Expression of components of the insulin-like growth factor system and gonadotropin receptors in bovine cumulus-oocyte complexes during oocyte maturation.

IGF system expression has been largely explored in the bovine follicular wall whereas it remains poorly studied in the COC. Using semi-quantitative RT-PCR and Western blot analysis, we have investigated spatial and temporal expression of IGF-1, IGFR-1, IGFBP-2, IGFBP-4, as well as gonadotropin receptors in bovine COC during oocyte maturation. In addition, we have compared changes in the IGF system and FSHR expression during in vitro maturation in TCM199 alone or in the presence of 10 ng/ml of EGF. The transcripts for IGFR-1 and IGFBP-2 were detected in cumulus and germinal cells whereas IGF-1, IGFBP-4 and FSHR mRNA were restricted to cumulus cells. Topography of the IGF system and gonadotropin receptor expression within COC were unaffected by the maturation step. In contrast, levels of IGFBP-2 and FSHR expression decreased (P < 0.05) in matured COC. Under defined culture conditions, IGFBP-2 and FSHR mRNA expression remained at a high level in TCM199 alone and were significantly reduced (P < 0.05) in the presence of 10 ng/ml EGF after a 24 h period of in vitro maturation. In conclusion, our results demonstrate a cell-specific pattern of IGF system member gene expression within bovine COC suggesting interaction between the somatic and germinal compartments. In addition, synchronized changes in the pattern of COC IGFBP-2 and FSHR expression during oocyte maturation suggest possible synergistic actions between IGF-1 and FSH.

The postmenopausal ovary is not a major androgen-producing gland.

It is currently believed that the postmenopausal ovary remains a gonadotropin-driven, androgen-producing gland. However, the adrenal contribution to circulating androgen levels may explain some conflicting results previously reported. In addition, the steroidogenic potential and gonadotropin responsiveness of the postmenopausal ovary have not been recently reassessed. Plasma T, bioavailable T, free T, androstenedione (Adione), and dehydroepiandrosterone sulfate levels were measured in postmenopausal or ovariectomized women with complete adrenal insufficiency, compared with women with intact adrenals. A stimulation human chorionic gonadotropin test (on d 0, 3, and 6) was performed in postmenopausal women with adrenal insufficiency. Dexamethasone was administered for 4 d in postmenopausal women with intact adrenals. Intraovarian T and androstenedione were also measured in homogenates of ovarian tissue from postmenopausal women. Immunocytochemistry was performed on postmenopausal ovaries and premenopausal controls to detect the presence of steroidogenic enzymes (P-450 aromatase, P-450 SCC, 3beta HSD, and P-450 C17) and gonadotropin receptors. Plasma androgen levels were below or close to the limit of the assay in all women with adrenal insufficiency. They were similar in postmenopausal and oophorectomized women with normal adrenals. No hormonal changes were observed after human chorionic gonadotropin injections in women with adrenal insufficiency. In contrast, a dramatic decrease of all steroids was observed after dexamethasone administration in postmenopausal women with intact adrenals. Intraovarian T and androstenedione levels were negligible in postmenopausal ovarian tissue. P-450 aromatase was absent from the 17 ovaries studied, and the enzymes for androgen biosynthesis were either absent (n = 13) or present in very low amounts (n = 4). In all the postmenopausal ovaries, FSH and LH receptors were completely absent. In the absence of adrenal steroids, postmenopausal women have no circulating androgens. This result is consistent with the immunocytochemical studies showing the almost constantly absent steroidogenic enzymes and LH receptors in the postmenopausal ovary. Thus, the climacteric ovary is not a critical source of androgens. The arrest of androgen secretion after menopause may impact significantly on women's health.

JAB1 interacts with both the progesterone receptor and SRC-1.

JAB1 (Jun activation domain-binding protein-1) has previously been described as a coactivator of AP1 transcription factor. We show here, by yeast and mammalian two-hybrid analyses and by pull-down experiments, that JAB1 also interacts with both the progesterone receptor (PR) and the steroid receptor coactivator 1 (SRC-1) and that it stabilizes PR-SRC-1 complexes. We also show that JAB1 potentiates the activity of a variety of transcription factors known to associate with SRC-1 (nuclear receptors, activator protein-1, and nuclear factor kappaB). This occurs without any modification of PR or SRC-1 concentration. JAB1 is a subunit of a large multiprotein complex that has been called the COP9 signalosome. The latter is present in plant and animal cells and has been shown to be involved in a variety of cellular mechanisms including transcription regulation, cell cycle control, and phosphorylation cascades. We now show that it is also involved in the mechanisms of action of nuclear receptors and of their coactivators.

