Induction of ornithine decarboxylase in normal and protein kinase C--depleted human colon carcinoma cells.

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.