Subcellular localization of prostaglandin endoperoxide H synthases-1 and -2 by immunoelectron microscopy

New insights into the retinal circulation: inflammatory lipid mediators in ischemic retinopathy

Ischemic proliferative retinopathy develops in various retinal disorders, including retinal vein occlusion, diabetic retinopathy and retinopathy of prematurity. Ischemic retinopathy remains a common cause of visual impairment and blindness in the industrialized world due to relatively ineffective treatment. Oxygen-induced retinopathy (OIR) is an established model of retinopathy of prematurity associated with vascular cell injury culminating in microvascular degeneration, which precedes an abnormal neovascularization. The retina is a tissue particularly rich in polyunsaturated fatty acids and the ischemic retina becomes highly sensitive to lipid peroxidation initiated by oxygenated free radicals. Consequently, the retina constitutes an excellent model for testing the functional consequences of membrane lipid peroxidation. Retinal tissue responds to physiological and pathophysiological stimuli by the activation of phospholipases and the consequent release from membrane phospholipids of biologically active metabolites. Activation of phospholipase A(2) is the first step in the synthesis of two important classes of lipid second messengers, the eicosanoids and a membrane-derived phospholipid mediator platelet-activating factor (PAF). These lipid mediators accumulate in the retina in response to injury and a physiologic role of these metabolites in retinal vasculature remains for the most part to be determined; albeit proposed roles have been suggested for some. The eicosanoids, in particular the prostanoids, thromboxane (TXA2) and PAF are abundantly generated following an oxidant stress and contribute to neurovascular injury. TXA2 and PAF play an important role in the retinal microvacular degeneration of OIR by directly inducing endothelial cell death and potentially could contribute to the pathogenesis of ischemic retinopathies. Despite these advances there are still a number of important questions that remain to be answered before we can confidently target pathological signals. This review focuses on mechanisms that precede the development of neovascularization, most notably regarding the role of lipid mediators that partake in microvascular degeneration.

Mitochondrial localization of cyclooxygenase-2 and calcium-independent phospholipase A2 in human cancer cells: Implication in apoptosis resistance

Cyclooxygenase-2 (COX-2) is inducible by myriad stimuli. The inducible COX-2 in primary cultured human cells has been reported to localize to nuclear envelope, endoplasmic reticulum, nucleus and caveolae. As COX-2 plays an important role in tumor growth, we were interested in its subcellular location in cancer cells. We examined COX-2 localization in several cancer cell lines by confocal microscopy. A majority of COX-2 was colocalized with heat shock protein 60, a mitochondrial protein, in colon cancer (HT-29, HCT-15 and DLD-1), breast cancer (MCF7), hepatocellular cancer (HepG2) and lung cancer cells (A549) with a similar distribution pattern. By contrast, COX-2 was not localized to mitochondria in human foreskin fibroblasts or endothelial cells. Immunoblot analysis of COX-2 in mitochondrial and cytosolic fractions confirmed localization of COX-2 to mitochondria in HT-29 and DLD-1 cells but not in fibroblasts. Calcium-independent phospholipase A2 was colocalized with heat shock protein 60 to mitochondria not only in cancer cells (HT-29 and DLD-1) but also in fibroblasts. HT-29 which expressed more abundant mitochondrial COX-2 than DLD-1 was highly resistant to arachidonic acid and H2O2-induced apoptosis whereas DLD-1 was less resistant and human fibroblasts were highly susceptible. Treatment of HT-29 cells with sulindac or SC-236, a selective COX-2 inhibitor, resulted in loss of resistance to apoptosis. These results suggest that mitochondrial COX-2 in cancer cells confer resistance to apoptosis by reducing the proapoptotic arachidonic acid.

Cyclooxygenase-1 Mediates the Final Stage of Morphine-Induced Delayed Cardioprotection in Concert With Cyclooxygenase-2

OBJECTIVES

We sought to investigate the time course of morphine-induced delayed cardioprotection and examine the role of cyclooxygenase (COX) in this cardioprotective effect.

BACKGROUND

Cyclooxygenase-2 has been shown to be essential for the delayed cardioprotection induced by ischemic preconditioning and delta-opioid agonists.

METHODS

Male mice were subjected to 45 min of coronary artery occlusion followed by 120 min of reperfusion. Expressions of COX-2 and COX-1 were assessed by Western blotting, and the myocardial prostaglandin (PG)E2 and 6-keto-PGF(1-alpha) contents were measured using enzyme immunoassays.

RESULTS

A powerful infarct-sparing effect appeared 24 and 48 h after morphine preconditioning and faded after 72 h. After 24 h, the anti-infarct effect was associated with enhanced myocardial levels of COX-2, PGE2, and 6-keto-PGF(1-alpha), and no changes in COX-1 protein levels were found. Cardioprotection and increases in PGE2 and 6-keto-PGF(1-alpha) were completely abolished by the COX-2-selective inhibitor NS-398 and the non-selective COX inhibitor indomethacin, whereas the COX-1-selective inhibitor SC-560 had no effect. After 48 h, up-regulation of myocardial PGE2 and 6-keto-PGF(1-alpha) was also observed, and COX-1 expression was enhanced markedly, but only a slight increase in COX-2 expression was apparent. Cardioprotection and the increases in PGE2 and 6-keto-PGF(1-alpha) 48 h after morphine administration were abrogated only by indomethacin, and not by SC-560 or NS-398.

CONCLUSIONS

Morphine confers delayed cardioprotection via a COX-dependent pathway; COX-2 is essential for the cardioprotection observed in the initial stage (24 h), whereas, in the final stage (48 h), cardioprotection is mediated by COX-1 in concert with COX-2.

Cytosolic phospholipase A2-alpha and cyclooxygenase-2 localize to intracellular membranes of EA.hy.926 endothelial cells that are distinct from the endoplasmic reticulum and the Golgi apparatus

Cytosolic phospholipase A2-alpha (cPLA2-alpha) is a calcium-activated enzyme that plays an important role in agonist-induced arachidonic acid release. In endothelial cells, free arachidonic acid can be converted subsequently into prostacyclin, a potent vasodilator and inhibitor of platelet activation, through the action of cyclooxygenase (COX) enzymes. Here we study the relocation of cPLA2-alpha in human EA.hy.926 endothelial cells following stimulation with the calcium-mobilizing agonist, A23187. Relocation of cPLA2-alpha was seen to be highly cell specific, and in EA.hy.926 cells occurred primarily to intracellular structures resembling the endoplasmic reticulum (ER) and Golgi. In addition, relocation to both the inner and outer surfaces of the nuclear membrane was observed. Colocalization studies with markers for these subcellular organelles, however, showed colocalization of cPLA2-alpha with nuclear membrane markers but not with ER or Golgi markers, suggesting that the relocation of cPLA2-alpha occurs to sites that are separate from these organelles. Colocalization with annexin V was also observed at the nuclear envelope, however, little overlap with staining patterns for the potential cPLA2-alpha interacting proteins, annexin I, vimentin, p11 or actin, was seen in this cell type. In contrast, cPLA2-alpha was seen to partially colocalize specifically with the COX-2 isoform at the ER-resembling structures, but not with COX-1. These studies suggest that cPLA2-alpha and COX-2 may function together at a distinct and novel compartment for eicosanoid signalling.

