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.

A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology

Ethical, economic and technical reasons hinder regular supply of freshly isolated hepatocytes from higher mammals such as monkey for preclinical evaluation of drugs. Hence, we aimed at developing optimal and reproducible protocols to cryopreserve and thaw parenchymal liver cells from this major toxicological species. Before the routine use of these protocols, we validated them through a multi-laboratory study. Dissociation of the whole animal liver resulted in obtaining 1-5 billion parenchymal cells with a viability of about 86%. An appropriate fraction (around 20%) of the freshly isolated cells was immediately set in primary culture and various hepato-specific tests were performed to examine their metabolic, biochemical and toxicological functions as well as their ultrastructural characteristics. The major part of the hepatocytes was frozen and their functionality checked using the same parameters after thawing. The characterization of fresh and thawed monkey hepatocytes demonstrated the maintenance of various hepato-specific functions. Indeed, cryopreserved hepatocytes were able to survive and to function in culture as well as their fresh counterparts. The ability for synthesis (proteins, ATP, GSH) and conjugation and secretion of biliary acids was preserved after deep freeze storage. A better stability of drug metabolizing activities than in rodent hepatocytes was observed in monkey. After thawing, Phase I and Phase II activities (cytochrome P450, ethoxycoumarin-O-deethylase, aldrin epoxidase, epoxide hydrolase, glutathione transferase, glutathione reductase and glutathione peroxidase) were well preserved. The metabolic patterns of several drugs were qualitatively and quantitatively similar before and after cryopreservation. Lastly, cytotoxicity tests suggested that the freezing/thawing steps did not change cell sensitivity to toxic compounds.

Mouse trp2, the homologue of the human trpc2 pseudogene, encodes mTrp2, a store depletion-activated capacitative Ca2+ entry channel

Capacitative Ca2+ entry (CCE) is Ca2+ entering after stimulation of inositol 1,4,5-trisphosphate (IP3) formation and initiation of Ca2+ store depletion. One hallmark of CCE is that it can also be triggered merely by store depletion, as occurs after inhibition of internal Ca2+ pumps with thapsigargin. Evidence has accumulated in support of a role of transient receptor potential (Trp) proteins as structural subunits of a class of Ca2+-permeable cation channels activated by agonists that stimulate IP3 formation-very likely through a direct interaction between the IP3 receptor and a Trp subunit of the Ca2+ entry channel. The role of Trp's in Ca2+ entry triggered by store depletion alone is less clear. Only a few of the cloned Trp's appear to enhance this type of Ca2+ entry, and when they do, the effect requires special conditions to be observed, which native CCE does not. Here we report the full-length cDNA of mouse trp2, the homologue of the human trp2 pseudogene. Mouse Trp2 is shown to be readily activated not only after stimulation with an agonist but also by store depletion in the absence of an agonist. In contrast to other Trp proteins, Trp2-mediated Ca2+ entry activated by store depletion is seen under the same conditions that reveal endogenous store depletion-activated Ca2+ entry, i.e., classical CCE. The findings support the general hypothesis that Trp proteins are subunits of store- and receptor-operated Ca2+ channels.

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.

The membrane topology of human transient receptor potential 3 as inferred from glycosylation-scanning mutagenesis and epitope immunocytochemistry

Transient receptor potential (Trp) proteins form ion channels implicated in the calcium entry observed after stimulation of the phospholipase C pathway. Kyte-Doolittle analysis of the amino acid sequence of Trp proteins identifies seven hydrophobic regions (H1-H7) with potential of forming transmembrane segments. A limited sequence similarity to voltage-gated calcium channel alpha1 subunits lead to the prediction of six transmembrane (TM) segments flanked by intracellular N and C termini and a putative pore region between TM5 and TM6. However, experimental evidence supporting this model is missing. Using human Trp 3 to test Trp topology, we now confirm the intracellular nature of the termini by immunocytochemistry. We also demonstrate presence of a unique glycosylation site in position 418, which defines one extracellular loop between H2 and H3. After removal of this site and insertion of ten separate glycosylation sites, we defined two additional extracellular loops between H4 and H5, and H6 and H7. This demonstrated the existence of six transmembrane segments formed of H2-H7. Thus, the first hydrophobic region of Trp rather than being a transmembrane segment is intracellular and available for protein-protein interactions. A site placed in the center of the putative pore region was glycosylated, suggesting that this region may have been luminal and was reinserted into the membrane at a late stage of channel assembly.

