G protein Gαq/11 and Gαi1,2 are activated by pancreastatin receptors in rat liver: Studies with GTP-γ35S and azido-GTP-α-32P
✍ Scribed by José Santos-Álvarez; Víctor Sánchez-Margalet
- Book ID
- 101259798
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 131 KB
- Volume
- 73
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
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 ␥-35 S-GTP; specific anti-G protein ␣ 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-␣-32 P-GTP into liver membranes and into specific immunoprecipitates of different G␣ subunits from soluble rat liver membranes. Pancreastatin stimulation of rat liver membranes increases the binding of ␥-35 S-GTP in a time-and dose-dependent manner. Activation of the soluble receptors still led to the pancreastatin dose-dependent stimulation of ␥-35 S-GTP binding. Besides, WGA semipurified receptors also stimulates GTP binding. The binding was inhibited by treatment with anti-G␣ q/11 (85%) and anti-G␣ i1,2 (15%) sera, whereas anti-G␣ 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-␣-32 P-GTP into G␣ q/11 and G␣, but not into G␣ o,i3 from soluble rat liver membranes. In conclusion, pancreastatin stimulation of rat liver membranes led to the activation of G␣ q/11 and G␣ i1,2 proteins. These results suggest that G␣ q/11 and G␣ i1,2 may play a functional role in the signaling of pancreastatin receptor by mediating the production of IP 3 and cGMP respectively.