A lung type prostaglandin F synthase is expressed in bovine liver: cDNA sequence and expression in E. coli

Enhanced glucocorticoid exposure facilitates the expression of genes involved in prostaglandin and estrogen syntheses in bovine placentomes at induced parturition

The mechanism by which the fetal membrane detaches after parturition in cattle is poorly understood, but the upregulation of placentomal prostaglandin and estrogen synthesis are considered to be important. This study investigated whether enhanced glucocorticoid exposure affected the functional maturation of placentomes at induced parturition. Placentomes were collected immediately after spontaneous (beef; n = 5, dairy; n = 5) or induced parturition in beef and dairy cattle. Parturition was induced conventionally using prostaglandin F2α (beef; n = 7, dairy; n = 6) or dexamethasone (beef; n = 6) or with a combination of triamcinolone acetonide (a long-acting glucocorticoid) and a high dose of betamethasone (TABET treatment, beef; n = 6, dairy; n = 9). Gene expression levels and protein localization in placentomes were analyzed by RT-qPCR and immunohistochemistry, respectively. Compared with the conventional methods, TABET treatment resulted in upregulated PTGS2 expression in cotyledons. The expression levels of PTGS2 and PGES were positively correlated in both cotyledons and caruncles. TABET treatment also upregulated the expression of CYP17A1, but not of CYP19A1, in cotyledons. The results revealed, for the first time, that PLA2G4A was localized in microvascular endothelial cells in the cotyledonary villi and the maternal septum. PTGS2 and PGES were colocalized in mononucleated cells of the cotyledonary villi and caruncle epithelial cells adjacent to the chorionic plate. TABET treatment upregulated the expression of placentomal genes involved in PGE2 synthesis and the conversion of pregnenolone to androstenedione. Thus, enhanced glucocorticoid exposure might partially facilitate the functional maturation of placentomes at induced parturition in cattle.

Molecular evolution, characterization and expression profiling of uterine aldoketoreductase 1B5 gene in endometrium of goat (Capra hircus)

Aldoketoreductase 1B5 (AKR1B5), a member of the Aldoketoreductase family, is involved in the production of Prostaglandin F2α (PGF2α) as one of vital prostaglandin F synthase (PGFS). PGs (Prostaglandins) play a crucial role in female reproductive system. In the present study, we cloned and characterized the full-length open reading frame of AKR1B5 gene in Black Bengal (BB) goat. The complete coding sequence of AKR1B5 comprises an entire open reading frame of 951 bp, encoding 316 amino acid (AA) residues. BB AKR1B5 showed >82.9% identity with that of cattle, rabbit, human, and rat at nucleotide and amino acid levels, respectively. Further, a systematic study of AKR1B5 sequence evolution was also conducted using Phylogenetic Analysis by Maximum Likelihood (PAML), entropy plot, and Blossum 62 in a phylogenetic context. Analysis of nonsynonymous to synonymous nucleotide substitution rate ratios (Ka/Ks) revealed that negative selection may have been operating on this gene during evolution in goat, cattle, rabbit, human, and rat, which showed its conservation across species. Further, expression of AKR1B5 was determined by quantitative real-time PCR in goat endometrial tissues at different stages of the estrous cycle and early pregnancy. Our results indicated its high expression at luteolytic phase (stage III; day 16-21) during the estrous cycle. However, during early (day ∼30-40) pregnancy the expression was highest as compared to estrous cycle.

Molecular evolution of enzymes involved in the arachidonic acid cascade

The metabolic pathway called the arachidonic acid cascade produces a wide range of eicosanoids, such as prostaglandins, thromboxanes and leukotrienes with potent biological activities. Recombinant DNA techniques have made it possible to determine the nucleotide sequences of cDNAs and/or genomic structures for the enzymes involved in the pathway. Sequence comparison analyses of the accumulated sequence data have brought great insights into the structure, function and molecular evolution of the enzymes. This paper reviews the sequence comparison analyses of the enzymes involved in the arachidonic acid cascade.

