Critical amino acid residues for ligand binding are clustered in a predicted beta-turn of the third N-terminal repeat in the integrin alpha 4 and alpha 5 subunits

Integrin alpha 4 beta 1 is a receptor for vascular cell adhesion molecule (VCAM)-1 and fibronectin (CS-1). The alpha 4 beta 1-ligand interaction is involved in the pathogenesis of diseases and is, therefore, a therapeutic target. Here, we identified critical residues of alpha 4 for ligand binding using alanine-scanning mutagenesis of the previously localized putative ligand binding sites (residues 108-268). Among 43 mutations tested, mutations of Tyr187, Trp188 and Gly190 significantly inhibited cell adhesion to both VCAM-1 and CS-1. This inhibition was not due to any gross structural changes of alpha 4 beta 1. These critical residues are clustered in a predicted beta-turn structure (residues 181-190) of the third N-terminal repeat in alpha 4. The repeat does not contain divalent cation binding motifs. Notably, the mutations within the corresponding region of alpha 5 significantly reduced fibronectin-alpha 5 beta 1 interaction. These findings suggest that the predicted beta-turn structure could be ubiquitously involved in ligand binding of non-I domain integrins.

[Radical prostatectomy in a patient with hemophilia B]

We describe our experience with radical prostatectomy in a patient with hemophilia B. whose factor IX activity was 7% and partial thromboplastin time was 55.9 sec. A total of 43,000 units of factor IX concentrate (PCC) was given perioperatively for 2 weeks. No abnormal hemorrhage was noted. An algorithm for perioperative management of hemophilia B patient is discussed.

Selective coupling of prostaglandin E receptor EP3D to Gi and Gs through interaction of alpha-carboxylic acid of agonist and arginine residue of seventh transmembrane domain

Prostaglandin (PG) E receptor EP3D is coupled to both Gi and Gs. To examine the roles of the interaction of alpha-carboxylic acid of PGE2 and its putative binding site, the arginine residue in the seventh transmembrane domain of EP3D, in receptor-G protein coupling, we have mutated the arginine residue to the noncharged glutamine. PGE2 with a negatively charged alpha-carboxylic acid and sulprostone, an EP3 agonist with a noncharged modified alpha-carboxylic acid, inhibited the forskolin-stimulated adenylate cyclase activity via Gi activation in the EP3D receptor in the same concentration-dependent manner. In contrast, the adenylate cyclase stimulation via Gs activation by sulprostone was much lower than that by PGE2. On the other hand, both PGE2 and sulprostone showed potent Gi activity but failed to show Gs activity in the mutant receptor. EP3D receptor showed a high affinity binding for PGE2 in the form coupled to either Gi or Gs. Although the mutant receptor showed high affinity binding when coupled to Gi, it lost high affinity binding in the condition of Gs coupling. Furthermore, sulprostone bound to the Gi-coupled EP3D receptor with higher affinity than the Gs-coupled receptor. Among various EP3 agonists, alpha-carboxylic acid-unmodified agonists showed both Gi and Gs activities, but the modified agonists showed only Gi activity. These findings suggest that the interaction between the alpha-carboxylic acid of PGE2 and the arginine residue of the receptor regulates the selectivity of the G protein coupling.

Characterization of neutral glycosphingolipids in rat lens

Neutral glycosphingolipids were purified from non-cataractous lenses of Sprague-Dawley rats by a combination of solvent extraction, Folch's partition, and column chromatography using DEAE-Sephadex and Iatrobeads. Six major GSLs from monohexosylceramide to pentahexosylceramide were identified by sugar composition analysis, methylation analysis and glycosidase digestion. Structural relationships among the six neutral glycosphingolipids revealed metabolic pathways leading to the synthesis of Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1 ceramide (IV3Gal alpha nLc4), instead of a Lewis(x) glycolipid (Gal beta 1- 4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1 ceramide, III3FucnLc4), from neolactotetraosylceramide (nLc4), together with isoglobotriaosylceramide (iGb3). The alpha-galactosyl epitope, Gal alpha 1-3Gal-R, is evolutionarily conserved in many types of cells of non-primate mammals, prosimians and New World monkeys, but not in those of Old World monkeys or humans. This evolution-related difference in carbohydrate epitopes suggests different cell-to-cell attachments, which may be mediated through cell surface glycosphingolipids, between rat and human lenses.

