Characterization of the subunit structure of gonadotropin receptor in luteinized rat ovary

mRNAs in the methanogenic archaeon Methanococcus vannielii: numbers, half-lives and processing

Cells from the early exponential growth phase of cultures of the methanogenic archaeon Methanococcus vannielii have been shown to contain c. 180 transcripts of the mcrBDCGA (mcr) operon, c. 100 transcripts of the MvaL1,L10,L12 (Mva) operon, c. 8 transcripts of the argG gene and c. 1 transcript of the secY gene. These values decreased to c. 50 mcr transcripts, c. 30 Mva transcripts, c. 3 argG transcripts and < 1 secY transcript per cell as the cultures entered the stationary phase of growth. Addition of bromo-ethanesulphonate (BES) or removal of H2 inhibited growth and RNA synthesis in vivo and, at 37 degrees C in the presence of BES, the half-lives of the mcr, Mva, argG and secY transcripts were found to be 15 min, 30 min, 57 min and 7 min, respectively. Addition of puromycin, pseudomonic acid or virginiamycin also inhibited growth but did not inhibit transcription. In the presence of puromycin the half-lives of the mcr and Mva transcripts increased c. 4.6-fold and c. 3.5-fold, respectively, and there was a net accumulation of the Mva transcript. Addition of pseudomonic acid or virginiamycin also increased the half-life of the Mva transcript and also resulted in the accumulation of a second, shorter Mva transcript but did not increase the half-life of the mcr transcript. Transcription of the mcr operon was not stimulated by partial inhibition of methanogenesis.

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.

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)

Receptors for B-cell stimulatory factor-1 expressed on cells of haematopoietic lineage

B-cell stimulatory factor-1 (BSF-1) is a T-cell product of relative molecular mass 20,000 (Mr, 20K) initially described as a cofactor required for DNA synthesis by resting mouse B cells stimulated with low concentrations of anti-IgM antibodies. It acts on resting B cells to enhance the expression of class II major histocompatibility complex (MHC) molecules, to prepare these cells to respond more promptly to subsequent stimuli, such as anti-IgM antibodies, and causes the secretion of IgG1 and IgE by B cells stimulated with lipopolysaccharide (LPS). BSF-1 has been shown to stimulate T cell lines, resting T cells and some mast cell lines. Recently, the designation interleukin-4 (IL-4) has been suggested for BSF-1. We report here the existence of high-affinity cell-surface receptors specific for BSF-1 on both B and T lymphocytes, and on cells of several other haematopoietic lineages, including mast cell, macrophage and undifferentiated haematopoietic cell lines. Resting B and T lymphocytes express receptors, which increase in number upon activation of B cells with LPS or anti-IgM, and of T cells with concanavalin A. Cross-linking of 125I-labelled-BSF-1 to its receptors creates a complex of Mr approximately 80,000.

Covalent cross-linking of radiolabeled human chorionic gonadotropin to rat ovarian luteinizing hormone receptor with glutaraldehyde

Crude plasma membranes of pseudopregnant rat ovaries were incubated with 125I-labeled human chorionic gonadotropin (125I-hCG) and the formed luteinizing hormone (LH)/hCG receptor-125I-hCG complex was solubilized, partially purified by Sepharose 6B gel filtration, cross-linked with glutaraldehyde and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. An apparent molecular weight (mol wt) of 130,000 was obtained for the non-reduced complex. A similar-sized complex was observed, when 3H-hCG (beta-subunit labeled) instead of 125I-hCG (alpha-subunit labeled) was used, indicating that the complex contains intact hCG. Upon reduction of the cross-linked receptor-125I-hCG complex, a 105,000 mol wt complex in addition to the 130,000 one was observed. No smaller complexes appeared, however, upon reduction of the receptor-3H-hCG complex, suggesting that the alpha-subunit of hCG predominantly interacts with the receptor. The cross-linking efficiency was dependent on protein concentration, glutaraldehyde concentration, pH, reaction time and temperature. Under optimal conditions (2 mM glutaraldehyde, pH 7.0-8.0, 60 min, 20 degrees C) no nonspecific complexes appeared and the efficiency of cross-linking of the partially purified detergent-solubilized receptor-125I-hCG complex was approximately 30%. Glutaraldehyde thus provides a rapid and efficient cross-linking reagent to covalently attach 125I-hCG to its receptor and is likely to be highly applicable to other receptor-ligand systems as well.

