The porcine ovarian luteinizing hormone/human chorionic gonadotropin receptor II. Is the purified receptor an oligomer of identical subunits?

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.

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)