Failure of parturition in mice lacking the prostaglandin F receptor

Mice lacking the gene encoding the receptor for prostaglandin F2alpha (FP) developed normally but were unable to deliver normal fetuses at term. Although these FP-deficient mice showed no abnormality in the estrous cycle, ovulation, fertilization, or implantation, they did not respond to exogenous oxytocin because of the lack of induction of oxytocin receptor (a proposed triggering event in parturition), and they did not show the normal decline of serum progesterone concentrations that precedes parturition. Ovariectomy at day 19 of pregnancy restored induction of the oxytocin receptor and permitted successful delivery in the FP-deficient mice. These results indicate that parturition is initiated when prostaglandin F2alpha interacts with FP in ovarian luteal cells of the pregnant mice to induce luteolysis.

Characterization of functional interaction of carboxylic acid group of agonists and arginine of the seventh transmembrane domains of four prostaglandin E receptor subtypes

Prostaglandin (PG) E2 binds to four PGE receptor subtypes, EP1, EP2, EP3 and EP4, and induces a variety of functions through the interaction of carboxylic acid of PGE2 and Arg residue in the seventh transmembrane domain of the receptor. To assess the role of the interaction of the carboxylic acid group of agonists and the Arg residue, which can form both ionic bonding and hydrogen bonding as a hydrogen donor, we examined the agonist activities of three types of agonist, PGE2 with a negatively charged carboxylic acid, PGE2 methylester, which is a hydrogen acceptor, and 1-OH PGE2, which can accept as well as donate hydrogen but prefers to donate hydrogen rather than accept it, for four PGE receptor subtypes. Although PGE2 methylester had slightly lower agonist activities than PGE2 for EP1 and EP4 receptors, PGE2 and its methylester showed the same agonist activities for EP2 and EP3 receptors, indicating that PGE2 methylester is a potent agonist for all of the four subtypes. In contrast, 1-OH PGE2 was a very weak agonist for all receptors. These findings demonstrate that the hydrogen bonding interaction of agonists and the Arg residue is generally sufficient for the functional activation of all of the PGE receptor subtypes.

Immunosuppressive drugs inhibit the production of interleukin-6 and interleukin-8 in cultured cardiac myxoma cells

Cardiac myxoma cells produce large amounts of interleukin (IL)-6 and IL-8. To determine whether immunosuppressive agents could be used to treat cardiac myxoma, we tested the effects of dexamethasone and three of the newer second-generation immunosuppressive drugs, cyclosporin A, tacrolimus, and deoxyspergualin, on the production of IL-6 and IL-8 in these cells. Cultured cardiac myxoma cells were used as in vitro model of cardiac myxoma. Cells were tested for 24 hours with 10(-7) M dexamethasone, 10(-6) M cyclosporin A, 10(-8) M tacrolimus, and 10(-6) M 15-deoxyspergualin, with aliquots of conditioned medium being assayed for cytokine levels at 0, 6, 12, and 24 hours. Cardiac myxoma cells isolated from 4 patients all produced quantities of IL-6 and IL-8. The concentrations of IL-6 in the medium after 7 days in culture ranged from 79,000 to 2,740,000 pg/ml, and the concentrations of IL-8 ranged from 40,000 to 1,000,000 pg/ml. Exposure of cyclosporin A and dexamethasone almost completely inhibited the production of IL-6 and IL-8 after 24 hours of treatment. Tacrolimus inhibited the production of both cytokines by 55%, while 15-deoxyspergualin reduced IL-6 levels by 24% and IL-8 levels by 48% after separate 24 hour treatments. These results suggest that these newer immunosuppressive agents may be useful in reducing the production of IL-6 and IL-8 in patients with cardiac myxoma.

