Epidermal growth factor inhibits bombesin-induced activation of phospholipase C-β1 in rat pancreatic acinar cells

Abstract

Background and Aims: 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. Methods: Intact pancreatic acini were pretreated with pertussis toxin to study the role of G(j/o)-type heterotrimeric guanosine triphosphate-binding regulatory proteins (G proteins) in EGF-induced modulation of PLC activity. To identify the PLC isoenzyme(s) and G(j/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-β isoenzymes or G protein α-subunits. The association of PLC-β1 and G(i/o)-type G proteins was studied by pertussis toxin-catalyzed [32P]adenosine diphosphate ribosylation of PLC-β1 immunoprecipitates. Results: Pertussis toxin pretreatment of pancreatic acini abolished the inhibitory effect of EGF on bombesin-induced PLC activation and amylase release. Anti-PLC-β1, -β3, and G(q/11)α antibodies inhibited bombesin- induced PLC activity by 50%, 35%, and 65%, respectively. Anti-G,1-2α, but not a G(j)3α-specific antibody, abolished the inhibitory effect of EGF on bombesin-induced PLC activity. Pertussis toxin-sensitive G proteins coimmunoprecipitated with PLC-β1 in an EGF-dependent fashion. Conclusions: EGF inhibits bombesin-induced activation of PLC-β1 by a mechanism involving activation of G(j)1-2 proteins in pancreatic acinar membranes.