Showing papers on "Receptor published in 1991"

Cloning of the gene for a human dopamine D4 receptor with high affinity for the antipsychotic clozapine.

Abstract: DOPAMINE receptors belong to the family of G protein-coupled receptors. On the basis of the homology between these receptors, three different dopamine receptors (D1,D2,D3) have been cloned1–7. Dopamine receptors are primary targets for drugs used in the treatment of psychomotor disorders such as Parkinson's disease and schizophrenia8,9. In the management of socially withdrawn and treatment-resistant schizophrenics, clozapine10 is one of the most favoured antipsychotics because it does not cause tardive dyskinesia11. Clozapine, however, has dissociation constants for binding to D2 and D3 that are 4 to 30 times the therapeutic free concentration of clozapine in plasma water12,13. This observation suggests the existence of other types of dopamine receptors which are more sensitive to clozapine. Here we report the cloning of a gene that encodes such a receptor (D4). The D4 receptor gene has high homology to the human dopamine D2 and D3 receptor genes. The pharmacological characteristics of this receptor resembles that of the D2 and D3 receptors, but its affinity for clozapine is one order of magnitude higher. Recognition and characterization of this clozapine neuroleptic site may prove useful in the design of new types of drugs.

Molecular cloning and characterization of the rat NMDA receptor

Abstract: A complementary DNA encoding the rat NMDA receptor has been cloned and characterized. The single protein encoded by the cDNA forms a receptor-channel complex that has electrophysiological and pharmacological properties characteristic of the NMDA receptor. This protein has a significant sequence similarity to the AMPA/kainate receptors and contains four putative transmembrane segments following a large extracellular domain. The NMDA receptor messenger RNA is expressed in neuronal cells throughout the brain regions, particularly in the hippocampus, cerebral cortex and cerebellum.

The role of the hippocampus in feedback regulation of the hypothalamic-pituitary-adrenocortical axis.

Abstract: There is considerable, although not entirely consistent, evidence that the hippocampus inhibits most aspects of HPA activity, including basal (circadian nadir) and circadian peak secretion as well as the onset and termination of responses to stress. Although much of the evidence for these effects rests only on the measurement of corticosteroids, recent lesion and implant studies indicate that the hippocampus regulates adrenocortical activity at the hypothalamic level, via the expression and secretion of ACTH secretagogues. Such inhibition results largely from the mediation of corticosteroid feedback, although more work is required to determine whether the hippocampus supplies a tonic inhibitory input in the absence of corticosteroids. It must be noted that the hippocampus is not the only feedback site in the adrenocortical system, since removal of its input only reduces, but does not abolish, the efficacy of corticosteroid inhibition, and since other elements of the axis appear eventually to compensate for deficits in feedback regulation. The importance of other feedback sites is further suggested not only by the presence of corticosteroid receptors in other parts of the brain and pituitary, but also by the improved prediction of CRF levels by combined hypothalamic and hippocampal receptor occupancy. The likelihood of feedback mediated by nonhippocampal sites underscores the need for future work to characterize hippocampal influence on HPA activity in the absence of changes in corticosteroid secretion. However, despite the fact that the hippocampus is not the only feedback site, it is distinguished from most potential feedback sites, including the hypothalamus and pituitary, by its high content of both type I and II corticosteroid receptors. The hippocampus is therefore capable of mediating inhibition over a wide range of steroid levels. The low end of this range is represented by corticosteroid inhibition of basal (circadian nadir) HPA activity. The apparent type I receptor specificity of this inhibition and the elevation of trough corticosteroid levels after hippocampal damage support a role for hippocampal type I receptors in regulating basal HPA activity. It is possible that basal activity is controlled in part through hippocampal inhibition of vasopressin, since the inhibition of portal blood vasopressin correlates with lower levels of hippocampal receptor occupancy, and the expression of vasopressin by some CRF neurons is sensitive to very low corticosteroid levels. At the high end of the physiological range, stress-induced or circadian peak corticosteroid secretion correlates strongly with occupancy of the lower affinity hippocampal type II receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

High-affinity NGF binding requires coexpression of the trk proto-oncogene and the low-affinity NGF receptor.

