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Expression of the Rous sarcoma virus src gene in avian macrophages fails to elicit transformed cell phenotype
Abstract:
Infection of avian macrophages with Rous sarcoma virus does not induce any changes in the morphology, growth behavior, or expression of macrophage-specific proteins. The absence of cellular transformation does not result from a block in the synthesis of viral proteins, since infectious viruses are released from a majority of cells in the culture. In this report, we examine the synthesis, processing, and functional activity of pp60src in Rous sarcoma virus-infected macrophages to determine whether the absence of transformation is due to an alteration in the functional expression of pp60src. Although the absolute level of pp60src was reduced compared with fibroblasts, the protein exhibited the same phosphorylation pattern and subcellular distribution and was able to phosphorylate immunoglobulin in the immune complex-protein kinase assay. These results imply that the failure of Rous sarcoma virus to transform macrophage may be due to a restriction in the cellular response to a functional src protein, perhaps due to the absence of cellular products which are essential for mediating pp60src-induced transformation.
Insights
Rous sarcoma virus infects avian macrophages without causing transformation. The functional src protein is present, suggesting cellular factors, not viral ones, may prevent macrophage transformation.
Area of Science:
- Virology
- Cell Biology
- Immunology
Background:
- Rous sarcoma virus (RSV) typically transforms cells.
- Avian macrophages infected with RSV show no morphological or growth changes.
- Viral protein synthesis and release are not blocked in infected macrophages.
Purpose of the Study:
- To investigate the synthesis, processing, and functional activity of the pp60src protein in RSV-infected macrophages.
- To determine if altered pp60src function explains the lack of cellular transformation in macrophages.
Main Methods:
- Analysis of pp60src protein levels, phosphorylation patterns, and subcellular localization.
- Immune complex-protein kinase assays to assess pp60src enzymatic activity.
- Comparison of pp60src in macrophages versus fibroblasts.
Main Results:
- pp60src levels were lower in macrophages than in fibroblasts.
- The protein maintained its phosphorylation pattern and subcellular distribution in macrophages.
- Functional pp60src kinase activity was confirmed in infected macrophages.
Conclusions:
- The functional pp60src protein is present in RSV-infected macrophages.
- The absence of transformation is likely due to a restricted cellular response to pp60src.
- Macrophage transformation may require specific cellular products absent in these cells.