Distinct cellular localization of mRNAs for three subtypes of prostaglandin E receptor in kidney

Distribution of the mRNAs for three subtypes of prostaglandin E (PGE) receptors in the mouse kidney was investigated by in situ hybridization. The mRNA for EP1 subtype, which is coupled to Ca2+ mobilization, was specifically localized to the collecting ducts from the cortex to the papilla. The mRNA for EP2 subtype, which is linked to stimulation of adenylate cyclase, was localized to the glomeruli. The mRNA for EP3 subtype, which is coupled to inhibition of adenylate cyclase, was located densely in the tubules in the outer medulla and in the distal tubules in the cortex. These results exhibit distinct cellular localization of three subtypes of PGE receptor in the kidney and suggest that PGE2 exerts multiple functions via these subtypes expressed in different segments of the nephron.

cDNA cloning of a mouse prostacyclin receptor. Multiple signaling pathways and expression in thymic medulla

A functional cDNA for a mouse prostacyclin receptor was isolated from a mouse cDNA library by reverse transcription polymerase chain reaction and hybridization screening. The cDNA encodes a polypeptide of 417 amino acid residues with putative seven transmembrane domains and an calculated molecular weight of 44,722. The amino acid sequence is 30-40% identical in the transmembrane domains to those of the mouse prostaglandin (PG) E receptor subtypes and thromboxane A2 receptor. [3H]Iloprost, a specific prostacyclin receptor radioligand, specifically bound to the membrane of Chinese hamster ovary cells permanently expressing the cDNA with Kd of 4.6 nM. This binding was displaced with unlabeled prostanoids in the order of cicaprost > iloprost, both prostacyclin agonists > PGE1 > carbacyclin >> PGD2 approximately STA2, a thromboxane A2 agonist approximately PGE2 > PGF2 alpha. Iloprost in a concentration-dependent fashion increased cAMP level and generated inositol phosphates in these cells, indicating that the receptor couples to multiple signal transduction pathways. Northern blot analysis revealed that the mRNA is expressed most abundantly in thymus, followed by spleen, heart, and lung. In situ hybridization of thymus showed that it is expressed exclusively in medulla and not in cortex.

Inherent versatility of P-450 oxygenase. Conferring dehydroepiandrosterone hydroxylase activity to P-450 2a-4 by a single amino acid mutation at position 117

Mouse steroid 15 alpha-hydroxylase P-450 2a-4 is restricted in its substrate specificity to the delta 4, 3-ketone steroids such as androstenedione. As a result, the P-450 exhibits little hydroxylase activity toward delta 5, 3-hydroxysteroids including dehydroepiandrosterone (DHEA). A single amino acid mutation of Ala at position 117 to Val, however, is enough to confer a high DHEA hydroxylase activity to P-450 2a-4 with 7 alpha-OH DHEA as one of the two major hydroxylated metabolites. Mouse coumarin 7-hydroxylase P-450 2a-5 contains Val at position 117, but it exhibits very low DHEA hydroxylase activity. P-450 2a-5 acquires high DHEA hydroxylase activity, however, by a mutation of Phe-209 to Asn. Moreover, the mutant P-450 2a-5 loses its activity when Val is replaced by Ala at position 117. The residue at position 117, therefore, plays the principal role in the determination of the DHEA hydroxylase activity of the P-450s. Conversely, mutations at residue 117 have little effect on the androstenedione hydroxylase activities of the P-450s. Further modeling of the DHEA binding orientation in the substrate-heme pocket of bacterial P-450cam (Iwasaki, M., Darden, T., Pedersen, L., Davis, D. G., Juvonen, R. O., Sueyoshi, T., and Negishi, M. (1993) J. Biol. Chem. 268, 759-762) provides support for the hypothesis that the type of residue at position 117 determines the steroid-substrate specificity of the P-450 depending on the substituent at the C3 position of steroid molecule.

cDNA cloning and sequence of CYP2C29 encoding P-450 MUT-2, a microsomal aldehyde oxygenase

