The porcine LH/hCG receptor. Characterization and purification

Purification of two types of gonadotropin receptors from carp ovarian follicles: overlapping recognition by two different ligands

Teleostean gonadotropin receptors were solubilized from the plasma membrane preparation of carp ovarian follicles by lithium diiodosalicylate and Triton X-100. Solubilization resulted fourfold increase in GTH binding activity as compared to the crude plasma membrane preparation. An addition of 25% glycerol and protease inhibitors to the solubilized receptor retained more than 90% original activity at -20 degrees C for 30 days. Gel filtration through Sephadex G 100 significantly increased the specific binding capacity from 70fmol/mg protein (soluble receptor) to 250fmol/mg protein. Peak I of gel filtration showing the receptor activity was further purified by affinity chromatography on purified salmon GTH II - Sepharose with a remarkable increase in specific binding capacity from 250fmol/mg protein (gel filtration peak) to 2300pmol/mg protein for salmon GTH I ligand and 2800pmol/mg protein for GTH II ligand. In SDS-PAGE affinity eluate the active peak showed two distinct bands corresponding to 66 and 62kDa molecular masses. These two proteins were clearly separated in FPLC Mono S chromatography, 62kDa as GTHR I and 66kDa as GTHR II. The former preferably binds to GTH I ligand, while the latter to GTH II, although both demonstrated overlapping recognition to both the ligands. GTH receptor protein I (GTHR I) and II (GTHR II) were purified 42,000- and 54,000-fold, respectively. Competitive binding inhibition studies indicate GTH I and ovine FSH a better ligand for GTHR I, while GTH II and ovine LH were preferable ligands for GTHR II. Biological relevance of these two receptor proteins was ascertained by monitoring the specific binding capacity of GTHR I and II at different stages of the annual reproductive cycle. GTHR I-GTH I was a prevailing complex during preparatory and pre-spawning stages, while GTHR II-GTH II was the dominant one at the maturational and final maturational stages. It may be concluded there are two GTH receptor proteins, each having a preferred ligand. The overlapping ligand-binding activity and profile of each receptor ligand complex suggest their link to seasonal development and maturation of carp ovarian follicle.

Purification of putative thyroid hormone receptor from the ovarian nuclei of fresh water perch, Anabas testudineus

Perch ovarian putative T3 (3,5,3'-triiodo-L-thyroxine) receptor was purified to 580-fold by extracting the ovarian nuclear preparation with 0.4 M KCl, gel filtration on Sephadex G-25, DEAE-Sephacel chromatography and FPLC Superose 6 chromatography. To monitor the T3 binding protein at each purification step, aliquots from each peak protein fractions were incubated with (125)I-T3 (0.16 pmol to 3.2 nmol) in the absence or presence of 500-fold excess of unlabelled T3. Maximum binding capacity (Bmax) obtained from the Scatchard plot analysis was estimated to determine the extent of purification at each step. Purified putative T3 receptors showed a single band in polyacrylamide gel electrophoresis (PAGE) indicating homogeneity of the putative receptor protein. The molecular weight of the putative T3 receptor protein, as determined on a FPLC Superose 6 column, was 50 kD. Treatment of putative T3 receptor protein with β-mercaptoethanol followed by SDS-PAGE resulted in two subunits of 26 and 31 kD. Purification increased the specific activity of the receptor, but did not alter its affinity. Analogue specificity of the purified receptor corresponded to that of the crude nuclear preparation. Triiodothyroacetic acid (Triac) and T3 equally competed in inhibiting radiolabelled T3 binding while thyroxine (T4) was a poor competitor. T3 receptor antiserum crossreacted with the receptor protein. (125)I-labelled receptor protein binding with its antiserum was inhibited by increasing logarithmic concentrations of unlabelled receptor. In contrast to earlier reports on hepatic T3 receptor, which is a monomer, present investigation demonstrated T3 binding protein in the perch ovary to be a heterodimer held together by disulphide bond.

