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The Journal of Immunology, 2006, 177: 1092-1100.
Copyright © 2006 by The American Association of Immunologists

Prostaglandin E2 Augments IL-10 Signaling and Function1

HyeonJoo Cheon*, Young Hee Rho{dagger}, Seong Jae Choi{dagger}, Young Ho Lee{dagger}, Gwan Gyu Song{dagger}, Jeongwon Sohn{ddagger}, Nam Hee Won* and Jong Dae Ji2,{dagger}

* Department of Pathology, {dagger} Department of Rheumatology, and {ddagger} Department of Biochemistry, College of Medicine, Korea University, Seoul, Korea


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
 References
 
In inflamed joints of rheumatoid arthritis, PGE2 is highly expressed, and IL-10 and IL-6 are also abundant. PGE2 is a well-known activator of the cAMP signaling pathway, and there is functional cross-talk between cAMP signaling and the Jak-STAT signaling pathway. In this study, we evaluated the modulating effect of PGE2 on STAT signaling and its biological function induced by IL-10 and IL-6, and elucidated its mechanism in THP-1 cells. STAT phosphorylation was determined by Western blot, and gene expression was analyzed using real-time PCR. Pretreatment with PGE2 significantly augmented IL-10-induced STAT3 and STAT1 phosphorylation, as well as suppressors of cytokine signaling 3 (SOCS3) and IL-1R antagonist gene expression. In contrast, PGE2 suppressed IL-6-induced phosphorylation of STAT3 and STAT1. These PGE2-induced modulating effects were largely reversed by actinomycin D. Pretreatment with dibutyryl cAMP augmented IL-10-induced, but did not change IL-6-induced STAT3 phosphorylation. Misoprostol, an EP2/3/4 agonist, and butaprost, an EP2 agonist, augmented IL-10-induced STAT3 phosphorylation and SOCS3 gene expression, but sulprostone, an EP1/3 agonist, had no effect. H89, a protein kinase A inhibitor, and LY294002, a PI3K inhibitor, diminished PGE2-mediated augmentation of IL-10-induced STAT3 phosphorylation. In this study, we found that PGE2 selectively regulates cytokine signaling via increased intracellular cAMP levels and de novo gene expression, and these modulating effects may be mediated through EP2 or EP4 receptors. PGE2 may modulate immune responses by alteration of cytokine signaling in THP-1 cells.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Disclosures
 References
 
The mediator PGE2 is produced during inflammatory responses, and increased levels of PGE2 mediate some of the cardinal features of inflammation, including pain, edema, and fever (1). In contrast, several studies suggest that in addition to its proinflammatory actions, PGE2 may also exert strong anti-inflammatory effects such that PGE2 suppresses the production of proinflammatory cytokines and enhances the synthesis of anti-inflammatory cytokines (2, 3). PGE2 also promotes humoral and Th2-type immune responses and inhibits Th1-type immune responses (4). Therefore, PGE2 is regarded not simply as a proinflammatory molecule but as a modulator of immune responses. The biological actions of PGE2 are mediated by four distinct G protein-coupled E prostanoid (EP)3 receptors, termed EP1, EP2, EP3, and EP4 (5). The EP1 receptor is a well-known activator of a G protein, Gq, which enhances intracellular Ca2+ levels. The EP3 receptor inhibits adenylate cyclase via Gi, reducing cAMP levels. The EP2 and EP4 receptors activate G proteins that stimulate cAMP production via adenylate cyclase activation.

IL-10 is a strong anti-inflammatory cytokine that plays an important role in limiting tissue injury during infection by regulating the duration and intensity of immune and inflammatory reactions (6). The IL-10R system consists of two subunits, IL-10R1 and IL-10R2, both of which are members of the IFN receptor family. Ligation of the heterodimeric IL-10R results in activation of receptor-associated protein tyrosine kinases, Jak1 and Tyk2, and leads to subsequent tyrosine residue phosphorylation of STAT3 and STAT1. In myeloid cells, IL-10 predominantly activates STAT3 and activated STAT3 is primarily involved in the negative regulation of macrophage activation (6). The role of STAT1 in IL-10 biology and its signal transduction remains unclear.

IL-6 is a pleiotropic cytokine required for immune and inflammatory responses (7). IL-6 binds to its receptor (IL-6R{alpha}), and the IL-6-IL-6R{alpha} complex induces gp130 homodimerization. The dimerized gp130 activates receptor-associated protein tyrosine kinases Jak1, Jak2, and Tyk2, leading to subsequent tyrosine phosphorylation and DNA binding of STAT3 and STAT1 (8). In many cells, IL-6 activates predominantly STAT3, although STAT1 may also be also activated.

Several reports have demonstrated a functional cross-talk between the cAMP signaling pathway and the Jak-STAT signaling pathway in various cell types. Activators of the cAMP signaling pathway, such as PGE2, inhibit STAT1 DNA binding activity in mononuclear cells (9), and also inhibit IL-6-induced STAT activation in NFS-60 cells (10). In addition, PGE2 activates IL-6 signaling via stimulation of the soluble IL-6R release in prostatic intraepithelial neoplasia (PIN) cells (11).

In the inflamed joints of rheumatoid arthritis, PGE2 is highly expressed (12), and IL-10 and IL-6 are also abundant (13). In this study, we evaluate whether PGE2 modulates STAT signaling and its biological function induced by IL-10 and IL-6, and identify the mechanisms by which PGE2 regulates cytokine signaling in THP-1 cells.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Disclosures
 References
 
Materials

Actinomycin D, H89, and PGE2 were purchased from Sigma-Aldrich. Dibutyryl cAMP and LY294002 were purchased from Calbiochem. Sulprostone, misoprostol, and butaprost were purchased from Cayman Chemicals. Phospho-specific (Tyr705) STAT3 Ab and phospho-specific (Tyr701) STAT1 Ab were purchased from Cell Signaling Technology. Monoclonal STAT3 and STAT1 Ab were purchased from BD Transduction Laboratories.