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.

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.

On the molecular basis and regulation of cellular capacitative calcium entry: roles for Trp proteins

During the last 2 years, our laboratory has worked on the elucidation of the molecular basis of capacitative calcium entry (CCE) into cells. Specifically, we tested the hypothesis that CCE channels are formed of subunits encoded in genes related to the Drosophila trp gene. The first step in this pursuit was to search for mammalian trp genes. We found not one but six mammalian genes and cloned several of their cDNAs, some in their full length. As assayed in mammalian cells, overexpression of some mammalian Trps increases CCE, while expression of partial trp cDNAs in antisense orientation can interfere with endogenous CCE. These findings provided a firm connection between CCE and mammalian Trps. This article reviews the known forms of CCE and highlights unanswered questions in our understanding of intracellular Ca2+ homeostasis and the physiological roles of CCE.

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.

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.

Formation of bile canaliculi in long-term primary cultures of adult rat hepatocytes on permeable membrane: an ultrastructural study

Adult rat hepatocytes were cultured for 15 days on type I collagen-coated permeable membranes in a hormonally defined Waxman's modified medium supplemented with very low concentrations of insulin, glucagon and dexamethasone. Phase contrast examination showed that 15-day-old cultures still formed a regular monolayer of polygonal cells. In similarly aged cultures, intracellular glycogen was abundant and evenly distributed, while steatosis remained very limited. Scanning and transmission electron microscopy showed that well developed bile canaliculi could be observed on the lateral side of the hepatocyte membrane after 4 days of incubation and persisted for 2 weeks. These canalicular structures probably originated from coalescence of membrane invaginations observed in 1-day-old cultures. Transmission electron microscopy showed that the ultrastructure of the cells was very close to that of normal rat hepatocytes in the intact liver. These results suggest that rat hepatocytes cultured under these experimental conditions are able to develop and maintain tissue-specific cytochemical and morphological properties for at least 15 days.

Polarity and transport properties of rabbit kidney proximal tubule cells on collagen IV-coated porous membranes

A high degree of functional polarity has been obtained in primary cultures of rabbit kidney proximal tubule cells grown on collagen IV-coated porous membranes. Tight confluency was attained 6 days after seeding and maintained for at least 6 more days, as shown by analysis of paracellular inulin diffusion. From day 6 onward, L-lactate, ammonia, and D-glucose concentration gradient and a pH difference of approximately 1 unit developed between the two nutrient medium compartments. Confluent monolayers expressed organic ion transport properties higher than those formerly reported for other cell models. Transcellular transport of 20 microM tetraethylammonium was directed from basal to apical compartment and was specifically inhibited by mepiperphenidol (1 mM). Unidirectional transport of 2.4 microM p-aminohippurate also occurred from basal to apical compartment, was saturable, and specifically inhibited by probenecid (1 mM). These results suggest that rabbit kidney proximal tubule cells, cultured under the experimental conditions described here, may be a useful model for the in vitro study of highly polarized renal transport processes.

A microtiter plate assay for total glutathione and glutathione disulfide contents in cultured/isolated cells: performance study of a new miniaturized protocol

The microtiter plate technique reported by Baker and colleagues for the glutathione reductase-DTNB recycling assay of total glutathione (GSx) and glutathione disulfide (GSSG) has been modified according to Anderson's recommendations, in order to improve the reliability and accuracy of this miniaturized method for the measurement of glutathione status in cultured/isolated cells. Dilute HCl (10 mmol/L) has been used to lyse cells, before protein removal by centrifugation in the presence of 1.3% sulfosalicylic acid. The final DTNB, GSSG-reductase and NADPH concentrations in the reaction mixture have been increased to 0.7 mmol/L, 1.2 IU/ml and 0.24 mmol/L, respectively. The procedure specificity has been tested by spiking and dilution assays, showing that about 90% of the expected GSx amounts could actually be recovered, while no changes of GSSG concentrations were caused in the cells. Accuracy has been assessed by analysis of within-series precision as well as of intra- and interassay reproducibility, showing coefficient variation of < 10%. Glutathione changes measured either in control rat hepatocytes or in primary cultures treated with paracetamol or menadione were in good agreement with well-known literature data. These data suggest that the experimental conditions reported in this paper are suitable for the analysis of total glutathione and glutathione disulfide concentrations in cultured/isolated cells.

