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A glycoprotein in the plasma membrane matrix as a major potential substrate of p60v-src
M Hamaguchi1, M Matsuda, H Hanafusa
1Rockefeller University, New York, New York 10021.
Abstract:
A potential substrate of p60v-src in Rous sarcoma virus-transformed cells was found to be a 130-kilodalton (kDa) glycoprotein which binds to lectin-Sepharose and can be immunoprecipitated by an anti-phosphotyrosine antibody. This glycoprotein was shown to be distinct from the fibronectin receptor and a cellular protein phosphorylated in p60v-src immune complexes. The protein was a transmembrane protein localized in the plasma membrane and resistant to extraction with Triton X-100. The 130-kDa protein was also highly phosphorylated in cells transformed by Fujinami sarcoma virus or Y73 but not in cells infected with Rous sarcoma virus mutants that encode p60v-src lacking myristoylated N termini. Phosphorylation of this glycoprotein was temperature dependent in cells infected with temperature-sensitive mutants. The good correlation between its phosphorylation and morphological transformation, together with its relative abundance among phosphorylated proteins and its subcellular localization, suggests that phosphorylation of the 130-kDa glycoprotein is one of the primary events important for cell transformation by p60v-src and related oncogene products.
Insights
Researchers identified a 130-kilodalton (kDa) glycoprotein phosphorylated by p60v-src in Rous sarcoma virus-transformed cells. Its phosphorylation correlates with cell transformation, suggesting a key role in oncogenesis.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Rous sarcoma virus (RSV) transformation involves oncogene products like p60v-src.
- Identifying cellular substrates of viral oncogenes is crucial for understanding transformation mechanisms.
Purpose of the Study:
- To identify and characterize a potential substrate of p60v-src involved in cell transformation.
- To investigate the role of this substrate's phosphorylation in oncogenic transformation.
Main Methods:
- Affinity purification using lectin-Sepharose.
- Immunoprecipitation with anti-phosphotyrosine antibodies.
- Analysis of protein phosphorylation in cells transformed by various sarcoma viruses and mutants.
Main Results:
- A 130-kDa glycoprotein, distinct from the fibronectin receptor, was identified as a p60v-src substrate.
- This glycoprotein is a transmembrane protein located in the plasma membrane.
- Phosphorylation of the 130-kDa glycoprotein was observed in cells transformed by RSV, Fujinami sarcoma virus, and Y73, but not by RSV mutants lacking N-terminal myristoylation.
- Phosphorylation levels were temperature-dependent in cells infected with temperature-sensitive RSV mutants.
Conclusions:
- Phosphorylation of the 130-kDa glycoprotein is strongly correlated with morphological cell transformation induced by p60v-src.
- This glycoprotein is likely a primary target and plays a significant role in p60v-src-mediated cell transformation.