Luteinizing hormone/human chorionic gonadotrophin receptors in various epidermal structures.

Two different monoclonal antibodies recognizing different epitopes were used to study the localization of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in human skin. Immunolabelling was observed only in the epidermis and derived structures but not in the dermis. The basal, spinal and granular layers were stained, whereas no receptors were detected in the non-nucleated horny cells. In the growing (anagen) hair, immunostaining was found in the inner root sheath below the level of the sebaceous glands and in the outer root sheath above this level. In the resting (telogen) hair, only the latter staining was observed. In the sebaceous glands, only the thin cells close to the walls of the ducts were immunolabelled. In the eccrine sweat glands, the external clear cells were stained in the secretory portion of the gland, whereas only the cells close to the lumen were labelled in the ducts. The distribution of LH/hCG receptors was compared with that of steroidogenic enzymes (side chain cleavage cytochrome P450, adrenodoxin, 3-beta-hydroxy-5-ene steroid dehydrogenase Delta5-Delta4 isomerase, 17-hydroxylase cytochrome P450 and cytochrome P450 aromatase). Only partial overlaps were observed. The presence of LH receptor mRNA in the skin was confirmed by reverse transcription-polymerase chain reaction. Monoclonal antibodies raised against the human follicle-stimulating hormone receptor failed to detect the latter in the epidermal structures and in the dermis. The role of LH and hCG in skin modifications occurring during pregnancy and after the menopause is unknown. These hormones may possibly act by regulating steroidogenic enzymes or by modulating cell growth and differentiation.

Internalization and recycling pathways of the thyrotropin receptor.

Scant information is available to date on the intracellular trafficking of the TSH receptor. In the present study we have used stably transfected L cells that express the TSH receptor, 225I-labeled TSH, and antireceptor antibodies as well as gold-conjugated antireceptor monoclonal antibodies and hormone. The latter allowed us to study, by electron microscopy, the cellular distribution and endocytosis of TSH receptor. The receptor was initially localized on the plasmalemma proper and in clathrin-coated pits but was excluded from smooth vesicles open to the cell surface. It was internalized through clathrin-coated vesicles. Constitutive endocytosis represented 10% of cell surface receptor molecules. Endocytosis was increased 3-fold by incubation with hormone. The majority of internalized receptor molecules (90%) was recycled to the cell surface, whereas the hormone was degraded in lysosomes. This recycling of receptor was inhibited by administration of monensin. Electron microscopic and confocal microscopic studies were repeated in primary cultures of human thyroid cells and showed a distribution, and endocytosis pathways, very similar to those observed in transfected L cells. A previous study has shown the LH receptor to be endocytosed in high proportion and to be degraded in lysosomes. Confocal microscopy and colocalization studies with transferrin receptor confirmed that the highly homologous LH and TSH receptors exhibit, when expressed in the same cells, very different cellular trafficking properties. The use of LH/TSH receptor chimeras showed that transmembrane-intracellular domains contain information orienting the protein toward recycling or degradative pathways. The extracellular domain seems to play a role in the extent of intemalization. These observations should now allow the identification of the molecular signals involved.

Gonadotropin receptors.

Gonadotropin receptors belong to a subgroup of G-protein coupled receptors characterized by a large extracellular domain responsible for the binding of the hormone. Soluble, hormone-binding, alternative splicing variants of the LH receptor, are present in high concentration. A mannose rich precursor form of LH and FSH receptor is accumulated inside target cells. FSH receptors are addressed to the basolateral domain of cells through specific signaling mechanisms. Gonadotropin receptors are also present in endothelial cells of target organ vessels and are involved in hormone transcytosis. Various genetic abnormalities of these receptors (and of the GnRH receptor) are discussed.

Sequential cleavage and excision of a segment of the thyrotropin receptor ectodomain.