A cDNA clone encoding a cytochrome P-450 (P-450) isozyme was isolated from a mouse liver cDNA library. This P-450, designated CYP2C29, the first member of the mouse CYP2C subfamily to be reported, contained the complete coding region of 490 amino acid residues. The deduced amino acid sequence of CYP2C29 exhibited 83% identity with that of the rat CYP2C7 and had an N-terminal sequence identical to that of P-450 MUT-2, a microsomal aldehyde oxygenase. Two peptides, derived from BrCN cleavage of P-450 MUT-2, were also identical to the cDNA deduced protein of CYP2C29. These results indicate that CYP2C29 cDNA encodes P-450 MUT-2.

Overexpression of a cytochrome P-450 of the 2a family (Cyp2a-5) in chemically induced hepatomas from female mice

Chemical hepatocarcinogenesis in female mice, induced by 5,9-dimethyl(7H)dibenzo[c,g]carbazole, leads to the overexpression of a cytochrome P-450 of the 2a family. This protein was identified as Cyp2a-5, by the use of immunoblots obtained from isoelectric focusing gels. This method allowed the distinction of Cyp2a-5 from Cyp2a-4, another mouse liver cytochrome P-450, by taking advantage of their slightly different pI values. The theoretical pI values, determined from the amino acid sequence, were pI 9.91 for Cyp2a-4 and pI 10.01 for Cyp2a-5. Other structurally related forms were not detected. In hepatomas from female mice, only the Cyp2a-5 form was overexpressed (2-3 fold). Male mice showed a weak expression of Cyp2a-4 and Cyp2a-5 in control liver samples and in hepatomas. The expression of both forms was increased more than fivefold upon castration. Pyrazole induces specifically the Cyp2a-5 form. The Cyp2a-5 overexpression was correlated with enhanced microsomal coumarin-7-hydroxylase and testosterone-15 alpha-hydroxylase activities. An immunohistochemical study showed that Cyp2a-4 and Cyp2a-5 are expressed uniformly in female livers, but centrilobularly in male livers. In hepatomas, this localisation is perturbed; in females we observed a focal cell localisation, and the Cyp2a-containing cells were often hypertrophic and polyploid. In hepatomas from male mice, the Cyp2a-containing cells became dispersed. From a comparison with other studies, the Cyp2a-5 overexpression appears to be a general feature of hepatocarcinogenesis in mice.

Lack of the steroid 15 alpha-hydroxylase gene (Cyp2a-4) in wild mouse strain Mus spretus: rapid evolution of the P450 gene superfamily

Steroid 15 alpha-hydroxylase P450(15 alpha) and coumarin 7-hydroxylase P450coh genes Cyp2a-4 and Cyp2a-5 are members of the mouse P450 2A subfamily. Whereas Mus musclus domesticus strains contain both genes, wild mouse strain Mus spretus contains only Cyp2a-5. Evolutionarily, therefore, Cyp2a-5 is ancestral to Cyp2a-4. Moreover, the line to Cyp2a-4 descended as recently as 3 million years ago in an ancestral mouse. This evidence implies a rapid evolution of the P450 gene superfamily.

Mapping of the genes encoding mouse thromboxane A2 receptor and prostaglandin E receptor subtypes EP2 and EP3

Thromboxane A2 (TXA2) and prostaglandin E2 (PGE2) are two of the most representative eicosanoids that are formed from arachidonic acid. They produce a broad spectrum of biological effects mediated through specific cell surface receptors. We have mapped genetic loci for TXA2 receptor, Tbxa2r, and for PGE2 receptor subtypes EP2 and EP3, Ptgerep2 and Ptgerep3, respectively, using restriction fragment length variants in interspecific backcross mice. None of the three loci cosegregated with each other. Tbxa2r mapped to Chr 10, Ptgerep2 mapped to the distal end of Chr 3. Possible human loci for these receptors are predicted based on the homology between mouse and human chromosomes.

