Activation of protein kinase C by non-phorbol tumor promoter, mezerein.

Mezerein, classified as a second-stage tumor promoter, has no diacylglycerol-like structure in its molecule, but can activate protein kinase C both in vitro and in vivo. This non-phorbol diterpene competitively inhibits the specific binding of a radioactive tumor-promoting phorbol ester to the enzyme. It is suggestive that tumor-promoting phorbol esters and mezerein cause analogous changes in the membrane to activate protein kinase C, and utilize this protein kinase as a common receptive protein for tumor promotion.