Transcriptional regulation by HNF-4 of the steroid 15alpha-hydroxylase P450 (Cyp2a-4) gene in mouse liver

The mouse P450 gene Cyp2a-4 encodes the hepatic steroid 15apha-hydroxylase. We have defined in the 5'-flanking sequence of Cyp2a-4 gene, a composite regulatory element (-61AGACCAAAGTCCGGCCTTC-42) which contains a potential CpG methylation site at position -50. Gel-shift assays indicate that this element consists of overlapped binding sites for a hepatocyte-enriched transcription factor HNF-4 and a Sp1-like protein. Moreover, transcription of the Cyp2a-4 gene is activated by coexpression of HNF-4 in HepG2 cells. A mutation (C at -50 to A) abolishes the binding of HNF-4 to the element as well as the transcriptional activation by HNF-4. The methylated C at position -50, however, does not affect HNF-4 binding. Neither the mutation nor the methylation at position -50 affect the binding of Sp1-like protein to the element. It appears, therefore, that HNF-4 activates the hepatic transcription of Cyp2a-4 gene through its direct binding to the regulatory element regardless of the methylation at position -50.

Characterization of a phenobarbital-responsive enhancer module in mouse P450 Cyp2b10 gene

Induction of drug- and carcinogen-metabolizing cytochrome P450s by xenobiotic chemicals is a common cellular defense mechanism, usually leading to increased detoxification of xenobiotics but sometimes, paradoxically, to formation of more toxic and carcinogenic metabolites. Phenobarbital (PB) is an archetypal representative for chemicals including industrial solvents, pesticides, plant products, and clinically used drugs that induce several genes within CYP subfamilies 2B, 2A, 2C, and 3A in rodents and humans. Although the transcription of these CYP genes is activated by PB, the associated molecular mechanisms have not yet been elucidated. Here we have analyzed, in detail, enhancer activity of a far upstream region of mouse Cyp2b10 gene and report a 132-base pair PB-responsive enhancer module (PBREM) with a 33-base pair core element containing binding sites for nuclear factor I- and nuclear receptor-like factors. Mutations of these binding sites abolish the ability of PBREM to respond to inducers in mouse primary hepatocytes.

Two isoforms of prostaglandin EP3 receptor exhibiting constitutive activity and agonist-dependent activity in Rho-mediated stress fiber formation

We have cloned two isoforms of the mouse prostaglandin E receptor EP3 subtype, EP3alpha and EP3beta, with different carboxyl-terminal tails, produced through alternative splicing. To determine the functional differences between the two isoforms, we examined the role of the isoforms in regulation of the actin cytoskeleton using Mardin-Darby canine kidney cells expressing these isoforms. The EP3alpha isoform constitutively induced stress fiber formation, independent of an agonist, while the EP3beta isoform agonist-dependently induced stress fiber formation. Pertussis toxin did not prevent stress fiber formation. This signaling pathway is mediated by Rho, because C3 transferase microinjection inhibited stress fiber formation. Therefore, the physiological significance of these isoforms of the EP3 receptor may lie in their different agonist dependency in Rho-mediated stress fiber formation via a pertussis toxin-insensitive G protein.

Reciprocal size-effect relationship of the key residues in determining regio- and stereospecificities of DHEA hydroxylase activity in P450 2a5

Collectively, the P450 2a4/2a5 system hyrdoxylates DHEA in at least three positions (7alpha, 7beta, and 2alpha). An individual P450, however, exhibits high specificity to one of these products. Using site-directed mutagenesis of mP450 2a5 from the wild mouse Mus minutoides and bacterial expression, we have associated the function of residues 117, 209, and 481 with the respective specificity observed in each P450. Ala at position 117 determines the 7beta-hydroxylase activity, whereas Val at this position defines the 2alpha-hydroxylase activity. Leu at position 209 is essential for high DHEA 7alpha-hydroxylase activity. The substitutions of residue 481 with various hydrophobic amino acids elicited a profound alteration of the specific hydroxylation rates, but did not influence the regio- and stereospecificities at either of the three positions of DHEA. The alterations caused by residue 481 also depended on the residue identity at position 117 or 209. The results indicate that the sizes of several key residues obey a concerted reciprocal relationship whereby the substrate pocket of the P450s adjusts to accommodate DHEA. A limited molecular modeling study successfully correlates DHEA binding to experimental DHEA hydroxylase activities for a series of mutants at key positions.