Lithium treatment inhibits renal GSK-3 activity and promotes cyclooxygenase 2-dependent polyuria

The use of LiCl in clinical psychiatry is routinely complicated by overt nephrogenic diabetes insipidus (NDI), the mechanism of which is incompletely understood. In vitro studies indicate that lithium can induce renal medullary interstitial cell cyclooxygenase 2 (COX2) protein expression via inhibition of glycogen synthase kinase-3β (GSK-3β). Both COX1 and COX2 are expressed in the kidney. Renal prostaglandins have been suggested to play an important role in lithium-induced polyuria. The present studies examined whether induction of the COX2 isoform contributes to LiCl-induced polyuria. Four days after initiation of lithium treatment in C57 BL/6J mice, urine volume increased in LiCl-treated mice by fourfold compared with controls ( P < 0.0001) and was accompanied by decreased urine osmolality. This was temporally associated with increased renal COX2 protein expression and increased urinary PGE2 excretion, whereas COX1 levels remained unchanged. COX2 inhibition significantly blunted lithium-induced polyuria ( P < 0.0001) and reduced urinary PGE2 levels. Lithium-associated polyuria was also seen in COX1−/− mice and was associated with increased urinary PGE2. COX2 inhibition completely prevented polyuria and PGE2 excretion in COX1−/− mice, suggesting that COX2, but not COX1, plays a critical role in lithium-induced polyuria. Lithium also induced renal medullary COX2 protein expression in congenitally polyuric antidiuretic hormone (AHD)-deficient rats, demonstrating that lithium-induced COX2 protein expression is not secondary to altered ADH levels or polyuria. Lithium also decreased renal medullary GSK-3β activity, and this was temporally related to increased COX2 expression in the kidney from lithium-treated mice, consistent with a tonic in vivo suppression of COX2 expression by GSK-3 activity. In conclusion, these findings temporally link decreased GSK-3 activity to enhanced renal COX2 expression and COX2-derived urine PGE2 excretion. Suppression of COX2-derived PGE2 blunts lithium-associated polyuria.

Cyclooxygenase-2 interacts with p53 and interferes with p53-dependent transcription and apoptosis

Cyclooxygenase-2 (COX-2) has been implicated in a variety of human malignancies and, accordingly, COX-2 selective inhibitors are being investigated as important chemopreventive and therapeutic agents. How COX-2 overexpression results in tumorigenesis and how COX-2 selective agents mediate their chemopreventive effects are issues that remain poorly understood. Here we report that the tumor suppressor p53 upregulates COX-2 expression and that COX-2 can in turn inhibit p53-dependent transcription. Additionally, a COX-2-selective inhibitor potentiates p53-induced apoptosis, which also supports the notion that COX-2 activity appears to interfere with p53 function. Expression of exogenous COX-2 in p53 wild-type cells does not affect the cytoplasmic or nuclear levels of p53, suggesting that COX-2 may not affect p53 turnover or subcellular localization. We further demonstrate that endogenous COX-2 interacts with p53 and that COX-2 and p53 interactions are a physiologically relevant event. Thus, p53 upregulates COX-2 and COX-2 in turn appears to negatively affect p53 activity via mechanisms that could involve physical interactions between COX-2 and p53. Based on our results, we propose that p53-dependent upregulation and activation of COX-2 appear to be yet another novel mechanism by which p53 could abate its own growth-inhibitory and apoptotic effects.

Membrane fluidity is a key modulator of membrane binding, insertion, and activity of 5-lipoxygenase

Mammalian 5-lipoxygenase (5-LO) catalyzes conversion of arachidonic acid to leukotrienes, potent mediators of inflammation and allergy. Upon cell stimulation, 5-LO selectively binds to nuclear membranes and becomes activated, yet the mechanism of recruitment of 5-LO to nuclear membranes and the mode of 5-LO-membrane interactions are poorly understood. Here we show that membrane fluidity is an important determinant of membrane binding strength of 5-LO, penetration into the membrane hydrophobic core, and activity of the enzyme. The membrane binding strength and activity of 5-LO increase with the degree of lipid acyl chain cis-unsaturation and reach a plateau with 1-palmitoyl-2-arachidonolyl-sn-glycero-3-phosphocholine (PAPC). A fraction of tryptophans of 5-LO penetrate into the hydrocarbon region of fluid PAPC membranes, but not into solid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine membranes. Our data lead to a novel concept of membrane binding and activation of 5-LO, suggesting that arachidonic-acid-containing lipids, which are present in nuclear membranes at higher fractions than in other cellular membranes, may facilitate preferential membrane binding and insertion of 5-LO through increased membrane fluidity and may thereby modulate the activity of the enzyme. The data presented in this article and earlier data allow construction of a model for membrane-bound 5-LO, including the angular orientation and membrane insertion of the protein.

15d-PGJ2: the anti-inflammatory prostaglandin?

15-Deoxy-Delta-12,14-prostaglandin J2 (15d-PGJ2) is the most recently discovered prostaglandin. This cyclopentanone, the dehydration end product of PGD2, differs from other prostaglandins in several respects. There is no specific prostaglandin synthase (PGS) leading to 15d-PGJ2 production and no specific 15d-PGJ2 receptor has been identified to date. Instead, 15d-PGJ2 has been shown to act via PGD2 receptors (DP1 and DP2) and through interaction with intracellular targets. In particular, 15d-PGJ2 is recognized as the endogenous ligand for the intranuclear receptor PPARgamma. This property is responsible for many of the 15d-PGJ2 anti-inflammatory functions. In this review, we summarize the current understanding of 15d-PGJ2 synthesis, biology and main effects both in molecular physiology and pathological states.

Signal-transduction pathways that regulate smooth muscle function I. Signal transduction in phasic (esophageal) and tonic (gastroesophageal sphincter) smooth muscles

Contraction of esophageal (Eso) and lower esophageal sphincter (LES) circular muscle depends on distinct signal-transduction pathways. ACh-induced contraction of Eso muscle is linked to phosphatidylcholine metabolism, production of diacylglycerol and arachidonic acid (AA), and activation of the Ca(2+)-insensitive PKCepsilon. Although PKCepsilon does not require Ca(2+) for activation, either influx of extracellular Ca(2+) or release of Ca(2+) from stores is needed to activate the phospholipases responsible for hydrolysis of membrane phospholipids and production of second messengers, which activate PKCepsilon. In contrast, the LES uses two distinct intracellular pathways: 1) a PKC-dependent pathway activated by low doses of agonists or during maintenance of spontaneous tone, and 2) a Ca(2+)-calmodulin-myosin light chain kinase (MLCK)-dependent pathway activated in response to maximally effective doses of agonists during the initial phase of contraction. The Ca(2+) levels, released by agonist-induced activity of phospholipase C, determine which contractile pathway is activated in the LES. The Ca(2+)-calmodulin-MLCK-dependent contractile pathway has been well characterized in a variety of smooth muscles. The steps linking activation of PKC to myosin light chain (MLC20) phosphorylation and contraction, however, have not been clearly defined for LES, Eso, or other smooth muscles. In addition, in LES circular muscle, a low-molecular weight pancreatic-like phospholipase A2 (group I PLA2) causes production of AA, which is metabolized to prostaglandins and thromboxanes. These AA metabolites act on receptors linked to heterotrimeric G proteins to induce activation of phospholipases and production of second messengers to maintain contraction of LES circular muscle. We have examined the signal-transduction pathways activated by PGF(2alpha) and by thromboxane analogs during the initial contractile phase and found that these pathways are the same as those activated by other agonists. In response to low doses of agonists or during maintenance of tone, presumably due to low levels of calcium release, a PKC-dependent pathway is activated, whereas at high doses of PGF(2alpha) and thromboxane analogs, in the initial phase of contraction, calmodulin is activated, PKC activity is reduced, and contraction is mediated, in part, through a Ca(2+)-calmodulin-MLCK-dependent pathway. The PKC-dependent signaling pathways activated by PGF(2alpha) and by thromboxanes during sustained LES contraction, however, remain to be examined, but preliminary data indicate that a distinct PKC-dependent pathway may be activated during maintenance of tonic contraction, which is different from the one activated during the initial contractile response. The initial contractile response to low levels of agonists depends on activation of G(q). Sustained contraction in response to PGF(2alpha) may involve activation of the monomeric G protein RhoA, because the contraction is inhibited by the RhoA-kinase antagonist Y27632. This shift in signal-transduction pathways between initial and sustained contraction has been recently reported in intestinal smooth muscle.

