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Protein kinases play a key role in intracellular signalling, participating at multiple levels along the transduction cascades that trigger mitogenic response. Because protein kinases are involved in mitogenic pathways, they are likely to play a role in the abnormal proliferation of malignant cells. In this study we compared activity of mitogen-activated protein (MAP) kinase and several renaturable kinases in homogenates of 30 surgically resected colorectal cancers and their adjacent normal tissues. Using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and membrane autophosphorylation assay on homogenates obtained from normal colon mucosa and adenocarcinoma, we identified at least four renaturable kinases (50, 55, 85, 200 kDa). Compared with adjacent tissue, in most of the cancer samples only the 85-kDa kinase exhibited a higher level of autophosphorylation activity than those in normal matched tissue (P < 0.001). Moreover, the 85-kDa kinase from nearly all cancer homogenates showed faster electrophoretic mobility than the 85-kDa kinase from normal tissue homogenates. Interestingly, the 50-kDa kinase had significantly lower autophosphorylation activity in cancer tissues than those of normal tissue (P< 0.05). To assess p42-p44 MAP kinase activity, proteins were immunoprecipitated from adjacent colon mucosa and adenocarcinoma with anti-extracellular signal-related kinase (ERK) 1/2 antibodies, and MAP kinase activity was measured using MBP as a substrate. These studies revealed that MAP kinase activity in colorectal cancer was significantly higher (P < 0.001) than that in adjacent mucosa. Thus, the constitutive activity of MAP kinase and autophosphorylation activity of 85-kDa kinase are increased, whereas the autophosphorylation activity of another kinase, 50 kDa, is decreased in colorectal adenocarcinoma. However, although signal transduction pathways are markedly altered in this cancer, neither p42/p44 MAP kinase activity nor 85-kDa autokinase activity could be correlated with the established prognostic indicators.

To examine the role of protein kinase C (PKC) in induction of human colon adenocarcinoma cell line, DETA/W, by polypeptide growth-promoting factors, ornithine decarboxylase activity (ODC) and DNA synthesis were determined in cells depleted of PKC. PKC depletion was achieved by prolonged cultivation (more than 30 passages) with 10(-6) M phorbol 12-myristate 13-acelate. Lack of PKC in studied cells was proved by measurements of PKC activity and immunoreactivity. Although ODC activities and DNA syntheses in PKC-depleted cells were decreased by about 40-50% compared to normal DETA/W cells, the percentage increase of these mitogen-responsive reactions was quantitatively similar in both cell sublines. These results raise the possibility that not all of the biological responses to growth factors are connected with the activation of calcium-dependent PKC.