Cell isolation and culture

Monocytes were obtained from PBMC by positive selection, using anti-CD14 magnetic beads, as recommended by the manufacturer (Miltenyi Biotec). Monocytes were used fresh in RPMI 1640 medium supplemented with 10% FBS. THP-1 cells were cultured at 37°C in 5% CO2 using RPMI 1640 medium with 10% FBS.

Protein extraction and immunoblotting

Total cellular protein was extracted from several conditioned cells using Pro-prep protein extraction solution (Intron). Extracts corresponding to 2 x 105 cells were separated on 7.5% SDS-polyacrylamide gels, transferred to polyvinylidene difluoride membranes by semidry electrophoretic transfer, and incubated with phospho-specific (Tyr705) STAT3 Ab, phospho-specific (Tyr701) STAT1 Ab, and with monoclonal STAT3 and STAT1 Ab. ECL Western blotting detection reagent (Amersham Biosciences) was used for detection. For quantitative analysis, the density of the blots for phosphorylated STAT3 and total STAT3 was measured and expressed as the ratio of phosphorylated STAT3 to total STAT3.

RNA extraction and real-time PCR

Total cellular RNA was isolated using TRIzol reagent (Invitrogen Life Technologies) according to the manufacturer’s instruction. cDNA was prepared by reverse transcription with a random hexamer according to the manufacturer’s protocol (TaqMan Reverse Transcription Reagent; Applied Biosystems). Oligonucleotide primers used are as follows: GAPDH, AAG GTG AAG GTC GGA GTC AAC G and CCT TCT CCA TGG TGG TGA AGA C; EP1, ATG GTG GGC CAG CTT GTC and GCC ACC AAC ACC AGC ATT G; EP2, CTG CTG CTG CTTCTC ATT GT and ATG CGG ATG AGG TTG AGA AT; EP3, GGT CTC CGC TCC TGA TAA TG and CTC CGT GTG TGT CTT GCA GT; EP4, CGA CCT TCT ACA CGC TGG TAT G and CCG GGC TCA CCA ACA AAG T; IL-1R antagonist, GAA GAT GTG CCT GTC CTG TGT and TCG CTC AGG TCA GTG ATG TT; and suppressors of cytokine signaling 3 (SOCS3), CAC TCT TCA GCA TCT CTG TCG GAA G and CAT AGG AGT CCA GGT GGC CGT TGA C. Real-time PCR was performed in a SYBR Green PCR Master mix (Applied Biosystems) using the GeneAmp 7000 Sequence Detection System (Applied Biosystems) with the following protocol: initial activation at 95°C for 10 min, 40 cycles at 95°C for 15 s, and 60°C for 1 min. The mRNA amount of the target gene was normalized relative to GAPDH using the threshold cycle ({Delta}Ct) method as described in the manufacturer’s protocol.

Flow cytometric detection of IL-10R or IL-6R on cell surfaces

The binding of IL-10 or IL-6 to cell surface receptors was measured using a Fluorokine kit according to the manufacturer’s protocol (R&D Systems). Analyses were done using a FACScan flow cytometer with CellQuest software (BD Biosciences).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Disclosures
 References
 
PGE2 modulates cytokine-induced STAT phosphorylation in THP-1 cells

PGE2 has been shown to inhibit STAT1 DNA binding activity in mononuclear cells and to inhibit IL-6-induced STAT activation in NFS-60 cells (9, 10). We began the present study by examining whether PGE2 modulates cytokine-induced STAT activation in THP-1 cells. IL-10 and IL-6 (20 ng/ml) induced phosphorylation of STAT3 and STAT1 within 10 min. To determine the effects of PGE2 on cytokine-induced STAT phosphorylation, the cells were pretreated with PGE2 (1 µM) for 2 h, followed by the indicated cytokine stimulation for 10 min. Pretreatment with PGE2 significantly suppressed IL-6-induced phosphorylation of STAT3 and STAT1. In contrast, pretreatment with PGE2 significantly augmented IL-10-induced phosphorylation of STAT3 and STAT1. PGE2 had no effect on the protein expression of STAT3 and STAT1 (Fig. 1A). PGE2 modulated cytokine-induced STAT3 activation at 0.01–1 µM (Fig. 1, B and C). Because it has been reported that PGE2 increases production of both IL-10 and IL-6 in macrophages (14), and activates the STAT3 signaling pathway via release of IL-6 and soluble IL-6R in PIN cells (11), we examined whether PGE2 itself could augment IL-10-induced STAT3 phosphorylation by increased production of cytokines. Fig. 1D shows that PGE2 itself did not activate STAT3 phosphorylation, so we excluded the possibility that PGE2 may augment IL-10 signaling via PGE2-induced cytokine production.


Figure 1
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  		FIGURE 1. Differential modulating effect of PGE2 on cytokine-induced STAT phosphorylation in THP-1 cells. A–C, IL-10 and IL-6 (20 ng/ml) were treated for 10 min, and PGE2 (1 µM) was pretreated 2 h before cytokine stimulation. IL-10-induced STAT activation was augmented and IL-6-induced STAT activation was inhibited by pretreatment with PGE2. D, PGE2 (1 µM) was treated for 0.5–2 h in THP-1 cells. Control is a sample stimulated with IL-10 for 10 min. E, In THP-1 cells, IL-10 and IL-6 (20 ng/ml) were treated for 10 min, and PGD2 (1 µM) was pretreated 2 h before cytokine stimulation. F, In primary monocytes, IL-10 and IL-6 (20 ng/ml) were treated for 10 min, and PGE2 (1 µM) was pretreated 2 h before cytokine stimulation. All sample incubations were followed by immunoblot analysis as described in Materials and Methods. PGE2 itself did not induce STAT3 phosphorylation. These experiments are representative of three independent experiments, all displaying similar results.

 
To examine the specificity of PGE2 on modulation of cytokine signaling, THP-1 cells were pretreated with PGD2. Cytokine-induced phosphorylation of STAT3 was not changed by PGD2, indicating that PGE2 specifically modulates cytokine-induced phosphorylation of STAT3 (Fig. 1E).

