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Reduced protein kinase C activity in a ras-resistant cell line derived from Ki-MSV transformed cells
T Kamata1, N F Sullivan, M W Wooten
1Cold Spring Harbor Laboratory, New York 11724.
Abstract:
We have examined phosphatidylinositol turnover and C-kinase distribution in a flat cellular ras-resistant cell line (C11) derived from Kirsten murine sarcoma virus (Ki-MSV) transformed NIH/3T3 cells (DT). This cell type has been shown to express high levels of the p21 Ki-ras gene product yet is resistant to the transforming effects of this protein. Our data indicate that C11 cells have reduced levels of total C-kinase activity when compared to NIH/3T3 cells and do not retain the ability to phosphorylate the growth associated 80-kDa C-kinase substrate either in vivo or in vitro. Furthermore, whilst the steady state levels of diacylglycerol and the sum of inositol phosphates are elevated in DT cells, in C11 cells these levels are reduced to an amount equivalent to that seen in NIH/3T3 cells. These data indicate a correlation between a protein kinase C dependent pathway and resistance to transformation by ras.
Insights
Ras-resistant cells show reduced protein kinase C activity and altered phosphatidylinositol turnover. These findings suggest a link between protein kinase C pathways and resistance to ras-mediated cell transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Kirsten murine sarcoma virus (Ki-MSV) transforms cells via the p21 Ki-ras gene product.
- Ras-resistant cell lines are crucial for understanding oncogenic signaling pathways.
- Phosphatidylinositol turnover and protein kinase C (PKC) are implicated in cell growth and transformation.
Purpose of the Study:
- To investigate phosphatidylinositol turnover and C-kinase distribution in a ras-resistant cell line.
- To determine the role of PKC in ras-mediated transformation resistance.
Main Methods:
- Analysis of phosphatidylinositol turnover and C-kinase activity in NIH/3T3 and C11 cells.
- Measurement of diacylglycerol and inositol phosphate levels.
- Assessment of 80-kDa C-kinase substrate phosphorylation in vivo and in vitro.
Main Results:
- C11 ras-resistant cells exhibit reduced total C-kinase activity compared to NIH/3T3 cells.
- C11 cells lack the ability to phosphorylate the 80-kDa C-kinase substrate.
- Diacylglycerol and inositol phosphate levels are normalized in C11 cells, unlike in transformed DT cells.
Conclusions:
- A correlation exists between a protein kinase C dependent pathway and resistance to ras-mediated transformation.
- Altered phosphatidylinositol signaling contributes to ras resistance.
- PKC pathway modulation may be a target for overcoming ras-driven oncogenesis.