Abstract
G-protein-coupled receptors (GPCRs) trigger various physiological functions. GPCR-mediated effects largely depend on the receptor-associated G-protein subtypes. However, compelling evidence suggests that single receptor proteins activate multiple G-protein subtypes to induce diverse physiological responses. This study compared responses mediated by three different Gq-binding uridine nucleotide receptors, P2Y2, P2Y4, and P2Y6, by measuring Ca2+ signaling and interleukin (IL)-8 production. In 1321N1 human astrocytoma cells stably expressing these receptors, agonist stimulation evoked concentration-dependent intracellular Ca2+ elevation to a similar extent. In contrast, agonist-induced IL-8 production was prominent in P2Y6-expressing cells, but not in P2Y2- and P2Y4-expressing cells. In addition to inhibition of Gq signaling, G12 signal blockade attenuated uridine 5'-diphosphate (UDP)-induced IL-8 production, suggesting the involvement of a small G-protein pathway. The Rac inhibitor EHop-16 prevented UDP-induced IL-8 release. The P2Y6-triggered IL-8 production was also inhibited by extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and protein kinase B (Akt) inhibitors. These results suggest that P2Y6 receptor-induced IL-8 production requires Gq-mediated Ca2+ signaling as well as G12-mediated activation of Rac. The results also suggest the importance of considering the involvement of multiple G proteins in understanding GPCR-mediated functions.