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Expression of ras oncogene leads to down-regulation of protein kinase C
T Haliotis1, W Trimble, S Chow
1Mount Sinai Hospital Research Institute, University of Toronto, Ontario, Canada.
Abstract:
The effect of mutated c-Ha-ras expression on Ca2+ and phospholipid-dependent protein kinase C (PKC) activity during the process of transformation was analysed using an inducible metallothionein-ras hybrid oncogene system. A close correlation was found between the timing of ras expression and the loss of PKC enzymatic activity measured in a cell-free system. Examination of the subcellular distribution of the enzyme in inducible and constitutive ras-transformants revealed that expression of ras was associated with an apparent translocation of PKC to the plasma membrane concomitant with down-regulation of PKC enzymatic activity in particulate as well as cytosolic fractions. Quantitation of PKC protein utilizing a PKC-specific antiserum showed that ras expression was associated with a decrease in the total amount of PKC protein present in the cell. We conclude that transformation by c-Ha-ras is accompanied by down-regulation of PKC activity and that the basis of this effect may, to a large extent, lie in the down-regulation of the amount of PKC protein.
Insights
Mutated c-Ha-ras expression during cell transformation correlates with reduced protein kinase C (PKC) activity. This decrease is linked to lower PKC protein levels and altered enzyme distribution, suggesting a key role for PKC in ras-induced transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Protein kinase C (PKC) plays a crucial role in cellular signaling pathways.
- Ras oncogenes are frequently implicated in human cancers and cellular transformation.
- Understanding the interplay between ras and PKC is vital for cancer research.
Purpose of the Study:
- To investigate the effect of mutated c-Ha-ras expression on protein kinase C (PKC) activity during cellular transformation.
- To analyze the correlation between ras expression timing and PKC enzymatic activity.
- To examine the subcellular localization and protein levels of PKC in response to ras expression.
Main Methods:
- Utilized an inducible metallothionein-ras hybrid oncogene system for controlled ras expression.
- Measured PKC enzymatic activity in cell-free systems.
- Assessed the subcellular distribution of PKC in inducible and constitutive ras-transformants.
- Quantitated PKC protein levels using a PKC-specific antiserum.
Main Results:
- A strong correlation was observed between the timing of ras expression and the loss of PKC enzymatic activity.
- Ras expression led to an apparent translocation of PKC to the plasma membrane.
- PKC enzymatic activity was down-regulated in both particulate and cytosolic fractions.
- Ras expression was associated with a decrease in the total cellular amount of PKC protein.
Conclusions:
- Cellular transformation induced by c-Ha-ras is accompanied by a significant down-regulation of PKC activity.
- The reduction in PKC activity is largely attributed to a decrease in the total amount of PKC protein.
- These findings highlight a critical regulatory link between ras oncogene activity and PKC signaling in transformation.