Antibody against a peptide corresponding to the extracellular domain of the luteinizing hormone/chorionic gonadotropin receptor stimulates testosterone production in rat Leydig cells.
In order to study the function of LH/CG receptor, we prepared four synthetic peptides (RP1, 2, 3, and 4 for residues 242-255, 49-66, 493-504, and 573-584) corresponding to extracellular domains of rat ovary LH/CG receptor and raised antibodies against RP1 and RP2 (anti-receptor peptide IgGs). These peptides and IgGs were assayed for inhibition of 125I-labeled hCG binding to Leydig cell membrane receptors. However, neither the peptides nor the IgGs inhibited hCG binding to the receptor at doses up to 10(-3) and 10(-5) M, respectively. On the other hand, although anti-receptor peptide IgGs did not show inhibition of hCG binding to the receptor, it was found that one of the IgGs (anti-RP1IgG) was bound to the cell membrane and stimulated testosterone production in rat Leydig cells. F(ab')2 fragment lacking the N-linked sugar chain in the IgG molecule, whose sugar chains are similar to those of hCG, was prepared from anti-RP1IgG. Anti-RP1F(ab')2 was still bound to the cell membrane but no longer stimulated testosterone production. These results suggested that when LH/CG receptor binds to a glycoprotein, even if it is different from the native ligand hCG, it may interact with sugar chains of the glycoprotein to cause signal transduction. Thus, a lectin-like domain in or near the receptor may play a key role in the receptor function.
Ohwaki
K
K
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University.
Sakakibara
R
R
Ishiguro
M
M
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000378:metabolism; D006063:Chorionic Gonadotropin / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism; D007985:Leydig Cells / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D011974:Receptors, LH / Q000276:immunology / Q000378:metabolism*; D013739:Testosterone / Q000096:biosynthesis*
D000906:Antibodies; D006063:Chorionic Gonadotropin; D007074:Immunoglobulin G; D011974:Receptors, LH; D013739:Testosterone