To examine the biological significance of these modulating effects in physiological condition, we used primary human monocytes for evaluating the effects of PGE2 on cytokine signaling. Disappointingly, PGE2 did not influence the cytokine signaling in primary human monocytes (Fig. 1F). Based on this result, we can conclude PGE2 did not change the cytokine signaling in physiological condition. However, we cannot exclude the possibility that PGE2 influences the cytokine-induced STAT phosphorylation in other pathological condition, similar to the results in THP-1 cells. Therefore, we need additional experiments to evaluate the PGE2 effects on cytokine signaling in various conditioned monocytes and macrophages.

Fig. 2 shows the time course during which PGE2 modulates cytokine-induced STAT3 phosphorylation in THP-1 cells. Augmentation of IL-10-induced STAT3 phosphorylation was detectable after 2 h of PGE2 pretreatment, and reached a maximal level after 6 h of PGE2 pretreatment (Fig. 2A). In contrast, inhibition of IL-6-induced STAT3 phosphorylation was induced very rapidly, occurring after 30 min of PGE2 pretreatment, and was maintained for 6 h of PGE2 pretreatment (Fig. 2B).


Figure 2
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  		FIGURE 2. Time course analysis of PGE2-induced modulation of cytokine signaling in THP-1 cells. PGE2 (1 µM) was added before treatment for 0.5, 1, 2, 4, and 6 h with IL-10 (A) and IL-6 (B). IL-10 and IL-6 (20 ng/ml) were added for 10 min, followed by immunoblot analysis as described in Materials and Methods. Augmentation of IL-10 signaling is initiated after 2 h of pretreatment with PGE2 (A). In contrast, inhibition of IL-6 signaling is induced rapidly within 30 min after pretreatment with PGE2 (B). These experiments are representative of three independent experiments, all displaying similar results.

 
All four EP receptors are expressed in THP-1 cells

PGE2 exerts its action through four distinct membrane-associated G protein-coupled receptors, EP1, EP2, EP3, and EP4. We examined the expression of EP receptors in THP-1 cells using real-time PCR. Fig. 3 shows that all four EP receptor genes were expressed and that the EP4 receptor was expressed at a higher level when compared with EP1, EP2, and EP3 in THP-1 cells.


Figure 3
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  		FIGURE 3. Gene expression of EP receptors in THP-1 cells. Total RNA was subjected to real-time PCR with primers specific for EP1, EP2, EP3, and EP4. Results are shown as an amplification plot for each EP receptor. These experiments are representative of three independent experiments, all displaying similar results.

 
PGE2 augments IL-10 biological activity

It has been previously reported that IL-10 up-regulates gene expression of SOCS3 and of the IL-1R antagonist in human monocytes (15). SOCS3 and IL-1R antagonist have been suggested to be mediators of anti-inflammatory and immune-modulating effects in several studies (16, 17, 18). We assessed the biological significance of PGE2-mediated augmentation of IL-10 signaling by examining the effects of PGE2 on IL-10-induced SOCS3 and IL-1R antagonist gene expressions. IL-10 increased SOCS3 gene expression by 2.3-fold, and the addition of PGE2 enhanced IL-10-induced SOCS3 gene expression by 52.8-fold (Fig. 4A). PGE2 also synergistically increased IL-10-induced IL-1R antagonist gene expression (Fig. 4B).


Figure 4
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  		FIGURE 4. PGE2-derived modulation of IL-10- and IL-6-induced gene expression in THP-1 cells. After 2 h of PGE2 (1 µM) treatment, 20 ng/ml IL-10 (A and B) or IL-6 (C) were added for 1 h. Total RNA was reverse-transcribed and used in real-time PCR with SOCS3 (A and C) and IL-1R antagonist (B) primer pairs. PGE2 synergistically augmented IL-10-induced SOCS3 and IL-1R antagonist gene expression, and additively enhanced IL-6-induced SOCS3 expression. Data represent relative mRNA amounts of SOCS3 or IL-1R antagonist normalized to GAPDH mRNA amounts. The mean values of three independent experiments are presented, and error bars indicate SD.

 
Because it has been reported that IL-6 also up-regulates SOCS3 gene expression (19), we examined the effect of PGE2 on IL-6-induced SOCS3 expression. IL-6 increased SOCS3 gene expression by 7.7-fold in THP-1 cells. However, surprisingly PGE2 induced an additional increase of IL-6-induced SOCS3 gene expression, in contrast to its effect upon STAT3 phosphorylation (Fig. 4C). This result is inconsistent with a previous report, which found that inhibition of STAT3 activation contributes to inhibition of IL-6-induced SOCS3 gene expression (19). Our result suggests that IL-6-induced SOCS3 gene expression is not mediated by STAT3 phosphorylation, and this is supported by a recent report which shows that IL-6-induced SOCS3 expression is mediated by p38 MAPK activation (20).

The cAMP signaling pathway is involved in PGE2-induced augmentation of IL-10-induced STAT3 phosphorylation by PGE2

Intracellular cAMP production by adenylate cyclase is involved in many biological activities of PGE2. To analyze the mechanism for the modulation of cytokine signaling induced by PGE2, we examined whether cAMP mediates the effects of PGE2 on cytokine signaling. Pretreatment with dibutyryl cAMP, which increases intracellular concentration of cAMP, augmented IL-10-induced STAT3 phosphorylation in THP-1 cells (Fig. 5A). STAT3 phosphorylation levels are quantified by densitometry and normalized to STAT3 levels. Pretreatment with dibutyryl cAMP (50 µM) significantly augmented IL-10-induced phosphorylation of STAT3 (Fig. 5B). As with PGE2 treatment, dibutyryl cAMP augmented IL-10-induced STAT3 phosphorylation after 2 h of treatment (Fig. 5C). In contrast to IL-10, IL-6-induced STAT3 phosphorylation was not affected by exogenous cAMP (Fig. 5, A and B). These results indicate that PGE2 augments IL-10-stimulated STAT3 phosphorylation through a cAMP-dependent pathway.