Avoidance coping behaviors and low social support are related to depressive symptoms in HIV-positive patients in Japan

The authors examined the influences of several psychosocial factors (i.e., coping behavior responses, social support, etc.) on mood states in 47 human immunodeficiency virus (HIV)-positive patients without the acquired immunodeficiency syndrome (AIDS). No patients fulfilled the DSM-III-R diagnostic criteria for mood disorders, including major depression. However, the HIV group indicate significantly stronger depressive symptoms and lower social support than the healthy control group. The strength of depressive symptoms and poor social support were significantly correlated with one another. Although the HIV group indicated significantly stronger active coping behaviors than the healthy control group, depressive symptoms were significantly and positively correlated with avoidance coping behaviors. When existence of social support was controlled for, this significant correlation was not noted, indicating that avoidance coping behaviors are independently and significantly related to depressive symptoms. The results suggest that, although depressive symptoms are not strong enough to warrant a psychiatric diagnosis of mood disorders, including major depression, avoidance coping behaviors and poor existence of social support may be a high-risk combination for the manifestation of depressive symptoms in HIV-positive patients without AIDS in Japan.

Functional interaction of the carboxylic acid group of agonists and the arginine residue of the seventh transmembrane domain of prostaglandin E receptor EP3 subtype

Prostaglandin (PG) E2 binds to PGE receptor EP3 subtype and induces Gi activity. To assess the role of the interaction of the carboxylic acid group of agonists and its putative binding site, Arg-309 in the seventh transmembrane domain of EP3alpha receptor, in receptor activation, we have mutated the positively charged Arg-309 to the polar but uncharged Gln (EP3alpha-R309Q) and Asn (EP3alpha-R309N), and to the non-polar Leu (EP3alpha-R309L). Wild-type, EP3alpha-R309Q and EP3alpha-R309N receptors showed high-affinity binding for PGE2, but the EP3alpha-R309L receptor showed very-low-affinity binding. Guanosine 5'-[gamma-thio]triphosphate increased the PGE2 binding to the wild-type receptor, decreased the binding to EP3alpha-R309Q and EP3alpha-R309N receptors, but did not affect that to the EP3alpha-R309L receptor. Furthermore we examined the Gi activities of two types of EP3 agonist, TEI-3356 with a negatively charged carboxylic acid, and TEI-4343, a methyl ester of TEI-3356 with an uncharged but polar group, towards those receptors. Both agonists inhibited the forskolin-stimulated cAMP formation in wild-type, EP3alpha-R309Q and EP3alpha-R309N receptors in the same concentration-dependent manner, but the agonists showed a very low inhibition of EP3alpha-R309L receptor. These findings demonstrate that the hydrogen-bonding interaction of EP3 agonists and residue 309 in the seventh transmembrane domain of the EP3alpha receptor is sufficient for the functional activation of the EP3alpha receptor.

Distribution of prostaglandin E receptors in the rat gastrointestinal tract

AIMS

In order to study the role of prostaglandin in the regulation of the gastrointestinal functions, gene expression of prostaglandin receptors along the rat gastrointestinal tracts were investigated.

METHODS

Rats were used for the study. The combination of counterflow elutriation separation of mucosal cells and Northern blot analysis was used to detect the gene expression of prostaglandin receptors in gastrointestinal tracts.

RESULTS

In small intestine and colon, prostaglandin E2 EP1 and EP3 receptor mRNAs were mainly localized in the deeper intestinal wall containing muscle layers. EP4 receptor gene expression, on the other hand, was detected in the intestinal mucosal layer. In the stomach, EP1 mRNA was detected in gastric muscle layers, whereas EP3 and EP4 receptor gene expression was mainly present in the gastric mucosal layer containing epithelial cells. In gastric epithelial cells, parietal cells were found to have both EP3 and EP4 receptors. At lower concentrations, prostaglandin E2 inhibited gastric acid secretion by parietal cells probably through EP4 receptors. At higher concentrations, however, it stimulated it. On the other hand, mucous cells possessed only EP4 receptor mRNA.

CONCLUSIONS

Thus, it is suggested that prostaglandin E2 modulates gastrointestinal functions through at least three different prostaglandin receptors (EP1, EP3, and EP4), each of which has a distinct contribution in the gastrointestinal tract.