Mouse prostaglandin E receptor EP3 subtype mediates calcium signals via Gi in cDNA-transfected Chinese hamster ovary cells

We recently cloned the mouse prostaglandin (PG) E receptor EP3 subtype that is coupled to adenylate cyclase inhibition through Gi and identified three isoforms which are produced through alternative splicing. In Chinese hamster ovary cells expressing each EP3 isoform, PGE2 induced an immediate increase in the intracellular Ca2+ concentration ([Ca2+]i) due to both Ca2+ mobilization from internal stores and influx from the extracellular medium. This increase was abolished by prior treatment with pertussis toxin (PT). PGE2 also stimulated an accumulation of inositol trisphosphate (IP3) in a PT-sensitive manner. Both the PGE2-induced increase in [Ca2+]i and accumulation of IP3 were blocked by the phospholipase C inhibitor U-73122. Thus, EP3 is linked to phospholipase C activation via Gi, and this activation leads to Ca2+ mobilization from internal stores and influx from the extracellular medium.

[Long-term results and complications of intravesical instillation of bacillus Calmette-Guerin for prophylaxis of bladder cancer recurrence]

Since 1982, we treated 22 patients with superficial bladder cancer via intravesical bacillus Calmette-Guerin (Tokyo 172 strain) for prophylaxis against tumor recurrence. To determine the long-term efficacy and complications of BCG therapy, retrospective analysis was performed. The BCG therapy was initiated one to two weeks after complete transurethral resection of visible tumors. One hundred twenty mg or 80 mg of BCG suspended in 40 ml of 0.9% NaCl solution was instilled into the bladder once a week for 6 times, then monthly for 10 times. Of 22 patients, 10 tumor recurrences were recognized in 4 patients (mean followup 74 months). Recurrent free rate at 5 years was 78.5%. Common side effects were low grade fever and bladder irritability. Although these side effects were self-limiting, 15 patients (68%) refused instillation of BCG before completion of our protocol because of the bladder irritation. No relationship was observed between total dose of BCG instilled and tumor recurrence. Severe side effects such as permanent structural or functional alterations of the bladder or mycobacterial infection of other organs were not observed. Intravesical administration of Tokyo 172 strain of BCG seemed to be safe and useful for long-term prophylaxis of superficial bladder cancer recurrence.

The C-terminus of the prostaglandin-E-receptor EP3 subtype is essential for activation of GTP-binding protein

Three isoforms of the mouse prostaglandin-E-receptor EP3 subtype (EP3), EP3 alpha, EP3 beta and EP3 gamma, with different C-termini, which are produced through alternative splicing, showed different efficiencies with respect to heterotrimeric GTP-binding protein activation and adenylate cyclase inhibition [Sugimoto, Y., Negishi, M., Hayashi, Y., Namba, T., Honda, A., Watabe, A., Hirata, M., Narumiya, S. & Ichikawa, A. (1993) J. Biol. Chem. 268, 2712-2718; Irie, A., Sugimoto, Y., Namba, T., Harazono, A., Honda, A., Watabe, A., Negishi, M., Narumiya, S. & Ichikawa, A. (1993) Eur. J. Biochem. 217, 313-318]. To assess the role of the C-terminus in GTP-binding protein coupling, we truncated the C-terminus of EP3 at an alternative splicing site and expressed the mutant receptor. The truncated receptor retained the ability to physically associate with Gi2, forming an agonist/receptor/Gi2 ternary complex, and to undergo the characteristic conversion of its agonist-binding affinity, mediated by a guanine nucleotide from a low-affinity state to a high-affinity state. However, sulprostone, an EP3 agonist, failed not only to inhibit the forskolin-induced cAMP accumulation in the mutant receptor-expressing cells but also to stimulate the GTPase activity in the mutant receptor-expressing cell membrane. These results indicated that the C-terminus of EP3 is essential for the activation of GTP-binding protein.