Preferential localization of prostamide/prostaglandin F synthase in myelin sheaths of the central nervous system

Prostaglandin (PG) F(₂α) is a product of cyclooxygenase (COX)-catalyzed metabolism of arachidonic acid and exerts biological functions in various tissues. Prostaglandin ethanolamide (prostamide) F(₂α) is a COX-2-catalyzed metabolite of arachidonoyl ethanolamide (anandamide) that induces pharmacological actions in ocular tissues. Although PGF(₂α) is one of the most abundant prostaglandins in the brain, function of PGF(₂α) in the central nervous system (CNS) has not been extensively investigated. Recently identified prostamide/PGF synthase catalyzes the reductions of prostamide H₂ to prostamide F(₂α) and PGH₂ to PGF(₂α), chiefly in the CNS. We examined tissue distribution of the enzyme in the CNS by immunohistochemistry, double immunofluorescence, and immuno-electron microscopy. We confirmed histological findings by immunofluorescence analyses of brain cell cultures. Prostamide/PGF synthase was expressed preferentially in the white matter bundles of the entire CNS of adult mice with less marked expression in neuronal cell bodies. The enzyme was colocalized with myelin basic protein (MBP) in myelin sheaths but not in axons. At the ultrastructural level, the enzyme was localized to myelin sheaths. Expression of the enzyme increased between P9 and P14 during the postnatal development, presumably in accordance with myelinogenesis. Cultured oligodendrocytes at 7 days in vitro expressed the enzyme in cytoplasmic processes where the enzyme was colocalized with MBP. Immunoreactivity for COX-2 was detected in white matter and cultured oligodendrocytes. Relatively selective localization of prostamide/PGF synthase suggests that myelin sheaths of the CNS may serve as the sites for producing prostamide F(₂α) and/or PGF(₂α), which may contribute to the formation and maintenance of central myelin.

Prostaglandin F2alpha synthase activities of aldo-keto reductase 1B1, 1B3 and 1B7

Here, we show that three enzymes belonging to the 1B group of the aldo-keto reductase (AKR) superfamily, i.e., human placental aldose reductase (AKR1B1), mouse kidney aldose reductase (AKR1B3) and mouse vas deferens protein (AKR1B7), catalyse the reduction of prostaglandin (PG) H(2), a common intermediate of various prostanoids, to form PGF(2alpha) in the presence of NADPH. AKR1B1, AKR1B3 and AKR1B7 displayed higher affinities for PGH(2) (K(m) = 1.9, 9.3 and 3.8 microM, respectively) and V(max) values (26, 53 and 44 nmol/min/mg protein, respectively) than did the human lung PGF(2alpha) synthase (AKR1C3; 18 microM and 4 nmol/min/mg protein, respectively). The PGF(2alpha) synthase activity of AKR1B1 and AKR1B3 was efficiently inhibited by two AKR inhibitors, tolrestat (K(i) = 3.6 and 0.26 microM, respectively) and sorbinil (K(i) = 21.7 and 0.89 microM, respectively), in a non-competitive or mixed-type manner, whereas that of AKR1B7 was not sensitive to these inhibitors (K(i) = 9.2 and 18 mM, respectively). These data provide a molecular basis for investigating novel functional roles for AKR1B members and PGF(2alpha) as mediators of physiological and pathological processes in mammalian organisms.

Substrate specificity and catalytic efficiency of aldo-keto reductases with phospholipid aldehydes

