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The Journal of Biochemistry
Vol. 115 (1994) No. 1 P 1-5


Okadaic acid is a potent tumor promoter on mouse skin and in rat glandular stomach, and an inhibitor of PP-1 and PP-2A. How okadaic acid biochemically induces tumor promotion in these tissues was reviewed. Okadaic acid bound to a catalytic subunit of PP-1 and PP-2A and induced hyperphosphorylation of proteins, such as vimentin, cytokeratins, HSP 27, and tumor suppressor gene products. Since one of the okadaic acid class compounds, microcystin-LR, induced tumor promotion in rat liver, the okadaic acid pathway mediated through inhibition of PP-1 and PP-2A is seen to be a general biochemical process of tumor promotion in various organs. The biochemical mimicry of okadaic acid by TNF-α led us to find that TNF-α is an endogenous tumor promoter. The study of tumor promotion in two-stage carcinogenesis experiments with the okadaic acid class of compounds engender-ed a new tumor promoter applicable to human cancer development.

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