Common Pathways for Activation of Proinflammatory Gene Expression by G Protein–coupled Receptors in Primary Lung Epithelial and Endothelial Cells

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). Our earlier studies showed that substance P (SP), a ligand for the tachykinin 1 receptor, induced NF-κB activation and IL-8 upregulation through a Gq-dependent pathway. Here we extend these findings by examining effects of multiple ligands for Gq-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 upregulated CINC-1 (a rat IL-8 homolog) in RLMVECs. Using signaling inhibitors, we 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/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 Gq-coupled GPCRs following lung injury.

Store-Operated Ca2+ Release-Activated Ca2+ Channels Regulate PAR2-Activated Ca2+ Signaling and Cytokine Production in Airway Epithelial Cells

“…To examine this, we screened several ligands that are coupled to the generation of IP 3 in NHBE cells. Although several receptors coupled to PLC-IP 3 signaling are thought to be expressed in AECs (30), this screen revealed that only a subset of ligands, including agonists for PAR2 and purinergic P2Y receptors (and to a smaller extent, thrombin and bradykinin) evoked Ca 2+ signals consistent with store-operated Ca 2+ entry (Table I). PAR2 receptors are important for the ability of AECs to sense allergens and endogenous proteases and for mediating the subsequent inflammatory responses in the lung (31).…”

PAR2-induced inflammatory responses in human kidney tubular epithelial cells

“…Without causing toxicity, the secretion of GM-CSF and TNF-␣ were almost completely abolished, suggesting the importance of PKC in PAR2-mediated GM-CSF and TNF-␣ secretion. Recent studies have also shown the important involvement of PKC in PAR2-induced inflammation (2,10).…”

RhoA–Rho kinase and platelet‐activating factor stimulation of ovine foetal pulmonary vascular smooth muscle cell proliferation

“…Physiological and pathological effects of PAF are mediated by its specific G protein coupled receptor reported to be G q (30,31). We have shown in previous reports that PAF induces expression of its own receptors in vivo and in vitro suggesting that PAF activates intracellular molecules that regulate gene expression and cell growth (9,23).…”