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Plasma membrane glycoproteins encoded by cloned Rauscher and Friend spleen focus-forming viruses
Abstract:
Rauscher spleen focus-forming virus (SFFV) was cloned free of its helper virus into normal rat kidney and mouse fibroblasts, and the resulting nonproducer fibroblast clones were analyzed. Our results suggested that Rauscher SFFV encodes a glycoprotein with an apparent Mr of 54,000 (gp54) that reacts with antisera made to the envelope glycoprotein (gp70) of ecotropic murine leukemia viruses, as well as with a rat antiserum that reacts with the gp70's of dual-tropic mink cell focus-inducing and HIX viruses but not with the gp70's of ecotropic viruses. In these respects and in its tryptic peptide map, Rauscher SFFV-encoded gp54 is nearly identical to the gp55 glycoprotein which we previously reported to be encoded by Friend SFFV (Dresler et al., J. Virol. 30:564--575, 1979). However, gp54 is slightly smaller, and it lacks one methionine-containing tryptic peptide that occurs in gp55. Studies with cytotoxic antiserum in the presence of complement and with a rosetting technique which employed sheep erythrocytes coupled to protein A suggested that the gp54 and gp55 glycoproteins are weakly expressed on the surface membranes of SFFV-infected cells. In addition, the Rauscher SFFV genome also encodes gag polyproteins which appear to be identical to the gag polyproteins encoded by helper Rauscher murine leukemia virus, but differ from the antigenically related polyproteins encoded by some but not all clones of Friend SFFV. Furthermore, the glycosylated gag polyproteins encoded by Rauscher SFFV and by some Friend SFFVs also appear to be expressed on the surface membranes of infected cells. These results suggest that similar env gene recombination and partial deletion events were involved in the independent origins of two different strains of acute erythroleukemia virus.
Insights
Rauscher spleen focus-forming virus (SFFV) encodes a glycoprotein (gp54) similar to Friend SFFV
Area of Science:
- Virology
- Molecular Biology
- Oncology
Background:
- Rauscher spleen focus-forming virus (SFFV) is a replication-defective retrovirus that causes erythroleukemia in mice.
- Understanding the molecular basis of SFFV pathogenesis is crucial for developing effective antiviral therapies.
- Previous studies have characterized Friend SFFV-encoded glycoproteins, but Rauscher SFFV requires further investigation.
Purpose of the Study:
- To characterize the Rauscher SFFV-encoded glycoproteins and gag polyproteins.
- To compare the molecular properties of Rauscher SFFV-encoded proteins with those of Friend SFFV.
- To investigate the cell surface expression of these viral proteins.
Main Methods:
- Cloning of Rauscher SFFV free of helper virus into fibroblast cell lines.
- Analysis of viral glycoproteins using antisera, tryptic peptide mapping, and cell surface expression assays (cytotoxic antiserum, rosetting technique).
- Characterization of gag polyproteins through immunological comparisons.
Main Results:
- Rauscher SFFV encodes a glycoprotein (gp54) antigenically related to ecotropic and dual-tropic murine leukemia virus envelope glycoproteins (gp70).
- gp54 is nearly identical to Friend SFFV-encoded gp55 but is slightly smaller and lacks a methionine-containing tryptic peptide.
- Both gp54 and gp55 are weakly expressed on the surface membranes of infected cells. Rauscher SFFV also encodes gag polyproteins similar to helper Rauscher murine leukemia virus.
Conclusions:
- Rauscher SFFV and Friend SFFV share similarities in their encoded glycoproteins, suggesting common mechanisms of viral evolution.
- The findings indicate that env gene recombination and partial deletion events likely contributed to the independent origins of these acute erythroleukemia viruses.
- The cell surface expression of viral glycoproteins and gag polyproteins may play a role in SFFV-induced leukemogenesis.