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Immunoselection of mutants deficient in cell surface glycoproteins encoded by murine erythroleukemia viruses
Abstract:
We have described a heterogeneously processed glycoprotein with an apparent molecular weight of 55,000 (gp55) that is encoded by the Friend spleen focus-forming virus, an acute erythroleukemia virus [Dresler, S., Ruta, M., Murray, M.J. & Kabat, D. (1976) J. Virol. 30, 564-573]. Several lines of evidence suggest that a small proportion of the gp55 in infected cells is located on the surface membranes. First, different nonproducer cell lines infected with cloned Friend spleen focus-forming virus were efficiently killed in the presence of complement by cytotoxic antisera that react with gp55. Furthermore, a clone of cells selected for resistance to the cytotoxic antibody synthesized an altered intracellular form of gp55. This immunoselection procedure appears to also be useful for isolating glycoprotein mutants of other RNA tumor viruses. Analysis of cell surface proteins labeled with [125I]iodine supported the idea that gp55 occurs on the plasma membranes. However, the cell surface gp55 had more highly processed oligosaccharides than the majority of the gp55, which occurs within the infected cells. In addition, we have found that leukemia cells from mice infected with the erythroleukemic Rauscher virus complex contain a membrane glycoprotein that appears similar to the gp55 encoded by Friend spleen focus-forming virus. The encoding of similar glycoproteins by independently isolated acute erythroleukemia viruses suggests that these glycoproteins may be important in leukemogenesis.
Insights
Researchers identified a glycoprotein (gp55) from Friend spleen focus-forming virus. This protein is present on the surface membranes of infected cells and may play a role in acute erythroleukemia.
Area of Science:
- Virology
- Molecular Biology
- Oncology
Background:
- Friend spleen focus-forming virus (SFFV) is an acute erythroleukemia virus.
- A specific glycoprotein, gp55, is encoded by SFFV.
- The cellular location and function of gp55 are not fully understood.
Purpose of the Study:
- To investigate the presence and location of gp55 in Friend virus-infected cells.
- To determine the role of gp55 in the pathogenesis of acute erythroleukemia.
- To explore the potential of gp55 as a target for immunoselection of viral mutants.
Main Methods:
- Cytotoxic antisera assays to detect gp55 on cell surfaces.
- Immunoselection to isolate cells with altered gp55 expression.
- Radioiodination ([125I]) of cell surface proteins to analyze gp55.
- Comparison of gp55 from Friend virus with glycoproteins from Rauscher virus-infected cells.
Main Results:
- A fraction of gp55 is located on the plasma membranes of infected cells.
- Cell surface gp55 exhibits more processed oligosaccharides than intracellular gp55.
- Immunoselection with cytotoxic antibodies yields cells with altered intracellular gp55.
- Leukemia cells from Rauscher virus-infected mice contain a similar membrane glycoprotein.
Conclusions:
- gp55 is a cell surface glycoprotein encoded by Friend SFFV.
- The presence of similar glycoproteins in different acute erythroleukemia viruses suggests their importance in leukemogenesis.
- The immunoselection technique is a viable method for isolating viral glycoprotein mutants.