Cloning and expression of a cDNA for the human prostacyclin receptor

A functional cDNA for the human prostacyclin receptor was isolated from a cDNA library of CMK cells, a human megakaryocytic leukaemia cell line. The cDNA encodes a protein consisting of 386 amino acid residues with seven putative transmembrane domains and a deduced molecular weight of 40,956. [3H]Iloprost specifically bound to the membrane of CHO cells stably expressing the cDNA with a Kd of 3.3 nM. This binding was displaced by unlabelled prostanoids in the order of iloprost = cicaprost >> carbacyclin > prostaglandin E1 (PGE1) > STA2. PGE2, PGD2 and PGF 2 alpha did not inhibit it. Iloprost in a concentration-dependent manner increased the cAMP level and generated inositol trisphosphate in these cells, indicating that this human receptor can couple to multiple signal transduction pathways.

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.

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.

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.

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.

[Leiomyosarcoma of ileocecal mesentery--a case report]

We report a case of leiomyosarcoma whose origin was near the root of ileocecal mesentery and extended into the retroperitoneum. Preoperative imaging examination, including CT, MRI and angiography clearly displayed its origin and retroperitoneal extension. These results contributed to treatment planning.

[Prevalence of anti C100-3 and HBsAg in blood donors--comparative study of total collected blood units, total collection adjusted to exclude repeat blood donations, and in first time blood donors]

Prevalence of anti C100-3 and HBsAg in donor blood collected at the Hiroshima Red Cross Blood Center during the period of Aug., 1990 to July, 1991 was studied in three groups--total received blood units (187,532 units) without any adjustment, blood units after adjustment by excluding repeat donations of blood units by the same donors (142,160 units), and blood units of first time donors (28,596 units). The results of the study is summarized as follows. 1) There was no significant difference in the prevalence of anti C100-3 between the group comprising the total collected units, and the group after the adjustment. This result suggests that repeat donors do not necessarily belong to any fixed age group. 2) The prevalence of HBsAg is significantly higher in the first time donor group than in the other two groups. In both the total blood units group and the group after the adjustment, prevalence of HBsAg among older age groups was as low as that of younger age groups. This is presumably because of the introduction of selective exclusion of HBsAg positive subjects from donors since 1980. When data from blood donors are used for the epidemiological studies of viral infection among healthy subjects, it is important to know the characteristics of such donor subjects and whether or not they are pre-screened for the viral markers in question.

Characterization of neutral glycosphingolipids in human cataractous lens

Neutral glycosphingolipids were purified from human senile cataractous lenses by a combination of solvent extraction, Folch's partition, acetylation, and column chromatography using DEAE-Sephadex and Iatrobeads. Six major glycosphingolipids (A-F) from monohexosylceramide to pentahexosylceramide were identified by sugar composition analysis, methylation analysis, secondary ion-mass spectrometry, glycosidase digestion, and chromium trioxide oxidation. Their structures suggested that they were closely related in their metabolism: their sugar chains were in sequence and their ceramide moieties were similarly composed, namely C16:0 and C24:1 constituted most of the fatty acids, and long-chain base components were mostly C18-dihydrosphingosine with a small portion of C18-sphingosine. The sugar chains implied two pathways branching from lactosylceramide: one to globotriaosylceramide and the other to lactotriaosylceramide, which leads to the production of Le(x) glycolipid via neolacto type 2 core chain.

Two isoforms of prostaglandin E receptor EP3 subtype. Different COOH-terminal domains determine sensitivity to agonist-induced desensitization

We recently identified two isoforms of mouse prostaglandin (PG) E receptor EP3 subtype, EP3 alpha and EP 3 beta, which are produced by alternative splicing and different only in the carboxyl-terminal domain (Sugimoto, Y., Negishi, M., Hayashi, Y., Namba, Y., T., Honda, A., Watabe, A., Hirata, M., Narumiya, S., and Ichikawa, A. (1993) J. Biol. Chem. 268, 2712-2718). We examined here agonist-induced desensitization of the two isoforms using Chinese hamster ovary cells stably expressing these isoforms. Exposure of the EP3 alpha isoform to PGE2 for 30 min did not change maximal response but increased PGE2 concentration needed to inhibit forskolin-induced cAMP accumulation in the cells. Further exposure of this isoform to PGE2 suppressed the maximal response as well as sensitivity to PGE2 in a time-dependent manner; after 24-h exposure, it elicited only 50% of the maximal response of the control cells. Consistent with these results, short term exposure sequestered the EP3 alpha isoform away from the cell surface and long term incubation decreased the total receptor number in the cells. In contrast, exposure of the EP3 beta isoform to PGE2 did not affect its dose-response curve for PGE2, and no sequestration or decrease in the receptor number was observed in this isoform. Thus, alternative splicing produced the two isoforms with different carboxyl-terminal domains, which are different in sensitivity to agonist-induced desensitization.