Two-subunit structure of the human thyrotropin receptor

The extracellular and intracellular domains of the human thyrotropin receptor were expressed in Escherichia coli and the proteins were used to produce monoclonal anti-receptor antibodies. Immunoblot studies and immunoaffinity purification showed that the receptor is composed of two subunits linked by disulfide bridges and probably derived by proteolytic cleavage of a single 90-kDa precursor. The extracellular alpha subunit (hormone binding) had an apparent molecular mass of 53 kDa (35 kDa after deglycosylation with N-glycosidase F). The membrane-spanning beta subunit seemed heterogeneous and had an apparent molecular mass of 33-42 kDa. Human thyroid membranes contained a 2.5- to 3-fold excess of beta subunits over alpha subunits. Immunocytochemistry showed the presence of both subunits in all the follicular thyroid cells, and both subunits were restricted to the basolateral region of the cell membrane.

Action of allopurinol and aspirin on rat whole-embryo cultures

The effects of allopurinol (HPP) at concentrations ranging from 0.33-1.83 mM and of aspirin (ASA) from 0.28-2.22 mM, were studied on the rat whole-embryo culture system. Embryos were explanted at day 10 of gestation and cultured for 48 h, either in the absence or in the presence of rat and human S9. HPP proved to be potentially embryolethal and teratogenic without any S9, while it was embryolethal with rat S9 and dysmorphogenic with human S9. ASA showed an embryolethal and teratogenic potency without any S9 samples. These responses were increased in the presence of rat S9, while ASA embryolethality was predominant with human S9. These results obtained on rat embryos in culture suggest a correlation between the species origin of the biotransforming system and the known teratogenicity of HPP in sensitive animal models. However, ASA elicited responses not in agreement with the known teratogenic response in rodents.

[Diagnosis of disorders affecting hollow intra-abdominal organs]

Modern imaging methods, including ultrasonography, computerized tomography and magnetic resonance imaging, add considerably to the information provided by the classical exploratory methods for hollow intra-abdominal viscera. They evaluate the size of these viscera and especially their wall and they are particularly useful when the lesion is transparietal, submucosal or even sub-adventitial. They also detect abscesses originating in the gastrointestinal tract, measure the extent of tumoral expansion beyond the mucosa and reveal intra-abdominal abnormalities associated with the lesions. The new methods, therefore, are very useful and often indispensable as a complement to other methods used to explore the digestive tract.

Methodological proposal in behavioural teratogenicity testing: assessment of propoxyphene, chlorpromazine, and vitamin A as positive controls

Pregnant Sprague-Dawley rats received either 80 mg/kg d-propoxyphene HCl or 20 mg/kg chlorpromazine HCl or 80,000 and 160,000 IU/kg vitamin A palmitate daily between the 6th and 20th days of gestation. Vehicle control groups were similarly treated with saline or corn oil and considered as negative controls. Offspring were examined for physical landmarks, neuromotor development, and behaviour using righting reflex, swimming, negative geotaxis, open field, rotarod, water maze, and nocturnal activity. This test battery included biochemical measurements. No reduction in parental weight and physical offspring development was observed. All these treatments produced long-term changes in more than one test. Vitamin A palmitate (160,000 IU/kg) was judged as the best positive control with this test battery for future investigation of the behavioural teratology of drugs.

Long-term effects of prenatal oestrogen treatment on genital morphology and reproductive function in the rat

Prenatal exposure to RU 2858 (11 beta-methoxy-19-nor-17 alpha-pregna-1,3,5(10)-trien-20-yne-3,17-diol) alters the genital tract of rat offspring more markedly than does oestradiol which is bound to a specific plasma protein. The morphological changes observed in the male fetus are partly restored during infancy and maturity. The main effect of the treatment is seen in the female offspring and consists of alterations of the genital tract and of reproductive function.

Effect of estrogen plasma binding on sexual differentiation of the rat fetus

alpha-Fetoprotein, the estradiol-binding plasma protein (EBP), binds estradiol but not R 2858 (11beta-methoxy-17-ethynyl-estradiol) specifically. R 2858 interferes more markedly than estradiol with the sexual differentiation of the male rat fetus following treatment of the mother during the final stages of gestation. Moreover, its tissular uptake is higher. These facts suggest that alpha-fetoprotein protects the fetus from the high circulating hormone concentrations present in the pregnant mother. The hormone, once transferred to the fetus, is retained in its vascular bed by EBP.