Identification and localization of prostaglandin E2 receptors in upper and lower segment human myometrium during pregnancy

Prostaglandin E2 (PGE2) plays a key role in the maintenance of human pregnancy and labour onset. PGE2 can elicit diverse actions within the uterus depending on the PGE2 receptors (EP1, EP2, EP3 and EP4) expressed. By signalling through different intracellular pathways the EP receptors may inhibit or promote smooth muscle contractility. Nine different EP3 receptor splice variants have been identified with divergent signalling pathways. RT-PCR and immunohistochemistry were utilized to identify and localize EP receptor isoforms within the upper segment (US) and lower segment (LS) myometrium. EP1 was significantly increased in the LS myometrium with term labour. EP3 (and EP3 splice variants EP3I(1b), EP3II, EP3III and EP3IV) was down-regulated in pregnancy (US and/or LS) with a further decrease at term labour in the LS. Overall, expression of EP2 was significantly higher in the LS while EP3 was significantly higher in the US. No significant EP4 changes were observed. Consistent with the RT-PCR results, immunohistochemistry confirmed the presence and, interestingly, showed nuclear localization of EP receptors in the myometrium with higher EP1 expression and lower expression of EP3. The differential regulation of EP receptors within the myometrium indicates that they may play a role in controlling the onset and maintenance of human labour.

Cytoplasmic phospholipase A2 alpha overexpression in stromal cells is correlated with angiogenesis in human colorectal cancer

In colorectal cancer, cyclooxygenase-2 (COX-2) overexpression in stromal cells induces angiogenesis through EP2 prostaglandin E2 receptor signaling. Cytoplasmic phospholipase A2 (PLA2) alpha preferentially hydrolyses arachidonic acid, which is the limiting substrate for prostaglandin production, from membrane phospholipids. We therefore investigated a possible relationship between cytoplasmic PLA2 and COX-2 overexpression in stromal cells, angiogenesis and microsatellite instability in 48 human colorectal adenocarcinomas. Cytoplasmic PLA2 and COX-2 expression in stromal cells and vascular endothelial growth factor (VEGF) expression in tumor cells were evaluated by immunohistochemistry. Microvessel density was assessed in 10 x 400 fields after CD31 staining. Microsatellite instability was evaluated by PCR and immunohistochemistry. A total of 16 tumors had microsatellite instability. We found an overexpression of cytoplasmic PLA2 in superficial stromal cells. These cells corresponded to fibroblasts and myofibroblasts. There was an association between the number of cytoplasmic PLA2 and COX-2-expressing cells (P=0.006). Cytoplasmic PLA2-positive stromal cells usually also expressed COX-2. A high number of cytoplasmic PLA2-positive stromal cells was correlated with a high microvessel density (P=0.002), a strong VEGF (P=0.01) and the absence of microsatellite instability (P=0.001). The coordinate overexpression of cytoplasmic PLA2 and COX-2 in stromal cells could lead to an important prostaglandin production. These results suggest that cytoplasmic PLA2 overexpression in these cells regulates COX-induced angiogenesis probably by providing arachidonic acid, which is the limiting factor for prostaglandin production. The lower number of cytoplasmic PLA2-positive stromal cells in carcinomas with microsatellite instability could be related to their lower microvessel density and VEGF expression.

Prostaglandin E2 and microsomal prostaglandin E synthase-2 expression are decreased in the cyclooxygenase-2-deficient mouse brain despite compensatory induction of cyclooxygenase-1 and Ca2+-dependent phospholipase A2

We previously demonstrated that brain cyclooxygenase (COX)-2 mRNA and protein levels, and prostaglandin E2 (PGE2) level, are down-regulated in cytosolic phospholipase A2 (cPLA2) -deficient mice. To further investigate the interaction between upstream and downstream enzymes involved in brain prostaglandin synthesis, we examined expression and activity of COX-1, of different PLA2 enzymes and of prostaglandin E synthase (PGES) enzymes in COX-2(-/-) mice. We found that the PGE2 level was decreased by 51.5% in the COX-2(-/-) mice brains, indicating a significant role of COX-2 in brain formation of PGE2. However, when we supplied exogenous arachidonic acid (AA) to brain homogenates, COX activity was increased in the COX-2(-/-) mice, suggesting a compensatory activation of COX-1 and an intracellular compartmentalization of the COX isozymes. Consistent with COX-1 increased activity, brain expression of COX-1 protein and mRNA also was increased. Activity and expression of cPLA2 and secretory PLA2 (sPLA2) enzymes, supplying AA to COX, were significantly increased. Also, the PGE2 biosynthetic pathway downstream from COX-2 was affected in the COX-2(-/-) mice, as decreased expression of microsomal prostaglandin E synthase-2 (mPGES-2), but not mPGES-1 or cytosolic PGES, was observed. Overall, the data suggest that compensatory mechanisms exist in COX-2(-/-) mice and that mPGES-2 is functionally coupled with COX-2.

Synthetic glycoprotein mimics inhibit L-selectin-mediated rolling and promote L-selectin shedding

L-selectin is a leukocyte cell-surface protein that facilitates the rolling of leukocytes along the endothelium, a process that leads to leukocyte migration to a site of infection. Preventing L-selectin-mediated rolling minimizes leukocyte adhesion and extravasation; therefore, compounds that inhibit rolling may act as anti-inflammatory agents. To investigate the potential role of multivalent ligands as rolling inhibitors, compounds termed neoglycopolymers were synthesized that possess key structural features of physiological L-selectin ligands. Sulfated neoglycopolymers substituted with sialyl Lewis x derivatives (3',6-disulfo Lewis x or 6-sulfo sialyl Lewis x) or a sulfatide analog (3,6-disulfo galactose) inhibited L-selectin-mediated rolling of lymphoid cells. Functional analysis of the inhibitory ligands indicates that they also induce proteolytic release of L-selectin. Thus, their inhibitory potency may arise from their ability to induce shedding. Our data indicate that screening for compounds that promote L-selectin release can identify ligands that inhibit rolling.

