Synergistic effect of PGD2 via prostanoid DP receptor on TNF-alpha-induced production of MCP-1 and IL-8 in human monocytic THP-1 cells

Prostaglandin (PG) D₂, a major cyclooxygenase metabolite generated predominantly from immunologically stimulated mast cells, is thought to contribute to the pathogenesis of allergic diseases via the two PGD₂ receptors, prostanoid DP receptor and chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2). Monocytes are known to express the prostanoid DP receptor, however, the role of it in inflammatory responses is still unclear. In the present study, to clarify the functional roles of prostanoid DP receptor on monocytes, we examined the effect of PGD₂ on the production of monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-8 from a human monocytic cell line, THP-1. Single activation of prostanoid DP receptor hardly produced any cytokines or chemokines. However, activation with PGD₂ in the presence of tumor necrosis factor (TNF)-α mediated significant production of MCP-1 and IL-8, but not the other cytokines and chemokines, in comparison to single stimulation with TNF-α. In addition, the selective prostanoid DP receptor antagonist, pinagladin ((Z)-7-[(1R,2R,3S,5S)-2-(benzothiophen-3-ylcarbonylamide)-10-norpinan-3-yl]hept-5-enoic acid) inhibited the production of MCP-1 and IL-8 upon combined stimulation with PGD₂ and TNF-α. The synergistic production of MCP-1 and IL-8 by PGD₂ was mimicked by dibutyryl cAMP (db-cAMP) and was inhibited by a protein kinase A (PKA) inhibitor. Our findings suggest that activation of the prostanoid DP receptor on THP-1 cells enhances TNF-α-induced MCP-1 and IL-8 production via the cAMP/PKA signaling pathway.