Selective inhibition of luteinizing hormone action by ethanol in cultured human granulosa cells

To extend further our previous observations on the inhibition of luteinizing hormone (LH)-induced increases in steroid secretion by ethanol (EtOH) (Alcohol. Clin. Exp. Res. 14:522-527, 1990), cultured human granulosa cells were pretreated with several EtOH concentrations (0-100 mM), and cells were stimulated with human LH (25 ng/ml) or human follicle stimulating hormone (FSH) (100 ng/ml) and the secretion of 17-beta-estradiol (E2) and progesterone (P) was measured. EtOH significantly increased basal E2 secretion in a dose-related manner (0-20 mM); however, in the same concentration range EtOH did not produce consistent changes in FSH-stimulated E2 secretion. In contrast, EtOH decreased LH-stimulated E2 secretion between 0-20 mM such that at 20 mM EtOH, the positive effect of LH was abolished. EtOH increased P secretion by 40% at 20 mM and at 100 mM, there was a 100% increase. The FSH-stimulated P secretion was not consistently changed by EtOH, whereas LH-stimulated P secretion was decreased in a dose-dependent manner. LH/human chorionic gonadotropin (hCG) receptors in cells exposed to EtOH showed a 15% (p < 0.01) and a 47% decrease at 20 mM and 50 mM EtOH, respectively. At 50 mM EtOH, there was a decrease in LH/hCG receptor number from 2900/cell to 1670/cell, without a change in receptor affinity for hCG and 50 mM EtOH decreased LH/hCG receptors in intact granulosa cells in a time-dependent manner. These results indicate that the selective effects of EtOH on LH action in human granulosa cells may be mediated in part by an action on LH/hCG receptors.

The effect of peritoneal macrophage-derived factor(s) on ovarian progesterone secretion and LH receptors: the role of calcium

Macrophages and their secretory products, cytokines, play an integral role in many reproductive processes. In this study we examined the effect of conditioned media from cultured human peritoneal macrophages on progesterone production by granulosa cells and the role of calcium in this process. Macrophages were pretreated with various concentrations of a calcium channel blocker (verapamil) or a calcium ionophore (A23187). Macrophage-conditioned media (MCM) or cell-free media that contained calcium channel modifiers were added at three dose levels to cultured porcine granulosa cells. Progesterone production and LH receptor content were determined. Macrophage-conditioned media alone elevated basal progesterone production, but significantly attenuated granulosa cell LH receptor content. These effects were neither potentiated nor suppressed by pretreating macrophages with verapamil. However, production of the LH receptor lowering factor(s) appeared to be suppressed by calcium ionophore. We conclude that (1) one or more factors produced by macrophages have a net stimulatory effect on basal progesterone production and these factor(s) may not be calcium-dependent and (2) macrophage-derived secretory products reduce granulosa cell LH receptor content. The production of these factor(s) may be calcium-dependent.

Human epithelial ovarian cancer cell steroid secretion and its control by gonadotropins

To elucidate the role of gonadotropins in regulating steroid metabolism in human epithelial ovarian carcinoma (OV Ca), cells were cultured from a number of OV Ca localized to the ovary. These cells uniformly secreted 17-beta-estradiol (E2), and cells from some OV Ca also secreted progesterone (P), as well as CA 125. Secretion rates decreased with time in culture and number of subcultures. In the original and first few subcultures, 1-10 pg/ml/microgram DNA/24 hr of E2 was secreted and P secretion varied from 1 to 8 ng/ml/microgram DNA/24 hr under basal conditions. Secretion rates for CA 125 were between 5 and 300 U/ml/day. Approximately 30% of the primary cultures from cystadenocarcinomas responded to hCG and hFSH and 70% of cultures responded to 8-Br-cAMP with 2- to 10-fold increases in secretion of E2. In one primary culture, hCG produced a dose-related increase in E2 production between 1 and 5 ng/ml, but the response declined to zero at 25 ng/ml. In the same cells, exposure to hCG and cAMP for 72 hr produced cell death, whereas hFSH had no such effect. Subculturing reduced steroidogenic responses to the hormones but the response to cAMP was maintained to a greater degree. These results suggest that some OV Ca-derived cells are steroidogenic in vitro and that some of these cells respond with increased E2 secretion to agents which are well-known stimulators of steroidogenesis in normal ovarian cells.

