Mezerein is a toxic diterpene ester found in the sap of Daphne mezereum and related plants. Plants of the genera Euphorbiaceae and Thymelaeaceae possess a wide variety of different phorbol esters, which share the capacity of mimicking diacylglycerol (DAG) and thus activating different isoforms of protein kinase C. Mezerein was first isolated in 1975. It has antileukemic properties in mice, but it is also defined as a weak promoter of skin cancers in the same species. All parts of the plants contain an acrid and irritant sap that contains mezerein, thought to be the principal poison. The sap is especially prevalent in the bark and berries.