Expression of members of the putative olfactory receptor gene family in mammalian germ cells

A series of genomic and complementary DNA clones encoding new putative members of G protein-coupled receptors were isolated using homology cloning and low-stringency polymerase chain reaction. Among the unidentified receptors ('orphan receptors'), a human genomic clone (HGMP07) was characterized by the presence of its transcripts in the testis and by its belonging to a large subfamily of genes sharing extensive sequence similarities. Sequence comparison demonstrated that this gene subfamily is the human counterpart of the putative rat olfactory receptors cloned recently. Another 48 members of the family were cloned. Northern blotting further demonstrated the presence of olfactory receptor transcripts in germ cells. Our finding suggests that a common receptor gene family encodes olfactory receptors and sperm cell receptors that could be involved in chemotaxis during fertilization.

The orphan receptor cDNA RDC4 encodes a 5-HT1D serotonin receptor

The cDNA of RDC4, a putative receptor of the G protein-coupled receptor family, has been cloned by PCR methodology. The primary structure of this receptor showed homology with the serotonin 5-HT1A receptor. In this work, RDC4 mRNA has been injected in Y1 adrenal cells and Xenopus oocytes and RDC4 cDNA has been transfected transiently in cos-7 cells. In all these systems serotonin elicited a rise in cyclic AMP levels. Binding studies on membranes of the transfected cos-7 cells using [3H]-LSD showed a pattern of drug affinities consistent with the known properties of a 5-HT1D receptor. RDC4 therefore codes for a 5-HT1D receptor which in the studied systems is positively coupled to adenylate cyclase.

Thyroperoxidase, but not the thyrotropin receptor, contains sequential epitopes recognized by autoantibodies in recombinant peptides expressed in the pUEX vector

The sequential epitopes on the human thyroperoxidase (TPO) recognized by antibodies in the sera of patients with autoimmune thyroid disease were investigated using a recombinant DNA technique. Previous studies led to the isolation of two overlapping cDNA clones that encode polypeptides of TPO (85 residues, C2; 100 residues, C21) recognized by sera from several patients with autoimmune disease that contained antimicrosomal autoantibodies. In this report the vector pUEX1 was used to clone and express small random fragments of TPO cDNA in Escherichia coli as a beta-galactosidase fusion protein. Colonies were screened with a serum from a patient with Hashimoto's thyroiditis, and immunoreactive peptides were identified by sequencing the corresponding DNA inserts. Two linear epitopes of human TPO (amino acids 590-622 and 710-722) were recognized by the autoantibodies. This confirmed our previous results and provide a more precise localization of the antigenic determinants involved. The same approach has been applied in an attempt to identify the binding site(s) for autoantibodies on the human TSH receptor. In contrast to the data obtained with TPO, sera from patients with blocking (from idiopathic myxoedema) or stimulating (from Graves' disease) activity did not recognize the linear TSH receptor peptide fragments generated in our libraries.

Distribution of adenosine A2 receptor mRNA in the human brain

The distribution of the messenger RNA coding for the recently cloned adenosine A2 receptor was studied in the human brain using in situ hybridization histochemistry. A2 receptor mRNA is exclusively detected in the medium-sized neurons of the caudate, putamen and accumbens nuclei but not elsewhere in the brain. This highly selective distribution of adenosine A2 receptor mRNA in human dorsal and ventral striatum, similar to that of adenosine A2 binding sites reported in rodents, suggests a major role in the basal ganglia physiology.

Chromosomal mapping of A1 and A2 adenosine receptors, VIP receptor, and a new subtype of serotonin receptor

cDNA clones encoding four new receptors of the G-protein-coupled receptor family were obtained by selective amplification and cloning from thyroid cDNA and termed RDC1, RDC4, RDC7, and RDC8. RDC7 and RDC8 have recently been identified as A1 and A2 adenosine receptors, respectively. These cDNAs were utilized for chromosomal in situ hybridization to establish the genomic location of the corresponding genes in man. The results indicate that human RDC1, RDC4, RDC7, and RDC8 are in regions 2q37, 1p34.3-1p36.3, 22q11.2-22q13.1, and 11q11-11q13, respectively.

The orphan receptor cDNA RDC7 encodes an A1 adenosine receptor

The extensive amino acid sequence conservation among G protein-coupled receptors has been exploited to clone new members of this large family by homology screening or by PCR. Out of four such receptor cDNAs we cloned recently, RDC7 corresponds to a relatively abundant transcript in the brain cortex, the thyroid follicular cell and the testis. We have now identified RDC7 as an A1 adenosine receptor. The A1 agonist CPA [N6-cyclopentyladenosine] decreased by 80% cAMP accumulation in forskolin-stimulated CHO cells stably transfected with RDC7. Specific binding of another A1 adenosine agonist, [3H]CHA [N6-cyclohexyladenosine], was demonstrated on membranes from Cos cells transfected with a pSVL construct harbouring the RDC7 cDNA insert. The binding characteristics were similar to those of the natural brain A1 receptor. The recombinant and the natural receptors behaved also in the same way in displacement experiments involving a series of A1 adenosine agonists. The binding characteristics of RDC7 were compared to those of RDC8, another orphan receptor recently identified as an A2 adenosine receptor. The two molecular species RDC7 and RDC8 correspond clearly to the A1 and A2 receptor entities defined hitherto on a purely pharmacological basis.

