Abstract
Acute lung injury is associated with an inflammatory response resulting from the action of multiple mediators. Many proinflammatory mediators released during lung injury exert effects by binding to G protein-coupled receptors (GPCRs). The authors' earlier studies showed that substance P (SP), a ligand for the tachykinin 1 receptor, induced nuclear factor (NF)-kappa B activation and interleukin (IL)-8 up-regulation through a G(q)-dependent pathway. Here the authors extend these findings by examining effects of multiple ligands for G(q)-coupled GPCRs in primary human small airway epithelial cells (SAECs) and rat lung microvessel endothelial cells (RLMVECs). SP, bradykinin, protease activated receptor 2 agonist, and platelet-activating factor (PAF) stimulated IL-8 production in SAECs, whereas only SP and PAF up-regulated CINC-1 (a rat IL-8 homolog) in RLMVECs. Using signaling inhibitors, the authors investigated PAF-induced IL-8 expression and SP-induced CINC-1 expression in primary cells. Signaling cascades were similar in SAECs and RLMVECs and involved phospholipase C/calcium/protein kinase C (PKC) and Ras/Raf/Erk pathways. In addition, the tyrosine kinase inhibitor AG 17 and the proteasome inhibitor MG132 significantly reduced IL-8 and CINC-1 expression induced by GPCR ligands. The results demonstrate a common signaling pathway in primary lung epithelial and endothelial cells, suggesting a generalized mechanism for the induction of proinflammatory gene expression by G(q)-coupled GPCRs following lung injury.