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.