Cloning and expression of a cDNA for mouse prostaglandin F receptor

A functional cDNA clone for mouse prostaglandin (PG) F receptor was isolated from a mouse cDNA library using polymerase chain reaction based on the sequence of cloned prostanoid receptors, and cross-hybridization screening. The mouse PGF receptor consists of 366 amino acid residues with putative seven transmembrane domains. The sequence revealed the highest homology to the EP1 subtype of PGE receptor and thromboxane (TX) A2 receptor. Ligand binding studies using membranes of COS cells transfected with the cDNA revealed specific [3H]PGF2 alpha binding. The binding was displaced with unlabeled PGs in the order of PGF2 alpha = 9 alpha, 11 beta PGF2 > PGF 1 alpha > PGD2 > STA2 (a stable TXA2 agonist) > PGE2 > iloprost (a stable PGI2 agonist). PGF2 alpha increased inositol trisphosphate formation in a concentration-dependent manner in COS cells expressing PGF receptor. RNA blot and in situ hybridization analyses demonstrated that the PGF receptor transcripts are abundantly expressed in luteal cells of corpus luteum and in a lesser amount in kidney, heart, stomach, and lung.

Activation volume and energetic properties of the binding of CO to hemoproteins

We have investigated the CO binding to various reduced hemoproteins by stopped-flow rapid mixing as a function of pressure (from 0.1 to 200 MPa) and temperature (from 4 to 35 degrees C). In particular, we studied several varieties of cytochrome P-450: CYP11A1 (scc), CYP2B4 (LM2), CYP3A6 (LM3c), and Cyp2a (7 alpha), as well as chloroperoxidase and lactoperoxidase, and compared the results to data reported for other hemoproteins. Whereas the CO binding activation enthalpy delta H++ and entropy delta S++ (correlated through a compensation effect) varied greatly between the hemoproteins, with no apparent relation to structural features, the pressure effect depended on the nature of the proximal axial heme ligand: the activation volume was very small for cysteine (S-) ligand hemoproteins (delta V++ = +1 to +6 ml mol-1), and markedly negative for histidine (N) ligand hemoproteins (delta V++ = -3 to -36 ml mol-1). Furthermore, the transition state volume of the histidine ligand class enzymes, but not that of the cysteine ligand enzymes, depended on the solvent composition. These results suggest that the CO-binding transition state of the S-ligand class has a molecular conformation similar to the ground state. In the histidine class, however, the transition state appears to involve protein conformational changes and/or solvation processes.

Prostacyclin (PGI) receptor binding and cyclic AMP synthesis activities of PGI1 analogues, SM-10906 and its methyl ester, SM-10902, in mastocytoma P-815 cells

The prostacyclin I1 (PGI1) analogue, SM-10906 and its methyl ester, SM-10902, have been compared with the PGI2 analogue, iloprost, with respect to binding to the PGI2 receptor, stimulation of adenylate cyclase activity and inhibition of thrombin-induced Ca2+ mobilization in mastocytoma P-815 cells. SM-10906 displaced [3H]iloprost binding to the membrane fraction, the IC50 value being 100 nM, but showed very low affinity for the prostaglandin E (PGE) receptor. SM-10906 dose-dependently stimulated GTP-dependent adenylate cyclase activity in the membrane fraction, the EC50 value being 35 nM. Furthermore, SM-10906 prevented a thrombin-induced increase in the intracellular Ca2+ concentration, the IC50 value being 300 nM. These IC50 and EC50 values are much lower than those of SM-10902. These results demonstrate that SM-10906, a stable PGI1 derivative, is an agonist for the [3H]iloprost-binding (PGI2) receptor, and that it prevents thrombin-induced Ca2+ mobilization through stimulation of the adenylate cyclase system in mastocytoma cells. On the other hand, a methyl ester derivative of PGI1, SM-10902, was inactive in the binding assay, but it seems to be a partial agonist for adenylate cyclase activity [corrected].

