The phorbol ester analog, mezerein, is a weak complete and Stage 1 tumor promoter; however, it is as potent as the most active phorbol esters as a second stage promoter and inflammatory agent. Therefore, mezerein is a useful compound for studying responses associated with Stage 1 or Stage 2 promotion. In this paper, we show that in G-292 osteosarcoma cells in culture, mezerein is 25-fold more potent in causing a decrease in binding of epidermal growth factor to its specific cellular receptor than in inducing prostaglandin E2 production. This differential potency for these two actions was not noted for other phorbol esters. Our findings indicate that mezerein interacts with the major phorbol dibutyrate receptor to increase prostaglandin E2 production and also either with a distinct cellular target with a higher affinity or the same target with increased efficacy to cause a decrease in the binding of epidermal growth factor. These human osteosarcoma cells thus provide a model system to facilitate analysis of phorbol ester receptor heterogeneity.

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