Cellular localization of mRNAs for prostaglandin E receptor subtypes in mouse gastrointestinal tract

Regional and cellular distribution of mRNAs for prostaglandin E (PGE) receptor subtypes was investigated in the mouse gastrointestinal tract by in situ hybridization. Strong signals for EP1 transcripts were detected in cells of the muscularis mucosae layer, especially in the body of the stomach. Intense signals for EP3 transcripts were detected in neurons of the myenteric ganglia throughout the tract. Moderate EP3 mRNA expression was also observed in fundic gland epithelial cells, except for surface mucous cells in the stomach. Expression of EP4 mRNA was moderate in surface epithelial cells of the corpus and in glands from the surface to the base of the antrum. Strong EP4 signals were observed in the epithelium in the duodenum, jejunum, and ileum. In the ileum, signals were only observed in the upper part of the villi. However, no or weak signals for EP2 transcripts were detected. These findings suggest that PGE2 modulates various gastric or intestinal functions via at least three different PGE receptors.

7,7-Difluoroprostacyclin derivative, AFP-07, a highly selective and potent agonist for the prostacyclin receptor

Recently, we cloned cDNAs for the prostacyclin receptor (IP) and the four mouse PGE receptor subtypes, EP1, EP2, EP3, and EP4, and established Chinese hamster ovary cells that stably express each receptor. We examined the agonist potency and selectivity of AFP-07, a 7,7-difluoroprostacyclin derivative, compared with widely used stable prostacyclin analogue, iloprost, using the cells expressing each cloned receptor. AFP-07 strongly displaced the [3H] iloprost binding to the IP receptor-expressing cell membranes, the half maximal concentration for the displacement being 3 nM, which was one order lower than that of iloprost. AFP-07 concentration-dependently stimulated cAMP formation in the IP-expressing cells, the half-maximal concentration for the stimulation being 10 pM, which was one order lower than that of iloprost. On the other hand, AFP-07 showed lower affinity for EP1, EP2, EP3, and EP4 than PGE2, but iloprost had the same affinity as PGE2 for the EP1, These results demonstrate that AFP-07 is a potent and highly selective agonist for the IP receptor.

Liaison psychiatry and HIV infection (I): Avoidance coping responses associated with depressive symptoms accompanying somatic complaints

We examined the relationship of somatic complaints to coping behaviors and mood states among 50 HIV-positive patients without AIDS. Although no patients fulfilled the DSM-III-R criteria for mood disorders including major depression, scores for depressive symptoms were significantly higher in the HIV-positive patients than in healthy persons. Although depressive symptoms in HIV patients may not be strong enough to warrant a psychiatric diagnosis of mood disorders, these patients may be prone to depressive symptoms. The HIV patients indicated a tendency toward somatic complaints more frequently than their healthy counterparts. The scores for depressive symptoms were significantly and positively correlated with scores for avoidance coping responses. The presence or absence of six complaints (i.e., general fatigue, abdominal distress, chest pain or discomfort, and numbness or chills) could be discriminated based on the score of avoidance coping responses. The results of this study suggest that avoidance coping responses associated with depressive symptoms accompany several somatic complaints in HIV patients without AIDS.

Liaison psychiatry and HIV infection (II): Application of relaxation in HIV positive patients

We examined the efficacy of relaxation techniques in a sample of HIV patients without AIDS in the early stages after infection, by comparing the three groups: relaxation group (progressive muscle relaxation and modified autogenic training); ordinary supportive psychotherapy group, and finally no psychiatric treatment group. Scores for anxiety, fatigue, depression and confusion, as measured by the profile of mood states (POMS), were significantly lower after relaxation than before. There were no significant differences in the POMS scores (except for anger) among the three groups. These two results suggest that a combination of progressive muscle relaxation and modified autogenic training is a useful method, which can be easily employed in HIV patients without AIDS.

Association of expression of mRNA encoding the PGF2 alpha receptor with luteal cell apoptosis in ovaries of pseudopregnant mice