Regulation of the membrane-localized prostaglandin E synthases mPGES-1 and mPGES-2 in cardiac myocytes and fibroblasts

The proinflammatory mediator cyclooxygenase (COX)-2 and its product PGE2 are induced in the ischemic heart, contributing to inflammatory cell infiltration, fibroblast proliferation, and cardiac hypertrophy. PGE2 synthesis coupled to COX-2 involves two membrane-localized PGE synthases, mPGES-1 and mPGES-2; however, it is not clear how these synthases are regulated in cardiac myocytes and fibroblasts. To study this, we used primary cultures of neonatal ventricular myocytes (VM) and fibroblasts (VF) treated with IL-1β for 24 h. To test for involvement of MAPKs in IL-1β regulation of mPGES-1 and-2, cells were pretreated with the pharmacological inhibitors of p42/44 MAPK, p38 MAPK, and c-Jun kinase (JNK). mRNA was analyzed by RT-PCR. Protein was analyzed by densitometry of Western blots. mPGES-1 was undetectable in untreated VF but induced by IL-1β; inhibition of either p42/44 MAPK or JNK, but not p38 MAPK, was almost completely inhibitory. In VM, inhibition of the three MAPKs reduced IL-1β-stimulated mPGES-1 protein by 70–90%. mPGES-2 was constitutively synthesized in both VM and VF and was not regulated by IL-1β or MAPKs. Confocal microscopy revealed colocalization of both mPGES-1 and mPGES-2 with COX-2 in the perinuclear area of both VF and VM. Finally, PGE2 production was higher in VM than VF. Our data show that 1) mPGES-1 is induced in both VF and VM, 2) regulation of mPGES-1 by MAPK family members is different in the two cell types, 3) mPGES-2 is constitutively synthesized in both VM and VF and is not regulated, and 4) mPGES-1 and mPGES-2 are colocalized with COX-2 in both cells. Thus differences in activity of mPGES-1 and COX-2 or coupling of COX-2 with mPGES-1 may contribute to differences in PGE2 production by myocytes and fibroblasts.

Cyclooxygenase-2 expression and relationship to tumour progression in human renal cell carcinoma

AIMS

Cyclooxygenase (COX), which catalyses the synthesis of prostaglandins from arachidonic acid, has two isoforms; COX-1 and COX-2. There is ample evidence to suggest an important role for COX-2 in cancer. The aim of this study was to evaluate the clinical significance of COX-2 expression and its localization in the development and progression of human renal cell carcinoma (RCC).

METHODS AND RESULTS

The expression and localization of COX-2 were evaluated in human RCC tissues from 75 patients by immunohistochemistry. Immunoreactive COX-2 protein was observed in all cases of RCC, and the levels of COX-2 expression were correlated with tumour grade and pathological stage. Expression of COX-2 was higher in the granular cell subtype than in the clear cell subtype of RCC. Immunoelectron microscopy revealed that COX-2 was expressed in the nuclear membrane, rough endoplasmic reticulum, Golgi complex and mitochondrial membrane of RCC cells.

CONCLUSION

COX-2 overexpression within these intracellular organelles in RCC may be associated with renal cell carcinogenesis and COX-2 may be a useful biomarker in RCC.

Expression of cyclooxygenase-2 in corneal cells after photorefractive keratectomy and laser in situ keratomileusis in rabbits

PURPOSE

To compare the expression pattern of cyclooxygenase-2 (COX-2) in rabbit corneal cells after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with the same refractive correction.

SETTING

Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan.

METHODS

Thirty adult albino rabbits were used in the study. Photorefractive keratectomy or LASIK was performed in 1 eye of each animal for the same refractive correction. Each animal was killed after healing intervals up to 6 months. Paraffin sections of the cornea were processed for immunohistochemistry for COX-2 and NFkappaB (p65).

RESULTS

After PRK, the central and peripheral corneal epithelia up-regulated COX-2 at 3 days; the central epithelium was positive at 4 weeks. Central and peripheral epithelia returned to negative 3 months later. After LASIK, the central epithelium on the corneal flap up-regulated COX-2 at 1 and 2 weeks; it returned to negative at 4 weeks. The peripheral epithelium was labeled with the antibody. Keratocytes around the stromal incision between the flap and the stromal bed up-regulated COX-2 and returned to negative at 3 months. COX-1 was not detected immunohistochemically in corneal tissue during the healing intervals after both procedures. Nuclear factor kappaB was detected in the cytoplasm and nuclei of migrating corneal epithelial cells 1 day after PRK, was positive in the cytoplasm at 3 days and negative in cytoplasm and nuclei at week and later.

CONCLUSIONS

Migrating injured epithelium expressed COX-2 until week 4 during post-PRK healing. Central uninjured epithelium as well as stromal keratocytes expressed COX-2 from 3 days to 2 weeks after LASIK. Uninjured peripheral epithelium also expressed COX-2 at 4 weeks. Activation of stromal keratocytes may induce expression of COX-2 in overlying uninjured epithelium via the inflammatory cytokine(s)/NFkappaB pathway.

Endothelial Cell Confluence Regulates Cyclooxygenase-2 and Prostaglandin E2 Production That Modulate Motility

Endothelial cells line the vasculature and, after mechanical denudation during invasive procedures or cellular loss from natural causes, migrate to reestablish a confluent monolayer. We find confluent monolayers of human umbilical vein endothelial cells were quiescent and expressed low levels of cyclooxygenase-2, but expressed cyclooxygenase-2 at levels comparable with cytokine-stimulated cells when present in a subconfluent culture. Mechanically wounding endothelial cell monolayers stimulated rapid cyclooxygenase-2 expression that increased with the level of wounding. Cyclooxygenase-2 re-expression occurred throughout the culture, suggesting signaling from cells proximal to the wound to distal cells. Media from wounded monolayers stimulated cyclooxygenase-2 expression in confluent monolayers, which correlated with the level of wounding of the donor monolayer. Wounded monolayers and cells in subconfluent cultures secreted enhanced levels of prostaglandin (PG) E(2) that depended on cyclooxygenase-2 activity, and PGE(2) stimulated cyclooxygenase-2 expression in confluent endothelial cell monolayers. Cells from subconfluent monolayers migrated through filters more readily than those from confluent monolayers, and the cyclooxygenase-2-selective inhibitor NS-398 suppressed migration. Adding PGE(2) to NS-398-treated cells augmented migration. Endothelial cells also migrated into mechanically denuded areas of confluent monolayers, and this too was suppressed by NS-398. We conclude that endothelial cells not in contact with neighboring cells express cyclooxygenase-2 that results in enhanced release of PGE(2), and that this autocrine and paracrine loop enhances endothelial cell migration to cover denuded areas of the endothelium.

Intracellular-specific colocalization of prostaglandin E2synthases and cyclooxygenases in the brain

Prostaglandin E2(PGE2) is the major primary prostaglandin generated by brain cells. However, the coordination and intracellular localization of the cyclooxygenases (COXs) and prostaglandin E synthases (PGESs) that convert arachidonic acid to PGE2in brain tissue are not known. We aimed to determine whether microsomal and cytosolic PGES (mPGES-1 and cPGES) colocalize and coordinate activity with either COX-1 or COX-2 in brain tissue, particularly during development. Importantly, we found that cytosolic PGES also associates with microsomes (cPGES-m) from the cerebrum and cerebral vasculature of the pig and rat as well as microsomes from various cell lines; this seemed dependent on the carboxyl terminal 35-amino acid domain and a cysteine residue (C58) of cPGES. In microsomal membranes from the postnatal brain and cerebral microvessels of mature animals, cPGES-m colocalized with both COX-1 and COX-2, whereas mPGES-1 was undetectable in these microsomes. Accordingly, in this cell compartment, cPGES could coordinate its activity with COX-2 and COX-1 (partly inhibited by NS398); albeit in microsomes of the brain microvasculature from newborns, mPGES-1 was also present. In contrast, in nuclei of brain parenchymal and endothelial cells, mPGES-1 and cPGES colocalized exclusively with COX-2 (determined by immunoblotting and immunohistochemistry); these PGESs contributed to conversion of PGH2into PGE2. Hence, contrary to a previously proposed model of exclusive COX-2/mPGES-1 coordination, COX-2 can coordinate with mPGES-1 and/or cPGES in the brain, depending on the cell compartment and the age group.

