U. K. No uchil*, K. Iwasaki', M. Shitashije2,

Prostaglandin E2 (PGE2), which exerts its actions via EP receptors (EP1, EP2, EP3, and EP4), is a bioactive metabolite of arachidonic acid produced by cyclooxygenase (COX)-1 and/or COX-2. We have previously demonstrated that PGE2 down-regulates intercellular adhesion molecule-I (ICAM-1) expression in interleukin-I1 (IL-IB)-stimulated human gingival fibroblasts (HGF). In the present study, we investigated which COX was involved in down-regulation of ICAM-1 expression by PGE2 in IL-IB-stimulated HGF and which subtypes of EP receptors modulated the ICAM-1 expression. NS-398, a specific COX-2 inhibitor, completely inhibited PGE2 production by IL-lB-stimulated HGF, as did indomethacin, a COX-1/COX-2 inhibitor. Northern blot analysis and immunocytochemical staining showed that mRNA and protein of COX-2 were expressed in IL-1B-challenged HGF, but not in unstimulated HGF, and that the expression of mRNA and protein of COX-1 was similar both in unstimulated and in stimulated cells. NS-398 and indomethacin enhanced ICAM-1 expression in IL-113-challenged HGF. EP1, EP2, and EP4 receptor mRNA was expressed in HGF according to reverse-transcription/polymerase chain-reaction. PGE2, 11-deoxy-PGE1 (a selective EP2/EP4 agonist), and Butaprost (a selective EP2 agonist) attenuated IL-I1B-elicited ICAM- 1 expression, although Butaprost was less potent than PGE2 and 11-deoxy-PGE1. AH-23848B, an EP4 antagonist, antagonized the inhibitory effect of IL-1B-elicited ICAM-1 expression by PGE2. Sulprostone, an EP1/EP3 agonist, had no effect on IL-lB-elicited ICAM-1 expression. Analysis of these data suggests that COX-2-derived PGE2 down-regulates ICAM-1 expression via EP2/EP4 receptors in IL- I B-stimulated HGF