Opposite coupling of prostaglandin E receptor EP3C with Gs and G(o). Stimulation of Gs and inhibition of G(o)

We recently identified four isoforms of bovine prostaglandin E receptor EP3 subtype, which are coupled to different signaling pathways; EP3A is coupled to inhibition of adenylate cyclase, while EP3B and EP3C are coupled to its stimulation and EP3D is coupled to phosphatidylinositol turnover, in addition to the adenylate cyclase system (Namba, T., Sugimoto, Y., Negishi, M., Irie, A., Ushikubi, F., Kakizuka, Ito, S., A., Ichikawa, A., and Narumiya, S. (1993) Nature 365, 166-170). We examined here the identity of coupled G proteins and their regulation by one of the isoforms, EP3C, in the membranes of EP3C cDNA-transfected Chinese hamster ovary cells. M&B 28767, an EP3 agonist, stimulated the GTPase activity in the pertussis toxin (PT)-treated cell membrane, but inhibited it in the cholera toxin (CT)-treated cell membrane, while the agonist neither stimulated nor inhibited it in the both PT- and CT-treated cell membrane. In the PT- and CT-treated cell membrane reconstituted with various G proteins, M&B 28767 inhibited the GTPase activity of G(o), but stimulated that of Gs. On the other hand, M&B 28767 did not affect the GTPase activity of Gi1, Gi2, or Gi3. M&B 28767 increased the apparent affinity of G(o) for GDP without any change in that for GTP, as assessed by displacement of [35S]GTP gamma S (guanosine 5'-O-(3-thiotriphosphate)) binding to G(o). In contrast, M&B 28767 increased the apparent affinity of Gs for GTP but decreased that for GDP. These results demonstrated that the EP3 receptor isoform is coupled to two different G proteins, and oppositely regulates their activities, inhibition of G(o), and stimulation of Gs.

Arachidonic acid activates cation channels in bovine adrenal chromaffin cells

Microscopic fluorescence analysis of fura-2-loaded bovine adrenal chromaffin cells demonstrates that approximately 70% of the cells responded to arachidonic acid in increasing the intracellular Ca2+ concentration. Because this increase was markedly less in the absence of external Ca2+, we examined the effect of arachidonic acid on Ca2+ influx electrophysiologically. Bath application of 10 microM arachidonic acid induced a long-lasting inward current when the cell was clamped at -50 mV. Other fatty acids, such as oleic acid, linoleic acid, eicosatrienoic acid, and eicosapentaenoic acid, were all ineffective. The current-voltage relationships suggest that arachidonic acid may activate voltage-insensitive channels. Arachidonic acid (> or = 2 microM) activated a single-channel current in the inside-out patch, even in the presence of inhibitors of cyclooxygenase and lipoxygenase, possibly suggesting that arachidonic acid could activate channels directly. The onset delay of the inward channel current in the outside-out patch configuration (54.2 +/- 63.5 s; mean +/- SD) was significantly shorter than that in the inside-out patch one (197.3 +/- 177.7 s). Washout of arachidonic acid decreased the probability of channel openings in the outside-out patch but not in the inside-out one. These results suggest that arachidonic acid activates channels reversibly from outside of the plasma membrane. The unitary conductance for Ca2+ of arachidonic acid-activated channel was approximately 17 pS. The arachidonic acid-activated channel was permeable to Ba2+, Ca2+, and Na+ but not to Cl-. The opening probability of the arachidonic acid-activated channel did not depend on membrane potential.(ABSTRACT TRUNCATED AT 250 WORDS)

A trans-acting locus regulates transcriptional repression of the female-specific steroid 15 alpha-hydroxylase gene in male mice