The regulation of chondrocyte function by proinflammatory mediators: prostaglandins and nitric oxide

Within the mature articular cartilage matrix, which has no blood or nerve supply, chondrocytes show little metabolic activity with low turnover of matrix components. Under conditions of stress because of biomechanical factors, however, chondrocytes are capable of producing mediators that are associated with inflammation, including cytokines such as interleukin-1 and tumor necrosis factor-alpha, which in turn stimulate the production of prostaglandins and nitric oxide. Chondrocytes also express receptors for these mediators, which accumulate at high local concentrations and can act in an autocrine-paracrine fashion to feedback-regulate chondrocyte responses. Prostaglandin E2 can exert catabolic or anabolic effects depending on the microenvironment. Nitric oxide can promote cellular injury and increase chondrocyte susceptibility to cytokine-induced apoptosis. Because cross-talk between these mediators produces complex modulation of catabolic and anabolic pathways, further studies in vitro and in vivo are required to elucidate their precise roles in osteoarthritis.

Electron microscope immunocytochemical localization of cyclooxygenase-1 and -2 in pseudopregnant rat corpus luteum during luteolysis

Prostaglandins converted from arachidonic acid by cyclooxygenases play an important regulatory role in regression of the corpus luteum. To reveal luteal distribution of cyclooxygenase isoforms during luteolysis, an electron microscope immunocytochemical study was performed. Cyclooxygenase-1 and -2 were found both in luteal steroid-producing and interstitial cells on days 13, 15 and 18 of the adult pseudopregnant rat. Cyclooxygenase-2 immunolabelling was predominantly seen in non-luteal cells. The two enzymes were localized in similar fashion to the plasma membrane, rough and smooth endoplasmic reticulum, lipid bodies and mitochondria, but differently in the nuclear compartment. Cyclooxygenase-1 labelling was found only in the perinuclear region, while cyclooxygenase-2 was localized to the nuclear envelope, region of condensed heterochromatin as well as at the perimeter of the heterochromatin. Nuclear residence may indicate additional roles for cyclooxygenase-2 in regulating gene expression. Identification of both enzymes on lipid bodies suggests that these inclusions may be involved in luteal prostanoid production.

Prostanoids and their receptors that modulate dendritic cell‐mediated immunity

Dendritic cells (DC) are essential for the initiation of immune responses by capturing, processing and presenting antigens to T cells. In addition to their important role as professional APC, they are able to produce immunosuppressive and pro-inflammatory prostanoids from arachidonic acid (AA) by the action of cyclooxygenase (COX) enzymes. In an autocrine and paracrine fashion, the secreted lipid mediators subsequently modulate the maturation, cytokine production, Th-cell polarizing ability, chemokine receptor expression, migration, and apoptosis of these extremely versatile APC. The biological actions of prostanoids, including their effects on APC-mediated immunity and acute inflammatory responses, are exerted by G protein-coupled receptors on plasma membrane. Some COX metabolites act as anti-inflammatory lipid mediators by binding to nuclear receptors and modulating DC functions. Although the role of cytokines in DC function has been studied extensively, the effects of prostanoids on DC biology have only recently become the focus of investigation. This review summarizes the current knowledge about the role of prostanoids and their receptors in modulating DC function and the subsequent immune responses.

Cyclooxygenase-2 modulates cellular growth and promotes tumorigenesis

Cyclooxygenase (COX)-2 and the prostaglandins resulting from its enzymatic activity have been shown to play a role in modulating cell growth and development of human neoplasia. Evidence includes a direct relationship between COX-2 expression and cancer incidence in humans and animal models, increased tumorigenesis after genetic manipulation of COX-2, and significant anti-tumor properties of non-steroidal anti-inflammatory drugs in animal models and in some human cancers. Recent data showed that COX-2 and the derived prostaglandins are involved in control of cellular growth, apoptosis, and signal through a group of nuclear receptors named peroxisome proliferator-activated receptors (PPARs). In this article we will review some of the findings suggesting that COX-2 is involved in multiple cellular mechanisms that lead to tumorigenesis.

Activation of nuclear receptors by prostaglandins

Deletion of membrane receptors for prostaglandins has revealed their importance in diverse biological systems. Some evidence has accrued to support the contention that they may also ligate nuclear receptors, particularly peroxisomal proliferator activator receptors (PPARs). This is most pronounced in the case of 15-deoxy PGJ2, a cyclopentanone derivative of PGJ2 as a ligand for PPARgamma. However, while this compound can ligate the PPAR, the quantities formed in vivo suggest that this is an unlikely endogenous ligand. Furthermore, biosynthesis is unaltered in murine atherosclerosis and other inflammatory and metabolic disorders where activation of this PPAR has been implicated. The suggestion that prostaglandins serve as endogenous ligands for nuclear receptors is presently configured on the use of synthetic compounds and immunoreactive quantitation of dubious validity. The application of quantitatively precise and sensitive physicochemical methodology will enhance experiments designed to address this hypothesis.

Constitutive spinal cyclooxygenase-2 participates in the initiation of tissue injury-induced hyperalgesia

Inhibitors of the isozyme cyclooxygenase-2 (COX-2) represent an important advance in pain management, although where and when these inhibitors can exert their antihyperalgesic actions are not completely understood. Here we show that unlike many peripheral tissues in which COX-2 is only expressed in physiologically significant levels after tissue injury, in the normal rat lumbar spinal cord, the majority of neurons and radial glia constitutively express high levels of COX-2 protein. Immediately after peripheral tissue injury and before any measurable upregulation of COX-2 protein in peripheral tissue or spinal cord, inhibition of constitutively expressed spinal COX-2 reduced injury-induced activation of primary afferent neurons, activation of spinal neurons, and the mechanical and thermal hyperalgesia that normally occurs after peripheral tissue injury. The present data demonstrate that constitutively expressed spinal COX-2 plays an important role in the initial hyperalgesia that follows peripheral tissue injury. These results suggest that blocking constitutive spinal COX-2 before tissue injury may reduce the initial peripheral and central sensitization that occurs after tissue injury.

The role and regulation of COX-2 during viral infection

Prostaglandins are lipid mediators, generated by cyclooxygenase (COX), that have been shown to participate in the regulation of virus replication and the modulation of inflammatory responses following infection. A number of studies support a role for PGE2 in the modulation of virus replication and virulence in a cell type and virus selective manner. Virus infection also stimulates the expression of a number of proinflammatory gene products, including COX-2, inducible nitric oxide synthase (iNOS) as well as proinflammatory cytokines. This review will focus on the mechanisms by which proinflammatory prostaglandin production regulates virus replication and virulence. In addition, the signaling pathways that are activated during a virus infection, and that regulate proinflammatory gene expression in macrophages will be reviewed. Specific attention will be placed on the ability of virus infection to activate multiple signaling cascades (such as PKR, MAPK, iPLA2, NF-kappaB) and how these pathways are integrated in the regulation of individual target gene expression.

Cytosolic Phospholipase A2 Translocates to Forming Phagosomes during Phagocytosis of Zymosan in Macrophages

Resident tissue macrophages mediate early innate immune responses to microbial infection. Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is activated in macrophages during phagocytosis of non-opsonized yeast (zymosan) triggering arachidonic acid release and eicosanoid production. cPLA(2)alpha translocates from cytosol to membrane in response to intracellular calcium concentration ([Ca(2+)](i)) increases. Enhanced green fluorescent protein (EGFP)-cPLA(2)alpha translocated to forming phagosomes, surrounding the zymosan particle by 5 min and completely overlapping with early endosome (Rab5) and plasma membrane (F4/80) markers but only partially overlapping with resident endoplasmic reticulum proteins (GRP78 and cyclooxygenase 2). EGFP-cPLA(2)alpha also localized to membrane ruffles during phagocytosis. Zymosan induced an initial high amplitude calcium transient that preceded particle uptake followed by a low amplitude sustained calcium increase. Both phases were required for optimal phagocytosis. Extracellular calcium chelation prevented only the sustained phase but allowed a limited number of phagocytic events, which were accompanied by translocation of cPLA(2)alpha to the phagosome although [Ca(2+)](i) remained at resting levels. The results demonstrate that cPLA(2)alpha targets the phagosome membrane, which may serve as a source of arachidonic acid for eicosanoid production.

