Flat reversion by okadaic acid of raf and ret-II transformants.
Okadaic acid is a non-phorbol 12-myristate 13-acetate (PMA)-type tumor promoter on mouse skin and known to be a potent inhibitor of serine/threonine protein phosphatases. Contrary to expectation from its tumor-promoting activity, okadaic acid was shown to have a potential to revert the phenotypes of cells transformed by raf and ret-II to that of normal cells. Two to 3 days after addition of 8 ng of okadaic acid per ml to the culture medium, raf and ret-II transformants changed to flat cells and gained contact inhibition. The amount of fibronectin, which was decreased in malignant transformed cells, was increased in the flat revertants. Moreover, okadaic acid caused a dose-dependent loss of ability to grow in soft agar. The morphology of the cells reverted to malignant phenotype within 1 week after removal of okadaic acid. The levels of mRNA and protein of activated c-raf in flat revertants were similar to those in parental transformed cells. The level of mRNA of ret-II was also not changed by flat reversion. No induction of flat reversion was observed with okadaic acid tetramethyl ether, an inactive compound, or a phorbol ester, PMA. As okadaic acid is a potent inhibitor of protein phosphatases 1 and 2A, the possibility that these phosphatases are involved in signal transduction from the raf and ret-II oncogenes is suggested.
Sakai
R
R
Carcinogenesis Division, National Cancer Center Research Institute, Tokyo, Japan.
Ikeda
I
I
Kitani
H
H
Fujiki
H
H
Takaku
F
F
Rapp
U
U
Sugimura
T
T
Nagao
M
M
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D002478:Cells, Cultured; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005353:Fibronectins / Q000032:analysis / Q000096:biosynthesis; D005455:Fluorescent Antibody Technique; D011905:Genes, ras; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D019319:Okadaic Acid; D009857:Oncogenes; D011519:Proto-Oncogenes; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
D004988:Ethers, Cyclic; D005353:Fibronectins; D007476:Ionophores; D019319:Okadaic Acid; D013755:Tetradecanoylphorbol Acetate