Increase in Pit-1 mRNA is not required for the estrogen-induced expression of prolactin gene and lactotroph proliferation.
Estrogen has been shown to stimulate lactotroph proliferation and expression of the prolactin (PRL) gene. Recently it has been established that Pit-1, a pituitary-specific transcription factor, is required for lactotroph proliferation. Furthermore, in vitro studies showed that an increase in the PRL promoter activity caused by estrogen was dependent of the amount of cotransfected Pit-1-expressing plasmid. These findings led us to examine whether the induction of Pit-1 mRNA is required for the estrogen-increased PRL gene expression in the rat anterior pituitary in vivo. Short term estrogen treatment was achieved by means of a single intramuscular injection of estradiol dipropionate. DNA synthesis, the levels of PRL and Pit-1 messenger RNAs in the anterior pituitary were determined. Estradiol dipropionate resulted in a significant increase in DNA synthesis 24 h after administration and in PRL mRNA after 48 h. In contrast, the Pit-1 mRNA level was not altered. Since Pit-1 is expressed not only in lactotroph but also in somatotroph and thyrotroph, and the lactotroph cell population has been reported to be less than 10% in the pituitary, the change in the Pit-1 mRNA level in lactotrophs was not seen following only short term estrogen treatment. An increase in the lactotroph cell population was therefore achieved by chronic estrogen treatment (subcutaneous implantation of a silastic tube containing 17 beta-estradiol powder for 30 days). This treatment resulted in the marked proliferation of lactotrophs and a 3-fold increase in PRL mRNA. However, no alteration in Pit-1 mRNA was observed. These results suggest that the increase in Pit-1 mRNA is not required for the estrogen-induced lactotroph proliferation or PRL gene expression.
Tsukahara
S
S
Department of Endocrinology and Metabolism, Nagoya University, Japan.
Kambe
F
F
Suganuma
N
N
Tomoda
Y
Y
Seo
H
H
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D010903:Pituitary Gland, Anterior / Q000166:cytology* / Q000378:metabolism; D011388:Prolactin / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D004268:DNA-Binding Proteins; D004967:Estrogens; C494186:Pou1f1 protein, rat; D012333:RNA, Messenger; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D011388:Prolactin; D004247:DNA