Protein tyrosine nitration and thiol oxidation by peroxynitrite-strategies to prevent these oxidative modifications.

The reaction product of nitric oxide and superoxide, peroxynitrite, is a potent biological oxidant. The most important oxidative protein modifications described for peroxynitrite are cysteine-thiol oxidation and tyrosine nitration. We have previously demonstrated that intrinsic heme-thiolate (P450)-dependent enzymatic catalysis increases the nitration of tyrosine 430 in prostacyclin synthase and results in loss of activity which contributes to endothelial dysfunction. We here report the sensitive peroxynitrite-dependent nitration of an over-expressed and partially purified human prostacyclin synthase (3.3 µM) with an EC50 value of 5 µM. Microsomal thiols in these preparations effectively compete for peroxynitrite and block the nitration of other proteins up to 50 µM peroxynitrite. Purified, recombinant PGIS showed a half-maximal nitration by 10 µM 3-morpholino sydnonimine (Sin-1) which increased in the presence of bicarbonate, and was only marginally induced by freely diffusing NO2-radicals generated by a peroxidase/nitrite/hydrogen peroxide system. Based on these observations, we would like to emphasize that prostacyclin synthase is among the most efficiently and sensitively nitrated proteins investigated by us so far. In the second part of the study, we identified two classes of peroxynitrite scavengers, blocking either peroxynitrite anion-mediated thiol oxidations or phenol/tyrosine nitrations by free radical mechanisms. Dithiopurines and dithiopyrimidines were highly effective in inhibiting both reaction types which could make this class of compounds interesting therapeutic tools. In the present work, we highlighted the impact of experimental conditions on the outcome of peroxynitrite-mediated nitrations. The limitations identified in this work need to be considered in the assessment of experimental data involving peroxynitrite.

Gene transfer therapy by either type 1 or type 2 adeno-associated virus expressing human prostaglandin I2 synthase gene is effective for treatment of pulmonary arterial hypertension.

Prostaglandin I(2) (PGI(2)) plays an important role in the clinical treatment of pulmonary arterial hypertension (PAH). However, the administration of PGI(2) involves continuous intravenous infusion using an indwelling catheter, which limits the patient's quality of life and increases the risk of infection. We therefore investigated whether human PGI(2) synthase (hPGIS) gene transfer using an adeno-associated virus (AAV) vector is still effective in a mouse model of PAH and tested for differences in the therapeutic efficacy of PAH among AAV serotypes. The PAH was induced by subjecting mice to hypoxia (10% O(2)). Type 1 AAV expressing hPGIS (AAV1-hPGIS) or type 2 AAV expressing hPGIS (AAV2-hPGIS) was injected into the thigh muscle of mice. Both vectors expressing hPGIS produced strong hPGIS protein expression in the mouse thigh skeletal muscles after 8 weeks of hypoxia. The administration of AAV1-hPGIS or AAV2-hPGIS also significantly inhibited the hypoxia-induced increase in right ventricular systolic pressure, the ratio of right ventricular weight to body weight (RV/BW), and the ratio of RV weight to left ventricular plus septal weight (RV/LV + S), and significantly attenuated the hypoxia-induced increase in medial wall thickness of peripheral pulmonary arteries. Furthermore, there were no significant differences in the degree of amelioration in RV systolic pressure, RV/BW, RV/LV + S, and percentage of wall thickness of peripheral pulmonary arteries between AAV1-hPGIS and AAV2-hPGIS administrations. In conclusion, we revealed that type 1 and type 2 AAV are equally effective for the treatment of PAH in a hypoxia-induced mouse model. Gene-transfer therapy using AAV expressing hPGIS is, therefore, a potential therapeutic breakthrough for PAH.

AAV-PGIS gene transfer improves hypoxia-induced pulmonary hypertension in mice.

