• Hiroyuki Komatsu, Shuhei Enjouji, Akihiro Ito, Takashi Ohama, and Koichi Sato.
• Laboratory of Veterinary Pharmacology, Joint Faculty of Veterinary Medicine, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8515, Japan.
• J. Vet. Med. Sci. 2013 Jan 1; 75 (3): 255-61.

AbstractProteinase-activated receptor (PAR) is expressed on various cells, and the PAR family consists of PAR1, PAR2, PAR3, and PAR4. Individual PARs are activated during inflammatory conditions in which they regulate inflammatory responses in various diseases. For example, PAR activation is known to induce prostaglandin E2 (PGE2) production, and then upregulated PGE2 suppresses PAR1 expression in a negative feedback loop. Surprisingly, PGE2 effects on PAR2, which is a well-researched and attractive target for drug development, remain unknown. Therefore, we investigated PAR2 regulation by PGE2. Using HEK293T cells, we showed that PGE2 inhibits extracellular signal-regulated kinase (ERK) phosphorylation induced by a PAR2-activating peptide (PAR2-AP). AH-6809 (an inhibitor of PGE2 receptors 1 [EP1] and 2 [EP2]), but not ONO-AE3-208 (a PGE2 receptor 4 [EP4] inhibitor), reversed the inhibitory effects of PGE2 on PAR2-AP-induced ERK phosphorylation. Studies on PAR2 expression revealed that PGE2 suppressed cell surface expression of PAR2 and induced internalization of PAR2, and not PAR4, in N2a mouse neuroblastoma cells that were transiently transfected with either PAR2 or PAR4. Furthermore, forskolin, an adenylate cyclase activator, induced PAR2 internalization and inhibited PAR2-AP-induced phosphorylation of ERK. Because EP2 (not EP1) also increases intracellular cyclic AMP, we conclude that PGE2 inhibited PAR2-dependent signal transduction by inducing the internalization of PAR2 through an EP2-dependent increase in intracellular cyclic AMP. This novel regulatory pathway in which PAR2 function is regulated by PGE2 will broaden our understanding of PAR2-dependent inflammation and could provide novel strategies for drug development.

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