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Signal transduction through extracellular signal-regulated kinase-like pp57 blocked in differentiated cells having
H Lee1, J Ghose-Dastidar, S Winawer
1Laboratory of GI Tumor Biology, Memorial Sloan Kettering Cancer Center, New York, New York 10021.
Abstract:
pp57 is a cytoplasmic kinase which is related antigenically and functionally to the extracellular signal regulated kinase or the mitogen-activated kinase family of signal transduction proteins. Two undifferentiated colon carcinoma cell lines responded to the diacylglycerol diolein by growth and a rapid 3-4-fold increase in tyrosine phosphorylation of pp57, and smaller increases in threonine and serine phosphorylation. By enhancing tyrosine phosphorylation of pp57, diolein increased pp57 kinase activity on myelin basic protein. Two enterocytic differentiated colon carcinoma cell lines, when treated with diolein, exhibited neither increased pp57 tyrosine phosphorylation nor increased growth. Both enterocytic lines exhibited 30% of the total PKC activity, 10-20% of the abundance of PKC beta as detected by Western blotting with anti-peptide antisera, and 10-20% of the PKC beta activity, by immune complex kinase reactions, that was expressed in the undifferentiated cell lines. The abundance of three other PKC isozymes, alpha, epsilon, and zeta appeared unchanged in the undifferentiated and enterocytic lines, reflecting their common parental cell line origin. The association between loss of PKC beta activity and blocked signaling through pp57 in each of two cell lines suggests that PKC beta is part of a signal transduction system activating pp57.
Insights
Diacylglycerol (DAG) stimulates colon cancer cell growth by increasing pp57 kinase activity through tyrosine phosphorylation. This signaling pathway is blocked in differentiated cells due to reduced Protein Kinase C beta (PKC beta) activity.
Area of Science:
- Cellular signaling pathways
- Cancer biology
- Signal transduction
Background:
- pp57 is a cytoplasmic kinase related to the extracellular signal-regulated kinase (ERK) and mitogen-activated protein kinase (MAPK) families.
- Signal transduction pathways regulate cell growth and differentiation in cancer.
Purpose of the Study:
- To investigate the role of pp57 kinase and Protein Kinase C beta (PKC beta) in colon carcinoma cell signaling.
- To determine the effect of diacylglycerol (diolein) on pp57 phosphorylation and kinase activity in different colon cancer cell lines.
Main Methods:
- Treatment of undifferentiated and enterocytic differentiated colon carcinoma cell lines with diolein.
- Analysis of pp57 phosphorylation (tyrosine, threonine, serine) and kinase activity.
- Quantification of total Protein Kinase C (PKC) activity and specific PKC isozyme abundance (PKC beta, alpha, epsilon, zeta) using Western blotting and immune complex kinase reactions.
Main Results:
- Diolein treatment induced growth and increased pp57 tyrosine phosphorylation in undifferentiated colon carcinoma cells, enhancing pp57 kinase activity.
- Differentiated colon carcinoma cell lines showed no response to diolein, with no increase in pp57 phosphorylation or growth.
- Enterocytic differentiated cell lines exhibited significantly lower total PKC activity, PKC beta abundance, and PKC beta activity compared to undifferentiated lines.
- Abundance of PKC alpha, epsilon, and zeta remained unchanged across cell lines.
Conclusions:
- Reduced PKC beta activity in differentiated colon cancer cells is associated with a block in diolein-induced signaling through pp57.
- PKC beta likely plays a crucial role in the signal transduction pathway that activates pp57 in response to diacylglycerol.