Abstract: Nerve growth factor (NGF) interacts with two different low-affinity receptors that can be distinguished by affinity crosslinking Reconstitution experiments by membrane fusion and transient transfection into heterologous cells indicate that high-affinity NGF binding requires coexpression and binding to both the low-affinity NGF receptor and the tyrosine kinase trk gene product These studies reveal a new growth factor receptor-mediated mechanism of cellular differentiation involving trk and the low-affinity NGF receptor

Isolation of a cDNA encoding the vascular type-1 angiotensin II receptor

Abstract: Angiotensin II is an important effector molecule controlling blood pressure and volume in the cardiovascular system. Its importance is manifested by the efficacy of angiotensin-converting enzyme inhibitors in the treatment of hypertension and congestive heart failure. Angiotensin II interacts with two pharmacologically distinct subtypes of cell-surface receptors, AT1 and AT2. AT1 receptors seem to mediate the major cardiovascular effects of angiotensin II. Here we report the isolation by expression cloning of a complementary DNA encoding a unique protein with the pharmacological specificity of a vascular AT1 receptor. Hydropathic modelling of the deduced protein suggests that it shares the seven-transmembrane-region motif with the G protein-coupled receptor superfamily. Knowledge of the AT1 receptor primary sequence should now permit structural analysis, definition of the angiotensin II receptor gene family and delineation of the contribution of AT receptors to the genetic component of hypertension.

Structure and functional expression of a human interleukin-8 receptor.

Abstract: Interleukin-8 (IL-8) is a member of a family of pro-inflammatory cytokines Although the best characterized activities of IL-8 include the chemoattraction and activation of neutrophils, other members of this family have a wide range of specific actions including the chemotaxis and activation of monocytes, the selective chemotaxis of memory T cells, the inhibition of hematopoietic stem cell proliferation, and the induction of neutrophil infiltration in vivo A complementary DNA encoding the IL-8 receptor from human neutrophils has now been isolated The amino acid sequence shows that the receptor is a member of the superfamily of receptors that couple to guanine nucleotide binding proteins (G proteins) The sequence is 29% identical to that of receptors for the other neutrophil chemoattractants, fMet-Leu-Phe and C5a Mammalian cells transfected with the IL-8 receptor cDNA clone bind IL-8 with high affinity and respond specifically to IL-8 by transiently mobilizing calcium The IL-8 receptor may be part of a subfamily of related G protein-coupled receptors that transduce signals for the IL-8 family of pro-inflammatory cytokines

Nuclear association of a T-cell transcription factor blocked by FK-506 and cyclosporin A.

Abstract: CYCLOSPORINA and FK506 inhibit T- and B-cell activation and other processes essential to an effective immune response1–3. In T lymphocytes these drugs disrupt an unknown step in the trans-mission of signals from the T-cell antigen receptor to cytokine genes that coordinate the immune response4–6. The putative intracellular receptors for FK506 and cyclosporin arecis-trans prolyl isomerases7–11. Binding of the drug inhibits isomerase activity8,10,11, but studies with other prolyl isomerase inhibitors12 and analysis of cyclosporin-resistant mutants in yeast suggest that the effects of the drug result from the formation of an inhibitory complex between the drug and isomerase13,14, and not from inhibi-tion of isomerase activity. A transcription factor, NF-AT, which is essential for early T-cell gene activation, seems to be a specific target of cyclosporin A and FK506 action because transcription directed by this protein is blocked in T cells treated with these drugs, with little or no effect on other transcription factors such as AP-1 and NF-κB (refs 15–17). Here we demonstrate that NF-AT is formed when a signal from the antigen receptor induces a pre-existing cytoplasmic subunit to translocate to the nucleus and combine with a newly synthesized nuclear subunit of NF-AT. FK506 and cyclosporin A block translocation of the cytoplasmic component without affecting synthesis of the nuclear subunit.

The two different receptors for tumor necrosis factor mediate distinct cellular responses.

