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Specific dephosphorylation of membrane proteins in Rous sarcoma virus-transformed chick embryo fibroblasts
Abstract:
Chick embryo fibroblasts (CEF) infected with avian sarcoma virus become rapidly transformed as a result of expression of the viral src gene in the form of a single polypeptide of molecular weight 60,000 (pp60src) with protein kinase activity and suggested preferential association with the plasma membrane. Studies with normal avian and mammalian cells have revealed the presence of an antigenically related protein which seems to have similar kinase activity, but which is present at less than 1% of the levels of virally induced src protein found in transformed cells. As dynamic phosphorylation is important in numerous regulatory processes, the phenotypic expression of transformation may arise from an imbalance in one or more regulatory mechanisms that are controlled by protein phosphorylation. The cell membrane is affected during transformation, including its phosphotransferase activity. The latter has been shown using isolated membrane fractions whose properties may be changed during preparation. Therefore, we have compared the phosphorylation state of individual membrane proteins found in intact normal and RSV-transformed cells and report here the identification of two heavily phosphorylated, acidic membrane proteins in normal CEF which are specifically dephosphorylated on transformation by wild-type and temperature-sensitive Rous sarcoma viruses.
Insights
Avian sarcoma virus transformation of chick embryo fibroblasts involves the viral src gene. This study identifies two key membrane proteins that are dephosphorylated upon transformation, offering insights into viral-induced cell changes.
Area of Science:
- Cell Biology
- Virology
- Biochemistry
Background:
- Avian sarcoma virus (ASV) infection rapidly transforms chick embryo fibroblasts (CEF) through the expression of the viral src gene.
- The viral pp60src protein possesses protein kinase activity and associates with the plasma membrane.
- Normal cells contain a related protein at much lower levels, suggesting a role for altered phosphorylation in transformation.
Purpose of the Study:
- To investigate changes in membrane protein phosphorylation during ASV-induced cell transformation.
- To identify specific membrane proteins affected by the transformation process.
Main Methods:
- Comparison of the phosphorylation state of individual membrane proteins in intact normal and ASV-transformed CEF.
- Analysis of protein dephosphorylation in cells transformed by wild-type and temperature-sensitive ASV.
Main Results:
- Identification of two heavily phosphorylated, acidic membrane proteins in normal CEF.
- These two proteins are specifically dephosphorylated upon transformation by ASV.
- This dephosphorylation occurs with both wild-type and temperature-sensitive ASV strains.
Conclusions:
- Viral transformation by ASV leads to specific dephosphorylation of key membrane proteins.
- Altered phosphorylation of these proteins may contribute to the phenotypic changes observed during transformation.
- Understanding these changes provides insight into the regulatory mechanisms disrupted by viral oncogenes.