Although prostaglandin I2 is used to treat pulmonary hypertension (PH), continuous intravenous administration is necessary. We investigated whether human PGIS (hPGIS) gene transfer using adeno-associated virus (AAV) vector was effective in treating an animal model of PH. PH was induced by subjecting mice to 10% O(2). Type 1-AAV-hPGIS was injected into the left thigh muscle after 24h. Significant PH was induced at 8 weeks, but AAV-hPGIS administration significantly inhibited the increase in RV systolic pressure. PH-induced BNP up-regulation in the RV was reduced to the control level. The severe medial thickening of pulmonary arteries in PH was significantly suppressed by AAV-hPGIS. The hPGIS gene was detected only on the injected side. No pathological changes were observed at the injected site. At 24 weeks, all PH mice were deceased, but 47% of AAV-hPGIS-treated mice survived. This study demonstrated that AAV-hPGIS administration was effective in treating PH and prolonging survival.

Extranodal spreading of esophageal squamous cell carcinoma: clinicopathological characteristics and prognostic impact.

BACKGROUND: Microscopic cancer spreading to extranodal connective tissues (extranodal spreading: ENS) is occasionally found in resected specimens from patients with esophageal squamous cell carcinoma (SCC), but the prognostic impact of ENS remains unclear. The aims of this study were to elucidate the prognostic impact of ENS to help determine the most suitable management for the patients with ENS. METHODS: We histologically re-evaluated 7,349 lymph nodes obtained from 171 patients with SCC of the thoracic esophagus who underwent potentially curable resection between 1992 and 2003. We defined ENS as microscopic penetration of tumor cells from metastatic lymph nodes or tumor cell dissemination into extranodal connective tissues. RESULTS: Extranodal spreading was found in 37 (21.6%) patients, and it had a significant relationship with diameter and depth of the tumor, lymphatic and venous invasion, intramural metastasis, and number of metastatic nodes. Patients who were ENS positive were at higher risk of recurrence, and their overall survival rate was lower than that for ENS-negative patients. Furthermore, recurrent risk was higher and overall survival rate was lower in ENS-positive patients than in ENS-negative patients when they had 1-3 metastatic nodes, but recurrent risk and overall survival rate of the patients with 4 or more metastatic nodes were very similar in ENS-positive and ENS-negative patients. CONCLUSIONS: The present findings suggest that in SCC of the thoracic esophagus, the presence of ENS increases recurrent risk and reduces the overall survival of the patients with 1-3 metastatic nodes. Patients showing ENS should be managed in the same way as patients with 4 or more metastatic nodes.

Activation of PPARbeta/delta induces endothelial cell proliferation and angiogenesis.

OBJECTIVE: The role of the nuclear receptor peroxisome-proliferator activated receptor (PPAR)-beta/delta in endothelial cells remains unclear. Interestingly, the selective PPARbeta/delta ligand GW501516 is in phase II clinical trials for dyslipidemia. Here, using GW501516, we have assessed the involvement of PPARbeta/delta in endothelial cell proliferation and angiogenesis. METHODS AND RESULTS: Western blot analysis indicated PPARbeta/delta was expressed in primary human umbilical and aortic endothelial cells, and in the endothelial cell line, EAHy926. Treatment with GW501516 increased human endothelial cell proliferation and morphogenesis in cultures in vitro, endothelial cell outgrowth from murine aortic vessels in vitro, and angiogenesis in a murine matrigel plug assay in vivo. GW501516 induced vascular endothelial cell growth factor mRNA and peptide release, as well as adipose differentiation-related protein (ADRP), a PPARbeta/delta target gene. GW501516-induced proliferation, morphogenesis, vascular endothelial growth factor (VEGF), and ADRP were absent in endothelial cells transfected with dominant-negative PPARbeta/delta. Furthermore, treatment of cells with cyclo-VEGFI, a VEGF receptor1/2 antagonist, abolished GW501516-induced endothelial cell proliferation and tube formation. CONCLUSIONS: PPARbeta/delta is a novel regulator of endothelial cell proliferation and angiogenesis through VEGF. The use of GW501516 to treat dyslipidemia may need to be carefully monitored in patients susceptible to angiogenic disorders.