Phospholipid oxidation generates several bioactive aldehydes that remain esterified to the glycerol backbone ('core' aldehydes). These aldehydes induce endothelial cells to produce monocyte chemotactic factors and enhance monocyte-endothelium adhesion. They also serve as ligands of scavenger receptors for the uptake of oxidized lipoproteins or apoptotic cells. The biochemical pathways involved in phospholipid aldehyde metabolism, however, remain largely unknown. In the present study, we have examined the efficacy of the three mammalian AKR (aldo-keto reductase) families in catalysing the reduction of phospholipid aldehydes. The model phospholipid aldehyde POVPC [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine] was efficiently reduced by members of the AKR1, but not by the AKR6 or the ARK7 family. In the AKR1 family, POVPC reductase activity was limited to AKR1A and B. No significant activity was observed with AKR1C enzymes. Among the active proteins, human AR (aldose reductase) (AKR1B1) showed the highest catalytic activity. The catalytic efficiency of human small intestinal AR (AKR1B10) was comparable with the murine AKR1B proteins 1B3 and 1B8. Among the murine proteins AKR1A4 and AKR1B7 showed appreciably lower catalytic activity as compared with 1B3 and 1B8. The human AKRs, 1B1 and 1B10, and the murine proteins, 1B3 and 1B8, also reduced C-7 and C-9 sn-2 aldehydes as well as POVPE [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphoethanolamine]. AKR1A4, B1, B7 and B8 catalysed the reduction of aldehydes generated in oxidized C(16:0-20:4) phosphatidylcholine with acyl, plasmenyl or alkyl linkage at the sn-1 position or C(16:0-20:4) phosphatidylglycerol or phosphatidic acid. AKR1B1 displayed the highest activity with phosphatidic acids; AKR1A4 was more efficient with long-chain aldehydes such as 5-hydroxy-8-oxo-6-octenoyl derivatives, whereas AKR1B8 preferred phosphatidylglycerol. These results suggest that proteins of the AKR1A and B families are efficient phospholipid aldehyde reductases, with non-overlapping substrate specificity, and may be involved in tissue-specific metabolism of endogenous or dietary phospholipid aldehydes.

Molecular cloning and spatiotemporal expression of prostaglandin F synthase and microsomal prostaglandin E synthase-1 in porcine endometrium

Endometrial prostaglandins (PGs) and the PGE2/PGF2alpha ratio play an important role in regulating the estrous cycle and establishment of pregnancy. The enzymes downstream of cyclooxygenase-2 may determine the PGE2/PGF2alpha ratio in the porcine uterus. Thus, we have cloned porcine PGF synthase (PGFS) and microsomal PGE synthase-1 (mPGES-1) and characterized their expression in porcine endometrium during the estrous cycle and early pregnancy. PGFS and mPGES-1 amino acid sequences possessed a high degree (>67% and >77%, respectively) of identity with the other mammalian homologs. There was little modulation of mPGES-1 throughout the estrous cycle; however, PGFS expression was highly up-regulated in endometrium around the time of luteolysis. During early pregnancy, PGFS at the protein level showed a time-dependent increase (low on d 10-13, intermediate on d 14-23, and high on d 24-25). In pregnancy, expression of mPGES-1 was intermediate on d 10-11 and low on d 14-17 and then increased after d 22, reaching the maximum on d 24-25. Immunohistochemistry showed localization of PGFS and mPGES-1 proteins mainly in luminal and glandular epithelium. Concluding, the spatiotemporal expression of PGFS throughout the estrous cycle indicates an involvement of PGFS in regulating luteolysis in the pig. The comparison of endometrial PGFS and mPGES-1 expression on d 10-13 of the estrous cycle and pregnancy suggest a supportive role of these enzymes in determining the increase of uterine PGE2/PGF2alpha ratio during maternal recognition of pregnancy. Moreover, high expression of both PG synthases after initiation of implantation may indicate their significant role in placentation.