Figure 5
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  		FIGURE 5. The effect of cAMP on cytokine-induced STAT3 phosphorylation in THP-1 cells. A, Dibutyryl cAMP (5 and 50 µM), which increases intracellular cAMP concentration, were added for 2 h, followed by stimulation with IL-10 or IL-6 (20 ng/ml) for 10 min. Dibutyryl cAMP increased IL-10-induced STAT3 phosphorylation. In contrast to IL-10, IL-6-induced STAT3 phosphorylation is not affected by exogenous cAMP. B, STAT3 phosphorylation levels are quantified by densitometry and normalized to STAT3 levels. *, p < 0.05; NS, no significant difference. C, Dibutyryl cAMP (50 mM) was added 0.5, 1, 2, and 4 h before IL-10 stimulation. STAT3 phosphorylation was detected by immunoblotting. IL-10-induced STAT3 phosphorylation was significantly augmented after 2 h of pretreatment with dibutyryl cAMP. These experiments are representative of three independent experiments, all displaying similar results.

 
Modulation of cytokine-induced STAT3 phosphorylation by PGE2 is not mediated by changes in cytokine receptor expression

We also determined whether PGE2 modulates proximal events in the IL-10 or IL-6 signaling pathway. Cell surface expressions of IL-10R or IL-6R were measured by flow cytometry after staining with biotinylated IL-10 or IL-6. Treatment with PGE2 for 2, 4, or 6 h did not result in an increased cell surface expression of IL-10R (Fig. 6A). Also treatment with PGE2 for 2 h did not result in a decreased cell surface expression of IL-6R (Fig. 6B).


Figure 6
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  		FIGURE 6. Cell surface expression of IL-10 and IL-6R in PGE2-treated THP-1 cells. THP-1 cells were harvested after 2, 4, or 6 h of incubation with PGE2 (1 µM) and were analyzed using flow cytometry after staining with biotinylated IL-10 (A). Also THP-1 cells were harvested after 2 h of incubation with PGE2 (1 µM) and were analyzed using flow cytometry after staining with biotinylated IL-6 (B). PGE2 changed neither IL-10 binding sites nor IL-6 binding sites on the cell surface. The thin line histogram indicates staining with negative control, and thick line histogram indicates staining with biotinylated cytokines. The black line represents PGE2-treated cells, and the gray line represents nontreated cells.

 
Modulation of cytokine-induced STAT3 phosphorylation is dependent on de novo gene expression

It is currently well known that modulation of the Jak-STAT signaling pathway is mediated via de novo gene expressions, including SOCSs (21). The requirement for newly produced molecules for PGE2-induced modulation of cytokine signaling was investigated by using actinomycin D. PGE2-induced modulations of IL-6- and IL-10-stimulated STAT3 phosphorylation were greatly reversed when de novo gene expression was blocked by the addition of actinomycin D (Fig. 7, A and B), indicating that PGE2-induced modulation of cytokine signaling is dependent on new gene expressions.


Figure 7
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  		FIGURE 7. Effect of actinomycin D on PGE2-induced modulation of cytokine signaling in THP-1 cells. A and B, THP-1 cells were pretreated with actinomycin D (2.5 µg/ml) 30 min before PGE2 (1 µM) treatment. After 2 h, IL-10 (A) or IL-6 (B) (20 ng/ml) was added for 10 min. STAT3 phosphorylation was measured by immunoblot assay. These data are representative of three independent experiments all displaying similar results. C and D, THP-1 cells were pretreated with cycloheximide (CHX, 50 µg/ml) 30 min before PGE2 (1 µM) treatment. After 2 h, IL-10 (A) or IL-6 (B) (20 ng/ml) was added for 10 min. STAT3 phosphorylation was measured by immunoblot assay. These data are representative of three independent experiments all displaying similar results. E, THP-1 cells were treated with PGE2 for the indicated time, followed by RNA extraction and real-time PCR with SOCS3 primer. PGE2 induced SOCS3 gene expression after 30 min of stimulation. F, Actinomycin D (2.5 and 5 µg/ml) was added 30 min before PGE2 (1 µM) treatment, followed by RNA extraction and real-time PCR with SOCS3 primer. Actinomycin D completely reversed PGE2-induced SOCS3 expression. Data represent relative mRNA amounts of SOCS3 normalized to GAPDH mRNA amounts. The mean value of three independent experiments are presented, and error bars indicate the SD.

 
To examine the possibility that PGE2 modulates cytokine signaling by increasing synthesis of new proteins, we performed experiments using the protein synthesis inhibitor cycloheximide. A recent report showed that cycloheximide can inhibit IL-6 signaling, and this inhibition by cycloheximide was dependent on the p38 stress kinase (22). Also we reported that cycloheximide itself inhibits IL-10-induced STAT3 phosphorylation in THP-1 cells (23). PGE2-induced augmentation of IL-10-stimulated STAT3 phosphorylation was greatly reversed by pretreatment of cycloheximide (Fig. 7C). Consistent with previous our report (23), cycloheximide itself inhibits IL-10-induced STAT3 phosphorylation. So we cannot rule out the possibility that cycloheximide directly inhibits PGE2-induced augmentation of IL-10-stimulated STAT3 phosphorylation, not by inhibiting the synthesis of new proteins. Also studies using cycloheximide on IL-6 signaling did not yield informative data, as cycloheximide treatment alone significantly blocked IL-6 signaling (Fig. 7D).

Because SOCS3 is a major feedback inhibitor of IL-6-induced STAT signaling (20, 24, 25), we suspected that SOCS3 may be involved in the PGE2-mediated inhibition of IL-6-induced STAT3 activation. PGE2 rapidly induced SOCS3 mRNA expression within 30 min (Fig. 7E), and this PGE2-induced SOCS3 expression was completely suppressed by pretreatment with actinomycin D (Fig. 7F). Thus, it is possible that the PGE2-induced inhibition of IL-6 signaling might be due to de novo synthesis of SOCS3. In our studies, IL-10-induced STAT3 phosphorylation was not affected by PGE2-mediated induction of SOCS3, which is consistent with another report suggesting that IL-10-induced STAT3 activation is much less sensitive to the inhibitory activity of SOCS3 (25).