Alpha2-adrenoreceptor mediated sympathoinhibition of heart rate during acute hypoxia is diminished in conscious prostacyclin synthase deficient mice.

Acute hypoxia increases ventilatory drive in conscious animals, resulting in tachycardia. Sustained hypoxia changes the initial chemoreflex ventilatory increase to secondary ventilatory depression, which then evokes a gradual secondary heart rate (HR) reduction. Prostacyclin (PGI(2)) release is known to potentiate alpha(2)-adrenoreceptor (alpha(2)-AR) mediated inhibition of sympathoactivation during ischaemia and hypoxia. We examined whether alpha(2)-AR mediated sympathoinhibition was responsible for limiting hypoxic heart rate increases during initial sympathoactivation, and subsequent secondary HR depression, and if PGI(2) is required for sympathoinhibition of HR. The responses of unrestrained PGI(2) synthase deficient (PGID) and wild type (WT) mice to acute hypoxia (10% O(2) for 30 min) were investigated by simultaneous telemetry, whole body plethysmography and open-flow respirometry. PGID mice exhibited potentiated .V(E) (p < 0.007) after intraperitoneal vehicle injection (n = 8), but not so HR responses compared to WT mice during sustained hypoxia. Idazoxan (alpha(2)-AR antagonist, i.p. bolus 3 mg/kg) pretreatment did not change hypoxic ventilatory response in either group, but significantly elevated hypoxic HR in WT mice only (p < 0.013). Sodium meclofenamate (cyclooxygenase inhibition, i.p. bolus 25 mg/kg) pretreatment eliminated the potentiated .V(E) of PGID and caused significant basal hypotension that led to a transient hypertensive response to hypoxia. From these results, we suggest that alpha(2)-AR activation is required for coupling HR to central inspiratory drive during acute hypoxia, and that PGI(2) is required to enhance the inhibition of sympathoactivation.

Successful management of esophageal perforation diagnosed 3 days after injury caused by an explosion in the workplace: report of a case.

We report a case of esophageal perforation caused by an explosion, but which was not diagnosed until 3 days after the injury. A 53-year-old worker sustained superficial dermal burns to his trachea, face, neck, and legs during an explosion. The burns were treated conservatively at a local hospital, but he was transferred to our hospital 3 days after the injury, when mediastinal emphysema and bilateral pleural effusion became evident. An esophagogram followed by computed tomography showed an esophageal perforation caused by the blast injury, and we performed an esophagectomy with recontruction of the gastric tube. After the operation, an X-ray showed a foreign body in the lower abdomen, which we found in the upper thoracic esophagus on the day of injury. We surmised that the patient had inadvertently swallowed a foreign body, which had been heated and scattered by the explosion, and it had melted the upper thoracic esophagus.

Heterogeneous expression of GAGE, NY-ESO-1, MAGE-A and SSX proteins in esophageal cancer: Implications for immunotherapy.

Cancer/testis antigens (CTAs) elicit immune response in cancer patients and are therefore targets of immunotherapy. Current information on CTA expression is primarily based on mRNA assays and little is known about their expression at the protein level. The objectives of our study are to analyze GAGE, NY-ESO-1, MAGE-A and SSX protein expression in esophageal cancer and to correlate their expression patterns with clinicopathologic parameters and survival. We examined CTA protein expression in 213 patients with esophageal cancer by immunohistochemistry. Antigen-positive tumors were evaluated once and antigen-negative tumors were evaluated 3 times by examining different parts of the cancer specimen. GAGE, NY-ESO-1 and MAGE-A were heterogeneously expressed in 42 (20%), 44 (21%) and 111 (52%) tumors, respectively, whereas SSX expression was not detected. Of the 126 (59%) patients expressing CTAs, 70 (33%) expressed 1, 41 (19%) expressed 2 and 15 (7%) expressed 3 antigens. The expression of MAGE-A was correlated with those of GAGE (p = 0.001) and NY-ESO-1 (p = 0.002), and the expression of GAGE was correlated with that of NY-ESO-1 (p = 0.002). One hundred fifty-six (79%) sections were positively stained in the first evaluation, whereas 37 (19%) and 4 (2%) positive sections were identified in the second and third evaluations, respectively. Particularly, MAGE and GAGE expression showed overlaps. GAGE, NY-ESO-1 and MAGE-A protein expression was not correlated with the disease progression, TNM factors or survival. The detection of immunonegative cells in every specimen suggests addition of other drugs such as 5-aza-2'-deoxycytidine to increase the therapeutic effect of CTA-specific cancer vaccines.