Current developments in G-protein-coupled receptors

The rate at which receptors have been cloned has recently increased dramatically--existing families have been extended and new families created. The rapid cloning by homology of 'orphan receptors' has also stimulated the development of a new reverse pharmacology.

RDC8 codes for an adenosine A2 receptor with physiological constitutive activity

The cDNA of an unidentified recently cloned G protein-coupled receptor, RDC8, has been expressed in Y1 adrenal cells, in dog thyrocytes in primary culture and in Xenopus oocytes. In all these systems this resulted in the activation of adenylyl cyclase and of the cyclic AMP cascade in the absence of any added external signal. However, this physiologically constitutive activator was inhibited by adenosine deaminase and by inhibitors of the adenosine A2 receptor. Cos 7 cells transfected with RDC8 cDNA constructs acquired binding characteristics of an adenosine A2 receptor. Moreover, RDC8 mRNA and adenosine A2 receptors display a very similar distribution in the brain. RDC8 therefore codes for an A2 adenosine receptor. Whether the physiologically constitutive activation of this receptor is entirely explained by endogeneously produced adenosine is as yet unknown.

Use of the recombinant human thyrotropin receptor (TSH-R) expressed in mammalian cell lines to assay TSH-R autoantibodies

We report on two assays for autoantibodies to the TSH-R which have been developed using materials from mammalian cells transfected with the cDNA for the human TSH-R. In the first, a particulate fraction has been prepared from COS cells, transiently expressing the human TSH-R and used in a radioreceptor assay in conjunction with bovine 125I-TSH. Immunoglobulins (IgGs) from patients with Graves' disease (n = 11) and idiopathic myxoedema (n = 2) have been used as competitors of 125I-TSH binding to the COS TSH-R membranes and the results have been compared with those obtained with a commercially available kit for measuring TSH-R autoantibodies, which uses solubilised porcine TSH-R. Both assays showed similar performance, being particularly sensitive to antibodies from patients with idiopathic myxoedema. In the second assay system we have used a CHO cloned cell line (JP26) stably transfected with the human TSH-R. A selection of IgG preparations from patients with Graves' disease and of six normal controls was used to test the ability of this cell line to detect thyroid stimulating immunoglobulins (TSAb) by increasing its cAMP production. The assay was performed under two conditions: in standard (isotonic) medium or in hypotonic medium. Freshly thawed human thyrocytes incubated in hypotonic medium served as a reference method. Only five patients scored positive when tested in the JP26 cell line under isotonic conditions. When the assay was performed in a hypotonic medium, a significant positive correlation was observed between the results given by JP26 cells and human thyrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Stable expression of the human TSH receptor in CHO cells and characterization of differentially expressing clones

The human thyrotropin receptor cDNA was transfected in CHO cells and individual clones were isolated. They were tested for their response to thyrotropin, forskolin and antibodies from a patient with high levels of thyroid stimulating antibodies. Several clones were characterized extensively with respect to membrane binding of labeled thyrotropin, cAMP accumulation in response to thyrotropin and kinetics of cAMP production. Data for three representative clones are presented. Receptor number as assessed by membrane binding of labeled thyrotropin, and cAMP production, measured in a thyrotropin response bioassay, are correlated. The Kd value for the human thyrotropin receptor expressed in CHO was estimated to be 50 pM.

A cloned G protein-coupled protein with a distribution restricted to striatal medium-sized neurons. Possible relationship with D1 dopamine receptor

RDC8, a recently cloned new putative member of the G protein-coupled receptor family, is exclusively present in the medium-sized neurons of the dorsal and ventral striatum in the rat and dog brains. The existence of a striatum-restricted putative G protein-coupled receptor is of major importance for the understanding of basal ganglia physiology and degenerative diseases pathogeny such as Huntington's and Parkinson's disease. This striatal restricted localization mimics the major striatal dopamine D1 receptor localization. RDC7, another putative G protein-coupled receptor presenting a close sequence similarity with RDC8, is mainly distributed in the cerebral cortex, the amygdala, the hippocampus and the claustrum. This localization is also compatible with that expected from a subtype of dopamine D1 receptors.

