BLV glycoprotein was HT1080/mCAT1, and the target cell line used for viruses with RSV Env A was D17 cells expressing subgroup A receptor.
Mentions: MLV Envs are polymorphic, and different viral isolates use different cell surface receptors in infection. We tested the glycogag requirement for MLV particles carrying a wide variety of Env proteins. The effects of glycogag on the specific infectivities are presented in Fig. 4 as the ratio of the specific infectivity of the virus produced with glycogag to that produced in the absence of glycogag. We found that there was a strong glycogag requirement for viruses carrying not only amphotropic (Ampho) or xenotropic Env (as reported by Pizzato [11]) but also with Env from 10A1 MLV, a highly leukemogenic recombinant derived from amphotropic MLV that uses both the amphotropic receptor SLC20A2 and a second, related receptor, SLC20A1, for entry into cells (18, 19). In contrast, as shown by Pizzato (11), the specific infectivity of virus with the Moloney MLV ecotropic Env [MLV(Eco) Env] and vesicular stomatitis virus glycoprotein [VSV(g)] is not significantly affected by the presence of glycogag (Fig. 4).

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