[Safety and efficacy of chemotherapy using TS-1 followed by paclitaxel for advanced or recurrent gastric cancer with peritoneal dissemination].

There has been no standard treatment for gastric cancer with peritoneal dissemination. We have used TS-1 followed by paclitaxel for advanced or recurrent gastric cancer patients with peritoneal dissemination since January 2002. Twenty-three patients were enrolled to our prospective study and 19 of 23 patients completed the protocol. There were less severe adverse events concerning paclitaxel despite of the second line therapy of TS-1, and 80 percent of all therapeutic courses was at an outpatient clinic. The median time to progression was 199 days. The median survival time was 363 days in all the enrolled patients, and was 436 days in 19 patients who completed the protocol. Chemotherapy using TS-1 followed by paclitaxel is considered to be safe and effective for gastric cancer with peritoneal dissemination.

[Safety and efficacy of hypotonic CDDP intraperitoneal administration for gastric cancer with peritoneal dissemination].

We examined safety and efficacy of hypotonic CDDP intraperitoneal administration followed by systemic chemotherapy using MTX/5-FU and UFT. Between 1998 and 2004, seven patients who had histologically proven gastric adenocarcinoma with peritoneal metastases underwent palliative gastrectomy at Niigata University Medical Hospital. For residual peritoneal tumors, 100 mg/body of CDDP diluted with distilled water was intraperitoneally administered to the patients before closure of abdominal wall and was drained 30 to 60 minutes after administration. During the postoperative period, a patient suffered from intraperitoneal abscess and another patient had a renal dysfunction with an increasing level of serum Cr (2.1 mg/dl). As adverse effects of the following systemic chemotherapy, three patients had grade 3 anemia and one had grade 3 leukopenia. The median time to progression was 109 days and the median survival time was 248 days. Although intraperitoneal CDDP administration is safe to be carried out intraoperatively, the effect on survival is not better than new anticancer drugs, such as TS-1 and paclitaxel.

[Indication of hepatic resection for metastatic liver tumors from gastric cancer].

To clarify the benefit and indication of resection for metastatic liver tumors from gastric cancer, we reviewed the therapeutic outcomes at the Niigata University Medical Hospital and at a referred institution. From January 1982 to April 2004, thirty-nine patients with synchronous and 40 with metachronous liver metastases from gastric cancer had been treated. In synchronous cases, forty percent of the patients had many metastatic tumors in bilateral hepatic lobes and the majority of them had advanced gastric cancer with serosal invasion and widely spread of lymphatic metastases. On the other hand, over 70% of metachronous patients had unilobar or scattered bilobar metastases and only 20% of them accompanied other types of metastases. A survival analysis showed that the prognoses of patients undergoing hepatic resection were statistically better than other treatments in both synchronous and metachronous cases. And there was no evidence for the benefit of palliative gastrectomy. So we conclude that surgical treatment for hepatic metastases from gastric cancer is a beneficial option if all the lesions including the primary and lymphatic ones can be eradicated in limited candidates of synchronous cases and in more candidates of metachronous cases, especially unilobar and a few scattered bilobar metastases.

Gene transfer of hepatocyte growth factor with prostacyclin synthase in severe pulmonary hypertension of rats.

