Epidermal growth factor inhibits bombesin-induced activation of phospholipase C-beta1 in rat pancreatic acinar cells.

Abstract

Epidermal growth factor (EGF) inhibits bombesin-induced activation of phosphoinositide-specific phospholipase C (PLC) in pancreatic acini. The aim of this study was to investigate the mechanism by which EGF inhibits bombesin-induced activation of PLC. Intact pancreatic acini were pretreated with pertussis toxin to study the role of Gi/o-type heterotrimeric guanosine triphosphate-binding regulatory proteins (G proteins) in EGF-induced modulation of PLC activity. To identify the PLC isoenzyme(s) and Gi/o protein subtype(s) involved in EGF-induced signaling, PLC activity was measured in isolated pancreatic acinar membranes that had been preincubated with immunoneutralizing antibodies raised against various PLC-beta isoenzymes or G protein alpha-subunits. The association of PLC-beta1 and Gi/o-type G proteins was studied by pertussis toxin-catalyzed [32P]adenosine diphosphate ribosylation of PLC-beta1 immunoprecipitates. Pertussis toxin pretreatment of pancreatic acini abolished the inhibitory effect of EGF on bombesin-induced PLC activation and amylase release. Anti-PLC-beta1, -beta3, and Gq/11alpha antibodies inhibited bombesin-induced PLC activity by 50%, 35%, and 65%, respectively. Anti-Gi1-2alpha, but not a Gi3alpha-specific antibody, abolished the inhibitory effect of EGF on bombesin-induced PLC activity. Pertussis toxin-sensitive G proteins coimmunoprecipitated with PLC-beta1 in an EGF-dependent fashion. EGF inhibits bombesin-induced activation of PLC-beta1 by a mechanism involving activation of Gi1-2 proteins in pancreatic acinar membranes.