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Reduced C-terminal Src kinase activity is correlated inversely with pp60(c-src) activity in colorectal carcinoma
W R Cam1, T Masaki, Y Shiratori
1Department of Gastroenterology, University of Tokyo, Tokyo, Japan.
Background:
Specific kinase activity of the proto-oncogene product pp60(c-src) is reported to be elevated in patients with carcinoma of the colon, and a novel cytoplasmic protein-tyrosine kinase, C-terminal Src kinase (Csk), has been found to inactivate the members of the Src family protein-tyrosine kinase. In this study, Csk activity and pp60(c-src) activity were examined in colorectal tumors as well as in colon carcinoma cell lines.
Methods:
Colorectal carcinoma tissue and adjacent nonneoplastic tissue from 24 patients, from 8 colon carcinoma cell lines, and from 1 normal colon cell line were used. The levels of pp60(c-src) and Csk in colorectal tissue and cell lines were analyzed by Western and/or Northern blot analysis, and their kinase activity levels were measured by in-gel kinase assay.
Results:
In the samples from 24 patients with colorectal carcinoma, pp60(c-src) kinase activity and protein levels were increased by 7.8 +/- 0.55 and 2.6 +/- 0.13 times the control levels, respectively. Conversely, the Csk protein level and its kinase activity were reduced by 0.53 +/- 0.08 and 0.53 +/- 0.09 times the control levels, respectively. pp60(c-src) kinase activity was correlated inversely with Csk activity (correlation coefficient = -0.71; P < 0.0001). Of the cell lines, pp60(c-src) kinase activity and protein levels, respectively, were 7.4 +/- 1.22 and 1.86 +/- 0.28 times greater than normal control levels. Csk protein level and kinase activity, respectively, were 0.54 +/- 0.13 and 0.52 +/- 0.11 times less normal control levels and were correlated with mRNA amount.
Conclusions:
Csk mRNA, protein, and its kinase activity were reduced in colorectal carcinoma and were correlated with pp60(c-src) kinase activity level. The reduced activity of Csk may be involved in the transformation of a subset of colorectal carcinoma.
Insights
Reduced C-terminal Src kinase (Csk) activity and elevated pp60(c-src) kinase activity were observed in colorectal carcinoma. This inverse correlation suggests Csk may play a role in colorectal cancer development.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Proto-oncogene pp60(c-src) kinase activity is elevated in colon carcinoma.
- C-terminal Src kinase (Csk) is a novel kinase that inactivates Src family kinases.
- This study investigates Csk and pp60(c-src) activity in colorectal tumors and cell lines.
Purpose of the Study:
- To examine the activity levels of Csk and pp60(c-src) in colorectal carcinoma.
- To determine the relationship between Csk and pp60(c-src) activity in colorectal cancer.
Main Methods:
- Western and Northern blot analyses were used to quantify protein and mRNA levels of pp60(c-src) and Csk.
- In-gel kinase assays measured the kinase activity of pp60(c-src) and Csk.
- Analyses were performed on colorectal carcinoma tissues, adjacent nonneoplastic tissues, and colon carcinoma cell lines.
Main Results:
- pp60(c-src) kinase activity and protein levels were significantly increased in colorectal carcinoma tissues compared to controls.
- Csk protein levels and kinase activity were significantly reduced in colorectal carcinoma tissues.
- A strong inverse correlation was found between pp60(c-src) kinase activity and Csk activity (r = -0.71, P < 0.0001).
- Similar alterations in pp60(c-src) and Csk were observed in colon carcinoma cell lines.
Conclusions:
- Csk mRNA, protein levels, and kinase activity are reduced in colorectal carcinoma.
- Reduced Csk activity is correlated with elevated pp60(c-src) kinase activity.
- The diminished activity of Csk may contribute to the transformation of colorectal carcinoma cells.