EP2 and/or EP4 receptor mediates PGE2 modulation of IL-10-induced STAT3 phosphorylation in THP-1 cells

Next, we examined which EP receptor mediates the effect of PGE2 on IL-10-induced STAT3 phosphorylation by using agonists specific for one or more subtypes of EP receptors, such as misoprostol (EP2/EP3/EP4 agonist), sulprostone (EP1/EP3 agonist), and butaprost (EP2 agonist). Misoprostol augmented IL-10-induced STAT3 phosphorylation, suggesting a dependence on EP2, EP3, and EP4 receptors (Fig. 8, A and B). In contrast to misoprostol and PGE2, sulprostone had no effect on IL-10-induced STAT3 phosphorylation (Fig. 8A); thus, we ruled out involvement of the EP1 and EP3 receptors in the modulation of IL-10-induced STAT3 phosphorylation. Because butaprost has a lower affinity for the EP receptor compared with misoprostol and PGE2, it was used at a higher concentration (10 µM) than the other agonists (1 µM). Butaprost augmented IL-10-induced STAT3 phosphorylation, but its modulating effect was much less potent than misoprostol and PGE2 (Fig. 8A). Misoprostol and butaprost each augmented IL-10-induced SOCS3 expression. The effect of misoprostol was similar to that of PGE2 (Fig. 8B), but butaprost was less potent than misoprostol and PGE2. The SOCS3 gene expression increase induced by the addition of 10 µM butaprost was only 15–20%, compared with the level of gene expression induced by 1 µM misoprostol and PGE2 (Fig. 8C). These results suggest that PGE2-induced modulation of IL-10 signaling occurs via the EP2 and/or EP4 receptors.


Figure 8
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  		FIGURE 8. Effects of specific EP receptor agonists on IL-10-induced STAT3 phosphorylation and SOCS3 gene expression. A, Sulprostone (1 µM), misoprostol (1 µM), or butaprost (1 and 10 µM) as well as PGE2 (1 µM) were added 2 h before IL-10 (20 ng/ml) stimulation for 10 min. STAT3 phosphorylation was observed by immunoblot assay. IL-10-induced STAT3 phosophorylation was increased by pretreatment with PGE2, misoprostol, and butaprost. These experiments are representative of three independent experiments all displaying similar results. B and C, Misoprostol (1 µM) or butabrost (1 and 10 µM) was added 2 h before IL-10 (20 ng/ml) stimulation for 1 h. The mRNA level was measured using real-time PCR. SOCS3 relative to GAPDH mRNA amount is presented. Misoprostol (B) and butaprost (C) augmented IL-10-induced SOCS3 gene expression. The mean value of three independent experiments are shown, and error bars indicate SD.

 
PGE2-induced augmentation of IL-10 signaling involves PI3K and protein kinase A (PKA)

EP2 and EP4 receptors activate adenylate cyclase, leading to cAMP production and activation of a cAMP-dependent protein kinase, known as PKA (26). In addition to this PKA signaling pathway, stimulation of the EP4 receptor leads to activation of the PI3K-dependent pathway (27). We therefore examined the effect of H89, a specific PKA inhibitor, and LY294002, a PI3K inhibitor, on PGE2-induced modulation of cytokine signaling. When THP-1 cells were pretreated with H89 for 30 min before PGE2 treatment, PGE2 augmentation of IL-10-induced STAT3 phosphorylation was greatly reversed (Fig. 9A). In addition, LY294002 partially diminished the augmentation of the IL-10-induced STAT3 phosphorylation by PGE2 (Fig. 9B). Pretreatment with H89 diminished the augmentation of IL-10-induced SOCS3 gene expression in a dose-dependent fashion, and combined pretreatment with LY294002 and H89 greatly suppressed it when compared with H89 alone (Fig. 9C). LY294002 did not reverse the PGE2-induced augmentation of SOCS3 gene expression in this experiment, which is inconsistent with our other results of STAT3 phosphorylation. The reason for this discrepancy is unclear at present and will need further evaluation in future studies. These findings indicate that the PKA and PI3K signaling pathways are involved in PGE2-mediated augmentation of IL-10-induced STAT3 phosphorylation.


Figure 9
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  		FIGURE 9. Effect of H89 and LY294002 on PGE2-induced augmentation of IL-10 signaling. A and B, H89 (10 µM) (A) or LY294002 (25 µM) (B) was added 30 min before PGE2 treatment. After 2 h of PGE2 treatment, cells were stimulated with IL-10 (20 ng/ml) for 10 min, followed by immunoblot analysis with anti-phospho-STAT3 Ab. These experiments are representative of three independent experiments all displaying similar results. C, After pretreatment with H89 (10 and 30 µM) and/or LY294002 (25 µM) for 30 min, PGE2 (1 µM) was added 2 h, before IL-10 (20 ng/ml) stimulation for 1 h. SOCS3 relative to GAPDH mRNA amounts are presented. The mean value of three independent experiments are shown, and error bars indicate SD.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Disclosures
 References
 
Our study demonstrates that PGE2 augments IL-10-induced STAT3 phosphorylation and its biological functions. We were surprised to find that PGE2 augments IL-10-induced STAT3 phosphorylation and gene expression because previous studies demonstrated that PGE2 and cAMP usually inhibit cytokine-induced STAT activation (9, 10, 28). To our knowledge, these data are the first demonstration that PGE2 augments IL-10 signaling and function. Our results suggest the possibility that PGE2 may cooperate with IL-10 to promote anti-inflammatory responses in inflammatory diseases in which there is a high expression of PGE2.

