Activation of the EP4 prostanoid receptor induces prostaglandin E2 and pro-inflammatory cytokine production in human airway epithelial cells

Prostaglandin (PG)E2 mediates its effects via activation of four distinct PGE2 receptors, termed EP1–4, all of which are present on the model human airway epithelial cell line, Calu-3. We previously reported that acute activation of the EP4 subtype of the PGE2 receptor is associated with increased anion efflux from these cells, via the CFTR chloride channel. In the present study we examine the effects of longer term activation of the EP4 receptor in Calu-3 cells in an attempt to determine whether this would prove beneficial or detrimental to the airway epithelial cell environment. Using PGE1-OH, an EP4 receptor selective agonist, we determined that EP4 receptor activation was associated with increased phosphorylation of extracellular signal-related kinases (ERKs) and induction of the transcription factor early growth response factor-1 (Egr-1). Additionally, using specific enzyme-linked immunosorbent assays and quantitative PCR, we detected increased production of PGE2, IL-6, IL-8 and the chemokine monocyte chemotactic protein-1 (MCP-1) at both the protein and gene level in response to EP4 receptor activation. Intriguingly, the enhanced production of PGE2 in response to EP4 receptor activation raises the possibility of a positive feedback situation. Generally, within the airways, PGE2 is considered to have pro-inflammatory effects, whilst the enhanced production of IL-6, IL-8 and MCP-1 would be associated with the recruitment and activation of inflammatory cells to the airways. Thus, we conclude that chronic activation of the EP4 receptor is associated with increased production of mediators likely to increase the pro-inflammatory milieu of airway epithelial cells.