The thyrotropin (TSH) receptor belongs to a subfamily of G protein-coupled receptors, which also includes luteinizing hormone and follicle-stimulating hormone receptors. The TSH receptor (TSHR) differs from the latter by the presence of an additional specific segment in the C-terminal part of its ectodomain. We show here that this insertion is excised in the majority of receptor molecules. Preparation of specific monoclonal antibodies to this region, microsequencing, enzyme-linked immunosorbent assay, and immunoblot studies have provided insight into the mechanisms of this excision. In the human thyroid gland, N termini of the transmembrane receptor beta subunit were found to be phenylalanine 366 and leucines 370 and 378. In transfected L cells a variety of other more proximal N termini were found, probably corresponding to incomplete excisions. The most extreme N terminus was observed to lie at Ser-314. These observations suggest that after initial cleavage at Ser-314 the inserted fragment of TSHR is progressively clipped out by a series of cleavage reactions progressing up to amino acids 366-378. The impossibility of recovering the excised fragment from purified receptor, cell membranes, or culture medium supports this interpretation. The cleavage enzyme has previously been shown to be inhibited by BB-2116, an inhibitor of matrix metalloproteases. However, we show here that it is unaffected by tissue inhibitors of metalloproteases. The cleavage enzyme is very similar to TACE (tumor necrosis factor alpha-converting enzyme) in both these characteristics. However, incubation of the TSH receptor with the purified recombinant catalytic domain of TACE, co-transfection of cells with TACE and TSHR expression vectors, and the use of mutated Chinese hamster ovary cells in which TACE is inactive suggested that the TSHR cleavage enzyme is different from TACE. TACE and TSHR cleavage enzyme may thus possibly be related but different members of the adamalysin family of metzincin metalloproteases.

The basolateral localization signal of the follicle-stimulating hormone receptor.

The follicle-stimulating hormone receptor (FSHR) is physiologically localized in the basolateral compartment of the membrane of Sertoli cells. This localization is also observed when the receptor is experimentally expressed in Madin-Darby canine kidney cells. We thus used in vitro mutagenesis and transfection into these polarized cells to delineate the basolateral localization signal of the receptor. The signal was localized in the C-terminal tail of the intracellular domain (amino acids 678-691) at a marked distance of the membrane. Mutation of individual amino acids highlighted the importance of Tyr684 and Leu689. The 14-amino acid sequence was grafted onto the p75 neurotrophin receptor and redirected this apical protein to the basolateral cell membrane compartment. Deletion of amino acids 677-695 did not modify the internalization of the FSHR, showing that the basolateral localization signal of the FSHR is not colinear with its internalization signal.

Gonadotropin receptors and the control of gonadal steroidogenesis: physiology and pathology.

Over the past few years, knowledge of the structure of gonadotropin receptors and their mode of action has rapidly advanced. The cDNA corresponding to the luteinizeng hormone (LH) receptor (LHR) has been cloned, leading to the identification of a novel family of G-protein-coupled receptors. The follicle stimulating hormone (FSH) receptor (FSHR) was thereafter cloned by cross-hybridization with the LHR. Structure-function relationships have been studied by mutagenesis experiments in several laboratories. The cloning and chromosomal localization to chromosome 2p21 of the two human gonadotropin receptor genes has provided insights into their evolutionary relationships. The LHR and FSHR genes are very large and contain 10 and 11 exons respectively. The obtention of monoclonal antibodies against the receptors resulted in the characterization of the receptor proteins. These antibodies also allowed the study of receptor expression in target cells in physiological and pathological conditions. The internalization of the LHR has been studied by electron microscopy. A mechanism of receptor-mediated transcytosis through the endothelial cells of the testes has been described for the LHR. The polarized expression of receptors has been studied. The cloning of gonadotropin receptor genes has opened the field of genetic study of the receptors. Inactivating mutations of the LHR have been described in Leydig cell agenesis or hypoplasia. Different phenotypes, including complete pseudohermaphroditism, ambiguous genitalia and male phenotype, have been described. In the case of the FSHR, only one mutation has been reported in familial ovarian dysgenesis with primary amenorrhea. Related males have variable alterations of spermatogenesis and fertility. Constitutive mutations of the LHR have been reported in familial testotoxicosis. One similar mutation has also been described for the FSHR. Such mutations may lead to the development of a model of receptor activation.

Comparison of immunocytochemical and molecular features with the phenotype in a case of incomplete male pseudohermaphroditism associated with a mutation of the luteinizing hormone receptor.