Abstract: The individual roles of the murine type 1 and type 2 tumor necrosis factor (TNF) receptors (TNF-R1 and TNF-R2) were investigated utilizing (i) the strong species specificity of TNF-R2 for murine TNF compared to human TNF and (ii) agonistic rabbit polyclonal antibodies directed against the individual TNF receptors. Proliferation of mouse thymocytes and the murine cytotoxic T-cell line CT-6 is stimulated by murine TNF but not by human TNF. Consistent with this observation, polyclonal antibodies directed against TNF-R2 induced proliferation in both of these cell types, whereas polyclonal antibodies directed against TNF-R1 had no effect. In contrast, cytotoxicity in murine LM cells (which are sensitive to murine and human TNF) was induced by antibodies against TNF-R1 but not by antibodies against TNF-R2. Also, the steady-state level of manganous superoxide dismutase mRNA in the murine NIH 3T3 cell line was induced by murine TNF, human TNF, and anti-TNF-R1 but not by anti-TNF-R2. These results suggest that TNF-R2 initiates signals for the proliferation of thymocytes and cytotoxic T cells, whereas TNF-R1 initiates signals for cytotoxicity and the induction of the protective activity, manganous superoxide dismutase. The nonredundant signaling observed for the two TNF receptors cannot be explained simply by the differential expression of the two TNF receptors in the various cell types, because LM cells express on their surface higher levels of TNF-R2 than TNF-R1, and LM cells, NIH 3T3 cells, and thymus cells all express mRNA corresponding to both receptor types. It is therefore likely that the two receptors initiate distinct signaling pathways that result in the induction of different cellular responses.

The role of inflammatory mediators in the pathogenesis of periodontal disease.

Abstract: The role of bacteria in the initiation of periodontitis is well-documented and the end result, destruction of the alveolar bone and periodontal connective tissue, is readily observed; but the events occurring between these two points in time remain obscure and are the focus of this paper. Bacteria induce tissue destruction indirectly by activating host defense cells, which in turn produce and release mediators that stimulate the effectors of connective tissue breakdown. Components of microbial plaque have the capacity to induce the initial infiltrate of inflammatory cells including lymphocytes, macrophages, and PMNs. Microbial components, especially lipopolysaccharide (LPS), have the capacity to activate macrophages to synthesize and secrete a wide array of molecules including the cytokines interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-alpha), prostaglandins, especially PGE2, and hydrolytic enzymes. Likewise, bacterial substances activate T lymphocytes and they produce IL-1 and lymphotoxin (LT), a molecule having properties very similar to TNF-alpha. These cytokines manifest potent proinflammatory and catabolic activities, and play key roles in periodontal tissue breakdown. They induce fibroblasts and macrophages to produce neutral metalloproteinases such as procollagenase and prostromelysin, the serine proteinase urokinase-type plasminogen activator (u-PA), tissue inhibitor of metalloproteinase (TIMP), and prostaglandins, u-PA converts plasminogen into plasmin, which can activate neutral metalloproteinase proenzymes, and these enzymes degrade the extracellular matrix components. TIMP inactivates the active enzymes and thereby blocks further tissue degradation. Several amplification and suppression mechanisms are involved in the process. While LPS activates macrophages to produce IL-1, IL-1 is autostimulatory and can therefore amplify and perpetuate its own production. Interferon-gamma (INF-gamma) suppresses autostimulation, but it enhances LPS-induced IL-1 production. PGE2 exerts a control over the whole process by suppressing production of both IL-1 and TNF-alpha. Furthermore, the activated cells produce an IL-1 receptor antagonist that binds to the IL-1 receptor but does not induce the biologic consequences of IL-1 binding. Other cytokines such as transforming growth factor-beta (TGF-beta) suppress production of metalloproteinases and u-PA. Thus the progression and extent of tissue degradation is likely to be determined in major part by relative concentrations and half-life of IL-1, TNF-alpha, and related cytokines, competing molecules such as the IL-1 receptor antagonist, and suppressive molecules such as TGF-beta and PGE2. These molecules control levels of latent and active metalloproteinase and u-PA, and the availability and concentration of TIMP determines the extent and duration of degradative activity.