Expression of key prostaglandin synthases in equine endometrium during late diestrus and early pregnancy

Luteolysis in domestic species is mediated by the release of luteolytic pulses of prostaglandin (PG) F(2alpha) by the uterus at the end of diestrus, which must be suppressed by the conceptus to permit maternal recognition of pregnancy. In many species, including the horse, both the conceptus and the endometrium also synthesize PGE(2), which may antagonize PGF(2alpha) by playing a luteotropic and/or antiluteolytic role. While the release of PGE(2) and PGF(2alpha) by the equine endometrium in late diestrus and early pregnancy has been previously studied, the underlying prostaglandin synthase gene regulatory mechanisms remain poorly defined. To resolve this issue, cyclooxygenase-2 (COX-2), microsomal PGE(2) synthase (PGES), and PGF(2alpha) synthase (PGFS) expression were examined in a series of endometrial biopsies obtained from cycling mares on Days 10, 13, and 15 postovulation, as well as from pregnant mares on Day 15. Quantification of COX-2 expression revealed significant (P < 0.01) increases in both mRNA and protein levels at Day 15 in cycling endometrium relative to other timepoints. Importantly, the level of COX-2 expression in Day 15 pregnant endometrium was found to be comparable with that observed in Day 10 and Day 13 cycling animals, suggesting that the presence of the conceptus blocks the induction of COX-2. Immunohistochemistry demonstrated that the induction of COX-2 expression on Day 15 occurs specifically in surface epithelial cells in cycling animals only. As equine PGFS had not been previously characterized, a 1380-base pair (bp) cDNA transcript was cloned by a combination of reverse transcription-PCR techniques and found to be highly homologous to bovine liver-type PGFS. The pattern of expression observed for the terminal PG synthases was distinct from that of COX-2, as PGES and PGFS mRNA and protein levels were found to be invariant throughout the timecourse and unaffected by pregnancy. Similar to COX-2, however, the PGES and PGFS proteins were found to localize mainly to the surface epithelium. Thus, this study describes for the first time the regulation and spatial distribution of COX-2, PGES, and PGFS expression in equine endometrium in late diestrus, with a marked induction of COX-2 but not of PGES and PGFS expression in uterine epithelial cells at Day 15. Furthermore, the presence of the conceptus was shown to block the induction of COX-2 expression at Day 15, suggesting an important mechanism by which it may suppress uterine PGF(2alpha) release and prevent luteolysis during early pregnancy.

An aldose reductase with 20 alpha-hydroxysteroid dehydrogenase activity is most likely the enzyme responsible for the production of prostaglandin f2 alpha in the bovine endometrium

Prostaglandins are important regulators of reproductive function. In particular, prostaglandin F2 alpha (PGF(2 alpha)) is involved in labor and is the functional mediator of luteolysis to initiate a new estrous cycle in many species. These actions have been extensively studied in ruminants, but the enzymes involved are not clearly identified. Our objective was to identify which prostaglandin F synthase is involved and to study its regulation in the endometrium and in endometrial primary cell cultures. The expression of all previously known prostaglandin F synthases (PGFSs), two newly discovered PGFS-like genes, and a 20 alpha-hydroxysteroid dehydrogenase was studied by Northern blot and reverse transcription PCR. These analyses revealed that none of the known PGFS or the PGFS-like genes were significantly expressed in the endometrium. On the other hand, the 20 alpha-hydroxysteroid dehydrogenase gene was strongly expressed in the endometrium at the time of luteolysis. The corresponding recombinant enzyme has a K(m) of 7 microM for PGH(2) and a PGFS activity higher than the lung PGFS. This enzyme has two different activities with the ability to terminate the estrous cycle; it metabolizes progesterone and synthesizes PGF(2 alpha). Taken together, these data point to this newly identified enzyme as the functional endometrial PGFS.

Gene expression of prostanoid forming enzymes along the rat nephron

BACKGROUND

To obtain information about the general capability of nephron segments to elaborate prostanoids, we determined the gene expression of key enzymes for prostanoid formation.

METHODS

For this goal mRNAs were assayed for cyclooxygenases-1 and -2 as well as for the synthases of prostaglandin D2 (PGD2), prostaglandin E2 (PGE2), prostacyclin (PGI2) and thromboxane A2 (TXA2) in microdissected rat nephron segments by RT-PCR.

