Phosphorylation of the gamma chain of the high affinity receptor for immunoglobulin E by receptor-associated protein kinase C-delta.

The gamma chain of the high affinity receptor for immunoglobulin E is a member of the T-cell antigen receptor zeta chain family and a functional subunit common to both T-cell and Fc receptors. Here we report that the gamma chain is phosphorylated on threonine in response to protein kinase C activation. Furthermore, the threonine phosphorylation of the gamma chain correlates with the endocytosis of this receptor. We identified a receptor-associated kinase as the calcium-independent protein kinase C-delta and found that it associates with the carboxyl-terminal cytoplasmic domain of the beta chain. In addition, protein kinase C-delta was the only isozyme capable of phosphorylating the gamma chain in vitro. These findings provide evidence for the functional role of protein kinase C-delta in early signal transduction events in the mast cell and suggest a more general mechanism of activation for receptors that share subunits of the zeta chain family.