ABSTRACT
Tumor promoters, derived from plants and marine organisms, have played a key role in studying the pathways involved in the regulation of cell growth. Naturally occurring compounds have proven to be useful tools for studying signal transduction. These compounds often interact with specific receptors in cell types of other species, causing the activation or inhibition of cellular pathways. A particularly good system for investigating the regulatory control of growth factor action is the interaction between tumor promoters and the cell surface receptor for epidermal growth factor (EGF). The cyclic nucleotide-independent, calcium-phospholipid stimulated protein kinase C, first described by Nishizuka and co-workers, is a serine- and threonine-specific protein kinase that is the major cellular receptor for TPA-type tumor promoters. The ability of factors which activate protein kinase C to modulate the EGF receptor suggests that protein kinase C has an important role in coordinating the response of cells to multiple factors present in their environment.
