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12,14-prostaglandin J2 action

* Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain
Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Cientificas-Universidad Autonoma de Madrid, Madrid, Spain
Published, JLR Papers in Press, January 16, 2005. DOI 10.1194/jlr.M400392-JLR200
1 To whom correspondence should be addressed. e-mail: piedras3{at}med.ucm.es (A.S.); aperez{at}iib.uam.es (A.P-C.)
| ABSTRACT |
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12,14-prostaglandin J2 (15d-PGJ2) is a very active compound with important effects on inflammation, apoptosis, and cell growth processes. To exert this broad range of effects, 15d-PGJ2 binds and alters the activity of diverse proteins, which consequently are postulated to be mediators of its action. Among them are the transcription factors peroxisome proliferator-activated receptor
and nuclear factor
B, which are thought to play an essential role in the antitumorigenic and anti-inflammatory actions of 15d-PGJ2. Here, we show that 15d-PGJ2, at micromolar concentrations, efficiently blocks state 3 oxygen consumption in intact nonsynaptic mitochondria isolated from rat cerebral cortex. This effect is attributable to the inhibition by this prostaglandin of the activity of the enzyme NADH-ubiquinone reductase (complex I) of the mitochondrial respiratory chain. In addition to this, 15d-PGJ2 dramatically increases the rate of reactive oxygen species generation by complex I. The inhibition by 15d-PGJ2 of complex I activity was abolished by dithiothreitol, which raises the possibility that adduct formation with a critical component of complex I accounts for the inhibitory effect of this prostaglandin. These results clearly identified mitochondrial complex I as a new target for 15d-PGJ2 actions.
Abbreviations: DCFH, dichlorofluorescin; 15d-PGJ2, 15-deoxy-
12,14-prostaglandin J2; I-
B, inhibitor
B; NF-
B, nuclear factor
B; PGJ2, prostaglandin J2; PPAR
, peroxisome proliferator-activated receptor
; ROS, reactive oxygen species
Supplementary key words respiratory chain reactive oxygen species cyclopentenone prostaglandins
| INTRODUCTION |
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12-PGJ2 and 15-deoxy-
12,14-PGJ2 (15d-PGJ2) are naturally occurring derivatives of prostaglandin D2, the most abundant prostaglandin in normal tissues (1). They have been shown to exert important effects on diverse biological processes, such as inflammation, cell growth, and apoptosis, with 15d-PGJ2 as the most active component of this group of cyclopentenone prostaglandins (2, 3).
Multiple mechanisms have been proposed to explain the diversity of action of 15d-PGJ2, although the relative importance of each of them is not completely established. 15d-PGJ2 is the most active natural ligand of the peroxisome proliferator-activated receptor
(PPAR
) (4, 5). PPAR
is a transcription factor that belongs to the superfamily of nuclear receptors and therefore regulates gene expression in a ligand-dependent manner (6, 7). In addition to 15d-PGJ2, many other compounds have been shown to activate PPAR
. Among them are the antidiabetic drugs thiazolidinedione and the nonsteroidal anti-inflammatory drugs (2). It is believed that PPAR
mediates, at least in part, the actions of 15d-PGJ2 on cell growth and apoptosis through the regulation by this transcription factor of the expression of genes critical to these processes, such as cyclin D1 and D2 (8, 9), cyclin-kinase inhibitors p21warf1/cip1 and p27kip1 (8, 10), tumor suppressors phosphatase and tensisn homologue deleted from chromosoma 10 (PTEN) and breast cancer susceptibility gene 1 (BRCA1) (11, 12), and bcl2 family members (13, 14).