The relationship between the expression of mRNA encoding the prostaglandin F2 alpha (PGF2 alpha) receptor and luteal cell apoptosis as determined by oligonucleosome formation was determined in mouse corpora lutea on days 2 (early phase), 6 (mid-phase), and 11 and 13 (late phase) of pseudopregnancy. No signals for mRNA encoding the PGF2 alpha receptor were detected in the ovary as shown by RNA blot analysis of pregnant mares' serum gonadotrophin (PMSG)-treated mice. The expression of the mRNA that could be detected in the corpora lutea on day 2 after hCG treatment was low, but it was increased on day 6 and reached a plateau on days 11 and 13. On days 11 and 13, in situ hybridization signals for mRNA encoding the PGF2 alpha receptor were localized to large luteal cells of the corpora lutea, especially the cells in the superficial layer. However, ethidium bromide staining revealed marked oligonucleosome formation in the corpora lutea on days 11 and 13. Similarly, positive signals of in situ nick-DNA-end labelling were also detected in the corpora lutea on days 11 and 13. Analysis of the adjacent sections of the corpora lutea on day 13 showed that both signals for DNA strand breaks and mRNA encoding the PGF2 alpha receptor were co-expressed in the corpus luteum. These results suggest that apoptosis during structural luteolysis closely associates with the increased expression of mRNA encoding the PGF2 alpha receptor in luteal cells of pseudopregnant mice.

'Distinct cellular localization' of the messenger ribonucleic acid for prostaglandin E receptor subtypes in the mouse uterus during pseudopregnancy

As an initial step to clarify the mechanisms of various uterine actions of PGE2, expression patterns of the messenger RNAs (mRNAs) for four subtypes of PGE receptors, EP1, EP2, EP3, and EP4, were investigated in the mouse uterus during pseudopregnancy. Relative expression levels were investigated by Northern blot analysis of mRNA levels in uteri obtained on days 0, 1, 3, 5, 7, and 9 of pseudopregnancy (day 0 = 48 h after PMSG injection), and cellular localization was determined by in situ hybridization in uteri obtained on days 0 and 5. EP2 mRNA was specifically expressed on day 5, and its expression was confined to the luminal epithelium. On the other hand, the level of the EP3 mRNA expression progressively increased until day 5. Cell populations expressing the EP3 mRNA were confined to the longitudinal smooth muscle on day 0, but they changed to the circular smooth muscle on day 5. The expression level of EP4 mRNA was low on days 0 and 1, but it became high on days 3 and 5. On day 0, EP4 mRNA was localized to the luminal epithelium. On day 5, diffuse, but significant, EP4 expression was observed over the endometrial stroma and epithelium. No EP1 mRNA signals were observed. Transient expression of EP2 on day 5 of pseudopregnancy in the luminal epithelium suggests its involvement in blastocyst implantation signaling. EP4 in the endometrial stroma is suggested to be involved in decidual transformation of the stromal cells, whereas EP3 in the myometrium is believed to be involved in regulation of myometrial activity.

Interaction of aflatoxin B1 with cytochrome P450 2A5 and its mutants: correlation with metabolic activation and toxicity

Among members of the mouse cytochrome P450 2A family, P450 2A5 is the best catalyst of aflatoxin B1 (AFB1) oxidation to its 8,9-epoxide (Pelkonen, P., Lang, M., Wild, C. P., Negishi, M., and Juvonen, R. O. (1994) Eur. J. Pharmacol., Environ. Toxicol. Pharmacol. Sect. 292, 67-73). Here we studied the role of amino acid residues 209 and 365 of the P450 2A5 in the metabolism and toxicity of AFB1 using recombinant yeasts. The two sites have previously been shown to be essential in the interaction of coumarin and steroids with the P450 2A5. Reducing the size of the amino acid at position 209 or introducing a negatively charged residue at this site increased the 8,9-epoxidation of AFB1 compared to the wild type. In addition, replacing the hydrophobic amino acid at the 365 position with a positively charged lysine residue strongly decreased the metabolism of AFB1. These mutations changed the KM values generally less than the Vmax values. The changes in AFB1 metabolism contrast with the changes in coumarin 7-hydroxylation caused by these amino acid substitutions, since reducing the size of the 209 residue strongly reduced coumarin metabolism and increased the K(M) values. On the other hand, the results with AFB1 are similar to those obtained with steroid hydroxylation. This suggests that the size of the substrate is important when interacting with the residue 209 of the protein. The catalytic parameters of AFB1 correlated generally with its toxicity to the recombinant yeasts expressing the activating enzyme and with the binding of AFB1 to yeast DNA. Furthermore high affinity substrates and inhibitors (e.g., methoxsalen, metyrapone, coumarin 311, 7-methylcoumarin, coumarin, and pilocarpine) of P450 2A5 could efficiently block the toxicity of AFB1. It is suggested that the recombinant yeasts expressing engineered P450 enzymes are a useful model to understand the substrate protein interactions, to study the relationship of metabolic parameters to toxicity, and to test potential inhibitors of metabolism based toxicity.