In human macrophages, IL-10 induces SOCS3 expression and this expression absolutely requires phosphorylation of STAT3 (18). In our study, we observed that PGE2 enhanced synergistically IL-10-induced SOCS3 gene expression. Another interesting finding is that the induction of SOCS3 gene expression by PGE2 alone is stronger than by IL-10 alone. We cannot exclude the possibility that augmentation of SOCS3 gene expression is the effect of IL-10 on PGE2-induced SOCS3 expression. However, recently published data from Antoniv et al. (29) reported that IL-10 induces increased degradation of PGE2 and suppresses PGE2-mediated gene expression. Gasperini et al. (30) have recently shown that PGE2 not only directly induces SOCS3 mRNA and protein expression in human leukocytes, but also cooperates with IL-10, via the mechanism that PGE2 prolongs the stability of SOCS3 mRNA. In contrast to our results, expression level of SOCS3 mRNA induced by PGE2 is lower than those induced by IL-10. Also another report demonstrated that PGE2 increases erythropoietin-dependent STAT5 regulatory genes, such as SOCS3 (31). This costimulatory effect of PGE2 on erythropoietin-mediated STAT5 transactivation is mediated by the cAMP/PKA/CREB pathway, without affecting the STAT5 tyrosine phosphorylation or STAT5 DNA binding. Thus, we can suggest that PGE2 modulates cytokine function via several different mechanisms, according to cell types and individual cytokines.

The molecular mechanisms for negative regulation of cytokine-induced Jak-STAT signaling have been extensively investigated. In contrast, its augmentation is poorly understood. In this study we have examined several possible mechanisms for augmented cytokine-induced STAT signaling, such as increased cell surface expression of cytokine receptors (11, 32), induction of cytokine to activate STAT phosphorylation (11, 33), and increased STAT protein expression (34).

First, we investigated whether PGE2-derived augmentation of IL-10 signaling is due to the increased cell surface expression of cytokine receptors. Crepaldi et al. (32) demonstrated that IL-10 induced STAT3 phosphorylation not seen in freshly isolated human neutrophils, but is found in LPS-treated neutrophils, thus demonstrating that IL-10R1 mRNA and protein expression are substantially increased in LPS-stimulated neutrophils. Another report demonstrated that PGE2 stimulates soluble IL-6R release, gp130 dimerization, and STAT3 phosphorylation (11). However, in our experiments, pretreatment with PGE2 had no discernible effect on cell surface IL-10R expression in THP-1 cells, ruling out this possibility in our study.

Next, we examined whether PGE2 augments STAT3 phosphorylation via production of new cytokines. It has been reported that PGE2 stimulates IL-6 secretion, as well as soluble IL-6R release, resulting in STAT3 activation in a PIN cell line (11). PGE2 also enhances IL-10 production in LPS-stimulated peripheral blood monocytes via an increase in intracellular cAMP. In activated murine macrophages, PGE2 increases the levels of both IL-10 and IL-6 via the p38 MAPK pathway (14). In our experiments, PGE2 itself did not activate STAT3 phosphorylation, suggesting that augmentation of IL-10 signaling is not mediated via PGE2-induced cytokine production, which results in STAT3 phosphorylation.

We then checked another possible mechanism for augmenting cytokine signaling, that of increased STAT3 protein expression. Low concentrations of IFN-{gamma} augmented STAT1 protein expression, and subsequently enhanced STAT1 activation and IFN-{gamma}-dependent gene expression (34). Prolonged insulin treatment has been shown to reduce STAT3 protein expression and resulting STAT3 phosphorylation (35). These studies suggest that altered STAT protein expression can have an influence in Jak-STAT signaling. However, in our experiments PGE2 did not change STAT3 protein expression in THP-1 cells.

The diverse and specific effects of PGE2 depend on different EP receptor subtypes. In THP-1 cells, all four EP receptor genes are expressed, and EP4 is expressed at a higher level when compared with EP1, EP2, and EP3. Misoprostol, an EP2/EP3/EP4 agonist, augmented IL-10-induced STAT3 phosphorylation, producing an effect similar to that of PGE2. Sulprostone, an EP1/3 agonist, had no effect on IL-10-induced STAT3 phosphorylation. These results suggest that PGE2-induced modulation of cytokine signaling occurs via EP2 and/or EP4 receptors. Because EP2/EP4 receptors are activated by increased cAMP levels, results showing that exogenous cAMP augmented IL-10-induced STAT3 phosphorylation corroborate this finding.

In PGE2 EP2/EP4 signaling, increased cAMP levels result in the activation of PKA. EP4 receptors lead to the activation of the PI3K-dependent pathway, in addition to PKA pathway. H89, a PKA inhibitor, strongly reversed PGE2-derived augmentation of IL-10-induced STAT3 phosphorylation and SOCS3 gene expression, suggesting that PKA mediates PGE2-induced augmentation of IL-10 signaling. LY294002, a PI3K inhibitor, partially diminished PGE2-derived augmentation of IL-10-induced STAT3 phosphorylation. Combined pretreatment with H89 and LY294002 provided a more effective suppression of PGE2-enhanced SOCS3 expression, when compared with H89 alone. These findings indicate that PI3K also mediates the PGE2 effect in the modulation of IL-10 signaling. Because inhibitors of PI3K, such as wortmannin and LY294002, inhibit relaxin-mediated cAMP production in THP-1 cells (36), PI3K is thought to be involved in cAMP production. We suggest that increased cAMP production and subsequent activation of PKA are a possible mechanism by which PGE2 modulates IL-10 signaling.

PGE2 augments or inhibits IL-6-induced STAT3 activation according to cell type (10, 11). In PIN cells, PGE2 stimulates soluble IL-6R release, STAT3 phosphorylation, and DNA binding activity. In the promyelocytic cell line, NFS-60, PGE2 suppresses IL-6R expression and STAT3 activation. In our current study, down-regulation of IL-6R became evident following 6 h of PGE2 treatment. In contrast to previous reports, our results show that PGE2 inhibited IL-6-induced STAT3 phosphorylation within 30 min, but it did not change the cell surface expression of IL-6R. These results suggest that PGE2 stimulates a direct and prompt inhibitory pathway, which can induce inhibitors within 30 min. Our experiments show that actinomycin D reversed PGE2-derived inhibition of IL-6-induced STAT3 phosphorylation, suggesting dependence on synthesis of new inhibitory molecules. PGE2 induced SOCS3 gene expression within 30 min, and this was completely suppressed by actinomycin D. These results indicate that SOCS3 may be involved in the PGE2-induced inhibition of IL-6 signaling. It remains to be determined which intracellular signaling pathway is involved in PGE2-derived inhibition of IL-6 signaling and PGE2-induced SOCS3 gene expression.

