Tumor necrosis factor-α, a new tumor promoter, engendered by biochemical studies of okadaic acid

Abstract

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 engendered a new tumor promoter applicable to human cancer development. © 1994 BY The Journal of Biochemistry.