Cholecystokinin-stimulated tyrosine phosphorylation of PKC-δ in pancreatic acinar cells is regulated bidirectionally by PKC activation

Abstract

PKC-δ is important in cell growth, apoptosis, and secretion. Recent studies show its stability is regulated by tyrosine phosphorylation (TYR-P), which can be stimulated by a number of agents. Many of these stimuli also activate phospholipase C (PLC) cascades and little is known about the relationship between these cascades and PKC-δ TYR-P. Cholecystokinin (CCK) stimulates PKCs but it is unknown if it causes PKC-δ TYR-P and if so, the relationship between these cascades is unknown. In rat pancreatic acini, CCK-8 stimulated rapid PKC-δ TYR-P by activation of the low affinity CCK A receptor state. TPA had a similar effect. BAPTA did not decrease CCK-stimulated PKC-δ TYR-P but instead, increased it. A23187 did not stimulate PKC-δ TYR-P. Wortmannin and LY 294002 did not alter CCK-stimulated PKC-δ TYR-P. GF 109203X, at low concentrations, increased PKC-δ TYR-P stimulated by CCK or TPA and at higher concentrations, inhibited it. The cPKC inhibitors, Gö 6976 and safingol, caused a similar increase in TPA- and CCK-stimulated PKC-δ TYR-P. These results demonstrate that CCK A receptor activation causes PKC-δ TYR-P through activation of only one of its two receptor affinity states. This PKC-δ TYR-P is not directly influenced by changes in [Ca 2+] i; however, the resultant activation of PKC-α has an inhibitory effect. Therefore, CCK activates both stimulatory and inhibitory PKC cascades regulating PKC-δ TYR-P and, hence, likely plays an important role in regulating PKC-δ degradation and cellular abundance.