In primary monocytes, PGE2 did not influence cytokine-induced STAT3 phosphorylation. These results suggest that PGE2 regulates cytokine-induced STAT3 phosphorylation in a cell-specific manner. We have not further addressed these findings in this article. Further study in various conditioned monocytes and macrophages will be necessary to prove the modulating effects of PGE2 on cytokine signaling in the inflammatory diseases, such as rheumatoid arthritis.

In this study, we found that PGE2 differentially regulates Jak-STAT signaling from different cytokines in THP-1. Our results demonstrate a previously unrecognized function of PGE2, the augmentation of IL-10-induced STAT3 phosphorylation and gene expression. It is also a novel finding that PGE2 can modulate effects on the immune response via the regulation of cytokine signaling, as well as of cytokine production.


   Acknowledgments
 
We thank Dr. Dae Hyun Yoo and Tae Hwan Kim for discussing the manuscript.


   Disclosures
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
References
 
The authors have no financial conflict of interest.


   Footnotes
 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

1 This work was supported by a Jeil Pharmaceutical Company grant and a Korea University grant. Back

2 Address correspondence and reprint requests to Dr. Jong Dae Ji, Department of Rheumatology, College of Medicine, Korea University, 126-1, Anam-Dong 5-Ga, Sungbuk-Gu, Seoul 136-705, South Korea. E-mail address: jjdjmesy{at}korae.ac.kr Back

3 Abbreviations used in this paper: EP, E prostanoid; PKA, protein kinase A; PIN, prostatic intraepithelial neoplasia; SOCS, suppressors of cytokine signaling. Back

Received for publication January 3, 2006. Accepted for publication May 2, 2006.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Disclosures
 References
 

