ABSTRACT
Prostaglandin E2 (PGE2), a major product of cyclooxygenase, binds to four different prostaglandin E2 receptors (EP1, EP2, EP3, and EP4) which are G-protein coupled transmembrane receptors (GPCRs). Although GPCRs including EP receptors have been shown to be associated with their specific G proteins, recent evidences suggest that GPCRs can regulate MAPK signaling via non-G protein coupled pathways including Src. EP2 is differentially expressed in various tissues and the expression of EP2 is induced by extracellular stimuli. We hypothesized that an increased level of EP2 expression may affect MAPK signaling. The overexpression of EP2 in HEK 293 cells resulted in significant increase in intracellular cAMP levels response to treatment with butaprost, a specific EP2 agonist, while overexpression of EP2 alone did not increase intracellular cAMP levels. However, EP2 overexpression in the absence of PGE2 induced an increase in the level of p38 phosphorylation as well as the kinase activity of p38, suggesting that up-regulation of EP2 may promote p38 activation via non-G protein coupled pathway. Inhibition of Src completely blocked EP2-induced p38 phosphorylation and overexpression of Src increased the level of p38 phosphorylation, indicating that Src is upstream kinase for EP2-induced p38 phosphorylation. EP2 overexpression also increased the Src activity and EP2 protein was co-immunoprecipitated with Src. Furthermore, sequential co-immunoprecipitation studies showed that EP2, Src, and beta-arrestin can form a complex. Our study found a novel pathway in which EP2 is associated with Src, regulating p38 pathway.
Subject(s)
Dinoprostone , GTP-Binding Proteins , HEK293 Cells , Immunoprecipitation , Phosphorylation , Phosphotransferases , Prostaglandin-Endoperoxide Synthases , Up-RegulationABSTRACT
Objective To evaluate the role of EP_2 in synaptic transmission in dentate gyrus of hippocampus. Methods Field excitatory post-synaptic potentials (fEPSP) were recorded at the perforated path-granule neurons in dentate gyrus in vitro. Results ① Butaprost, an agonist of EP_2, enhanced the synaptic transmission in dentate gyrus and decreased the paired-pulse ratio, and these effects were reversed by bath application of AH6809 (EP_2 antagonist). ② Application of Forskolin alone or with AH6809 elevated the slope of fEPSP. ③ The Butaprost-induced responses were mediated via PKA, ERK and IP_3 signal pathways. Conclusion Multiple signal pathways were involved in the EP_2 activation-mediated enhancement of synaptic transmission.
ABSTRACT
The interstitial cells of Cajal (ICCs) are the pacemaker cells in gastrointestinal tract and generate electrical rhythmicity in gastrointestinal muscles. Therefore, ICC may be modulated by endogenous agents such as neurotransmitter, hormones, and prostaglandins (PGs). In the present study, we investigated the effects of prostaglandins, especially PGE2, on pacemaker currents in cultured ICCs from murine small intestine by using whole-cell patch clamp techniques. ICCs generated spontaneous slow waves under voltage-clamp conditions and showed a mean amplitude of -452+/-39 pA and frequency of 18+/-2 cycles/min (n=6). Treatments of the cells with PGE2 (1muM) decreased both the frequency and amplitude of the pacemaker currents and increased the resting currents in the outward direction. PGE2 had only inhibitory effects on pacemaker currents and this inhibitory effect was dose-dependent. For characterization of specific membrane EP receptor subtypes, involved in the effects of PGE2 on pacemaker currents in ICCs, EP receptor agonists were used: Butaprost (1muM), EP2 receptor agonist, reduced the spontaneous inward current frequency and amplitude in cultured ICCs (n=5). However sulprostone (1muM), a mixed EP1 and EP3 agonist, had no effects on the frequency, amplitude and resting currents of pacemaker currents (n=5). SQ-22536 (an inhibitor of adenylate cyclase; 100muM) and ODQ (an inhibitor of guanylate cyclase; 100muM) had no effects on PGE2 actions of pacemaker currents. These observations indicate that PGE2 alter directly the pacemaker currents in ICCs, and that the PGE2 receptor subtypes involved are the EP2 receptor, independent of cyclic AMP- and GMP-dependent pathway.