CHARACTERIZATION OF ESTROGEN-DEPENDENT GROWTH OF CULTURED MCF-7 HUMANBREAST-CANCER CELLS EXPRESSING 17-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE-1

17 beta-hydroxysteroid dehydrogenase (17HSD) type I converts the weakl y active estrogen, estrone, into highly active estradiol. In addition to being essential for gonadal estradiol biosynthesis, the enzyme is a lso expressed in a significant proportion of breast tumors. In order t o study the role of the enzyme in estrogen-dependent growth of breast cancer, MCF-7 breast-cancer cells stably expressing human 17HSD type I were generated. In control MCF-7 cells a very low 17HSD activity was observed and, in line with its low estrogenic activity, estrone was de void of the growth-enhancing effect of estradiol. The presence of the enzyme in the stably transfected MCF-7 cells resulted in a rapid conve rsion of estrone into estradiol but did not alter the estrogen-recepto r concentration in the cells. However, in transfected cells, estrone h ad a growth-promoting effect practically identical to that elf estradi ol. The presence or absence of 17HSD type I in breast-cancer cells may therefore be decisive with regard to estrogen exposure and the estrog en-responsive growth of breast-cancer tissues. (C) 1996 Wiley-Liss, In c.