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Increased expression of protein kinase C beta activates ERK3
1Laboratory of Gastrointestinal Tumor Biology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
The Journal of Biological Chemistry
|May 10, 1996
Summary
Overexpression of protein kinase C beta (PKC beta) in colon cancer cells constitutively activates the mitogen-activated protein kinase ERK3, impacting cell growth and differentiation pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Prior studies established that stable transfection of protein kinase C beta 1 (PKC beta 1) or PKC beta 2 into colon cancer cells elevated PKC beta levels and kinase activity.
- These PKC beta transfectants showed blocked differentiation, increased growth in mice, and restored basic fibroblast growth factor response pathways.
Purpose of the Study:
- To investigate the effect of PKC beta overexpression on the mitogen-activated protein kinase ERK3 in differentiated colon cancer cells.
Main Methods:
- Analysis of cell lysates using in-gel kinase assays to measure kinase activity.
- Western blotting and immunoprecipitation with anti-ERK3 monoclonal antibody to assess ERK3 protein abundance.
- Immune complex kinase assays to quantify ERK3 activity post-immunoprecipitation.
Main Results:
- A significant increase (>10-fold) in ERK3 activity was observed in PKC beta 1 and PKC beta 2 transfectants compared to controls.
- ERK3 protein levels remained unchanged, indicating activation rather than overexpression.
- Treatment with 12-O-tetradecanoylphorbol-13-acetate down-regulated both PKC and ERK3 activities, establishing a causal link.
Conclusions:
- Overexpression of PKC beta leads to constitutive activation of ERK3 in colon cancer cells.
- Activated ERK3 was localized to nuclear and membrane fractions, potentially explaining its constitutive activity.
- This PKC beta-mediated ERK3 activation may contribute to the observed blocked differentiation and enhanced growth in these cancer cells.