[Pharmacology and classification of cyclooxygenase inhibitors]

The discovery of at least two cyclooxygenase (COX) isoenzymes had two major consequences: i) to give a new impetus to the research on lipid metabolism, giving rise to the crystallization of these peculiar membrane enzymes, the characterization of their active sites and their gene regulation, and the identification of new metabolic pathways; ii) the development of new NSAIDs aimed to have an improved safety profile, the coxibs. These drugs are defined by their COX-2 selectivity which is supported by a negligible inhibitory potency on platelet COX-1 in vitro and ex vivo after oral intake of maximal therapeutic doses. However, the coxibs marketed in France (celecoxib, rofecoxib, parecoxib) are not equivalent in terms of selectivity and some drugs developed by pharmaceutical companies (etoricoxib, lumiracoxib) will be even more selective for COX-2. These "new" coxibs are the final step in the theory of COX-2 selectivity and they will probably be helpful to better define the limitations of the therapeutic concept based on a selective inhibition of this iso-enzyme.

Steroid hormone modulation of prostaglandin secretion in the ruminant endometrium during the estrous cycle

Prostaglandins, produced from membrane phospholipids by the action of phospholipase A2, cyclooxygenase, and specific prostaglandin synthases, are important regulators of ovulation, luteolysis, implantation, and parturition in reproductive tissues. Destruction of the corpus luteum at the end of the estrous cycle in nonpregnant animals is brought about by the pulsatile secretion of prostaglandin F(2alpha) (PGF(2alpha)) from the endometrium. It has been known for many years that progesterone, estradiol, and oxytocin are the hormones responsible for luteolysis. To achieve luteolysis, two independent processes have to be coordinated; the first is an increase in the prostaglandin synthetic capability of the endometrium and the second is an increase in oxytocin receptor number. Although progesterone and estradiol can modulate the expression of the enzymes involved in prostaglandin synthesis, the primary reason for the initiation of luteolysis is the increase in oxytocin receptor on the endometrial epithelial cells. Results of many in vivo studies have shown that progesterone and estradiol are required for luteolysis, but it is still not fully understood exactly how these steroid hormones act. The purpose of this article is to review the recent data related to how progesterone and estradiol could regulate (initiate and then turn off) the uterine pulsatile secretion of PGF(2alpha) observed at luteolysis.

Nuclear prostaglandin receptors: role in pregnancy and parturition?

The key regulatory role of prostanoids [prostaglandins (PGs) and thromboxanes (TXs)] in the maintenance of pregnancy and initiation of parturition has been established. However, our understanding of how these events are fine-tuned by the recruitment of specific signaling pathways remains unclear. Whereas, initial thoughts were that PGs were lipophilic and would easily cross cell membranes without specific receptors or transport processes, it has since been realized that PG signaling occurs via specific cell surface G-protein coupled receptors (GPCRs) coupled to classical adenylate cyclase or inositol phosphate signaling pathways. Furthermore, specific PG transporters have been identified and cloned adding a further level of complexity to the regulation of paracrine action of these potent bioactive molecules. It is now apparent that PGs also activate nuclear receptors, opening the possibility of novel intracrine signaling mechanisms. The existence of intracrine signaling pathways is further supported by accumulating evidence linking the perinuclear localization of PG synthesizing enzymes with intracellular PG synthesis. This review will focus on the evidence for a role of nuclear actions of PGs in the regulation of pregnancy and parturition.

The expression of brain cyclooxygenase-2 is down-regulated in the cytosolic phospholipase A2 knockout mouse

We examined brain phospholipase A2 (PLA2) activity and the expression of enzymes metabolizing arachidonic acid (AA) in cytosolic PLA2 knockout () mice to see if other brain PLA2 can compensate for the absence of cPLA2 alpha and if cPLA2 couples with specific downstream enzymes in the eicosanoid biosynthetic pathway. We found that the rate of formation of prostaglandin E2 (PGE2), an index of net cyclooxygenase (COX) activity, was decreased by 62% in the compared with the control mouse brain. The decrease was accompanied by a 50-60% decrease in mRNA and protein levels of COX-2, but no change in these levels in COX-1 or in PGE synthase. Brain 5-lipoxygenase (5-LO) and cytochrome P450 epoxygenase (cyp2C11) protein levels were also unaltered. Total and Ca2+-dependent PLA2 activities did not differ significantly between and control mice, and protein levels of type VI iPLA2 and type V sPLA2, normalized to actin, were unchanged. These results show that type V sPLA2 and type VI iPLA2 do not compensate for the loss of brain cPLA2 alpha, and that this loss has significant downstream effects on COX-2 expression and PGE2 formation, sparing other AA oxidative enzymes. This suggests that cPLA2 is critical for COX-2-derived eicosanoid production in mouse brain.

Human microvascular endothelial cell prostaglandin E1 synthesis during in vitro ischemia-reperfusion

Ischemia-reperfusion injury is a microvascular event documented in numerous in vivo animal models. In animal models, prostaglandin and prostaglandin analogues have been found to ameliorate reperfusion injury. These studies were undertaken to evaluate human microvascular endothelial PGE(1) synthesis during in vitro ischemia followed by reperfusion. Human (neonatal) microvascular endothelial cell (MEC) cultures (n = 6) were subjected to sequential 2 h periods of normoxia (20% O(2)), ischemia (1.5% O(2)), and reperfusion (20% O(2)). Prostaglandin E(2) synthesis in conditioned media was determined by ELISA. Steady state levels of MEC prostaglandin H synthase (PGHS)-1 and -2 mRNA were assessed at the end of each 2-h period using RT-PCR and a quantitative mRNA ELISA. MEC PGHS protein levels were analyzed using an ELISA. PGE(1) release increased significantly during the initial 30 min of ischemia, but rapidly fell below normoxic levels by 90 and 120 min. During reperfusion, PGE(1) release returned to normoxic levels at 30, 60, and 90 min, and exceeded normoxic levels at 120 min. PGHS-1 mRNA levels were undetectable during all experimental conditions. PGHS-2 mRNA levels were unchanged by ischemia, but were decreased by reperfusion. In contrast, PGHS-2 protein levels increased 3-fold during ischemia, and remained elevated during reperfusion. Human MEC do not express PGHS-1 mRNA in vitro. Prolonged ischemia decreases MEC PGE(1) synthesis, and stimulates increased PGHS-2 protein levels without altering the steady state levels of COX-2 mRNA. During reperfusion, increased PGHS-2 protein levels persist and are associated with stimulated PGE(2) secretion, despite relative decreases in PGHS-2 mRNA.

Cyclooxygenase-2 and 5-lipoxygenase converging functions on cell proliferation and tumor angiogenesis: implications for cancer therapy

Cyclooxygenase (COX) and lipoxygenase (LO) metabolic pathways are emerging as key regulators of cell proliferation and neo-angiogenesis. COX and LO inhibitors are being investigated as potential anticancer drugs and results from clinical trials seem to be encouraging. In this article we will review evidence of COX-2 and 5-LO involvement in cancer pathobiology, propose a model of integrated control of cell proliferation by these enzymes, and discuss the pharmacologic implications of this model.