RESULTS

Cyclooxygenase-1 (COX-1) mRNA was strongly expressed in all segments of the collecting ducts and to a lesser extent in glomeruli. COX-2 mRNA was found in the cortical thick ascending limb of Henle, and weaker expression also was detected in glomeruli. The lipocalin-type PGD synthase mRNA displayed a broad expression pattern in the cortex and outer medulla, including proximal convoluted tubule, thick ascending limb of Henle, distal convoluted tubule, and cortical and outer medullary collecting duct. The hematopoietic PGD synthase mRNA was restricted to the outer medullary collecting duct, and the membrane-associated PGE-synthase mRNA was exclusively expressed in the whole collecting duct system. Prostacylin-synthase mRNA was found in the whole kidney, but not in any microdissected nephron segment analyzed in this study. TXA-synthase mRNA was expressed in glomeruli.

CONCLUSION

Given that the existence of cyclooxygenase in combination with the different PG-synthases is a prerequisite for the formation of prostanoids, our data suggest that PGD2 is mainly formed in the thick ascending limb and in the collecting duct, while PGE2 appears to be mainly generated by the collecting ducts. Probably no formation of PGI2 occurs within the nephron. Whether TXA2 can be formed by nephron segments remains questionable.

Identification of a novel prostaglandin f(2alpha) synthase in Trypanosoma brucei

Members of the genus Trypanosoma cause African trypanosomiasis in humans and animals in Africa. Infection of mammals by African trypanosomes is characterized by an upregulation of prostaglandin (PG) production in the plasma and cerebrospinal fluid. These metabolites of arachidonic acid (AA) may, in part, be responsible for symptoms such as fever, headache, immunosuppression, deep muscle hyperaesthesia, miscarriage, ovarian dysfunction, sleepiness, and other symptoms observed in patients with chronic African trypanosomiasis. Here, we show that the protozoan parasite T. brucei is involved in PG production and that it produces PGs enzymatically from AA and its metabolite, PGH(2). Among all PGs synthesized, PGF(2alpha) was the major prostanoid produced by trypanosome lysates. We have purified a novel T. brucei PGF(2alpha) synthase (TbPGFS) and cloned its cDNA. Phylogenetic analysis and molecular properties revealed that TbPGFS is completely distinct from mammalian PGF synthases. We also found that TbPGFS mRNA expression and TbPGFS activity were high in the early logarithmic growth phase and low during the stationary phase. The characterization of TbPGFS and its gene in T. brucei provides a basis for the molecular analysis of the role of parasite-derived PGF(2alpha) in the physiology of the parasite and the pathogenesis of African trypanosomiasis.

cDNA cloning, expression and characterization of human prostaglandin F synthase

A cDNA clone of prostaglandin F synthase (PGFS) was isolated from human lung by using cDNA of bovine lung-type PGFS as a probe and its protein expressed in Escherichia coli was purified to apparent homogeneity. The human PGFS catalyzed the reduction of prostaglandin (PG) D2, PGH2 and phenanthrenequinone (PQ), and the oxidation of 9alpha,11beta-PGF2 to PGD2. The kcat/Km values for PGD2 and 9alpha,11beta-PGF2 were 21000 and 1800 min(-1) mM(-1), respectively, indicating that the catalytic efficiency for PGD2 and 9alpha,11beta-PGF2 was the highest among the various substrates, except for PQ. The PGFS activity in the cytosol of human lung was completely absorbed with antihuman PGFS antiserum. Moreover, mRNA of PGFS was expressed in peripheral blood lymphocytes and the expression in lymphocytes was markedly suppressed by the T cell mitogen concanavalin A. These results support the notion that human PGFS plays an important role in the pathogenesis of allergic diseases such as asthma.

cDNA cloning, expression, and mutagenesis study of liver-type prostaglandin F synthase

