Estradiol stimulates prolactin gene transcription in primary cultures of rat anterior pituitary cells.

Dispersed cells were prepared from the anterior pituitary glands of 6-week old male and retired breeder female rats and were cultured for 3 days in a serum-containing medium which lacked estrogen. Following short-term treatments (1-24 h) with estradiol at a concentration of 10(-9) M, the levels of prolactin gene transcription were assayed by quantitating the amount of radiolabeled uridine monophosphate incorporated into prolactin mRNA sequences by pituitary cell nuclei prepared from these cultures. Estradiol significantly stimulated the transcription of the prolactin gene in these primary cultures within 6 h. Similar levels of stimulation were observed in cells from both male and female rats. Estradiol treatment had no effect on the transcription of the growth hormone gene, suggesting its stimulatory effects on prolactin gene transcription are specific. Estradiol also significantly stimulated the transcription of the prolactin gene in cultures in which protein synthesis was grossly inhibited by cycloheximide. These data illustrate that estrogen regulates the expression of the prolactin gene at the transcriptional level, through a direct action on the cells of the anterior pituitary gland, and by a mechanism which does not require the synthesis of any intermediary proteins.