CCK activates RhoA and Rac1 differentially through Gα13 and Gαq in mouse pancreatic acini

Sabbatini ME, Bi Y, Ji B, Ernst SA, Williams JA. CCK activates RhoA and Rac1 differentially through G alpha(13) and G alpha(q) in mouse pancreatic acini. Am J Physiol Cell Physiol 298: C592-C601, 2010. First published November 25, 2009; doi: 10.1152/ajpcell.00448.2009.-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. G alpha(13), but not G alpha(12), 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 G alpha(13) activated RhoA. By contrast, active G alpha(13) and G alpha(q), but not G alpha(s), slightly increased GTP-bound Rac1 levels. A greater increase in Rac1 activation was observed when active G alpha(13) and active G alpha(q) were coexpressed. G alpha(i) was 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 G alpha(12/13)-mediated signaling, abolished CCK-stimulated RhoA activation. By contrast, both RGS-2, an inhibitor of G alpha(q), and p115-RGS abolished CCK-induced Rac1 activation, which was PLC pathway-independent. Active G alpha(q) and G alpha(13), but not G alpha(s), 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, G alpha(13) links CCK stimulation to the activation of RhoA, whereas both G alpha(13) and G alpha(q) link CCK stimulation to the activation of Rac1. CCK-induced actin cytoskeletal reorganization is mainly mediated by G alpha(q). By contrast, G alpha(13) and G alpha(q) signaling are required for CCK-induced amylase secretion.