OBJECTIVE: Hepatocyte growth factor (HGF) is a multi-potent growth factor, which has anti-fibrotic effects for lung injuries. In this study, we investigated whether human HGF gene transfer may attenuate the medial hypertrophy of pulmonary arteries and enhance the ameliorating effect of prostacyclin in monocrotaline (MCT)-induced pulmonary hypertension in rats. METHODS AND RESULTS: The day before MCT injection, HVJ-liposome complex with the cDNA encoding HGF gene (H group), PGIS gene (P group), and both HGF and PGIS gene (HP group) were transfected to the liver of rats as drug delivery system for the lung. Rats transfected with control vector served as controls (C group). Twenty-eight days after MCT injection, histological examination showed marked thickening of medial wall of pulmonary arteries and right ventricular hypertrophy. Percent medial wall thickness (%WT) of peripheral pulmonary arteries, pressure ratio of the right ventricle (RV) to the left ventricle (LV), and weight ratio of the RV to the LV plus septum were significantly increased in the control. Percent medial wall thickness was significantly ameliorated in H group and HP group in comparison with C group. Pressure and weight ratio of RV to LV was significantly ameliorated in P group and HP group in comparison with C group, and was significantly ameliorated in HP group than P group. CONCLUSIONS: In vivo gene transfection with HGF gene attenuated the medial hypertrophy of pulmonary arteries and enhanced the ameliorating effect of prostacyclin for pulmonary hypertension in MCT rats. Thus, gene therapy with HGF and PGIS may be a promising strategy for severe pulmonary hypertension.

Purification and characterization of recombinant human prostacyclin synthase.

Prostacyclin synthase (PGIS), which catalyzes the conversion of prostaglandin (PG) H(2) to prostacyclin (PGI(2)), is a member of the cytochrome P-450 (P450) superfamily, CYP8A1. To study the enzymatic and protein characteristics of human PGIS, the enzyme was overexpressed in Spodoptera frugiperda 21 (Sf21) cells using the baculovirus expression system. PGIS was expressed in the microsomes of the infected Sf21 cells after culture in 5 microg/ml hematin-supplemented medium for 72 h. The holoenzyme was isolated from the solubilized microsomal fraction by calcium phosphate gel absorption and purified to homogeneity by DEAE-Sepharose and hydroxyapatite column chromatography. The K(m) and V(max) values of the purified human PGIS for PGH(2) were 30 microM and 15 micromol/min/mg of protein at 24 degrees C, respectively. The optical absorption and EPR spectra of the enzyme revealed the characteristics of a low-spin form of P450 in the oxidized state. The carbon monoxide-reduced difference spectrum, however, exhibited a peak at 418 nm rather than 450 nm. The addition of a PGH(2) analogue, U46619, to the enzyme produced an oxygen-ligand type of the difference spectrum with maximum absorption at 407 nm and minimum absorption at 430 nm. Treatment with another PGH(2) analogue, U44069, produced a peak at 387 nm and a trough at 432 nm in the spectrum (Type I), while treatment with tranylcypromine, a PGIS inhibitor, produced a peak at 434 nm and a trough at 412 nm (Type II). A Cys441His mutant of the enzyme possessed no heme-binding ability or enzyme activity. Thus, we succeeded in obtaining a sufficient amount of the purified recombinant human PGIS from infected insect cells for spectral analyses that has high specific activity and the characteristics of a P450, indicating substrate specificity.

Microsomal prostaglandin E synthase-1 is overexpressed in inflammatory bowel disease. Evidence for involvement of the transcription factor Egr-1.

