ABSTRACT
The receptor for platelet-derived growth factor (PDGF) is a 180-kdalton protein with tyrosine kinase activity that activates phosphoinositide metabolism when it binds PDGF. Although PK-C phosphorylated the insulin receptor, binding of insulin to its receptor did not have effects similar to activators of PK-C on the receptor tyrosine and phosphorylation of an 80-kdalton protein in BC3H-1 myocytes suggesting that phosphoinositide hydrolysis is not a component of the transduction of the insulin signal. More reports of inhibition of PK-C in vitro and in vivo by sphingosines provide further evidence supporting a mediator role for PK-C, although little is known of other effects of xenobiotic agents on cells. Observations have been made of the PK-A regulatory and catalytic subunits. The chapter discusses the roles of PK-C in mediating receptor-linked signals as well as modulating such signals. Signal transduction begun by extracellular signals and subsequent production of diacylglycerol results only in a brief activation of PK-C, after which the second messengers are metabolized.