A potent nonpeptide antagonist of the substance P (NK1) receptor

Abstract: CP-96,345 [(2S, 3S)-cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)- methyl]-1-azabicyclo[2.2.2]octan-3-amine] is a potent nonpeptide antagonist of the substance P (NK1) receptor. CP-96,345 inhibited 3H-labeled substance P binding and was a classical competitive antagonist in the NK1 monoreceptor dog carotid artery preparation. CP-96,345 inhibited substance P-induced salivation in the rat, a classical in vivo bioassay, but did not inhibit NK2, NK3, or numerous other receptors; it is thus a selective NK1 antagonist. This compound may prove to be a powerful tool for investigation of the physiological properties of substance P and exploration of its role in diseases.

Retinoids and their receptors in differentiation, embryogenesis, and neoplasia.

Abstract: The crucial role of retinoids in controlling differentiation processes has become evident from studies conducted in a variety of in vivo and in vitro systems. Most striking is the role of retinoic acid as a morphogenic substance in vertebrate limb development, but equally important is its role in the maintenance of epithelial integrity in most superficial linings of the body. The similarity of the mode of action of retinoids to that of the steroid and thyroid hormones has recently been demonstrated with the discovery of the nuclear receptors for retinoic acid, which belong to the steroid/thyroid hormone receptor superfamily. These receptors act as transcriptional activators by binding as heterodimers to specific nucleotide sequences in the response elements of target genes. Response elements for retinoic acid have so far been identified for the rat growth hormone and phosphoenolpyruvate carboxykinase, the mouse complement H and laminin B1, the human and mouse retinoic acid receptor beta, the human osteoca...

trkB, a neural receptor protein-tyrosine kinase: evidence for a full-length and two truncated receptors.

Abstract: We have screened an adult rat cerebellar cDNA library in search of novel protein tyrosine-kinase (PTK) cDNAs. A cDNA for a putative PTK, trkB, was cloned, and its sequence indicates that it is likely to be derived from a gene for a ligand-regulated receptor closely related to the human trk oncogene. Northern (RNA) analysis showed that the trkB gene is expressed predominantly in the brain and that trkB expresses multiple mRNAs, ranging from 0.7 to 9 kb. Hybridization of cerebral mRNAs with a variety of probes indicates that there are mRNAs encoding truncated trkB receptors. Two additional types of cDNA were isolated, and their sequences are predicted to encode two distinct C-terminally truncated receptors which have the complete extracellular region and transmembrane domain, but which differ in their short cytoplasmic tails.

Cloning and expression of a complementary DNA encoding a bovine adrenal angiotensin II type-1 receptor

Abstract: Angiotensin II elicits different responses which affect cardiovascular, neuronal and electrolyte transport regulation. To understand the mechanisms responsible for its various actions, the receptor for angiotensin II has long been sought, but numerous attempts to purify the receptor have been unsuccessful owing to its instability and low concentration. We report here the expression cloning of a complementary DNA encoding a bovine angiotensin II receptor to overcome these difficulties. The receptor cDNA encodes a protein of 359 amino-acid residues with a transmembrane topology similar to that of other G protein-coupled receptors. COS-7 cells transfected with the cDNA expressed specific and high-affinity binding sites for angiotensin II, angiotensin II antagonist and a non-peptide specific antagonist for type-1 receptor. Dithiothreitol inhibited ligand binding. The concentration of intracellular Ca2+ and of inositol-1,4,5-trisphosphate increased in the transfected COS-7 cells in response to angiotensin II or angiotensin III, indicating that this receptor is the type-1 receptor for angiotensin II. Northern blot analysis revealed that the messenger RNA for this receptor is expressed in bovine adrenal medulla, cortex and kidney.

The prolactin/growth hormone receptor family.