Purification and characterization of the human ovarian LH/hCG receptor and comparison of the properties of mammalian LH/hCG receptors

Methods previously published by us [Wimalasena et al., J Biol Chem 260: 10689-10697, 1985; Wimalasena et al., J Biol Chem 261: 9416-9420, 1986] were utilized to solubilize the human corpus luteal leuteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor with 3-[(3-cholamide-propyl)dimethylammonio]-1-propanesulfonate (CHAPS) and to purify the receptor by two steps of hCG-Sepharose affinity chromatography. The specific binding capacity (SBC) of the purified human receptor was 7510 pmol/mg protein, and KA = 2.2 x 10(9) M-1 when iodo hCG was competed by hCG; the yield was 4-7% of starting activity. When hLH was used in competition with hCG, specific binding capacity was 7900 pmol/mg protein and KA 1.0 x 10(9) M-1. Silver staining and autoradiography demonstrated a single protein of Mr 78,000 under reducing and Mr 58-62 x 10(3) under nonreducing conditions. Rat ovarian LH/hCG receptor was purified by similar methods and the KA of 3.5 x 10(10) M-1 for hCG was substantially different from the KA for hLH which was 2.1 x 10(9) M-1. Mr of the rat protein was 78-82 x 10(3) (reduced) and 58-62 x 10(3) (nonreduced) when analyzed by silver staining and autoradiography. For the first time, human LH/hCG receptor has been purified to apparent homogeneity, and its Mr of 78,000 was essentially identical to the Mr values of purified rat and porcine receptors.

Structure of the lutropin/choriogonadotropin receptor

In summary, the LH/CG receptor is a single polypeptide which contains a large hydrophilic domain that is situated extracellularly, attached to a region that spans the plasma membrane seven times, the carboxy-terminal region being intracellular. This topology was predicted by the amino acid sequence and has been confirmed by our immunofluorescence studies. The extracellular domain, which is related to a family of leucine-rich glycoproteins, is presumably involved in binding the large glycoprotein hormones hCG and LH. The carboxy-terminal half of the receptor, which is related to the family of rhodopsinlike receptors, is (by analogy with these receptors) presumably involved in the coupling of the receptor to the G protein. Our transfection studies confirm that this single polypeptide is capable of binding hormone and activating adenylyl cyclase. Therefore, not only is the structure of the LH/CG receptor unique compared to other cell surface receptors characterized to date, but also its structure suggests that the mechanism of the translation of hormone binding to G protein coupling in this receptor is different from other G protein-coupled receptors whose ligands are much smaller and intercalcate among the transmembrane helices. We predict that, due to the homology among the glycoprotein hormones, the structures of the FSH and TSH receptors share extensive amino acid and structural homology with the LH/CG receptor. Last, our newly acquired knowledge about the structure of the LH/CG receptor, and the development of a cDNA and antibodies for this receptor, should enable more detailed studies on the function and regulation of the LH/CG receptor, not previously possible.

Characterization and structure of ovarian and testicular LH/hCG receptors

Ovarian and Leydig cell LH/hCG receptors purified to homogeneity were identified as a single protein of Mr 80,000 and 90,000 respectively. The homogeneity of this protein was confirmed by microsequencing of the first 18 amino acids of the ovarian receptor. The unblocked N-terminal peptide consisted of NH2-R-E-L-S-G-S-R-X-P-E-P-X-D-X-A-P-D-G. These receptors are N-linked sialoglycoproteins which accounts for the size difference between testicular and ovarian receptors and may participate in the interaction with gonadotropin. Crosslinking of pure receptor with hCG with 125I label in either subunit indicated significant interaction of alpha-hCG with the receptor, while beta-hCG seems involved mostly through association and conformational influence on the alpha-subunit. Comparison of Mr derived from SDS with those from FPLC suggested that the native LH receptor are dimers of identical subunits. Autoradiographs of blotted receptors demonstrated that both monomeric and dimeric forms can bind hCG. Receptors from both tissues can be phosphorylated by the catalytic subunit of cAMP-dependent protein kinase and phosphopeptide maps were identical. Receptor occupancy by agonist leads to a conformational change which facilitates its phosphorylation during initial binding and reduces the rate of phosphorylation after more prolonged exposure to gonadotropin. Aggregation or dimerization of the hCG/LH receptors could promote clustering and or crosslinking of receptors in the membrane favouring the initial transduction steps in the action of these hormones.

