ACTIVATION OF IMMEDIATE-EARLY GENES BY ESTROGEN IS NOT SUFFICIENT TO ACHIEVE STIMULATION OF DNA-SYNTHESIS IN RAT UTERUS

17β-estradiol, a long acting estrogen that is mitogenic for rat uterus in vivo, or the short acting estrogens estriol and 16α-estradiol, not mitogenic on their own, were injected into adult, castrated rats and their effect on uterine gene expression and rate of DNA synthesis were compared. All three compounds increased steady-state mRNA concentration of c-fos, c-jun and c-myc protooncogenes to comparable levels (2 hrs after treatment), whereas only 17β-estradiol was found to stimulate significantly DNA synthesis (20-22 hrs later). Based on the different retention time of the tested estrogens in rat tissues, it is concluded that a short exposure to the hormone is sufficient to render uterine cells competent to progress through the cell cycle, via activation of 'immediate-early' genes expression, but that stimulation of DNA synthesis requires further changes, achieved via a prolonged exposure of the cells to the estrogenic stimulus. © 1990.