We report the case of an infant who presented at birth with a hypoplastic phallus associated with hypospadias. Low testosterone production, normal serum levels of steroid precursors, and increased LH in response to LH-releasing hormone supported a defect in Leydig cell differentiation or function. Conventional microscopic study of the testes showed fibroblastic cells in the interstitium. However immunocytochemical analysis using anti-LH receptor and anti-P450c17 antibodies demonstrated that about one third of these cells were Leydig cells or precursors of Leydig cells. No histological feature could distinguish the latter cells from fibroblasts. A homozygous substitution of cysteine 133 for arginine was found in the extracellular domain of the receptor. This is the first naturally occurring missense mutation found in the extracellular domain of the LH receptor. COS-7 cells transfected with the mutant receptor exhibited a marked impairment of hCG binding, whereas some cAMP production could be observed at high hCG concentrations. We propose that the partial impairment of LH receptor function, as reflected by the presence of Leydig cells, was responsible for the incomplete male pseudohermaphroditism observed in our patient.

Luteinizing hormone/human chorionic gonadotropin receptors in breast cancer.

Recent studies have suggested that human choriogonadotropin (hCG), in addition to its function in regulating steroidogenesis, may also play a role as a growth factor. Immunocytochemistry using two different monoclonal antibodies (LHR29 and LHR1055) raised against the human luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor allowed us to detect this receptor in breast cancer cell lines (T47D, MCF7, and ZR75) in individual cancer biopsies and in benign breast lesions. The receptor was also present in epithelial cells of normal human and sow breast. In the latter, its concentration increased after ovulation. The presence of LH/hCG receptor mRNA was confirmed by reverse transcription-PCR using primers extending over exons 2-4, 5-11, and 9-11. The proportion of LH/hCG-receptor positive cells and the intensity of the immunolabeling varied in individual biopsies, but there was no obvious correlation with the histological type of the cancer. These results are compatible with previous studies suggesting that during pregnancy, hCG is involved in the differentiation of breast glandular epithelium and that this hormone may play an inhibitory role in mammary carcinogenesis and in the growth of breast tumors.

Basolateral localization and transcytosis of gonadotropin and thyrotropin receptors expressed in Madin-Darby canine kidney cells.

The thyrotropin (TSH) and follicle-stimulating hormone (FSH) receptors are present mainly on the basolateral cell surface in the thyroid gland and in Sertoli cells, whereas in ovarian and in testicular cells, the luteinizing hormone (LH) receptors are distributed throughout the cell surface. When expressed in Madin-Darby canine kidney (MDCK) cells, all three receptors accumulated at the basolateral cell surface showing that they carry the corresponding targeting signals. The receptors were directly delivered to the basolateral surface of the MDCK cells. A minor fraction of the gonadotropin receptors but not of TSH receptors was secondarily targeted to the apical surface through transcytosis. The mechanisms of basolateral targeting and transcytosis were analyzed using the FSH receptor as a model. Both were insensitive to brefeldin A and pertussis toxin. Gs activation by AlF4- and cholera toxin provoked a marked enhancement of FSH receptor transcytosis. The population of Gs proteins involved in this mechanism was different from that involved in signal transduction since neither FSH nor forskolin mimicked the effects of AlF4- and cholera toxin. Gs activation provoked a similar effect on LH receptor distribution in MDCK cells, whereas it did not modify the compartmentalization of the TSH receptor. Hormone-specific transcytosis was observed in MDCK cells expressing the gonadotropin (FSH and LH) receptors and was increased after cholera toxin administration.

Gonadotrophin and thyrotrophin receptors.

Gonadotrophin and thyrotrophin receptors belong to a subgroup of G-protein-coupled receptors. These receptors are characterized by a large extracellular domain that is responsible for the binding of the hormone. Soluble receptors, such as some luteinizing hormone receptors, arise from premessenger RNA alternative splicing, or, in the case of thyroid-stimulating hormone (TSH) receptors, by the cleavage and shedding of the ectodomain. Follicle-stimulating hormone and TSH receptors are restricted to the basolateral domain of their target cells. These receptors are also present in endothelial cells of target organ vessels and are involved in hormone transcytosis. Various genetic abnormalities of these receptors have been described.

The LH/CG and FSH receptors: different molecular forms and intracellular traffic.