Localization of group V phospholipase A2 in caveolin-enriched granules in activated P388D1 macrophage-like cells

In murine P388D1 macrophages, the generation of prostaglandin E2 in response to long term stimulation by lipopolysaccharide involves the action of Group V secreted phospholipase A2 (PLA2), Group IV cytosolic PLA2 (cPLA2), and cyclooxygenase-2 (COX-2). There is an initial activation of cPLA2 that induces expression of Group V PLA2, which in turn induces both the expression of COX-2 and most of the arachidonic acid substrate for COX-2-dependent prostaglandin E2 generation. Because Group V PLA2 is a secreted enzyme, it has been assumed that after cellular stimulation, it must be released to the extracellular medium and re-associates with the outer membrane to release arachidonic acid from phospholipids. In the present study, confocal laser scanning microscopy experiments utilizing both immunofluorescence and green fluorescent protein-labeled Group V PLA2 shows that chronic exposure of the macrophages to lipopolysaccharide results in Group V PLA2 being associated with caveolin-2-containing granules close to the perinuclear region. Heparin, a cell-impermeable complex carbohydrate with high affinity for Group V PLA2, blocks that association, suggesting that the granules are formed by internalization of the Group V sPLA2 previously associated with the outer cellular surface. Localization of Group V PLA2 in perinuclear granules is not observed if the cells are treated with the Group IV PLA2 inhibitor methyl arachidonyl fluorophosphonate, confirming the important role for Group IV PLA2 in the activation process. Cellular staining with antibodies against COX-2 reveals the presence of COX-2-rich granules in close proximity to those containing Group V PLA2. Collectively, these results suggest that encapsulation of Group V PLA2 into granules brings the enzyme to the perinuclear envelope during cell activation where it may be closer to Group IV PLA2 and COX-2 for efficient prostaglandin synthesis.

Characterization and application of Raman labels for confocal Raman microspectroscopic detection of cellular proteins in single cells

A method using confocal Raman microspectroscopy for the detection of cellular proteins in single intact cells was developed. Two approaches were used to improve the detection of these cellular components. First, compounds with high Raman scattering were investigated for potential use as Raman labels. Raman labels were conjugated to either biomolecules or biotin and used as markers in the detection of cellular enzymes and receptors. Second, silver colloids were used to increase the surface-enhanced Raman scatter (SERS) of these Raman labels. Cresyl violet and dimethylaminoazobenzene are Raman labels that provide very sensitive SERS detection by a confocal Raman microscope with a HeNe laser at wavelength of 632.8 nm. The detection of 12-lipoxygenase and cyclooxygenase-1 in single bovine coronary artery endothelial cells and the binding of angiotensin II to its receptors in zona glomerulosa cells was demonstrated.

Identification and characterization of a cyclooxygenase-like enzyme from Entamoeba histolytica

The intestinal protozoan parasite Entamoeba histolytica remains a significant cause of morbidity and mortality worldwide. However, almost nothing is known about the molecules secreted by the parasite that modulate host immune responses or epithelial barrier function in the colon. Herein, we describe the isolation and characterization of a cyclooxygenase (COX)-like enzyme in E. histolytica that is responsible for the biosynthesis of prostaglandin (PG)E2. PGE2 produced by ameba was constitutive but highly dependent on exogenous arachidonic acid substrate. COX-like activity and the immunoreactive protein were localized to the nuclear fraction of E. histolytica. The COX-like protein (72 kDa) was microsequenced and cloned by reverse transcriptase PCR. Ameba COX showed little homology with COX-1/2 enzymes from different species at the nucleotide and amino acid levels. Surprisingly, the arachidonate-binding domain and heme-coordinating and catalytic sites, which are conserved in other species, were absent in ameba. Ameba COX expressed in Escherichia coli demonstrated COX-like enzyme activity in vitro by converting arachidonic acid into PGE2 but not into PGD2 or PGF2alpha. COX activity was inhibited with 1 mM aspirin but not with indomethacin or COX-1/2-specific inhibitors. Taken together, these studies reveal that E. histolytica produces PGE2, by means of a previously undescribed ancestral COX-like enzyme, which could play a major role in pathogenesis and immune evasion.

Co-localization of cytosolic phospholipase A2 and cyclooxygenase-2 in Rhesus monkey cerebellum

Cytosolic phospholipase A2 (cPLA2), cyclooxygenase (COX)-1 and COX-2 play important and integrated roles in the release and subsequent metabolism of arachidonic acid, an important second messenger, in brain and other tissues. Antibodies to each of these enzymes were used to examine their cellular localization and expression in the cerebellum of the adult macaque, using Western blotting and immunohistochemical methods. COX-2 and cPLA2 immunoreactivities co-localized on the plasma membrane of Purkinje cells, and within punctate intracellular regions. In contrast, COX-1 immunoreactivity was relatively uniform in Purkinje cell cytoplasm, and was more homogeneous in cells of the granular cell layer and occasionally of the molecular layer. COX-1 immunoreactivity was not found on the cell surface. Labeling of Purkinje cell dendrites was not marked for any of the enzymes. cPLA2 and COX-2 have been shown to be functionally coupled in a number of cell systems, and in brain following lithium chloride administration to rats. The co-localization of cPLA2 and COX-2 is consistent with evidence of their functional coupling at brain synapses, and of the presence of an unesterified brain arachidonate pool released by cPLA2 which is the precursor for prostaglandin formation via COX-2.

PGE(2) is generated by specific COX-2 activity and increases VEGF production in COX-2-expressing human pancreatic cancer cells

In some cancers cyclooxygenase (COX) inhibition appears to be anti-mitogenic and anti-angiogenic, but the actions of COX-derived prostaglandins in pancreatic cancer (PaCa) are unknown. In this study COX-2 was detected in three of six PaCa cell lines while COX-1 was identified in all cell lines. COX-2 expression correlated with basal and arachidonic acid (AA) stimulated PGE(2) production. PGE(2) production was inhibited by the COX-2 inhibitor nimesulide. In COX-2 expressing cells, exogenous AA and PGE(2) increased VEGF synthesis via the EP(2) receptor. Whereas PGE(2) stimulated intracellular cAMP formation in COX-2 positive and negative cells, 8-bromo cAMP stimulated VEGF production only in COX-2 expressing cells. Stimulating COX-2 expressing PaCa cell lines with AA enhanced migration of endothelial cells, an effect which was inhibited by a COX-2 inhibitor and EP(2) receptor antagonist. These data identify a subset of human PaCa cell lines that express functional COX-2 enzyme. PGE(2) generated by specific COX-2 activity increases VEGF secretion in human PaCa cells through an autocrine mechanism.

Cyclooxygenase-2 is instrumental in Parkinson's disease neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by the loss of the nigrostriatal dopaminergic neurons, which can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Increased expression of cyclooxygenase type 2 (COX-2) and production of prostaglandin E(2) have been implicated in neurodegeneration in several pathological settings. Here we show that COX-2, the rate-limiting enzyme in prostaglandin E(2) synthesis, is up-regulated in brain dopaminergic neurons of both PD and MPTP mice. COX-2 induction occurs through a JNKc-Jun-dependent mechanism after MPTP administration. We demonstrate that targeting COX-2 does not protect against MPTP-induced dopaminergic neurodegeneration by mitigating inflammation. Instead, we provide evidence that COX-2 inhibition prevents the formation of the oxidant species dopamine-quinone, which has been implicated in the pathogenesis of PD. This study supports a critical role for COX-2 in both the pathogenesis and selectivity of the PD neurodegenerative process. Because of the safety record of the COX-2 inhibitors, and their ability to penetrate the blood-brain barrier, these drugs may be therapies for PD.

