CCK activates RhoA and Rac1 differentially through Gα13and Gαqin mouse pancreatic acini

Abstract

Cholecystokinin (CCK) has been shown to activate RhoA and Rac1, as well as reorganize the actin cytoskeleton and, thereby, modify acinar morphology and amylase secretion in mouse pancreatic acini. The aim of the present study was to determine which heterotrimeric G proteins activate RhoA and Rac1 upon CCK stimulation. Gα13, but not Gα12, was identified in mouse pancreatic acini by RT-PCR and Western blotting. Using specific assays for RhoA and Rac1 activation, we showed that only active Gα13activated RhoA. By contrast, active Gα13and Gαq, but not Gαs, slightly increased GTP-bound Rac1 levels. A greater increase in Rac1 activation was observed when active Gα13and active Gαqwere coexpressed. Gαiwas not required for CCK-induced RhoA or Rac1 activation. The regulator of G protein signaling (RGS) domain of p115-Rho guanine nucleotide exchange factor (p115-RGS), a specific inhibitor of Gα12/13-mediated signaling, abolished CCK-stimulated RhoA activation. By contrast, both RGS-2, an inhibitor of Gαq, and p115-RGS abolished CCK-induced Rac1 activation, which was PLC pathway-independent. Active Gαqand Gα13, but not Gαs, induced morphological changes and actin redistribution similar to 1 nM CCK. CCK-induced actin cytoskeletal reorganization was inhibited by RGS-2, but not by p115-RGS, whereas CCK-induced amylase secretion was blocked by both inhibitors. Together, these findings indicate that, in mouse pancreatic acini, Gα13links CCK stimulation to the activation of RhoA, whereas both Gα13and Gαqlink CCK stimulation to the activation of Rac1. CCK-induced actin cytoskeletal reorganization is mainly mediated by Gαq. By contrast, Gα13and Gαqsignaling are required for CCK-induced amylase secretion.