Hydrogen peroxide and methyl mercury are primary stimuli of eicosanoid release in human platelets

Hydrogen peroxide (H2O2) and methyl mercury induced the liberation of arachidonate and its metabolites from human washed platelets. [14C]Eicosanoids were extracted from the supernatants of [14C] arachidonate-prelabelled platelets and analysed by thin layer chromatography and radioscanning. Thromboxane B2 (TXB2), 12(S)-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) were found as stable metabolites, together with unreacted arachidonate. In the presence of dazoxiben, a shift in eicosanoid metabolism was observed towards prostaglandin E2 (PGE2), prostaglandin D2 (PGD2) and prostaglandin F2 alpha (PGF2 alpha), while in the presence of indomethacin there was a shift towards 12-HETE and unmetabolized arachidonate. The concentration pattern of those metabolites resembled that found with the physiological agonist, thrombin. H2O2 and methyl mercury also induced platelet shape change, aggregation and secretion. The EC50 values for the induction of shape change and aggregation were 27 and 850 mumol/l for H2O2 and 0.33 and 2.7 mumol/l for methyl mercury, respectively. The [3H]serotonin release required higher stimulus concentrations and amounted to 45% with 2 mumol/l H2O2 and to 16% with 3 mumol/l methyl mercury. These effects on platelet function were absent in platelets exposed to acetylsalicylic acid and prevented by indomethacin, the prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist, daltroban, and the functional antagonist, iloprost. In contrast, none of these drugs suppressed the formation of [14C]eicosanoids, indicating that the platelet activation by H2O2 and methyl mercury essentially requires previous PGH2/TXA2 formation. As expected, the thromboxane synthase inhibitor, dazoxiben, did not prevent, but instead potentiated the activation by H2O2 and methyl mercury through accumulated PGH2.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactogen and LH receptors. Rat P-450 17 alpha, structural analysis and hormonal regulation of mRNA levels in the Leydig cell

A complete amino acid sequence for rat testis P-450 17 alpha was deduced from nucleotide analysis of a cDNA clone isolated from a rat Leydig cell library. This cDNA expressed in COS-1 cells both 17 alpha-hydroxylase and 17,20 lyase activities. Rat P-450 17 alpha exhibited significant similarity to the nucleotide and deduced amino acid sequences of the bovine and human P-450 17 alpha, particularly with the highly conserved regions and secondary structure. The rat P-450 17 alpha is anchored to the ER by two transmembrane regions: the N-terminal insertion peptide and the stop-transfer sequence. The C-terminal is associated with the ER by four hydrophobic clefts including the steroid-binding site. We have demonstrated a dual effect of hCG, causing early increases of Leydig cell P-450 17 alpha mRNA levels at low doses, while higher desensitizing doses caused marked subsequent reduction of mRNA levels. Our studies demonstrate that gonadotropin stimulation and desensitization of P-450 17 alpha dependent enzymes (17 alpha-hydroxylase/17,20 desmolase) in the adult rat testis and E2 induced desensitization in fetal Leydig cells are related to levels of P-450 17 alpha mRNA.