Steroid 15 alpha-hydroxylase (P450(15 alpha)) is a female-specific enzyme in the livers of many inbred mice including DBA/2J. Run-on assays using liver nuclei from GH-deficient Little mice indicated that the P450(15 alpha) gene is transcriptionally repressed by GH in male mice. BALB/cJ is a variant strain in which the gene is expressed in the males as well as in the females. Genetic crosses between DBA/2J and BALB/cJ indicated that expression of the P450(15 alpha) gene in BALB/cJ males is inherited as a recessive trait and is regulated by a single locus. The parental origin of the P450(15 alpha) genes, determined using restriction site polymorphism in the exons of the P450(15 alpha) genes, divided the F2 males expressing the P450(15 alpha) gene into three phenotypes at a ratio of 1:1:2, the individuals expressing the gene from only BALB/cJ or DBA/2J and the individuals expressing the genes from both parents respectively. The results indicate that the repression of the P450(15 alpha) gene in male mice is regulated by a trans-acting regulatory locus between the DBA/2J and BALB/cJ pairs. Because hypophysectomy derepressed the P450(15 alpha) gene in F1 males and GH repressed the gene in hypophysectomized F1 males, the hormone appears to regulate gene repression through a trans-acting locus, named GH-dependent repression, GDR.

Third isoform of the prostaglandin-E-receptor EP3 subtype with different C-terminal tail coupling to both stimulation and inhibition of adenylate cyclase

A functional cDNA clone for a third isoform of the mouse prostaglandin-E-receptor EP3 subtype, derived by alternative RNA splicing, named the EP3 gamma receptor, was obtained in addition to those for the two other isoforms, EP3 alpha and EP3 beta. The three isoforms are only different in the amino acid sequence of the putative cytoplasmic carboxy-terminal tail. When expressed, EP3 gamma shows identical ligand-binding properties to these of the other isoforms. The EP3-selective agonist, M&B 28767, increased the basal cAMP level and inhibited the forskolin-induced increase in the cAMP level in EP3 gamma, while it decreased both the basal and forskolin-elevated cAMP levels in EP3 alpha and EP3 beta. The M&B 28767-stimulated GTPase activity consisted of pertussis-toxin-sensitive and cholera-toxin-sensitive portions in the EP3 gamma-expressing cell membrane, suggested that EP3 gamma is coupled to both guanine nucleotide-binding inhibitory and stimulatory proteins. These results indicate that EP3 gamma is coupled to both stimulation and inhibition of adenylate cyclase, but that EP3 alpha and EP3 beta are exclusively coupled to inhibition of adenylate cyclase. Thus, alternative splicing produces a third isoform with a different carboxy-terminal tail, which differs from the other two isoforms in the specificity of coupling to a signal-transduction pathway.

Phase I/II trial of didanosine (2',3'-dideoxyinosine) in hemophiliac patients with AIDS or AIDS-related complex

Forty-three hemophiliacs with AIDS or ARC received a daily dose of 334 or 500 mg didanosine (2',3'-dideoxyinosine or ddI) orally in 2 divided doses in phase I/II, open-label clinical trial conducted in Japan. Twenty-eight patients completed 6 months of therapy. There was an increase in circulating CD4(+) cells in 19 valuable patients from 91 +/- 25 (mean +/- SE) at entry to 131 +/- 38 at 24 weeks of therapy P = 0.01; Wilcoxon signed rank). Fourteen of 37 patients met the criteria for CD4 rise >/= 50/mm3 rise or >/= 50% increase from entry values) for more than 4 consecutive weeks. Twenty patients were p24 positive at entry. Nine out of the 10 evaluable patients (90%) showed a decline in p24 antigen at weeks 20-24 (P = 0.02). Thirty-five patients had symptoms related to HIV-1 infection at entry. Twenty-seven patients reported improvements in constitutional symptoms during therapy. Nine patients presented with possible drug-related adverse effects, and didanosine was discontinued in 6 patients (one each with edema; abdominal pain with anorexia; hematuria with edema and rash; sense of abdominal distension with anorexia; diarrhea and abdominal pain; and irritability). One patient had a transient increase in serum amylase level to twice the upper limit of normal, but he continued to receive the drug. These data suggest that didanosine was generally well tolerated in hemophiliacs with AIDS or ARC, and its administration correlated with improvement in constitutional symptoms and laboratory findings. The adverse effects of didanosine seen in this population were moderate to mild, and no complications related to hemorrhagic diathesis were observed, although the relative risk of acute pancreatitis in this population (while not seen in the present study to date) requires more study.

