AJP - Gastrointestinal and Liver Physiology, Vol 263, Issue 3 396-G406, Copyright © 1992 by American Physiological Society
Effects of agonists on p21ras and ras-related proteins in rat pancreatic acinar cells
P. Zimmermann, S. Schnefel, S. Zeuzem, A. Profrock, W. Haase and I. Schulz
Max-Planck-Institut fur Biophysik, Frankfurt am Main, Federal Republic of Germany.
This study shows the presence of seven different low-molecular-weight GTP
binding proteins (smg proteins) with molecular masses between 18 and 27 kDa
in subfractions of rat pancreatic acinar cells. After stimulation of
isolated intact and permeabilized pancreatic acinar cells with
cholecystokinin octapeptide (CCK-OP), the diacylglycerol (DG) analogue
12-O-tetradecanoylphorbol 13-acetate (TPA), vasoactive intestinal peptide
(VIP), adenosine 3',5'-cyclic monophosphate (cAMP), or guanosine
5'-O-(3-thiotriphosphate) (GTP gamma S), [alpha-32P]GTP binding to 21- to
22-kDa smg protein(s) in microsomal membranes (MM) was reduced, whereas the
[alpha-32P]GTP binding to 23-kDa protein(s) was enhanced. In addition,
prestimulation of permeabilized cells with GTP gamma S caused enhancement
of [alpha-32P]GTP binding to a 19-kDa protein in MM [immunologically
identified as the ADP-ribosylation factor (arf)]. In the presence of
cytosol, direct addition of GTP gamma S to isolated MM resulted in an
apparent translocation of the 19-kDa protein (arf) from the cytosol to
membranes. This indicates increased association of arf with the membrane in
its GTP-bound state. In CCK-OP-prestimulated acinar cells, [alpha-32P]GTP
binding to plasma membrane-located 21- to 22-kDa proteins (immunologically
identified as p21ras proteins) was enhanced, suggesting that there is an
interrelationship between p21ras proteins and CCK receptors. Our results
give evidence for a role of 19-kDa, 21- to 22-kDa, and 23-kDa smg proteins
in cAMP-protein kinase A- and DG-protein kinase C-mediated stimulation of
intracellular pathways in pancreatic acinar cells.
