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G protein Gα q/11 and Gα i1,2 are activated by pancreastatin receptors in rat liver: Studies with GTP‐γ 35 S and azido‐GTP‐α‐ 32 P
Author(s) -
SantosÁlvarez José,
SánchezMargalet Víctor
Publication year - 1999
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/(sici)1097-4644(19990615)73:4<469::aid-jcb5>3.0.co;2-u
Subject(s) - gtp' , g protein , pertussis toxin , receptor , gtp binding protein regulators , biochemistry , phospholipase c , membrane , stimulation , biology , biophysics , microbiology and biotechnology , chemistry , endocrinology , enzyme
In the liver, pancreastatin exerts a glycogenolytic effect through interaction with specific receptors, followed by activation of phospholipase C and guanylate cyclase. Pancreastatin receptor seems to be coupled to two different G protein systems: a pertussis toxin‐insensitive G protein that mediates activation of phospholipase C, and a pertussis toxin sensitive G protein that mediates the cyclic GMP production. The aim of this study was to identify the specific G protein subtypes coupling pancreastatin receptors in rat liver membranes. GTP binding was determined by using γ‐ 35 S‐GTP; specific anti‐G protein α subtype sera were used to block the effect of pancreastatin receptor activation. Activation of G proteins was demonstrated by the incorporation of the photoreactive GTP analogue 8‐azido‐α‐ 32 P‐GTP into liver membranes and into specific immunoprecipitates of different Gα subunits from soluble rat liver membranes. Pancreastatin stimulation of rat liver membranes increases the binding of γ‐ 35 S‐GTP in a time‐ and dose‐dependent manner. Activation of the soluble receptors still led to the pancreastatin dose‐dependent stimulation of γ‐ 35 S‐GTP binding. Besides, WGA semipurified receptors also stimulates GTP binding. The binding was inhibited by treatment with anti‐Gα q/11 (85%) and anti‐Gα i1,2 (15%) sera, whereas anti‐Gα o,i3 serum failed to affect the binding. Finally, pancreastatin stimulates GTP photolabeling of particulate membranes. Moreover, it specifically increased the incorporation of 8‐azido‐α‐ 32 P‐GTP into Gα q/11 and Gα, but not into Gα o,i3 from soluble rat liver membranes. In conclusion, pancreastatin stimulation of rat liver membranes led to the activation of Gα q/11 and Gα i1,2 proteins. These results suggest that Gα q/11 and Gα i1,2 may play a functional role in the signaling of pancreastatin receptor by mediating the production of IP 3 and cGMP respectively. J. Cell. Biochem. 73:469–477, 1999. © 1999 Wiley‐Liss, Inc.