STEROID-BINDING AND METABOLISM IN THE LUTEINIZING-HORMONE-RELEASING HORMONE-PRODUCING NEURONAL CELL-LINE GT1-1

LHRH synthesis and release are modulated in vivo by gonadal steroids. Although immunocytochemical and autoradiographic studies failed to det ect appreciable amounts of estrogen or androgen receptor in LHRH-produ cing neurons, the recent finding that the promoter region of the LHRH gene contains several steroid hormone-responsive elements indicates a possible direct effect of sex steroids on these specialized neurons. T he immortalized LHRH-producing neuronal cell line, GT1, which became r ecently available, may allow the study of LHRH dynamics. The presence of specific binding sites for estrogen and androgens as well as the pr esence of the two major enzymatic pathways involved in modulation of a ndrogen action (the 5 alpha-reductase/ 3 alpha-hydroxysteroid dehydrog enase and the aromatase) have been studied in the GT1-1 clone. High af finity, low capacity binding sites for[H-3] estradiol (K-d, 0.11 nM; b inding capacity, 6.2 fmol/mg protein) and for a ligand of the androgen receptor, [H-3]R1881 (K-d, 0.054 nM; binding capacity, 9.58 fmol/mg p rotein), have been identified in this cell line. A 2-fold induction of androgen-binding sites has been observed after 3 days of treatment of GT1-1 cells with estradiol (1 mu M), indicating that the estradiol bi nding is probably linked to a functional estrogen receptor. Aromatase and 5 alpha-reductase/3 alpha-hydroxysteroid dehydrogenase activities have been also tested in GT1-1 cells. Under the culture conditions ado pted, no detectable aromatization of [1 beta(3)H]Delta(4)-androstenedi one to estrone was observed using the tritiated water method. On the o ther hand, GT1-1 cells efficiently converted testosterone into dihydro testosterone and subsequently into 5 alpha-androstan-3 alpha,17 beta-d iol. In conclusion, GT1-1 cells possess several elements of the machin ery through which sex steroids may influence LHRH dynamics.