Abstract: PRL and GH are hormones with a wide spectrum of actions. Specific receptors are widely distributed in a number of classical target organs, but other tissues that are not known targets also contain measurable binding sites or receptor mRNA. The most likely explanation is that PRL and GH cause effects that have not yet been characterized in certain tissues. Cloning of the cDNAs encoding PRL and GH receptors has led to the discovery that the receptors, like the hormones themselves, form a gene family. Multiple receptor forms have been identified, including a short form, which for PRL is a membrane-bound receptor or for GH is a soluble BP, and a long form, which for both PRL and GH is a membrane-bound receptor. PRL and GH receptors, and the mRNAs encoding them, can be up- and down-regulated. GH induces an up-regulation of both GH and PRL receptors, whereas PRL stimulates an increase of only its own receptor. High concentrations of either hormone induce a homologous down-regulation of receptor expression. An assay has been developed to measure the functional activity of different forms of PRL receptor by cotransfecting a milk protein fusion gene specific to PRL coupled to a reporter-gene along with the cDNA of the PRL receptor. Although the short form represents the major form present in rat mammary gland, only the long form of receptor is able to stimulate milk protein gene transcription. For GH, increased expression of the receptor in some target cells is accompanied by a modest enhancement of the response to GH. No single second messenger mediating the action of either PRL or GH has been identified. Several potential components of the signal transduction pathways have been identified, but as yet none has clearly been shown to be able to mimic the effect of PRL or GH. Because of the wide range of biological actions associated with PRL, and the existence of various forms of PRL receptors, it is doubtful that one unifying mechanism of action will be found for this hormone. No human or animal model of a genetic defect of the PRL receptor has thus far been published. Mutations in the GH receptor gene have been demonstrated in Laron type dwarfism. Different exon deletions or point or nonsense mutations resulting in modifications in the extracellular, GH binding region of the GH receptor have been reported.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and characterization of a ouabain-like compound from human plasma

Abstract: The plasma membrane sodium-potassium pumps that regulate intracellular sodium in most animal cells have specific, high-affinity receptors for the digitalis glycosides and their aglycones. This has fostered speculation that there is an endogenous ligand. We have purified and structurally identified by mass spectroscopy an endogenous substance from human plasma that binds with high affinity to this receptor and that is indistinguishable from the cardenolide ouabain. This human ouabain-like compound (OLC) displaces [3H]ouabain from its receptor, inhibits Na,K-ATPase and ouabain-sensitive 86Rb+ uptake, and has cardiotonic actions quantitatively similar to commercial ouabain. Immunoreactive OLC was detected in the plasma of many mammals, and high concentrations were found in the adrenals. The circulating OLC may modulate intracellular Na+ and affect numerous Na+ gradient-dependent processes including intracellular Ca2+ and pH homeostasis in many tissues. Furthermore, altered circulating levels of OLC may be associated with the pathogenesis of certain forms of hypertension.

Selective activation of the B natriuretic peptide receptor by C-type natriuretic peptide (CNP)

Abstract: The natriuretic peptides are hormones that can stimulate natriuretic, diuretic, and vasorelaxant activity in vivo, presumably through the activation of two known cell surface receptor guanylyl cyclases (ANPR-A and ANPR-B). Although atrial natriuretic peptide (ANP) and, to a lesser extent, brain natriuretic peptide (BNP) are efficient activators of the ANPR-A guanylyl cyclase, neither hormone can significantly stimulate ANPR-B. A member of this hormone family, C-type natriuretic peptide (CNP), potently and selectively activated the human ANPR-B guanylyl cyclase. CNP does not increase guanosine 3',5'-monophosphate accumulation in cells expressing human ANPR-A. The affinity of CNP for ANPR-B is 50- or 500-fold higher than ANP or BNP, respectively. This ligand-receptor pair may be involved in the regulation of fluid homeostasis by the central nervous system.

Cloning and expression of cDNA for a human thromboxane A2 receptor

Abstract: THROMBOXANE A2 is a very unstable arachidonate metabolite, yet a potent stimulator of platelet aggregation and a constrictor of vascular and respiratory smooth muscles1. It has been implicated as a mediator in diseases such as myocardial infarction, stroke and bronchial asthma2. Using a stable analogue of this compound we recently purified the human platelet thromboxane A2 receptor to apparent homogeneity3. Using an oligonucleotide probe corresponding to its partial amino-acid sequence, we have obtained a complementary DNA clone encoding this receptor from human placenta and a partial clone from cultured human megakaryocytic leukaemia cells. The placenta cDNA encodes a protein of 343 amino acids with seven putative transmembrane domains. The protein expressed in COS-7 cells binds drugs with affinities identical to those of the platelet receptor, and that in Xenopus oocytes opens Ca2+-activated Cl- channel on agonist stimulation. Northern blot analysis and nucleotide sequences of the two clones suggest that an identical species of the thromboxane A2 receptor is present in platelets and vascular tissues. This first report on the molecular structure of an eicosanoid receptor will promote the molecular pharmacology and pathophysiology of these bioactive compounds.