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.

Porcine follicular fluid containing water-soluble LH/hCG receptor

Porcine follicular fluid has been shown to have a specific water-soluble receptor for human chorionic gonadotropin (hCG). The binding of [125I] hCG to follicular fluid is inhibited by unlabelled hCG, LH but not FSH, ACTH and GH. The binding of hormone to the receptor in follicular fluid is a saturable phenomenon and Scatchard analysis suggested that the receptor has high affinity to hCG with no changes as the follicle enlarges. In contrast, follicular fluid from large follicles (6-12 mm) has higher binding capacity (2.04 +/- 0.12 fmol/mg protein) than follicular fluid isolated from medium (3-5 mm) and small (1-2 mm) follicles (0.60 +/- 0.05 and 0.44 +/- 0.04 fmol/mg protein, respectively). With the aid of affinity chromatography on hCG-CNBr-Sepharose 6-B a homogeneous fraction with Mr about 65,000 as estimated by SDS-PAGE was isolated. Treatment of follicular fluid with several protein-modifying reagents changed interactions of [125I] hCG with both soluble receptor and that bound to granulosa cell membrane in the similar manner. The [125I] hCG binding capacity of follicular fluid represents about 9.5% of the total binding capacity of granulosa cells. Finally, soluble LH/hCG receptor is probably secreted actively by follicular cells into follicular fluid. Dead granulosa cells do not release receptor into follicular fluid or incubation medium.

Evidence that the subunit structure of gonadotropin receptor is preserved during regression of rat corpus luteum

The level of hCG/LH receptor has been shown to undergo marked changes during the life span of rat corpus luteum. To evaluate whether these fluctuations are due to changes in the receptor subunit structure or receptor protein content, the 125I-hCG binding activity and the receptor subunit structure were determined during different time periods of pseudopregnancy. The maximum 125I-hCG binding activity was observed on day 7, after which it decreased by 20 and 45% on day 11 and day 14, respectively. The Scatchard analysis of 125I-hCG binding data showed that the decrease in binding activity was caused by a change in the number of binding sites rather than a change in the binding affinity. The LH/hCG receptor in ovarian membranes obtained on days 7, 11 and 14 were then characterized by the method of affinity cross-linking. All four subunits of the LH/hCG receptor were detected in the ovarian membranes at all stages while the intensity decreased parallel to a decrease in hCG binding from day 7 to day 14. These results suggest that the decrease in 125I-hCG binding activity in rat ovarian membranes from day 7 to day 14 of pseudopregnancy is due to a decrease in receptor concentration rather than a change in the receptor subunit structure.

Differential human interferon alpha receptor expression on proliferating and non-proliferating cells

The expression of interferon-alpha (IFN-alpha) receptors was studied on a variety of human cells, using monoiodinated IFN-alpha 2 probes. Steady-state binding at 4 degrees C revealed a single class of non-interacting IFN receptor on peripheral blood lymphocytes, and tonsillar B lymphocytes, which are both known to be G0/G1 resting cell populations. The binding affinity of this class of receptor was found to be on the order of 5 X 10(-10) M, expressed as an apparent dissociation constant (Kd). However, cells proliferating either in culture or in vivo were found to express a heterogeneity in IFN-alpha 2 binding. Such binding could be objectively resolved (by a version of the LIGAND program of P. Munson) into a two-site receptor model. Hill plots of binding to proliferating cells indicated a negative cooperativity in the interaction of IFN and receptor. The high-affinity component, expressed on proliferating cells, typically exhibits a Kd of (1-10) X 10(-11) M, while the lower-affinity component indicates a Kd of (1-10) X 10(-9) M. Furthermore, the low-affinity component is apparently expressed on the order of 10-200 times the copy number, per cell, of the high-affinity site. Affinity-labeling experiments revealed that, in addition to the 140-160-kDa IFN-binding complex reported by others, both the proliferating and non-proliferating cell populations possess a novel IFN-binding component of 60 kDa.