Immunocytochemical localization of prostaglandin F synthase II in the rat spinal cord

Prostaglandin F synthase has at least two isozymes, i.e. prostaglandin F synthase I and II. Recently, we demonstrated immunocytochemically that prostaglandin F synthase I was localized in neuronal dendrites and somata, and in endothelial cells of blood vessels in the whole area of rat spinal cord. In the present study, we immunocytochemically localized prostaglandin F synthase II in ependymal cells and tanycytes surrounding the central canal and in endothelial cells of blood vessels, but not in any neuronal elements at all segmental levels of the rat spinal cord. Immunoelectron microscopy and confocal laser scanning microscopy confirmed these findings and further revealed that strong immunoreactivity was found in the basal processes of the tanycytes. Our present and recent studies using antibodies against the two isozymes of prostaglandin F synthase clearly indicated that they were localized differentially in ependymal (prostaglandin F synthase II) and neuronal elements (prostaglandin F synthase I), but were co-localized in blood vessels in the rat spinal cord. The distinct localization of the two isozymes suggests that prostaglandin F(2) has different transcellular biological actions via different cell groups.

Free radicals and lipid signaling in endothelial cells

Lipid mediators generated by oxidative pathways play essential roles in vascular homeostasis and disease through activating signal transduction pathways that control a variety of cellular functions, including vascular tone, gene expression, and leukocyte and platelet activation. Several enzyme families generate oxidized lipids, and a number of these are either constitutively expressed or inducible in the endothelium, including prostaglandin H synthases, lipoxygenases, and cytochrome P450 isoforms. Mediators generated by these enzymes are predominantly arachidonate-derived and include lipid hydroxides, epoxides, hydroperoxides, and prostanoids. These enzymes may also generate low levels of lipid-derived radicals in the vasculature following escape of substrate radicals from the active site. Lipid oxidation enzymes are often up-regulated in atherosclerosis and hypertension, with several lines of evidence suggesting that they play a central role in the pathogenesis of the disease process itself. This review will describe the isoforms of lipid oxidation enzymes present in endothelial cells focusing on their physiological functions and proposed roles in initiation and progression of vascular disease.

Expression of cyclooxygenase-2 in rat testis

Cyclooxygenase, the rate-limiting enzyme in the production of prostaglandins, exists in two isoforms, the constitutive cyclooxygenase 1 (Cox-1) and the inducible cyclooxygenase 2 (Cox-2). Cox-1 is involved in homeostatic functions while Cox-2 is implicated in various pathological processes such as inflammation and cancer. The present study describes the constitutive expression of Cox-2 in immature and mature rat testis, primarily localized in the spermatogonial cells. An interesting observation is the presence of Cox-2 on the chromatin and also in cytosol, apart from nuclear and endoplasmic reticular membranes. The significance of this observation is not yet clear, though its presence in the nucleus raises the possibility of Cox-2 having a more direct role in gene regulation than was thought earlier. In addition, the Cox-2 mRNA in testis is the smaller (2.8 kb) of the two isoform transcripts reported for Cox-2. Further hormone treatment regimes (testosterone/follicle stimulating hormone) increased the levels of Cox-2 protein within 6 h after treatment, suggesting that the sustained levels of Cox-2 protein in testis can be further influenced by gonadotrophins and androgens.

Human group IVC phospholipase A2 (cPLA2gamma). Roles in the membrane remodeling and activation induced by oxidative stress

To create the unique properties of a certain cellular membrane, both the composition and the metabolism of membrane phospholipids are key factors. Phospholipase A(2) (PLA(2)), with hydrolytic enzyme activities at the sn-2 position in glycerophospholipids, plays critical roles in maintaining the phospholipid composition as well as producing bioactive lipid mediators. In this study we examined the contribution of a Ca(2+)-independent group IVC PLA(2) isozyme (cPLA(2)gamma), a paralogue of cytosolic PLA(2)alpha (cPLA(2)alpha), to phospholipid remodeling. The enzyme was localized in the endoplasmic reticulum and Golgi apparatus, as seen using green fluorescence fusion proteins. Electrospray ionization mass spectrometric analysis of membrane extracts revealed that overexpression of cPLA(2)gamma increased the proportion of polyunsaturated fatty acids in phosphatidylethanolamine, suggesting that the enzyme modulates the phospholipid composition. We also found that H(2)O(2) and other hydroperoxides induced arachidonic acid release in cPLA(2)gamma-transfected human embryonic kidney 293 cells, possibly through the tyrosine phosphorylation pathway. Thus, we propose that cPLA(2)gamma is constitutively expressed in the endoplasmic reticulum and plays important roles in remodeling and maintaining membrane phospholipids under various conditions, including oxidative stress.

Prosurvival and antiapoptotic effects of PGE2 in radiation injury are mediated by EP2 receptor in intestine

The biological activities of PGE(2) are mediated through EP receptors (EP(1)-EP(4)), plasma membrane G protein-coupled receptors that differ in ligand binding and signal-transduction pathways. We investigated gastrointestinal EP(2) receptor expression in adult mice before and after radiation injury and evaluated intestinal stem cell survival and crypt epithelial apoptosis after radiation injury in EP(2) null mice. EP(2) was expressed throughout the gut. Intestinal EP(2) mRNA increased fivefold after gamma-irradiation. Crypt survival was diminished in EP(2)-/- mice (4.06 crypts/cross section) compared with wild-type littermates (8.15 crypts/cross section). Radiation-induced apoptosis was significantly increased in EP(2)-/- mice compared with wild-type littermates. Apoptosis was 1.6-fold higher in EP(2) (-/-) mice (5.9 apoptotic cells/crypt) than in wild-type mice (3.5 apoptotic cells/crypt). The EP(2) receptor is expressed in mouse gastrointestinal epithelial cells and is upregulated following radiation injury. The effects of PGE(2) on both crypt epithelial apoptosis and intestinal crypt stem cell survival are mediated through the EP(2) receptor.

Stimulation of intestinal epithelial restitution by prostaglandin E(1) analogue

BACKGROUND

5-Fluorouracil (5-FU) causes intestinal mucosal damage and malabsorption. We have recently reported that coadministration of 17 S,20-dimethyl- trans- lower right triangle (2)-prostaglandin E(1) (OP-1206), a stable synthetic analogue of prostaglandin E(1), with 5-FU to rats protects the small intestine from 5-FU-induced damage. Enterocyte proliferation would contribute to the restitution of the wounded intestinal mucosa. Thus, we investigated the effect of OP-1206 on the proliferation of rat jejunal crypt cells (IEC-6 cells) treated with 5-FU.

METHODS

Proliferation of IEC-6 cells was evaluated in terms of [(3)H]-thymidine incorporation and using the 3-(4,5-dimethyl-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Mucosal healing was assessed by measuring the speed of resealing across the denuded area of an IEC-6 cell monolayer.

RESULTS

OP-1206 stimulated [(3)H]-thymidine incorporation into subconfluent IEC-6 cells pretreated with 5-FU and increased the number of IEC-6 cells. AH23848B, an EP4 prostaglandin receptor antagonist, blocked the OP-1206-stimulated [(3)H]-thymidine incorporation into IEC-6 cells. The speed of resealing across the denuded area of a wounded IEC-6 cell monolayer was found to increase following treatment with OP-1206.

CONCLUSIONS

OP-1206 stimulated the proliferation of IEC-6 cells treated with 5-FU, indicating a possible mechanism for the protective effect of OP-1206 against 5-FU-induced damage to the small intestine. OP-1206 was shown to be active in intestinal mucosal healing.