Molecular cloning of a human cannabinoid receptor which is also expressed in testis.

Abstract: A cDNA clone encoding a receptor protein which presents all the characteristics of a guanine-nucleotide-binding protein (G-protein)-coupled receptor was isolated from a human brain stem cDNA library. The probe used (HGMP08) was a 600 bp DNA fragment amplified by a low-stringency PCR, using human genomic DNA as template and degenerate oligonucleotide primers corresponding to conserved sequences amongst the known G-protein-coupled receptors. The deduced amino acid sequence encodes a protein of 472 residues which shares 97.3% identity with the rat cannabinoid receptor cloned recently [Matsuda, Lolait, Brownstein, Young & Bronner (1990) Nature (London) 346, 561-564]. Abundant transcripts were detected in the brain, as expected, but lower amounts were also found in the testis. The same probe was used to screen a human testis cDNA library. The cDNA clones obtained were partially sequenced, demonstrating the identity of the cannabinoid receptors expressed in both tissues. Specific binding of the synthetic cannabinoid ligand [3H]CP55940 was observed on membranes from Cos-7 cells transfected with the recombinant receptor clone. In stably transfected CHO-K1 cell lines, cannabinoid agonists mediated a dose-dependent and stereoselective inhibition of forskolin-induced cyclic AMP accumulation. The ability to express the human cannabinoid receptor in mammalian cells should help in developing more selective drugs, and should facilitate the search for the endogenous cannabinoid ligand(s).

The chemotactic receptor for human C5a anaphylatoxin

Abstract: HOST defence and inflammatory responses are controlled and amplified by receptor-mediated events often initiated by a chemotactic factor that directs the approach of phagocytic cells1. Complement receptors CR1 and CR3 are responsible for the phagocytic and adhesive properties of neutrophils 2,3, whereas the C5a receptor mediates the pro-inflammatory and chemotactic actions of the complement anaphylatoxin CSa4–6. In addition to stimulating chemotaxis, granule enzyme release and superoxide anion production, this receptor stimulates upregulation of expression and activity of the adhesion molecule MAC-1, and of CR1, and a decrease in cell-surface glycoprotein 1 GOMEL-14 on neutrophils7–9. In vivo, the C5a receptor may participate in anaphylactoid and septic shock 10–12. The human C5a receptor was cloned from U937 and HL-60 cells and identified by high affinity binding when expressed in COS-7 cells. The deduced amino-acid sequence of the receptor reveals the expected motifs befitting its interaction with cellular GTP-binding proteins.

Allelic association of the D2 dopamine receptor gene with receptor-binding characteristics in alcoholism.

Abstract: • The allelic association of the human D2dopamine receptor gene with the binding characteristics of the D2dopamine receptor was determined in 66 brains of alcoholic and nonalcoholic subjects. In a blinded experiment, DNA from the cerebral cortex was treated with the restriction endonuclease Taql and probed with a 1.5-kilobase (kb) digest of a clone (XhD2G1) of the human D2dopamine receptor gene. The binding characteristics (Kd[binding affinity] and Bmax[number of binding sites]) of the D2dopamine receptor were determined in the caudate nuclei of these brains using tritiated spiperone as the ligand. The adjusted Kdwas significantly lower in alcoholic than in nonalcoholic subjects. In subjects with the A1 allele, in whom a high association with alcoholism was found, the Bmaxwas significantly reduced compared with the Bmaxof subjects with the A2 allele. Moreover, a progressively reduced Bmaxwas found in subjects with A2/A2, A1/A2, and A1/A1 alleles, with subjects with A2/A2 having the highest mean values, and subjects with A1/A1, the lowest. The polymorphic pattern of the D2dopamine receptor gene and its differential expression of receptors suggests the involvement of the dopaminergic system in conferring susceptibility to at least one subtype of severe alcoholism.