Prostaglandin (PG) F synthase catalyzes the reduction of PGD2 to 9alpha,11beta-PGF2 and that of PGH2 to PGF2alpha on the same molecule. PGF synthase has at least two isoforms, the lung-type enzyme (Km value of 120 microM for PGD2 (Watanabe, K., Yoshida, R., Shimizu, T., and Hayaishi, O. (1985) J. Biol. Chem. 260, 7035-7041) and the liver-type one (Km value of 10 microM for PGD2 (Chen, L. -Y., Watanabe, K., and Hayaishi, O. (1992) Arch. Biochem. Biophys. 296, 17-26)). The liver-type enzyme was presently found to consist of a 969-base pair open reading frame coding for a 323-amino acid polypeptide with a Mr of 36,742. Sequence analysis indicated that the bovine liver PGF synthase had 87, 79, 77, and 76% identity with the bovine lung PGF synthase and human liver dihydrodiol dehydrogenase (DD) isozymes DD1, DD2, and DD4, respectively. Moreover, the amino acid sequence of the liver-type PGF synthase was identical with that of bovine liver DD3. The liver-type PGF synthase was expressed in COS-7 cells, and its recombinant enzyme had almost the same properties as the native enzyme. Furthermore, to investigate the nature of catalysis and/or substrate binding of PGF synthase, we constructed and characterized various mutant enzymes as follows: R27E, R91Q, H170C, R223L, K225S, S301R, and N306Y. Although the reductase activities toward PGH2 and phenanthrenequinone (PQ) of almost all mutants were not inactivated, the Km values of R27E, R91Q, H170C, R223L, and N306Y for PGD2 were increased from 15 to 110, 145, 75, 180, and 100 microM, respectively, indicating that Arg27, Arg91, His170, Arg223, and Asn306 are essential to give a low Km value for PGD2 of the liver-type PGF synthase and that these amino acid residues serve in the binding of PGD2. Moreover, the R223L mutant among these seven mutants especially has a profound effect on kcat for PGD2 reduction. The Km values of R223L, K225S, and S301R for PQ were about 2-10-fold lower than the wild-type value, indicating that the amino acid residues at 223, 225 and 301 serve in the binding of PQ to the enzyme. On the other hand, the Km value of H170C for PGH2 was 8-fold lower than that of the wild type, indicating that the amino acid residue at 170 is related to the binding of PGH2 to the enzyme and that Cys170 confer high affinity for PGH2. Additionally, the 5-fold increase in kcat/Km value of the N306Y mutant for PGH2 compared with the wild-type value suggests that the amino acid at 306 plays an important role in catalytic efficiency for PGH2.

Reduction of prostaglandin D2 to 9 alpha,11 beta-prostaglandin F2 by a human liver 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase isozyme

Prostaglandin (PG) specificity of two 3 alpha-hydroxysteroid/dihydrodiol dehydrogenase isozymes, DD2 and DD4, of human liver was examined. DD2 exhibited NADPH-linked reductase activity for 9-,11- and 15-ketoprostaglandins at a pH optimum of 6.0, whereas DD4 reduced only 15-ketoprostaglandin F2 alpha. DD2 showed the highest Vmax/Km value for PGD2 of the PG substrates, and the reduced product of PGD2 was identified to 9 alpha,11 beta-PGF2 by gas chromatography-mass spectrometry. In the reverse reaction with NADP+ as a cofactor, the two enzymes slowly oxidized several PGs with 9-, 11- and/or 15-hydroxy groups, except that DD2 showed high activity for 9 alpha,11 beta-PGF2 at a pH optimum of 10.0. The Km and Vmax values of DD2 for PGD2 were 57 microM and 250 nmol/min per mg, respectively, at pH 7.0 and 37 degrees C, and the respective values for 9 alpha,11 beta-PGF2 were 72 microM and 10 nmol/min per mg. PGD2 11-ketoreductase activity in human liver cytosol was recovered in 30-75% saturated ammonium sulfate fraction. More than 77% of the PGD2 11-ketoreductase activity in the ammonium sulfate fraction was immunoprecipitated by antibodies against DD2, and inhibited by known inhibitors of the enzyme. These results suggest that DD2 is a major soluble PGD2 11-ketoreductase species in human liver.