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


RESULTS
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.


CONCLUSIONS
EGF inhibits bombesin-induced activation of PLC-beta1 by a mechanism involving activation of Gi1-2 proteins in pancreatic acinar membranes.
Piiper
A
A
II Medical Department, University of Frankfurt, Germany.
Stryjek-Kaminska
D
D
Klengel
R
R
Zeuzem
S
S
D000681:Amylases / Q000378:metabolism; D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D008245:Lysophospholipase / Q000378:metabolism; D008297:Male; D010179:Pancreas / Q000187:drug effects* / Q000201:enzymology; D037342:Pertussis Toxin; D051381:Rats; D017207:Rats, Sprague-Dawley; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010566:Virulence Factors, Bordetella; D004815:Epidermal Growth Factor; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D008245:Lysophospholipase; D010738:Type C Phospholipases; D000681:Amylases; D019204:GTP-Binding Proteins; D001839:Bombesin