Reduced C-terminal Src kinase activity is correlated inversely with pp60(c-src) activity in colorectal carcinoma.
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.
Cam
W R
WR
Department of Gastroenterology, University of Tokyo, Tokyo, Japan.
Masaki
T
T
Shiratori
Y
Y
Kato
N
N
Ikenoue
T
T
Okamoto
M
M
Igarashi
K
K
Sano
T
T
Omata
M
M
D000368:Aged; D015152:Blotting, Northern; D000081247:CSK Tyrosine-Protein Kinase; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D005260:Female; D019073:HT29 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013223:Statistics as Topic; D014407:Tumor Cells, Cultured; D019061:src-Family Kinases
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; C000631346:CSK protein, human