The transcription factor nuclear factor
B (NF-
B) is another important target for 15d-PGJ2 action. In the unstimulated state, NF-
B is sequestered in the cytosol by the repressor protein inhibitor
B (I-
B) and consequently inactive. Upon cellular signaling, I-
B is phosphorylated by I-
B kinase, resulting in the degradation of I-
B and the translocation of NF-
B to the nucleus, where it regulates, among other functions, the expression of genes implicated in inflammatory processes (15). 15d-PGJ2 inhibits NF-
B action by blocking I-
B kinase activity and NF-
B binding to DNA (16, 17). NF-
B inhibition by 15d-PGJ2 is thought to represent the major pathway in the anti-inflammatory effects of this prostaglandin. In addition to PPAR
and NF-
B, other transcription factors, signal transduction proteins, and membrane receptors have been shown to be targeted by 15d-PGJ2 (1821).
Finally, it has been also shown that 15d-PGJ2 increases the intracellular production of reactive oxygen species (ROS), which is considered to be relevant for the induction of apoptosis and the activation of stress-activated and mitogen-activated protein kinases (2227).
Here, we show that 15d-PGJ2 is a potent inhibitor of mitochondrial respiration and that this inhibition is accomplished by efficiently blocking the activity of respiratory complex I. Consequently, oxygen consumption in respiratory state 3 is inhibited only in the presence of NADH-generating substrates, but not in the presence of succinate plus rotenone. In addition to this, 15d-PGJ2 dramatically increases the rate of ROS production. Altogether, these results identify mitochondrial respiratory complex I as a new target for 15d-PGJ2 action, which could be important for better understanding the biological effects of this prostaglandin.
| EXPERIMENTAL PROCEDURES |
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Mitochondria isolation
Rat cerebral cortex nonsynaptic mitochondria were isolated according to the method described by Dunkley et al. (28). Briefly, rat cerebral cortex was dissected from the brains of Wistar rats (100150 g), and 1g of tissue was homogenized in 10 ml of ice-cold medium containing 0.32 M sucrose, 0.5 mM EDTA, and 10 mM Tris-HCl, pH 7.4, in a Teflon-glass homogenizer and centrifuged at 1,000 g for 5 min. The supernatant was saved and centrifuged at 9,500 g for 10 min. The pellet was resuspended in 3 ml of a medium containing 0.32 M sucrose, 1 mM EDTA, 0.25 mM DTT, and 10 mM Tris-HCl, pH 7.4, then centrifuged in a discontinuous Percoll gradient (23, 10, and 3%) at 22,000 g for 10 min. The fraction enriched in nonsynaptic mitochondria was resuspended and washed in the homogenization buffer and immediately used for oxygen consumption and ROS generation or frozen at 80°C until used for the determination of complex I activity. All of the preparative steps were performed at 04°C. Protein content was measured by Bradford's procedure (29) using BSA as a standard.
Determination of the rate of oxygen consumption and hydrogen peroxide production
Oxygen consumption in freshly prepared mitochondria was measured polarographically with a Clark-type electrode (Oxigraph Hansatech) at 30°C with constant stirring. Mitochondria (0.7 mg of protein) were suspended in 1 ml of respiratory medium containing 75 mM sucrose, 50 mM KCl, 5 mM KH2PO4, 0.5 mM EDTA, 5 mM MgCl2, and 30 mM Tris-HCl, pH 7.4. The basal rate of respiration (state 4) was determined in the presence of diverse substrates: glutamate/malate (5 mM each), pyruvate (5 mM), or succinate (5 mM). When succinate was the substrate, 5 µM rotenone was also added. The active state of respiration (state 3) was initiated by the addition of 0.5 mM ADP.
Mitochondrial generation of ROS was determined in freshly prepared mitochondria by measuring hydrogen peroxide-dependent oxidation of DCFH in the presence of horseradish peroxidase. For that purpose, DCFH was obtained from the stable reagent DCFH diacetate by alkaline treatment (30). Mitochondria (0.1 mg of protein) were incubated with 1.5 µM DCFH at 22°C in 1 ml of medium containing 75 mM sucrose, 5 mM K2HPO4, 40 mM KCl, 3 mM MgCl2, 0.5 mM EDTA, 30 mM Tris-HCl, pH 7.4, and 0.5 µM horseradish peroxidase, and the rate of hydrogen peroxide production was estimated by measuring the linear fluorescence increase (excitation at 475 nm, emission at 525 nm) in a Perkin-Elmer 650 fluorimeter.