Cloning and expression of a cDNA for mouse prostaglandin E receptor EP2 subtype

A functional cDNA clone encoding mouse EP2 subtype of prostaglandin (PG) E receptor was isolated from a mouse cDNA library by cross-hybridization with the mouse EP3 subtype PGE receptor cDNA. The mouse EP2 receptor consists of 513 amino acid residues with putative seven-transmembrane domains. In contrast to EP3 receptor, this receptor possesses long third intracellular loop and carboxyl-terminal tail. [3H] PGE2 specifically bound to the membrane of mammalian COS cells transfected with the cDNA. The binding to the membrane was displaced with unlabeled PG in the order of PGE2 = PGE1 >> iloprost > or = PGF2 alpha > or = PGD2. The binding was also inhibited by misoprostol, an EP2 and EP3 agonist, but not by sulprostone, an EP1 and EP3 agonist, and SC-19220, an EP1 antagonist. PGE2 markedly increased cAMP level in COS cells transfected with the cDNA. These results suggest that this receptor is EP2 subtype. Northern blot analysis demonstrated that the EP2 mRNA is widely expressed in various tissues, the abundant expression being observed in ileum, thymus, and mastocytoma P-815 cells.

Glycyrrhetinic acid bound to 11 beta-hydroxysteroid dehydrogenase in rat liver microsomes

A binding protein which exhibits high affinity to [3H]glycyrrhetinic-acid in the rat liver microsomal fraction was solubilized with 0.2% Triton DF-18 and then purified to homogeneity. The equilibrium dissociation constant of the [3H]glycyrrhetinic-acid binding reaction and the maximal concentration for the binding of the purified protein, as determined by Scatchard plot analysis, were 27.6 nM and 7.79 nmol/mg protein, respectively. The molecular mass of the subunit (34 kDa) and 30 amino acids of N-terminal sequence of the purified protein were entirely the same as those of the reported 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). In each purification step, the recovery and purification (fold) of the glycyrrhetinic-acid binding activity corresponded to the values of 11 beta-HSD activity. These results show that the purified [3H]glycyrrhetinic-acid binding protein is 11 beta-HSD. From the molecular mass of 11 beta-HSD (135 kDa) and the maximal concentration of the binding site, it was calculated that one glycyrrhetinic acid molecule binds to one 11 beta-HSD molecule. The inhibitory effects of various glycyrrhetinic-acid derivatives on [3H]glycyrrhetinic acid binding and 11 beta-HSD activity indicate that the C30-carboxyl and C11-carbonyl groups of glycyrrhetinic acid are the principal structures for the 11 beta-HSD inhibition.

A novel difucosylated neutral glycosphingolipid from the eggs of the sea urchin, Hemicentrotus pulcherrimus: I. Purification and structural determination of the glycolipid

A novel fucose-containing neutral glycosphingolipid (GL-5) was purified from the eggs of the sea urchin, Hemicentrotus pulcherrimus. The chemical structure was determined to be Fuc alpha 1-3GalNAc beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-4Glc beta 1-1Cer by methylation analysis, partial acid hydrolysis, fast atom bombardment mass spectrometry, and proton nuclear magnetic resonance spectroscopy. The unique characteristics of GL-5 are that: the reducing terminal disaccharide portion is not Gal beta 1-4Glc but GlcNAc beta 1-4Glc; it includes a GalNAc beta 1-4GlcNAc sequence and a Fuc-GalNAc linkage; the defucosylated core is a novel trisaccharide chain; and the sugar structure is one of the smallest ever characterized for a difucosylated glycolipid. The major fatty acids were 22:1 and 22h:1, and about 30% of the total acids was 2-hydroxylated. All the long-chain bases were phytosphingosines, of which about 90% was n-t18:0. The similarity of the ceramide moiety to that of glucosylceramide from the same eggs [Kubo, H. et al. (1992) J. Biochem. 111, 726-731] suggests a close biosynthetic relationship between GL-5 and the glucosylceramide.