Monoclonal antibodies have been raised against the LH/CG receptor [1] and have allowed to perform immunochemical studies of the receptor in target cells. Three different forms of the LH/CG receptor are physiologically expressed: a mature approximately 85 kDa transmembrane species corresponding to the full length receptor, a approximately 68 kDa high mannose containing species corresponding to a precursor which accumulates inside the cells, and truncated soluble approximately 45-48 kDa molecular weight species corresponding to the variant messanger RNAs generated by alternative splicing. Monoclonal antibodies against the human FSH receptor were also prepared. They allow to observe the existence of two forms of the FSH receptor in the ovaries: a major approximately 87 kDa species corresponding to the mature receptor and a minor approximately 81 kDa species corresponding to a high mannose rich precursor. No variant forms of the receptor corresponding to alternative mRNA transcripts were detected. The transport of hCG was examined in rat testicular microvasculature by electron microscopy and by analyzing the transfer of radiolabeled hormone and antireceptor antibodies. LH/CG receptors were present in endothelial cells and were involved in hormone transcytosis through these cells. Immunocytochemical experiments have shown that the FSH receptor has a polarized expression in the Sertoli cells of the testes whereas the LH/Cg receptor is spread on the surface of thecal granulosa and luteal cells in the ovary and Leydig cells in the testes. To study the mechanism of this polarization FSH, LH and TSH receptors were expressed in polarized MDCK cells. The mechanism of basolateral localization and of transcytosis of the receptors was studied using this model. The effect of hormone, cAMP and agents acting on G proteins was examined.

Cell surface protein disulfide-isomerase is involved in the shedding of human thyrotropin receptor ectodomain.

In human thyroid glands the TSH receptor undergoes a cleavage reaction which yields to an extracellular alpha subunit and a membrane spanning beta subunit linked together by disulfide bridges. A similar reaction is observed in transfected L cells although some uncleaved monomers persist in these cells. We have recently shown that the alpha subunit of the TSH receptor undergoes partial shedding in human thyroid cells and heterologous cells permanently transfected with an expression vector encoding the receptor. This shedding is a two-step process. The first step consists in the cleavage of the proreceptor at the cell surface probably by a matrix metalloprotease and the second step in the reduction of the disulfide bridge(s) (Couet, J., Sar, S., Jolivet, A., Vu Hai, M. T., Milgrom, E., & Misrahi, M. 1996, J. Biol. Chem. 271, 4545-4552). We have used the transfected L cells to study the second step involved in sTSHR shedding. The membrane impermeant sulfhydryl reagent DTNB (5,5'-dithiobis(2-nitrobenzoic acid) allowed us to confirm that the reduction of the TSH receptor disulfide bonds occurred at the cell surface. The antibiotic bacitracin even at low concentrations also elicited a marked inhibition of TSH receptor shedding. This led us to implicate the enzyme protein disulfide isomerase (PDI, EC 5.3.4.1) in this process. We thus tested the inhibitory activity of specific monoclonal antibodies raised against PDI. All antibodies elicited a marked inhibition of sTSHR shedding. This confirmed that cell surface PDI is involved in the shedding of the TSH receptor ectodomain. The shed alpha subunit may be at the origin of circulating TSH receptor ectodomain detected in human blood.

Anti-human FSH receptor monoclonal antibodies: immunochemical and immunocytochemical characterization of the receptor.

The extracellular domain of the human FSH receptor was expressed in Escherichia coli as a fusion protein with ubiquitin. It was tagged with a poly-His tract which was used for its purification. Immunization of mice allowed the preparation of high affinity antireceptor monoclonal antibodies. The latter fell into two categories: some of them were inhibited hormone binding and adenylate cyclase activation whereas others were devoid of these properties. None of the antibodies had agonistic activity (i.e., stimulated adenylate cyclase). Immunoaffinity chromatography allowed us to purify the native receptor in a single step either from a permanently transfected L cell line (75% recovery) or from human ovaries (33% recovery). Immunoblotting of the receptor in human ovaries showed the presence of a major band of 87 kDa and of a minor band of 81 kDa. Endoglycosidase digestion and pulse-chase experiments showed the former to be the mature receptor and the latter the precursor containing mannose-rich carbohydrates. Thus, as in the case for the LH receptor, there was an accumulation (albeit to a lower degree) of the precursor in target cells. We did not detect variant forms of the protein corresponding to the alternative mRNA transcripts previously described. Additive binding to the receptor of several antibodies, but not of the same antibody, allowed us to establish a sandwich-type ELISA for the receptor (sensitivity approximately 1 fmol) and to obtain evidence against the existence of previously described oligomeric forms of the protein. All monoclonal antibodies were able to label the receptor immunocytochemically in transfected cells, and two of them were also able to detect it at the markedly lower physiological concentrations, i.e., in human Sertoli and granulosa cells.

[Pituitary glycoprotein hormone receptors]. / Les récepteurs des hormones glycoprotéiques hypophysaires.