Complex I activity
The enzymatic activity of NADH decylubiquinone reductase was spectrophotometrically assayed by following the decrease in absorbance at 340 nm resulting from the oxidation of NADH as previously described (31). Briefly, 50 µg of mitochondrial protein was resuspended in 1 ml of medium containing 20 mM KH2PO4, 8 mM MgCl2, 1 mM KCN, and 2.5 mg/ml BSA, pH 7.2, in the presence of 150 µM NADH and incubated at 30°C until the optical density value was stabilized. The reaction was then started by the addition of decylubiquinone at a final concentration of 50 µM. In parallel, NADH decylubiquinone reductase activity was determined in the presence of 10 µM rotenone.
| RESULTS |
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and the presence of these receptors has been described also within the mitochondrial matrix of certain tissues (32), we decided to test the action of rosiglitazone, a TZD that binds this nuclear receptor with high affinity, on mitochondrial respiration. As shown in Fig. 1C, no inhibition of complex I activity was observed with 30 µM rosiglitazone, a concentration known to efficiently activate PPAR
(12). Therefore, these results suggest that 15d-PGJ2 action in the mitochondria is PPAR
-independent.
Mitochondrial complex I activity
The activity of NADH-ubiquinone reductase complex I was enzymatically determined in nonsynaptic mitochondria isolated from rat cerebral cortex, as described in Experimental Procedures, and the effect of 15d-PGJ2 was analyzed. As shown in Fig. 2A, 15d
-PGJ2 blocks complex I activity; therefore, at a concentration of 5 µM, this prostaglandin inhibits 50% of the enzymatic activity of this complex. In contrast, no effect was observed in the presence of 30 µM rosiglitazone (Fig. 2B), a well-known PPAR
agonist. These results are clearly in agreement with those describing the effect of 15d-PGJ2 on mitochondrial respiration and thus suggest that the inhibition of complex I activity is a major target for 15d-PGJ2 action in the mitochondria. We next analyzed the effect on complex I activity of other prostaglandins. As shown in Fig. 2C, neither prostaglandin A2 nor prostaglandin D2 showed a significant inhibitory effect on complex I activity at concentrations as high as 50 µM. PGJ2 showed a modest inhibitory effect, and a concentration of 50 µM was required to obtain an
30% inhibition of complex I activity.
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,ß-unsaturated carbonyl moieties that can act as Michael acceptors by reacting with thiol groups (33, 34). 15d-PGJ2 has been reported to use this mechanism to modify the function of diverse proteins (17, 21). This reaction is sensitive to the reducing agent DTT, which has been shown to eliminate the inhibitory effect of this prostaglandin on NF-
B binding to DNA (17). Therefore, we next analyzed the possible effect of DTT on the inhibitory effect of 15d-PGJ2 on complex I activity. As shown in Fig. 4
, when mitochondrial membranes preincubated with 15d-PGJ2 were washed in the presence of 1 mM DTT, no inhibitory effect of 15d-PGJ2 was observed. In contrast, the inhibitory effect remained when the membranes were washed with the same buffer but in the absence of DTT, suggesting the formation by 15d-PGJ2 of an adduct with a critical component of complex I as a probable mechanism to account for the action of this prostaglandin.
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| DISCUSSION |
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When the complex I substrates glutamate/malate and pyruvate were assayed, 15d-PGJ2 blocked state 3 mitochondrial respiration. In contrast, when succinate, a complex II substrate, was added in the presence of rotenone, a complex I inhibitor, 15d-PGJ2 did not inhibit state 3 respiration. No effect of 15d-PGJ2 was observed on oxygen consumption in respiratory state 4, suggesting that this compound does not have an uncoupling effect. In contrast, other lipids known to inhibit the respiratory chain also altered the permeability of the mitochondrial membrane, causing an uncoupling effect (35, 36).