Hydrodynamic properties of the gonadotropin receptor from a murine Leydig tumor cell line are altered by desensitization

The murine Leydig tumor cell line 1 (MLTC-1) contains gonadotropin receptors (GR) that are coupled to adenylate cyclase through the stimulatory guanine nucleotide binding protein (Gs). The binding of human choriogonadotropin (hCG) causes MLTC-1 cells to accumulate cAMP. With time, the ability of MLTC-1 cells to respond to hCG is attenuated by a process called desensitization. The hydrodynamic properties of GR from control and desensitized MLTC-1 cells were studied. Sucrose density gradient sedimentation in H2O and D2O and gel filtration chromatography were used to estimate the Stokes radius (a), partial specific volume (vc), sedimentation coefficient (S20,w), and molecular weight (Mr) of the detergent-solubilized hormone-receptor complex (hCG-GR). [125I]hCG was bound to MLTC-1 cells under conditions that allow (37 degrees C) or prevent (0 degree C) desensitization, and hCG-GR was solubilized in Triton X-100. In the absence of desensitization, control hCG-GR had a Mr of 213,000 (a = 6.2; vc = 0.76; S20,w = 7.3), whereas desensitized hCG-GR had a Mr of 158,000 (a = 6.1; Vc = 0.71; S20,w = 6.6). Deglycosylated hCG (DG-hCG) is an antagonist that binds to GR with high affinity but fails to stimulate adenylate cyclase or cause desensitization. [125I]DG-hCG was bound to MLTC-1 cells and DG-hCG-GR solubilized in Triton X-100. The hydrodynamic properties of DG-hCG-GR (Mr 213,000; a = 5.8; Vc = 0.77; S20;w = 7.6) were the same as that for control hCG-GR. There was no evidence for the association of adenylate cyclase or Gs with GR in Triton X-100 solubilized preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of ovarian LH/hCG and prolactin receptors

We have purified the luteinizing hormone (LH)/human choriogonadotropin (hCG) receptor to homogeneity by sequential affinity column on wheat germ lectin-Sepharose and hCG-Sepharose. The method was designed to allow also the purification of lactogen receptor from the initial starting material. Comparable purification of lactogen receptor can be attained using Con A-Sepharose as initial step. The purified LH/hCG receptor was identified as a single protein of Mr = 75,000 on SDS gel electrophoresis. The lactogen receptor is composed of two dissimilar active subunits of Mr 88,000 and 40,000, the latter probably being an integral part of the larger form. Comparison of Mr's derived from SDS gels with those from fast performance liquid chromatography suggested that the native LH holoreceptor is present in a dimeric form, while the lactogen receptor seems to be composed of aggregates that could represent dimeric or trimeric forms of holoreceptor Mr 80,000. Cross-linking studies performed after binding of hCG (radiolabeled in the individual subunits) to the purified LH/hCG receptor indicated that the hCG alpha-subunit undergoes predominant interaction with the receptor molecule. The influence of the beta-subunit in this interaction seems to occur mainly through its association with the alpha-subunit, presumably by conferring specificity to the alpha-subunit for its interaction with the receptor. The alpha-subunit, which is identical within species, has an important role in the receptor binding interaction and biological activity of glycoprotein hormones.

Visualization of the rat ovarian lutropin receptor by ligand blotting

A ligand blotting technique was developed to identify the lutropin receptor after size separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. The separated proteins were transferred to a nitrocellulose sheet, which was subsequently incubated with 125I-labeled human choriogonadotropin (125I-hCG), and subjected to autoradiography. An Mr 90,000 band was specifically and intensely labeled with 125I-hCG. The band was not observed, when the hormone incubation was performed in the presence of an excess of unlabeled hCG or human lutropin. The presence of rat follitropin or rat prolactin did not, however, abolish the labeling. No specific labeling was found when down-regulated ovarian tissue or rat liver was used as starting material. The Mr 90,000 band disappeared when the protein samples were treated with reducing agent, showing that integrity of receptor disulfide bonds is essential for the hormone-receptor interaction. In addition, a receptor-positive murine Leydig tumor cell line produced an Mr 90,000-92,000 band in ligand blotting, thus demonstrating the similarity between rat and murine lutropin receptors. These results provide strong evidence that the lutropin receptor is an Mr 90,000 protein.