HIV/AIDS care at Tokyo Metropolitan Komagome Hospital

The mission of the Tokyo Metropolitan Komagome Hospital is to build a comprehensive system to provide treatment for people infected with HIV. It aims not only to provide HIV clinical care (medical and skilled nursing) but also to build psychological and social support systems for persons with HIV/AIDS. It is also working to organize the medical care system's response to HIV and to help decrease misunderstanding, prejudice, and discrimination against persons with HIV infection.

Prostaglandin E receptor EP3 subtype induces neurite retraction via small GTPase Rho

Prostaglandin E receptor EP3 subtype is widely distributed in the nervous system and is specifically localized to neurons, suggesting that the EP3 receptor plays important roles in the nervous system. We established a PC12 cell line that stably expresses the EP3B receptor isoform isolated from bovine adrenal chromaffin cells and examined the effect of agonist stimulation on the neuronal morphology of the PC12 cells. In the differentiated cells, M&B28767, an EP3 agonist, caused neurite retraction in a pertussis toxin-insensitive manner. 12-O-Tetradecanoylphorbol-13-acetate (TPA) also induced neurite retraction. However, when protein kinase C was down-regulated by long term exposure to TPA, TPA failed to induce neurite retraction, while the EP3B receptor-mediated retraction occurred normally. Clostridium botulinum C3 exoenzyme completely inhibited both EP3 agonist- and TPA-induced neurite retraction when microinjected into the cells, indicating that the morphological effect of the EP3B receptor is dependent on Rho activity. Thus, the activation of the EP3B receptor induced neurite retraction through a protein kinase C-independent Rho-activation pathway.

A high frequency of defective vif genes in peripheral blood mononuclear cells from HIV type 1-infected individuals

We studied the heterogeneity and intactness of the vif gene in six HIV-1-infected individuals at various clinical stages. The proviral vif sequences in peripheral blood mononuclear cells were amplified by PCR, followed by cloning and sequencing of 45 vif clones. The intraindividual diversity of the vif genes ranged from 0.45 to 3.3% and was not correlated with disease stage. Although the vif gene has been shown to be essential for infection of HIV-1 in vitro, a high frequency (31%) of defective vif genes was observed. In one patient, six vif clones carried double nonsense mutations at the same positions, five of which were clustered in the phylogenetic tree, suggesting that these vif-defective viruses may have replicated in vivo. Phylogenetic analysis revealed that the vif sequences from each individual were clustered into a separate group and that all of them belong to subtype B.

Mouse decay-accelerating factor: selective and tissue-specific induction by estrogen of the gene encoding the glycosylphosphatidylinositol-anchored form

Neonatal exposure of mice to estrogen (diethylstilbestrol) results in a high incidence (90%) of uterine tumor later in life. In an effort to screen for estrogen-regulated genes in the uterus of the neonatal mouse, we have isolated a murine homologue of the human decay-accelerating factor (DAF), a glycosylphosphatidylinositol (GPI)-anchored membrane glycoprotein and a member of the regulators of complement activation family of proteins that function to prevent autologous complement-mediated tissue damage. The induced mouse DAF cDNA has a 64% sequence identity with the human counterpart at the nucleotide level and a 50% identity in the deduced amino acid sequence. It consists of 390 amino acids and contains four short consensus repeats of internal homology characteristic of human DAF. It also contains a hydrophobic C-terminal that most likely serves as a signal for GPI anchor attachment. Sequence comparison with the recently reported mouse DAF cDNAs confirmed that the estrogen-inducible gene corresponds to the mouse GPI DAF gene. The induction of mouse DAF by estrogen is tissue specific and can be mimicked by the antiestrogen tamoxifen. Furthermore, the regulation of uterine DAF expression by estrogen is limited to the GPI DAF gene. The transmembrane DAF gene is not expressed in the mouse uterus, either with or without estrogen stimulation. These results suggest that the two mouse DAF genes are differentially regulated, and that the GPI-anchored DAF may play important roles in estrogen responses and other physiologic or pathophysiologic processes of the female reproductive system.

