G protein-coupled receptor-mediated mitogen-activated protein kinase activation through cooperation of G alpha(q), and G alpha(i) signals

G protein-coupled receptors (GPCRs) have been shown to stimulate extracellu lar regulated kinases (ERKs) through a number of linear pathways that are i nitiated by G(q/11) or G(i) proteins. We studied signaling to the ERK casca de by receptors that simultaneously activate both G protein subfamilies. In HEK293T cells, bradykinin B-2 receptor (B2R)-induced stimulation of ERK2 a nd transcriptional activity of Elk1 are dependent on G alpha(q)-mediated pr otein kinase C (PKC) and on Ga-i-induced Ras activation, while they are ind ependent of G beta gamma subunits, phosphatidylinositol 3-kinase, and tyros ine kinases. Similar results were obtained with m(1) and m(3) muscarinic re ceptors in HEK293T cells and with the B2R in human and mouse fibroblasts, i ndicating a general mechanism in signaling toward the ERK cascade. Furtherm ore, the bradykinin-induced activation of ERK is strongly reduced in G alph a(q/11)-deficient fibroblasts. In addition, we found that constitutively ac tive mutants of G alpha(q/11) or G alpha(i) proteins alone poorly stimulate ERK, whereas a combination of both led to synergistic effects. We conclude that dually coupled GPCRs require a cooperation of G alpha(i)- and G(q/11) -mediated pathways for efficient stimulation of the ERK cascade. Cooperativ e signaling by multiple G proteins thus might represent a novel concept imp licated in the regulation of cellular responses by GPCRs.