Cloning and expression of cDNA for a mouse EP1 subtype of prostaglandin E receptor

A functional cDNA clone encoding a mouse EP1 subtype of prostaglandin (PG) E receptor was isolated from a mouse cDNA library by cross-hybridization with the mouse thromboxane A2 receptor cDNA. The clone isolated encodes a protein consisting of 405 amino acid residues with putative seven-transmembrane domains. [3H]PGE2 specifically bound to the membrane of Chinese hamster ovary cells expressing this clone. The binding to the membrane was displaced with unlabeled PGs in the order of PGE2 > iloprost (a prostacyclin analogue) > PGE1 > PGF2 alpha > U-46619 (a thromboxane A2 analogue) > PGD2. The binding was also inhibited by 17-phenyl trinor PGE2 (an EP1 agonist) and sulprostone (an EP1 and EP3 agonist) but not by 11-deoxy PGE1 (an EP2 and EP3 agonist) and butaprost (an EP2 agonist). PGE2 induced a rapid increase in intracellular Ca2+ concentration in Chinese hamster ovary cells expressing the receptor. These results suggest that this receptor belongs to EP1 subtype of PGE receptor. Northern blot analysis demonstrated that the mRNA of this receptor is expressed abundantly in kidney and in a lessor amount in lung.

Alternative splicing of C-terminal tail of prostaglandin E receptor subtype EP3 determines G-protein specificity

Peptide hormones, neurotransmitters, and autacoids activate a family of seven-transmembrane-domain receptors. Each of these receptors specifically couples to one of several G proteins, Gs, Gi, G(o) and Gp, to activate a specific second messenger system. Cell surface receptors for prostanoids have been characterized pharmacologically and the complementary DNAs for thromboxane A2 receptor and the EP3 subtype of the prostaglandin (PG)E receptor reveal that they belong to the seven-transmembrane-domain receptor family. The EP3 receptor mediates the diverse physiological actions of PGE2 (ref. 3). Although most of them occur through coupling of the EP3 receptor to Gi and inhibition of adenylyl cyclase, the EP3-mediated contraction of uterine muscle can only occur by activation of another second messenger pathway. In chromaffin cells, two different second messenger pathways are activated by PGE2 binding to an apparently single EP3 receptor class. Here we show that at least four isoforms of the EP3 receptor, which differ only at their C-terminal tails and are produced by alternative splicing, couple to different G proteins to activate different second messenger systems.

Characterization of the prostaglandin E receptor expressed on a cultured mast cell line, BNu-2cl3

Interleukin 3-dependent BNu-2cl3 mast cells, mucosal type-like mast cells, exhibited a specific high-affinity binding site for [3H]prostaglandin (PG) E2. The binding was completely displaced by M&B 28767, an EP3-selective agonist, but not by EP1- or EP2-selective ligands, indicating that the PGE2 binding site is of the EP3 subtype PGE receptor. Whereas the EP3 subtype is presumed to be coupled to inhibition of adenylate cyclase in various tissues and cells, in BNu-2cl3 cells PGE2 had no ability to inhibit adenylate cyclase activity, while it induced concentration-dependent stimulation of phosphoinositide metabolism and caused an increase in the intracellular free Ca2+ concentration in a pertussis toxin-sensitive manner. PGE2 by itself did not evoke histamine release from the cells, but it markedly stimulated histamine release in concert with ionomycin, a Ca2+ ionophore. The PGE2-stimulated release was also completely blocked by pertussis toxin. Thus, the PGE receptor expressed on BNu-2cl3 mast cells is of the EP3 subtype and is linked to phosphoinositide metabolism via a pertussis toxin-sensitive G protein, and this activation leads to histamine release.