MAPK activity is down-regulated in human colon adenocarcinoma: correlation with PKC activity.

Cellular growth is regulated by a cascade of kinases, among which mitogen activated protein kinase (MAPK) is an integral member of the Ras-mediated pathway, while protein kinase C (PKC) is recognized as the intracellular receptor of tumor promoters. To assess the role of these two signal transduction enzymes in colonic carcinogenesis, we measured MAPK and PKC activities in cytosol and membrane compartments of: 1) normal colon, 2) colon adenocarcinoma, and 3) histologically normal colonic tissue taken from the margin of resection of neoplastic colon. Both MAPK and PKC activities were down-regulated in solubilized membranes from the cancers. MAPK activity was also down-regulated in the tissue adjacent to the cancer and designated as histologically normal (by routine histopathology). Therefore, MAPK activity appears to be more suitable than PKC as a marker for early detection of colonic transformation.