Epidermal growth factor activates phospholipase c-[gamma]1 via gi1
-2 proteins in isolated pancreatic acinar membranes.
Piiper, Albrecht, Danuta Stryjek-Kaminska, and Stefan Zeuzem.
II Medical Department, University of Frankfurt, 60590 Frankfurt a.
M., Germany
APStracts 3:0262G, 1996.
In the present study isolated pancreatic acinar membranes were used to
investigate the mechanism of epidermal growth factor (EGF)-induced
activation of phospholipase C (PLC). The data show that EGF caused
rapid and strong increase in tyrosine phosphorylation of the EGF
receptor with a maximum at 5 to 15 s after beginning of the
incubation followed by a decline. Using [3H]phosphatidylinositol 4,5
-bisphosphate as exogenous substrate PLC activity increased fourfold
upon exposure of the membranes to EGF (85 nM). In contrast, EGF
-induced tyrosine phosphorylation of PLC-[gamma]1 was rather small,
indicating that tyrosine phosphorylation of PLC-[gamma]1 is not
proportional to changes in PLC activity. EGF-induced activation of
PLC was strongly inhibited by pertussis toxin-pretreatment of the
membranes, by an antibody raised against a C-terminal sequence shared
by [alpha]-subunits of the G proteins Gi1 and Gi2, and by an anti
-PLC-[gamma]1 antibody, whereas anti-Gi3[alpha], anti-Gq/11[alpha],
and anti-PLC-[beta]1 antibodies had no effect. In contrast, pertussis
toxin or the anti-Gi1-2[alpha] antibody had no effect on EGF-induced
tyrosine phosphorylation of PLC-[gamma]1. EGF promoted association of
Gi proteins with both the EGF receptor and PLC-[gamma]1 with similar
kinetics as EGF receptor autophosphorylation. All EGF-induced
responses were abolished by the specific tyrosine kinase inhibitor
pp60v-src (137-157), suggesting that EGF receptor tyrosine kinase
activity is essential for Gi1-2-mediated activation of PLC-[gamma]1.
However, there was no evidence for tyrosine phosphorylation of Gi1
-2[alpha]. Taken together, these data show that EGF causes activation
of PLC-[gamma]1 by a mechanism requiring activation of Gi1-2 and only
a small increase in tyrosine phosphorylation of PLC-[gamma]1.
Received 24 April 1996; accepted in final form 21 October 1996.
APS Manuscript Number G192-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996