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Oncogenes and phosphatidylinositol turnover
Abstract:
Products of phosphatidylinositol turnover have recently been implicated as regulators of cell growth and differentiation. Transformation of cells in culture by infection with certain viruses (Rous sarcoma virus, Kirsten sarcoma virus, and polyoma virus) or by transfection with the oncogenes carried by these viruses affect the steady-state level of intermediates in the PI turnover pathway. In addition, immunoprecipitates of the transforming gene products of Rous sarcoma virus and polyoma virus contain activities of certain enzymes in the PI turnover pathway. We have previously reported that polyoma middle T immunoprecipitates can catalyze phosphorylation of PI to phosphatidylinositol-4-phosphate (PIP). This activity is not intrinsic to middle T or c-src but is due to a cellular enzyme that specifically associates with this complex. The PI kinase is found in immunoprecipitates of the middle T protein from polyoma viruses that are capable of cell transformation but does not associate with mutants of middle T defective in transformation suggesting that this association may be important for transformation.
Insights
Viral oncogenes impact cell growth by altering phosphatidylinositol (PI) turnover. A specific PI kinase associates with polyoma middle T oncoprotein, crucial for cell transformation.
Area of Science:
- Cell Biology
- Virology
- Biochemistry
Background:
- Phosphatidylinositol (PI) turnover products regulate cell growth and differentiation.
- Viral oncogenes and transforming viruses alter PI turnover pathway intermediates.
- Enzymatic activities in the PI turnover pathway are found in immunoprecipitates of viral transforming proteins.
Purpose of the Study:
- To investigate the role of PI turnover in viral transformation.
- To identify the specific PI turnover enzyme activity associated with polyoma middle T oncoprotein.
- To determine the significance of this association for cell transformation.
Main Methods:
- Cell culture and viral infection/transfection.
- Immunoprecipitation of viral oncoproteins.
- Enzyme activity assays (PI phosphorylation).
Main Results:
- Polyoma middle T immunoprecipitates catalyze the phosphorylation of PI to phosphatidylinositol-4-phosphate (PIP).
- This PI kinase activity is due to an associated cellular enzyme, not intrinsic to middle T or c-src.
- The PI kinase associates with transformation-competent middle T but not with transformation-defective mutants.
Conclusions:
- A specific PI kinase associates with polyoma middle T oncoprotein.
- This association is dependent on the transformation capability of the middle T protein.
- The association of PI kinase with middle T may be a critical mechanism for viral-induced cell transformation.