Microsomal prostaglandin E synthase-1 (mPGES-1) catalyzes the conversion of cyclooxygenase-derived prostaglandin (PG) H(2) to PGE(2). Increased amounts of mPGES-1 were detected in inflamed intestinal mucosa from patients with inflammatory bowel disease (IBD). Treatment with tumor necrosis factor (TNF)-alpha stimulated mPGES-1 transcription in human colonocytes, resulting in increased amounts of mPGES-1 mRNA and protein. The inductive effect of TNF-alpha localized to the GC box region of the mPGES-1 promoter. Binding of Egr-1 to the GC box region of the mPGES-1 promoter was enhanced by treatment with TNF-alpha. Notably, increased Egr-1 expression and binding activity were also detected in inflamed mucosa from IBD patients. Treatment with TNF-alpha induced the activities of phosphatidylcholine-phospholipase C (PC-PLC) and protein kinase (PK) C and enhanced NO production. A pharmacological approach was used to implicate PC-PLC --> PKC --> NO signaling as being important for the induction of mPGES-1 by TNF-alpha. TNF-alpha also enhanced guanylate cyclase activity and inhibitors of guanylate cyclase activity blocked the induction of mPGES-1 by TNF-alpha. YC-1, an activator of guanylate cyclase, induced mPGES-1. Overexpressing a dominant negative form of PKG blocked TNF-alpha-mediated stimulation of the mPGES-1 promoter. Taken together, these results suggest that overexpression of mPGES-1 in IBD is the result of Egr-1-mediated activation of transcription. Moreover, TNF-alpha induced mPGES-1 by stimulating PC-PLC --> PKC --> NO --> cGMP --> PKG signal transduction pathway.

Enhanced therapeutic angiogenesis by cotransfection of prostacyclin synthase gene or optimization of intramuscular injection of naked plasmid DNA.

BACKGROUND: Although clinical trials of therapeutic angiogenesis by angiogenic growth factors with intramuscular injection of naked plasmid DNA have been successful, there are still unresolved problems such as low transfection efficiency. From this viewpoint, we performed the following modifications: (1) combination with vasodilation using prostacyclin and (2) changing the agents or volume of naked plasmid DNA in vivo. METHODS AND RESULTS: First, we examined cotransfection of the VEGF gene with the prostacyclin synthase gene in a mouse hindlimb ischemia model. Cotransfection of the VEGF gene with the prostacyclin synthase gene resulted in a further increase in blood flow and capillary density compared with single VEGF gene. Similar results were obtained with other angiogenic growth factors, such as hepatocyte growth factor (HGF). Alternatively, we changed the injection volume of the solution of plasmid DNA. Luciferase activity was increased in a volume-dependent manner. An increase in injection volume at 1 site rather than separate injections at multiple sites resulted in high transfection efficiency, which suggests that transfection of naked plasmid DNA is mediated by pressure. Interestingly, treatment with hyperbaric oxygen increased the transfection efficiency. Finally, we also examined the effects of different solutions. Saline and PBS, but not water, achieved high transfection efficiency. In addition, sucrose solution but not glucose solution resulted in high luciferase activity. CONCLUSIONS: Overall, angiogenesis might be enhanced by cotransfection of prostacyclin synthase gene or an increase in injection volume and osmotic pressure. These data provide important information for the clinical application of therapeutic angiogenesis to treat peripheral arterial disease.

Immunohistochemically detected micrometastasis in lymph nodes from superficial esophageal squamous cell carcinoma.

BACKGROUND AND OBJECTIVES: This study was conducted to determine the incidence and clarify the patterns of nodal micrometastasis, to elucidate the histopathologic parameters of tumor extension correlating with micrometastasis, and to evaluate whether nodal micrometastasis has clinical significance in patients with superficial esophageal cancer. METHODS: Lymph nodes resected from 78 patients with superficial esophageal squamous cell carcinoma were examined immunohistochemically using the monoclonal antibody cocktail AE1/AE3 to define histologically undetectable micrometastasis. Clinical records and pathologic features of all cases were reviewed. RESULTS: Of the 78 patients, 34 had neither micro- nor overt disease in the lymph nodes, 12 had nodal micrometastasis only, and 32 had histologically overt metastasis. Nodal micrometastasis was found in carcinomas reaching the muscularis mucosae or deeper tissues of the esophagus. Multivariate analysis showed that intraesophageal multicentric cancer and venous invasion had significant correlation with nodal micrometastasis (P = 0.005 and 0.017, respectively). However, no clinical impact of nodal micrometastasis could be detected regarding patient outcome. CONCLUSIONS: Nodal micrometastasis is not rare in patients with superficial esophageal cancer, but it does not appear to have clinical significance in these patients. Nodal micrometastasis correlates with intraesophageal multicentric cancer and venous invasion.