Mouse decay-accelerating factor: selective and tissue-specific induction by estrogen of the gene encoding the glycosylphosphatidylinositol-anchored form

Neonatal exposure of mice to estrogen (diethylstilbestrol) results in a high incidence (90%) of uterine tumor later in life. In an effort to screen for estrogen-regulated genes in the uterus of the neonatal mouse, we have isolated a murine homologue of the human decay-accelerating factor (DAF), a glycosylphosphatidylinositol (GPI)-anchored membrane glycoprotein and a member of the regulators of complement activation family of proteins that function to prevent autologous complement-mediated tissue damage. The induced mouse DAF cDNA has a 64% sequence identity with the human counterpart at the nucleotide level and a 50% identity in the deduced amino acid sequence. It consists of 390 amino acids and contains four short consensus repeats of internal homology characteristic of human DAF. It also contains a hydrophobic C-terminal that most likely serves as a signal for GPI anchor attachment. Sequence comparison with the recently reported mouse DAF cDNAs confirmed that the estrogen-inducible gene corresponds to the mouse GPI DAF gene. The induction of mouse DAF by estrogen is tissue specific and can be mimicked by the antiestrogen tamoxifen. Furthermore, the regulation of uterine DAF expression by estrogen is limited to the GPI DAF gene. The transmembrane DAF gene is not expressed in the mouse uterus, either with or without estrogen stimulation. These results suggest that the two mouse DAF genes are differentially regulated, and that the GPI-anchored DAF may play important roles in estrogen responses and other physiologic or pathophysiologic processes of the female reproductive system.

Two Gs-coupled prostaglandin E receptor subtypes, EP2 and EP4, differ in desensitization and sensitivity to the metabolic inactivation of the agonist

There are at least four subtypes of prostaglandin E (PGE) receptors. The EP1 and EP3 receptors are coupled to Ca2+ mobilization and the inhibition of adenylate cyclase, respectively, and the EP2 and EP4 receptors are coupled to the same signal transduction pathway, stimulation of adenylate cyclase. To identify the functional differences between EP2 and EP4 receptors, we examined agonist-induced desensitization of these two receptors using Chinese hamster ovary cells, which stably express these receptors. The EP4 receptor underwent short term agonist-induced desensitization, but no such desensitization was observed for the EP2 receptor. In contrast, the EP2 and EP4 receptors displayed similar patterns of down-regulation in response to prolonged exposure to PGE2. On the other hand, PGE2 is rapidly metabolized to 15-keto-PGE2 and, subsequently, to 13,14-dihydro-15-keto-PGE2. Thus, we compared the sensitivities of the two receptors to these two metabolites. The EP4 receptor markedly lost the response at the first metabolism, whereas the EP2 receptor gradually lost the response according to the degree of metabolism, having higher sensitivity to the first metabolite, 15-keto-PGE2, than the EP4 receptor. Therefore, the physiological significance of EP2 and EP4 may lie in their different sensitivities to agonist-induced short term desensitization and their differential susceptibilities to the metabolic inactivation of the agonist.

Molecular aspects of the structures and functions of the prostaglandin E receptors

Prostaglandin (PG) E2 exerts a variety of biological activities for the maintenance of local homeostasis in the body. The effects of PGE2 are exerted by a variety of PGE receptors which are different in their signal transduction properties and are classified into four subtypes, EP1, EP2, EP3 and EP4. We have isolated the mouse cDNAs for these PGE receptors and characterized the cloned receptors. EP1, EP2, EP3 and EP4 receptors consist of 405, 362, 365 and 513 amino acid residues with a putative seven hydrophobic domains, respectively. When expressed in mammalian cells, EP1 showed elevation of intracellular [Ca2+], EP2 and EP4 stimulated adenylate cyclase and EP3 inhibited the enzyme. Northern blot and in situ hybridization analyses have shown that these subtypes are differently localized to specific tissues and cells. We have identified multiple isoforms of the EP3 receptor (EP3 alpha, EP3 beta, and EP3 gamma) which differ in their carboxy-terminal domains. These isoforms displayed identical agonist binding properties, but were functionally different in the efficiency of G protein activation, the specificity of G protein coupling, and sensitivity to agonist-induced desensitization. The diverse physiological actions of PGE2 are elicited by the molecular diversity of the receptor subtypes and isoforms distributed differently in the body.