pp60c-src activation in human colon carcinoma

c-src structure in human cancers with elevated pp60c-src activity

We used RNAase protection and restriction fragment length polymorphism assays to detect activating mutations of c-src in a spectrum of human tumours. No mutations were detected at codons 98, 381, 444, and 530. We conclude that mutational activation is not the mechanism of enhancement of pp60c-src-specific kinase activity found in a number of human cancer types.

Ribosomal protein genes are overexpressed in colorectal cancer: isolation of a cDNA clone encoding the human S3 ribosomal protein

We have isolated a cDNA clone encoding the human S3 ribosomal protein from a normal human colon cDNA library. The clone was identified as one of many that detected genes whose level of expression was increased in adenocarcinoma of the colon relative to normal colonic mucosa. Increased levels of the S3 transcript were present in the tumors of all eight patients examined. Moreover, the S3 mRNA was also more abundant in 7 of 10 adenomatous polyps, the presumed precursor of carcinoma. Additional studies demonstrated that increased levels of mRNAs encoding several other ribosomal proteins, including S6, S8, S12, L5, and P0, were present in colorectal tumors and polyps. These results suggest that there is increased synthesis of ribosomes in colorectal tumors and that this increase is an early event in colon neoplasia.

Ribosomal protein genes are overexpressed in colorectal cancer: isolation of a cDNA clone encoding the human S3 ribosomal protein

We have isolated a cDNA clone encoding the human S3 ribosomal protein from a normal human colon cDNA library. The clone was identified as one of many that detected genes whose level of expression was increased in adenocarcinoma of the colon relative to normal colonic mucosa. Increased levels of the S3 transcript were present in the tumors of all eight patients examined. Moreover, the S3 mRNA was also more abundant in 7 of 10 adenomatous polyps, the presumed precursor of carcinoma. Additional studies demonstrated that increased levels of mRNAs encoding several other ribosomal proteins, including S6, S8, S12, L5, and P0, were present in colorectal tumors and polyps. These results suggest that there is increased synthesis of ribosomes in colorectal tumors and that this increase is an early event in colon neoplasia.

Isolation and characterization of normal and neoplastic colonic epithelial cell populations

The aim of the present study was to characterize rat mucosal colonic cells harvested from the crypt continuum during differentiation and dimethylhydrazine-induced neoplasia. The collection of colonocytes was performed using a modified nonenzymatic isolation procedure based on Ca2+ chelation and gentle mechanical dissociation. Light and electron microscopy histomorphological examinations, [3H]thymidine incorporation studies, and activity gradients of alkaline phosphatase, thymidine kinase, and cytoskeleton-associated protein tyrosine kinase indicated that distinct cell populations were harvested from the various crypt regions in a temporal sequence mirroring their zonal and functional distribution in situ. After dimethylhydrazine administration, marked protein tyrosine kinase activity was noted in colonic cells harvested from upper crypt zones. The misplaced and sustained kinase activity preceded the actual polyp or tumor formation. This observation is consistent with the expansion of colonic proliferative compartments beyond allowable boundaries during the preneoplastic period. Companion studies in human colonic epithelial specimens corroborate the findings observed in normal and transformed murine colonocytes. It is believed that the characterization and manipulation of colonocytes using our in vitro model will provide important clues to the molecular events underlying the differentiation program and carcinogenic process in the colonic cell.

Generation and use of anti-phosphotyrosine antibodies for immunoblotting

The techniques of detecting phosphotyrosine-containing proteins by AIA and purifying these proteins by affinity chromatography with anti-phosphotyrosine monoclonal antibodies are both reliable and consistent. Although not every tyrosine-phosphorylated protein can be detected and purified by using these techniques, a majority can. No doubt future studies will employ these approaches both for analyzing the specific role that tyrosine protein phosphorylation plays in regulating cell division and for investigating the properties of heretofore uncharacterized proteins that contain phosphotyrosine.

Activation of the pp60c-src protein kinase is an early event in colonic carcinogenesis

Colonic neoplasia provides an opportunity to study tumor progression because most carcinomas arise from adenomas (polyps), which, in turn, arise from normal epithelia. The malignant potential of adenomas varies with size, histology, and degree of dysplasia. Polyps that are less than 2 cm with villous architecture and severe dysplasia are most likely to contain carcinoma. Previous studies demonstrated that the in vitro protein-tyrosine kinase activity of pp60c-src from colon carcinomas is significantly higher than that from adjacent normal mucosa. Here we report that the protein kinase activity of pp60c-src is also elevated in colonic polyps. Activity is highest in malignant polyps and in greater than 2-cm benign polyps that contain villous structure and severe dysplasia. Thus, pp60c-src activation occurs in benign polyps that are at greatest risk for developing cancer. These data suggest that activation of the protooncogene product pp60c-src may be an important event in the genesis of human colon carcinoma.