Monoclonal antibodies have been raised against the porcine LH receptor and have allowed to clone the corresponding messenger RNA from testicular cells. The stricture of the LH receptor has been determined. It shows similarities but also differences with other G protein coupled receptors. Specially a large extracellular domain is specific of that new family of receptors. Variant forms of the LH receptor generated by alternative splicing and lacking transmembrane domain have been isolated. Immunochemical and immunocytochemical studies have been performed. Three different forms of the LH receptor are physiologically expressed: a mature 85kDa transmembrane species, a 68 kDa high mannose containing species corresponding to a precursor which accumulates inside the cells, and truncated 45-48kDa molecular weight species corresponding to the variant messenger RNAs identified during the cloning of the receptor. A novel zonation of the ovary has been described by immunocytochemical studies. Cross hybridization with the LH receptor clone allowed to isolate the related TSH receptor from human thyroid tissue. The human LH and FSH receptor genes have been localized to chromosome 2p21 and the TSH receptor gene to chromosome 14q31. The genes are very large (> 60 kbp) and have introns only within the 5' part encoding the extracellular domain of the receptor. Immunoelectron microscopic studies performed in Leydig cells and in stably transfected L cells have allowed to study intracellular traffic of the LH receptor. The same approach was used to study the transendothelial transfer of hCG in testicular microvasculature.

Processing of the precursors of the human thyroid-stimulating hormone receptor in various eukaryotic cells (human thyrocytes, transfected L cells and baculovirus-infected insect cells).

The complementary DNA for human thyroid-stimulating hormone (TSH) receptor encodes a single protein with a deduced molecular mass of 84.5 kDa. This protein is cleaved during its maturation in the human thyroid since the receptor protein has been shown to be composed of two subunits (alpha subunit of approximately 53 kDa and beta subunit of approximately 38 kDa) held together by disulfide bridges [Loosfelt, H., Pichon, C., Jolivet, A., Misrahi, M., Caillou, B., Jamous, M., Vannier, B. & Miligrom, E. (1992) Proc. Natl Acad. Sci. USA 89, 3765-3769]. A similar processing occurs in an L cell line permanently expressing the human TSH receptor. The processing is however incomplete, resulting in a permanent accumulation of a 95-kDa high-mannose precursor which is present only in trace amounts in the thyroid. Pulse-chase experiments show the successive appearance in the L cells of two precursors: initially the approximately 95-kDa high-mannose glycoprotein followed by a approximately 120-kDa species containing mature oligosaccharides. This latter precursor is then processed into the alpha and beta subunits. In primary cultures of human thyrocytes precursors of similar size are detected. Spodoptera frugiperda insect cells (Sf9 and Sf21) infected with a recombinant baculovirus encoding the human TSH receptor synthesize a monomeric protein of about 90 kDa soluble only in denaturing conditions. Comparison with the product of in vitro transcription-translation experiments (approximately 80 kDa), suggests that it may be incompletely or improperly glycosylated. The TSH receptor expressed in these cells is unable to bind the hormone. Immunoelectron microscopy studies show that in human thyrocytes most of the receptor is present on the cell surface; in L cells the receptor is detected on the cell surface, as well as in the endoplasmic reticulum and in the Golgi apparatus (this intracellular pool of receptor molecules probably corresponding to the high-mannose precursor); in insect cells nearly all the receptor molecules are trapped in the endoplasmic reticulum. These differences in receptor distribution are concordant with the differences observed for receptor processing.

[LH receptors. A new family of G-protein receptors]. / Récepteur de la LH. Une nouvelle famille de récepteurs couplés à des protéines G.

Monoclonal antibodies have been raised against porcine LH receptor and allowed to clone the corresponding messenger RNA from testicular cells. The structure of the LH receptor have been determined. It shows similarities but also differences to other G protein coupled receptors. In particular a large extracellular domain is specific for that family of receptors. Variants forms of the LH receptor generated by alternative splicing and lacking transmembrane domains have been isolated. Immunochemical and immunocytochemical studies have been performed. Three different forms of the LH receptor are physiologically expressed: a mature 85 kDa transmembrane species, a 68 kDa high mannose containing species corresponding to a precursor which accumulate inside the cells, and truncated 45-48 kDa molecular weight species corresponding to the variant messenger RNAs identified during the cloning of the receptor. A novel zonation of the ovary has been described by immunocytochemical studies. Cross hybridisation with the LH receptor clone allowed to isolate the related human TSH receptor from thyroïds. The human LH and FSH receptor genes have been localized to chromosome 2p21 and the TSH receptor gene to chromosome 14q31. The genes are very large and have introns only within their 5' part corresponding to the extracellular domain of the receptor.