Cloning and expression of cDNAs for two distinct murine tumor necrosis factor receptors demonstrate one receptor is species specific

Abstract: Complementary DNA clones encoding two distinct tumor necrosis factor receptors were isolated from a mouse macrophage cDNA library. The cDNA for murine tumor necrosis factor receptor type 1 (mTNF-R1) predicts a mature polypeptide of 425 amino acids that is 64% identical to its human counterpart, whereas the cDNA of murine tumor necrosis factor receptor type 2 (mTNF-R2) predicts a mature protein of 452 amino acids that is 62% identical to human tumor necrosis factor receptor type 2. The two murine tumor necrosis factor receptors have limited sequence homology (approximately 20% identity) in their extracellular regions but no apparent similarity in their cytoplasmic portions. Northern (RNA) analysis indicates a single 2.6-kilobase (kb) transcript for mTNF-R1; a 3.6-kb and a more predominant 4.5-kb transcript are observed for mTNF-R2. A human cell line transfected with either mTNF-R1 or mTNF-R2 expression vectors specifically bound 125I-labeled recombinant murine tumor necrosis factor alpha (TNF-alpha). Although mTNF-R1 had a similar affinity for both recombinant murine TNF-alpha and human TNF-alpha, mTNF-R2 showed strong specificity for recombinant murine TNF-alpha. This result suggests that the various activities of human tumor necrosis factor alpha reported in mice or in murine cell lines are probably mediated by mTNF-R1.

Antagonist binding profiles of five cloned human muscarinic receptor subtypes.

Abstract: A variety of muscarinic antagonists are currently used as tools to pharmacologically subclassify muscarinic receptors into M1, M2 and M3 subtypes. In the present study, we have determined the affinity profiles of several of these antagonists at five cloned human muscarinic receptors (m1-m5) stably expressed in Chinese hamster ovary cells (CHO-K1). At all five receptors, the (R)-enantiomers of trihexyphenidyl and hexbutinol displayed considerably higher affinities (up to 525-fold) than their corresponding (S)-isomers. The stereoselectivity ratios [inhibition constant(S)/inhibition constant(R)] for both pairs of enantiomers were lowest at m2 receptors, suggesting that less stringent configurational demands are made by this receptor subtype. The "M1-selective" antagonist (R)-trihexyphenidyl displayed high affinities for m1 and m4 receptors. The "M2-selective" antagonists himbacine, (+-)-5,11-dihydro-11- ([(2-[(dipropylamino)methyl]-1- piperidinyl)ethyl)amino]carbonyl)-6H-pyrido(2,3-b)(1,4)benzodiazepine-6- one (AF-DX 384), 11-[4-[4-(diethylamino)butyl]-1-piperidinyl)acetyl)-5,11- dihydro-6H-pyrido(2,3-b) (1,4)benzodiazepine-6-one (AQ-RA 741) and (+)-(11-[2-[(diethylamino) methyl]-1-piperidinyl)acetyl)-5,11-di-hydro-6H-pyrido(2,3-b)(1,4) benzodiazepine-6-one [AF-DX 250; the (+)-enantiomer of AF-DX 116] exhibited high affinities for m2 and m4, intermediate affinities for m1 and m3 and low affinities for m5 receptors. This selectivity profile was most prominent for AQ-RA 741, which displayed 195- and 129-fold higher affinities for m2 and m4 receptors than for m5 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukemia inhibitory factor receptor is structurally related to the IL-6 signal transducer, gp130.

Abstract: Leukemia inhibitory factor (LIF) is a cytokine with a broad range of activities that in many cases parallel those of interleukin-6 (IL-6) although LIF and IL-6 appear to be structurally unrelated. A cDNA clone encoding the human LIF receptor was isolated by expression screening of a human placental cDNA library. The LIF receptor is related to the gp130 'signal-transducing' component of the IL-6 receptor and to the G-CSF receptor, with the transmembrane and cytoplasmic regions of the LIF receptor and gp130 being most closely related. This relationship suggests a common signal transduction pathway for the two receptors and may help to explain similar biological effects of the two ligands. Murine cDNAs encoding soluble LIF receptors were isolated by cross-hybridization and share 70% amino acid sequence identity to the human sequence.