  1. DeWitt, D. L.. 1991. Prostaglandin endoperoxide synthase: regulation of enzyme expression. Biochim. Biophys Acta 1083: 121-134. [Medline]
  2. Kambayashi, T., C. O. Jacob, D. Zhou, N. Mazurek, M. Fong, G. Strassmann. 1995. Cyclic nucleotide phosphodiesterase type IV participates in the regulation of IL-10 and in the subsequent inhibition of TNF-{alpha} and IL-6 release by endotoxin-stimulated macrophages. J. Immunol. 155: 4909-4916. [Abstract]
  3. Strassmann, G., V. Patil-Koota, F. Finkelman, M. Fong, T. Kambayashi. 1994. Evidence for the involvement of interleukin 10 in the differential deactivation of murine peritoneal macrophages by prostaglandin E2. J. Exp. Med. 180: 2365-2370. [Abstract/Free Full Text]
  4. Harris, S. G., J. Padilla, L. Koumas, D. Ray, R. P. Phipps. 2002. Prostaglandins as modulators of immunity. Trends Immunol. 23: 144-150. [Medline]
  5. Hata, A. N., R. M. Breyer. 2004. Pharmacology and signaling of prostaglandin receptors: multiple roles in inflammation and immune modulation. Pharmacol. Ther. 103: 147-166. [Medline]
  6. Moore, K. W., M. R. de Waal, R. L. Coffman, A. O’Garra. 2001. Interleukin-10 and the interleukin-10 receptor. Annu. Rev. Immunol. 19: 683-765. [Medline]
  7. Wong, P. K., I. K. Campbell, P. J. Egan, M. Ernst, I. P. Wicks. 2003. The role of the interleukin-6 family of cytokines in inflammatory arthritis and bone turnover. Arthritis Rheum. 48: 1177-1189. [Medline]
  8. Taga, T., T. Kishimoto. 1997. gp130 and the interleukin-6 family of cytokines. Annu. Rev. Immunol. 15: 797-819. [Medline]
  9. Ivashkiv, L. B., E. M. Schmitt, A. Castro. 1996. Inhibition of transcription factor Stat1 activity in mononuclear cell cultures and T cells by the cyclic AMP signaling pathway. J. Immunol. 157: 1415-1421. [Abstract]
  10. de Silva, K. I., A. N. Daud, J. Deng, S. B. Jones, R. L. Gamelli, R. Shankar. 2003. Prostaglandin E2 mediates growth arrest in NFS-60 cells by down-regulating interleukin-6 receptor expression. Biochem. J. 370: 315-321. [Medline]
  11. Liu, X. H., A. Kirschenbaum, M. Lu, S. Yao, A. Klausner, C. Preston, J. F. Holland, A. C. Levine. 2002. Prostaglandin E2 stimulates prostatic intraepithelial neoplasia cell growth through activation of the interleukin-6/gp130/STAT-3 signaling pathway. Biochem. Biophys. Res. Commun. 290: 249-255. [Medline]
  12. Goetzl, E. J., S. An, W. L. Smith. 1995. Specificity of expression and effects of eicosanoid mediators in normal physiology and human diseases. FASEB J. 9: 1051-1058. [Abstract]
  13. Feldmann, M., F. M. Brennan, R. N. Maini. 1996. Role of cytokines in rheumatoid arthritis. Annu. Rev. Immunol. 14: 397-440. [Medline]
  14. Williams, J. A., C. H. Pontzer, E. Shacter. 2000. Regulation of macrophage interleukin-6 (IL-6) and IL-10 expression by prostaglandin E2: the role of p38 mitogen-activated protein kinase. J. Interferon Cytokine Res. 20: 291-298. [Medline]
  15. Williams, L., G. Jarai, A. Smith, P. Finan. 2002. IL-10 expression profiling in human monocytes. J. Leukocyte Biol. 72: 800-809. [Abstract/Free Full Text]
  16. Berlato, C., M. A. Cassatella, I. Kinjyo, L. Gatto, A. Yoshimura, F. Bazzoni. 2002. Involvement of suppressor of cytokine signaling-3 as a mediator of the inhibitory effects of IL-10 on lipopolysaccharide-induced macrophage activation. J. Immunol. 168: 6404-6411. [Abstract/Free Full Text]
  17. Arend, W. P.. 2001. Cytokine imbalance in the pathogenesis of rheumatoid arthritis: the role of interleukin-1 receptor antagonist. Semin. Arthritis Rheum. 30: (Suppl. 2):1-6. [Medline]
  18. Williams, L., L. Bradley, A. Smith, B. Foxwell. 2004. Signal transducer and activator of transcription 3 is the dominant mediator of the anti-inflammatory effects of IL-10 in human macrophages. J. Immunol. 172: 567-576. [Abstract/Free Full Text]
  19. Ahmed, S. T., L. B. Ivashkiv. 2000. Inhibition of IL-6 and IL-10 signaling and Stat activation by inflammatory and stress pathways. J. Immunol. 165: 5227-5237. [Abstract/Free Full Text]
  20. Bode, J. G., S. Ludwig, C. A. Freitas, F. Schaper, M. Ruhl, S. Melmed, P. C. Heinrich, D. Haussinger. 2001. The MKK6/p38 mitogen-activated protein kinase pathway is capable of inducing SOCS3 gene expression and inhibits IL-6-induced transcription. Biol. Chem. 382: 1447-1453. [Medline]
  21. Yasukawa, H., A. Sasaki, A. Yoshimura. 2000. Negative regulation of cytokine signaling pathways. Annu. Rev. Immunol. 18: 143-164. [Medline]
  22. Ahmed, S. T., A. Mayer, J. D. Ji, L. B. Ivashkiv. 2002. Inhibition of IL-6 signaling by a p38-dependent pathway occurs in the absence of new protein synthesis. J. Leukocyte Biol. 72: 154-162. [Abstract/Free Full Text]
  23. Ji, J. D., H. J. Kim, Y. H. Rho, S. J. Choi, Y. H. Lee, H. J. Cheon, J. Sohn, G. G. Song. 2005. Inhibition of IL-10-induced STAT3 activation by 15-deoxy-{Delta}12,14-prostaglandin J2. Rheumatology 44: 983-988. [Abstract/Free Full Text]
  24. Fischer, P., U. Lehmann, R. M. Sobota, J. Schmitz, C. Niemand, S. Linnemann, S. Haan, I. Behrmann, A. Yoshimura, J. A. Johnston, et al 2004. The role of the inhibitors of interleukin-6 signal transduction SHP2 and SOCS3 for desensitization of interleukin-6 signalling. Biochem. J. 378: 449-460. [Medline]
  25. Niemand, C., A. Nimmesgern, S. Haan, P. Fischer, F. Schaper, R. Rossaint, P. C. Heinrich, G. Müller-Newen. 2003. Activation of STAT3 by IL-6 and IL-10 in primary human macrophages is differentially modulated by suppressor of cytokine signaling 3. J. Immunol. 170: 3263-3272. [Abstract/Free Full Text]
  26. Narumiya, S., G. A. FitzGerald. 2001. Genetic and pharmacological analysis of prostanoid receptor function. J. Clin. Invest. 108: 25-30. [Medline]
  27. Fujino, H., W. Xu, J. W. Regan. 2003. Prostaglandin E2 induced functional expression of early growth response factor-1 by EP4, but not EP2, prostanoid receptors via the phosphatidylinositol 3-kinase and extracellular signal-regulated kinases. J. Biol. Chem. 278: 12151-12156. [Abstract/Free Full Text]
  28. Sengupta, T. K., E. M. Schmitt, L. B. Ivashkiv. 1996. Inhibition of cytokines and JAK-STAT activation by distinct signaling pathways. Proc. Natl. Acad. Sci. USA 93: 9499-9504. [Abstract/Free Full Text]
  29. Antoniv, T. T., K. H. Park-Min, L. B. Ivashkiv. 2005. Kinetics of IL-10-induced gene expression in human macrophages. Immunobiology 210: 87-95. [Medline]
  30. Gasperini, S., L. Crepaldi, F. Calzetti, L. Gatto, C. Berlato, F. Bazzoni, A. Yoshimura, M. A. Cassatella. 2002. Interleukin-10 and cAMP-elevating agents cooperate to induce suppressor of cytokine signaling-3 via a protein kinase A-independent signal. Eur. Cytokine Network 13: 47-53. [Medline]
  31. Boer, A. K., A. L. Drayer, H. Rui, E. Vellenga. 2002. Prostaglandin-E2 enhances EPO-mediated STAT5 transcriptional activity by serine phosphorylation of CREB. Blood 100: 467-473. [Abstract/Free Full Text]
  32. Crepaldi, L., S. Gasperini, J. A. Lapinet, F. Calzetti, C. Pinardi, Y. Liu, S. Zurawski, R. de Waal Malefyt, K. W. Moore, M. A. Cassatella. 2001. Up-regulation of IL-10R1 expression is required to render human neutrophils fully responsive to IL-10. J. Immunol. 167: 2312-2322. [Abstract/Free Full Text]
  33. van der Pouw Kraan, T. C., L. C. Boeije, R. J. Smeenk, J. Wijdenes, L. A. Aarden. 1995. Prostaglandin-E2 is a potent inhibitor of human interleukin 12 production. J. Exp. Med. 181: 775-779. [Abstract/Free Full Text]
  34. Hu, X., C. Herrero, W. P. Li, T. T. Antoniv, E. Falck-Pedersen, A. E. Koch, J. M. Woods, G. K. Haines, L. B. Ivashkiv. 2002. Sensitization of IFN-{gamma} Jak-STAT signaling during macrophage activation. Nat. Immunol. 3: 859-866. [Medline]
  35. Xu, J., S. Ji, D. Y. Venable, J. L. Franklin, J. L. Messina. 2005. Prolonged insulin treatment inhibits GH signaling via STAT3 and STAT1. J. Endocrinol. 184: 481-492. [Abstract/Free Full Text]
  36. Nguyen, B. T., L. Yang, B. M. Sanborn, C. W. Dessauer. 2003. Phosphoinositide 3-kinase activity is required for biphasic stimulation of cyclic adenosine 3',5'-monophosphate by relaxin. Mol. Endocrinol. 17: 1075-1084. [Abstract/Free Full Text]



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