Antibody against a peptide corresponding to the extracellular domain of the luteinizing hormone/chorionic gonadotropin receptor stimulates testosterone production in rat Leydig cells

In vitro inhibition of the bioactivity of follicle-stimulating hormone by antisera against a peptide representing part of the FSH-receptor

The aim of the present work was to define an FSH receptor (FSHR) peptide that can induce antibodies that will inhibit the bioactivity of FSH. Therefore, the hFSHR sequence was aligned with that of all other known G-protein coupled receptors. An area with increased sequence homology was identified between the FSH-, LH-, TSH receptors, the C5a receptor and the IL8 receptor. The similarity consists of a richness in acidic (D and E) and hydrophobic (Y and F) residues. In hFSHR the sequence is EDNESSYSRGFDMTYTEFDYDLCNEVVD (amino acid 299-326). Research on both the C5a- and IL8-receptor has indicated that this part is responsible for hormone binding but not for signal transduction. Protamine. an antagonist for both the C5a- and IL8 receptor also inhibited the bioactivities of FSH and LH when tested in a bioassay. This suggests that in the hFSHR this region might also be involved in hormone binding. Specificity of this region towards the diverse ligands all binding to the C5a or to the IL8 receptor might be attributed to differences in the profile of alternating basic and hydrophobic residues. Therefore, the hypothesis was tested as to whether antisera raised against peptides of this FSHR-domain would inhibit FSH-bioactivity but not LH-bioactivity. Indeed antisera were found (anti-hFSHR 309-322) that inhibited the biological activity of FSH in a bioassay. These antisera proved to be specific since they did not inhibit the bioactivity of LH. These data suggest that the core sequence (hFSHR 309-322) of the aligned domain of the hFSHR, in analogy to the IL8- and C5a receptors, is involved in hormone binding and ligand specificity. This domain therefore forms a valuable tool in FSH- and FSHR research for scientific and medical purposes.

The rotational diffusion of LH receptors differs when receptors are occupied by hCG versus LH and is increased by cytochalasin D

We have examined the rotational diffusion of the luteinizing hormone (LH) receptors binding human chorionic gonadotropin (hCG) or ovine luteinizing hormone (oLH) in MA-10 Leydig tumor cells using time-resolved phosphorescence anisotropy techniques. LH receptors binding erythrosin isothiocyanate (ErITC)-derivatized oLH were rotationally mobile with rotational correlation times of 62 micros, 48 micros, 38 micros, and 29 micros at 4 degrees C, 15 degrees C, 25 degrees C, and 37 degrees C, respectively. ErITC-hCG bound to the LH receptor was rotationally immobile, showing no anisotropy decay at 4 degrees C, 15 degrees C, 25 degrees C, and 37 degrees C. To determine whether cytoskeletal components influenced the rotational diffusion of LH receptors, we measured rotational diffusion of LH receptors on MA-10 cells treated with 20 microg/ml cytochalasin D and on plasma membrane preparations. Following 1 h exposure to cytochalasin D, the rotational correlation times for hCG-occupied LH receptors were typically 11 micros at 37 degrees C compared to > 1000 micros on untreated cells. Treatment of MA-10 cells with cytochalasin B or colchicine had no affect on LH receptor rotational diffusion. Rotational correlation times for LH-occupied receptors decreased from 29 micros to 12 micros at 37 degrees C following cytochalasin D treatment. The rotational diffusion of LH receptors on plasma membrane preparations was similar to that observed for LH- and hCG-occupied receptors on intact cells treated with cytochalasin D. These various results indicate that there are differential effects of LH and hCG binding on the interactions of LH receptors with plasma membrane proteins and that microfilaments anchor the hCG- and LH-occupied receptors.