In addition to inhibiting complex I activity, 15d-PGJ2 strongly induces mitochondrial ROS production. Complex I is considered one of the major places of ROS production in the mitochondrion and, therefore, one of the major producers of ROS within the cell (3739). Here, we show that the classical complex I inhibitor rotenone clearly reduced ROS production induced by 15d-PGJ2 in isolated mitochondria, in agreement with recent work from our laboratory showing that rotenone in MCF-7 cells is a potent inhibitor of 15d-PGJ2-induced oxidative stress (40). These results clearly implicate complex I as the site of ROS production induced by 15d-PGJ2. Our results are in agreement with previous results by other groups showing that 15d-PGJ2, at micromolar concentrations, induces an increase in cellular ROS production (2226) and particularly with the suggestion by Kondo et al. (22) that the mitochondrion is the place of ROS production induced by this prostaglandin.
Regarding the biological consequences of the effects described here, we propose that these mitochondrial effects could be implicated in the loss of cell viability and the induction of antioxidant enzymes by 15d-PGJ2 shown in diverse cell lines (14, 4144). In this regard, it is interesting that the addition of antioxidant compounds, such as N-acetylcysteine, N-(2-mercapto-propionyl)-glycine, and pyrrolidine dithiocarbamate, prevent the induction by 15d-PGJ2 of cell death in human neuroblastoma SH-SY5Y and human hepatic myofibroblasts (22, 23), the activation of mitogen-activated protein and stress-activated kinases (25), and the decrease in mitochondrial potential in Jurkat T-cells (27). In addition to these data, we recently showed that rotenone and the radical scavengers ebselen and ascorbate prevented the induction of cell death in MCF-7 cells (40), a finding that clearly supports the proposal that the mitochondrial effects of this prostaglandin are important mediators in the loss of cell viability.
The possible mechanism of 15d-PGJ2 action on complex I activity was analyzed by studying the action of other PPAR
ligands on isolated mitochondria and the sensitivity of 15d-PGJ2 action to the reducing agent DTT. The presence of PPAR
receptors within the mitochondrial matrix of specific tissues has been described, although their possible physiological function is unclear (32). Here, we show that the high-affinity PPAR
ligand rosiglitazone, at a concentration known to efficiently induce gene expression (12), had no effect on oxygen consumption and the activity of complex I, suggesting that the inhibition of complex I by 15d-PGJ2 is PPAR
-independent. The present data also indicate that the observed effects of 15d-PGJ2 on mitochondrial complex I activity is specific for this prostaglandin, because other prostaglandins, such prostaglandins A2 and D2, do not exhibit this effect and the structurally more related PGJ2 showed only a modest effect.
15d-PGJ2 has electrophilic carbon moieties, which are susceptible to undergoing addition reactions (Michael addition) with nucleophiles such as the free thiol groups (33, 34). In this way, 15d-PGJ2 has been shown to modify the function of diverse proteins (17, 21). This reaction is sensitive to the reducing agent DTT, which has been shown to eliminate the inhibitory effect of this prostaglandin on NF-
B binding to DNA (17). Therefore, the results presented here show that the inhibitory effect of this prostaglandin on complex I activity is washed out in the presence of 1 mM DTT, suggesting the formation by 15d-PGJ2 of an adduct with a critical component of mitochondrial complex I.
In summary, our data support the hypothesis that 15d-PGJ2 could form a covalent complex with the respiratory complex I and, as a consequence, inhibit the function of this complex and increase ROS production, an effect that probably represents an important mechanism for the observed cytostatic effects of this prostaglandin.
| ACKNOWLEDGMENTS |
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Manuscript received October 7, 2004 and in revised form December 21, 2004.
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