Developmental exposure to diethylstilbestrol elicits demethylation of estrogen-responsive lactoferrin gene in mouse uterus.

Alteration of DNA demethylation in five CpG sites (-547, -533, -475, -464, and -454) immediately upstream from the estrogen response element of lactoferrin promoter was determined in the uteri of immature (17-day-old) and mature (21- and 30-day-old) mice treated neonatally with DES. Only the CpG/-464 was found to be abnormally demethylated by diethylstilbestrol (DES) treatment in the mature uteri. This abnormal demethylation occurred in specific response to DES in neonatal mice, because DES injected into the 30-day-old mature mice did not demethylate CpG/-464. This site, however, remained methylated in the neonatally DES-treated/ovariectomized mice, indicating that this DES-elicited demethylation is under hormonal control. Thus, neonatal DES treatment appeared to imprint an abnormal, site-specific demethylation of CpG/-464, which requires ovarian hormones to occur in adult mice. Moreover, the demethylation was maintained in uterine tumors of the neonatally DES-treated mice. This mode of demethylation is reminiscent of uterine tumor formation, which also depends on both neonatal DES exposure and ovarian hormone stimulation in adulthood. Thus, neonatal DES treatment may induce tumor formation as well as demethylation through a common cellular process.