An efficient screening morphological test for the identification and characterization of cyclic AMP-coupled hormone receptors

We describe here a new method for the identification of adenylate cyclase-regulating receptors using the morphological response of Y1 cells to cAMP. The efficiency of this method was demonstrated with a cloned beta 2-adrenergic receptor: the coding region of a genomic beta 2-adrenergic receptor clone was amplified using the polymerase chain reaction, so that in vitro RNA transcripts of this DNA could be obtained. Y1 cells were microinjected with this RNA and assayed for sensitivity to isoproterenol. In the presence of this agonist, the microinjected cells rapidly showed morphological changes identical to those observed in the presence of ACTH, forskolin, or cholera toxin, agents that enhance cAMP accumulation in the control uninjected cells. This suggests the integration, within the injected cell membrane, of a functional beta 2-adrenergic receptor, whose activation by isoproterenol resulted in the intracellular formation of cAMP. This new qualitative screening method for the identification of adenylate cyclase-regulating receptors can be extended to any unknown receptor coupled to adenylate cyclase and absent in these cells. It has been applied to the identification of the dog thyrotropin receptor.

Molecular cloning of a dog thyrotropin (TSH) receptor variant

A clone coding for a variant form of thyrotropin receptor was isolated from a dog thyroid cDNA library. It was characterized by a 75 bp deletion in the coding region, additionally to minor modifications in the 3' untranslated region. The corresponding 25 amino acids deletion is located in the long NH2 terminal extracellular domain which is characteristic of the glycoprotein hormone receptors. This region of the protein is composed of imperfect repeats and the deletion corresponds exactly to one of the repeat units. This suggests that the repeats correspond to individual exons in the thyrotropin receptor chromosomal gene. It is not known whether the deletion of the repeat and the concomitant suppression of one of the N-glycosylation sites of the molecule do alter the receptor function.

Localization of human calcyphosine gene (CAPS) to the p13.3 region of chromosome 19 by in situ hybridization

The gene for human calcyphosine (CAPS) was assigned to the pl3.3 region of chromosome 19 by in situ hybridization.

Localization of human thyrotropin receptor gene to chromosome region 14q3 by in situ hybridization

The gene for human thyrotropin receptor (TSHR) was assigned to chromosome J4, band q31, by in situ hybridization, using a probe for TSHR

Cloning, sequencing and expression of the human thyrotropin (TSH) receptor: evidence for binding of autoantibodies

A human thyroid cDNA library was screened by hybridization with a dog thyrotropin receptor (TSHr) cDNA. Sequencing of the resulting clones identified a 2292 residue open reading frame encoding a 744 amino acid mature polypeptide presenting 90.3% similarity with the dog TSHr. Two major transcripts (4.6 and 4.4 kilobases) were identified in the human thyroid which suggests that alternative splicing could generate multiple forms of human TSHr. Transfection of the coding sequence in COS-7 cells conferred to a membrane preparation of these cells the ability to bind specifically TSH. TSH binding was completely displaced by immunoglobulin preparations from patients with idiopathic myxoedema.

Molecular cloning of the thyrotropin receptor

The pituitary hormone thyrotropin, or thyroid-stimulating hormone (TSH), is the main physiological agent that regulates the thyroid gland. The thyrotropin receptor (TSHR) was cloned by selective amplification with the polymerase chain reaction of DNA segments presenting sequence similarity with genes for G protein-coupled receptors. Out of 11 new putative receptor clones obtained from genomic DNA, one had sequence characteristics different from all the others. Although this clone did not hybridize to thyroid transcripts, screening of a dog thyroid complementary DNA (cDNA) library at moderate stringency identified a cDNA encoding a 4.9-kilobase thyroid-specific transcript. The polypeptide encoded by this thyroid-specific transcript consisted of a 398-amino acid residue amino-terminal segment, constituting a putative extracellular domain, connected to a 346-residue carboxyl-terminal domain that contained seven putative transmembrane segments. Expression of the cDNA conferred TSH responsiveness to Xenopus oocytes and Y1 cells and a TSH binding phenotype to COS cells. The TSHR and the receptor for luteinizing hormone-choriogonadotropin constitute a subfamily of G protein-coupled receptors with distinct sequence characteristics.

Control of thyroperoxidase and thyroglobulin transcription by cAMP: evidence for distinct regulatory mechanisms

The expression of the genes coding for thyroglobulin (TG), and thyroperoxidase (TPO), are regulated by TSH. These effects are mediated by cAMP as they are reproduced by forskolin. In vitro run-on transcription assays performed on nuclei isolated from dog thyrocytes in culture or from dog thyroid slices, indicate that the forskolin-induced transcriptional stimulation of TG and TPO genes are very different. For the TG gene, the kinetics of transcriptional activation vary according to the experimental model: it is rapid (1 h) in thyroid slices and slow (8 h) in primary cultures. In contrast, TPO induction is rapid in both cases. In primary cultures, insulin is responsible for the basal level and for a part of forskolin-induced TG transcription, whereas TPO transcription is not affected by insulin. The forskolin-induced increase of TG transcription requires ongoing protein synthesis, as it is blocked by cycloheximide. TPO gene transcription is unaffected by cycloheximide. Taken together with previous data on the two genes, our results suggest that while TPO regulation corresponds to the classical model of genes in which the promoter is regulated directly via cAMP regulatory elements, TG gene regulation involves the synthesis of an intermediary, rapid turnover trans-acting protein.