Effects of retinoic acid on estrogen- and thyroid hormone-induced growth in a newly established rat pituitary tumor cell line.
In order to elucidate the complex mechanism(s) of action of steroid hormones, thyroid hormone and retinoic acid in pituitary mammotrophs, a clonal cell line (G3) was isolated from the rat pituitary tumor MtT/F84. G3 cells were found to secrete prolactin constitutively and to contain receptors for estrogen, glucocorticoid, progesterone and thyroid hormone. Stimulation of G3 cells with thyroid hormone resulted in a modest but significant increase in estrogen and progesterone receptor levels, however, retinoic acid treatment had no effect. Simultaneous addition of thyroid hormone and estrogen showed an additive effect on progesterone receptor levels in G3 cells. Thyroid hormone as well as estrogen enhanced the growth of G3 cells. Interestingly, retinoic acid was also found to enhance their growth but its enhancement was less potent than thyroid hormone and estrogen. Low concentrations of estradiol and thyroid hormone showed additive effects, but G3 cells stimulated with high concentrations of thyroid hormone failed to elicit an additive effect with estrogen, suggesting the presence of a common pathway in the growth-stimulatory actions of these hormones. In addition, exposure of G3 cells to retinoic acid completely abolished the effects of estrogen or thyroid hormone in terms of cell growth. These results suggest that there are complex interactions in the signalling pathways for estrogen, thyroid hormone and retinoic acid action in G3 cells.
Koga
M
M
Department of Medicine III, Osaka University Medical School, Japan.
Nakao
H
H
Sato
B
B
D000818:Animals; D002455:Cell Division / Q000187:drug effects*; D004958:Estradiol / Q000494:pharmacology*; D066298:In Vitro Techniques; D010902:Pituitary Gland / Q000166:cytology*; D051381:Rats; D011987:Receptors, Steroid / Q000502:physiology*; D011988:Receptors, Thyroid Hormone / Q000502:physiology*; D014212:Tretinoin / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D004958:Estradiol; D014212:Tretinoin