Enhanced angiogenesis and improvement of neuropathy by cotransfection of human hepatocyte growth factor and prostacyclin synthase gene.

The current therapeutic angiogenesis strategy to treat ischemic disease by using angiogenic growth factors has been limited to use of a single gene. However, as vasodilator substances such as prostacyclin are widely used for the treatment of peripheral arterial disease, it might be useful to combine angiogenesis with vasodilation of new vessels. In a mouse hind limb ischemia model, cotransfection of the hepatocyte growth factor (HGF) gene with the prostacyclin synthase gene demonstrated a further increase in blood flow and capillary density compared with a single gene. Even in the rabbit ischemia model, cotransfection of HGF plasmid with the prostacyclin synthase gene demonstrated a further increase in angiogenic activity compared with HGF alone. Because peripheral neuropathy due to diabetes is common for significant morbidity, we examined the hypothesis that experimental diabetic neuropathy can be reversed by HGF and prostacyclin synthase genes. Severe peripheral neuropathy, characterized by significant slowing of nerve conduction velocity compared with nondiabetic control animals, was ameliorated. Overall, cotransfection of the prostacyclin synthase and HGF genes is more effective than single-gene transfection to stimulate angiogenesis, and it significantly improved neuropathy. These data provide important information relating to the clinical application of therapeutic angiogenesis to treat peripheral arterial disease.

Cyclic mechanical stretch augments prostacyclin production in cultured human uterine myometrial cells from pregnant women: possible involvement of up-regulation of prostacyclin synthase expression.

Prostacyclin (PGI(2)), a potent smooth muscle relaxant, is a major prostaglandin secreted from human myometrium. The concentrations of PGI(2) metabolites in the maternal plasma were reported to be elevated during pregnancy, especially in labor. To clarify the mechanism in PGI(2) secretion from the myometrium, we first investigated the protein expression of cytosolic phospholipase A(2), cyclooxygenase (COX)-1, COX-2, and prostacyclin synthase (PGIS) in the human uterine myometrium at various gestational ages before labor. To elucidate the involvement of labor in the increase in PGI(2) production during labor, we next examined the effect of labor-like cyclic mechanical stretch on PGI(2) production by cultured human myometrial cells. Pregnancy specifically increased COX-1 and PGIS protein expression in the myometrial tissues before labor (P < 0.01 for both). Cyclic mechanical stretch augmented PGIS promoter activity, via activation of activator protein-1 site, and PGIS mRNA and protein expression in cultured human myometrial cells and resulted in a 3.5-fold increase in the concentration of 6-keto-prostaglandin F(1alpha), the stable metabolite of PGI(2), in the culture medium (P < 0.05). However, stretch did not affect the levels of prostaglandin E(2), prostaglandin F(2alpha), or thromboxane A(2) secreted into the same culture media. These results suggest that cyclic mechanical stretch during labor may contribute to the increase in the PGI(2) concentration in the maternal plasma during parturition.

Cyclooxygenase isozymes and their gene structures and expression.

The cyclooxygenase (COX, prostaglandin endoperoxide synthase) is a key enzyme in prostaglandin biosynthesis. Two isoforms of COX, COX-1 and COX-2, have been identified by molecular biological methods. The amino acid sequence homology between COX-1 and COX-2 is about 60% for the human enzymes. COX-1 is constitutively expressed in most tissues and cells in animal species. The COX-1 promoter region lacks a canonical TATA or CAAT box and is GC-rich. These features are consistent with those of a housekeeping gene. On the other hand, COX-2 is an inducible enzyme and is induced by various cytokines and mitogenic factors. The induction of COX-2 is suppressed by dexamethasone and PGJ2. There are many consensus cis-elements in the 5'-flanking region to regulate the expression of COX-2. Among them, a CRE, an NF-kappaB site, a NF-IL6 motif and an E-box, regulate transcription independently or synergistically. Most of the transcriptional signaling pathways require activation of the mitogen-activated protein kinase (MAPK) cascade. Moreover, MAPK signaling pathways are involved in regulating COX-2 gene expression at the post-transcriptional level.